netsurf/content/handlers/text/textplain.c

/*
 * Copyright 2006 James Bursa <bursa@users.sourceforge.net>
 * Copyright 2006 Adrian Lees <adrianl@users.sourceforge.net>
 *
 * This file is part of NetSurf, http://www.netsurf-browser.org/
 *
 * NetSurf is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; version 2 of the License.
 *
 * NetSurf is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

/**
 * \file
 *
 * plain text content handling implementation.
 */

#include <assert.h>
#include <errno.h>
#include <stddef.h>
#include <string.h>
#include <strings.h>
#include <math.h>

#include <parserutils/input/inputstream.h>
#include <parserutils/charset/utf8.h>

#include "utils/corestrings.h"
#include "utils/http.h"
#include "utils/log.h"
#include "utils/messages.h"
#include "utils/utils.h"
#include "utils/utf8.h"
#include "netsurf/content.h"
#include "netsurf/keypress.h"
#include "netsurf/browser_window.h"
#include "netsurf/plotters.h"
#include "netsurf/layout.h"
#include "content/content_protected.h"
#include "content/hlcache.h"
#include "css/utils.h"
#include "utils/nsoption.h"
#include "desktop/search.h"
#include "desktop/selection.h"
#include "desktop/gui_internal.h"

#include "html/search.h"
#include "text/textplain.h"

struct textplain_line {
	size_t	start;
	size_t	length;
};

typedef struct textplain_content {
	struct content base;

	lwc_string *encoding;
	void *inputstream;
	char *utf8_data;
	size_t utf8_data_size;
	size_t utf8_data_allocated;
	unsigned long physical_line_count;
	struct textplain_line *physical_line;
	int formatted_width;
	struct browser_window *bw;

	struct selection sel;	/** Selection state */

	/** Context for free text search, or NULL if none */
	struct search_context *search;
	/** Current search string, or NULL if none */
	char *search_string;
} textplain_content;


#define CHUNK 32768 /* Must be a power of 2 */
#define MARGIN 4

#define TAB_WIDTH 8  /* must be power of 2 currently */
#define TEXT_SIZE 10 * PLOT_STYLE_SCALE  /* Unscaled text size in pt */

static plot_font_style_t textplain_style = {
	.family = PLOT_FONT_FAMILY_MONOSPACE,
	.size = TEXT_SIZE,
	.weight = 400,
	.flags = FONTF_NONE,
	.background = 0xffffff,
	.foreground = 0x000000,
};

static int textplain_tab_width = 256;  /* try for a sensible default */

static lwc_string *textplain_default_charset;


/**
 * Clean up after the text content handler
 */
static void textplain_fini(void)
{
	if (textplain_default_charset != NULL) {
		lwc_string_unref(textplain_default_charset);
		textplain_default_charset = NULL;
	}
}


/**
 * Work around feature in libparserutils
 *
 * if the client provides an encoding up front, but does not provide a
 * charset detection callback, then libparserutils will replace the
 * provided encoding with UTF-8. This breaks our input handling.
 *
 * Avoid this by providing a callback that does precisely nothing,
 * thus preserving whatever charset information we decided on in
 * textplain_create.
 */
static parserutils_error
textplain_charset_hack(const uint8_t *data,
		       size_t len,
		       uint16_t *mibenum,
		       uint32_t *source)
{
	return PARSERUTILS_OK;
}


/**
 * setup plain text render.
 *
 * \param[in] c content object.
 * \param[in] encoding the encoding of the content.
 * \return NSERROR_OK else appropriate error code.
 */
static nserror
textplain_create_internal(textplain_content *c, lwc_string *encoding)
{
	char *utf8_data;
	parserutils_inputstream *stream;
	parserutils_error error;

	textplain_style.size = (nsoption_int(font_size) * PLOT_STYLE_SCALE) / 10;

	utf8_data = malloc(CHUNK);
	if (utf8_data == NULL)
		goto no_memory;

	error = parserutils_inputstream_create(lwc_string_data(encoding), 0,
					       textplain_charset_hack, &stream);
	if (error == PARSERUTILS_BADENCODING) {
		/* Fall back to Windows-1252 */
		error = parserutils_inputstream_create("Windows-1252", 0,
					textplain_charset_hack, &stream);
	}
	if (error != PARSERUTILS_OK) {
		free(utf8_data);
		goto no_memory;
	}

	c->encoding = lwc_string_ref(encoding);
	c->inputstream = stream;
	c->utf8_data = utf8_data;
	c->utf8_data_size = 0;
	c->utf8_data_allocated = CHUNK;
	c->physical_line = 0;
	c->physical_line_count = 0;
	c->formatted_width = 0;
	c->bw = NULL;

	selection_prepare(&c->sel, (struct content *)c, false);

	return NSERROR_OK;

no_memory:
	content_broadcast_error(&c->base, NSERROR_NOMEM, NULL);

