The document discusses protocol handlers in Gecko. It explains that protocol handlers allow Gecko to interact with different URI schemes like http, ftp, file etc. It provides an overview of how the awesome bar, browser UI, DocShell and Necko components work together to handle protocol requests from inputting a URL in the awesome bar to creating a channel and loading content. It also briefly introduces channels and stream listeners in Necko which are used for asynchronous loading of content.

1. PROTOCOL HANDLER
in Gecko
Tommy Kuo [:KuoE0]
kuoe0@mozilla.com
2015.03.03 @Mozilla Taiwan

2. Outline
• What Protocol Handlers Can Do
• The Walkthrough from Awesome Bar to Protocol
Handlers
• The Brief Introduction to Channels

3. What Protocol Handlers
Can Do

4. URI Syntax
<scheme name> : <hierarchical part> [ ? <query> ] [ # <fragment> ]
http : //google.com/search ? q=Mozilla
https : //www.facebook.com/pages/郝神好神/871866229523862
file : ///Downloads/郝神好帥.jpg
about : config
mailto : kuoe0@mozilla.com
chrome : //browser/skin/Info.png
line : //shop/detail/xxx

5. Protocol Handler
Format the URI Create the channel Get flags
NewChannel2(…)
NewProxiedChannel2(…)
NewURI(…) GetProtocolFlags(…)

6. nsresult
nsIOService::NewURI(const nsACString &aSpec, const char *aCharset, nsIURI *aBaseURI,
nsIURI **result)
{
NS_ASSERTION(NS_IsMainThread(), "wrong thread");
static uint32_t recursionCount = 0;
if (recursionCount >= MAX_RECURSION_COUNT)
return NS_ERROR_MALFORMED_URI;
AutoIncrement inc(&recursionCount);
nsAutoCString scheme;
nsresult rv = ExtractScheme(aSpec, scheme);
if (NS_FAILED(rv)) {
// then aSpec is relative
if (!aBaseURI)
return NS_ERROR_MALFORMED_URI;
rv = aBaseURI->GetScheme(scheme);
if (NS_FAILED(rv)) return rv;
}
// now get the handler for this scheme
nsCOMPtr<nsIProtocolHandler> handler;
rv = GetProtocolHandler(scheme.get(), getter_AddRefs(handler));
if (NS_FAILED(rv)) return rv;
return handler->NewURI(aSpec, aCharset, aBaseURI, result);
}
nsIOService::NewURI
(netwerk/base/nsIOService.cpp)

7. nsCOMPtr<nsIProtocolHandler> handler;
rv = GetProtocolHandler(scheme.get(), getter_AddRefs(handler));
if (NS_FAILED(rv))
return rv;
uint32_t protoFlags;
rv = handler->GetProtocolFlags(&protoFlags);
if (NS_FAILED(rv))
return rv;
bool newChannel2Succeeded = true;
nsCOMPtr<nsIProxiedProtocolHandler> pph = do_QueryInterface(handler);
if (pph) {
rv = pph->NewProxiedChannel2(aURI, nullptr, aProxyFlags, aProxyURI, aLoadInfo, result);
// if calling NewProxiedChannel2() fails we try to fall back to
// creating a new proxied channel by calling NewProxiedChannel().
if (NS_FAILED(rv)) {
newChannel2Succeeded = false;
rv = pph->NewProxiedChannel(aURI, nullptr, aProxyFlags, aProxyURI, result);
}
}
else {
rv = handler->NewChannel2(aURI, aLoadInfo, result);
// if calling newChannel2() fails we try to fall back to
// creating a new channel by calling NewChannel().
if (NS_FAILED(rv)) {
newChannel2Succeeded = false;
rv = handler->NewChannel(aURI, result);
}
}
nsIOService::NewChannelFromURIWithProxyFlagsInternal
(netwerk/base/nsIOService.cpp)

