From 51f3cbabfc58c0db89b1142f94d794b59727f572 Mon Sep 17 00:00:00 2001
From: "Guillaume J. Charmes" <guillaume@charmes.net>
Date: Wed, 14 May 2014 10:15:43 -0700
Subject: [PATCH] archive/tar: Fix bug preventing untar

Do not use ustar format if we need the GNU one.
Change \000 to \x00 for consistency
Check for "ustar\x00" instead of "ustar\x00\x00" for conistency with tar
and compatiblity with archive generated with older code (which was ustar\x00\x20\x00)
Add test for long name + big file.

LGTM=iant
R=golang-codereviews, iant
CC=golang-codereviews
https://golang.org/cl/99050043
---
 src/pkg/archive/tar/reader.go                 |   6 ++---
 .../archive/tar/testdata/writer-big-long.tar  | Bin 0 -> 4096 bytes
 src/pkg/archive/tar/writer.go                 |   4 +--
 src/pkg/archive/tar/writer_test.go            |  23 ++++++++++++++++++
 4 files changed, 28 insertions(+), 5 deletions(-)
 create mode 100644 src/pkg/archive/tar/testdata/writer-big-long.tar

diff --git a/src/pkg/archive/tar/reader.go b/src/pkg/archive/tar/reader.go
index d15e120792..e6ac538aad 100644
--- a/src/pkg/archive/tar/reader.go
+++ b/src/pkg/archive/tar/reader.go
@@ -468,14 +468,14 @@ func (tr *Reader) readHeader() *Header {
 	// so its magic bytes, like the rest of the block, are NULs.
 	magic := string(s.next(8)) // contains version field as well.
 	var format string
-	switch magic {
-	case "ustar\x0000": // POSIX tar (1003.1-1988)
+	switch {
+	case magic[:6] == "ustar\x00": // POSIX tar (1003.1-1988)
 		if string(header[508:512]) == "tar\x00" {
 			format = "star"
 		} else {
 			format = "posix"
 		}
-	case "ustar  \x00": // old GNU tar
+	case magic == "ustar  \x00": // old GNU tar
 		format = "gnu"
 	}
 
diff --git a/src/pkg/archive/tar/testdata/writer-big-long.tar b/src/pkg/archive/tar/testdata/writer-big-long.tar
new file mode 100644
index 0000000000000000000000000000000000000000..5960ee824784ffeacb976a9c648be41b0281508b
GIT binary patch
literal 4096
zcmeIuJqp7x3<Y2fJ%~?`%0IEr;~|)U<3MUd#~!^lfo!2u=#cjYOIU-@r+u8`P~L^E
z3%7XZs1+?EAN8}ZeDtD?wMK+T7Gmew2r1s@*S_^t!lo3(I;RxsGM%jZHSb5Z^y7Lc
jtvTkfOwYeIC&%C$0uX=z1Rwwb2tWV=5P$##?k4aBT?$NV

literal 0
HcmV?d00001

diff --git a/src/pkg/archive/tar/writer.go b/src/pkg/archive/tar/writer.go
index 9ee9499297..6eff6f6f84 100644
--- a/src/pkg/archive/tar/writer.go
+++ b/src/pkg/archive/tar/writer.go
@@ -218,8 +218,8 @@ func (tw *Writer) writeHeader(hdr *Header, allowPax bool) error {
 				tw.cString(prefixHeaderBytes, prefix, false, paxNone, nil)
 
 				// Use the ustar magic if we used ustar long names.
-				if len(prefix) > 0 {
-					copy(header[257:265], []byte("ustar\000"))
+				if len(prefix) > 0 && !tw.usedBinary {
+					copy(header[257:265], []byte("ustar\x00"))
 				}
 			}
 		}
diff --git a/src/pkg/archive/tar/writer_test.go b/src/pkg/archive/tar/writer_test.go
index 2b9ea658db..512fab1a6f 100644
--- a/src/pkg/archive/tar/writer_test.go
+++ b/src/pkg/archive/tar/writer_test.go
@@ -103,6 +103,29 @@ var writerTests = []*writerTest{
 			},
 		},
 	},
+	// The truncated test file was produced using these commands:
+	//   dd if=/dev/zero bs=1048576 count=16384 > (longname/)*15 /16gig.txt
+	//   tar -b 1 -c -f- (longname/)*15 /16gig.txt | dd bs=512 count=8 > writer-big-long.tar
+	{
+		file: "testdata/writer-big-long.tar",
+		entries: []*writerTestEntry{
+			{
+				header: &Header{
+					Name:     strings.Repeat("longname/", 15) + "16gig.txt",
+					Mode:     0644,
+					Uid:      1000,
+					Gid:      1000,
+					Size:     16 << 30,
+					ModTime:  time.Unix(1399583047, 0),
+					Typeflag: '0',
+					Uname:    "guillaume",
+					Gname:    "guillaume",
+				},
+				// fake contents
+				contents: strings.Repeat("\x00", 4<<10),
+			},
+		},
+	},
 	// This file was produced using gnu tar 1.17
 	// gnutar  -b 4 --format=ustar (longname/)*15 + file.txt
 	{
-- 
2.50.0