Commit 93372673 authored by Brad Fitzpatrick's avatar Brad Fitzpatrick

io: fix infinite loop bug in MultiReader

If an io.Reader returned (non-zero, EOF), MultiReader would yield
bytes forever.

This bug has existed before Go 1 (!!), introduced in the original
MultiReader implementation in https://golang.org/cl/1764043 and also
survived basically the only update to this code since then
(https://golang.org/cl/17873, git rev ccdca832), which was added in
Go 1.7.

This just bit me when writing a test for some unrelated code.

Fixes #16795

Change-Id: I36e6a701269793935d19a47ac12f67b07179fbff
Reviewed-on: https://go-review.googlesource.com/27397
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: default avatarKeith Randall <khr@golang.org>
Reviewed-by: default avatarJoe Tsai <thebrokentoaster@gmail.com>
parent 244efebe
......@@ -18,15 +18,16 @@ func (mr *multiReader) Read(p []byte) (n int, err error) {
}
}
n, err = mr.readers[0].Read(p)
if err == EOF {
mr.readers = mr.readers[1:]
}
if n > 0 || err != EOF {
if err == EOF {
// Don't return EOF yet. There may be more bytes
// in the remaining readers.
if err == EOF && len(mr.readers) > 0 {
// Don't return EOF yet. More readers remain.
err = nil
}
return
}
mr.readers = mr.readers[1:]
}
return 0, EOF
}
......
......@@ -196,3 +196,41 @@ func TestMultiReaderFlatten(t *testing.T) {
myDepth+2, readDepth)
}
}
// byteAndEOFReader is a Reader which reads one byte (the underlying
// byte) and io.EOF at once in its Read call.
type byteAndEOFReader byte
func (b byteAndEOFReader) Read(p []byte) (n int, err error) {
if len(p) == 0 {
// Read(0 bytes) is useless. We expect no such useless
// calls in this test.
panic("unexpected call")
}
p[0] = byte(b)
return 1, EOF
}
// In Go 1.7, this yielded bytes forever.
func TestMultiReaderSingleByteWithEOF(t *testing.T) {
got, err := ioutil.ReadAll(LimitReader(MultiReader(byteAndEOFReader('a'), byteAndEOFReader('b')), 10))
if err != nil {
t.Fatal(err)
}
const want = "ab"
if string(got) != want {
t.Errorf("got %q; want %q", got, want)
}
}
// Test that a reader returning (n, EOF) at the end of an MultiReader
// chain continues to return EOF on its final read, rather than
// yielding a (0, EOF).
func TestMultiReaderFinalEOF(t *testing.T) {
r := MultiReader(bytes.NewReader(nil), byteAndEOFReader('a'))
buf := make([]byte, 2)
n, err := r.Read(buf)
if n != 1 || err != EOF {
t.Errorf("got %v, %v; want 1, EOF", n, err)
}
}
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