8. nsCOMPtr<nsIProtocolHandler> handler;
rv = GetProtocolHandler(scheme.get(), getter_AddRefs(handler));
if (NS_FAILED(rv))
return rv;
uint32_t protoFlags;
rv = handler->GetProtocolFlags(&protoFlags);
if (NS_FAILED(rv))
return rv;
bool newChannel2Succeeded = true;
nsCOMPtr<nsIProxiedProtocolHandler> pph = do_QueryInterface(handler);
if (pph) {
rv = pph->NewProxiedChannel2(aURI, nullptr, aProxyFlags, aProxyURI, aLoadInfo, result);
// if calling NewProxiedChannel2() fails we try to fall back to
// creating a new proxied channel by calling NewProxiedChannel().
if (NS_FAILED(rv)) {
newChannel2Succeeded = false;
rv = pph->NewProxiedChannel(aURI, nullptr, aProxyFlags, aProxyURI, result);
}
}
else {
rv = handler->NewChannel2(aURI, aLoadInfo, result);
// if calling newChannel2() fails we try to fall back to
// creating a new channel by calling NewChannel().
if (NS_FAILED(rv)) {
newChannel2Succeeded = false;
rv = handler->NewChannel(aURI, result);
}
}
nsIOService::NewChannelFromURIWithProxyFlagsInternal
(netwerk/base/nsIOService.cpp)

9. Create An Protocol Handler
• Implementation
• NewURI
• NewChannel2 / NewChannel (not recommended)
• GetProtocolFlags
• Registration
• See 謀智菜逼⼋八談 XPCOM 實務⼊入⾨門

10. ./extensions/gnomevfs/nsGnomeVFSProtocolHandler.cpp: { NS_NETWORK_PROTOCOL_CONTRACTID_PREFIX MOZ_GNOMEVFS_SCHEME,
&kNS_GNOMEVFSPROTOCOLHANDLER_CID },
./extensions/gio/nsGIOProtocolHandler.cpp: { NS_NETWORK_PROTOCOL_CONTRACTID_PREFIX MOZ_GIO_SCHEME,
&kNS_GIOPROTOCOLHANDLER_CID },
./netwerk/build/nsNetModule.cpp: { NS_NETWORK_PROTOCOL_CONTRACTID_PREFIX "file", &kNS_FILEPROTOCOLHANDLER_CID },
./netwerk/build/nsNetModule.cpp: { NS_NETWORK_PROTOCOL_CONTRACTID_PREFIX "http", &kNS_HTTPPROTOCOLHANDLER_CID },
./netwerk/build/nsNetModule.cpp: { NS_NETWORK_PROTOCOL_CONTRACTID_PREFIX "https", &kNS_HTTPSPROTOCOLHANDLER_CID },
./netwerk/build/nsNetModule.cpp: { NS_NETWORK_PROTOCOL_CONTRACTID_PREFIX "ftp", &kNS_FTPPROTOCOLHANDLER_CID },
./netwerk/build/nsNetModule.cpp: { NS_NETWORK_PROTOCOL_CONTRACTID_PREFIX "resource", &kNS_RESPROTOCOLHANDLER_CID },
./netwerk/build/nsNetModule.cpp: { NS_NETWORK_PROTOCOL_CONTRACTID_PREFIX "about", &kNS_ABOUTPROTOCOLHANDLER_CID },
./netwerk/build/nsNetModule.cpp: { NS_NETWORK_PROTOCOL_CONTRACTID_PREFIX "moz-safe-about",
&kNS_SAFEABOUTPROTOCOLHANDLER_CID },
./netwerk/build/nsNetModule.cpp: { NS_NETWORK_PROTOCOL_CONTRACTID_PREFIX "app", &kNS_APPPROTOCOLHANDLER_CID },
./netwerk/build/nsNetModule.cpp: { NS_NETWORK_PROTOCOL_CONTRACTID_PREFIX "data", &kNS_DATAPROTOCOLHANDLER_CID },
./netwerk/build/nsNetModule.cpp: { NS_NETWORK_PROTOCOL_CONTRACTID_PREFIX "moz-device",
&kNS_DEVICEPROTOCOLHANDLER_CID },
./netwerk/build/nsNetModule.cpp: { NS_NETWORK_PROTOCOL_CONTRACTID_PREFIX "view-source",
&kNS_VIEWSOURCEHANDLER_CID },
./netwerk/build/nsNetModule.cpp: { NS_NETWORK_PROTOCOL_CONTRACTID_PREFIX "wyciwyg",
&kNS_WYCIWYGPROTOCOLHANDLER_CID },
./netwerk/build/nsNetModule.cpp: { NS_NETWORK_PROTOCOL_CONTRACTID_PREFIX "ws", &kNS_WEBSOCKETPROTOCOLHANDLER_CID },
./netwerk/build/nsNetModule.cpp: { NS_NETWORK_PROTOCOL_CONTRACTID_PREFIX "wss", &kNS_WEBSOCKETSSLPROTOCOLHANDLER_CID
},
./netwerk/build/nsNetModule.cpp: { NS_NETWORK_PROTOCOL_CONTRACTID_PREFIX "rtsp", &kNS_RTSPPROTOCOLHANDLER_CID },
./image/decoders/icon/nsIconModule.cpp: { NS_NETWORK_PROTOCOL_CONTRACTID_PREFIX "moz-icon", &kNS_ICONPROTOCOL_CID },
./xpcom/build/XPCOMInit.cpp: { NS_NETWORK_PROTOCOL_CONTRACTID_PREFIX "chrome", &kNS_CHROMEPROTOCOLHANDLER_CID },
./toolkit/components/places/nsPlacesModule.cpp: { NS_NETWORK_PROTOCOL_CONTRACTID_PREFIX "moz-anno",
&kNS_ANNOPROTOCOLHANDLER_CID },
./widget/android/nsWidgetFactory.cpp: { NS_NETWORK_PROTOCOL_CONTRACTID_PREFIX "android",
&kNS_ANDROIDPROTOCOLHANDLER_CID },
./layout/build/nsLayoutModule.cpp: { NS_NETWORK_PROTOCOL_CONTRACTID_PREFIX BLOBURI_SCHEME,
&kNS_BLOBPROTOCOLHANDLER_CID },
./layout/build/nsLayoutModule.cpp: { NS_NETWORK_PROTOCOL_CONTRACTID_PREFIX MEDIASTREAMURI_SCHEME,
&kNS_MEDIASTREAMPROTOCOLHANDLER_CID },
./layout/build/nsLayoutModule.cpp: { NS_NETWORK_PROTOCOL_CONTRACTID_PREFIX MEDIASOURCEURI_SCHEME,
&kNS_MEDIASOURCEPROTOCOLHANDLER_CID },
./layout/build/nsLayoutModule.cpp: { NS_NETWORK_PROTOCOL_CONTRACTID_PREFIX FONTTABLEURI_SCHEME,
&kNS_FONTTABLEPROTOCOLHANDLER_CID },
./modules/libjar/nsJARFactory.cpp: { NS_NETWORK_PROTOCOL_CONTRACTID_PREFIX "jar", &kNS_JARPROTOCOLHANDLER_CID },
$ grep -ir -E "{ NS_NETWORK_PROTOCOL_CONTRACTID_PREFIX [^,]+,[^}]+ }" .

