libvips/libvips/foreign/jpeg2vips.c

/* wrap jpeg library for read
 *
 * 28/11/03 JC
 *	- better no-overshoot on tile loop
 * 12/11/04
 *	- better demand size choice for eval
 * 30/6/05 JC
 *	- update im_error()/im_warn()
 *	- now loads and saves exif data
 * 30/7/05
 * 	- now loads ICC profiles
 * 	- now saves ICC profiles from the VIPS header
 * 24/8/05
 * 	- jpeg load sets vips xres/yres from exif, if possible
 * 	- jpeg save sets exif xres/yres from vips, if possible
 * 29/8/05
 * 	- cut from old vips_jpeg.c
 * 13/10/06
 * 	- add </libexif/ prefix if required
 * 11/2/08
 * 	- spot CMYK jpegs and set Type
 * 	- spot Adobe CMYK JPEG and invert ink density
 * 15/2/08
 * 	- added "shrink" parameter
 * 16/6/09
 *	- added "fail" option ... fail on any warnings
 * 12/10/09
 * 	- also set scale_num on shrink (thanks Guido)
 * 4/2/10
 * 	- gtkdoc
 * 4/12/10
 * 	- attach the jpeg thumbnail and multiscan fields (thanks Mike)
 * 21/2/10
 * 	- only accept the first APP1 block which starts "Exif..." as exif
 * 	  data, some jpegs seem to have several APP1s, argh
 * 20/4/2011
 * 	- added im_bufjpeg2vips()
 * 12/10/2011
 * 	- read XMP data
 * 3/11/11
 * 	- attach exif tags as coded values 
 * 24/11/11
 * 	- turn into a set of read fns ready to be called from a class
 * 9/1/12
 * 	- read jfif resolution as well as exif
 * 19/2/12
 * 	- switch to lazy reading
 * 7/8/12
 * 	- note EXIF resolution unit in VIPS_META_RESOLUTION_UNIT
 * 16/11/12
 * 	- tag exif fields with their ifd
 * 	- attach rationals as a/b, don't convert to double
 * 21/11/12
 * 	- don't insist exif must have data
 * 	- attach IPTC data (app13), thanks Gary
 * 6/7/13
 * 	- null-terminate exif strings, thanks Mike
 * 24/2/14
 * 	- don't write to our input buffer, thanks Lovell
 * 9/9/14
 * 	- support "none" as a resolution unit
 * 16/10/14
 * 	- add "autorotate" option
 * 20/1/15
 * 	- don't call jpeg_finish_decompress(), all it does is read and check 
 * 	  the tail of the file
 * 26/2/15
 * 	- close the jpeg read down early for a header read ... this saves an
 * 	  fd during jpg read, handy for large numbers of input images 
 * 15/7/15
 * 	- save exif tags using @name, not @title ... @title is subject to i18n
 * 21/2/16
 * 	- _destroy the decompress object as soon as we can, frees loads of
 * 	  memory for progressive jpg files
 * 26/5/16
 * 	- switch to new orientation tag
 * 11/7/16
 * 	- new --fail handling
 * 07/09/16
 *      - don't use the exif resolution if x_resolution / y_resolution /
 *        resolution_unit is missing
 * 7/11/16
 * 	- exif handling moved out to exif.c
 * 4/1/17
 * 	- don't warn for missing exif res, since we fall back to jfif now
 * 17/1/17
 * 	- invalidate operation on read error
 * 12/5/17
 * 	- fail aborts on error, not warning
 * 25/8/17
 * 	- revise read from buffer functions in line with latest libjpeg
 * 	  recommendations -- fixes a segv with crafted jpeg images
 * 29/8/17
 * 	- revert previous warning change: libvips reports serious corruption, 
 * 	  like a truncated file, as a warning and we need to be able to catch
 * 	  that
 * 9/4/18
 * 	- set interlaced=1 for interlaced images
 * 10/4/18
 * 	- strict round down on shrink-on-load
 * 16/8/18
 * 	- shut down the input file as soon as we can [kleisauke]
 * 20/7/19
 * 	- close input on minimise rather than Y read position
 * 3/10/19
 * 	- restart after minimise
 * 14/10/19
 * 	- revise for source IO
 * 5/5/20 angelmixu
 * 	- better handling of JFIF res unit 0
 * 13/9/20
 * 	- set resolution unit from JFIF 
 * 24/7/21
 * 	- add fail_on support
 * 2/8/22       
 *      - add "unlimited"
 */

/*

    This file is part of VIPS.
    
