Deduplicate setting Accept-Language HTTP header.

This adds a new function conf.defaultHttpHeaders that can be used by plugins
to get all the default HTTP headers for a given network/channel.

plugins/Web/plugin.py

@@ -149,14 +149,7 @@ class Web(callbacks.PluginRegexp):
     def getTitle(self, irc, url, raiseErrors, msg):
         size = conf.supybot.protocols.http.peekSize()
         timeout = self.registryValue('timeout')
-        headers = dict(utils.web.defaultHeaders)
-        language = conf.supybot.protocols.http.requestLanguage.getSpecific(
-                irc.network, msg.channel)()
-        lkey = 'Accept-Language'
-        if language:
-            headers[lkey] = language
-        elif lkey in headers:
-            del headers[lkey]
+        headers = conf.defaultHttpHeaders(irc.network, msg.channel)
         try:
             (target, text) = utils.web.getUrlTargetAndContent(url, size=size,
                 timeout=timeout, headers=headers)

src/conf.py

@@ -1299,16 +1299,26 @@ registerGlobalValue(supybot.protocols.http, 'proxy',
     through.  The value should be of the form 'host:port'.""")))
 utils.web.proxy = supybot.protocols.http.proxy
 
+def defaultHttpHeaders(network, channel):
+    """Returns the default HTTP headers to use for this channel/network."""
+    headers = utils.web.baseDefaultHeaders.copy()
+    try:
+        language = supybot.protocols.http.requestLanguage.getSpecific(
+                network, channel)()
+    except registry.NonExistentRegistryEntry:
+        pass # Starting up; language will be set by HttpRequestLanguage later
+    else:
+        if language:
+            headers['Accept-Language'] = language
+        elif 'Accept-Language' in headers:
+            del headers['Accept-Language']
+    return headers
+
 class HttpRequestLanguage(registry.String):
     """Must be a valid HTTP Accept-Language value."""
     __slots__ = ()
     def setValue(self, v):
-        headers = utils.web.defaultHeaders
-        lkey = 'Accept-Language'
-        if v:
-            headers[lkey] = v
-        elif lkey in headers:
-            del headers[lkey]
+        utils.web.defaultHeaders = defaultHttpHeaders(None, None)
         super(HttpRequestLanguage, self).setValue(v)
 
 registerChannelValue(supybot.protocols.http, 'requestLanguage',

src/utils/web.py

@@ -115,10 +115,14 @@ def strError(e):
     else:
         return str(e)
 
-defaultHeaders = {
+# Used to build defaultHeaders
+baseDefaultHeaders = {
     'User-agent': 'Mozilla/5.0 (compatible; utils.web python module)'
     }
 
+# overridable by other modules/plugins.
+defaultHeaders = baseDefaultHeaders.copy()
+
 # Other modules should feel free to replace this with an appropriate
 # application-specific function.  Feel free to use a callable here.
 proxy = None