11. Awesome Bar to
Protocol Handlers

13. http://google.com/

14. http://google.com/
How to interact to HTTP protocol?

15. handleCommand
openUILinkIn
openLinkIn
loadURIWithFlags (tabbrowser)
loadURIWithFlags (browser)
LoadURI(char16_t*, …)
LoadURIWithBase
LoadURI(nsIURI*, …)
InternalLoad
DoURILoad
DoChannelLoad
NS_NewURI
NS_NewChannelInternal
Browser UI
(XUL)
DocShell Necko
GetProtocolHandler
GetProtocolHandler
nsIURI
nsIChannel
NewURI
NewChannel2

16. Browser UI

17. <textbox id=“urlbar"></text>
browser/base/content/browser.xul
<tabbrowser />

18. <textbox id="urlbar" flex="1"
placeholder="&urlbar.placeholder2;"
type="autocomplete"
autocompletesearch="urlinline history"
autocompletesearchparam="enable-actions"
autocompletepopup="PopupAutoCompleteRichResult"
completeselectedindex="true"
tabscrolling="true"
showcommentcolumn="true"
showimagecolumn="true"
enablehistory="true"
maxrows="6"
newlines="stripsurroundingwhitespace"
ontextentered="this.handleCommand(param);"
ontextreverted="return this.handleRevert();"
pageproxystate="invalid"
onfocus="document.getElementById('identity-
box').style.MozUserFocus= 'normal'"
onblur="setTimeout(() =>
{ document.getElementById('identity-box').style.MozUserFocus = ''; }, 0);”>
. . . . . .
</textbox>
browser/base/content/urlbarBindings.xml

