socket: add define for socket name length

The function osmo_sock_get_name_buf() can be used to write a string
representation to a user provided memory. Unfortunately the proper
length for the user provided memory is not obvious. To make using
osmo_sock_get_name_buf() more practical, add a define constant that
defines the length of the required memory. Also use this define in
socket.c.

Change-Id: If8be8c2c0d4935da17ab13b2c2127b719ceefbcc

include/osmocom/core/socket.h

@@ -28,6 +28,8 @@ struct osmo_fd;
 #define OSMO_SOCK_F_NO_MCAST_ALL  (1 << 4)
 /*! use SO_REUSEADDR on UDP ports (required for multicast) */
 #define OSMO_SOCK_F_UDP_REUSEADDR (1 << 5)
+/*! maximum length of a socket name ("r=1.2.3.4:123<->l=5.6.7.8:987") */
+#define OSMO_SOCK_NAME_MAXLEN (2 + INET6_ADDRSTRLEN + 1 + 5 + 3 + 2 + INET6_ADDRSTRLEN + 1 + 5 + 1)
 
 int osmo_sock_init(uint16_t family, uint16_t type, uint8_t proto,
 		   const char *host, uint16_t port, unsigned int flags);

src/socket.c

@@ -783,8 +783,7 @@ int osmo_sock_get_remote_ip_port(int fd, char *port, size_t len)
  */
 char *osmo_sock_get_name(void *ctx, int fd)
 {
-	/* "r=1.2.3.4:123<->l=5.6.7.8:987" */
-	char str[2 + INET6_ADDRSTRLEN + 1 + 5 + 3 + 2 + INET6_ADDRSTRLEN + 1 + 5 + 1];
+	char str[OSMO_SOCK_NAME_MAXLEN];
 	int rc;
 	rc = osmo_sock_get_name_buf(str, sizeof(str), fd);
 	if (rc <= 0)
@@ -823,8 +822,7 @@ int osmo_sock_get_name_buf(char *str, size_t str_len, int fd)
  */
 const char *osmo_sock_get_name2(int fd)
 {
-	/* "r=1.2.3.4:123<->l=5.6.7.8:987" */
-	static char str[2 + INET6_ADDRSTRLEN + 1 + 5 + 3 + 2 + INET6_ADDRSTRLEN + 1 + 5 + 1];
+	static char str[OSMO_SOCK_NAME_MAXLEN];
 	osmo_sock_get_name_buf(str, sizeof(str), fd);
 	return str;
 }