From 08177fa58119f9e67fdffb32ee20dbf05bd4fa78 Mon Sep 17 00:00:00 2001
From: James Bursa <james@netsurf-browser.org>
Date: Thu, 10 Jun 2004 20:41:26 +0000
Subject: [project @ 2004-06-10 20:41:26 by bursa] Add global content list.
 Better error handling in content code. Improved code documentation. Remove
 some obsolete functions. Implement debug window listing contents.

svn path=/import/netsurf/; revision=951
---
 !NetSurf/Resources/en/Messages      |   3 +
 !NetSurf/Resources/en/Templates,fec | Bin 6298 -> 6410 bytes
 !NetSurf/Resources/fr/Messages      |   3 +
 !NetSurf/Resources/fr/Templates,fec | Bin 6404 -> 6516 bytes
 content/content.c                   | 292 +++++++++++++++++++++++++-----------
 content/content.h                   | 100 ++++++++++--
 content/fetch.c                     |   8 +-
 content/fetchcache.c                |  41 +++--
 css/css.c                           | 119 ++++++++-------
 css/css.h                           |   4 +-
 debug/netsurfd.c                    |  10 +-
 desktop/browser.c                   |   1 +
 desktop/gui.h                       |   2 -
 desktop/netsurf.c                   |  12 +-
 makefile                            |  14 +-
 render/html.c                       | 111 ++++++--------
 render/html.h                       |  15 +-
 render/textplain.c                  |  10 +-
 render/textplain.h                  |   4 +-
 riscos/dialog.c                     |   3 +-
 riscos/draw.c                       |  51 +++----
 riscos/draw.h                       |   8 +-
 riscos/gif.c                        |  64 +++++---
 riscos/gif.h                        |  11 +-
 riscos/gifread.c                    |  29 ++--
 riscos/gui.c                        |  11 +-
 riscos/gui.h                        |   8 +-
 riscos/htmlredraw.c                 |   6 +-
 riscos/jpeg.c                       |  35 +++--
 riscos/jpeg.h                       |  10 +-
 riscos/png.c                        |  72 +++++----
 riscos/png.h                        |  13 +-
 riscos/sprite.c                     |  92 +++++++-----
 riscos/sprite.h                     |  15 +-
 riscos/wimp.c                       |   1 +
 utils/utils.h                       |   1 +
 36 files changed, 743 insertions(+), 436 deletions(-)

diff --git a/!NetSurf/Resources/en/Messages b/!NetSurf/Resources/en/Messages
index 6d727b91d..25a7e3acb 100644
--- a/!NetSurf/Resources/en/Messages
+++ b/!NetSurf/Resources/en/Messages
@@ -117,6 +117,9 @@ FetchStyle2:Loading %u stylesheets: %s
 NotCSS:Warning: stylesheet is not CSS
 BadObject:Warning: bad object type
 ObjError:Error loading object: %s
+ParsingFail:Parsing the document failed.
+BadGIF:Reading GIF failed.
+PNGError:PNG library error.
 
 DrawTitle:Draw image (%lux%lu, %lu bytes)
 GIFTitle:GIF image (%lux%lu)
diff --git a/!NetSurf/Resources/en/Templates,fec b/!NetSurf/Resources/en/Templates,fec
index 58f6c17c5..afad82c15 100644
Binary files a/!NetSurf/Resources/en/Templates,fec and b/!NetSurf/Resources/en/Templates,fec differ
diff --git a/!NetSurf/Resources/fr/Messages b/!NetSurf/Resources/fr/Messages
index 67cc4cc18..5077b78c9 100644
--- a/!NetSurf/Resources/fr/Messages
+++ b/!NetSurf/Resources/fr/Messages
@@ -115,6 +115,9 @@ FetchStyle2:Chargement de %u feuilles de styles: %s
 NotCSS:Attention: feuille de style non CSS
 BadObject:Attention: mauvais type d'objet
 ObjError:Erreur lors du chargement de: %s
+ParsingFail:Parsing the document failed.
+BadGIF:Reading GIF failed.
+PNGError:PNG library error.
 
 DrawTitle:Image Draw (%lux%lu, %lu octets)
 GIFTitle:Image GIF (%lux%lu)
diff --git a/!NetSurf/Resources/fr/Templates,fec b/!NetSurf/Resources/fr/Templates,fec
index ec487e3d1..1f2934814 100644
Binary files a/!NetSurf/Resources/fr/Templates,fec and b/!NetSurf/Resources/fr/Templates,fec differ
diff --git a/content/content.c b/content/content.c
index a002c04fd..268b36433 100644
--- a/content/content.c
+++ b/content/content.c
@@ -45,6 +45,10 @@
 #include "netsurf/utils/utils.h"
 
 
+/** Linked list of all content structures. May include more than one content
+ *  per URL. Doubly-linked. */
+struct content *content_list = 0;
+
 /** An entry in mime_map. */
 struct mime_entry {
 	char mime_type[40];
@@ -79,17 +83,50 @@ static const struct mime_entry mime_map[] = {
 };
 #define MIME_MAP_COUNT (sizeof(mime_map) / sizeof(mime_map[0]))
 
+const char *content_type_name[] = {
+	"HTML",
+	"TEXTPLAIN",
+	"CSS",
+#ifdef WITH_JPEG
+	"JPEG",
+#endif
+#ifdef WITH_GIF
+	"GIF",
+#endif
+#ifdef WITH_PNG
+	"PNG",
+#endif
+#ifdef WITH_SPRITE
+	"SPRITE",
+#endif
+#ifdef WITH_DRAW
+	"DRAW",
+#endif
+#ifdef WITH_PLUGIN
+	"PLUGIN",
+#endif
+	"OTHER",
+	"UNKNOWN"
+};
+
+const char *content_status_name[] = {
+	"TYPE_UNKNOWN",
+	"LOADING",
+	"READY",
+	"DONE",
+	"ERROR"
+};
+
 /** An entry in handler_map. */
 struct handler_entry {
-	void (*create)(struct content *c, const char *params[]);
-	void (*process_data)(struct content *c, char *data, unsigned long size);
-	int (*convert)(struct content *c, unsigned int width, unsigned int height);
-	void (*revive)(struct content *c, unsigned int width, unsigned int height);
-	void (*reformat)(struct content *c, unsigned int width, unsigned int height);
+	bool (*create)(struct content *c, const char *params[]);
+	bool (*process_data)(struct content *c, char *data, unsigned int size);
+	bool (*convert)(struct content *c, int width, int height);
+	void (*reformat)(struct content *c, int width, int height);
 	void (*destroy)(struct content *c);
-	void (*redraw)(struct content *c, long x, long y,
-			unsigned long width, unsigned long height,
-			long clip_x0, long clip_y0, long clip_x1, long clip_y1,
+	void (*redraw)(struct content *c, int x, int y,
+			int width, int height,
+			int clip_x0, int clip_y0, int clip_x1, int clip_y1,
 			float scale);
 	void (*add_instance)(struct content *c, struct browser_window *bw,
 			struct content *page, struct box *box,
@@ -104,39 +141,39 @@ struct handler_entry {
 /** A table of handler functions, indexed by ::content_type.
  * Must be ordered as enum ::content_type. */
 static const struct handler_entry handler_map[] = {
-	{html_create, html_process_data, html_convert, html_revive,
+	{html_create, html_process_data, html_convert,
 		html_reformat, html_destroy, html_redraw,
 		html_add_instance, html_remove_instance, html_reshape_instance},
 	{textplain_create, html_process_data, textplain_convert,
-		0, 0, 0, 0, 0, 0, 0},
-	{0, 0, css_convert, css_revive, 0, css_destroy, 0, 0, 0, 0},
+		0, 0, 0, 0, 0, 0},
+	{0, 0, css_convert, 0, css_destroy, 0, 0, 0, 0},
 #ifdef WITH_JPEG
-	{nsjpeg_create, 0, nsjpeg_convert, 0,
+	{nsjpeg_create, 0, nsjpeg_convert,
 		0, nsjpeg_destroy, nsjpeg_redraw, 0, 0, 0},
 #endif
 #ifdef WITH_GIF
-	{nsgif_create, 0, nsgif_convert, 0,
+	{nsgif_create, 0, nsgif_convert,
 	        0, nsgif_destroy, nsgif_redraw, 0, 0, 0},
 #endif
 #ifdef WITH_PNG
-	{nspng_create, nspng_process_data, nspng_convert, 0,
+	{nspng_create, nspng_process_data, nspng_convert,
 		0, nspng_destroy, nspng_redraw, 0, 0, 0},
 #endif
 #ifdef WITH_SPRITE
-	{sprite_create, sprite_process_data, sprite_convert, sprite_revive,
-		sprite_reformat, sprite_destroy, sprite_redraw, 0, 0, 0},
+	{sprite_create, sprite_process_data, sprite_convert,
+		0, sprite_destroy, sprite_redraw, 0, 0, 0},
 #endif
 #ifdef WITH_DRAW
-	{0, 0, draw_convert, 0,
+	{0, 0, draw_convert,
 		0, draw_destroy, draw_redraw, 0, 0, 0},
 #endif
 #ifdef WITH_PLUGIN
-	{plugin_create, plugin_process_data, plugin_convert, plugin_revive,
+	{plugin_create, plugin_process_data, plugin_convert,
 	        plugin_reformat, plugin_destroy, plugin_redraw,
 		plugin_add_instance, plugin_remove_instance,
 		plugin_reshape_instance},
 #endif
-	{0, 0, 0, 0, 0, 0, 0, 0, 0, 0}
+	{0, 0, 0, 0, 0, 0, 0, 0, 0}
 };
 #define HANDLER_MAP_COUNT (sizeof(handler_map) / sizeof(handler_map[0]))
 
@@ -166,33 +203,62 @@ content_type content_lookup(const char *mime_type)
 /**
  * Create a new content structure.
  *
+ * \param  url  URL of content, copied
+ * \return  the new content structure, or 0 on memory exhaustion
+ *
  * The type is initialised to CONTENT_UNKNOWN, and the status to
  * CONTENT_STATUS_TYPE_UNKNOWN.
  */
 
-struct content * content_create(char *url)
+struct content * content_create(const char *url)
 {
 	struct content *c;
 	struct content_user *user_sentinel;
 	LOG(("url %s", url));
-	c = xcalloc(1, sizeof(struct content));
-	c->url = xstrdup(url);
+	c = malloc(sizeof(struct content));
+	if (!c)
+		return 0;
+	user_sentinel = malloc(sizeof *user_sentinel);
+	if (!user_sentinel) {
+		free(c);
+		return 0;
+	}
+	c->url = strdup(url);
+	if (!c->url) {
+		free(c);
+		free(user_sentinel);
+		return 0;
+	}
 	c->type = CONTENT_UNKNOWN;
+	c->mime_type = 0;
 	c->status = CONTENT_STATUS_TYPE_UNKNOWN;
+	c->width = 0;
+	c->height = 0;
+	c->available_width = 0;
 	c->cache = 0;
 	c->size = sizeof(struct content);
-	c->fetch = 0;
-	c->source_data = 0;
-	c->source_size = 0;
-	c->mime_type = 0;
-	content_set_status(c, messages_get("Loading"));
-	user_sentinel = xcalloc(1, sizeof(*user_sentinel));
+	c->title = 0;
+	c->active = 0;
 	user_sentinel->callback = 0;
 	user_sentinel->p1 = user_sentinel->p2 = 0;
 	user_sentinel->next = 0;
 	c->user_list = user_sentinel;
+	content_set_status(c, messages_get("Loading"));
+	c->fetch = 0;
+	c->source_data = 0;
+	c->source_size = 0;
+	c->total_size = 0;
 	c->lock = 0;
 	c->destroy_pending = false;
+	c->no_error_pages = false;
+	c->error_count = 0;
+
+	c->prev = 0;
+	c->next = content_list;
+	if (content_list)
+		content_list->prev = c;
+	content_list = c;
+
 	return c;
 }
 
@@ -200,34 +266,51 @@ struct content * content_create(char *url)
 /**
  * Initialise the content for the specified type.
  *
+ * \param c        content structure
+ * \param type     content_type to initialise to
+ * \param mime_type  MIME-type string for this content
+ * \param params   array of strings, ordered attribute, value, attribute, ..., 0
+ * \return  true on success, false on error and error broadcast to users and
+ *		possibly reported
+ *
  * The type is updated to the given type, and a copy of mime_type is taken. The
  * status is changed to CONTENT_STATUS_LOADING. CONTENT_MSG_LOADING is sent to
  * all users. The create function for the type is called to initialise the type
  * specific parts of the content structure.
- *
- * \param c content structure
- * \param type content_type to initialise to
- * \param mime_type MIME-type string for this content
- * \param params array of strings, ordered attribute, value, attribute, ..., 0
  */
 
-void content_set_type(struct content *c, content_type type,
+bool content_set_type(struct content *c, content_type type,
 		const char *mime_type, const char *params[])
 {
-	union content_msg_data data;
+	union content_msg_data msg_data;
+
 	assert(c != 0);
 	assert(c->status == CONTENT_STATUS_TYPE_UNKNOWN);
 	assert(type < CONTENT_UNKNOWN);
+
 	LOG(("content %s, type %i", c->url, type));
+
+	c->mime_type = strdup(mime_type);
+	if (!c->mime_type) {
+		c->status = CONTENT_STATUS_ERROR;
+		msg_data.error = messages_get("NoMemory");
+		content_broadcast(c, CONTENT_MSG_ERROR, msg_data);
+		warn_user("NoMemory", 0);
+		return false;
+	}
+
 	c->type = type;
-	c->mime_type = xstrdup(mime_type);
 	c->status = CONTENT_STATUS_LOADING;
-	c->source_data = xcalloc(0, 1);
-	if (handler_map[type].create)
-		handler_map[type].create(c, params);
-	content_broadcast(c, CONTENT_MSG_LOADING, data);
-	/* c may be destroyed at this point as a result of
-	 * CONTENT_MSG_LOADING, so must not be accessed */
+
+	if (handler_map[type].create) {
+		if (!handler_map[type].create(c, params)) {
+			c->status = CONTENT_STATUS_ERROR;
+			return false;
+		}
+	}
+
+	content_broadcast(c, CONTENT_MSG_LOADING, msg_data);
+	return true;
 }
 
 
@@ -255,19 +338,44 @@ void content_set_status(struct content *c, const char *status_message, ...)
  * Process a block of source data.
  *
  * Calls the process_data function for the content.
+ *
+ * \param   c     content structure
+ * \param   data  new data to process
+ * \param   size  size of data
+ * \return  true on success, false on error and error broadcast to users and
+ *		possibly reported
  */
 
-void content_process_data(struct content *c, char *data, unsigned long size)
+bool content_process_data(struct content *c, char *data, unsigned int size)
 {
-	assert(c != 0);
+	char *source_data;
+	union content_msg_data msg_data;
+
+	assert(c);
+	assert(c->type < HANDLER_MAP_COUNT);
 	assert(c->status == CONTENT_STATUS_LOADING);
-	LOG(("content %s, size %lu", c->url, size));
-	c->source_data = xrealloc(c->source_data, c->source_size + size);
+	LOG(("content %s, size %u", c->url, size));
+
+	source_data = realloc(c->source_data, c->source_size + size);
+	if (!source_data) {
+		c->status = CONTENT_STATUS_ERROR;
+		msg_data.error = messages_get("NoMemory");
+		content_broadcast(c, CONTENT_MSG_ERROR, msg_data);
+		warn_user("NoMemory", 0);
+		return false;
+	}
+	c->source_data = source_data;
 	memcpy(c->source_data + c->source_size, data, size);
 	c->source_size += size;
 	c->size += size;
-	if (handler_map[c->type].process_data)
-		handler_map[c->type].process_data(c, data, size);
+
+	if (handler_map[c->type].process_data) {
+		if (!handler_map[c->type].process_data(c, data, size)) {
+			c->status = CONTENT_STATUS_ERROR;
+			return false;
+		}
+	}
+	return true;
 }
 
 
@@ -281,54 +389,34 @@ void content_process_data(struct content *c, char *data, unsigned long size)
  *   CONTENT_MSG_READY is sent to all users.
  * - If the conversion succeeds and is complete, the content gets status
  *   CONTENT_STATUS_DONE, and CONTENT_MSG_READY then CONTENT_MSG_DONE are sent.
- * - If the conversion fails, CONTENT_MSG_ERROR is sent. The content is then
- *   destroyed and must no longer be used.
+ * - If the conversion fails, CONTENT_MSG_ERROR is sent. The content will soon
+ *   be destroyed and must no longer be used.
  */
 
-void content_convert(struct content *c, unsigned long width, unsigned long height)
+void content_convert(struct content *c, int width, int height)
 {
-	union content_msg_data data;
-	assert(c != 0);
+	union content_msg_data msg_data;
+
+	assert(c);
 	assert(c->type < HANDLER_MAP_COUNT);
 	assert(c->status == CONTENT_STATUS_LOADING);
 	LOG(("content %s", c->url));
+
 	c->available_width = width;
 	if (handler_map[c->type].convert) {
-		if (handler_map[c->type].convert(c, width, height)) {
-			/* convert failed, destroy content */
-			data.error = "Conversion failed";
-			content_broadcast(c, CONTENT_MSG_ERROR, data);
-			if (c->cache)
-				cache_destroy(c);
-			content_destroy(c);
+		if (!handler_map[c->type].convert(c, width, height)) {
+			c->status = CONTENT_STATUS_ERROR;
 			return;
 		}
 	} else {
 		c->status = CONTENT_STATUS_DONE;
 	}
+
 	assert(c->status == CONTENT_STATUS_READY ||
 			c->status == CONTENT_STATUS_DONE);
-	content_broadcast(c, CONTENT_MSG_READY, data);
+	content_broadcast(c, CONTENT_MSG_READY, msg_data);
 	if (c->status == CONTENT_STATUS_DONE)
-		content_broadcast(c, CONTENT_MSG_DONE, data);
-}
-
-
-/**
- * Fix content that has been loaded from the cache.
- *
- * Calls the revive function for the content. The content will be processed for
- * display, for example dependencies loaded or reformated to current width.
- */
-
-void content_revive(struct content *c, unsigned long width, unsigned long height)
-{
-	assert(0);  /* unmaintained */
-	assert(c != 0);
-	if (c->status != CONTENT_STATUS_DONE)
-		return;
-	c->available_width = width;
-	handler_map[c->type].revive(c, width, height);
+		content_broadcast(c, CONTENT_MSG_DONE, msg_data);
 }
 
 
@@ -338,7 +426,7 @@ void content_revive(struct content *c, unsigned long width, unsigned long height
  * Calls the reformat function for the content.
  */
 
-void content_reformat(struct content *c, unsigned long width, unsigned long height)
+void content_reformat(struct content *c, int width, int height)
 {
 	union content_msg_data data;
 	assert(c != 0);
@@ -352,6 +440,29 @@ void content_reformat(struct content *c, unsigned long width, unsigned long heig
 }
 
 
+/**
+ * Destroys any contents in the content_list with no users or in
+ * CONTENT_STATUS_ERROR, and not with an active fetch or cached.
+ */
+
+void content_clean(void)
+{
+	struct content *c, *next;
+
+	for (c = content_list; c; c = next) {
+		next = c->next;
+		if (((!c->user_list->next && !c->cache) ||
+				c->status == CONTENT_STATUS_ERROR) &&
+				!c->fetch) {
+			LOG(("%p %s", c, c->url));
+			if (c->cache)
+				cache_destroy(c);
+			content_destroy(c);
+		}
+	}
+}
+
+
 /**
  * Destroy and free a content.
  *
@@ -371,6 +482,13 @@ void content_destroy(struct content *c)
 		return;
 	}
 
+	if (c->next)
+		c->next->prev = c->prev;
+	if (c->prev)
+		c->prev->next = c->next;
+	else
+		content_list = c->next;
+
 	if (c->type < HANDLER_MAP_COUNT && handler_map[c->type].destroy)
 		handler_map[c->type].destroy(c);
 	for (user = c->user_list; user != 0; user = next) {
@@ -411,9 +529,9 @@ void content_reset(struct content *c)
  * Calls the redraw function for the content, if it exists.
  */
 
-void content_redraw(struct content *c, long x, long y,
-		unsigned long width, unsigned long height,
-		long clip_x0, long clip_y0, long clip_x1, long clip_y1,
+void content_redraw(struct content *c, int x, int y,
+		int width, int height,
+		int clip_x0, int clip_y0, int clip_x1, int clip_y1,
 		float scale)
 {
 	assert(c != 0);
@@ -570,3 +688,9 @@ void content_reshape_instance(struct content *c, struct browser_window *bw,
 		handler_map[c->type].reshape_instance(c, bw, page, box, params, state);
 }
 
+
+
+void content_add_error(struct content *c, const char *token,
+		unsigned int line)
+{
+}
diff --git a/content/content.h b/content/content.h
index 13c4092ce..3fcbd39fe 100644
--- a/content/content.h
+++ b/content/content.h
@@ -14,12 +14,73 @@
  * Each content has a type. The type is used to call a specific implementation
  * of functions such as content_process_data().
  *
+ * The source data fetched from the URL is placed in the source_data buffer as
+ * it arrives.
+ *
  * Contents have an associated set of users, which are informed by a callback
  * when the state of the content changes or something interesting happens.
  *
  * Optionally, contents may have instances (depending on type). Instances
  * represent copies of the same URL, for example if a page is open in two
  * windows, or a page contains the same image twice.
+ *
+ * The status of a content follows a fixed order. Certain content functions
+ * change the state, and each change of state results in a message to all users
+ * of the content. The diagram below shows this:
+ * \dot
+ *   digraph status {
+ *     node [shape=plaintext, fontname=Helvetica, fontsize=9];
+ *     edge [fontname=Helvetica, fontsize=9];
+ *
+ *     content_create -> TYPE_UNKNOWN [style=bold];
+ *     TYPE_UNKNOWN -> content_set_type [style=bold];
+ *     content_set_type -> LOADING [label=MSG_LOADING, style=bold];
+ *     content_set_type -> ERROR [label=MSG_ERROR];
+ *     LOADING -> content_process_data [style=bold];
+ *     content_process_data -> LOADING [style=bold];
+ *     content_process_data -> ERROR [label=MSG_ERROR];
+ *     LOADING -> content_convert [style=bold];
+ *     content_convert -> READY [label=MSG_READY, style=bold];
+ *     content_convert -> DONE [label="MSG_READY\nMSG_DONE", style=bold];
+ *     content_convert -> ERROR [label=MSG_ERROR];
+ *     READY -> READY [style=bold];
+ *     READY -> DONE [label=MSG_DONE, style=bold];
+ *
+ *     TYPE_UNKNOWN [shape=ellipse];
+ *     LOADING [shape=ellipse];
+ *     READY [shape=ellipse];
+ *     DONE [shape=ellipse];
+ *     ERROR [shape=ellipse];
+ *   }
+ * \enddot
+ *
+ * To implement a new content type, implement the following functions:
+ *
+ * - <i>type</i>_create(): called to initialise type-specific fields in the
+ *   content structure. Optional.
+ *
+ * - <i>type</i>_process_data(): called when some data arrives. Optional.
+ *
+ * - <i>type</i>_convert(): called when data has finished arriving. The
+ *   content needs to be converted for display. Must set the status to one of
+ *   CONTENT_STATUS_READY or CONTENT_STATUS_DONE if no error occurs. Optional,
+ *   but probably required for non-trivial types.
+ *
+ * - <i>type</i>_reformat(): called when, for example, the window has been
+ *   resized, and the content needs reformatting for the new size. Optional.
+ *
+ * - <i>type</i>_destroy(): called when the content is being destroyed. Free all
+ *   resources. Optional.
+ *
+ * - <i>type</i>_redraw(): called to plot the content to screen.
+ *
+ * - <i>type</i>_(add|remove|reshape)_instance: ask James, this will probably
+ *   be redesigned sometime.
+ *
+ * - <i>type</i>_create(), <i>type</i>_process_data(), <i>type</i>_convert():
+ *   if an error occurs, must broadcast CONTENT_MSG_ERROR and return false.
+ *   Optionally use warn_user() for serious errors. The _destroy function will
+ *   be called soon after.
  */
 
