archive/tar: make output deterministic

Replaces PID in PaxHeaders with 0.  Sorts PAX header keys before writing
them to the archive.

Fixes #12358

Change-Id: If239f89c85f1c9d9895a253fb06a47ad44960124
Reviewed-on: https://go-review.googlesource.com/13975
Reviewed-by: Russ Cox <rsc@golang.org>
Reviewed-by: Joe Tsai <joetsai@digital-static.net>

diff --git a/src/archive/tar/writer.go b/src/archive/tar/writer.go
index 3547c1760a8a51c962ea021658e530d1dcd8e510..0165b2259c21d23c437f3168aa033d3ba21aec8b 100644 (file)
--- a/src/archive/tar/writer.go
+++ b/src/archive/tar/writer.go
@@ -12,8 +12,8 @@ import (
        "errors"
        "fmt"
        "io"
-       "os"
        "path"
+       "sort"
        "strconv"
        "strings"
        "time"
@@ -288,11 +288,11 @@ func (tw *Writer) writePAXHeader(hdr *Header, paxHeaders map[string]string) erro
        // succeed, and seems harmless enough.
        ext.ModTime = hdr.ModTime
        // The spec asks that we namespace our pseudo files
-       // with the current pid.
-       pid := os.Getpid()
+       // with the current pid.  However, this results in differing outputs
+       // for identical inputs.  As such, the constant 0 is now used instead.
+       // golang.org/issue/12358
        dir, file := path.Split(hdr.Name)
-       fullName := path.Join(dir,
-               fmt.Sprintf("PaxHeaders.%d", pid), file)
+       fullName := path.Join(dir, "PaxHeaders.0", file)
 
        ascii := toASCII(fullName)
        if len(ascii) > 100 {
@@ -302,8 +302,15 @@ func (tw *Writer) writePAXHeader(hdr *Header, paxHeaders map[string]string) erro
        // Construct the body
        var buf bytes.Buffer
 
-       for k, v := range paxHeaders {
-               fmt.Fprint(&buf, paxHeader(k+"="+v))
+       // Keys are sorted before writing to body to allow deterministic output.
+       var keys []string
+       for k := range paxHeaders {
+               keys = append(keys, k)
+       }
+       sort.Strings(keys)
+
+       for _, k := range keys {
+               fmt.Fprint(&buf, paxHeader(k+"="+paxHeaders[k]))
        }
 
        ext.Size = int64(len(buf.Bytes()))

diff --git a/src/archive/tar/writer_test.go b/src/archive/tar/writer_test.go
index caf40a836fc20297407f27637e7fc2dae878be2f..25d88dc7e17ff6ab258056a447f59e93ab439855 100644 (file)
--- a/src/archive/tar/writer_test.go
+++ b/src/archive/tar/writer_test.go
@@ -11,6 +11,7 @@ import (
        "io/ioutil"
        "os"
        "reflect"
+       "sort"
        "strings"
        "testing"
        "testing/iotest"
@@ -291,7 +292,7 @@ func TestPax(t *testing.T) {
                t.Fatal(err)
        }
        // Simple test to make sure PAX extensions are in effect
-       if !bytes.Contains(buf.Bytes(), []byte("PaxHeaders.")) {
+       if !bytes.Contains(buf.Bytes(), []byte("PaxHeaders.0")) {
                t.Fatal("Expected at least one PAX header to be written.")
        }
        // Test that we can get a long name back out of the archive.
@@ -330,7 +331,7 @@ func TestPaxSymlink(t *testing.T) {
                t.Fatal(err)
        }
        // Simple test to make sure PAX extensions are in effect
-       if !bytes.Contains(buf.Bytes(), []byte("PaxHeaders.")) {
+       if !bytes.Contains(buf.Bytes(), []byte("PaxHeaders.0")) {
                t.Fatal("Expected at least one PAX header to be written.")
        }
        // Test that we can get a long name back out of the archive.
@@ -380,7 +381,7 @@ func TestPaxNonAscii(t *testing.T) {
                t.Fatal(err)
        }
        // Simple test to make sure PAX extensions are in effect
-       if !bytes.Contains(buf.Bytes(), []byte("PaxHeaders.")) {
+       if !bytes.Contains(buf.Bytes(), []byte("PaxHeaders.0")) {
                t.Fatal("Expected at least one PAX header to be written.")
        }
        // Test that we can get a long name back out of the archive.
@@ -439,6 +440,52 @@ func TestPaxXattrs(t *testing.T) {
        }
 }
 
+func TestPaxHeadersSorted(t *testing.T) {
+       fileinfo, err := os.Stat("testdata/small.txt")
+       if err != nil {
+               t.Fatal(err)
+       }
+       hdr, err := FileInfoHeader(fileinfo, "")
+       if err != nil {
+               t.Fatalf("os.Stat: %v", err)
+       }
+       contents := strings.Repeat(" ", int(hdr.Size))
+
+       hdr.Xattrs = map[string]string{
+               "foo": "foo",
+               "bar": "bar",
+               "baz": "baz",
+               "qux": "qux",
+       }
+
+       var buf bytes.Buffer
+       writer := NewWriter(&buf)
+       if err := writer.WriteHeader(hdr); err != nil {
+               t.Fatal(err)
+       }
+       if _, err = writer.Write([]byte(contents)); err != nil {
+               t.Fatal(err)
+       }
+       if err := writer.Close(); err != nil {
+               t.Fatal(err)
+       }
+       // Simple test to make sure PAX extensions are in effect
+       if !bytes.Contains(buf.Bytes(), []byte("PaxHeaders.0")) {
+               t.Fatal("Expected at least one PAX header to be written.")
+       }
+
+       // xattr bar should always appear before others
+       indices := []int{
+               bytes.Index(buf.Bytes(), []byte("bar=bar")),
+               bytes.Index(buf.Bytes(), []byte("baz=baz")),
+               bytes.Index(buf.Bytes(), []byte("foo=foo")),
+               bytes.Index(buf.Bytes(), []byte("qux=qux")),
+       }
+       if !sort.IntsAreSorted(indices) {
+               t.Fatal("PAX headers are not sorted")
+       }
+}
+
 func TestPAXHeader(t *testing.T) {
        medName := strings.Repeat("CD", 50)
        longName := strings.Repeat("AB", 100)