xgethostname: handle long hostnames

If the full hostname doesn't fit in the buffer supplied to
gethostname, POSIX does not specify whether the buffer will be
null-terminated, so to be safe, we should do it ourselves.  Introduce
new function, xgethostname, which ensures that there is always a \0
at the end of the buffer.

Signed-off-by: David Turner <dturner@twosigma.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/gc.c

@@ -232,7 +232,7 @@ static const char *lock_repo_for_gc(int force, pid_t* ret_pid)
 		/* already locked */
 		return NULL;
 
-	if (gethostname(my_host, sizeof(my_host)))
+	if (xgethostname(my_host, sizeof(my_host)))
 		xsnprintf(my_host, sizeof(my_host), "unknown");
 
 	pidfile_path = git_pathdup("gc.pid");

builtin/receive-pack.c

@@ -1660,7 +1660,7 @@ static const char *unpack(int err_fd, struct shallow_info *si)
 		argv_array_pushl(&child.args, "index-pack",
 				 "--stdin", hdr_arg, NULL);
 
-		if (gethostname(hostname, sizeof(hostname)))
+		if (xgethostname(hostname, sizeof(hostname)))
 			xsnprintf(hostname, sizeof(hostname), "localhost");
 		argv_array_pushf(&child.args,
 				 "--keep=receive-pack %"PRIuMAX" on %s",

fetch-pack.c

@@ -746,7 +746,7 @@ static int get_pack(struct fetch_pack_args *args,
 			argv_array_push(&cmd.args, "--fix-thin");
 		if (args->lock_pack || unpack_limit) {
 			char hostname[HOST_NAME_MAX + 1];
-			if (gethostname(hostname, sizeof(hostname)))
+			if (xgethostname(hostname, sizeof(hostname)))
 				xsnprintf(hostname, sizeof(hostname), "localhost");
 			argv_array_pushf(&cmd.args,
 					"--keep=fetch-pack %"PRIuMAX " on %s",

git-compat-util.h

@@ -882,6 +882,8 @@ extern int xsnprintf(char *dst, size_t max, const char *fmt, ...);
 #define HOST_NAME_MAX 256
 #endif
 
+extern int xgethostname(char *buf, size_t len);
+
 /* in ctype.c, for kwset users */
 extern const unsigned char tolower_trans_tbl[256];
 

ident.c

@@ -122,7 +122,7 @@ static void add_domainname(struct strbuf *out, int *is_bogus)
 {
 	char buf[HOST_NAME_MAX + 1];
 
-	if (gethostname(buf, sizeof(buf))) {
+	if (xgethostname(buf, sizeof(buf))) {
 		warning_errno("cannot get host name");
 		strbuf_addstr(out, "(none)");
 		*is_bogus = 1;

wrapper.c

@@ -679,3 +679,16 @@ void sleep_millisec(int millisec)
 {
 	poll(NULL, 0, millisec);
 }
+
+int xgethostname(char *buf, size_t len)
+{
+	/*
+	 * If the full hostname doesn't fit in buf, POSIX does not
+	 * specify whether the buffer will be null-terminated, so to
+	 * be safe, do it ourselves.
+	 */
+	int ret = gethostname(buf, len);
+	if (!ret)
+		buf[len - 1] = 0;
+	return ret;
+}