[tor-bugs] #29347 [Obfuscation/meek]: Rewrite meek-http-helper as a WebExtension

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#29347: Rewrite meek-http-helper as a WebExtension
------------------------------+------------------------------
 Reporter:  dcf               |          Owner:  dcf
     Type:  enhancement       |         Status:  needs_review
 Priority:  Medium            |      Milestone:
Component:  Obfuscation/meek  |        Version:
 Severity:  Normal            |     Resolution:
 Keywords:  webextension      |  Actual Points:
Parent ID:                    |         Points:
 Reviewer:                    |        Sponsor:
------------------------------+------------------------------
Changes (by dcf):

 * status:  assigned => needs_review


Comment:

 I worked on integrating the WebExtension into Tor Browser. It's working
 now and ready to be looked at.
  * [https://gitweb.torproject.org/pluggable-
 transports/meek.git/log/?h=webextension&id=de03366fbe1f23cbb21d41aec8f4913f189ecb8b
 meek]
  * [https://gitweb.torproject.org/user/dcf/tor-browser-build.git/commit/?h
 =meek-webextension&id=45192a1adcb29e6200f2b9e46d97bbdbbfb0a509 tor-
 browser-build]
 I tested it on linux-x86_64 and windows-x86_64, but I'm not set up to test
 on osx.

 Recall that the native messaging API requires us to install a JSON "host
 manifest" for the native executable--this both authorizes the extension to
 run a native executable, and tells the browser the (absolute) path to the
 native executable. The absolute path inside the manifest means we cannot
 just use a static file; we need to know where the browser is installed. So
 now, meek-client-torbrowser [https://gitweb.torproject.org/pluggable-
 transports/meek.git/commit/?h=webextension&id=5b539a2c5f2a8474cee3dc2c2312ad365bdb1cca
 writes a host manifest] (taking into account platform-specific paths)
 before starting the browser.

 Two things I'd specifically like feedback on:
  * I'm not able to test the osx version, which is slightly tricky because
 the data directory can be in different places depending on
 `TOR_BROWSER_TOR_DATA_DIR` (#18904). [https://gitweb.torproject.org
 /pluggable-transports/meek.git/diff/meek-client-
 torbrowser/mac.go?h=webextension&id=5b539a2c5f2a8474cee3dc2c2312ad365bdb1cca
 This is what I'm doing], but I'm not sure if it works:
      if `TOR_BROWSER_TOR_DATA_DIR` is set:
        install in `$TOR_BROWSER_TOR_DATA_DIR/../Browser`
      else:
        install in `$PWD/../../../../TorBrowser-Data/Browser`
    The documentation [https://developer.mozilla.org/en-US/docs/Mozilla
 /Add-ons/WebExtensions/Native_manifests#Mac_OS_X says] that the host
 manifest should be installed in `$HOME/Library/Application
 Support/Mozilla/NativeMessagingHosts/`, but the code actually does a
 [https://dxr.mozilla.org/mozilla-
 central/rev/c2593a3058afdfeaac5c990e18794ee8257afe99/toolkit/components/extensions/NativeManifests.jsm#44
 Services.dirsvc.get] for [https://dxr.mozilla.org/mozilla-
 central/source/toolkit/xre/nsXREDirProvider.cpp#420
 XRE_USER_NATIVE_MANIFESTS], which calls `GetUserDataDirectoryHome` and
 then into some Tor Browser–overriden code that replaces the home
 directory.
  * As noted in comment:9, on windows we cannot simply write the host
 manifest to a well-known path. You have to set a well-known registry key
 whose value is the path to the manifest. So [https://gitweb.torproject.org
 /pluggable-transports/meek.git/diff/meek-client-
 torbrowser/windows.go?h=webextension&id=5b539a2c5f2a8474cee3dc2c2312ad365bdb1cca
 what the code does now] is write a registry key at
 `HKEY_CURRENT_USER\SOFTWARE\Mozilla\NativeMessagingHosts\meek.http.helper`.
 That works, but I don't like the fact that it leaves a permanent trace
 outside the installation directory. I'd like to know if there are any
 ideas for removing this step.

 The tor-browser-build changes are minimal: just packaging the webextension
 directory instead of the firefox directory, building the native
 executable, and adding a dependency on golang.org/x/sys/windows/registry
 to write the registry key on windows.

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/29347#comment:13>
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