 #ifndef _NETSURF_DESKTOP_CONTENT_H_
@@ -111,7 +172,9 @@ struct content {
 					  converted and is not safe to display. */
 		CONTENT_STATUS_READY,	/**< Some parts of content still being
 					  loaded, but can be displayed. */
-		CONTENT_STATUS_DONE	/**< All finished. */
+		CONTENT_STATUS_DONE,	/**< All finished. */
+		CONTENT_STATUS_ERROR	/**< Error occurred, content will be
+					  destroyed imminently. */
 	} status;		/**< Current status. */
 
 	int width, height;	/**< Dimensions, if applicable. */
@@ -147,7 +210,6 @@ struct content {
 	char *title;			/**< Title for browser window. */
 	unsigned int active;		/**< Number of child fetches or
 					  conversions currently in progress. */
-	int error;			/**< Non-0 if an error has occurred. */
 	struct content_user *user_list;	/**< List of users. */
 	char status_message[80];	/**< Text for status bar. */
 
@@ -159,26 +221,40 @@ struct content {
 	int lock;			/**< Content in use, do not destroy. */
 	bool destroy_pending;		/**< Destroy when lock returns to 0. */
 	bool no_error_pages;		/**< Used by fetchcache(). */
+
+	/** Array of first n rendering errors or warnings. */
+	struct {
+		const char *token;
+		unsigned int line;	/**< Line no, 0 if not applicable. */
+	} error_list[40];
+	unsigned int error_count;	/**< Number of valid error entries. */
+
+	struct content *prev;		/**< Previous in global content list. */
+	struct content *next;		/**< Next in global content list. */
 };
 
+extern struct content *content_list;
+extern const char *content_type_name[];
+extern const char *content_status_name[];
+
 
 struct browser_window;
 
 
 content_type content_lookup(const char *mime_type);
-struct content * content_create(char *url);
-void content_set_type(struct content *c, content_type type,
+struct content * content_create(const char *url);
+bool content_set_type(struct content *c, content_type type,
 		const char *mime_type, const char *params[]);
 void content_set_status(struct content *c, const char *status_message, ...);
-void content_process_data(struct content *c, char *data, unsigned long size);
-void content_convert(struct content *c, unsigned long width, unsigned long height);
-void content_revive(struct content *c, unsigned long width, unsigned long height);
-void content_reformat(struct content *c, unsigned long width, unsigned long height);
+bool content_process_data(struct content *c, char *data, unsigned int size);
+void content_convert(struct content *c, int width, int height);
+void content_reformat(struct content *c, int width, int height);
+void content_clean(void);
 void content_destroy(struct content *c);
 void content_reset(struct content *c);
-void content_redraw(struct content *c, long x, long y,
-		unsigned long width, unsigned long height,
-		long clip_x0, long clip_y0, long clip_x1, long clip_y1,
+void content_redraw(struct content *c, int x, int y,
+		int width, int height,
+		int clip_x0, int clip_y0, int clip_x1, int clip_y1,
 		float scale);
 void content_add_user(struct content *c,
 		void (*callback)(content_msg msg, struct content *c, void *p1,
@@ -199,5 +275,7 @@ void content_remove_instance(struct content *c, struct browser_window *bw,
 void content_reshape_instance(struct content *c, struct browser_window *bw,
 		struct content *page, struct box *box,
 		struct object_params *params, void **state);
+void content_add_error(struct content *c, const char *token,
+		unsigned int line);
 
 #endif
diff --git a/content/fetch.c b/content/fetch.c
index c8630f343..52d7effc5 100644
--- a/content/fetch.c
+++ b/content/fetch.c
@@ -31,9 +31,6 @@
 #include "curl/curl.h"
 #include "netsurf/utils/config.h"
 #include "netsurf/content/fetch.h"
-#ifdef riscos
-#include "netsurf/desktop/gui.h"
-#endif
 #include "netsurf/desktop/options.h"
 #ifdef WITH_AUTH
 #include "netsurf/desktop/401login.h"
@@ -587,6 +584,11 @@ size_t fetch_curl_data(void * data, size_t size, size_t nmemb, struct fetch *f)
 	/* send data to the caller */
 	LOG(("FETCH_DATA"));
 	f->callback(FETCH_DATA, f->p, data, size * nmemb);
+	if (f->aborting) {
+		f->locked--;
+		f->stopped = true;
+		return 0;
+	}
 
 	f->locked--;
 	return size * nmemb;
diff --git a/content/fetchcache.c b/content/fetchcache.c
index 164a11231..359b59809 100644
--- a/content/fetchcache.c
+++ b/content/fetchcache.c
@@ -59,7 +59,7 @@ static void fetchcache_error_page(struct content *c, const char *error);
  * \param post_urlenc url encoded post data, or 0 if none
  * \param post_multipart multipart post data, or 0 if none
  * \param cookies send and accept cookies
- * \return a new content, or 0 if an error occurred and no_error_pages is true
+ * \return a new content, or 0 if an error occurred
  */
 
 struct content * fetchcache(const char *url, char *referer,
@@ -77,12 +77,16 @@ struct content * fetchcache(const char *url, char *referer,
 		)
 {
 	struct content *c;
-	char *url1 = xstrdup(url);
-	char *hash = strchr(url1, '#');
+	char *url1;
+	char *hash;
 	char error_message[500];
 
+	url1 = strdup(url);
+	if (!url1)
+		return 0;
+
 	/* strip fragment identifier */
-	if (hash != 0)
+	if ((hash = strchr(url1, '#')))
 		*hash = 0;
 
 	LOG(("url %s", url1));
@@ -100,6 +104,10 @@ struct content * fetchcache(const char *url, char *referer,
 	}
 
 	c = content_create(url1);
+	if (!c) {
+		free(url1);
+		return 0;
+	}
 	content_add_user(c, callback, p1, p2);
 
 #ifdef WITH_POST
@@ -118,12 +126,10 @@ struct content * fetchcache(const char *url, char *referer,
 			,cookies
 #endif
 			);
-	if (c->fetch == 0) {
+	if (!c->fetch) {
 		LOG(("warning: fetch_start failed"));
-		if (c->cache)
-			cache_destroy(c);
+		c->status = CONTENT_STATUS_ERROR;
 		if (no_error_pages) {
-			content_destroy(c);
 			free(url1);
 			return 0;
 		}
@@ -144,6 +150,7 @@ struct content * fetchcache(const char *url, char *referer,
 
 void fetchcache_callback(fetch_msg msg, void *p, char *data, unsigned long size)
 {
+	bool res;
 	struct content *c = p;
 	content_type type;
 	char *mime_type, *url;
@@ -159,11 +166,13 @@ void fetchcache_callback(fetch_msg msg, void *p, char *data, unsigned long size)
 			mime_type = fetchcache_parse_type(data, &params);
 			type = content_lookup(mime_type);
 			LOG(("FETCH_TYPE, type %u", type));
-			content_set_type(c, type, mime_type, (const char**)params);
+			res = content_set_type(c, type, mime_type, params);
 			free(mime_type);
 			for (i = 0; params[i]; i++)
 				free(params[i]);
 			free(params);
+			if (!res)
+				fetch_abort(c->fetch);
 			if (c->cache && c->type == CONTENT_OTHER)
 				cache_destroy(c);
 			break;
@@ -181,7 +190,8 @@ void fetchcache_callback(fetch_msg msg, void *p, char *data, unsigned long size)
 						messages_get("Received"),
 						human_friendly_bytesize(c->source_size + size));
 			content_broadcast(c, CONTENT_MSG_STATUS, msg_data);
-			content_process_data(c, data, size);
+			if (!content_process_data(c, data, size))
+				fetch_abort(c->fetch);
 			break;
 
 		case FETCH_FINISHED:
@@ -199,9 +209,10 @@ void fetchcache_callback(fetch_msg msg, void *p, char *data, unsigned long size)
 			if (c->cache)
 				cache_destroy(c);
 			if (c->no_error_pages) {
+				c->status = CONTENT_STATUS_ERROR;
 				msg_data.error = data;
-				content_broadcast(c, CONTENT_MSG_ERROR, msg_data);
-				content_destroy(c);
+				content_broadcast(c, CONTENT_MSG_ERROR,
+						msg_data);
 			} else {
 				content_reset(c);
 				fetchcache_error_page(c, data);
@@ -233,15 +244,15 @@ void fetchcache_callback(fetch_msg msg, void *p, char *data, unsigned long size)
 			c->fetch = 0;
 			msg_data.auth_realm = data;
 			content_broadcast(c, CONTENT_MSG_AUTH, msg_data);
-			cache_destroy(c);
+			if (c->cache)
+				cache_destroy(c);
 			break;
 #endif
 		default:
 			assert(0);
 	}
 
-	if (--(c->lock) == 0 && c->destroy_pending)
-		content_destroy(c);
+	c->lock--;
 }
 
 
diff --git a/css/css.c b/css/css.c
index c42ad3d21..8239d77bf 100644
--- a/css/css.c
+++ b/css/css.c
@@ -87,6 +87,7 @@
 #include "netsurf/desktop/gui.h"
 #endif
 #include "netsurf/utils/log.h"
+#include "netsurf/utils/messages.h"
 #include "netsurf/utils/url.h"
 #include "netsurf/utils/utils.h"
 
@@ -241,7 +242,7 @@ const struct css_style css_blank_style = {
  * Convert a CONTENT_CSS for use.
  */
 
-int css_convert(struct content *c, unsigned int width, unsigned int height)
+bool css_convert(struct content *c, int width, int height)
 {
 	unsigned char *source_data;
 	unsigned char *current, *end, *token_text;
@@ -250,6 +251,7 @@ int css_convert(struct content *c, unsigned int width, unsigned int height)
 	void *parser;
 	struct css_parser_params param = {false, c, 0, false, false};
 	struct css_parser_token token_data;
+	union content_msg_data msg_data;
 
 	c->data.css.css = malloc(sizeof *c->data.css.css);
 	parser = css_parser_Alloc(malloc);
@@ -258,7 +260,11 @@ int css_convert(struct content *c, unsigned int width, unsigned int height)
 	if (!c->data.css.css || !parser || !source_data) {
 		free(c->data.css.css);
 		css_parser_Free(parser, free);
-		return 1;
+
+		msg_data.error = messages_get("NoMemory");
+		content_broadcast(c, CONTENT_MSG_ERROR, msg_data);
+		warn_user("NoMemory", 0);
+		return false;
 	}
 
 	for (i = 0; i != HASH_SIZE; i++)
@@ -292,8 +298,12 @@ int css_convert(struct content *c, unsigned int width, unsigned int height)
 	css_parser_(parser, 0, token_data, &param);
 	css_parser_Free(parser, free);
 
-	if (param.memory_error)
-		return 1;
+	if (param.memory_error) {
+		msg_data.error = messages_get("NoMemory");
+		content_broadcast(c, CONTENT_MSG_ERROR, msg_data);
+		warn_user("NoMemory", 0);
+		return false;
+	}
 
 	/*css_dump_stylesheet(c->data.css.css);*/
 
@@ -305,35 +315,7 @@ int css_convert(struct content *c, unsigned int width, unsigned int height)
 	}
 
 	c->status = CONTENT_STATUS_DONE;
-	return 0;
-}
-
-
-void css_revive(struct content *c, unsigned int width, unsigned int height)
-{
-	unsigned int i;
-	/* imported stylesheets */
-	for (i = 0; i != c->data.css.import_count; i++) {
-		c->data.css.import_content[i] = fetchcache(
-				c->data.css.import_url[i], c->url,
-				css_atimport_callback, c, (void*)i,
-				c->width, c->height, true
-#ifdef WITH_POST
-				, 0, 0
-#endif
-#ifdef WITH_COOKIES
-				, false
-#endif
-				);
-		if (c->data.css.import_content[i] == 0)
-			continue;
-		if (c->data.css.import_content[i]->status != CONTENT_STATUS_DONE)
-			c->active++;
-	}
-	while (c->active != 0) {
-		fetch_poll();
-		gui_multitask();
-	}
+	return true;
 }
 
