getaddrinfo() returns 0 if it succeeds, or one of the following
nonzero error codes:
EAI_ADDRFAMILY
The specified network host does not have any network
addresses in the requested address family.
EAI_AGAIN
The name server returned a temporary failure indication.
Try again later.
EAI_BADFLAGS
hints.ai_flags contains invalid flags; or, hints.ai_flags
included AI_CANONNAME and name was NULL.
EAI_FAIL
The name server returned a permanent failure indication.
EAI_FAMILY
The requested address family is not supported.
EAI_MEMORY
Out of memory.
EAI_NODATA
The specified network host exists, but does not have any
network addresses defined.
EAI_NONAME
The node or service is not known; or both node and service
are NULL; or AI_NUMERICSERV was specified in
hints.ai_flags and service was not a numeric port-number
string.
EAI_SERVICE
The requested service is not available for the requested
socket type. It may be available through another socket
type. For example, this error could occur if service was
"shell" (a service available only on stream sockets), and
either hints.ai_protocol was IPPROTO_UDP, or
hints.ai_socktype was SOCK_DGRAM; or the error could occur
if service was not NULL, and hints.ai_socktype was
SOCK_RAW (a socket type that does not support the concept
of services).
EAI_SOCKTYPE
The requested socket type is not supported. This could
occur, for example, if hints.ai_socktype and
hints.ai_protocol are inconsistent (e.g., SOCK_DGRAM and
IPPROTO_TCP, respectively).
EAI_SYSTEM
Other system error; errno is set to indicate the error.
The gai_strerror() function translates these error codes to a
human readable string, suitable for error reporting.
