use skip_prefix to avoid magic numbers

It's a common idiom to match a prefix and then skip past it
with a magic number, like:

  if (starts_with(foo, "bar"))
	  foo += 3;

This is easy to get wrong, since you have to count the
prefix string yourself, and there's no compiler check if the
string changes.  We can use skip_prefix to avoid the magic
numbers here.

Note that some of these conversions could be much shorter.
For example:

  if (starts_with(arg, "--foo=")) {
	  bar = arg + 6;
	  continue;
  }

could become:

  if (skip_prefix(arg, "--foo=", &bar))
	  continue;

However, I have left it as:

  if (skip_prefix(arg, "--foo=", &v)) {
	  bar = v;
	  continue;
  }

to visually match nearby cases which need to actually
process the string. Like:

  if (skip_prefix(arg, "--foo=", &v)) {
	  bar = atoi(v);
	  continue;
  }

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

1 files changed, 38 insertions, 35 deletions

diff --git a/daemon.c b/daemon.c
index 18818c3..6d25828 100644
--- a/daemon.c
+++ b/daemon.c
@@ -235,8 +235,10 @@ static int service_enabled;
 
 static int git_daemon_config(const char *var, const char *value, void *cb)
 {
-	if (starts_with(var, "daemon.") &&
-	    !strcmp(var + 7, service_looking_at->config_name)) {
+	const char *service;
+
+	if (skip_prefix(var, "daemon.", &service) &&
+	    !strcmp(service, service_looking_at->config_name)) {
 		service_enabled = git_config_bool(var, value);
 		return 0;
 	}
@@ -1133,16 +1135,17 @@ int main(int argc, char **argv)
 
 	for (i = 1; i < argc; i++) {
 		char *arg = argv[i];
+		const char *v;
 
-		if (starts_with(arg, "--listen=")) {
-			string_list_append(&listen_addr, xstrdup_tolower(arg + 9));
+		if (skip_prefix(arg, "--listen=", &v)) {
+			string_list_append(&listen_addr, xstrdup_tolower(v));
 			continue;
 		}
-		if (starts_with(arg, "--port=")) {
+		if (skip_prefix(arg, "--port=", &v)) {
 			char *end;
 			unsigned long n;
-			n = strtoul(arg+7, &end, 0);
-			if (arg[7] && !*end) {
+			n = strtoul(v, &end, 0);
+			if (*v && !*end) {
 				listen_port = n;
 				continue;
 			}
@@ -1168,20 +1171,20 @@ int main(int argc, char **argv)
 			export_all_trees = 1;
 			continue;
 		}
-		if (starts_with(arg, "--access-hook=")) {
-			access_hook = arg + 14;
+		if (skip_prefix(arg, "--access-hook=", &v)) {
+			access_hook = v;
 			continue;
 		}
-		if (starts_with(arg, "--timeout=")) {
-			timeout = atoi(arg+10);
+		if (skip_prefix(arg, "--timeout=", &v)) {
+			timeout = atoi(v);
 			continue;
 		}
-		if (starts_with(arg, "--init-timeout=")) {
-			init_timeout = atoi(arg+15);
+		if (skip_prefix(arg, "--init-timeout=", &v)) {
+			init_timeout = atoi(v);
 			continue;
 		}
-		if (starts_with(arg, "--max-connections=")) {
-			max_connections = atoi(arg+18);
+		if (skip_prefix(arg, "--max-connections=", &v)) {
+			max_connections = atoi(v);
 			if (max_connections < 0)
 				max_connections = 0;	        /* unlimited */
 			continue;
@@ -1190,16 +1193,16 @@ int main(int argc, char **argv)
 			strict_paths = 1;
 			continue;
 		}
-		if (starts_with(arg, "--base-path=")) {
-			base_path = arg+12;
+		if (skip_prefix(arg, "--base-path=", &v)) {
+			base_path = v;
 			continue;
 		}
 		if (!strcmp(arg, "--base-path-relaxed")) {
 			base_path_relaxed = 1;
 			continue;
 		}
-		if (starts_with(arg, "--interpolated-path=")) {
-			interpolated_path = arg+20;
+		if (skip_prefix(arg, "--interpolated-path=", &v)) {
+			interpolated_path = v;
 			continue;
 		}
 		if (!strcmp(arg, "--reuseaddr")) {
@@ -1210,12 +1213,12 @@ int main(int argc, char **argv)
 			user_path = "";
 			continue;
 		}
-		if (starts_with(arg, "--user-path=")) {
-			user_path = arg + 12;
+		if (skip_prefix(arg, "--user-path=", &v)) {
+			user_path = v;
 			continue;
 		}
-		if (starts_with(arg, "--pid-file=")) {
-			pid_file = arg + 11;
+		if (skip_prefix(arg, "--pid-file=", &v)) {
+			pid_file = v;
 			continue;
 		}
 		if (!strcmp(arg, "--detach")) {
@@ -1223,28 +1226,28 @@ int main(int argc, char **argv)
 			log_syslog = 1;
 			continue;
 		}
-		if (starts_with(arg, "--user=")) {
-			user_name = arg + 7;
+		if (skip_prefix(arg, "--user=", &v)) {
+			user_name = v;
 			continue;
 		}
-		if (starts_with(arg, "--group=")) {
-			group_name = arg + 8;
+		if (skip_prefix(arg, "--group=", &v)) {
+			group_name = v;
 			continue;
 		}
-		if (starts_with(arg, "--enable=")) {
-			enable_service(arg + 9, 1);
+		if (skip_prefix(arg, "--enable=", &v)) {
+			enable_service(v, 1);
 			continue;
 		}
-		if (starts_with(arg, "--disable=")) {
-			enable_service(arg + 10, 0);
+		if (skip_prefix(arg, "--disable=", &v)) {
+			enable_service(v, 0);
 			continue;
 		}
-		if (starts_with(arg, "--allow-override=")) {
-			make_service_overridable(arg + 17, 1);
+		if (skip_prefix(arg, "--allow-override=", &v)) {
+			make_service_overridable(v, 1);
 			continue;
 		}
-		if (starts_with(arg, "--forbid-override=")) {
-			make_service_overridable(arg + 18, 0);
+		if (skip_prefix(arg, "--forbid-override=", &v)) {
+			make_service_overridable(v, 0);
 			continue;
 		}
 		if (!strcmp(arg, "--informative-errors")) {