 
@@ -371,6 +353,7 @@ void css_destroy(struct content *c)
 /**
  * Create a new struct css_node.
  *
+ * \param  stylesheet  content of type CONTENT_CSS
  * \param  type  type of node
  * \param  data  string for data, not copied
  * \param  data_length  length of data
@@ -610,7 +593,7 @@ void css_atimport_callback(content_msg msg, struct content *css,
 				content_remove_user(css, css_atimport_callback, c, (void*)i);
 				c->data.css.import_content[i] = 0;
 				c->active--;
-				c->error = 1;
+				content_add_error(c, "NotCSS", 0);
 			}
 			break;
 
@@ -626,7 +609,7 @@ void css_atimport_callback(content_msg msg, struct content *css,
 		case CONTENT_MSG_ERROR:
 			c->data.css.import_content[i] = 0;
 			c->active--;
-			c->error = 1;
+			content_add_error(c, "?", 0);
 			break;
 
 		case CONTENT_MSG_STATUS:
@@ -638,7 +621,7 @@ void css_atimport_callback(content_msg msg, struct content *css,
 			c->data.css.import_url[i] = strdup(data.redirect);
 			if (!c->data.css.import_url[i]) {
 				/** \todo report to user */
-				c->error = 1;
+				/* c->error = 1; */
 				return;
 			}
 			c->data.css.import_content[i] = fetchcache(
@@ -996,9 +979,41 @@ void css_dump_style(const struct css_style * const style)
 	if (style->z != css_empty_style.z)				\
 		fprintf(stderr, s ": %s; ", n[style->z]);
 
-        DUMP_KEYWORD(background_attachment, "background-attachment", css_background_attachment_name);
 	DUMP_COLOR(background_color, "background-color");
-	DUMP_KEYWORD(background_repeat, "background-repeat", css_background_repeat_name);
+	if (style->background_attachment !=
+			css_empty_style.background_attachment ||
+			style->background_image.type !=
+			css_empty_style.background_image.type ||
+			style->background_position.horz.pos !=
+			css_empty_style.background_position.horz.pos ||
+			style->background_position.vert.pos !=
+			css_empty_style.background_position.vert.pos ||
+			style->background_repeat !=
+			css_empty_style.background_repeat) {
+		fprintf(stderr, "background: ");
+		switch (style->background_image.type) {
+			case CSS_BACKGROUND_IMAGE_NONE:
+				fprintf(stderr, "none");
+				break;
+			case CSS_BACKGROUND_IMAGE_INHERIT:
+				fprintf(stderr, "inherit");
+				break;
+			case CSS_BACKGROUND_IMAGE_URI:
+				fprintf(stderr, "(%p) \"%s\"",
+						style->background_image.uri,
+						style->background_image.uri);
+				break;
+			default:
+				fprintf(stderr, "UNKNOWN");
+				break;
+		}
+		fprintf(stderr, " %s %s ",
+				css_background_attachment_name[
+						style->background_attachment],
+				css_background_repeat_name[
+						style->background_repeat]);
+		fprintf(stderr, "; ");
+	}
 	DUMP_KEYWORD(clear, "clear", css_clear_name);
 	DUMP_COLOR(color, "color");
 	DUMP_KEYWORD(cursor, "cursor", css_cursor_name);
@@ -1078,7 +1093,7 @@ void css_dump_style(const struct css_style * const style)
 	if (style->margin[0].margin != css_empty_style.margin[0].margin ||
 			style->margin[1].margin != css_empty_style.margin[1].margin ||
 			style->margin[2].margin != css_empty_style.margin[2].margin ||
-      			style->margin[3].margin != css_empty_style.margin[3].margin) {
+			style->margin[3].margin != css_empty_style.margin[3].margin) {
 		fprintf(stderr, "margin:");
 		for (i = 0; i != 4; i++) {
 			switch (style->margin[i].margin) {
@@ -1152,19 +1167,19 @@ void css_dump_style(const struct css_style * const style)
 	if (style->text_indent.size != css_empty_style.text_indent.size) {
 		fprintf(stderr, "text-indent: ");
 		switch (style->text_indent.size) {
-		        case CSS_TEXT_INDENT_LENGTH:
-		        	css_dump_length(&style->text_indent.value.length);
-		        	break;
-		        case CSS_TEXT_INDENT_PERCENT:
-		        	fprintf(stderr, "%g%%",
-		        		style->text_indent.value.percent);
-		        	break;
-		        case CSS_TEXT_INDENT_INHERIT:
-		        	fprintf(stderr, "inherit");
-		        	break;
-		        default:
-		        	fprintf(stderr, "UNKNOWN");
-		        	break;
+			case CSS_TEXT_INDENT_LENGTH:
+				css_dump_length(&style->text_indent.value.length);
+				break;
+			case CSS_TEXT_INDENT_PERCENT:
+				fprintf(stderr, "%g%%",
+					style->text_indent.value.percent);
+				break;
+			case CSS_TEXT_INDENT_INHERIT:
+				fprintf(stderr, "inherit");
+				break;
+			default:
+				fprintf(stderr, "UNKNOWN");
+				break;
 		}
 		fprintf(stderr, "; ");
 	}
diff --git a/css/css.h b/css/css.h
index d80df9333..e3ebca02e 100644
--- a/css/css.h
+++ b/css/css.h
@@ -311,8 +311,7 @@ struct css_parser_token {
 
 struct content;
 
-int css_convert(struct content *c, unsigned int width, unsigned int height);
-void css_revive(struct content *c, unsigned int width, unsigned int height);
+bool css_convert(struct content *c, int width, int height);
 void css_destroy(struct content *c);
 
 #ifdef CSS_INTERNALS
@@ -340,6 +339,7 @@ void *css_parser_Alloc(void *(*mallocProc)(/*size_t*/ int));
 void css_parser_Free(void *p, void (*freeProc)(void*));
 void css_parser_(void *yyp, int yymajor, struct css_parser_token yyminor,
 		struct css_parser_params *param);
+const char *css_parser_TokenName(int tokenType);
 
 #endif
 
diff --git a/debug/netsurfd.c b/debug/netsurfd.c
index fefc5d483..417af1d50 100644
--- a/debug/netsurfd.c
+++ b/debug/netsurfd.c
@@ -119,9 +119,9 @@ void plugin_decode(void *a, void *b, void *c, void *d)
 }
 #endif
 
-void html_redraw(struct content *c, long x, long y,
-		unsigned long width, unsigned long height,
-		long x0, long y0, long x1, long y1,
+void html_redraw(struct content *c, int x, int y,
+		int width, int height,
+		int x0, int y0, int x1, int y1,
 		float scale)
 {
 }
@@ -262,9 +262,9 @@ extern os_t os_read_monotonic_time(void)
 }
 #endif
 
-void warn_user(const char *warn)
+void warn_user(const char *warning, const char *detail)
 {
-	printf("WARNING: %s\n", warn);
+	printf("WARNING: %s %s\n", warning, detail);
 }
 
 void *ro_gui_current_redraw_gui = 0;
diff --git a/desktop/browser.c b/desktop/browser.c
index 8f1bb9a0c..2c8c28441 100644
--- a/desktop/browser.c
+++ b/desktop/browser.c
@@ -260,6 +260,7 @@ void browser_window_callback(content_msg msg, struct content *c,
 
 		case CONTENT_MSG_ERROR:
 			browser_window_set_status(bw, data.error);
+			warn_user(data.error, 0);
 			if (c == bw->loading_content)
 				bw->loading_content = 0;
 			else if (c == bw->current_content)
diff --git a/desktop/gui.h b/desktop/gui.h
index d7f98609d..f388f2d7d 100644
--- a/desktop/gui.h
+++ b/desktop/gui.h
@@ -62,6 +62,4 @@ void gui_window_place_caret(gui_window *g, int x, int y, int height);
 
 void gui_launch_url(const char *url);
 
-void warn_user(const char *warning, const char *detail);
-
 #endif
diff --git a/desktop/netsurf.c b/desktop/netsurf.c
index 106a33193..21f01177e 100644
--- a/desktop/netsurf.c
+++ b/desktop/netsurf.c
@@ -54,6 +54,7 @@ void netsurf_init(int argc, char** argv)
   struct utsname utsname;
 
   stdout = stderr;
+  curl_memdebug("memdump");
   if (uname(&utsname) != 0)
     LOG(("Failed to extract machine information\n"));
   else
@@ -63,12 +64,6 @@ void netsurf_init(int argc, char** argv)
   fetch_init();
   cache_init();
   fetchcache_init();
-#ifdef WITH_PNG
-  nspng_init();
-#endif
-#ifdef WITH_GIF
-  nsgif_init();
-#endif
   url_init();
 }
 
@@ -79,8 +74,9 @@ void netsurf_init(int argc, char** argv)
 
 void netsurf_poll(void)
 {
-  gui_poll(fetch_active);
-  fetch_poll();
+	content_clean();
+	gui_poll(fetch_active);
+	fetch_poll();
 }
 
 
diff --git a/makefile b/makefile
index 93940fa2a..22573d354 100644
--- a/makefile
+++ b/makefile
@@ -24,13 +24,13 @@ OBJECTS_COMMON += imagemap.o loginlist.o options.o		# desktop/
 
 OBJECTS_RISCOS = $(OBJECTS_COMMON)
 OBJECTS_RISCOS += browser.o netsurf.o version.o			# desktop/
-OBJECTS_RISCOS += 401login.o about.o constdata.o dialog.o download.o \
-	draw.o filetype.o font.o gif.o gifread.o gui.o help.o \
-	history.o htmlinstance.o htmlredraw.o jpeg.o menus.o \
-	mouseactions.o plugin.o png.o save.o save_complete.o \
-	save_draw.o save_text.o schedule.o sprite.o \
-	textselection.o theme.o thumbnail.o toolbar.o uri.o \
-	url_protocol.o wimp.o window.o				# riscos/
+OBJECTS_RISCOS += 401login.o about.o constdata.o debugwin.o \
+	dialog.o download.o draw.o filetype.o font.o gif.o \
+	gifread.o gui.o help.o history.o htmlinstance.o \
+	htmlredraw.o jpeg.o menus.o mouseactions.o plugin.o \
+	png.o save.o save_complete.o save_draw.o save_text.o \
+	schedule.o sprite.o textselection.o theme.o thumbnail.o \
+	toolbar.o uri.o url_protocol.o wimp.o window.o		# riscos/
 
 OBJECTS_DEBUG = $(OBJECTS_COMMON)
 OBJECTS_DEBUG += filetyped.o fontd.o netsurfd.o			# debug/
diff --git a/render/html.c b/render/html.c
index f3d19a072..d39dd32da 100644
--- a/render/html.c
+++ b/render/html.c
@@ -51,10 +51,11 @@ static bool html_object_type_permitted(const content_type type,
  * created.
  */
 
-void html_create(struct content *c, const char *params[])
+bool html_create(struct content *c, const char *params[])
 {
 	unsigned int i;
 	struct content_html_data *html = &c->data.html;
+	union content_msg_data msg_data;
 	xmlCharEncoding encoding = XML_CHAR_ENCODING_NONE;
 
 	html->encoding = NULL;
@@ -74,7 +75,7 @@ void html_create(struct content *c, const char *params[])
 	}
 
 	html->parser = htmlCreatePushParserCtxt(0, 0, "", 0, 0, encoding);
-	html->base_url = xstrdup(c->url);
+	html->base_url = strdup(c->url);
 	html->layout = 0;
 	html->background_colour = TRANSPARENT;
 	html->stylesheet_count = 0;
@@ -85,9 +86,24 @@ void html_create(struct content *c, const char *params[])
 	html->object = 0;
 	html->imagemaps = 0;
 	html->string_pool = pool_create(8000);
-	assert(html->string_pool);
 	html->box_pool = pool_create(sizeof (struct box) * 100);
-	assert(html->box_pool);
+
+	if (!html->parser || !html->base_url || !html->string_pool ||
+			!html->box_pool) {
+		htmlFreeParserCtxt(html->parser);
+		free(html->base_url);
+		if (html->string_pool)
+			pool_destroy(html->string_pool);
+		if (html->box_pool)
+			pool_destroy(html->box_pool);
+
+		msg_data.error = messages_get("NoMemory");
+		content_broadcast(c, CONTENT_MSG_ERROR, msg_data);
+		warn_user("NoMemory", 0);
+		return false;
+	}
+
+	return true;
 }
 
