add im_bufjpeg2vips()

add a thing to open a jpeg from a memory buffer, handy for processing
thumbnails from exif data

ChangeLog

@@ -49,6 +49,7 @@
 - im_tiff2vips() int/uint mixup for rows_per_strip, thanks Bubba
 - removed the links feature, won't work with vips8
 - got rid of the tools/ subdirs
+- added im_bufjpeg2vips()
 
 30/11/10 started 7.24.0
 - bump for new stable

TODO

@@ -1,4 +1,4 @@
-- add open jpeg from a mem buffer
+- need vips_image_invalidate_area()
 
 
 - leak check, again

libvips/format/im_jpeg2vips.c

@@ -33,6 +33,8 @@
  * 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()
  */
 
 /*
@@ -698,7 +700,7 @@ jpeg2vips( const char *name, IMAGE *out, gboolean header_only )
 			fail_on_warn = TRUE;
 	}
 
-	/* Make jpeg compression object.
+	/* Make jpeg dcompression object.
  	 */
         cinfo.err = jpeg_std_error( &eman.pub );
 	eman.pub.error_exit = new_error_exit;
@@ -752,6 +754,226 @@ jpeg2vips( const char *name, IMAGE *out, gboolean header_only )
 	return( result );
 }
 
+/* Just like the above, but we read from a memory buffer.
+ */
+typedef struct {
+	/* Public jpeg fields.
+	 */
+	struct jpeg_source_mgr pub;
+
+	/* Private stuff during read.
+	 */
+	gboolean start_of_file;	/* have we gotten any data yet? */
+	JOCTET *buf;
+	size_t len;
+} InputBuffer;
+
+/*
+ * Initialize source --- called by jpeg_read_header
+ * before any data is actually read.
+ */
+
+static void
+init_source (j_decompress_ptr cinfo)
+{
+  InputBuffer *src = (InputBuffer *) cinfo->src;
+
+  /* We reset the empty-input-file flag for each image,
+   * but we don't clear the input buffer.
+   * This is correct behavior for reading a series of images from one source.
+   */
+  src->start_of_file = TRUE;
+}
+
+/*
+ * Fill the input buffer --- called whenever buffer is emptied.
+ *
+ * In typical applications, this should read fresh data into the buffer
+ * (ignoring the current state of next_input_byte & bytes_in_buffer),
+ * reset the pointer & count to the start of the buffer, and return TRUE
+ * indicating that the buffer has been reloaded.  It is not necessary to
+ * fill the buffer entirely, only to obtain at least one more byte.
+ *
+ * There is no such thing as an EOF return.  If the end of the file has been
+ * reached, the routine has a choice of ERREXIT() or inserting fake data into
+ * the buffer.  In most cases, generating a warning message and inserting a
+ * fake EOI marker is the best course of action --- this will allow the
+ * decompressor to output however much of the image is there.  However,
+ * the resulting error message is misleading if the real problem is an empty
+ * input file, so we handle that case specially.
+ *
+ * In applications that need to be able to suspend compression due to input
+ * not being available yet, a FALSE return indicates that no more data can be
+ * obtained right now, but more may be forthcoming later.  In this situation,
+ * the decompressor will return to its caller (with an indication of the
+ * number of scanlines it has read, if any).  The application should resume
+ * decompression after it has loaded more data into the input buffer.  Note
+ * that there are substantial restrictions on the use of suspension --- see
+ * the documentation.
+ *
+ * When suspending, the decompressor will back up to a convenient restart point
+ * (typically the start of the current MCU). next_input_byte & bytes_in_buffer
+ * indicate where the restart point will be if the current call returns FALSE.
+ * Data beyond this point must be rescanned after resumption, so move it to
+ * the front of the buffer rather than discarding it.
+ */
+
+static boolean
+fill_input_buffer (j_decompress_ptr cinfo)
+{
+  InputBuffer *src = (InputBuffer *) cinfo->src;
+  size_t nbytes;
+
+  if (src->start_of_file) {
+    nbytes = src->len;
+  }
+  else {
+    WARNMS(cinfo, JWRN_JPEG_EOF);
+    /* Insert a fake EOI marker */
+    src->buf[0] = (JOCTET) 0xFF;
+    src->buf[1] = (JOCTET) JPEG_EOI;
+    nbytes = 2;
+  }
+
+  src->pub.next_input_byte = src->buf;
+  src->pub.bytes_in_buffer = nbytes;
+  src->start_of_file = FALSE;
+
+  return TRUE;
+}
+
+/*
+ * Skip data --- used to skip over a potentially large amount of
+ * uninteresting data (such as an APPn marker).
+ *
+ * Writers of suspendable-input applications must note that skip_input_data
+ * is not granted the right to give a suspension return.  If the skip extends
+ * beyond the data currently in the buffer, the buffer can be marked empty so
+ * that the next read will cause a fill_input_buffer call that can suspend.
+ * Arranging for additional bytes to be discarded before reloading the input
+ * buffer is the application writer's problem.
+ */
+
+static void
+skip_input_data (j_decompress_ptr cinfo, long num_bytes)
+{
+  InputBuffer *src = (InputBuffer *) cinfo->src;
+
+  /* Just skip fwd.
+   */
+  if (num_bytes > 0) {
+    src->pub.next_input_byte += (size_t) num_bytes;
+    src->pub.bytes_in_buffer -= (size_t) num_bytes;
+  }
+}
+
+/*
+ * An additional method that can be provided by data source modules is the
+ * resync_to_restart method for error recovery in the presence of RST markers.
+ * For the moment, this source module just uses the default resync method
+ * provided by the JPEG library.  That method assumes that no backtracking
+ * is possible.
+ */
+
+/*
+ * Terminate source --- called by jpeg_finish_decompress
+ * after all data has been read.  Often a no-op.
+ *
+ * NB: *not* called by jpeg_abort or jpeg_destroy; surrounding
+ * application must deal with any cleanup that should happen even
+ * for error exit.
+ */
+
+static void
+term_source (j_decompress_ptr cinfo)
+{
+  /* no work necessary here */
+}
+
+/*
+ * Prepare for input from a memory buffer. The caller needs to free the
+ * buffer after decompress is done, we don't take ownership.
+ */
+
+static void
+buf_source (j_decompress_ptr cinfo, void *buf, size_t len)
+{
+  InputBuffer *src;
+
+  /* The source object and input buffer are made permanent so that a series
+   * of JPEG images can be read from the same file by calling jpeg_stdio_src
+   * only before the first one.  (If we discarded the buffer at the end of
+   * one image, we'd likely lose the start of the next one.)
+   * This makes it unsafe to use this manager and a different source
+   * manager serially with the same JPEG object.  Caveat programmer.
+   */
+  if (cinfo->src == NULL) {	/* first time for this JPEG object? */
+    cinfo->src = (struct jpeg_source_mgr *)
+      (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,
+				  sizeof(InputBuffer));
+    src = (InputBuffer *) cinfo->src;
+    src->buf = buf;
+    src->len = len;
+  }
+
+  src = (InputBuffer *) cinfo->src;
+  src->pub.init_source = init_source;
+  src->pub.fill_input_buffer = fill_input_buffer;
+  src->pub.skip_input_data = skip_input_data;
+  src->pub.resync_to_restart = jpeg_resync_to_restart; /* use default method */
+  src->pub.term_source = term_source;
+  src->pub.bytes_in_buffer = 0; /* forces fill_input_buffer on first read */
+  src->pub.next_input_byte = NULL; /* until buffer loaded */
+}
+
+/* Read a JPEG memory buffer into a VIPS image.
+ */
+static int
+bufjpeg2vips( void *buf, size_t len, IMAGE *out, gboolean header_only )
+{
+	char *p, *q;
+	struct jpeg_decompress_struct cinfo;
+        ErrorManager eman;
+	int result;
+	gboolean invert_pels;
+
+	/* Make jpeg dcompression object.
+ 	 */
+        cinfo.err = jpeg_std_error( &eman.pub );
+	eman.pub.error_exit = new_error_exit;
+	eman.pub.output_message = new_output_message;
+	eman.fp = NULL;
+	if( setjmp( eman.jmp ) ) {
+		/* Here for longjmp() from new_error_exit().
+		 */
+		jpeg_destroy_decompress( &cinfo );
+
+		return( -1 );
+	}
+        jpeg_create_decompress( &cinfo );
+
+	/* Make input.
+	 */
+	buf_source( &cinfo, buf, len );
+
+	/* Need to read in APP1 (EXIF metadata) and APP2 (ICC profile).
+	 */
+	jpeg_save_markers( &cinfo, JPEG_APP0 + 1, 0xffff );
+	jpeg_save_markers( &cinfo, JPEG_APP0 + 2, 0xffff );
+
+	/* Convert!
+	 */
+	result = read_jpeg_header( &cinfo, out, &invert_pels, 1 );
+	if( !header_only && !result )
+		result = read_jpeg_image( &cinfo, out, invert_pels );
+
+	/* Close and tidy.
+	 */
+	jpeg_destroy_decompress( &cinfo );
+
+	return( result );
+}
+
 /**
  * im_jpeg2vips:
  * @filename: file to load
@@ -818,6 +1040,27 @@ im_jpeg2vips( const char *filename, IMAGE *out )
 	return( jpeg2vips( filename, out, FALSE ) );
 }
 
