chore: Remove 'cgi' import from Python (#7479)

The cgi modue disappears in the next version of Python.  This PR adds an import of urllib.parse, but that's not a new dependency since cgi already imported it.

Author: Neil Fraser

appengine/storage.py

@@ -15,15 +15,15 @@
 limitations under the License.
 """
 
-"""Store and retrieve XML with App Engine.
+"""Store and retrieve Blockly XML/JSON with App Engine.
 """
 
 __author__ = "q.neutron@gmail.com (Quynh Neutron)"
 
-import cgi
 import hashlib
-from random import randint
 from google.cloud import ndb
+from random import randint
+from urllib.parse import unquote
 
 
 class Xml(ndb.Model):
@@ -32,6 +32,7 @@ class Xml(ndb.Model):
   xml_content = ndb.TextProperty()
   last_accessed = ndb.DateTimeProperty(auto_now=True)
 
+
 def keyGen():
   # Generate a random string of length KEY_LEN.
   KEY_LEN = 6
@@ -40,8 +41,23 @@ def keyGen():
   return "".join([CHARS[randint(0, max_index)] for x in range(KEY_LEN)])
 
 
+# Parse POST data (e.g. a=1&b=2) into a dictionary (e.g. {"a": 1, "b": 2}).
+# Very minimal parser.  Does not combine repeated names (a=1&a=2), ignores
+# valueless names (a&b), does not support isindex or multipart/form-data.
+def parse_post(environ):
+  fp = environ["wsgi.input"]
+  data = fp.read().decode()
+  parts = data.split("&")
+  dict = {}
+  for part in parts:
+    tuple = part.split("=", 1)
+    if len(tuple) == 2:
+      dict[tuple[0]] = unquote(tuple[1])
+  return dict
+
+
 def xmlToKey(xml_content):
-  # Store XML and return a generated key.
+  # Store XML/JSON and return a generated key.
   xml_hash = int(hashlib.sha1(xml_content.encode("utf-8")).hexdigest(), 16)
   xml_hash = int(xml_hash % (2 ** 64) - (2 ** 63))
   client = ndb.Client()
@@ -65,7 +81,7 @@ def xmlToKey(xml_content):
 
 
 def keyToXml(key_provided):
-  # Retrieve stored XML based on the provided key.
+  # Retrieve stored XML/JSON based on the provided key.
   # Normalize the string.
   key_provided = key_provided.lower().strip()
   # Check datastore for a match.
@@ -91,13 +107,17 @@ def app(environ, start_response):
   ]
   if environ["REQUEST_METHOD"] != "POST":
     start_response("405 Method Not Allowed", headers)
-    return ["Storage only accepts POST".encode('utf-8')]
+    return ["Storage only accepts POST".encode("utf-8")]
+  if ("CONTENT_TYPE" in environ and
+      environ["CONTENT_TYPE"] != "application/x-www-form-urlencoded"):
+    start_response("405 Method Not Allowed", headers)
+    return ["Storage only accepts application/x-www-form-urlencoded".encode("utf-8")]
 
-  forms = cgi.FieldStorage(fp=environ["wsgi.input"], environ=environ)
+  forms = parse_post(environ)
   if "xml" in forms:
-    out = xmlToKey(forms["xml"].value)
+    out = xmlToKey(forms["xml"])
   elif "key" in forms:
-    out = keyToXml(forms["key"].value)
+    out = keyToXml(forms["key"])
   else:
     out = ""