compress/flate: always return uncompressed data in the event of error

In the event of an unexpected error, we should always flush available
decompressed data to the user.

Fixes #16924

Change-Id: I0bc0824c3201f3149e84e6a26e3dbcba72a1aae5
Reviewed-on: https://go-review.googlesource.com/28216
Run-TryBot: Joe Tsai <thebrokentoaster@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

src/compress/flate/inflate.go

@@ -344,6 +344,9 @@ func (f *decompressor) Read(b []byte) (int, error) {
 			return 0, f.err
 		}
 		f.step(f)
+		if f.err != nil && len(f.toRead) == 0 {
+			f.toRead = f.dict.readFlush() // Flush what's left in case of error
+		}
 	}
 }
 

src/compress/flate/inflate_test.go

@@ -7,6 +7,8 @@ package flate
 import (
 	"bytes"
 	"io"
+	"io/ioutil"
+	"strings"
 	"testing"
 )
 
@@ -38,6 +40,33 @@ func TestReset(t *testing.T) {
 	}
 }
 
+func TestReaderTruncated(t *testing.T) {
+	vectors := []struct{ input, output string }{
+		{"\x00", ""},
+		{"\x00\f", ""},
+		{"\x00\f\x00", ""},
+		{"\x00\f\x00\xf3\xff", ""},
+		{"\x00\f\x00\xf3\xffhello", "hello"},
+		{"\x00\f\x00\xf3\xffhello, world", "hello, world"},
+		{"\x02", ""},
+		{"\xf2H\xcd", "He"},
+		{"\xf2H͙0a\u0084\t", "Hel\x90\x90\x90\x90\x90"},
+		{"\xf2H͙0a\u0084\t\x00", "Hel\x90\x90\x90\x90\x90"},
+	}
+
+	for i, v := range vectors {
+		r := strings.NewReader(v.input)
+		zr := NewReader(r)
+		b, err := ioutil.ReadAll(zr)
+		if err != io.ErrUnexpectedEOF {
+			t.Errorf("test %d, error mismatch: got %v, want io.ErrUnexpectedEOF", i, err)
+		}
+		if string(b) != v.output {
+			t.Errorf("test %d, output mismatch: got %q, want %q", i, b, v.output)
+		}
+	}
+}
+
 func TestResetDict(t *testing.T) {
 	dict := []byte("the lorem fox")
 	ss := []string{

src/compress/gzip/gunzip_test.go

@@ -339,6 +339,26 @@ var gunzipTests = []gunzipTest{
 		},
 		nil,
 	},
+	{
+		"",
+		"truncated gzip file amid raw-block",
+		"hello",
+		[]byte{
+			0x1f, 0x8b, 0x08, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xff,
+			0x00, 0x0c, 0x00, 0xf3, 0xff, 0x68, 0x65, 0x6c, 0x6c, 0x6f,
+		},
+		io.ErrUnexpectedEOF,
+	},
+	{
+		"",
+		"truncated gzip file amid fixed-block",
+		"He",
+		[]byte{
+			0x1f, 0x8b, 0x08, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xff,
+			0xf2, 0x48, 0xcd,
+		},
+		io.ErrUnexpectedEOF,
+	},
 }
 
 func TestDecompressor(t *testing.T) {

src/compress/zlib/reader_test.go

@@ -121,6 +121,24 @@ var zlibTests = []zlibTest{
 		},
 		ErrDictionary,
 	},
+	{
+		"truncated zlib stream amid raw-block",
+		"hello",
+		[]byte{
+			0x78, 0x9c, 0x00, 0x0c, 0x00, 0xf3, 0xff, 0x68, 0x65, 0x6c, 0x6c, 0x6f,
+		},
+		nil,
+		io.ErrUnexpectedEOF,
+	},
+	{
+		"truncated zlib stream amid fixed-block",
+		"He",
+		[]byte{
+			0x78, 0x9c, 0xf2, 0x48, 0xcd,
+		},
+		nil,
+		io.ErrUnexpectedEOF,
+	},
 }
 
 func TestDecompressor(t *testing.T) {