	return NSERROR_NOMEM;
}


/**
 * Create a CONTENT_TEXTPLAIN.
 */
static nserror
textplain_create(const content_handler *handler,
		 lwc_string *imime_type,
		 const http_parameter *params,
		 llcache_handle *llcache,
		 const char *fallback_charset,
		 bool quirks,
		 struct content **c)
{
	textplain_content *text;
	nserror error;
	lwc_string *encoding;

	text = calloc(1, sizeof(textplain_content));
	if (text == NULL) {
		return NSERROR_NOMEM;
	}

	error = content__init(&text->base, handler, imime_type, params,
			      llcache, fallback_charset, quirks);
	if (error != NSERROR_OK) {
		free(text);
		return error;
	}

	error = http_parameter_list_find_item(params, corestring_lwc_charset,
					      &encoding);
	if (error != NSERROR_OK) {
		encoding = lwc_string_ref(textplain_default_charset);
	}

	error = textplain_create_internal(text, encoding);
	if (error != NSERROR_OK) {
		lwc_string_unref(encoding);
		free(text);
		return error;
	}

	lwc_string_unref(encoding);

	*c = (struct content *) text;

	return NSERROR_OK;
}


/**
 * copy utf8 encoded data
 */
static bool
textplain_copy_utf8_data(textplain_content *c, const uint8_t *buf, size_t len)
{
	if (c->utf8_data_size + len >= c->utf8_data_allocated) {
		/* Compute next multiple of chunk above the required space */
		size_t allocated;
		char *utf8_data;

		allocated = (c->utf8_data_size + len + CHUNK - 1) & ~(CHUNK - 1);
		utf8_data = realloc(c->utf8_data, allocated);
		if (utf8_data == NULL)
			return false;

		c->utf8_data = utf8_data;
		c->utf8_data_allocated = allocated;
	}

	memcpy(c->utf8_data + c->utf8_data_size, buf, len);
	c->utf8_data_size += len;

	return true;
}


/**
 * drain input
 */
static bool
textplain_drain_input(textplain_content *c,
		      parserutils_inputstream *stream,
		      parserutils_error terminator)
{
	static const uint8_t *u_fffd = (const uint8_t *) "\xef\xbf\xfd";
	const uint8_t *ch;
	size_t chlen, offset = 0;

	while (parserutils_inputstream_peek(stream, offset, &ch, &chlen) !=
	       terminator) {
		/* Replace all instances of NUL with U+FFFD */
		if (chlen == 1 && *ch == 0) {
			if (offset > 0) {
				/* Obtain pointer to start of input data */
				parserutils_inputstream_peek(stream, 0,
							     &ch, &chlen);
				/* Copy from it up to the start of the NUL */
				if (textplain_copy_utf8_data(c, ch,
							     offset) == false)
					return false;
			}

			/* Emit U+FFFD */
			if (textplain_copy_utf8_data(c, u_fffd, 3) == false)
				return false;

			/* Advance inputstream past the NUL we just read */
			parserutils_inputstream_advance(stream, offset + 1);
			/* Reset the read offset */
			offset = 0;
		} else {
			/* Accumulate input */
			offset += chlen;

			if (offset > CHUNK) {
				/* Obtain pointer to start of input data */
				parserutils_inputstream_peek(stream, 0,
							     &ch, &chlen);

				/* Emit the data we've read */
				if (textplain_copy_utf8_data(c, ch,
							     offset) == false)
					return false;

				/* Advance the inputstream */
				parserutils_inputstream_advance(stream, offset);
				/* Reset the read offset */
				offset = 0;
			}
		}
	}

	if (offset > 0) {
		/* Obtain pointer to start of input data */
		parserutils_inputstream_peek(stream, 0, &ch, &chlen);
		/* Emit any data remaining */
		if (textplain_copy_utf8_data(c, ch, offset) == false)
			return false;

		/* Advance the inputstream past the data we've read */
		parserutils_inputstream_advance(stream, offset);
	}

	return true;
}


/**
 * Process data for CONTENT_TEXTPLAIN.
 */
static bool
textplain_process_data(struct content *c, const char *data, unsigned int size)
{
	textplain_content *text = (textplain_content *) c;
	parserutils_inputstream *stream = text->inputstream;
	parserutils_error error;

	error = parserutils_inputstream_append(stream,
					       (const uint8_t *) data, size);
	if (error != PARSERUTILS_OK) {
		goto no_memory;
	}

	if (textplain_drain_input(text, stream, PARSERUTILS_NEEDDATA) == false)
		goto no_memory;

	return true;

no_memory:
	content_broadcast_error(c, NSERROR_NOMEM, NULL);
	return false;
}


/**
 * Convert a CONTENT_TEXTPLAIN for display.
 */
static bool textplain_convert(struct content *c)
{
	textplain_content *text = (textplain_content *) c;
	parserutils_inputstream *stream = text->inputstream;
	parserutils_error error;

	error = parserutils_inputstream_append(stream, NULL, 0);
	if (error != PARSERUTILS_OK) {
		return false;
	}

	if (textplain_drain_input(text, stream, PARSERUTILS_EOF) == false)
		return false;

	parserutils_inputstream_destroy(stream);
	text->inputstream = NULL;

	content_set_ready(c);
	content_set_done(c);
	content_set_status(c, messages_get("Done"));

	return true;
}


/**
 * Calculate the line height, in pixels
 *
 * \return Line height, in pixels
 */
static float textplain_line_height(void)
{
	/* Size is in points, so convert to pixels.
	 * Then use a constant line height of 1.2 x font size.
	 */
	return FIXTOFLT(FDIV((FMUL(FLTTOFIX(1.2), FMUL(nscss_screen_dpi, INTTOFIX((textplain_style.size / PLOT_STYLE_SCALE))))), F_72));
}


