From 38c1f4ffe81ebcd2355e1997f495897576787098 Mon Sep 17 00:00:00 2001
From: Patrick Riley <pfr@google.com>
Date: Mon, 12 May 2014 16:41:44 +1000
Subject: [PATCH] go.image/tiff: Support missing Compression tag

no_compress.tiff is no_rps.tiff that was read in by go.image/tiff and written out again (with a hack to avoid creating the Compression tag on the way out).

$ tiffdump no_compress.tiff
no_compress.tiff:
Magic: 0x4949 <little-endian> Version: 0x2a
Directory 0: offset 968 (0x3c8) next 0 (0)
ImageWidth (256) SHORT (3) 1<16>
ImageLength (257) SHORT (3) 1<15>
BitsPerSample (258) SHORT (3) 4<8 8 8 8>
Photometric (262) SHORT (3) 1<2>
StripOffsets (273) LONG (4) 1<8>
SamplesPerPixel (277) SHORT (3) 1<4>
RowsPerStrip (278) SHORT (3) 1<15>
StripByteCounts (279) LONG (4) 1<960>
XResolution (282) RATIONAL (5) 1<72>
YResolution (283) RATIONAL (5) 1<72>
ResolutionUnit (296) SHORT (3) 1<2>
ExtraSamples (338) SHORT (3) 1<2>

LGTM=bsiegert, nigeltao
R=bsiegert, nigeltao
CC=golang-codereviews
https://golang.org/cl/95930044
---
 testdata/no_compress.tiff | Bin 0 -> 1142 bytes
 tiff/reader.go            |   9 +++++++--
 tiff/reader_test.go       |   9 +++++++++
 3 files changed, 16 insertions(+), 2 deletions(-)
 create mode 100644 testdata/no_compress.tiff

diff --git a/testdata/no_compress.tiff b/testdata/no_compress.tiff
new file mode 100644
index 0000000000000000000000000000000000000000..3f72b29ae12590119d5d8a2b6bcdc5601a859f75
GIT binary patch
literal 1142
zcmaKsZAg<*6vyxOXh@k(!$lUUEZ35pX@dDiTf|T#22*;O)8^)iURLv^Wm>Zj;znX(
zOUt*^8KLc4q;oA(E1@V!EGyrV`cQ_0^g|zn;B@ZT;F-PLhx45ObI<vmd+z1(WM{{b
z7Yrc);Aa+#h2SVwWMxk3v_;Fgxr*<Jae^-?3Bs=#85uj)=Ci+TwjL%y9N*qzE`=d`
z6NUh4YAtZJ<Tx1Aa?ohB8SH$Y*6DOanXe+-Bl&jc;2<>Jya8AADj0G(;rYm87`@*B
zWA^JH$xN?MtBZ(ArSj{U%jHNT`C+}L^98W7`~zOT8i(|hBsiG58~Uu3@WIs%pPt%4
zohO?K-xR@>NF;uINbvf~{VC#aeby>)^;*GYZ-LqiMNn=y3;kVYc;{?|x6U?jbk;yx
z>OTE3rP7bb^9n>uI;A?awD7DOCLOmhzZC{-b@2K@lSk7Uv%{TGe!37ghVsn5y;JWS
z5#gcM@rTVYIoJvl1Giy{u8Vr4uK^rbi}Ge;F$Mh2(Z{3bX%A;D%no;Xcu$Q-ZO~qK
z5gN@^@ZQx19oNbzzw2-7(>ehRbHr)0czUKhwKv$)M1M2#9dNJl66KTs#bYe|vOfRk
z4EE~deV+2&^+w9?`47(&AI)Bz8}0sspTT`ujM`twZ(;KSfq+npjg2K-CXhL)%vqdY
z!_#w|!=8+K4QvPw(Xn~A+fAsguC9`j(z1}W#GNaj$L_)up54cxJ1~!Thwh<7o3|7%
z7S~Co2XffFP$(qSL?RL4@p!@5pSI#m!Lp;L9y%-rFlZF+=xzM2sHmuDlgUJ;r>EE6
zA4L4e-sI#bGMTJjE|*I&5=NsjF)^gNy4sJ&#W)P%V3dc(@#;|2T+{*R3-PtiJI}@M
zFiwCcKL~Y%cb?|)S?p$S&ItY?A~}Jc{1ce8)vM2;7O`q7SQ<-_An%ifn)c@NzX67Q
B2$TQ-

literal 0
HcmV?d00001

diff --git a/tiff/reader.go b/tiff/reader.go
index fcb2b56..ea4f1f2 100644
--- a/tiff/reader.go
+++ b/tiff/reader.go
@@ -11,6 +11,7 @@ import (
 	"compress/lzw"
 	"compress/zlib"
 	"encoding/binary"
+	"fmt"
 	"image"
 	"image/color"
 	"io"
@@ -553,7 +554,11 @@ func Decode(r io.Reader) (img image.Image, err error) {
 			offset := int64(blockOffsets[j*blocksAcross+i])
 			n := int64(blockCounts[j*blocksAcross+i])
 			switch d.firstVal(tCompression) {
-			case cNone:
+
+			// According to the spec, Compression does not have a default value,
+			// but some tools interpret a missing Compression value as none so we do
+			// the same.
+			case cNone, 0:
 				if b, ok := d.r.(*buffer); ok {
 					d.buf, err = b.Slice(int(offset), int(n))
 				} else {
@@ -574,7 +579,7 @@ func Decode(r io.Reader) (img image.Image, err error) {
 			case cPackBits:
 				d.buf, err = unpackBits(io.NewSectionReader(d.r, offset, n))
 			default:
-				err = UnsupportedError("compression")
+				err = UnsupportedError(fmt.Sprintf("compression value %d", d.firstVal(tCompression)))
 			}
 			if err != nil {
 				return nil, err
diff --git a/tiff/reader_test.go b/tiff/reader_test.go
index 8539e9c..d62e277 100644
--- a/tiff/reader_test.go
+++ b/tiff/reader_test.go
@@ -44,6 +44,15 @@ func TestNoRPS(t *testing.T) {
 	}
 }
 
+// TestNoCompression tries to decode an images that has no Compression tag.
+// This tag is mandatory, but most tools interpret a missing value as no compression.
+func TestNoCompression(t *testing.T) {
+	_, err := load("no_compress.tiff")
+	if err != nil {
+		t.Fatal(err)
+	}
+}
+
 // TestUnpackBits tests the decoding of PackBits-encoded data.
 func TestUnpackBits(t *testing.T) {
 	var unpackBitsTests = []struct {