 
@@ -97,7 +113,7 @@ void html_create(struct content *c, const char *params[])
  * The data is parsed in chunks of size CHUNK, multitasking in between.
  */
 
-void html_process_data(struct content *c, char *data, unsigned long size)
+bool html_process_data(struct content *c, char *data, unsigned int size)
 {
 	unsigned long x;
 
@@ -120,6 +136,8 @@ void html_process_data(struct content *c, char *data, unsigned long size)
 		gui_multitask();
 	}
 	htmlParseChunk(c->data.html.parser, data + x, (int) (size - x), 0);
+
+	return true;
 }
 
 
@@ -138,11 +156,11 @@ void html_process_data(struct content *c, char *data, unsigned long size)
  * being fetched.
  */
 
-int html_convert(struct content *c, unsigned int width, unsigned int height)
+bool html_convert(struct content *c, int width, int height)
 {
 	xmlDoc *document;
 	xmlNode *html, *head;
-	union content_msg_data data;
+	union content_msg_data msg_data;
 
 	/* finish parsing */
 	htmlParseChunk(c->data.html.parser, "", 0, 1);
@@ -150,9 +168,12 @@ int html_convert(struct content *c, unsigned int width, unsigned int height)
 	/*xmlDebugDumpDocument(stderr, c->data.html.parser->myDoc);*/
 	htmlFreeParserCtxt(c->data.html.parser);
 	c->data.html.parser = 0;
-	if (document == NULL) {
+	if (!document) {
 		LOG(("Parsing failed"));
-		return 1;
+		msg_data.error = messages_get("ParsingFail");
+		content_broadcast(c, CONTENT_MSG_ERROR, msg_data);
+		warn_user("ParsingFail", 0);
+		return false;
 	}
 	/* Last change to pick the Content-Type charset information if the
 	 * server didn't send it (or we're reading the HTML from disk)
@@ -168,7 +189,10 @@ int html_convert(struct content *c, unsigned int width, unsigned int height)
 	if (html == 0 || strcmp((const char *) html->name, "html") != 0) {
 		LOG(("html element not found"));
 		xmlFreeDoc(document);
-		return 1;
+		msg_data.error = messages_get("ParsingFail");
+		content_broadcast(c, CONTENT_MSG_ERROR, msg_data);
+		warn_user("ParsingFail", 0);
+		return false;
 	}
 	for (head = html->children;
 			head != 0 && head->type != XML_ELEMENT_NODE;
@@ -188,7 +212,7 @@ int html_convert(struct content *c, unsigned int width, unsigned int height)
 	/* convert xml tree to box tree */
 	LOG(("XML to box"));
 	content_set_status(c, messages_get("Processing"));
-	content_broadcast(c, CONTENT_MSG_STATUS, data);
+	content_broadcast(c, CONTENT_MSG_STATUS, msg_data);
 	xml_to_box(html, c);
 	/*box_dump(c->data.html.layout->children, 0);*/
 
@@ -201,7 +225,7 @@ int html_convert(struct content *c, unsigned int width, unsigned int height)
 
 	/* layout the box tree */
 	content_set_status(c, messages_get("Formatting"));
-	content_broadcast(c, CONTENT_MSG_STATUS, data);
+	content_broadcast(c, CONTENT_MSG_STATUS, msg_data);
 	LOG(("Layout document"));
 	layout_document(c->data.html.layout->children, width,
 			c->data.html.box_pool);
@@ -218,7 +242,7 @@ int html_convert(struct content *c, unsigned int width, unsigned int height)
 		content_set_status(c, messages_get("FetchObjs"), c->active);
 	}
 
-	return 0;
+	return true;
 }
 
 
@@ -281,7 +305,6 @@ void html_find_stylesheets(struct content *c, xmlNode *head)
 	c->data.html.stylesheet_content[1] = 0;
 	c->data.html.stylesheet_count = 2;
 
-	c->error = 0;
 	c->active = 0;
 
 	c->data.html.stylesheet_content[0] = fetchcache(
@@ -396,6 +419,8 @@ void html_find_stylesheets(struct content *c, xmlNode *head)
 				const char *params[] = { 0 };
 				c->data.html.stylesheet_content[1] =
 						content_create(c->data.html.base_url);
+				if (!c->data.html.stylesheet_content[1])
+					return false;
 				content_set_type(c->data.html.stylesheet_content[1],
 						CONTENT_CSS, "text/css", params);
 			}
@@ -434,10 +459,10 @@ void html_find_stylesheets(struct content *c, xmlNode *head)
 		gui_multitask();
 	}
 
-	if (c->error) {
-		content_set_status(c, "Warning: some stylesheets failed to load");
-		content_broadcast(c, CONTENT_MSG_STATUS, msg_data);
-	}
+/* 	if (c->error) { */
+/* 		content_set_status(c, "Warning: some stylesheets failed to load"); */
+/* 		content_broadcast(c, CONTENT_MSG_STATUS, msg_data); */
+/* 	} */
 }
 
 
@@ -457,7 +482,7 @@ void html_convert_css_callback(content_msg msg, struct content *css,
 			if (css->type != CONTENT_CSS) {
 				c->data.html.stylesheet_content[i] = 0;
 				c->active--;
-				c->error = 1;
+				content_add_error(c, "NotCSS", 0);
 				content_set_status(c, messages_get("NotCSS"));
 				content_broadcast(c, CONTENT_MSG_STATUS, data);
 				content_remove_user(css, html_convert_css_callback, c, (void*)i);
@@ -475,7 +500,7 @@ void html_convert_css_callback(content_msg msg, struct content *css,
 		case CONTENT_MSG_ERROR:
 			c->data.html.stylesheet_content[i] = 0;
 			c->active--;
-			c->error = 1;
+			content_add_error(c, "?", 0);
 			break;
 
 		case CONTENT_MSG_STATUS:
@@ -506,7 +531,7 @@ void html_convert_css_callback(content_msg msg, struct content *css,
 		case CONTENT_MSG_AUTH:
 		        c->data.html.stylesheet_content[i] = 0;
 			c->active--;
-			c->error = 1;
+			content_add_error(c, "?", 0);
 		        break;
 #endif
 
@@ -590,7 +615,7 @@ void html_object_callback(content_msg msg, struct content *object,
 			/* not acceptable */
 			c->data.html.object[i].content = 0;
 			c->active--;
-			c->error = 1;
+			content_add_error(c, "?", 0);
 			content_set_status(c, messages_get("BadObject"));
 			content_broadcast(c, CONTENT_MSG_STATUS, data);
 			content_remove_user(object, html_object_callback, c, (void*)i);
@@ -611,7 +636,7 @@ void html_object_callback(content_msg msg, struct content *object,
 		case CONTENT_MSG_ERROR:
 			c->data.html.object[i].content = 0;
 			c->active--;
-			c->error = 1;
+			content_add_error(c, "?", 0);
 			content_set_status(c, messages_get("ObjError"),
 					data.error);
 			content_broadcast(c, CONTENT_MSG_STATUS, data);
@@ -674,7 +699,7 @@ void html_object_callback(content_msg msg, struct content *object,
 		case CONTENT_MSG_AUTH:
 		        c->data.html.object[i].content = 0;
 			c->active--;
-			c->error = 1;
+			content_add_error(c, "?", 0);
 		        break;
 #endif
 
@@ -754,47 +779,11 @@ bool html_object_type_permitted(const content_type type,
 }
 
 
-void html_revive(struct content *c, unsigned int width, unsigned int height)
-{
-	unsigned int i;
-
-	assert(0);  /* dead code, do not use as is */
-
-	/* reload objects and fix pointers */
-	for (i = 0; i != c->data.html.object_count; i++) {
-		if (c->data.html.object[i].content != 0) {
-			c->data.html.object[i].content = fetchcache(
-					c->data.html.object[i].url, c->url,
-					html_object_callback,
-					c, (void*)i, 0, 0, true
-#ifdef WITH_POST
-					, 0, 0
-#endif
-#ifdef WITH_COOKIES
-					, false
-#endif
-					);
-			if (c->data.html.object[i].content &&
-					c->data.html.object[i].content->status != CONTENT_STATUS_DONE)
-				c->active++;
-		}
-	}
-
-	layout_document(c->data.html.layout->children, width,
-			c->data.html.box_pool);
-	c->width = c->data.html.layout->children->width;
-	c->height = c->data.html.layout->children->height;
-
-	if (c->active != 0)
-		c->status = CONTENT_STATUS_READY;
-}
-
-
 /**
  * Reformat a CONTENT_HTML to a new width.
  */
 
-void html_reformat(struct content *c, unsigned int width, unsigned int height)
+void html_reformat(struct content *c, int width, int height)
 {
 	layout_document(c->data.html.layout->children, width,
 			c->data.html.box_pool);
diff --git a/render/html.h b/render/html.h
index 683c5dc73..9580beacb 100644
--- a/render/html.h
+++ b/render/html.h
@@ -83,11 +83,10 @@ struct content_html_data {
 };
 
 
-void html_create(struct content *c, const char *params[]);
-void html_process_data(struct content *c, char *data, unsigned long size);
-int html_convert(struct content *c, unsigned int width, unsigned int height);
-void html_revive(struct content *c, unsigned int width, unsigned int height);
-void html_reformat(struct content *c, unsigned int width, unsigned int height);
+bool html_create(struct content *c, const char *params[]);
+bool html_process_data(struct content *c, char *data, unsigned int size);
+bool html_convert(struct content *c, int width, int height);
+void html_reformat(struct content *c, int width, int height);
 void html_destroy(struct content *c);
 void html_fetch_object(struct content *c, char *url, struct box *box,
 		const content_type *permitted_types,
@@ -106,9 +105,9 @@ void html_remove_instance(struct content *c, struct browser_window *bw,
 		struct object_params *params, void **state);
 
 /* in riscos/htmlredraw.c */
-void html_redraw(struct content *c, long x, long y,
-		unsigned long width, unsigned long height,
-		long clip_x0, long clip_y0, long clip_x1, long clip_y1,
+void html_redraw(struct content *c, int x, int y,
+		int width, int height,
+		int clip_x0, int clip_y0, int clip_x1, int clip_y1,
 		float scale);
 
 #endif
diff --git a/render/textplain.c b/render/textplain.c
index 72ad98a4f..0a7f5db7c 100644
--- a/render/textplain.c
+++ b/render/textplain.c
@@ -15,14 +15,18 @@ static const char header[] = "<html><body><pre>";
 static const char footer[] = "</pre></body></html>";
 
 
-void textplain_create(struct content *c, const char *params[])
+bool textplain_create(struct content *c, const char *params[])
 {
-	html_create(c, params);
+	if (!html_create(c, params))
+		/* html_create() must have broadcast MSG_ERROR already, so we
+		 * don't need to. */
+		return false;
 	htmlParseChunk(c->data.html.parser, header, sizeof(header) - 1, 0);
+	return true;
 }
 
 
-int textplain_convert(struct content *c, unsigned int width, unsigned int height)
+bool textplain_convert(struct content *c, int width, int height)
 {
 	htmlParseChunk(c->data.html.parser, footer, sizeof(footer) - 1, 0);
 	c->type = CONTENT_HTML;
diff --git a/render/textplain.h b/render/textplain.h
index 859ff9e62..63550e181 100644
--- a/render/textplain.h
+++ b/render/textplain.h
@@ -10,7 +10,7 @@
 
 struct content;
 
-void textplain_create(struct content *c, const char *params[]);
-int textplain_convert(struct content *c, unsigned int width, unsigned int height);
+bool textplain_create(struct content *c, const char *params[]);
+bool textplain_convert(struct content *c, int width, int height);
 
