Update networking layer w/ CURL and emscripten impl

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

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+---
+c: Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
+SPDX-License-Identifier: curl
+Title: curl_easy_upkeep
+Section: 3
+Source: libcurl
+See-also:
+  - CURLOPT_TCP_KEEPALIVE (3)
+  - CURLOPT_TCP_KEEPIDLE (3)
+Protocol:
+  - All
+Added-in: 7.62.0
+---
+
+# NAME
+
+curl_easy_upkeep - keep existing connections alive
+
+# SYNOPSIS
+
+~~~c
+#include <curl/curl.h>
+
+CURLcode curl_easy_upkeep(CURL *handle);
+~~~
+
+# DESCRIPTION
+
+Some protocols have "connection upkeep" mechanisms. These mechanisms usually
+send some traffic on existing connections in order to keep them alive; this
+can prevent connections from being closed due to overzealous firewalls, for
+example.
+
+For HTTP/2 we have an upkeep mechanism: when
+the connection upkeep interval is exceeded and curl_easy_upkeep(3)
+is called, an HTTP/2 PING frame is sent on the connection.
+
+For MQTT the upkeep interval defines when to send ping requests to prevent the
+server from disconnecting.
+
+This function must be explicitly called in order to perform the upkeep work.
+The connection upkeep interval is set with
+CURLOPT_UPKEEP_INTERVAL_MS(3).
+
+If you call this function on an easy handle that uses a shared connection cache
+then upkeep is performed on the connections in that cache, even if those
+connections were never used by the easy handle. (Added in 8.10.0)
+
+# %PROTOCOLS%
+
+# EXAMPLE
+
+~~~c
+int main(void)
+{
+  CURL *curl = curl_easy_init();
+  if(curl) {
+    /* Make a connection to an HTTP/2 server. */
+    curl_easy_setopt(curl, CURLOPT_URL, "https://example.com");
+
+    /* Set the interval to 30000ms / 30s */
+    curl_easy_setopt(curl, CURLOPT_UPKEEP_INTERVAL_MS, 30000L);
+
+    curl_easy_perform(curl);
+
+    /* Perform more work here. */
+
+    /* While the connection is being held open, curl_easy_upkeep() can be
+       called. If curl_easy_upkeep() is called and the time since the last
+       upkeep exceeds the interval, then an HTTP/2 PING is sent. */
+    curl_easy_upkeep(curl);
+
+    /* Perform more work here. */
+
+    /* always cleanup */
+    curl_easy_cleanup(curl);
+  }
+}
+~~~
+
+# %AVAILABILITY%
+
+# RETURN VALUE
+
+This function returns a CURLcode indicating success or error.
+
+CURLE_OK (0) means everything was OK, non-zero means an error occurred, see
+libcurl-errors(3). If CURLOPT_ERRORBUFFER(3) was set with curl_easy_setopt(3)
+there can be an error message stored in the error buffer when non-zero is
+returned.