Review 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
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Gerrit-MessageType: newchange
Gerrit-Change-Id: I2988cc52b196fc8476703d1287e24cb4a48491c2
Gerrit-PatchSet: 1
Gerrit-Project: libosmocore
Gerrit-Branch: master
Gerrit-Owner: dexter <[email protected]>
