getaddrinfo: improve the service/port resolution (#524)

Hello,

While experimenting with the `wasm32-wasip2` target and CPython, I
discovered an issue with the `getaddrinfo()` implementation: it fails to
resolve the provided service into a port number, causing `sin_port` to
always be set to 0. This issue leads to failures in network-related
functions that rely on `getaddrinfo()`, such as Python's `urllib3`
library, which passes the result directly to `connect()`. This results
in connection attempts using a port value of 0, which naturally fails.

### Minimal example to reproduce the problem
```c
#include <arpa/inet.h>
#include <netdb.h>
#include <stdio.h>

int main(void) {
    struct addrinfo *res = NULL;
    getaddrinfo("google.com", "443", NULL, &res);

    for (struct addrinfo *i = res; i != NULL; i = i->ai_next) {
        char str[INET6_ADDRSTRLEN];
        if (i->ai_addr->sa_family == AF_INET) {
            struct sockaddr_in *p = (struct sockaddr_in *)i->ai_addr;
            int port = ntohs(p->sin_port);
            printf("%s: %i\n", inet_ntop(AF_INET, &p->sin_addr, str, sizeof(str)), port);
        } else if (i->ai_addr->sa_family == AF_INET6) {
            struct sockaddr_in6 *p = (struct sockaddr_in6 *)i->ai_addr;
            int port = ntohs(p->sin6_port);
            printf("%s: %i\n", inet_ntop(AF_INET6, &p->sin6_addr, str, sizeof(str)), port);
        }
    }

    return 0;
}
```
```
$ /opt/wasi-sdk/bin/clang -target wasm32-wasip2 -o foo foo.c
$ wasmtime run -S allow-ip-name-lookup=y foo
216.58.211.238: 0
2a00:1450:4026:808::200e: 0
```
Expected output:
```
216.58.211.238: 443
2a00:1450:4026:808::200e: 443
```
### Root Cause

The root cause is that `getaddrinfo()` does not correctly translate the
provided service into a port number. As described in the `getaddrinfo()`
man [page](https://man7.org/linux/man-pages/man3/getaddrinfo.3.html),
the function should:

> service sets the port in each returned address structure. If
this argument is a service name (see
[services(5)](https://man7.org/linux/man-pages/man5/services.5.html)),
it is
translated to the corresponding port number. This argument can
also be specified as a decimal number, which is simply converted
to binary. If service is NULL, then the port number of the
returned socket addresses will be left uninitialized.

### Proposed Fix

This pull request addresses the issue by implementing the following
behavior for `getaddrinfo()`:

* If the service is `NULL`, the port number in the returned socket
addresses remains uninitialized.
* The value is converted to an integer and validated if the service is
numeric.

The PR does not currently add support for translating named services
into port numbers because `getservbyname()` has not been implemented. In
cases where a named service is provided, the `EAI_NONAME` error code is
returned.

expected/wasm32-wasip2/defined-symbols.txt

@@ -309,6 +309,7 @@ __wasi_sockets_utils__map_error
 __wasi_sockets_utils__output_addr_validate
 __wasi_sockets_utils__output_addr_write
 __wasi_sockets_utils__parse_address
+__wasi_sockets_utils__parse_port
 __wasi_sockets_utils__posix_family
 __wasi_sockets_utils__stream
 __wasi_sockets_utils__tcp_bind

libc-bottom-half/headers/private/wasi/sockets_utils.h

@@ -49,5 +49,6 @@ bool __wasi_sockets_utils__stream(udp_socket_t *socket,
 				  udp_socket_streams_t *result,
 				  network_error_code_t *error);
 void __wasi_sockets_utils__drop_streams(udp_socket_streams_t streams);
+int __wasi_sockets_utils__parse_port(const char *port);
 
 #endif

libc-bottom-half/sources/netdb.c

@@ -1,6 +1,7 @@
 #include <netdb.h>
 #include <errno.h>
 #include <stdlib.h>
+#include <arpa/inet.h>
 
 #include <wasi/sockets_utils.h>
 
@@ -25,6 +26,7 @@ static int map_error(ip_name_lookup_error_code_t error)
 }
 
 static int add_addr(ip_name_lookup_option_ip_address_t address,
+		    in_port_t port,
 		    const struct addrinfo *restrict hint,
 		    struct addrinfo **restrict current,
 		    struct addrinfo **restrict res)
@@ -51,7 +53,7 @@ static int add_addr(ip_name_lookup_option_ip_address_t address,
 
 		struct sockaddr_in sockaddr = {
 			.sin_family = AF_INET,
-			.sin_port = 0,
+			.sin_port = port,
 			.sin_addr = { .s_addr = ip.f0 | (ip.f1 << 8) |
 						(ip.f2 << 16) | (ip.f3 << 24) },
 		};
@@ -76,7 +78,7 @@ static int add_addr(ip_name_lookup_option_ip_address_t address,
 
 		struct sockaddr_in6 sockaddr = {
 		    .sin6_family = AF_INET6,
-		    .sin6_port = 0,
+		    .sin6_port = port,
 		    .sin6_addr = {
 			.s6_addr = {
 			    ip.f0 >> 8,
@@ -152,12 +154,25 @@ int getaddrinfo(const char *restrict host, const char *restrict serv,
 		    &error)) {
 		ip_name_lookup_borrow_resolve_address_stream_t stream_borrow =
 			ip_name_lookup_borrow_resolve_address_stream(stream);
+		// The 'serv' parameter can be either a port number or a service name.
+		//
+		// TODO wasi-sockets: If the conversion of 'serv' to a valid port
+		// number fails, use getservbyname() to resolve the service name to
+		// its corresponding port number. This can be done after the
+		// getservbyname function is implemented.)
+		int port = 0;
+		if (serv != NULL) {
+			port = __wasi_sockets_utils__parse_port(serv);
+			if (port < 0) {
+				return EAI_NONAME;
+			}
+		}
 		while (true) {
 			ip_name_lookup_option_ip_address_t address;
 			if (ip_name_lookup_method_resolve_address_stream_resolve_next_address(
 				    stream_borrow, &address, &error)) {
 				if (address.is_some) {
-					int error = add_addr(address, hint,
+					int error = add_addr(address, htons(port), hint,
 							     &current, res);
 					if (error) {
 						return error;

libc-bottom-half/sources/sockets_utils.c

@@ -1,4 +1,6 @@
 #include <errno.h>
+#include <stdlib.h>
+#include <ctype.h>
 
 #include <wasi/sockets_utils.h>
 
@@ -460,3 +462,23 @@ bool __wasi_sockets_utils__stream(
 
 	return true;
 }
+
+int __wasi_sockets_utils__parse_port(const char *restrict port_str)
+{
+    char *end = NULL;
+    errno = 0;
+    long port = strtol(port_str, &end, 10);
+
+    // Check for various possible errors:
+    //   - the input is not a valid number
+    //   - the entire input string is not consumed
+    //   - the number is not within the valid port range
+    //   - the input does not start with a digit (strtol allows leading
+    //     whitespace and optional sign)
+    if (errno != 0 || end == NULL || *end != '\0' || port < 0
+            || port > 65535 || !isdigit(*port_str)) {
+        return -1;
+    }
+
+    return (int)port;
+}