pack.h: define largest possible encoded object size

Several callers use fixed buffers for storing the pack
object header, and they've picked 10 as a magic number. This
is reasonable, since it handles objects up to 2^67. But
let's give them a constant so it's clear that the number
isn't pulled out of thin air.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/pack-objects.c

@@ -239,7 +239,8 @@ static unsigned long write_no_reuse_object(struct sha1file *f, struct object_ent
 					   unsigned long limit, int usable_delta)
 {
 	unsigned long size, datalen;
-	unsigned char header[10], dheader[10];
+	unsigned char header[MAX_PACK_OBJECT_HEADER],
+		      dheader[MAX_PACK_OBJECT_HEADER];
 	unsigned hdrlen;
 	enum object_type type;
 	void *buf;
@@ -353,7 +354,8 @@ static off_t write_reuse_object(struct sha1file *f, struct object_entry *entry,
 	off_t offset;
 	enum object_type type = entry->type;
 	off_t datalen;
-	unsigned char header[10], dheader[10];
+	unsigned char header[MAX_PACK_OBJECT_HEADER],
+		      dheader[MAX_PACK_OBJECT_HEADER];
 	unsigned hdrlen;
 
 	if (entry->delta)

pack.h

@@ -84,6 +84,12 @@ extern int verify_pack(struct packed_git *, verify_fn fn, struct progress *, uin
 extern off_t write_pack_header(struct sha1file *f, uint32_t);
 extern void fixup_pack_header_footer(int, unsigned char *, const char *, uint32_t, unsigned char *, off_t);
 extern char *index_pack_lockfile(int fd);
+
+/*
+ * The "hdr" output buffer should be at least this big, which will handle sizes
+ * up to 2^67.
+ */
+#define MAX_PACK_OBJECT_HEADER 10
 extern int encode_in_pack_object_header(unsigned char *hdr, int hdr_len,
 					enum object_type, uintmax_t);