 #endif
diff --git a/riscos/dialog.c b/riscos/dialog.c
index e59b3ba02..47c279515 100644
--- a/riscos/dialog.c
+++ b/riscos/dialog.c
@@ -33,7 +33,7 @@ wimp_w dialog_info, dialog_saveas, dialog_config, dialog_config_br,
 	dialog_401li,
 #endif
 	dialog_zoom, dialog_pageinfo, dialog_objinfo, dialog_tooltip,
-	dialog_warning, dialog_config_th_pane;
+	dialog_warning, dialog_config_th_pane, dialog_debug;
 
 static int font_size;
 static int font_min_size;
@@ -83,6 +83,7 @@ void ro_gui_dialog_init(void)
 	dialog_objinfo = ro_gui_dialog_create("objectinfo");
 	dialog_tooltip = ro_gui_dialog_create("tooltip");
 	dialog_warning = ro_gui_dialog_create("warning");
+	dialog_debug = ro_gui_dialog_create("debug");
 
 	set_browser_choices();
 	set_proxy_choices();
diff --git a/riscos/draw.c b/riscos/draw.c
index b59a96261..fbe4251cf 100644
--- a/riscos/draw.c
+++ b/riscos/draw.c
@@ -18,56 +18,47 @@
 
 #ifdef WITH_DRAW
 
-int draw_convert(struct content *c, unsigned int width, unsigned int height)
+bool draw_convert(struct content *c, int width, int height)
 {
+	union content_msg_data msg_data;
+	os_box bbox;
 	os_error *error;
-	os_trfm *matrix = xcalloc(1, sizeof(os_trfm));
-	os_box *bbox = xcalloc(1, sizeof(os_box));
-
-        /* Full size image (1:1) */
-        matrix->entries[0][0] = 1 << 16;
-        matrix->entries[0][1] = 0;
-        matrix->entries[1][0] = 0;
-        matrix->entries[1][1] = 1 << 16;
-        matrix->entries[2][0] = 0;
-        matrix->entries[2][1] = 0;
 
         /* BBox contents in Draw units (256*OS unit) */
 	error = xdrawfile_bbox(0, (drawfile_diagram*)(c->source_data),
-	                       (int)c->source_size, matrix, bbox);
-
+			(int) c->source_size, 0, &bbox);
         if (error) {
-                LOG(("error: %s", error->errmess));
-                xfree(matrix);
-                xfree(bbox);
-                return 1;
+                LOG(("xdrawfile_bbox: 0x%x: %s",
+                		error->errnum, error->errmess));
+		msg_data.error = error->errmess;
+		content_broadcast(c, CONTENT_MSG_ERROR, msg_data);
+                return false;
         }
 
         /* c->width & c->height stored as (OS units/2)
            => divide by 512 to convert from draw units */
-	c->width = ((bbox->x1 - bbox->x0) / 512);
-	c->height = ((bbox->y1 - bbox->y0) / 512);
-	c->data.draw.x0 = bbox->x0 / 2;
-	c->data.draw.y0 = bbox->y0 / 2;
-	c->title = xcalloc(100, 1);
-	sprintf(c->title, messages_get("DrawTitle"), c->width,
+	c->width = ((bbox.x1 - bbox.x0) / 512);
+	c->height = ((bbox.y1 - bbox.y0) / 512);
+	c->data.draw.x0 = bbox.x0 / 2;
+	c->data.draw.y0 = bbox.y0 / 2;
+	c->title = malloc(100);
+	if (c->title)
+		snprintf(c->title, 100, messages_get("DrawTitle"), c->width,
 	                                c->height, c->source_size);
 	c->status = CONTENT_STATUS_DONE;
-	xfree(matrix);
-	xfree(bbox);
-	return 0;
+	return true;
 }
 
 
 void draw_destroy(struct content *c)
 {
-	xfree(c->title);
+	free(c->title);
 }
 
 
-void draw_redraw(struct content *c, long x, long y,
-		unsigned long width, unsigned long height,
-		long clip_x0, long clip_y0, long clip_x1, long clip_y1,
+void draw_redraw(struct content *c, int x, int y,
+		int width, int height,
+		int clip_x0, int clip_y0, int clip_x1, int clip_y1,
 		float scale)
 {
         os_trfm matrix;
diff --git a/riscos/draw.h b/riscos/draw.h
index bb1f88d3f..67752a3dd 100644
--- a/riscos/draw.h
+++ b/riscos/draw.h
@@ -14,10 +14,10 @@ struct content_draw_data {
 	int x0, y0;
 };
 
-int draw_convert(struct content *c, unsigned int width, unsigned int height);
+bool draw_convert(struct content *c, int width, int height);
 void draw_destroy(struct content *c);
-void draw_redraw(struct content *c, long x, long y,
-		unsigned long width, unsigned long height,
-		long clip_x0, long clip_y0, long clip_x1, long clip_y1,
+void draw_redraw(struct content *c, int x, int y,
+		int width, int height,
+		int clip_x0, int clip_y0, int clip_x1, int clip_y1,
 		float scale);
 #endif
diff --git a/riscos/gif.c b/riscos/gif.c
index e15c5ebe4..9cd50829a 100644
--- a/riscos/gif.c
+++ b/riscos/gif.c
@@ -21,6 +21,7 @@
 #include "netsurf/riscos/options.h"
 #include "netsurf/riscos/tinct.h"
 #include "netsurf/utils/log.h"
+#include "netsurf/utils/messages.h"
 #include "netsurf/utils/utils.h"
 
 
@@ -38,19 +39,27 @@
 
 static void nsgif_animate(void *p);
 
-void nsgif_init(void) {
-}
 
-void nsgif_create(struct content *c, const char *params[]) {
+bool nsgif_create(struct content *c, const char *params[]) {
+	union content_msg_data msg_data;
   	/*	Initialise our data structure
   	*/
-  	c->data.gif.gif = (gif_animation *)xcalloc(sizeof(gif_animation), 1);
+  	c->data.gif.gif = calloc(sizeof(gif_animation), 1);
+  	if (!c->data.gif.gif) {
+		msg_data.error = messages_get("NoMemory");
+		content_broadcast(c, CONTENT_MSG_ERROR, msg_data);
+		warn_user("NoMemory", 0);
+  		return false;
+  	}
 	c->data.gif.current_frame = 0;
+	return true;
 }
 
 
-int nsgif_convert(struct content *c, unsigned int iwidth, unsigned int iheight) {
+bool nsgif_convert(struct content *c, int iwidth, int iheight) {
+	int res;
 	struct gif_animation *gif;
+	union content_msg_data msg_data;
 
 	/*	Create our animation
 	*/
@@ -61,38 +70,59 @@ int nsgif_convert(struct content *c, unsigned int iwidth, unsigned int iheight)
 
 	/*	Initialise the GIF
 	*/
-	gif_initialise(gif);
+	res = gif_initialise(gif);
+	if (res < 0) {
+		if (res == GIF_INSUFFICIENT_MEMORY) {
+			msg_data.error = messages_get("NoMemory");
+			content_broadcast(c, CONTENT_MSG_ERROR, msg_data);
+			warn_user("NoMemory", 0);
+		} else {
+			msg_data.error = messages_get("BadGIF");
+			content_broadcast(c, CONTENT_MSG_ERROR, msg_data);
+		}
+		return false;
+	}
 
 	/*	Abort on bad GIFs
 	*/
-	if ((gif->frame_count_partial == 0) || (gif->width == 0) || (gif->height == 0)) return 1;
+	if ((gif->frame_count_partial == 0) || (gif->width == 0) ||
+			(gif->height == 0)) {
+		msg_data.error = messages_get("BadGIF");
+		content_broadcast(c, CONTENT_MSG_ERROR, msg_data);
+		return false;
+	}
 
 	/*	Store our content width
 	*/
 	c->width = gif->width;
 	c->height = gif->height;
 
+	/*	Initialise the first frame so if we try to use the image data directly prior to
+		a plot we get some sensible data
+	*/
+	res = gif_decode_frame(c->data.gif.gif, 0);
+	if (res < 0 && res != GIF_INSUFFICIENT_FRAME_DATA) {
+		msg_data.error = messages_get("BadGIF");
+		content_broadcast(c, CONTENT_MSG_ERROR, msg_data);
+		return false;
+	}
+
 	/*	Schedule the animation if we have one
 	*/
 	if (gif->frame_count > 1) {
 		schedule(gif->frames[0].frame_delay, nsgif_animate, c);
 	}
 
-	/*	Initialise the first frame so if we try to use the image data directly prior to
-		a plot we get some sensible data
-	*/
-	gif_decode_frame(c->data.gif.gif, 0);
-
 	/*	Exit as a success
 	*/
 	c->status = CONTENT_STATUS_DONE;
-	return 0;
+	return true;
 }
 
 
-void nsgif_redraw(struct content *c, long x, long y,
-		unsigned long width, unsigned long height,
-		long clip_x0, long clip_y0, long clip_x1, long clip_y1,
+void nsgif_redraw(struct content *c, int x, int y,
+		int width, int height,
+		int clip_x0, int clip_y0, int clip_x1, int clip_y1,
 		float scale) {
 
 	int previous_frame;
@@ -152,7 +182,7 @@ void nsgif_destroy(struct content *c)
 	*/
 	schedule_remove(nsgif_animate, c);
 	gif_finalise(c->data.gif.gif);
-	xfree(c->data.gif.gif);
+	free(c->data.gif.gif);
 }
 
 
diff --git a/riscos/gif.h b/riscos/gif.h
index 526716dec..f6365071a 100644
--- a/riscos/gif.h
+++ b/riscos/gif.h
@@ -25,13 +25,12 @@ struct content_gif_data {
 	unsigned int current_frame;
 };
 
-void nsgif_init(void);
-void nsgif_create(struct content *c, const char *params[]);
-int nsgif_convert(struct content *c, unsigned int width, unsigned int height);
+bool nsgif_create(struct content *c, const char *params[]);
+bool nsgif_convert(struct content *c, int width, int height);
 void nsgif_destroy(struct content *c);
-void nsgif_redraw(struct content *c, long x, long y,
-		unsigned long width, unsigned long height,
-		long clip_x0, long clip_y0, long clip_x1, long clip_y1,
+void nsgif_redraw(struct content *c, int x, int y,
+		int width, int height,
+		int clip_x0, int clip_y0, int clip_x1, int clip_y1,
 		float scale);
 
 #endif
diff --git a/riscos/gifread.c b/riscos/gifread.c
index 3f4306374..3e9d39b69 100644
--- a/riscos/gifread.c
+++ b/riscos/gifread.c
@@ -96,11 +96,12 @@ static int clear_image = FALSE;
 	any information that hasn't already been decoded.
 	If an error occurs, all previously decoded frames are retained.
 
-	@return -5 for GIF frame data error
-		-4 for insufficient data to process any more frames
-		-3 for memory error
-		-2 for GIF error
-		-1 for insufficient data to do anything
+	@return GIF_FRAME_DATA_ERROR for GIF frame data error
+		GIF_INSUFFICIENT_FRAME_DATA for insufficient data to process
+		          any more frames
+		GIF_INSUFFICIENT_MEMORY for memory error
+		GIF_DATA_ERROR for GIF error
+		GIF_INSUFFICIENT_DATA for insufficient data to do anything
 		0 for successful decoding
 		1 for successful decoding (all frames completely read)
 */
@@ -112,7 +113,7 @@ int gif_initialise(struct gif_animation *gif) {
 
 	/*	Check for sufficient data to be a GIF
 	*/
-	if (gif->buffer_size < 13) return -1;
+	if (gif->buffer_size < 13) return GIF_INSUFFICIENT_DATA;
 
 	/*	Get our current processing position
 	*/
@@ -244,12 +245,12 @@ int gif_initialise(struct gif_animation *gif) {
 	if (gif->frame_count_partial > 0) {
 		/*	Set the redraw for the first frame to the maximum frame size
 		*/
-		gif->frames[0].redraw_required = 0;	
+		gif->frames[0].redraw_required = 0;
 		gif->frames[0].redraw_x = 0;
 		gif->frames[0].redraw_y = 0;
 		gif->frames[0].redraw_width = gif->width;
 		gif->frames[0].redraw_height = gif->height;
-		
+
 		/*	We now work backwards to update the redraw characteristics of frames
 			with clear codes to stop a snowball effect of the redraw areas. It doesn't
 			really make much difference for most images, and will not work as well
@@ -282,7 +283,7 @@ int gif_initialise(struct gif_animation *gif) {
 				}
 			}
 		}
-		
+
 	}
 
 	/*	If there was a memory error tell the caller
@@ -512,7 +513,7 @@ int gif_initialise_frame(struct gif_animation *gif) {
 			gif->frames[frame].redraw_width = width;
 			gif->frames[frame].redraw_height = height;
 		}
-		
+
 		/*	if we are clearing the background then we need to redraw enough to cover the previous
 			frame too
 		*/
@@ -584,10 +585,10 @@ int gif_initialise_frame(struct gif_animation *gif) {
 
 /**	Decodes a GIF frame.
 
