urllib.urequest: Add absolutely minimal urlopen() implementation.

Optimized for low-memory bare-metal systems.

urllib.urequest/urllib/urequest.py

@@ -0,0 +1,35 @@
+import usocket
+
+def urlopen(url, data=None):
+    if data:
+        raise NotImplementedError("POST is not yet supported")
+    try:
+        proto, dummy, host, path = url.split("/", 3)
+    except ValueError:
+        proto, dummy, host = url.split("/", 2)
+        path = ""
+    if proto != "http:":
+        raise ValueError("Unsupported protocol: " + proto)
+
+    ai = usocket.getaddrinfo(host, 80)
+    addr = ai[0][4]
+    s = usocket.socket()
+    s.connect(addr)
+    s.send(b"GET /%s HTTP/1.0\r\nHost: %s\r\n\r\n" % (path, host))
+
+    l = s.readline()
+    protover, status, msg = l.split(None, 2)
+    status = int(status)
+    #print(protover, status, msg)
+    while True:
+        l = s.readline()
+        if not l or l == b"\r\n":
+            break
+        #print(line)
+        if l.startswith(b"Transfer-Encoding:"):
+            if b"chunked" in line:
+                raise ValueError("Unsupported " + l)
+        elif l.startswith(b"Location:"):
+            raise NotImplementedError("Redirects not yet supported")
+
+    return s