/**
 * Reformat a CONTENT_TEXTPLAIN to a new width.
 */
static void textplain_reformat(struct content *c, int width, int height)
{
	textplain_content *text = (textplain_content *) c;
	char *utf8_data = text->utf8_data;
	size_t utf8_data_size = text->utf8_data_size;
	unsigned long line_count = 0;
	struct textplain_line *line = text->physical_line;
	struct textplain_line *line1;
	size_t i, space, col;
	size_t columns = 80;
	int character_width;
	size_t line_start;
	nserror res;

	NSLOG(netsurf, INFO, "content %p w:%d h:%d", c, width, height);

	/* compute available columns (assuming monospaced font) - use 8
	 * characters for better accuracy
	 */
	res = guit->layout->width(&textplain_style,
				  "ABCDEFGH", 8,
				  &character_width);
	if (res != NSERROR_OK) {
		return;
	}

	columns = (width - MARGIN - MARGIN) * 8 / character_width;
	textplain_tab_width = (TAB_WIDTH * character_width) / 8;

	text->formatted_width = width;

	text->physical_line_count = 0;

	if (!line) {
		text->physical_line = line =
			malloc(sizeof(struct textplain_line) * (1024 + 3));
		if (!line)
			goto no_memory;
	}

	line[line_count++].start = line_start = 0;
	space = 0;
	i = 0;
	col = 0;
	while (i < utf8_data_size) {
		size_t csize; /* number of bytes in character */
		uint32_t chr;
		bool term;
		size_t next_col;
		parserutils_error perror;

		perror = parserutils_charset_utf8_to_ucs4((const uint8_t *)utf8_data + i, utf8_data_size - i, &chr, &csize);
		if (perror != PARSERUTILS_OK) {
			chr = 0xfffd;
		}

		term = (chr == '\n' || chr == '\r');

		next_col = col + 1;

		if (chr == '\t') {
			next_col = (next_col + TAB_WIDTH - 1) & ~(TAB_WIDTH - 1);
		}

		if (term || next_col >= columns) {
			if (line_count % 1024 == 0) {
				line1 = realloc(line,
						sizeof(struct textplain_line) *
						(line_count + 1024 + 3));
				if (!line1)
					goto no_memory;
				text->physical_line = line = line1;
			}

			if (term) {
				line[line_count-1].length = i - line_start;

				/* skip second char of CR/LF or LF/CR pair */
				if (i + 1 < utf8_data_size &&
				    utf8_data[i+1] != utf8_data[i] &&
				    (utf8_data[i+1] == '\n' ||
				     utf8_data[i+1] == '\r')) {
					i++;
				}
			} else {
				if (space) {
					/* break at last space in line */
					i = space;
					line[line_count-1].length = (i + 1) - line_start;
				} else
					line[line_count-1].length = i - line_start;
			}

			line[line_count++].start = line_start = i + 1;
			col = 0;
			space = 0;
		} else {
			col++;
			if (chr == ' ')
				space = i;
		}
		i += csize;
	}
	line[line_count-1].length = i - line[line_count-1].start;
	line[line_count].start = utf8_data_size;

	text->physical_line_count = line_count;
	c->width = width;
	c->height = line_count * textplain_line_height() + MARGIN + MARGIN;

	return;

no_memory:
	NSLOG(netsurf, INFO, "out of memory (line_count %lu)", line_count);
	return;
}


/**
 * Destroy a CONTENT_TEXTPLAIN and free all resources it owns.
 */

static void textplain_destroy(struct content *c)
{
	textplain_content *text = (textplain_content *) c;

	lwc_string_unref(text->encoding);

	if (text->inputstream != NULL) {
		parserutils_inputstream_destroy(text->inputstream);
	}

	if (text->physical_line != NULL) {
		free(text->physical_line);
	}

	if (text->utf8_data != NULL) {
		free(text->utf8_data);
	}
}


static nserror textplain_clone(const struct content *old, struct content **newc)
{
	const textplain_content *old_text = (textplain_content *) old;
	textplain_content *text;
	nserror error;
	const uint8_t *data;
	size_t size;

	text = calloc(1, sizeof(textplain_content));
	if (text == NULL)
		return NSERROR_NOMEM;

	error = content__clone(old, &text->base);
	if (error != NSERROR_OK) {
		content_destroy(&text->base);
		return error;
	}