    VIPS is free software; you can redistribute it and/or modify
    it under the terms of the GNU Lesser General Public License as published by
    the Free Software Foundation; either version 2 of the License, or
    (at your option) any later version.

    This program 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 Lesser General Public License for more details.

    You should have received a copy of the GNU Lesser General Public License
    along with this program; if not, write to the Free Software
    Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
    02110-1301  USA

 */

/*

    These files are distributed with VIPS - http://www.vips.ecs.soton.ac.uk

 */

/*
#define DEBUG_VERBOSE
#define DEBUG
 */

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif /*HAVE_CONFIG_H*/
#include <glib/gi18n-lib.h>

#ifdef HAVE_JPEG

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include <vips/vips.h>
#include <vips/buf.h>
#include <vips/internal.h>

#include "pforeign.h"

#include "jpeg.h"

/* Stuff we track during a read.
 */
typedef struct _ReadJpeg {
        VipsImage *out;

	/* Shrink by this much during load. 1, 2, 4, 8.
	 */
	int shrink;

	/* Types of error to cause failure.
	 */
	VipsFailOn fail_on;

	struct jpeg_decompress_struct cinfo;
        ErrorManager eman;
	gboolean invert_pels;

	/* Track the y pos during a read with this.
	 */
	int y_pos;

	/* Use orientation tag to automatically rotate and flip image
	 * during load.
	 */
	gboolean autorotate;

	/* Remove DoS limits.
	 */
	gboolean unlimited;

	/* cinfo->output_width and height can be larger than we want since
	 * libjpeg rounds up on shrink-on-load. This is the real size we will
	 * output, as opposed to the size we decompress to.
	 */
	int output_width;
	int output_height;

	/* The source we read from.
	 */
	VipsSource *source;

} ReadJpeg;

#define SOURCE_BUFFER_SIZE (4096)

/* Private struct for source input.
 */
typedef struct {
	/* Public jpeg fields.
	 */
	struct jpeg_source_mgr pub;

	/* Private stuff during read.
	 */
	ReadJpeg *jpeg;
	VipsSource *source;
	unsigned char buf[SOURCE_BUFFER_SIZE];

} Source;

static void
source_init_source( j_decompress_ptr cinfo )
{
	Source *src = (Source *) cinfo->src;

	/* Start off empty ... libjpeg will call fill_input_buffer to get the
	 * first bytes.
	 */
	src->pub.next_input_byte = src->buf;
	src->pub.bytes_in_buffer = 0;
}

/* Fill the input buffer --- called whenever buffer is emptied.
 */
static boolean
source_fill_input_buffer( j_decompress_ptr cinfo )
{
	static const JOCTET eoi_buffer[4] = {
		(JOCTET) 0xFF, (JOCTET) JPEG_EOI, 0, 0
	};

	Source *src = (Source *) cinfo->src;

	gint64 bytes_read;

	if( (bytes_read = vips_source_read( src->source, 
		src->buf, SOURCE_BUFFER_SIZE )) > 0 ) {
		src->pub.next_input_byte = src->buf;
		src->pub.bytes_in_buffer = bytes_read;
	}
	else {
		if( src->jpeg->fail_on >= VIPS_FAIL_ON_TRUNCATED ) {
                        /* Knock the output out of cache.
                         */
                        vips_foreign_load_invalidate( src->jpeg->out );
			ERREXIT( cinfo, JERR_INPUT_EOF );
                }
		else
			WARNMS( cinfo, JWRN_JPEG_EOF );

		src->pub.next_input_byte = eoi_buffer;
		src->pub.bytes_in_buffer = 2;
	}

	return( TRUE );
}

static void
skip_input_data( j_decompress_ptr cinfo, long num_bytes )
{
	Source *src = (Source *) cinfo->src;

	if( num_bytes > 0 ) {
		while (num_bytes > (long) src->pub.bytes_in_buffer) {
			num_bytes -= (long) src->pub.bytes_in_buffer;
			(void) (*src->pub.fill_input_buffer) (cinfo);

