modules/mime-type-override.js

   1 /**
   2  * (C) Copyright 2008 Jeremy Maitin-Shepard
   3  *
   4  * Portions of this file are derived from the "Open in Browser" extension,
   5  * (C) Copyright 2006 Sylvain Pasche.
   6  *
   7  * Use, modification, and distribution are subject to the terms specified in the
   8  * COPYING file.
   9  **/
  10
  11 /**
  12  * This module was inspired by the "Open in Browser" extension by Sylvain
  13  * Pasche, available at http://www.spasche.net/mozilla/.
  14  *
  15  * This module implements (in a somewhat hacky way) overriding of the
  16  * server-specified mime type for specified URLs. It works by registering an
  17  * observer for the "http-on-examine-response" and
  18  * "http-on-examine-merged-response" topics and changes the response MIME type
  19  * of the nsIHTTPChannel object passed as the subject, as well as clearing any
  20  * "Content-disposition" header.
  21  *
  22  * Unfortunately, due to the design, this hack does not work for FTP.
  23  *
  24  **/
  25
  26 let EXAMINE_TOPIC = "http-on-examine-response";
  27 let EXAMINE_MERGED_TOPIC = "http-on-examine-merged-response";
  28
  29 let table = new string_hashmap();
  30
  31 let timeout = 10000; // 10000 milliseconds = 10 seconds
  32
  33 let table_size = 0;
  34
  35 // uri must be an instance of nsIURI
  36 function can_override_mime_type_for_uri(uri) {
  37     return uri.schemeIs("http") || uri.schemeIs("https");
  38 }
  39
  40 const cache_service = Cc["@mozilla.org/network/cache-service;1"].getService(Ci.nsICacheService);
  41
  42 function clear_http_cache_entry(uri_string) {
  43     var http_cache_session = cache_service.createSession("HTTP", 0, true);
  44     http_cache_session.doomEntriesIfExpired = false;
  45     try {
  46         // Remove the ref component of the URL
  47         var cache_key = uri_string.replace(/#.*$/, "");
  48         var entry = http_cache_session.openCacheEntry(cacheKey, Ci.nsICache.ACCESS_READ, false);
  49         entry.doom();
  50         entry.close();
  51     } catch (e) { }
  52 }
  53
  54 let clear_override = function(uri_string) {
  55     table.remove(uri_string);
  56     table_size--;
  57
  58     if (table_size == 0) {
  59         observer_service.removeObserver(observer, EXAMINE_TOPIC);
  60         observer_service.removeObserver(observer, EXAMINE_MERGED_TOPIC);
  61     }
  62 }
  63
  64 let observer = {
  65     observe: function (subject, topic, data) {
  66         if (topic != EXAMINE_TOPIC && topic != EXAMINE_MERGED_TOPIC)
  67             return;
  68
  69         subject.QueryInterface(Ci.nsIHttpChannel);
  70
  71         var uri_string = subject.originalURI.spec;
  72         var obj = table.get(uri_string);
  73         if (!obj)
  74             return;
  75
  76         obj.timer.cancel();
  77
  78         subject.contentType = obj.mime_type;
  79
  80         // drop content-disposition header
  81         subject.setResponseHeader("Content-Disposition", "", false);
  82
  83         clear_override(uri_string);
  84     }
  85 };
  86
  87
  88
  89 // uri must be an instance of nsIURI and can_override_mime_type_for_uri must
  90 // return true for the passed uri.
  91
  92 // mime_type must be a string
  93 function override_mime_type_for_next_load(uri, mime_type) {
  94
  95     clear_http_cache_entry(uri.spec);
  96
  97     var obj = table.get(uri.spec);
  98     if (obj)
  99         obj.timer.cancel();
 100     else
 101         table_size++;
 102
 103     obj = { mime_type: mime_type };
 104
 105     obj.timer = call_after_timeout(function () {
 106                                        clear_override(uri.spec);
 107                                    }, timeout);
 108
 109     if (table_size == 1) {
 110         observer_service.addObserver(observer, EXAMINE_TOPIC, false);
 111         observer_service.addObserver(observer, EXAMINE_MERGED_TOPIC, false);
 112     }
 113     table.put(uri.spec, obj);
 114 }