	/* Simply replay create/process/convert */
	error = textplain_create_internal(text, old_text->encoding);
	if (error != NSERROR_OK) {
		content_destroy(&text->base);
		return error;
	}

	data = content__get_source_data(&text->base, &size);
	if (size > 0) {
		if (textplain_process_data(&text->base,
					   (const char *)data,
					   size) == false) {
			content_destroy(&text->base);
			return NSERROR_NOMEM;
		}
	}

	if (old->status == CONTENT_STATUS_READY ||
	    old->status == CONTENT_STATUS_DONE) {
		if (textplain_convert(&text->base) == false) {
			content_destroy(&text->base);
			return NSERROR_CLONE_FAILED;
		}
	}

	return NSERROR_OK;
}


static content_type textplain_content_type(void)
{
	return CONTENT_TEXTPLAIN;
}


/**
 * Handle mouse clicks and movements in a TEXTPLAIN content window.
 *
 * \param c	  content of type textplain
 * \param bw	  browser window
 * \param mouse  mouse state on action
 * \param x	  coordinate of mouse
 * \param y	  coordinate of mouse
 */
static void
textplain_mouse_action(struct content *c,
		       struct browser_window *bw,
		       browser_mouse_state mouse,
		       int x, int y)
{
	textplain_content *text = (textplain_content *) c;
	browser_pointer_shape pointer = BROWSER_POINTER_DEFAULT;
	union content_msg_data msg_data;
	const char *status = 0;
	size_t idx;
	int dir = 0;

	browser_window_set_drag_type(bw, DRAGGING_NONE, NULL);

	idx = textplain_offset_from_coords(c, x, y, dir);
	if (selection_click(&text->sel, mouse, idx)) {

		if (selection_dragging(&text->sel)) {
			browser_window_set_drag_type(bw,
						     DRAGGING_SELECTION, NULL);
			status = messages_get("Selecting");
		}

	} else {
		if (mouse & (BROWSER_MOUSE_DRAG_1 | BROWSER_MOUSE_DRAG_2)) {
			browser_window_page_drag_start(bw, x, y);
			pointer = BROWSER_POINTER_MOVE;
		}
	}

	msg_data.explicit_status_text = status;
	content_broadcast(c, CONTENT_MSG_STATUS, &msg_data);

	msg_data.pointer = pointer;
	content_broadcast(c, CONTENT_MSG_POINTER, &msg_data);
}


/**
 * Handle mouse tracking (including drags) in a TEXTPLAIN content window.
 *
 * \param  c	  content of type textplain
 * \param  bw	  browser window
 * \param  mouse  state of mouse buttons and modifier keys
 * \param  x	  coordinate of mouse
 * \param  y	  coordinate of mouse
 */
static void
textplain_mouse_track(struct content *c,
		      struct browser_window *bw,
		      browser_mouse_state mouse,
		      int x, int y)
{
	textplain_content *text = (textplain_content *) c;

	if (browser_window_get_drag_type(bw) == DRAGGING_SELECTION && !mouse) {
		int dir = -1;
		size_t idx;

		if (selection_dragging_start(&text->sel))
			dir = 1;

		idx = textplain_offset_from_coords(c, x, y, dir);
		selection_track(&text->sel, mouse, idx);

		browser_window_set_drag_type(bw, DRAGGING_NONE, NULL);
	}

	switch (browser_window_get_drag_type(bw)) {

	case DRAGGING_SELECTION: {
		int dir = -1;
		size_t idx;

		if (selection_dragging_start(&text->sel)) dir = 1;

		idx = textplain_offset_from_coords(c, x, y, dir);
		selection_track(&text->sel, mouse, idx);
	}
		break;

	default:
		textplain_mouse_action(c, bw, mouse, x, y);
		break;
	}
}


/**
 * Handle keypresses.
 *
 * \param  c	content of type CONTENT_TEXTPLAIN
 * \param  key	The UCS4 character codepoint
 * \return true if key handled, false otherwise
 */
static bool textplain_keypress(struct content *c, uint32_t key)
{
	textplain_content *text = (textplain_content *) c;
	struct selection *sel = &text->sel;

	switch (key) {
	case NS_KEY_COPY_SELECTION:
		selection_copy_to_clipboard(sel);
		return true;

	case NS_KEY_CLEAR_SELECTION:
		selection_clear(sel, true);
		return true;

	case NS_KEY_SELECT_ALL:
		selection_select_all(sel);
		return true;

	case NS_KEY_ESCAPE:
		if (selection_defined(sel)) {
			selection_clear(sel, true);
			return true;
		}

		/* if there's no selection, leave Escape for the caller */
		return false;
	}

	return false;
}


/**
 * Terminate a search.
 *
 * \param c content of type text
 */
static void textplain_search_clear(struct content *c)
{
	textplain_content *text = (textplain_content *) c;

	assert(c != NULL);

	free(text->search_string);
	text->search_string = NULL;

	if (text->search != NULL) {
		search_destroy_context(text->search);
	}
	text->search = NULL;
}