			/* note we assume that fill_input_buffer will never 
			 * return FALSE, so suspension need not be handled.
			 */
		}

		src->pub.next_input_byte += (size_t) num_bytes;
		src->pub.bytes_in_buffer -= (size_t) num_bytes;
	}
}

static int
readjpeg_open_input( ReadJpeg *jpeg )
{
	j_decompress_ptr cinfo = &jpeg->cinfo;

	if( jpeg->source &&
		!cinfo->src ) {
		Source *src;

		if( vips_source_rewind( jpeg->source ) )
			return( -1 );

		cinfo->src = (struct jpeg_source_mgr *)
			(*cinfo->mem->alloc_small)( 
				(j_common_ptr) cinfo, JPOOL_PERMANENT,
				sizeof( Source ) );

		src = (Source *) cinfo->src;
		src->jpeg = jpeg;
		src->source = jpeg->source;
		src->pub.init_source = source_init_source;
		src->pub.fill_input_buffer = source_fill_input_buffer;
		src->pub.resync_to_restart = jpeg_resync_to_restart; 
		src->pub.skip_input_data = skip_input_data; 
		src->pub.bytes_in_buffer = 0;
		src->pub.next_input_byte = src->buf;
	}

	return( 0 );
}

static void
readjpeg_emit_message( j_common_ptr cinfo, int msg_level )
{
        ReadJpeg *jpeg  = (ReadJpeg *) cinfo->client_data;

	long num_warnings;

	if( msg_level < 0 ) {
		/* Always count warnings in num_warnings.
		 */
		num_warnings = ++cinfo->err->num_warnings;

		/* Corrupt files may give many warnings, the policy here is to
		 * show only the first warning and treat many warnings as fatal,
                 * unless unlimited is set.
		 */
		if( num_warnings == 1 )
			(*cinfo->err->output_message)( cinfo );
		else if( !jpeg ||
                        (!jpeg->unlimited && num_warnings >= 100) )
			cinfo->err->error_exit( cinfo );
	}
	else if( cinfo->err->trace_level >= msg_level )
		/* It's a trace message. Show it if trace_level >= msg_level.
		 */
		(*cinfo->err->output_message)( cinfo );
}

/* This can be called many times.
 */
static int
readjpeg_free( ReadJpeg *jpeg )
{
	if( jpeg->eman.pub.num_warnings != 0 ) {
		g_warning( _( "read gave %ld warnings" ), 
			jpeg->eman.pub.num_warnings );
		g_warning( "%s", vips_error_buffer() );

		/* Make the message only appear once.
		 */
		jpeg->eman.pub.num_warnings = 0;
	}

	/* Don't call jpeg_finish_decompress(). It just checks the tail of the
	 * file and who cares about that. All mem is freed in
	 * jpeg_destroy_decompress().
	 */

	/* I don't think this can fail. It's harmless to call many times. 
	 */
	jpeg_destroy_decompress( &jpeg->cinfo );

	VIPS_UNREF( jpeg->source );

	return( 0 );
}

static void
readjpeg_close_cb( VipsImage *image, ReadJpeg *jpeg )
{
	(void) readjpeg_free( jpeg );
}

static void
readjpeg_minimise_cb( VipsImage *image, ReadJpeg *jpeg )
{
	vips_source_minimise( jpeg->source );
}

static ReadJpeg *
readjpeg_new( VipsSource *source, VipsImage *out, 
	int shrink, VipsFailOn fail_on, gboolean autorotate, 
        gboolean unlimited )
{
	ReadJpeg *jpeg;

	if( !(jpeg = VIPS_NEW( out, ReadJpeg )) )
		return( NULL );

