Expose Port 8000 for easy testing

Add ``serve`` module as a command line subcommand which enables us to start a server within the docker environment.
This is helpful in testing the ``pyodide`` builds running within the docker environment using external browser
programs of the same machine.

pyodide_build/__main__.py

@@ -4,6 +4,7 @@ import argparse
 from . import buildall
 from . import buildpkg
 from . import pywasmcross
+from . import serve
 
 
 def main():
@@ -12,7 +13,8 @@ def main():
 
     for command_name, module in (("buildpkg", buildpkg),
                                  ("buildall", buildall),
-                                 ("pywasmcross", pywasmcross)):
+                                 ("pywasmcross", pywasmcross),
+                                 ("serve", serve)):
         parser = module.make_parser(subparsers.add_parser(command_name))
         parser.set_defaults(func=module.main)
 

pyodide_build/serve.py

+import os
+import sys
+import argparse
+import http.server
+import socketserver
+import pathlib
+
+TEST_PATH = pathlib.Path(__file__).parents[0].resolve()
+BUILD_PATH = TEST_PATH / '..' / 'build'
+
+class Handler(http.server.SimpleHTTPRequestHandler):
+    def end_headers(self):
+        self.send_header('Access-Control-Allow-Origin', '*')
+        super().end_headers()
+
+Handler.extensions_map['.wasm'] = 'application/wasm'
+
+def make_parser(parser):
+    parser.description = ('Start a server with the supplied build_dir and port.')
+    parser.add_argument('--build_dir', action='store', type=str, default=BUILD_PATH, help='set the build directory')
+    parser.add_argument('--port', action='store', type=int, default=8000, help='set the PORT number')
+    return parser
+
+def server(port):
+    httpd = socketserver.TCPServer(('', port), Handler)
+    return httpd
+
+def main(args):
+    build_dir = args.build_dir
+    port = args.port
+    httpd = server(port)
+    try:
+        os.chdir(build_dir)
+        print("serving from {0} at localhost:".format(build_dir) + str(port))
+        httpd.serve_forever()
+    except KeyboardInterrupt:
+        print("\n...shutting down http server")
+        httpd.shutdown()
+        sys.exit()
+
+if __name__ == "__main__":
+    parser = make_parser(argparse.ArgumentParser())
+    args = parser.parse_args()
+    main(args)
\ No newline at end of file

run_docker

 #!/bin/sh
-docker run --rm -v $PWD:/src --user root -e NB_UID=$UID -e NB_GID=$GID -it iodide/pyodide-env:0.3.1 /bin/bash
+docker run -p 8000:8000 --rm -v $PWD:/src --user root -e NB_UID=$UID -e NB_GID=$GID -it iodide/pyodide-env:0.3.1 /bin/bash