[feat]: Add support to external downloader aria2p (#31500)

* feat: add class Aria2pFD

* feat: create call_downloader function

* feat: a colorful download interface to aria2pFD

* feat: change value name

* Apply suggestions from code review

Co-authored-by: dirkf <fieldhouse@gmx.net>

* Typo in suggestion

* fix: remove unused value

* fix: add not function to return value(0 is normal); add total_seconds to download.eta(timedelta object); add waiting status when hook progress

* fix: remove unuse method ..utils.format_bytes

* fix: be up to flake8

* fix: be up to flake8

* Apply suggestions from code review

* [feat] test external downloader aria2p

* [feat] test external downloader aria2p

* [fix] test_external_downloader.py

* Apply suggestions from code review

Co-authored-by: dirkf <fieldhouse@gmx.net>

* Apply suggestions from code review

Co-authored-by: dirkf <fieldhouse@gmx.net>

* Update test/test_external_downloader.py

Co-authored-by: dirkf <fieldhouse@gmx.net>

* Update test/test_external_downloader.py

Co-authored-by: dirkf <fieldhouse@gmx.net>

* Update youtube_dl/downloader/external.py

Co-authored-by: dirkf <fieldhouse@gmx.net>

* refactoring code and fix bugs

* Apply suggestions from code review

* Rename test_external_downloader.py to test_downloader_external.py

---------

Co-authored-by: dirkf <fieldhouse@gmx.net>

test/test_downloader_external.py

@@ -0,0 +1,115 @@
+#!/usr/bin/env python
+# coding: utf-8
+from __future__ import unicode_literals
+
+# Allow direct execution
+import os
+import re
+import sys
+import subprocess
+import unittest
+sys.path.insert(0, os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
+
+from test.helper import (
+    FakeLogger,
+    http_server_port,
+    try_rm,
+)
+from youtube_dl import YoutubeDL
+from youtube_dl.compat import compat_http_server
+from youtube_dl.utils import encodeFilename
+from youtube_dl.downloader.external import Aria2pFD
+import threading
+
+TEST_DIR = os.path.dirname(os.path.abspath(__file__))
+
+
+TEST_SIZE = 10 * 1024
+
+
+class HTTPTestRequestHandler(compat_http_server.BaseHTTPRequestHandler):
+    def log_message(self, format, *args):
+        pass
+
+    def send_content_range(self, total=None):
+        range_header = self.headers.get('Range')
+        start = end = None
+        if range_header:
+            mobj = re.match(r'bytes=(\d+)-(\d+)', range_header)
+            if mobj:
+                start, end = (int(mobj.group(i)) for i in (1, 2))
+        valid_range = start is not None and end is not None
+        if valid_range:
+            content_range = 'bytes %d-%d' % (start, end)
+            if total:
+                content_range += '/%d' % total
+            self.send_header('Content-Range', content_range)
+        return (end - start + 1) if valid_range else total
+
+    def serve(self, range=True, content_length=True):
+        self.send_response(200)
+        self.send_header('Content-Type', 'video/mp4')
+        size = TEST_SIZE
+        if range:
+            size = self.send_content_range(TEST_SIZE)
+        if content_length:
+            self.send_header('Content-Length', size)
+        self.end_headers()
+        self.wfile.write(b'#' * size)
+
+    def do_GET(self):
+        if self.path == '/regular':
+            self.serve()
+        elif self.path == '/no-content-length':
+            self.serve(content_length=False)
+        elif self.path == '/no-range':
+            self.serve(range=False)
+        elif self.path == '/no-range-no-content-length':
+            self.serve(range=False, content_length=False)
+        else:
+            assert False, 'unrecognised server path'
+
+
+@unittest.skipUnless(Aria2pFD.available(), 'aria2p module not found')
+class TestAria2pFD(unittest.TestCase):
+    def setUp(self):
+        self.httpd = compat_http_server.HTTPServer(
+            ('127.0.0.1', 0), HTTPTestRequestHandler)
+        self.port = http_server_port(self.httpd)
+        self.server_thread = threading.Thread(target=self.httpd.serve_forever)
+        self.server_thread.daemon = True
+        self.server_thread.start()
+
+    def download(self, params, ep):
+        with subprocess.Popen(
+            ['aria2c', '--enable-rpc'],
+            stdout=subprocess.DEVNULL,
+            stderr=subprocess.DEVNULL
+        ) as process:
+            if not process.poll():
+                filename = 'testfile.mp4'
+                params['logger'] = FakeLogger()
+                params['outtmpl'] = filename
+                ydl = YoutubeDL(params)
+                try_rm(encodeFilename(filename))
+                self.assertEqual(ydl.download(['http://127.0.0.1:%d/%s' % (self.port, ep)]), 0)
+                self.assertEqual(os.path.getsize(encodeFilename(filename)), TEST_SIZE)
+                try_rm(encodeFilename(filename))
+            process.kill()
+
+    def download_all(self, params):
+        for ep in ('regular', 'no-content-length', 'no-range', 'no-range-no-content-length'):
+            self.download(params, ep)
+
+    def test_regular(self):
+        self.download_all({'external_downloader': 'aria2p'})
+
+    def test_chunked(self):
+        self.download_all({
+            'external_downloader': 'aria2p',
+            'http_chunk_size': 1000,
+        })
+
+
+if __name__ == '__main__':
+    unittest.main()