WebMonkey

No-frills light-weight Android web browser with support for Greasemonkey userscripts.

Builds upon the WebView GM library demo application.

Background

• the WebView GM library enhances the native Android System WebView
  • with userscript management:
    • detecting and downloading *.user.js URLs
    • parsing and saving to a DB
    • automatic updates
  • with userscript injection:
    • on top-level HTML pages that match URL patterns
  • with support for Greasemonkey API ( 1, 2, 3 ) functions:
    • GM_addStyle
    • GM_deleteValue
    • GM_getResourceText
    • GM_getResourceURL
    • GM_getValue
    • GM_listValues
    • GM_log
    • GM_setValue
    • GM_xmlhttpRequest

Improvements

• supplements the list of supported Greasemonkey API functions:
  • legacy:
    • GM_addElement
    • GM_cookie.delete
    • GM_cookie.list
    • GM_cookie.set
    • GM_fetch
      • drop-in replacement for window.fetch that uses GM_xmlhttpRequest to make network requests
    • GM_info
    • GM_registerMenuCommand
    • GM_unregisterMenuCommand
  • GM 4:
    • GM.addElement
    • GM.addStyle
    • GM.cookie.delete
    • GM.cookie.list
    • GM.cookie.set
    • GM.cookies.delete
    • GM.cookies.list
    • GM.cookies.set
    • GM.deleteValue
    • GM.fetch
    • GM.getResourceText
    • GM.getResourceUrl
    • GM.getValue
    • GM.info
    • GM.listValues
    • GM.log
    • GM.registerMenuCommand
    • GM.setValue
    • GM.unregisterMenuCommand
    • GM.xmlHttpRequest
• adds an additional Javascript API interface to expose Android-specific capabilities:
  • legacy:
    • GM_exit()
      • causes WebMonkey to close
    • GM_getUrl()
      • returns a String containing the URL that is currently loaded in the WebView
      • use case:
        • allows the userscript to detect whether the page has been redirected
          • server response status codes: 301, 302
      • example:
        • var is_redirect = (GM_getUrl() !== unsafeWindow.location.href)
    • GM_getUserAgent()
      • returns a String containing the User Agent that is currently configured in Settings for use by the WebView
    • GM_loadFrame(urlFrame, urlParent, proxyFrame)
      • loads an iframe into the WebView
      • where:
        • [required] urlFrame is a String URL: the page loaded into the iframe
        • [required] urlParent is a String URL: value for window.top.location.href and window.parent.location.href as observed from within the iframe
        • [optional] proxyFrame is a boolean: a truthy value causes urlFrame to be downloaded in Java
          • urlParent is sent in the Referer header
          • a successful (200-299) response is dynamically loaded into iframe.srcdoc
          • the benefit:
            • same-origin policy does not apply
            • when urlParent and urlFrame belong to different domains, a userscript running in the top window can access the DOM within the iframe window
          • special use case:
            • when urlFrame only serves the desired web page content if urlParent is sent in the Referer header
      • example:
        • ('http://example.com/iframe_window.html', 'http://example.com/parent_window.html')
      • use case:
        • "parent_window.html" contains:
          • an iframe to display "iframe_window.html"
          • other content that is not wanted
        • though a userscript could easily do the necessary housekeeping:
          • detach the iframe
          • remove all other DOM elements from body
          • reattach the iframe
        • this method provides a better solution:
          • removes all scripts that are loaded into the parent window
          • handles all the css needed to resize the iframe to maximize its display within the parent window
          • makes it easy to handle this common case
      • why this is a common case:
        • "iframe_window.html" performs a check to verify that it is loaded in the proper parent window
        • example 1:

            const urlParent = 'http://example.com/parent_window.html'
            try {
              // will throw when either:
              // - `top` is loaded from a different domain
              // - `top` is loaded from the same origin, but the URL path does not match 'parent_window.html'
              if(window.top.location.href !== urlParent)
                throw ''
            }
            catch(e) {
              // will redirect `top` window to the proper parent window
              window.top.location = urlParent
            }

        • example 2:

            const urlParent = 'http://example.com/parent_window.html'
            {
              // will redirect to proper parent window when 'iframe_window.html' is loaded without a `top` window
              if(window === window.top)
                window.location = urlParent
            }

