encoding/base64: don't ignore underlying souce read error in decode

Fixes #3577

R=golang-dev, dsymonds
CC=golang-dev
https://golang.org/cl/6137054

diff --git a/src/pkg/encoding/base64/base64.go b/src/pkg/encoding/base64/base64.go
index f8a51a4e7568fc8c5087718bb0057c1b5db306dc..0b842f066105d14ed3a724af215e970bb540ea84 100644 (file)
--- a/src/pkg/encoding/base64/base64.go
+++ b/src/pkg/encoding/base64/base64.go
@@ -318,7 +318,7 @@ func (d *decoder) Read(p []byte) (n int, err error) {
        }
        nn, d.err = io.ReadAtLeast(d.r, d.buf[d.nbuf:nn], 4-d.nbuf)
        d.nbuf += nn
-       if d.nbuf < 4 {
+       if d.err != nil || d.nbuf < 4 {
                return 0, d.err
        }
 

diff --git a/src/pkg/encoding/base64/base64_test.go b/src/pkg/encoding/base64/base64_test.go
index 9c35372598cb292220b4bdb5781cff92e636a806..f9b863c364c90a75033f388b648b809f5c40ff32 100644 (file)
--- a/src/pkg/encoding/base64/base64_test.go
+++ b/src/pkg/encoding/base64/base64_test.go
@@ -6,9 +6,11 @@ package base64
 
 import (
        "bytes"
+       "errors"
        "io"
        "io/ioutil"
        "testing"
+       "time"
 )
 
 type testpair struct {
@@ -226,3 +228,50 @@ func TestNewLineCharacters(t *testing.T) {
                }
        }
 }
+
+type nextRead struct {
+       n   int   // bytes to return
+       err error // error to return
+}
+
+// faultInjectReader returns data from source, rate-limited
+// and with the errors as written to nextc.
+type faultInjectReader struct {
+       source string
+       nextc  <-chan nextRead
+}
+
+func (r *faultInjectReader) Read(p []byte) (int, error) {
+       nr := <-r.nextc
+       if len(p) > nr.n {
+               p = p[:nr.n]
+       }
+       n := copy(p, r.source)
+       r.source = r.source[n:]
+       return n, nr.err
+}
+
+// tests that we don't ignore errors from our underlying reader
+func TestDecoderIssue3577(t *testing.T) {
+       next := make(chan nextRead, 10)
+       wantErr := errors.New("my error")
+       next <- nextRead{5, nil}
+       next <- nextRead{10, wantErr}
+       d := NewDecoder(StdEncoding, &faultInjectReader{
+               source: "VHdhcyBicmlsbGlnLCBhbmQgdGhlIHNsaXRoeSB0b3Zlcw==", // twas brillig...
+               nextc:  next,
+       })
+       errc := make(chan error)
+       go func() {
+               _, err := ioutil.ReadAll(d)
+               errc <- err
+       }()
+       select {
+       case err := <-errc:
+               if err != wantErr {
+                       t.Errorf("got error %v; want %v", err, wantErr)
+               }
+       case <-time.After(5 * time.Second):
+               t.Errorf("timeout; Decoder blocked without returning an error")
+       }
+}