io: SectionReader.ReadAt should return EOF when buf is not fully read

Fixes #4392.

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/6858062

diff --git a/src/pkg/io/io.go b/src/pkg/io/io.go
index bddb701786bb41bed7068d612763b062d1af3925..859adaf1b710a132b2ab07860daad9a98dfcef0b 100644 (file)
--- a/src/pkg/io/io.go
+++ b/src/pkg/io/io.go
@@ -468,6 +468,11 @@ func (s *SectionReader) ReadAt(p []byte, off int64) (n int, err error) {
        off += s.base
        if max := s.limit - off; int64(len(p)) > max {
                p = p[0:max]
+               n, err = s.r.ReadAt(p, off)
+               if err == nil {
+                       err = EOF
+               }
+               return n, err
        }
        return s.r.ReadAt(p, off)
 }

diff --git a/src/pkg/io/io_test.go b/src/pkg/io/io_test.go
index 1e671b59b3368b87f0df0daf2130d10365bbdbf6..f3ec050fad9ed1de7c5b9c60038f4c0186c74d3c 100644 (file)
--- a/src/pkg/io/io_test.go
+++ b/src/pkg/io/io_test.go
@@ -203,3 +203,35 @@ func TestTeeReader(t *testing.T) {
                t.Errorf("closed tee: ReadFull(r, dst) = %d, %v; want 0, EPIPE", n, err)
        }
 }
+
+func TestSectionReader_ReadAt(tst *testing.T) {
+       dat := "a long sample data, 1234567890"
+       tests := []struct {
+               data   string
+               off    int
+               n      int
+               bufLen int
+               at     int
+               exp    string
+               err    error
+       }{
+               {data: "", off: 0, n: 10, bufLen: 2, at: 0, exp: "", err: EOF},
+               {data: dat, off: 0, n: len(dat), bufLen: 0, at: 0, exp: "", err: nil},
+               {data: dat, off: len(dat), n: 1, bufLen: 1, at: 0, exp: "", err: EOF},
+               {data: dat, off: 0, n: len(dat) + 2, bufLen: len(dat), at: 0, exp: dat, err: nil},
+               {data: dat, off: 0, n: len(dat), bufLen: len(dat) / 2, at: 0, exp: dat[:len(dat)/2], err: nil},
+               {data: dat, off: 0, n: len(dat), bufLen: len(dat), at: 0, exp: dat, err: nil},
+               {data: dat, off: 0, n: len(dat), bufLen: len(dat) / 2, at: 2, exp: dat[2 : 2+len(dat)/2], err: nil},
+               {data: dat, off: 3, n: len(dat), bufLen: len(dat) / 2, at: 2, exp: dat[5 : 5+len(dat)/2], err: nil},
+               {data: dat, off: 3, n: len(dat) / 2, bufLen: len(dat)/2 - 2, at: 2, exp: dat[5 : 5+len(dat)/2-2], err: nil},
+               {data: dat, off: 3, n: len(dat) / 2, bufLen: len(dat)/2 + 2, at: 2, exp: dat[5 : 5+len(dat)/2-2], err: EOF},
+       }
+       for i, t := range tests {
+               r := strings.NewReader(t.data)
+               s := NewSectionReader(r, int64(t.off), int64(t.n))
+               buf := make([]byte, t.bufLen)
+               if n, err := s.ReadAt(buf, int64(t.at)); n != len(t.exp) || string(buf[:n]) != t.exp || err != t.err {
+                       tst.Fatalf("%d: ReadAt(%d) = %q, %v; expected %q, %v", i, t.at, buf[:n], err, t.exp, t.err)
+               }
+       }
+}