/**
 * Handle search.
 *
 * \param c         content of type text
 * \param gui_data  front end private data
 * \param flags     search flags
 * \param string    search string
 */
static void textplain_search(struct content *c, void *gui_data,
			     search_flags_t flags, const char *string)
{
	textplain_content *text = (textplain_content *) c;

	assert(c != NULL);

	if (string != NULL && text->search_string != NULL &&
	    strcmp(string, text->search_string) == 0 &&
	    text->search != NULL) {
		/* Continue prev. search */
		search_step(text->search, flags, string);

	} else if (string != NULL) {
		/* New search */
		free(text->search_string);
		text->search_string = strdup(string);
		if (text->search_string == NULL)
			return;

		if (text->search != NULL) {
			search_destroy_context(text->search);
			text->search = NULL;
		}

		text->search = search_create_context(c, CONTENT_TEXTPLAIN,
						     gui_data);

		if (text->search == NULL)
			return;

		search_step(text->search, flags, string);

	} else {
		/* Clear search */
		textplain_search_clear(c);

		free(text->search_string);
		text->search_string = NULL;
	}
}


/**
 * Redraw a text string with highlighting
 * (for selection/search)
 *
 * \param utf8_text pointer to UTF-8 text string
 * \param utf8_len  length of string, in bytes
 * \param offset    byte offset within textual representation
 * \param x         x ordinate at which to plot text
 * \param y         y ordinate at which to plot text
 * \param clip      pointer to current clip rectangle
 * \param height    height of text string
 * \param scale     current display scale (1.0 = 100%)
 * \param text      Content being redrawn.
 * \param sel       Selection context
 * \param search    Search context
 * \param ctx	    current redraw context
 * \return true iff successful and redraw should proceed
 */
static bool
text_draw(const char *utf8_text,
	    size_t utf8_len,
	    size_t offset,
	    int x,
	    int y,
	    const struct rect *clip,
	    int height,
	    float scale,
	    textplain_content *text,
	    const struct selection *sel,
	    struct search_context *search,
	    const struct redraw_context *ctx)
{
	bool highlighted = false;
	plot_font_style_t plot_fstyle;
	nserror res;

	/* Need scaled text size to pass to plotters */
	plot_fstyle = textplain_style;
	plot_fstyle.size *= scale;

	/* is this box part of a selection? */
	if (ctx->interactive == true) {
		unsigned len = utf8_len;
		unsigned start_idx;
		unsigned end_idx;

		/* first try the browser window's current selection */
		if (selection_defined(sel) &&
		    selection_highlighted(sel,
					  offset,
					  offset + len,
					  &start_idx,
					  &end_idx)) {
			highlighted = true;
		}

		/* what about the current search operation, if any? */
		if (!highlighted &&
		    (search != NULL) &&
		    search_term_highlighted((struct content *)text,
					    offset,
					    offset + len,
					    &start_idx,
					    &end_idx,
					    search)) {
			highlighted = true;
		}

		/* \todo make search terms visible within selected text */
		if (highlighted) {
			struct rect r;
			unsigned endtxt_idx = end_idx;
			bool clip_changed = false;
			bool text_visible = true;
			int startx, endx;
			plot_style_t pstyle_fill_hback = *plot_style_fill_white;
			plot_font_style_t fstyle_hback = plot_fstyle;

			if (end_idx > utf8_len) {
				/* adjust for trailing space, not present in
				 * utf8_text
				 */
				assert(end_idx == utf8_len + 1);
				endtxt_idx = utf8_len;
			}

			res = guit->layout->width(&textplain_style,
						  utf8_text,
						  start_idx,
						  &startx);
			if (res != NSERROR_OK) {
				startx = 0;
			}

			res = guit->layout->width(&textplain_style,
						  utf8_text,
						  endtxt_idx,
						  &endx);
			if (res != NSERROR_OK) {
				endx = 0;
			}

			if (scale != 1.0) {
				startx *= scale;
				endx *= scale;
			}

			/* draw any text preceding highlighted portion */
			if (start_idx > 0) {
				res = ctx->plot->text(ctx,
					      &plot_fstyle,
					      x,
					      y + (int)(height * 0.75 * scale),
					      utf8_text,
					      start_idx);
				if (res != NSERROR_OK) {
					return false;
				}
			}

			pstyle_fill_hback.fill_colour = textplain_style.foreground;

			/* highlighted portion */
			r.x0 = x + startx;
			r.y0 = y;
			r.x1 = x + endx;
			r.y1 = y + height * scale;
			res = ctx->plot->rectangle(ctx, &pstyle_fill_hback, &r);
			if (res != NSERROR_OK) {
				return false;
			}

			if (start_idx > 0) {
				int px0 = max(x + startx, clip->x0);
				int px1 = min(x + endx, clip->x1);

				if (px0 < px1) {
					r.x0 = px0;
					r.y0 = clip->y0;
					r.x1 = px1;
					r.y1 = clip->y1;
					res = ctx->plot->clip(ctx, &r);
					if (res != NSERROR_OK) {
						return false;
					}

					clip_changed = true;
				} else {
					text_visible = false;
				}
			}

			fstyle_hback.background =
				pstyle_fill_hback.fill_colour;
			fstyle_hback.foreground = colour_to_bw_furthest(
				pstyle_fill_hback.fill_colour);

			if (text_visible &&
			    (ctx->plot->text(ctx,
					     &fstyle_hback,
					     x,
					     y + (int)(height * 0.75 * scale),
					     utf8_text,
					     endtxt_idx) != NSERROR_OK)) {
				return false;
			}