+/**
+ * im_bufjpeg2vips:
+ * @buf: memory area to load
+ * @len: size of memory area
+ * @out: image to write
+ *
+ * Read a JPEG-formatted memory block into a VIPS image. It can read most 
+ * 8-bit JPEG images, including CMYK and YCbCr.
+ *
+ * This function is handy for processing JPEG image thumbnails.
+ *
+ * See also: #VipsFormat, im_jpeg2vips().
+ *
+ * Returns: 0 on success, -1 on error.
+ */
+int
+im_bufjpeg2vips( void *buf, size_t len, IMAGE *out )
+{
+	return( bufjpeg2vips( buf, len, out, FALSE ) );
+}
+
 static int
 isjpeg( const char *filename )
 {

libvips/include/vips/format.h

@@ -123,6 +123,7 @@ int vips_format_write( VipsImage *in, const char *filename );
 /* Low-level read/write operations.
  */
 int im_jpeg2vips( const char *filename, VipsImage *out );
+int im_bufjpeg2vips( void *buf, size_t len, VipsImage *out );
 int im_vips2jpeg( VipsImage *in, const char *filename );
 int im_vips2mimejpeg( VipsImage *in, int qfac );
 int im_vips2bufjpeg( VipsImage *in, VipsImage *out, int qfac, char **obuf, int *olen );