	jpeg->out = out;
	jpeg->source = source;
	g_object_ref( source );
	jpeg->shrink = shrink;
	jpeg->fail_on = fail_on;
        jpeg->cinfo.err = jpeg_std_error( &jpeg->eman.pub );
	jpeg->eman.pub.error_exit = vips__new_error_exit;
	jpeg->eman.pub.emit_message = readjpeg_emit_message;
	jpeg->eman.pub.output_message = vips__new_output_message;
	jpeg->eman.fp = NULL;
	jpeg->y_pos = 0;
	jpeg->autorotate = autorotate;
	jpeg->unlimited = unlimited;
        jpeg->cinfo.client_data = jpeg;

	/* jpeg_create_decompress() can fail on some sanity checks. Don't
	 * readjpeg_free() since we don't want to jpeg_destroy_decompress().
	 */
	if( setjmp( jpeg->eman.jmp ) ) 
		return( NULL );

        jpeg_create_decompress( &jpeg->cinfo );

	g_signal_connect( out, "close", 
		G_CALLBACK( readjpeg_close_cb ), jpeg ); 
	g_signal_connect( out, "minimise", 
		G_CALLBACK( readjpeg_minimise_cb ), jpeg ); 

	return( jpeg );
}

static const char *
find_chroma_subsample( struct jpeg_decompress_struct *cinfo )
{
	/* libjpeg only uses 4:4:4 and 4:2:0, confusingly. 
	 *
	 * http://poynton.ca/PDFs/Chroma_subsampling_notation.pdf
	 */
	gboolean has_subsample = cinfo->max_h_samp_factor > 1 ||
		cinfo->max_v_samp_factor > 1;
	gboolean is_cmyk = cinfo->num_components > 3;

	return( is_cmyk ? 
		(has_subsample ? "4:2:0:4" : "4:4:4:4" ) :
		(has_subsample ? "4:2:0" : "4:4:4") );
}

static int
attach_blob( VipsImage *im, const char *field, void *data, size_t data_length )
{
	/* Only use the first one.
	 */
	if( vips_image_get_typeof( im, field ) ) {
#ifdef DEBUG
		printf( "attach_blob: second %s block, ignoring\n", field );
#endif /*DEBUG*/

		return( 0 );
	}

#ifdef DEBUG
	printf( "attach_blob: attaching %zd bytes of %s\n", 
		data_length, field );
#endif /*DEBUG*/

	vips_image_set_blob_copy( im, field, data, data_length );

	return( 0 );
}

/* data is the XMP string ... it'll have something like 
 * "http://ns.adobe.com/xap/1.0/" at the front, then a null character, then
 * the real XMP.
 */
static int
attach_xmp_blob( VipsImage *im, void *data, size_t data_length )
{
	char *p = (char *) data;
	int i;

	if( data_length < 4 ||
		!vips_isprefix( "http", p ) ) 
		return( 0 );

	/* Search for a null char within the first few characters. 80
	 * should be plenty for a basic URL.
	 *
	 * -2 for the extra null.
	 */
	for( i = 0; i < VIPS_MIN( 80, data_length - 2 ); i++ )
		if( !p[i] ) 
			break;
	if( p[i] )
		return( 0 );

	return( attach_blob( im, VIPS_META_XMP_NAME, 
		p + i + 1, data_length - i - 1 ) );
}

/* Number of app2 sections we can capture. Each one can be 64k, so 6400k should
 * be enough for anyone (haha).
 */
#define MAX_APP2_SECTIONS (100)

/* Read a cinfo to a VIPS image. Set invert_pels if the pixel reader needs to
 * do 255-pel.
 */
static int
read_jpeg_header( ReadJpeg *jpeg, VipsImage *out )
{
	struct jpeg_decompress_struct *cinfo = &jpeg->cinfo;

	jpeg_saved_marker_ptr p;
	VipsInterpretation interpretation;
	double xres, yres;

	/* Capture app2 sections here for assembly.
	 */
	void *app2_data[MAX_APP2_SECTIONS] = { 0 };
	size_t app2_data_length[MAX_APP2_SECTIONS] = { 0 };
	size_t data_length;
	int i;