			/* draw any text succeeding highlighted portion */
			if (endtxt_idx < utf8_len) {
				int px0 = max(x + endx, clip->x0);
				if (px0 < clip->x1) {

					r.x0 = px0;
					r.y0 = clip->y0;
					r.x1 = clip->x1;
					r.y1 = clip->y1;
					res = ctx->plot->clip(ctx, &r);
					if (res != NSERROR_OK) {
						return false;
					}

					clip_changed = true;

					res = ctx->plot->text(ctx,
							      &plot_fstyle,
							      x,
							      y + (int)(height * 0.75 * scale),
							      utf8_text,
							      utf8_len);
					if (res != NSERROR_OK) {
						return false;
					}
				}
			}

			if (clip_changed &&
			    (ctx->plot->clip(ctx, clip) != NSERROR_OK)) {
				return false;
			}
		}
	}

	if (!highlighted) {
		res = ctx->plot->text(ctx,
				      &plot_fstyle,
				      x,
				      y + (int) (height * 0.75 * scale),
				      utf8_text,
				      utf8_len);
		if (res != NSERROR_OK) {
			return false;
		}
	}
	return true;
}


/**
 * Draw a CONTENT_TEXTPLAIN using the current set of plotters (plot).
 *
 * x, y, clip_[xy][01] are in target coordinates.
 *
 * \param  c	 content of type CONTENT_TEXTPLAIN
 * \param  data	 redraw data for this content redraw
 * \param  clip	 current clip region
 * \param  ctx	 current redraw context
 * \return true if successful, false otherwise
 */
static bool
textplain_redraw(struct content *c,
		 struct content_redraw_data *data,
		 const struct rect *clip,
		 const struct redraw_context *ctx)
{
	textplain_content *text = (textplain_content *) c;
	struct browser_window *bw = text->bw;
	char *utf8_data = text->utf8_data;
	long lineno;
	int x = data->x;
	int y = data->y;
	unsigned long line_count = text->physical_line_count;
	float line_height = textplain_line_height();
	float scaled_line_height = line_height * data->scale;
	long line0 = (clip->y0 - y * data->scale) / scaled_line_height - 1;
	long line1 = (clip->y1 - y * data->scale) / scaled_line_height + 1;
	struct textplain_line *line = text->physical_line;
	size_t length;
	plot_style_t *plot_style_highlight;
	nserror res;

	if (line0 < 0)
		line0 = 0;
	if (line1 < 0)
		line1 = 0;
	if (line_count < (unsigned long) line0)
		line0 = line_count;
	if (line_count < (unsigned long) line1)
		line1 = line_count;
	if (line1 < line0)
		line1 = line0;

	res = ctx->plot->rectangle(ctx, plot_style_fill_white, clip);
	if (res != NSERROR_OK) {
		return false;
	}

	if (!line)
		return true;

	/* choose a suitable background colour for any highlighted text */
	if ((data->background_colour & 0x808080) == 0x808080)
		plot_style_highlight = plot_style_fill_black;
	else
		plot_style_highlight = plot_style_fill_white;

	/* Set up font plot style */
	textplain_style.background = data->background_colour;

	x = (x + MARGIN) * data->scale;
	y = (y + MARGIN) * data->scale;
	for (lineno = line0; lineno != line1; lineno++) {
		const char *text_d = utf8_data + line[lineno].start;
		int tab_width = textplain_tab_width * data->scale;
		size_t offset = 0;
		int tx = x;

		if (!tab_width) tab_width = 1;

		length = line[lineno].length;
		if (!length)
			continue;

		while (offset < length) {
			size_t next_offset = offset;
			int width;
			int ntx;
			nserror res;

			while ((next_offset < length) &&
			       (text_d[next_offset] != '\t')) {
				next_offset = utf8_next(text_d,
							length,
							next_offset);
			}

			if (!text_draw(text_d + offset,
				       next_offset - offset,
				       line[lineno].start + offset,
				       tx,
				       y + (lineno * scaled_line_height),
				       clip,
				       line_height,
				       data->scale,
				       text,
				       &text->sel,
				       text->search,
				       ctx)) {
				return false;
			}

			if (next_offset >= length)
				break;

			res = guit->layout->width(&textplain_style,
						  &text_d[offset],
						  next_offset - offset,
						  &width);
			/* locate end of string and align to next tab position */
			if (res == NSERROR_OK) {
				tx += (int)(width * data->scale);
			}

			ntx = x + ((1 + (tx - x) / tab_width) * tab_width);

