tif_jpeg.c: do not emit progressive scans with mozjpeg

Relates to #266

- On writing, explicitly disable progressive scans, which is normally
  not enabled, except with mozjpeg.
- On reading, emit a warning when encountering progressive scans.

1 files changed, 17 insertions, 0 deletions

diff --git a/libtiff/tif_jpeg.c b/libtiff/tif_jpeg.c
index 6076c117..a3bf448c 100644
--- a/libtiff/tif_jpeg.c
+++ b/libtiff/tif_jpeg.c
@@ -179,6 +179,7 @@ typedef struct {
 
         int             ycbcrsampling_fetched;
         int             max_allowed_scan_number;
+        int             has_warned_about_progressive_mode;
 } JPEGState;
 
 #define	JState(tif)	((JPEGState*)(tif)->tif_data)
@@ -1202,6 +1203,16 @@ JPEGPreDecode(TIFF* tif, uint16_t s)
 	}
 #endif
 
+    if( sp->cinfo.d.progressive_mode && !sp->has_warned_about_progressive_mode )
+    {
+        TIFFWarningExt(tif->tif_clientdata, module,
+                       "The JPEG strip/tile is encoded with progressive mode, "
+                       "which is normally not legal for JPEG-in-TIFF.\n"
+                       "libtiff should be able to decode it, but it might "
+                       "cause compatibility issues with other readers");
+        sp->has_warned_about_progressive_mode = TRUE;
+    }
+
         /* In some cases, libjpeg needs to allocate a lot of memory */
         /* http://www.libjpeg-turbo.org/pmwiki/uploads/About/TwoIssueswiththeJPEGStandard.pdf */
         if( TIFFjpeg_has_multiple_scans(sp) )
@@ -1770,6 +1781,12 @@ JPEGSetupEncode(TIFF* tif)
 	}
 	if (!TIFFjpeg_set_defaults(sp))
 		return (0);
+
+    /* mozjpeg by default enables progressive JPEG, which is illegal in JPEG-in-TIFF */
+    /* So explicitly disable it. */
+    sp->cinfo.c.num_scans = 0;
+    sp->cinfo.c.scan_info = NULL;
+
 	/* Set per-file parameters */
 	switch (sp->photometric) {
 	case PHOTOMETRIC_YCBCR: