Question

I’m new to iOS/MacOS programming and have not found any examples I understand. I imagine it is only a few lines of code to do this, so sorry if this is covered already but for the life of me I cannot find it.

I’m using CFStreamCreatePairWithSocketToHost to create in/out streams. I just want to get the local endpoint info (specifically the IP address, don’t care about port really). I already obtain the public IP info from my server, but for security/logging reasons I need the local address as well.

This is on iOS, not MacOS, if it matters.

Answer 1

The following code demonstrates how to get the local socket address. It works with IPv4 and IPv6 addresses. (It is more than a few lines, perhaps somebody knows a shorter solution.)

#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>

// Create socket pair:
CFReadStreamRef readStream;
CFWriteStreamRef writeStream;
CFStringRef remoteHost = CFSTR("localhost");
CFStreamCreatePairWithSocketToHost(NULL, remoteHost, 5555, &readStream, &writeStream);

// Write something (the socket is not valid before you read or write):
CFWriteStreamOpen(writeStream);
CFWriteStreamWrite(writeStream, "Hello\n", 6);

// Get the native socket handle:
CFDataRef socketData = CFWriteStreamCopyProperty(writeStream, kCFStreamPropertySocketNativeHandle);
CFSocketNativeHandle socket;
CFDataGetBytes(socketData, CFRangeMake(0, sizeof(CFSocketNativeHandle)), (UInt8 *)&socket);

// Get the local socket address from the socket handle:
struct sockaddr_storage sa;
socklen_t salen = sizeof(sa);
getsockname(socket, (struct sockaddr *)&sa, &salen);

// Get numeric host and port from socket address:
char host[NI_MAXHOST];
char service[NI_MAXSERV];
getnameinfo((struct sockaddr *)&sa, salen, host, sizeof(host), service, sizeof(service), NI_NUMERICHOST|NI_NUMERICSERV);

NSLog(@"local address: %s, local port: %s", host, service);