			/* if the tab character lies within the
			 *  selection, if any, then we must draw it as
			 *  a filled rectangle so that it's consistent
			 *  with background of the selected text
			 */

			if (bw) {
				unsigned tab_ofst = line[lineno].start + next_offset;
				struct selection *sel = &text->sel;
				bool highlighted = false;

				if (selection_defined(sel)) {
					unsigned start_idx, end_idx;
					if (selection_highlighted(sel,
								  tab_ofst,
								  tab_ofst + 1,
								  &start_idx,
								  &end_idx))
						highlighted = true;
				}

				if (!highlighted && (text->search != NULL)) {
					unsigned start_idx, end_idx;
					if (search_term_highlighted(c,
								    tab_ofst,
								    tab_ofst + 1,
								    &start_idx,
								    &end_idx,
								    text->search))
						highlighted = true;
				}

				if (highlighted) {
					struct rect rect;
					rect.x0 = tx;
					rect.y0 = y + (lineno * scaled_line_height);
					rect.x1 = ntx;
					rect.y1 = rect.y0 + scaled_line_height;
					res = ctx->plot->rectangle(ctx,
								   plot_style_highlight,
								   &rect);
					if (res != NSERROR_OK) {
						return false;
					}
				}
			}

			offset = next_offset + 1;
			tx = ntx;
		}
	}

	return true;
}


/**
 * Handle a window containing a CONTENT_TEXTPLAIN being opened.
 */
static nserror
textplain_open(struct content *c,
	       struct browser_window *bw,
	       struct content *page,
	       struct object_params *params)
{
	textplain_content *text = (textplain_content *) c;

	text->bw = bw;

	/* text selection */
	selection_init(&text->sel, NULL, NULL);

	return NSERROR_OK;
}


/**
 * Handle a window containing a CONTENT_TEXTPLAIN being closed.
 */
static nserror textplain_close(struct content *c)
{
	textplain_content *text = (textplain_content *) c;

	if (text->search != NULL) {
		search_destroy_context(text->search);
	}

	text->bw = NULL;

	return NSERROR_OK;
}


/**
 * Return an textplain content's selection context
 */
static char *textplain_get_selection(struct content *c)
{
	textplain_content *text = (textplain_content *) c;

	return selection_get_copy(&text->sel);
}


/**
 * Convert a character offset within a line of text into the
 * horizontal co-ordinate
 *
 * The conversion takes into account the font being used and any tabs
 * in the text
 *
 * \param  text    line of text
 * \param  offset  char offset within text
 * \param  length  line length
 * \return x ordinate
 */
static int
textplain_coord_from_offset(const char *text, size_t offset, size_t length)
{
	int x = 0;

	while (offset > 0) {
		size_t next_offset = 0;
		int tx;

		while (next_offset < offset && text[next_offset] != '\t') {
			next_offset = utf8_next(text, length, next_offset);
		}

		guit->layout->width(&textplain_style, text, next_offset, &tx);

		x += tx;

		if (next_offset >= offset)
			break;

		/* align to next tab boundary */
		next_offset++;
		x = (1 + (x / textplain_tab_width)) * textplain_tab_width;
		offset -= next_offset;
		text += next_offset;
		length -= next_offset;
	}

	return x;
}


/**
 * plain text content handler table
 */
static const content_handler textplain_content_handler = {
	.fini = textplain_fini,
	.create = textplain_create,
	.process_data = textplain_process_data,
	.data_complete = textplain_convert,
	.reformat = textplain_reformat,
	.destroy = textplain_destroy,
	.mouse_track = textplain_mouse_track,
	.mouse_action = textplain_mouse_action,
	.keypress = textplain_keypress,
	.search = textplain_search,
	.search_clear = textplain_search_clear,
	.redraw = textplain_redraw,
	.open = textplain_open,
	.close = textplain_close,
	.get_selection = textplain_get_selection,
	.clone = textplain_clone,
	.type = textplain_content_type,
	.no_share = true,
};


/* exported interface documented in html/textplain.h */
nserror textplain_init(void)
{
	lwc_error lerror;
	nserror error;

	lerror = lwc_intern_string("Windows-1252",
				   SLEN("Windows-1252"),
				   &textplain_default_charset);
	if (lerror != lwc_error_ok) {
		return NSERROR_NOMEM;
	}

	error = content_factory_register_handler("text/plain",
						 &textplain_content_handler);
	if (error != NSERROR_OK) {
		lwc_string_unref(textplain_default_charset);
	}

	error = content_factory_register_handler("application/json",
						 &textplain_content_handler);
	if (error != NSERROR_OK) {
		lwc_string_unref(textplain_default_charset);
	}

	return error;
}


/* exported interface documented in html/textplain.h */
unsigned long textplain_line_count(struct content *c)
{
	textplain_content *text = (textplain_content *) c;

	assert(c != NULL);

	return text->physical_line_count;
}


/* exported interface documented in html/textplain.h */
size_t textplain_size(struct content *c)
{
	textplain_content *text = (textplain_content *) c;

	assert(c != NULL);