	/* Read JPEG header. libjpeg will set out_color_space sanely for us 
	 * for YUV YCCK etc.
	 */
	jpeg_read_header( cinfo, TRUE );
	cinfo->scale_denom = jpeg->shrink;
	cinfo->scale_num = 1;
	jpeg_calc_output_dimensions( cinfo );

	jpeg->invert_pels = FALSE;
	switch( cinfo->out_color_space ) {
	case JCS_GRAYSCALE:
		interpretation = VIPS_INTERPRETATION_B_W;
		break;

	case JCS_CMYK:
		interpretation = VIPS_INTERPRETATION_CMYK;

		/* CMYKs are almost always returned inverted, but see below.
		 */
		jpeg->invert_pels = TRUE;
		break;

	case JCS_RGB:
	default:
		interpretation = VIPS_INTERPRETATION_sRGB;
		break;
	}

#ifdef DEBUG
	if( cinfo->saw_JFIF_marker )
		printf( "read_jpeg_header: jfif _density %d, %d, unit %d\n",
			cinfo->X_density, cinfo->Y_density,
			cinfo->density_unit );
#endif /*DEBUG*/

	/* Get the jfif resolution. exif may overwrite this later. Default to
	 * 72dpi (as EXIF does).
	 */
	xres = 72.0 / 25.4;
	yres = 72.0 / 25.4;
	if( cinfo->saw_JFIF_marker &&
		cinfo->X_density != 1U && 
		cinfo->Y_density != 1U ) {
		switch( cinfo->density_unit ) {
		case 0:
			/* X_density / Y_density gives the pixel aspect ratio.
			 * Leave xres, but adjust yres.
			 */
			if( cinfo->Y_density > 0 )
				yres = xres * cinfo->X_density / 
					cinfo->Y_density;
			break;

		case 1:
			/* Pixels per inch.
			 */
			xres = cinfo->X_density / 25.4;
			yres = cinfo->Y_density / 25.4;
			vips_image_set_string( out, 
				VIPS_META_RESOLUTION_UNIT, "in" );
			break;

		case 2:
			/* Pixels per cm.
			 */
			xres = cinfo->X_density / 10.0;
			yres = cinfo->Y_density / 10.0;
			vips_image_set_string( out, 
				VIPS_META_RESOLUTION_UNIT, "cm" );
			break;

		default:
			g_warning( "%s", _( "unknown JFIF resolution unit" ) );
			break;
		}

#ifdef DEBUG
		printf( "read_jpeg_header: seen jfif resolution %g, %g p/mm\n",
			       xres, yres );
#endif /*DEBUG*/
	}

	/* Set VIPS header.
	 */
	vips_image_init_fields( out,
		cinfo->output_width, cinfo->output_height,
		cinfo->output_components,
		VIPS_FORMAT_UCHAR, VIPS_CODING_NONE,
		interpretation,
		xres, yres );

	VIPS_SETSTR( out->filename, 
		vips_connection_filename( VIPS_CONNECTION( jpeg->source ) ) );

	if( vips_image_pipelinev( out, VIPS_DEMAND_STYLE_FATSTRIP, NULL ) )
		return( -1 );

	/* cinfo->output_width and cinfo->output_height round up with
	 * shrink-on-load. For example, if the image is 1801 pixels across and
	 * we shrink by 4, the output will be 450.25 pixels across, 
	 * cinfo->output_width with be 451, and libjpeg will write a black
	 * column of pixels down the right.
	 *
	 * We must strictly round down, since we don't want fractional pixels
	 * along the bottom and right.
	 */
	jpeg->output_width = cinfo->image_width / jpeg->shrink;
	jpeg->output_height = cinfo->image_height / jpeg->shrink;

	/* Interlaced jpegs need lots of memory to read, so our caller needs
	 * to know.
	 */
	(void) vips_image_set_int( out, "jpeg-multiscan", 
		jpeg_has_multiple_scans( cinfo ) );

	/* 8.7 adds this for PNG as well, so we have a new format-neutral name.
	 */
	if( jpeg_has_multiple_scans( cinfo ) )
		vips_image_set_int( out, "interlaced", 1 ); 