19. handleCommand
1.Canonize URI
2.Detect target in the current tab or a new tab
3.Call openUILinkIn
browser/base/content/urlbarBindings.xml
google mozilla https://www.google.com.tw/search?q=mozilla search engine
tv http://tv.atmovies.com.tw/tv/attv.cfm?action=todaytime bookmark keyword
google http://www.google.com
hotkey
(Ctrl/Cmd+Enter)
google http://www.google.net
hotkey
(Shift+Enter)

20. openUILinkIn
1. Set parameters
• third-party fix-up permission
• post data
• referrer URI
2. Call openLinkIn
browser/base/content/utilityOverlay.js

21. openLinkIn
1. Set target to open URI
• current tab
• new tab
• new window
2. Call loadURIWithFlags (tabbrowser)
browser/base/content/utilityOverlay.js

22. loadURIWithFlags (tabbrowser)
1. Call loadURIWithFlags of its member browser
object
browser/base/content/tabbrowser.xml

23. loadURIWithFlags (browser)
1. Set “about:blank” for empty URI
2. Call loadURI
• Call nsDocShell::LoadURI actually
source/toolkit/content/widgets/browser.xml

24. DocShell

25. LoadURI(char16_t*, …)
1. Call LoadURIWithBase
docshell/base/nsDocShell.cpp

26. LoadURIWithBase
1. Check navigatable or not
2. Call NS_NewURI to create an instance of nsIURI
3. Fix up URI if allowed
4. Call LoadURI
docshell/base/nsDocShell.cpp
ttp → http
ps → https
le → file

27. LoadURI(nsIURI*, …)
1. Check navigatable or not
2. Redirect if needed
3. Call LoadHistoryEntry to load from history if
shEntry exists
4. Call InternalLoad
docshell/base/nsDocShell.cpp
session history

28. InternalLoad
1. Get content policy
2. Decide to load or not according to the content policy
3. Do shortcut loading if only hash tags are different
4. Call DoURILoad
docshell/base/nsDocShell.cpp

29. DoURILoad
1. URI is not a source document
• Call NS_NewChannelInternal to create channel
2. URI is a source document
• Get “view-source” channel if protocol is “view-source”
• Call NS_NewInputStreamChannelInternal to create
channel for “text/html”
3. Setup some data for specific protocols
4. Call DoChannelLoad to load channel
docshell/base/nsDocShell.cpp

30. Necko

31. NS_NewURI NS_NewChannelInternal (7 parameter)
nsIOService::NewURI
GetProtocolHandler
NS_NewChannelInternal (11 parameter)
NewChannelFromURI2
NewChannelFromURIWithProxyFlagsInternal
GetProtocolHandler
DoURILoadLoadURIWithBase
Call Stack

32. GetProtocolHandler
1.Return protocol handler if the protocol handler was
cached
2.For internal protocol
• Cache the protocol handler and return
3.For external protocol
• Get default external protocol handler for external
protocol
netwerk/base/nsIOService.cpp
Protocols are not provided in gecko.

34. The Brief Introduction to
Channels

35. Channel (nsIChannel)
AsyncOpen() (Non-blocking IO)
Asynchronously open this channel. Data is fed to the
specified stream listener as it becomes available.
Open() (Blocking IO)
Synchronously open the channel.

36. Listener (nsIStreamListener)
OnStartRequest()
Called to signify the beginning of an asynchronous request.
OnStopRequest()
Called to signify the end of an asynchronous request.
OnDataAvailable()
Called when the next chunk of data may be read without
blocking the calling thread.

37. nsDocShell::DoChannelLoad
nsURILoader::OpenURI nsDocumentOpenInfo
nsIChannel::AsyncOpen
nsIChannel
create
call
call
nsIAsyncInputStream
create
nsInputStreamPump::AsyncRead
call

38. nsDocShell
nsIChannel
nsIAsyncStream
listen by nsDocmentOpenInfo
listen by self (nsIChannel)

39. nsDocShell nsIChannel nsIAsyncStream
OnStartRequest
OnDataAvailable
OnStopRequest
OnStartRequest
OnDataAvailable
OnStopRequest
Read

40. Thank you!