Use exceptions for non-200 responses.

This simplifies the code slightly.

mp3wavweb.py

@@ -29,19 +29,43 @@ def os_path_split_asunder(path):
     parts.reverse()
     return parts
 
+class Response(Exception):
+    def __init__(self, code, headers, body=""):
+        self.__code = code
+        self.__headers = headers
+        self.__body = body
+
+    def response(self, start_response):
+        start_response(self.__code, self.__headers)
+        return [self.__body]
+
+class MethodNotAllowed(Response):
+    def __init__(self, allowed):
+        super().__init__("405 Method Not Allowed", [('Allow', allowed)])
+
+class MovedPermanently(Response):
+    def __init__(self, location):
+        super().__init__("301 Moved Permanently", [("Location", location)])
+
+class NotFound(Response):
+    def __init__(self):
+        super().__init__("404 Not Found", [])
+
 def application(environ, start_response):
+    try:
+        return process_request(environ, start_response)
+    except Response as r:
+        return r.response(start_response)
+
+def process_request(environ, start_response):
     if environ["REQUEST_METHOD"] not in ["GET", "POST"]:
-       start_response("405 Method Not Allowed",
-                      [('Allow', 'GET')])
-       return []
+        raise MethodNotAllowed('GET, POST')
 
     path = environ['PATH_INFO']
 
     # We want a trailing slash at the root.
     if path == "" and environ.get("SCRIPT_NAME", "") != "":
-        start_response("301 Moved Permanently",
-                       [("Location", environ["SCRIPT_NAME"] + "/")])
-        return []
+        raise MovedPermanently(environ["SCRIPT_NAME"] + "/")
 
     parts = os_path_split_asunder(path)
     if len(parts) > 0 and parts[0] == "/":
@@ -65,9 +89,7 @@ def application(environ, start_response):
                 return MP3_OPS[ops[0]](environ, start_response,
                                        rel_base, ops[1:])
 
-        start_response("404 Not found", [])
-
-        return []
+        raise NotFound()
 
     if stat.S_ISDIR(status.st_mode):
         return handle_directory(environ, start_response,
@@ -76,13 +98,11 @@ def application(environ, start_response):
         return handle_file(environ, start_response,
                            os.path.join(*parts))
 
-    start_response("404 Not found", [])
-    return []
+    raise NotFound()
 
 def convert(environ, start_response, rel_base, ops):
     if len(ops) > 0:
-        start_response("404 Not found", [])
-        return []
+        raise NotFound()
 
     if environ["REQUEST_METHOD"] == "GET":
         start_response("200 OK",
@@ -93,8 +113,7 @@ def convert(environ, start_response, rel_base, ops):
                 "</form></body></html>"]
 
     if environ["REQUEST_METHOD"] != "POST":
-       start_response("405 Method Not Allowed",
-                      [('Allow', 'GET, POST')])
+        raise MethodNotAllowed('GET, POST')
 
     c = multiprocessing.connection.Client(mp3wavcfg.socketpath, 'AF_UNIX')
     c.send(("encode", rel_base))
@@ -103,10 +122,7 @@ def convert(environ, start_response, rel_base, ops):
         if msg[0] != "progress":
             break
 
-    start_response("301 Moved Permanently",
-                   [("Content-Type", "text/plain"),
-                    ("Location", "..")])
-    return ["File converted to mp3"]
+    raise MovedPermanently("..")
 
 MP3_OPS = {
     'convert': convert,