	(void) vips_image_set_string( out, "jpeg-chroma-subsample", 
		find_chroma_subsample( cinfo ) );

	/* Look for EXIF and ICC profile.
	 */
	for( p = cinfo->marker_list; p; p = p->next ) {
#ifdef DEBUG
{
		printf( "read_jpeg_header: seen %u bytes of APP%d\n",
			p->data_length,
			p->marker - JPEG_APP0 );

		for( i = 0; i < 10; i++ ) 
			printf( "\t%d) '%c' (%d)\n", 
				i, p->data[i], p->data[i] );
}
#endif /*DEBUG*/

		switch( p->marker ) {
		case JPEG_APP0 + 1:
			/* Possible EXIF or XMP data.
			 */
			if( p->data_length > 4 &&
				vips_isprefix( "Exif", (char *) p->data ) &&
				attach_blob( out, VIPS_META_EXIF_NAME, 
					p->data, p->data_length ) )
				return( -1 );

			if( p->data_length > 4 &&
				vips_isprefix( "http", (char *) p->data ) &&
				attach_xmp_blob( out, 
					p->data, p->data_length ) )
				return( -1 );

			break;

		case JPEG_APP0 + 2:
			/* Possible ICC profile.
			 */
			if( p->data_length > 14 &&
				vips_isprefix( "ICC_PROFILE", 
					(char *) p->data ) ) {
				/* cur_marker numbers from 1, according to
				 * spec.
				 */
				int cur_marker = p->data[12] - 1;

				if( cur_marker >= 0 &&
					cur_marker < MAX_APP2_SECTIONS ) {
					app2_data[cur_marker] = p->data + 14;
					app2_data_length[cur_marker] = 
						p->data_length - 14;
				}
			}
			break;

		case JPEG_APP0 + 13:
			/* Possible IPTC data block.
			 */
			if( p->data_length > 5 &&
				vips_isprefix( "Photo", (char *) p->data ) ) {
				if( attach_blob( out, VIPS_META_IPTC_NAME,
					p->data, p->data_length ) )
					return( -1 );

				/* Older versions of libvips used this misspelt
				 * name :-( attach under this name too for
				 * compatibility.
				 */
				if( attach_blob( out, "ipct-data",
					p->data, p->data_length ) )
					return( -1 );
			}
			break;

		case JPEG_APP0 + 14:
			/* Adobe block. There's a lot of confusion about
			 * whether or not CMYK jpg images are inverted. For
			 * the images we have, it seems they should always
			 * invert.
			 *
			 * See: https://sno.phy.queensu.ca/~phil/exiftool/\
			 * 	TagNames/JPEG.html#Adobe
			 *
			 * data[11] == 0 - unknown
			 * data[11] == 1 - YCbCr
			 * data[11] == 2 - YCCK
			 *
			 * Leave this code here in case we come up with a
			 * better rule.
			 */
			if( p->data_length >= 12 &&
				vips_isprefix( "Adobe", (char *) p->data ) ) {
				if( p->data[11] == 0 ) {
#ifdef DEBUG
					printf( "complete Adobe block, not YCCK image\n" );
#endif /*DEBUG*/
					//jpeg->invert_pels = FALSE;
				}
			}
			break;

		default:
#ifdef DEBUG
			printf( "read_jpeg_header: "
				"ignoring %u byte APP%d block\n", 
				p->data_length, p->marker - JPEG_APP0 );
#endif /*DEBUG*/
			break;
		}
	}

	/* Assemble ICC sections.
	 */
	data_length = 0;
	for( i = 0; i < MAX_APP2_SECTIONS && app2_data[i]; i++ )
		data_length += app2_data_length[i];
	if( data_length ) {
		unsigned char *data;
		int p;

