compress/gzip: specify when Reader.Header is valid

The gzip package is asymmetrical in the way it handles headers.
In Writer, the Header is written on the first call to Write, Flush, or Close.
In Reader, the Header is read on calls to NewReader or Reset as opposed to
after the first Read. Thus, we document this difference.

Fixes #13211

Change-Id: I5f87beff036e5e2fd68a02a15fdb7137e9ca4c37
Reviewed-on: https://go-review.googlesource.com/16838
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

diff --git a/src/compress/gzip/gunzip.go b/src/compress/gzip/gunzip.go
index 91473bf59833e660d7113158930b2a79ac5a364b..3d331454a695bf065c5f1e57170ee5bd16ea98bc 100644 (file)
--- a/src/compress/gzip/gunzip.go
+++ b/src/compress/gzip/gunzip.go
@@ -69,7 +69,7 @@ type Header struct {
 // returned by Read as tentative until they receive the io.EOF
 // marking the end of the data.
 type Reader struct {
-       Header
+       Header       // valid after NewReader or Reader.Reset
        r            flate.Reader
        decompressor io.ReadCloser
        digest       hash.Hash32
@@ -83,7 +83,10 @@ type Reader struct {
 // NewReader creates a new Reader reading the given reader.
 // If r does not also implement io.ByteReader,
 // the decompressor may read more data than necessary from r.
+//
 // It is the caller's responsibility to call Close on the Reader when done.
+//
+// The Reader.Header fields will be valid in the Reader returned.
 func NewReader(r io.Reader) (*Reader, error) {
        z := new(Reader)
        z.r = makeReader(r)

diff --git a/src/compress/gzip/gzip.go b/src/compress/gzip/gzip.go
index 8c76144a0cc221b772f37d5b25b211492436f923..4d945e47fe819d83a1d2bb5cd90b2ffdf8a016de 100644 (file)
--- a/src/compress/gzip/gzip.go
+++ b/src/compress/gzip/gzip.go
@@ -25,7 +25,7 @@ const (
 // A Writer is an io.WriteCloser.
 // Writes to a Writer are compressed and written to w.
 type Writer struct {
-       Header
+       Header      // written at first call to Write, Flush, or Close
        w           io.Writer
        level       int
        wroteHeader bool