-	@return -5 for GIF frame data error
-		-4 for insufficient data to complete the frame
-		-2 for GIF error (invalid frame header)
-		-1 for insufficient data to do anything
+	@return GIF_FRAME_DATA_ERROR for GIF frame data error
+		GIF_INSUFFICIENT_FRAME_DATA for insufficient data to complete the frame
+		GIF_DATA_ERROR for GIF error (invalid frame header)
+		GIF_INSUFFICIENT_DATA for insufficient data to do anything
 		0 for successful decoding
 */
 int gif_decode_frame(struct gif_animation *gif, unsigned int frame) {
diff --git a/riscos/gui.c b/riscos/gui.c
index 3f33e0581..dc36dd1bf 100644
--- a/riscos/gui.c
+++ b/riscos/gui.c
@@ -374,7 +374,7 @@ void ro_gui_check_resolvers(void)
 	if (resolvers) {
 		LOG(("Inet$Resolvers '%s'", resolvers));
 	} else {
-		LOG(("Inet$Resolvers not set", resolvers));
+		LOG(("Inet$Resolvers not set"));
 		warn_user("Resolvers", 0);
 	}
 }
@@ -613,6 +613,8 @@ void ro_gui_redraw_window_request(wimp_draw *redraw)
 		ro_gui_redraw_config_th_pane(redraw);
 	else if (redraw->w == history_window)
 		ro_gui_history_redraw(redraw);
+	else if (redraw->w == dialog_debug)
+		ro_gui_debugwin_redraw(redraw);
 	else {
 		g = ro_lookup_gui_from_w(redraw->w);
 		if (g != NULL)
@@ -660,6 +662,11 @@ void ro_gui_close_window_request(wimp_close *close)
 {
 	gui_window *g;
 
+	if (close->w == dialog_debug) {
+		ro_gui_debugwin_close();
+		return;
+	}
+
 	g = ro_lookup_gui_from_w(close->w);
 
 	if (g) {
@@ -719,6 +726,8 @@ void ro_gui_icon_bar_click(wimp_pointer *pointer)
 				"file:///%%3CNetSurf$Dir%%3E/Docs/intro_%s",
 				option_language)) >= 0 && length < sizeof(url))
 			browser_window_create(url, NULL);
+	} else if (pointer->buttons == wimp_CLICK_ADJUST) {
+		ro_gui_debugwin_open();
 	}
 }
 
diff --git a/riscos/gui.h b/riscos/gui.h
index db56bbc77..91839cc76 100644
--- a/riscos/gui.h
+++ b/riscos/gui.h
@@ -23,7 +23,8 @@
 
 extern wimp_w dialog_info, dialog_saveas, dialog_config, dialog_config_br,
 	dialog_config_prox, dialog_config_th, dialog_zoom, dialog_pageinfo,
-	dialog_objinfo, dialog_tooltip, dialog_warning, dialog_config_th_pane;
+	dialog_objinfo, dialog_tooltip, dialog_warning, dialog_config_th_pane,
+	dialog_debug;
 extern wimp_w history_window;
 extern wimp_menu *iconbar_menu, *browser_menu, *combo_menu;
 extern int iconbar_menu_height;
@@ -195,6 +196,11 @@ void schedule(int t, void (*callback)(void *p), void *p);
 void schedule_remove(void (*callback)(void *p), void *p);
 void schedule_run(void);
 
+/* in debugwin.c */
+void ro_gui_debugwin_open(void);
+void ro_gui_debugwin_close(void);
+void ro_gui_debugwin_redraw(wimp_draw *redraw);
+
 /* icon numbers */
 #define ICON_TOOLBAR_BACK 0
 #define ICON_TOOLBAR_FORWARD 1
diff --git a/riscos/htmlredraw.c b/riscos/htmlredraw.c
index 3e40aa6ac..d39acc1f4 100644
--- a/riscos/htmlredraw.c
+++ b/riscos/htmlredraw.c
@@ -60,9 +60,9 @@ static os_trfm trfm = { {
 		{ 0, 0 } } };
 
 
-void html_redraw(struct content *c, long x, long y,
-		unsigned long width, unsigned long height,
-		long clip_x0, long clip_y0, long clip_x1, long clip_y1,
+void html_redraw(struct content *c, int x, int y,
+		int width, int height,
+		int clip_x0, int clip_y0, int clip_x1, int clip_y1,
 		float scale)
 {
 	bool select_on = false;
diff --git a/riscos/jpeg.c b/riscos/jpeg.c
index 14128192d..ea8cb120b 100644
--- a/riscos/jpeg.c
+++ b/riscos/jpeg.c
@@ -40,6 +40,9 @@
 #endif
 
 
+static char nsjpeg_error_buffer[JMSG_LENGTH_MAX];
+
+
 struct nsjpeg_error_mgr {
 	struct jpeg_error_mgr pub;
 	jmp_buf setjmp_buffer;
@@ -57,9 +60,10 @@ static void nsjpeg_term_source(j_decompress_ptr cinfo);
  * Create a CONTENT_JPEG.
  */
 
-void nsjpeg_create(struct content *c, const char *params[])
+bool nsjpeg_create(struct content *c, const char *params[])
 {
 	c->data.jpeg.sprite_area = 0;
+	return true;
 }
 
 
@@ -67,7 +71,7 @@ void nsjpeg_create(struct content *c, const char *params[])
  * Convert a CONTENT_JPEG for display.
  */
 
-int nsjpeg_convert(struct content *c, unsigned int w, unsigned int h)
+bool nsjpeg_convert(struct content *c, int w, int h)
 {
 	struct jpeg_decompress_struct cinfo;
 	struct nsjpeg_error_mgr jerr;
@@ -80,13 +84,17 @@ int nsjpeg_convert(struct content *c, unsigned int w, unsigned int h)
 	unsigned int area_size;
 	osspriteop_area *sprite_area = 0;
 	osspriteop_header *sprite;
+	union content_msg_data msg_data;
 
 	cinfo.err = jpeg_std_error(&jerr.pub);
 	jerr.pub.error_exit = nsjpeg_error_exit;
 	if (setjmp(jerr.setjmp_buffer)) {
 		jpeg_destroy_decompress(&cinfo);
 		free(sprite_area);
-		return 1;
+
+		msg_data.error = nsjpeg_error_buffer;
+		content_broadcast(c, CONTENT_MSG_ERROR, msg_data);
+		return false;
 	}
 	jpeg_create_decompress(&cinfo);
 	source_mgr.next_input_byte = c->source_data;
@@ -104,7 +112,12 @@ int nsjpeg_convert(struct content *c, unsigned int w, unsigned int h)
 	sprite_area = malloc(area_size);
 	if (!sprite_area) {
 		LOG(("malloc failed"));
-		return 1;
+		jpeg_destroy_decompress(&cinfo);
+
+		msg_data.error = messages_get("NoMemory");
+		content_broadcast(c, CONTENT_MSG_ERROR, msg_data);
+		warn_user("NoMemory", 0);
+		return false;
 	}
 
 	/* area control block */
@@ -142,10 +155,10 @@ int nsjpeg_convert(struct content *c, unsigned int w, unsigned int h)
 	c->data.jpeg.sprite_area = sprite_area;
 	c->title = malloc(100);
 	if (c->title)
-		sprintf(c->title, messages_get("JPEGTitle"),
+		snprintf(c->title, 100, messages_get("JPEGTitle"),
 				width, height, c->source_size);
 	c->status = CONTENT_STATUS_DONE;
-	return 0;
+	return true;
 }
 
 
@@ -158,7 +171,7 @@ int nsjpeg_convert(struct content *c, unsigned int w, unsigned int h)
 void nsjpeg_error_exit(j_common_ptr cinfo)
 {
 	struct nsjpeg_error_mgr *err = (struct nsjpeg_error_mgr *) cinfo->err;
-	(*cinfo->err->output_message) (cinfo);
+	err->pub.format_message(cinfo, nsjpeg_error_buffer);
 	longjmp(err->setjmp_buffer, 1);
 }
 
@@ -229,9 +242,9 @@ void nsjpeg_destroy(struct content *c)
  * Redraw a CONTENT_JPEG.
  */
 
-void nsjpeg_redraw(struct content *c, long x, long y,
-		   unsigned long width, unsigned long height,
-		   long clip_x0, long clip_y0, long clip_x1, long clip_y1,
+void nsjpeg_redraw(struct content *c, int x, int y,
+		   int width, int height,
+		   int clip_x0, int clip_y0, int clip_x1, int clip_y1,
 		   float scale)
 {
 	unsigned int tinct_options;
@@ -255,7 +268,7 @@ void nsjpeg_redraw(struct content *c, long x, long y,
 			_IN(2) | _IN(3) | _IN(4) | _IN(5) | _IN(6) | _IN(7),
 			(char *) c->data.jpeg.sprite_area +
 				c->data.jpeg.sprite_area->first,
-			x, (int) (y - height),
+			x, y - height,
 			width, height,
 			tinct_options);
 }
diff --git a/riscos/jpeg.h b/riscos/jpeg.h
index 928ec252f..8db1ba502 100644
--- a/riscos/jpeg.h
+++ b/riscos/jpeg.h
@@ -16,12 +16,12 @@ struct content_jpeg_data {
 	osspriteop_area *sprite_area;
 };
 
-void nsjpeg_create(struct content *c, const char *params[]);
-int nsjpeg_convert(struct content *c, unsigned int width, unsigned int height);
+bool nsjpeg_create(struct content *c, const char *params[]);
+bool nsjpeg_convert(struct content *c, int width, int height);
 void nsjpeg_destroy(struct content *c);
-void nsjpeg_redraw(struct content *c, long x, long y,
-		unsigned long width, unsigned long height,
-		long clip_x0, long clip_y0, long clip_x1, long clip_y1,
+void nsjpeg_redraw(struct content *c, int x, int y,
+		int width, int height,
+		int clip_x0, int clip_y0, int clip_x1, int clip_y1,
 		float scale);
 
 #endif
diff --git a/riscos/png.c b/riscos/png.c
index 2c269c839..b31c992d3 100644
--- a/riscos/png.c
+++ b/riscos/png.c
@@ -32,19 +32,29 @@ static void row_callback(png_structp png, png_bytep new_row,
 static void end_callback(png_structp png, png_infop info);
 
 
-void nspng_init(void)
+bool nspng_create(struct content *c, const char *params[])
 {
-}
-
+	union content_msg_data msg_data;
 
-void nspng_create(struct content *c, const char *params[])
-{
 	c->data.png.sprite_area = 0;
 	c->data.png.png = png_create_read_struct(PNG_LIBPNG_VER_STRING,
 			0, 0, 0);
-	assert(c->data.png.png != 0);
+	if (!c->data.png.png) {
+		msg_data.error = messages_get("NoMemory");
+		content_broadcast(c, CONTENT_MSG_ERROR, msg_data);
+		warn_user("NoMemory", 0);
+		return false;
+	}
 	c->data.png.info = png_create_info_struct(c->data.png.png);
-	assert(c->data.png.info != 0);
+	if (!c->data.png.info) {
+		png_destroy_read_struct(&c->data.png.png,
+				&c->data.png.info, 0);
+
+		msg_data.error = messages_get("NoMemory");
+		content_broadcast(c, CONTENT_MSG_ERROR, msg_data);
+		warn_user("NoMemory", 0);
+		return false;
+	}
 
 	if (setjmp(png_jmpbuf(c->data.png.png))) {
 		png_destroy_read_struct(&c->data.png.png,
@@ -52,30 +62,38 @@ void nspng_create(struct content *c, const char *params[])
 		LOG(("Failed to set callbacks"));
 		c->data.png.png = NULL;
 		c->data.png.info = NULL;
-		return;
+
+		msg_data.error = messages_get("PNGError");
+		content_broadcast(c, CONTENT_MSG_ERROR, msg_data);
+		return false;
 	}
 
 	png_set_progressive_read_fn(c->data.png.png, c,
 			info_callback, row_callback, end_callback);
+
+	return true;
 }
 