    • GM_loadUrl(url, ...headers)
      • loads a URL into the WebView with additional HTTP request headers
      • where:
        • [required] url is a String URL
        • [optional] headers is a list of String name/value pairs
      • example:
        • ('http://example.com/iframe_window.html', 'Referer', 'http://example.com/parent_window.html')
    • GM_removeAllCookies()
      • completely removes all cookies for all web sites
    • GM_resolveUrl(urlRelative, urlBase)
      • returns a String containing urlRelative resolved relative to urlBase
      • where:
        • [required] urlRelative is a String URL: relative path
        • [optional] urlBase is a String URL: absolute path
          • default value: the URL that is currently loaded in the WebView
      • examples:
        • ('video.mp4', 'http://example.com/iframe_window.html')
        • ('video.mp4')
    • GM_setUserAgent(value)
      • changes the User Agent value that is configured in Settings
      • where:
        • [optional] value is a String
          • special cases:
            • WebView (or falsy)
            • Chrome
    • GM_startIntent(action, data, type, ...extras)
      • starts an implicit Intent
      • where:
        • [required, can be empty] action is a String
        • [required, can be empty] data is a String URL
        • [required, can be empty] type is a String mime-type for format of data
        • [optional] extras is a list of String name/value pairs
      • example:
        • ('android.intent.action.VIEW', 'http://example.com/video.mp4', 'video/mp4', 'referUrl', 'http://example.com/videos.html')
    • GM_toastLong(message)
    • GM_toastShort(message)
  • GM 4:
    • GM.exit
    • GM.getUrl
    • GM.getUserAgent
    • GM.loadFrame
    • GM.loadUrl
    • GM.removeAllCookies
    • GM.resolveUrl
    • GM.setUserAgent
    • GM.startIntent
    • GM.toastLong
    • GM.toastShort

Settings

• default browser home page
  • Continue where you left off
  • Blank page
  • Userscripts by developer
  • Userscripts at Greasy Fork
  • Custom URL
• User Agent
  • WebView
  • Chrome desktop
  • Custom User Agent
• page load behavior on HTTPS certificate error
  • cancel
  • proceed
  • ask
• script update interval
  • number of days to wait between checks
  • special case: 0 disables automatic script updates
• shared secret for JS to access low-level API method:

    window.WebViewWM.getUserscriptJS(secret, url)

  • specific use case: mitmproxy script to inject JS code to bootstrap userscripts in iframes
• enable remote debugger
  • allows remote access over an adb connection, such as:

      adb connect "${IP_of_phone_on_LAN}:5555"

  • remote debugger is accessible in Chrome at:

      chrome://inspect/#devices
    

  • the interface uses Chrome DevTools

Security

1. closure
   • by default, all JS code injected into web pages is wrapped by a closure
   • the closure is implemented as a self-executing anonymous function, also known as an immediately invoked function expression
   • this security feature can be disabled by a userscript by adding any of the following declarations to its header block:

     // @unwrap
     // @flag noJsClosure
     // @flags noJsClosure
     

   • SANDBOX.txt contains more details
2. sandbox
   • when a closure is disabled, a sandbox is also disabled
   • when a closure is enabled, by default, all JS global variables saved to the window Object are stored in a sandbox
   • as such, JS code outside of the userscript cannot see or access these variables
   • however, the JS code inside of the userscript can see and access all global variables… including its own
   • the sandbox is implemented as an ES6 Proxy
   • this security feature can be disabled by a userscript by adding any of the following declarations to its header block:

     // @grant none
     // @flag noJsSandbox
     // @flags noJsSandbox
     

   • SANDBOX.txt contains more details
3. API-level permissions
   • // @grant <API> is only required to use API methods that I would consider to be potentially dangerous
   • several of these API methods are grouped together,
     and permission granted for any one…
     also grants permission to use all other API methods in the same group
     1. group:
        • GM_setValue
        • GM_getValue
        • GM_deleteValue
        • GM_listValues
        • GM.setValue
        • GM.getValue
        • GM.deleteValue
        • GM.listValues
     2. group:
        • GM_cookie
        • GM_cookie.list
        • GM_cookie.set
        • GM_cookie.delete
        • GM.cookie
        • GM.cookie.list
        • GM.cookie.set
        • GM.cookie.delete
        • GM.cookies
        • GM.cookies.list
        • GM.cookies.set
        • GM.cookies.delete
     3. group:
        • GM_removeAllCookies
        • GM.removeAllCookies
     4. group:
        • GM_setUserAgent
        • GM.setUserAgent

Caveats

• userscripts only run in the top window
  • a mitmproxy script is required to load userscripts into iframes

Legal:

• copyright: Warren Bank
• license: GPL-2.0