Return a zero width or zero height image of the appropriate type.

Fixes golang/go#10393.
chai2010 · Apr 28, 2015 · 2e6993a · 2e6993a
1 parent 5dec728
commit 2e6993a
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Showing 3 changed files with 43 additions and 23 deletions.
diff --git a/decoder_test.go b/decoder_test.go
@@ -157,6 +157,31 @@ func TestDecompress(t *testing.T) {
 	}
 }
 
+// Do not panic when image dimensions are zero, return zero-sized
+// image instead.
+// Issue golang/go#10393.
+func TestZeroSizedImages(t *testing.T) {
+	testsizes := []struct {
+		w, h int
+	}{
+		{0, 0},
+		{1, 0},
+		{0, 1},
+		{1, 1},
+	}
+	for _, r := range testsizes {
+		img := image.NewRGBA(image.Rect(0, 0, r.w, r.h))
+		var buf bytes.Buffer
+		if err := Encode(&buf, img, nil); err != nil {
+			t.Errorf("encode w=%d h=%d: %v", r.w, r.h, err)
+			continue
+		}
+		if _, err := Decode(&buf); err != nil {
+			t.Errorf("decode w=%d h=%d: %v", r.w, r.h, err)
+		}
+	}
+}
+
 // benchmarkDecode benchmarks the decoding of an image.
 func benchmarkDecode(b *testing.B, filename string) {
 	b.StopTimer()

diff --git a/tiff_ifd_block.go b/tiff_ifd_block.go
@@ -12,28 +12,31 @@ import (
 )
 
 func (p *IFD) BlocksAcross() int {
-	if _, ok := p.TagGetter().GetTileWidth(); ok {
-		imageWidth, _ := p.TagGetter().GetImageWidth()
-		blockWidth, _ := p.TagGetter().GetTileWidth()
+	imageWidth, _ := p.TagGetter().GetImageWidth()
+	if imageWidth == 0 {
+		return 0
+	}
+	blockWidth, _ := p.TagGetter().GetTileWidth()
+	if blockWidth > 0 {
 		return int((imageWidth + blockWidth - 1) / blockWidth)
-	} else {
-		return 1
 	}
+	return 1
 }
 
 func (p *IFD) BlocksDown() int {
-	if _, ok := p.TagGetter().GetTileLength(); ok {
-		imageHeight, _ := p.TagGetter().GetImageLength()
-		blockHeight, _ := p.TagGetter().GetTileLength()
-		return int((imageHeight + blockHeight - 1) / blockHeight)
-	} else {
-		imageHeight, _ := p.TagGetter().GetImageLength()
-		blockHeight, ok := p.TagGetter().GetRowsPerStrip()
-		if !ok || blockHeight == 0 || blockHeight > imageHeight {
-			blockHeight = imageHeight
-		}
+	imageHeight, _ := p.TagGetter().GetImageLength()
+	if imageHeight == 0 {
+		return 0
+	}
+	blockHeight, _ := p.TagGetter().GetTileLength()
+	if blockHeight > 0 {
 		return int((imageHeight + blockHeight - 1) / blockHeight)
 	}
+	blockHeight, _ = p.TagGetter().GetRowsPerStrip()
+	if blockHeight == 0 || blockHeight > imageHeight {
+		blockHeight = imageHeight
+	}
+	return int((imageHeight + blockHeight - 1) / blockHeight)
 }
 
 func (p *IFD) BlockBounds(col, row int) image.Rectangle {

diff --git a/tiff_ifd_helper.go b/tiff_ifd_helper.go
@@ -174,14 +174,6 @@ func (p *IFD) ImageConfig() (config image.Config, err error) {
 		bitsPerSample, _ = p.TagGetter().GetBitsPerSample()
 		extraSamples, _  = p.TagGetter().GetExtraSamples()
 	)
-	if imageWidth == 0 {
-		err = fmt.Errorf("tiff: IFD.ImageWidth, zero width")
-		return
-	}
-	if imageHeight == 0 {
-		err = fmt.Errorf("tiff: IFD.ImageLength, zero length")
-		return
-	}
 	if len(bitsPerSample) == 0 {
 		err = fmt.Errorf("tiff: IFD.ColorModel, bad bitsPerSample length")
 		return