 
-void nspng_process_data(struct content *c, char *data, unsigned long size)
+bool nspng_process_data(struct content *c, char *data, unsigned int size)
 {
+	union content_msg_data msg_data;
+
 	if (setjmp(png_jmpbuf(c->data.png.png))) {
 		png_destroy_read_struct(&c->data.png.png,
 				&c->data.png.info, 0);
 		LOG(("Failed to process data"));
 		c->data.png.png = NULL;
 		c->data.png.info = NULL;
-		return;
+
+		msg_data.error = messages_get("PNGError");
+		content_broadcast(c, CONTENT_MSG_ERROR, msg_data);
+		return false;
 	}
 
-	LOG(("data %p, size %li", data, size));
-	png_process_data(c->data.png.png, c->data.png.info,
-			data, size);
+	png_process_data(c->data.png.png, c->data.png.info, data, size);
 
-	c->size += size;
+	return true;
 }
 
 
@@ -224,30 +242,32 @@ void end_callback(png_structp png, png_infop info)
 
 
 
-int nspng_convert(struct content *c, unsigned int width, unsigned int height)
+bool nspng_convert(struct content *c, int width, int height)
 {
-	if (c->data.png.png == NULL || c->data.png.info == NULL)
-		return 1;
+	assert(c->data.png.png);
+	assert(c->data.png.info);
 
 	png_destroy_read_struct(&c->data.png.png, &c->data.png.info, 0);
 
-	c->title = xcalloc(100, 1);
-	sprintf(c->title, messages_get("PNGTitle"), c->width, c->height);
+	c->title = malloc(100);
+	if (c->title)
+		snprintf(c->title, 100, messages_get("PNGTitle"),
+				c->width, c->height);
 	c->status = CONTENT_STATUS_DONE;
-	return 0;
+	return true;
 }
 
 
 void nspng_destroy(struct content *c)
 {
-	xfree(c->title);
-	xfree(c->data.png.sprite_area);
+	free(c->title);
+	free(c->data.png.sprite_area);
 }
 
 
-void nspng_redraw(struct content *c, long x, long y,
-		unsigned long width, unsigned long height,
-		long clip_x0, long clip_y0, long clip_x1, long clip_y1,
+void nspng_redraw(struct content *c, int x, int y,
+		int width, int height,
+		int clip_x0, int clip_y0, int clip_x1, int clip_y1,
 		float scale)
 {
 	unsigned int tinct_options;
@@ -269,7 +289,7 @@ void nspng_redraw(struct content *c, long x, long y,
 	*/
 	_swix(Tinct_PlotScaledAlpha, _IN(2) | _IN(3) | _IN(4) | _IN(5) | _IN(6) | _IN(7),
 			((char *) c->data.png.sprite_area + c->data.png.sprite_area->first),
-			x, (int)(y - height),
+			x, y - height,
 			width, height,
 			tinct_options);
 }
diff --git a/riscos/png.h b/riscos/png.h
index ead45d290..49d311efd 100644
--- a/riscos/png.h
+++ b/riscos/png.h
@@ -22,13 +22,12 @@ struct content_png_data {
 	char *sprite_image;
 };
 
-void nspng_init(void);
-void nspng_create(struct content *c, const char *params[]);
-void nspng_process_data(struct content *c, char *data, unsigned long size);
-int nspng_convert(struct content *c, unsigned int width, unsigned int height);
+bool nspng_create(struct content *c, const char *params[]);
+bool nspng_process_data(struct content *c, char *data, unsigned int size);
+bool nspng_convert(struct content *c, int width, int height);
 void nspng_destroy(struct content *c);
-void nspng_redraw(struct content *c, long x, long y,
-		unsigned long width, unsigned long height,
-		long clip_x0, long clip_y0, long clip_x1, long clip_y1,
+void nspng_redraw(struct content *c, int x, int y,
+		int width, int height,
+		int clip_x0, int clip_y0, int clip_x1, int clip_y1,
 		float scale);
 #endif
diff --git a/riscos/sprite.c b/riscos/sprite.c
index b7d2bf068..b5c5f64bb 100644
--- a/riscos/sprite.c
+++ b/riscos/sprite.c
@@ -19,74 +19,90 @@
 
 #ifdef WITH_SPRITE
 
-void sprite_create(struct content *c, const char *params[])
+bool sprite_create(struct content *c, const char *params[])
 {
-	c->data.sprite.data = xcalloc(4, 1);
+	union content_msg_data msg_data;
+
+	c->data.sprite.data = malloc(4);
+	if (!c->data.sprite.data) {
+		msg_data.error = messages_get("NoMemory");
+		content_broadcast(c, CONTENT_MSG_ERROR, msg_data);
+		warn_user("NoMemory", 0);
+		return false;
+	}
 	c->data.sprite.length = 4;
+	return true;
 }
 
 
-void sprite_process_data(struct content *c, char *data, unsigned long size)
+bool sprite_process_data(struct content *c, char *data, unsigned int size)
 {
-	c->data.sprite.data = xrealloc(c->data.sprite.data, c->data.sprite.length + size);
-	memcpy((char*)(c->data.sprite.data) + c->data.sprite.length, data, size);
+	char *sprite_data;
+	union content_msg_data msg_data;
+
+	sprite_data = realloc(c->data.sprite.data,
+			c->data.sprite.length + size);
+	if (!sprite_data) {
+		msg_data.error = messages_get("NoMemory");
+		content_broadcast(c, CONTENT_MSG_ERROR, msg_data);
+		warn_user("NoMemory", 0);
+		return false;
+	}
+	c->data.sprite.data = sprite_data;
+	memcpy((char*)(c->data.sprite.data) + c->data.sprite.length,
+			data, size);
 	c->data.sprite.length += size;
 	c->size += size;
+	return true;
 }
 
 
-int sprite_convert(struct content *c, unsigned int width, unsigned int height)
+bool sprite_convert(struct content *c, int width, int height)
 {
 	os_error *error;
 	int w, h;
+	union content_msg_data msg_data;
 	osspriteop_area *area = (osspriteop_area*)c->data.sprite.data;
 
-        /* fill in the size (first word) of the area */
+	/* fill in the size (first word) of the area */
 	area->size = c->data.sprite.length;
 
 	error = xosspriteop_read_sprite_info(osspriteop_PTR,
-	     area,
-	     (osspriteop_id)((char*)(c->data.sprite.data) + area->first),
-	     &w, &h, NULL, NULL);
-
-        if (error) {
-                LOG(("error: %s", error->errmess));
-                return 1;
-        }
+			area,
+			(osspriteop_id)((char*)(c->data.sprite.data) + area->first),
+			&w, &h, NULL, NULL);
+	if (error) {
+		LOG(("xosspriteop_read_sprite_info: 0x%x: %s",
+				error->errnum, error->errmess));
+		msg_data.error = error->errmess;
+		content_broadcast(c, CONTENT_MSG_ERROR, msg_data);
+		return false;
+	}
 
 	c->width = w;
 	c->height = h;
-	c->title = xcalloc(100, 1);
-	sprintf(c->title, messages_get("SpriteTitle"), c->width,
-	                                c->height, c->data.sprite.length);
+	c->title = malloc(100);
+	if (c->title)
+		snprintf(c->title, 100, messages_get("SpriteTitle"), c->width,
+					c->height, c->data.sprite.length);
 	c->status = CONTENT_STATUS_DONE;
-	return 0;
-}
-
-
-void sprite_revive(struct content *c, unsigned int width, unsigned int height)
-{
-}
-
-
-void sprite_reformat(struct content *c, unsigned int width, unsigned int height)
-{
+	return true;
 }
 
 
 void sprite_destroy(struct content *c)
 {
-	xfree(c->data.sprite.data);
-	xfree(c->title);
+	free(c->data.sprite.data);
+	free(c->title);
 }
 
 
-void sprite_redraw(struct content *c, long x, long y,
-		unsigned long width, unsigned long height,
-		long clip_x0, long clip_y0, long clip_x1, long clip_y1,
+void sprite_redraw(struct content *c, int x, int y,
+		int width, int height,
+		int clip_x0, int clip_y0, int clip_x1, int clip_y1,
 		float scale)
 {
-        unsigned int size;
+	unsigned int size;
 	osspriteop_area *area = (osspriteop_area*)c->data.sprite.data;
 	osspriteop_trans_tab *table;
 	os_factors factors;
@@ -94,14 +110,14 @@ void sprite_redraw(struct content *c, long x, long y,
 	xcolourtrans_generate_table_for_sprite(
 			area,
 			(osspriteop_id)((char*)(c->data.sprite.data) +
-			                 area->first),
+					 area->first),
 			colourtrans_CURRENT_MODE, colourtrans_CURRENT_PALETTE,
 			0, colourtrans_GIVEN_SPRITE, 0, 0, &size);
 	table = xcalloc(size, 1);
 	xcolourtrans_generate_table_for_sprite(
 			area,
 			(osspriteop_id)((char*)(c->data.sprite.data) +
-			                 area->first),
+					 area->first),
 			colourtrans_CURRENT_MODE, colourtrans_CURRENT_PALETTE,
 			table, colourtrans_GIVEN_SPRITE, 0, 0, 0);
 
@@ -113,7 +129,7 @@ void sprite_redraw(struct content *c, long x, long y,
 	xosspriteop_put_sprite_scaled(osspriteop_PTR,
 			area,
 			(osspriteop_id)((char*)(c->data.sprite.data) +
-			                 area->first),
+					 area->first),
 			x, (int)(y - height),
 			osspriteop_USE_MASK | osspriteop_USE_PALETTE, &factors, table);
 
diff --git a/riscos/sprite.h b/riscos/sprite.h
index 183a5494f..39cf23eb1 100644
--- a/riscos/sprite.h
+++ b/riscos/sprite.h
@@ -17,15 +17,12 @@ struct content_sprite_data {
 	unsigned long length;
 };
 
-void sprite_init(void);
-void sprite_create(struct content *c, const char *params[]);
-void sprite_process_data(struct content *c, char *data, unsigned long size);
-int sprite_convert(struct content *c, unsigned int width, unsigned int height);
-void sprite_revive(struct content *c, unsigned int width, unsigned int height);
-void sprite_reformat(struct content *c, unsigned int width, unsigned int height);
+bool sprite_create(struct content *c, const char *params[]);
+bool sprite_process_data(struct content *c, char *data, unsigned int size);
+bool sprite_convert(struct content *c, int width, int height);
 void sprite_destroy(struct content *c);
-void sprite_redraw(struct content *c, long x, long y,
-		unsigned long width, unsigned long height,
-		long clip_x0, long clip_y0, long clip_x1, long clip_y1,
+void sprite_redraw(struct content *c, int x, int y,
+		int width, int height,
+		int clip_x0, int clip_y0, int clip_x1, int clip_y1,
 		float scale);
 #endif
diff --git a/riscos/wimp.c b/riscos/wimp.c
index b5f16e69b..8880232c9 100644
--- a/riscos/wimp.c
+++ b/riscos/wimp.c
@@ -21,6 +21,7 @@
 #include "netsurf/desktop/gui.h"
 #include "netsurf/riscos/wimp.h"
 #include "netsurf/utils/log.h"
+#include "netsurf/utils/utils.h"
 
 /*	Wimp_Extend,11 block
 */
diff --git a/utils/utils.h b/utils/utils.h
index b727b7ca8..e606baa6c 100644
--- a/utils/utils.h
+++ b/utils/utils.h
@@ -31,5 +31,6 @@ void regcomp_wrapper(regex_t *preg, const char *regex, int cflags);
 void clean_cookiejar(void);
 void unicode_transliterate(unsigned int c, char **r);
 char *human_friendly_bytesize(unsigned long bytesize);
+void warn_user(const char *warning, const char *detail);
 
 #endif
-- 
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