Add protocol interceptor API.

spec/api/protocol.coffee

@@ -80,3 +80,53 @@ describe 'protocol API', ->
       assert.equal protocol.isHandledProtocol('http'), true
       assert.equal protocol.isHandledProtocol('https'), true
       assert.equal protocol.isHandledProtocol('atom'), false
+
+  describe 'protocol.interceptProtocol', ->
+    it 'throws error when scheme is not a registered one', ->
+      register = -> protocol.interceptProtocol('test-intercept', ->)
+      assert.throws register, /Cannot intercept procotol/
+
+    it 'throws error when scheme is a custom protocol', (done) ->
+      protocol.once 'unregistered', (scheme) ->
+        assert.equal scheme, 'atom'
+        done()
+      protocol.once 'registered', (scheme) ->
+        assert.equal scheme, 'atom'
+        register = -> protocol.interceptProtocol('test-intercept', ->)
+        assert.throws register, /Cannot intercept procotol/
+        protocol.unregisterProtocol scheme
+      protocol.registerProtocol('atom', ->)
+
+    it 'returns original job when callback returns nothing', (done) ->
+      targetScheme = 'file'
+      protocol.once 'intercepted', (scheme) ->
+        assert.equal scheme, targetScheme
+        free = -> protocol.uninterceptProtocol targetScheme
+        $.ajax
+          url: "#{targetScheme}://#{__filename}",
+          success: ->
+            protocol.once 'unintercepted', (scheme) ->
+              assert.equal scheme, targetScheme
+              done()
+            free()
+          error: (xhr, errorType, error) ->
+            free()
+            assert false, 'Got error: ' + errorType + ' ' + error
+      protocol.interceptProtocol targetScheme, (request) ->
+        assert.equal request.url, "#{targetScheme}://#{__filename}"
+
+    it 'can override original protocol handler', (done) ->
+      handler = remote.createFunctionWithReturnValue 'valar morghulis'
+      protocol.once 'intercepted', ->
+        free = -> protocol.uninterceptProtocol 'file'
+        $.ajax
+          url: 'file://fake-host'
+          success: (data) ->
+            protocol.once 'unintercepted', ->
+              assert.equal data, handler()
+              done()
+            free()
+          error: (xhr, errorType, error) ->
+            assert false, 'Got error: ' + errorType + ' ' + error
+            free()
+      protocol.interceptProtocol 'file', handler