Update networking layer w/ CURL and emscripten impl

External/curl-8.17.0/docs/libcurl/opts/CURLOPT_CLOSESOCKETFUNCTION.md

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+---
+c: Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
+SPDX-License-Identifier: curl
+Title: CURLOPT_CLOSESOCKETFUNCTION
+Section: 3
+Source: libcurl
+See-also:
+  - CURLOPT_CLOSESOCKETDATA (3)
+  - CURLOPT_OPENSOCKETFUNCTION (3)
+Protocol:
+  - All
+Added-in: 7.21.7
+---
+
+# NAME
+
+CURLOPT_CLOSESOCKETFUNCTION - callback to socket close replacement
+
+# SYNOPSIS
+
+~~~c
+#include <curl/curl.h>
+
+int closesocket_callback(void *clientp, curl_socket_t item);
+
+CURLcode curl_easy_setopt(CURL *handle, CURLOPT_CLOSESOCKETFUNCTION,
+                          closesocket_callback);
+~~~
+
+# DESCRIPTION
+
+Pass a pointer to your callback function, which should match the prototype
+shown above.
+
+This callback function gets called by libcurl instead of the *close(3)* or
+*closesocket(3)* call when sockets are closed (not for any other file
+descriptors). This is pretty much the reverse to the
+CURLOPT_OPENSOCKETFUNCTION(3) option. Return 0 to signal success and 1
+if there was an error.
+
+The *clientp* pointer is set with
+CURLOPT_CLOSESOCKETDATA(3). *item* is the socket libcurl wants to be
+closed.
+
+Note that when using multi/share handles, your callback may get invoked even
+after the easy handle has been cleaned up. The callback and data is
+inherited by a new connection and that connection may live longer
+than the transfer itself in the multi/share handle's connection cache.
+
+# DEFAULT
+
+Use the standard socket close function.
+
+# %PROTOCOLS%
+
+# EXAMPLE
+
+~~~c
+struct priv {
+  void *custom;
+};
+
+static int closesocket(void *clientp, curl_socket_t item)
+{
+  struct priv *my = clientp;
+  printf("our ptr: %p\n", my->custom);
+
+  printf("libcurl wants to close %d now\n", (int)item);
+  return 0;
+}
+
+int main(void)
+{
+  struct priv myown;
+  CURL *curl = curl_easy_init();
+
+  /* call this function to close sockets */
+  curl_easy_setopt(curl, CURLOPT_CLOSESOCKETFUNCTION, closesocket);
+  curl_easy_setopt(curl, CURLOPT_CLOSESOCKETDATA, &myown);
+
+  curl_easy_perform(curl);
+  curl_easy_cleanup(curl);
+}
+~~~
+
+# %AVAILABILITY%
+
+# RETURN VALUE
+
+curl_easy_setopt(3) returns a CURLcode indicating success or error.
+
+CURLE_OK (0) means everything was OK, non-zero means an error occurred, see
+libcurl-errors(3).