io: fix Copyn EOF handling

Fixes #1383.

R=r
CC=golang-dev
https://golang.org/cl/3821044

diff --git a/src/pkg/io/io.go b/src/pkg/io/io.go
index fa1c0d2b06400e22259b3e2aa84d8dea588b6c35..1a6eca95a0d9ab9536a842c67aa5c1ca9220d130 100644 (file)
--- a/src/pkg/io/io.go
+++ b/src/pkg/io/io.go
@@ -206,7 +206,12 @@ func Copyn(dst Writer, src Reader, n int64) (written int64, err os.Error) {
        // If the writer has a ReadFrom method, use it to do the copy.
        // Avoids a buffer allocation and a copy.
        if rt, ok := dst.(ReaderFrom); ok {
-               return rt.ReadFrom(LimitReader(src, n))
+               written, err = rt.ReadFrom(LimitReader(src, n))
+               if written < n && err == nil {
+                       // rt stopped early; must have been EOF.
+                       err = os.EOF
+               }
+               return
        }
        buf := make([]byte, 32*1024)
        for written < n {

diff --git a/src/pkg/io/io_test.go b/src/pkg/io/io_test.go
index 20f240a51a5efbc582dace07c3e9e41957078763..4fcd85e693e9f4fe8514c8398494c7dc1bf0e5ae 100644 (file)
--- a/src/pkg/io/io_test.go
+++ b/src/pkg/io/io_test.go
@@ -8,6 +8,7 @@ import (
        "bytes"
        . "io"
        "os"
+       "strings"
        "testing"
 )
 
@@ -80,6 +81,41 @@ func TestCopynWriteTo(t *testing.T) {
        }
 }
 
+type noReadFrom struct {
+       w Writer
+}
+
+func (w *noReadFrom) Write(p []byte) (n int, err os.Error) {
+       return w.w.Write(p)
+}
+
+func TestCopynEOF(t *testing.T) {
+       // Test that EOF behavior is the same regardless of whether
+       // argument to Copyn has ReadFrom.
+
+       b := new(bytes.Buffer)
+
+       n, err := Copyn(&noReadFrom{b}, strings.NewReader("foo"), 3)
+       if n != 3 || err != nil {
+               t.Errorf("Copyn(noReadFrom, foo, 3) = %d, %v; want 3, nil", n, err)
+       }
+
+       n, err = Copyn(&noReadFrom{b}, strings.NewReader("foo"), 4)
+       if n != 3 || err != os.EOF {
+               t.Errorf("Copyn(noReadFrom, foo, 4) = %d, %v; want 3, EOF", n, err)
+       }
+
+       n, err = Copyn(b, strings.NewReader("foo"), 3) // b has read from
+       if n != 3 || err != nil {
+               t.Errorf("Copyn(bytes.Buffer, foo, 3) = %d, %v; want 3, nil", n, err)
+       }
+
+       n, err = Copyn(b, strings.NewReader("foo"), 4) // b has read from
+       if n != 3 || err != os.EOF {
+               t.Errorf("Copyn(bytes.Buffer, foo, 4) = %d, %v; want 3, EOF", n, err)
+       }
+}
+
 func TestReadAtLeast(t *testing.T) {
        var rb bytes.Buffer
        rb.Write([]byte("0123"))