websocket_helper.py: Add websocket helper functions for handshaking.

Authored by @pfalcon.

Author: dpgeorge

websocket_helper.py

@@ -0,0 +1,75 @@
+import sys
+try:
+    import ubinascii as binascii
+except:
+    import binascii
+try:
+    import uhashlib as hashlib
+except:
+    import hashlib
+
+DEBUG = 0
+
+def server_handshake(sock):
+    clr = sock.makefile("rwb", 0)
+    l = clr.readline()
+    #sys.stdout.write(repr(l))
+
+    webkey = None
+
+    while 1:
+        l = clr.readline()
+        if not l:
+            raise OSError("EOF in headers")
+        if l == b"\r\n":
+            break
+    #    sys.stdout.write(l)
+        h, v = [x.strip() for x in l.split(b":", 1)]
+        if DEBUG:
+            print((h, v))
+        if h == b'Sec-WebSocket-Key':
+            webkey = v
+
+    if not webkey:
+        raise OSError("Not a websocket request")
+
+    if DEBUG:
+        print("Sec-WebSocket-Key:", webkey, len(webkey))
+
+    respkey = webkey + b"258EAFA5-E914-47DA-95CA-C5AB0DC85B11"
+    respkey = hashlib.sha1(respkey).digest()
+    respkey = binascii.b2a_base64(respkey)[:-1]
+
+    resp = b"""\
+HTTP/1.1 101 Switching Protocols\r
+Upgrade: websocket\r
+Connection: Upgrade\r
+Sec-WebSocket-Accept: %s\r
+\r
+""" % respkey
+
+    if DEBUG:
+        print(resp)
+    sock.send(resp)
+
+
+# Very simplified client handshake, works for MicroPython's
+# websocket server implementation, but probably not for other
+# servers.
+def client_handshake(sock):
+    cl = sock.makefile("rwb", 0)
+    cl.write(b"""\
+GET / HTTP/1.1\r
+Host: echo.websocket.org\r
+Connection: Upgrade\r
+Upgrade: websocket\r
+Sec-WebSocket-Key: foo\r
+\r
+""")
+    l = cl.readline()
+#    print(l)
+    while 1:
+        l = cl.readline()
+        if l == b"\r\n":
+            break
+#        sys.stdout.write(l)