[PATCH 13/16] vcs-svn: Learn to check for SVN\0 magic

[Jonathan Nieder <jrnieder@gmail.com>]

The magic number of svn deltas is SVN followed by a null byte.
An alternative format (with compressed text) uses magic number SVN\1,
but that is deprecated in favor of compressing the deltas as a whole
as far as I can tell.

Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
---
 vcs-svn/svndiff.c |   18 ++++++++++++++++++
 1 files changed, 18 insertions(+), 0 deletions(-)

diff --git a/vcs-svn/svndiff.c b/vcs-svn/svndiff.c
index 4d122a5..df0b1a2 100644
--- a/vcs-svn/svndiff.c
+++ b/vcs-svn/svndiff.c
@@ -11,6 +11,7 @@
  *
  * See http://svn.apache.org/repos/asf/subversion/trunk/notes/svndiff.
  *
+ * svndiff0 ::= 'SVN\0' window window*;
  * int ::= highdigit* lowdigit;
  * highdigit ::= # binary 1000 0000 OR-ed with 7 bit value;
  * lowdigit ::= # 7 bit value;
@@ -20,6 +21,23 @@
 #define VLI_DIGIT_MASK	0x7f
 #define VLI_BITS_PER_DIGIT 7
 
+static int read_magic(struct line_buffer *in, off_t *len)
+{
+	static const char magic[] = {'S', 'V', 'N', '\0'};
+	struct strbuf sb = STRBUF_INIT;
+	if (*len < sizeof(magic))
+		return error("Invalid delta: no file type header");
+	buffer_read_binary(&sb, sizeof(magic), in);
+	if (sb.len != sizeof(magic))
+		return error("Invalid delta: no file type header");
+	if (memcmp(sb.buf, magic, sizeof(magic)))
+		return error("Unrecognized file type %.*s",
+			     (int) sizeof(magic), sb.buf);
+	*len -= sizeof(magic);
+	strbuf_release(&sb);
+	return 0;
+}
+
 static int read_int(struct line_buffer *in, uintmax_t *result, off_t *len)
 {
 	off_t sz = *len;
-- 
1.7.2.3