diff options
| -rw-r--r-- | include/osmocom/core/socket.h | 2 | ||||
| -rw-r--r-- | src/socket.c | 53 |
2 files changed, 55 insertions, 0 deletions
diff --git a/include/osmocom/core/socket.h b/include/osmocom/core/socket.h index ebfcab3a..47d9f308 100644 --- a/include/osmocom/core/socket.h +++ b/include/osmocom/core/socket.h @@ -57,4 +57,6 @@ int osmo_sock_mcast_ttl_set(int fd, uint8_t ttl); int osmo_sock_mcast_all_set(int fd, bool enable); int osmo_sock_mcast_subscribe(int fd, const char *grp_addr); +int osmo_sock_local_ip(char *local_ip, const char *remote_ip); + /*! @} */ diff --git a/src/socket.c b/src/socket.c index 457c991d..b516abfd 100644 --- a/src/socket.c +++ b/src/socket.c @@ -784,6 +784,59 @@ int osmo_sock_mcast_subscribe(int fd, const char *grp_addr) } } +/*! Determine the matching local IP-address for a given remote IP-Address. + * \param[out] local_ip caller provided memory for resulting local IP-address + * \param[in] remote_ip remote IP-address + * \param[in] fd file descriptor of related scoket + * \returns 0 on success; negative otherwise + * + * The function accepts IPv4 and IPv6 address strings. The caller must provide + * at least INET6_ADDRSTRLEN bytes for local_ip if an IPv6 is expected as + * as result. For IPv4 addresses the required amount is INET_ADDRSTRLEN. */ +int osmo_sock_local_ip(char *local_ip, const char *remote_ip) +{ + int sfd; + int rc; + struct addrinfo addrinfo_hint; + struct addrinfo *addrinfo = NULL; + struct sockaddr_in local_addr; + socklen_t local_addr_len; + uint16_t family; + + /* Find out the address family (AF_INET or AF_INET6?) */ + memset(&addrinfo_hint, '\0', sizeof(addrinfo_hint)); + addrinfo_hint.ai_family = PF_UNSPEC; + addrinfo_hint.ai_flags = AI_NUMERICHOST; + rc = getaddrinfo(remote_ip, NULL, &addrinfo_hint, &addrinfo); + if (rc) + return -EINVAL; + family = addrinfo->ai_family; + freeaddrinfo(addrinfo); + + /* Connect a dummy socket to trick the kernel into determining the + * ip-address of the interface that would be used if we would send + * out an actual packet */ + sfd = osmo_sock_init2(family, SOCK_DGRAM, IPPROTO_UDP, NULL, 0, remote_ip, 0, OSMO_SOCK_F_CONNECT); + if (sfd < 0) + return -EINVAL; + + /* Request the IP address of the interface that the kernel has + * actually choosen. */ + memset(&local_addr, 0, sizeof(local_addr)); + local_addr_len = sizeof(local_addr); + rc = getsockname(sfd, (struct sockaddr *)&local_addr, &local_addr_len); + if (rc < 0) + return -EINVAL; + if (local_addr.sin_family == AF_INET) + strncpy(local_ip, inet_ntoa(local_addr.sin_addr), INET_ADDRSTRLEN); + else if (local_addr.sin_family == AF_INET6) + strncpy(local_ip, inet_ntoa(local_addr.sin_addr), INET6_ADDRSTRLEN); + else + return -EINVAL; + + return 0; +} + #endif /* HAVE_SYS_SOCKET_H */ /*! @} */ |