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dexter gerrit-no-reply at lists.osmocom.orgReview at https://gerrit.osmocom.org/4372 socket: add function osmo_sock_local_ip() to query local ip In some cases it is required to know the ip-address of the interface through that a given remote IP-Address can be reached. Add function osmo_sock_local_ip() to determine the local ip-address for a given remote ip-address Change-Id: I2988cc52b196fc8476703d1287e24cb4a48491c2 --- M include/osmocom/core/socket.h M src/socket.c 2 files changed, 50 insertions(+), 0 deletions(-) git pull ssh://gerrit.osmocom.org:29418/libosmocore refs/changes/72/4372/1 diff --git a/include/osmocom/core/socket.h b/include/osmocom/core/socket.h index ebfcab3..47d9f30 100644 --- a/include/osmocom/core/socket.h +++ b/include/osmocom/core/socket.h @@ -57,4 +57,6 @@ 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 457c991..9e3d842 100644 --- a/src/socket.c +++ b/src/socket.c @@ -786,4 +786,52 @@ #endif /* HAVE_SYS_SOCKET_H */ +/*! 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 */ +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; +} + /*! @} */ -- To view, visit https://gerrit.osmocom.org/4372 To unsubscribe, visit https://gerrit.osmocom.org/settings Gerrit-MessageType: newchange Gerrit-Change-Id: I2988cc52b196fc8476703d1287e24cb4a48491c2 Gerrit-PatchSet: 1 Gerrit-Project: libosmocore Gerrit-Branch: master Gerrit-Owner: dexter <pmaier at sysmocom.de>