Support HTTP-Keep-Alive in our XMLHttpRequest implementation

python/pythonmonkey/builtin_modules/XMLHttpRequest-internal.py

@@ -12,6 +12,8 @@
 import pythonmonkey as pm
 from typing import Union, ByteString, Callable, TypedDict
 
+keepAliveConnector: Union[aiohttp.TCPConnector, None] = None
+
 
 class XHRResponse(TypedDict, total=True):
   """
@@ -46,6 +48,12 @@ async def request(
 ):
   debug = pm.bootstrap.require("debug")
 
+  # to support HTTP-Keep-Alive
+  global keepAliveConnector
+  if (not keepAliveConnector):
+    # seconds before closing Keep-Alive connection.
+    keepAliveConnector = aiohttp.TCPConnector(keepalive_timeout=5)  # 5s is the default for Node.js's `http.globalAgent`
+
   class BytesPayloadWithProgress(aiohttp.BytesPayload):
     _chunkMaxLength = 2**16  # aiohttp default
 
@@ -80,6 +88,7 @@ async def write(self, writer) -> None:
                                headers=headers,
                                data=BytesPayloadWithProgress(body) if body else None,
                                timeout=timeoutOptions,
+                               connector=keepAliveConnector,
                                ) as res:
       debug('xhr:aiohttp')('got', res.content_type, 'result')
 

python/pythonmonkey/builtin_modules/XMLHttpRequest.js

@@ -49,14 +49,15 @@ class ProgressEvent extends Event
 {
   /**
    * @param {string} type
-   * @param {{ lengthComputable?: boolean; loaded?: number; total?: number; }} eventInitDict
+   * @param {{ lengthComputable?: boolean; loaded?: number; total?: number; error?: Error;  }} eventInitDict
    */
   constructor (type, eventInitDict = {})
   {
     super(type);
     this.lengthComputable = eventInitDict.lengthComputable ?? false;
     this.loaded = eventInitDict.loaded ?? 0;
     this.total = eventInitDict.total ?? 0;
+    this.error = eventInitDict.error ?? null;
     this.debugTag = 'xhr:';
   }
 }
@@ -446,12 +447,12 @@ class XMLHttpRequest extends XMLHttpRequestEventTarget
       this.#uploadCompleteFlag = true;
       if (this.#uploadListenerFlag)
       {
-        this.#uploadObject.dispatchEvent(new ProgressEvent(event, { loaded:0, total:0 }));
+        this.#uploadObject.dispatchEvent(new ProgressEvent(event, { loaded:0, total:0, error: exception }));
         this.#uploadObject.dispatchEvent(new ProgressEvent('loadend', { loaded:0, total:0 }));
       }
     }
 
-    this.dispatchEvent(new ProgressEvent(event, { loaded:0, total:0 })); // step 7
+    this.dispatchEvent(new ProgressEvent(event, { loaded:0, total:0, error: exception })); // step 7
     this.dispatchEvent(new ProgressEvent('loadend', { loaded:0, total:0 })); // step 8
   }
 

tests/js/xhr-http-keep-alive.bash

@@ -0,0 +1,72 @@
+#! /bin/bash
+#
+# @file        xhr-http-keep-alive.bash
+#              For testing HTTP-Keep-Alive automatically in the CI.
+#
+#              We use `strace` to track system calls within the process that open a TCP connection.
+#              If HTTP-Keep-Alive is working, the total number of TCP connections opened should be 1 for a single remote host.
+#
+# @author      Tom Tang (xmader@distributive.network)
+# @date        May 2024
+
+set -u
+set -o pipefail
+
+panic()
+{
+  echo "FAIL: $*" >&2
+  exit 2
+}
+
+cd `dirname "$0"` || panic "could not change to test directory"
+
+if [[ "$OSTYPE" != "linux-gnu"* ]]; then
+  exit 0
+  # Skip non-Linux for this test
+  # TODO: add tests on Windows and macOS. What's the equivalence of `strace`?
+fi
+
+code='
+function newRequest(url) {
+  return new Promise(function (resolve, reject) 
+  {
+    let xhr = new XMLHttpRequest();
+    xhr.open("GET", url);
+    xhr.onload = function () 
+    {
+      if (this.status >= 200 && this.status < 300) resolve(this.response);
+      else reject(new Error(this.status));
+    };
+    xhr.onerror = (ev) => reject(ev.error);
+    xhr.send();
+  });
+}
+
+async function main() {
+  await newRequest("http://www.example.org/");
+  await newRequest("http://www.example.org/");
+  await newRequest("http://http.badssl.com/");
+}
+
+main();
+'
+
+# Trace the `socket` system call https://man.archlinux.org/man/socket.2
+# AF_INET: IPv4, IPPROTO_TCP: TCP connection
+TRACE=$(strace -f -e socket \
+        "${PMJS:-pmjs}" -e "$code" \
+        < /dev/null 2>&1
+)
+
+# We have 3 HTTP requests, but we should only have 2 TCP connections open,
+# as HTTP-Keep-Alive reuses the socket for a single remote host.
+echo "$TRACE" \
+| tr -d '\r' \
+| grep -c -E 'socket\(AF_INET, \w*(\|\w*)+, IPPROTO_TCP\)' \
+| while read qty
+  do
+    echo "$TRACE"
+    echo "TCP connections opened: $qty"
+    [ "$qty" != "2" ] && panic qty should not be $qty
+    break
+  done || exit $?

tests/js/xhr.simple

@@ -69,19 +69,16 @@ new Promise(function (resolve, reject)
     }
     else 
     {
-      reject(new Error({
+      reject(new Error(JSON.stringify({
         status: this.status,
-        statusText:  this.statusText
-      }));
+        statusText: this.statusText
+      })));
     }
   };
 
-  xhr.onerror = function () 
+  xhr.onerror = function (ev) 
   {
-    reject(new Error({
-      status: this.status,
-      statusText: this.statusText
-    }));
+    reject(ev.error);
   };
 
   xhr.send();
@@ -112,19 +109,16 @@ new Promise(function (resolve, reject)
     }
     else 
     {
-      reject(new Error({
+      reject(new Error(JSON.stringify({
         status: this.status,
-        statusText:  this.statusText
-      }));
+        statusText: this.statusText
+      })));
     }
   };
 
-  xhr.onerror = function () 
+  xhr.onerror = function (ev) 
   {
-    reject(new Error({
-      status: this.status,
-      statusText: this.statusText
-    }));
+    reject(ev.error);
   };
 
   xhr.send();