Update networking layer w/ CURL and emscripten impl

External/curl-8.17.0/docs/libcurl/curl_formget.md

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+---
+c: Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
+SPDX-License-Identifier: curl
+Title: curl_formget
+Section: 3
+Source: libcurl
+See-also:
+  - curl_formadd (3)
+  - curl_mime_init (3)
+Protocol:
+  - HTTP
+Added-in: 7.15.5
+---
+
+# NAME
+
+curl_formget - serialize a multipart form POST chain
+
+# SYNOPSIS
+
+~~~c
+#include <curl/curl.h>
+
+int curl_formget(struct curl_httppost * form, void *userp,
+                 curl_formget_callback append);
+~~~
+
+# DESCRIPTION
+
+The form API (including this function) is deprecated since libcurl 7.56.0.
+
+curl_formget() serializes data previously built with curl_formadd(3). It
+accepts a void pointer as second argument named *userp* which is passed as the
+first argument to the curl_formget_callback function.
+
+~~~c
+ typedef size_t (*curl_formget_callback)(void *userp, const char *buf,
+                                         size_t len);"
+~~~
+
+The *curl_formget_callback* is invoked for each part of the HTTP POST chain.
+The character buffer passed to the callback must not be freed. The callback
+should return the buffer length passed to it on success.
+
+If the **CURLFORM_STREAM** option is used in the formpost, it prevents
+curl_formget(3) from working until you have performed the actual HTTP request.
+This, because first then does libcurl known which actual read callback to use.
+
+# %PROTOCOLS%
+
+# EXAMPLE
+
+~~~c
+size_t print_httppost_callback(void *arg, const char *buf, size_t len)
+{
+  fwrite(buf, len, 1, stdout);
+  (*(size_t *) arg) += len;
+  return len;
+}
+
+size_t print_httppost(struct curl_httppost *post)
+{
+  size_t total_size = 0;
+  if(curl_formget(post, &total_size, print_httppost_callback)) {
+    return (size_t) -1;
+  }
+  return total_size;
+}
+~~~
+
+# %AVAILABILITY%
+
+# RETURN VALUE
+
+0 means everything was OK, non-zero means an error occurred