#ifdef DEBUG
		printf( "read_jpeg_header: assembled %zd byte ICC profile\n",
			data_length );
#endif /*DEBUG*/

		if( !(data = vips_malloc( NULL, data_length )) ) 
			return( -1 );

		p = 0;
		for( i = 0; i < MAX_APP2_SECTIONS && app2_data[i]; i++ ) {
			memcpy( data + p, app2_data[i], app2_data_length[i] );
			p += app2_data_length[i];
		}

		vips_image_set_blob( out, VIPS_META_ICC_NAME, 
			(VipsCallbackFn) vips_area_free_cb, data, data_length );
	}

	return( 0 );
}

static int
read_jpeg_generate( VipsRegion *or, 
	void *seq, void *a, void *b, gboolean *stop )
{
        VipsRect *r = &or->valid;
	ReadJpeg *jpeg = (ReadJpeg *) a;
	struct jpeg_decompress_struct *cinfo = &jpeg->cinfo;
	int sz = cinfo->output_width * cinfo->output_components;

	int y;

#ifdef DEBUG_VERBOSE
	printf( "read_jpeg_generate: %p line %d, %d rows\n", 
		g_thread_self(), r->top, r->height );
#endif /*DEBUG_VERBOSE*/

	VIPS_GATE_START( "read_jpeg_generate: work" );

	/* We're inside a tilecache where tiles are the full image width, so
	 * this should always be true.
	 */
	g_assert( r->left == 0 );
	g_assert( r->width == or->im->Xsize );
	g_assert( VIPS_RECT_BOTTOM( r ) <= or->im->Ysize );

	/* Tiles should always be on a 8-pixel boundary.
	 */
	g_assert( r->top % 8 == 0 );

	/* Tiles should always be a strip in height, unless it's the final
	 * strip.
	 */
	g_assert( r->height == VIPS_MIN( 8, or->im->Ysize - r->top ) ); 

	/* And check that y_pos is correct. It should be, since we are inside
	 * a vips_sequential().
	 */
	if( r->top != jpeg->y_pos ) {
		VIPS_GATE_STOP( "read_jpeg_generate: work" );
		vips_error( "VipsJpeg", 
			_( "out of order read at line %d" ), jpeg->y_pos );

		return( -1 );
	}

	/* Here for longjmp() from vips__new_error_exit() during
	 * jpeg_read_scanlines().
	 */
	if( setjmp( jpeg->eman.jmp ) ) {
		VIPS_GATE_STOP( "read_jpeg_generate: work" );

#ifdef DEBUG
		printf( "read_jpeg_generate: longjmp() exit\n" ); 
#endif /*DEBUG*/

		return( -1 );
	}

	if( jpeg->eman.pub.num_warnings > 0 &&
		jpeg->fail_on >= VIPS_FAIL_ON_WARNING ) {
		VIPS_GATE_STOP( "read_jpeg_generate: work" );

		/* Only fail once.
		 */
		jpeg->eman.pub.num_warnings = 0;

		return( -1 );
	}

	for( y = 0; y < r->height; y++ ) {
		JSAMPROW row_pointer[1];

		row_pointer[0] = (JSAMPLE *) 
			VIPS_REGION_ADDR( or, 0, r->top + y );

		jpeg_read_scanlines( cinfo, &row_pointer[0], 1 );

		if( jpeg->invert_pels ) {
			int x;

			for( x = 0; x < sz; x++ )
				row_pointer[0][x] = 255 - row_pointer[0][x];
		}

		jpeg->y_pos += 1; 
	}

	VIPS_GATE_STOP( "read_jpeg_generate: work" );

	return( 0 );
}

/* Read a cinfo to a VIPS image.
 */
static int
read_jpeg_image( ReadJpeg *jpeg, VipsImage *out )
{
	struct jpeg_decompress_struct *cinfo = &jpeg->cinfo;
	VipsImage **t = (VipsImage **) 
		vips_object_local_array( VIPS_OBJECT( out ), 5 );

	VipsImage *im;

	/* Here for longjmp() from vips__new_error_exit() during
	 * jpeg_read_header() or jpeg_start_decompress().
	 */
	if( setjmp( jpeg->eman.jmp ) ) 
		return( -1 );

	t[0] = vips_image_new();
	if( read_jpeg_header( jpeg, t[0] ) )
		return( -1 );

