png: Add stdlibfuzz.go

internal/png/gen.go

@@ -32,6 +32,7 @@ import (
 )
 
 func run() error {
+	// TODO: Use go/packages with specifying build tags so that stdlibfuzz can be avoided.
 	dir := filepath.Join(runtime.GOROOT(), "src", "image", "png")
 
 	files, err := ioutil.ReadDir(dir)

internal/png/stdlibfuzz.go

@@ -0,0 +1,54 @@
+// Code generated by gen.go. DO NOT EDIT.
+
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build gofuzz
+
+package png
+
+import (
+	"bytes"
+	"fmt"
+)
+
+func Fuzz(data []byte) int {
+	cfg, err := DecodeConfig(bytes.NewReader(data))
+	if err != nil {
+		return 0
+	}
+	if cfg.Width*cfg.Height > 1e6 {
+		return 0
+	}
+	img, err := Decode(bytes.NewReader(data))
+	if err != nil {
+		return 0
+	}
+	levels := []CompressionLevel{
+		DefaultCompression,
+		NoCompression,
+		BestSpeed,
+		BestCompression,
+	}
+	for _, l := range levels {
+		var w bytes.Buffer
+		e := &Encoder{CompressionLevel: l}
+		err = e.Encode(&w, img)
+		if err != nil {
+			panic(err)
+		}
+		img1, err := Decode(&w)
+		if err != nil {
+			panic(err)
+		}
+		got := img1.Bounds()
+		want := img.Bounds()
+		if !got.Eq(want) {
+			fmt.Printf("bounds0: %#v\n", want)
+			fmt.Printf("bounds1: %#v\n", got)
+			panic("bounds have changed")
+		}
+	}
+	return 1
+}