UDP address name resolution is limited to dotted IPv4 rather than being capable of IPv4, IPv6, and hostname lookup

[robwiss]

Issue description

The udp transport requires addresses passed into it be in IPv4 dotted notation. Take this sample program:

#include <assert.h>
#include <cstdio>
#include <zmq.h>

int main(int argc, char** argv) {
  char address[4096];
  sprintf(address, "udp://%s:5555", argv[1]);

  void* ctx = zmq_ctx_new();
  void* skt = zmq_socket(ctx, ZMQ_DISH);
  int rc = zmq_bind(skt, address);
  assert(0 == rc);
  printf("Success\n");
}

this is ok:

$ ./udp_bind_test 127.0.0.1
Success

but this is not ok

$ ./udp_bind_test localhost
udp_bind_test: udp_bind_test.cpp:12: int main(int, char**): Assertion `0 == rc' failed.
Aborted (core dumped)

This is different from the behavior of the tcp transport, which allows binding to localhost and many other types of address names.

I believe the issue stems from zmq::udp_address_t::resolve(const char *name_, bool bind_) in src/udp_address.cpp. This function expects the endpoint name to be a ":" separated address and port. After splitting the name argument into addr_str and port_str, addr_str is translated to a in_addr_t struct using inet_addr(). The manpage for inet_addr, man inet_addr says:

The inet_addr() function converts the Internet host address cp from IPv4 numbers-and-dots notation into binary data in network byte order. If the input is invalid, INADDR_NONE (usually -1) is returned. Use of this function is problematic because -1 is a valid address (255.255.255.255). Avoid its use in favor of inet_aton(), inet_pton(3), or getaddrinfo(3) which provide a cleaner way to indicate error return.

Were getaddrinfo used instead of inet_addr (as it is in the zmq::tcp_address_t::resolve_interface (const char *interface_, bool ipv6_, bool is_src_) function from src/tcp_address.cpp) a name like "localhost" or even an IPv6 address would work. From the getaddrinfo manpage:

int getaddrinfo(const char *node, const char *service, const struct addrinfo *hints, struct addrinfo **res);
node specifies either a numerical network address (for IPv4, numbers-and-dots notation as supported by inet_aton(3); for IPv6, hexadecimal string format as supported by inet_pton(3)), or a network hostname, whose network addresses are looked up and resolved.
service sets the port in each returned address structure. If this argument is a service name (see services(5)), it is translated to the corresponding port number. This argument can also be specified as a decimal number, which is simply converted to binary.

Is there a reason the udp resolve function cannot be switched from using inet_addr() to getaddrinfo() so as to support name lookups and possibly also IPv6?

Environment

• libzmq version (commit hash if unreleased): 4.2.3
• OS: CentOS 6.9

[bluca]

No particular reason, it's just work-in-progress hence why it's marked as DRAFT. IPv6 (especially for multicast) is not yet supported. PRs welcome!

[bluca]

Fixed by #3075 and #3081