	/* Switch to pixel decode.
	 */
	if( vips_source_decode( jpeg->source ) )
		return( -1 );

	jpeg_start_decompress( cinfo );

#ifdef DEBUG
	printf( "read_jpeg_image: starting decompress\n" );
#endif /*DEBUG*/

	/* We must crop after the seq, or our generate may not be asked for
	 * full lines of pixels and will attempt to write beyond the buffer.
	 */
	if( vips_image_generate( t[0], 
		NULL, read_jpeg_generate, NULL, 
		jpeg, NULL ) ||
		vips_sequential( t[0], &t[1], 
			"tile_height", 8,
			NULL ) ||
		vips_extract_area( t[1], &t[2], 
			0, 0, jpeg->output_width, jpeg->output_height, NULL ) )
		return( -1 );
	im = t[2];

	if( jpeg->autorotate &&
		vips_image_get_orientation( im ) != 1 ) {
		/* We have to copy to memory before calling autorot, since it
		 * needs random access.
		 */
		if( !(t[3] = vips_image_copy_memory( im )) ||
			vips_autorot( t[3], &t[4], NULL ) )
			return( -1 );
		im = t[4];
	}

	if( vips_image_write( im, out ) )
		return( -1 );

	return( 0 );
}

static int
vips__jpeg_read( ReadJpeg *jpeg, VipsImage *out, gboolean header_only )
{
	/* Need to read in APP1 (EXIF metadata), APP2 (ICC profile), APP13
	 * (photoshop IPTC) and APP14 (Adobe flags).
	 */
	jpeg_save_markers( &jpeg->cinfo, JPEG_APP0 + 1, 0xffff );
	jpeg_save_markers( &jpeg->cinfo, JPEG_APP0 + 2, 0xffff );
	jpeg_save_markers( &jpeg->cinfo, JPEG_APP0 + 13, 0xffff );
	jpeg_save_markers( &jpeg->cinfo, JPEG_APP0 + 14, 0xffff );

#ifdef DEBUG
{
	int i;

	/* Handy for debugging ... spot any extra  markers.
	 */
	for( i = 0; i < 16; i++ ) 
		jpeg_save_markers( &jpeg->cinfo, JPEG_APP0 + i, 0xffff );
}
#endif /*DEBUG*/

	/* Convert!
	 */
	if( header_only ) {
		if( read_jpeg_header( jpeg, out ) )
			return( -1 ); 

		/* Patch in the correct size.
		 */
		out->Xsize = jpeg->output_width;
		out->Ysize = jpeg->output_height;

		/* Swap width and height if we're going to rotate this image.
		 */
		if( jpeg->autorotate ) {
			if( vips_image_get_orientation_swap( out ) ) 
				VIPS_SWAP( int, out->Xsize, out->Ysize );

			vips_autorot_remove_angle( out ); 
		}
	}
	else {
		if( read_jpeg_image( jpeg, out ) )
			return( -1 );
	}

	return( 0 );
}

int
vips__jpeg_read_source( VipsSource *source, VipsImage *out,
	gboolean header_only, int shrink, VipsFailOn fail_on, 
	gboolean autorotate, gboolean unlimited )
{
	ReadJpeg *jpeg;

	if( !(jpeg = readjpeg_new( source, out, shrink, fail_on, 
		autorotate, unlimited )) )
		return( -1 );

	/* Here for longjmp() from vips__new_error_exit() during
	 * cinfo->mem->alloc_small() or jpeg_read_header().
	 */
	if( setjmp( jpeg->eman.jmp ) ) 
		return( -1 );

	if( readjpeg_open_input( jpeg ) ||
		vips__jpeg_read( jpeg, out, header_only ) )
		return( -1 );

	if( header_only )
		vips_source_minimise( source );

	return( 0 );
}

int
vips__isjpeg_source( VipsSource *source )
{
	const unsigned char *p;

	if( (p = vips_source_sniff( source, 2 )) &&
		p[0] == 0xff && 
		p[1] == 0xd8 )
		return( 1 );

	return( 0 );
}

#endif /*HAVE_JPEG*/