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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
This commit is contained in:
Philipp Maier 2017-10-20 19:41:26 +02:00 committed by Harald Welte
parent a19c126e76
commit 2d2490ed4e
2 changed files with 55 additions and 0 deletions
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2
include/osmocom/core/socket.h
View File

@ -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);
/*! @} */

53
src/socket.c
View File

@ -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 */
/*! @} */