	return text->utf8_data_size;
}


/* exported interface documented in html/textplain.h */
size_t textplain_offset_from_coords(struct content *c, int x, int y, int dir)
{
	textplain_content *textc = (textplain_content *) c;
	float line_height = textplain_line_height();
	struct textplain_line *line;
	const char *text;
	unsigned nlines;
	size_t length;
	int idx;

	assert(c != NULL);

	y = (int)((float)(y - MARGIN) / line_height);
	x -= MARGIN;

	nlines = textc->physical_line_count;
	if (!nlines)
		return 0;

	if (y <= 0) y = 0;
	else if ((unsigned)y >= nlines)
		y = nlines - 1;

	line = &textc->physical_line[y];
	text = textc->utf8_data + line->start;
	length = line->length;
	idx = 0;

	while (x > 0) {
		size_t next_offset = 0;
		int width = INT_MAX;

		while (next_offset < length && text[next_offset] != '\t') {
			next_offset = utf8_next(text, length, next_offset);
		}

		if (next_offset < length) {
			guit->layout->width(&textplain_style,
					    text,
					    next_offset,
					    &width);
		}

		if (x <= width) {
			int pixel_offset;
			size_t char_offset;

			guit->layout->position(&textplain_style,
					       text, next_offset, x,
					       &char_offset, &pixel_offset);

			idx += char_offset;
			break;
		}

		x -= width;
		length -= next_offset;
		text += next_offset;
		idx += next_offset;

		/* check if it's within the tab */
		width = textplain_tab_width - (width % textplain_tab_width);
		if (x <= width) break;

		x -= width;
		length--;
		text++;
		idx++;
	}

	return line->start + idx;
}


/* exported interface documented in html/textplain.h */
void
textplain_coords_from_range(struct content *c,
			    unsigned start,
			    unsigned end,
			    struct rect *r)
{
	textplain_content *text = (textplain_content *) c;
	float line_height = textplain_line_height();
	char *utf8_data;
	struct textplain_line *line;
	unsigned lineno = 0;
	unsigned nlines;

	assert(c != NULL);
	assert(start <= end);
	assert(end <= text->utf8_data_size);

	utf8_data = text->utf8_data;
	nlines = text->physical_line_count;
	line = text->physical_line;

	/* find start */
	lineno = textplain_find_line(c, start);

	r->y0 = (int)(MARGIN + lineno * line_height);

	if (lineno + 1 <= nlines || line[lineno + 1].start >= end) {
		/* \todo - it may actually be more efficient just to
		 *   run forwards most of the time
		 */

		/* find end */
		lineno = textplain_find_line(c, end);

		r->x0 = 0;
		r->x1 = text->formatted_width;
	} else {
		/* single line */
		const char *text = utf8_data + line[lineno].start;

		r->x0 = textplain_coord_from_offset(text,
						    start - line[lineno].start,
						    line[lineno].length);

		r->x1 = textplain_coord_from_offset(text,
						    end - line[lineno].start,
						    line[lineno].length);
	}

	r->y1 = (int)(MARGIN + (lineno + 1) * line_height);
}


/* exported interface documented in html/textplain.h */
char *
textplain_get_line(struct content *c,
		   unsigned lineno,
		   size_t *poffset,
		   size_t *plen)
{
	textplain_content *text = (textplain_content *) c;
	struct textplain_line *line;

	assert(c != NULL);

	if (lineno >= text->physical_line_count)
		return NULL;
	line = &text->physical_line[lineno];

	*poffset = line->start;
	*plen = line->length;
	return text->utf8_data + line->start;
}


/* exported interface documented in html/textplain.h */
int textplain_find_line(struct content *c, unsigned offset)
{
	textplain_content *text = (textplain_content *) c;
	struct textplain_line *line;
	int nlines;
	int lineno = 0;

	assert(c != NULL);

	line = text->physical_line;
	nlines = text->physical_line_count;

	if (offset > text->utf8_data_size) {
		return -1;
	}

/* \todo - implement binary search here */
	while (lineno < nlines && line[lineno].start < offset) {
		lineno++;
	}
	if (line[lineno].start > offset) {
		lineno--;
	}

	return lineno;
}


/* exported interface documented in html/textplain.h */
char *
textplain_get_raw_data(struct content *c,
		       unsigned start,
		       unsigned end,
		       size_t *plen)
{
	textplain_content *text = (textplain_content *) c;
	size_t utf8_size;

	assert(c != NULL);

	utf8_size = text->utf8_data_size;

	/* any text at all? */
	if (!utf8_size) return NULL;

	/* clamp to valid offset range */
	if (start >= utf8_size) start = utf8_size;
	if (end >= utf8_size) end = utf8_size;

	*plen = end - start;

	return text->utf8_data + start;
}


/* exported interface documented in html/textplain.h */
struct browser_window *textplain_get_browser_window(struct content *c)
{
	textplain_content *text = (textplain_content *) c;

	assert(c != NULL);
	assert(c->handler == &textplain_content_handler);

	return text->bw;
}