diff --git a/src/server/session.ts b/src/server/session.ts
index c95b1a7cc1b..e0c540db18b 100644
--- a/src/server/session.ts
+++ b/src/server/session.ts
@@ -839,6 +839,127 @@ namespace ts.server {
         exit() {
         }
 
+        private handlers : Map<(request: protocol.Request) => {response?: any, responseRequired?: boolean}> = {
+            [CommandNames.Exit]: () => {
+                this.exit();
+                return {};
+            },
+            [CommandNames.Definition]: (request: protocol.Request) => {
+                var defArgs = <protocol.FileLocationRequestArgs>request.arguments;
+                return {response: this.getDefinition(defArgs.line, defArgs.offset, defArgs.file)};
+            },
+            [CommandNames.TypeDefinition]: (request: protocol.Request) => {
+                var defArgs = <protocol.FileLocationRequestArgs>request.arguments;
+                return {response: this.getTypeDefinition(defArgs.line, defArgs.offset, defArgs.file)};
+            },
+            [CommandNames.References]: (request: protocol.Request) => {
+                var defArgs = <protocol.FileLocationRequestArgs>request.arguments;
+                return {response: this.getReferences(defArgs.line, defArgs.offset, defArgs.file)};
+            },
+            [CommandNames.Rename]: (request: protocol.Request) => {
+                var renameArgs = <protocol.RenameRequestArgs>request.arguments;
+                return {response: this.getRenameLocations(renameArgs.line, renameArgs.offset, renameArgs.file, renameArgs.findInComments, renameArgs.findInStrings)}
+            },
+            [CommandNames.Open]: (request: protocol.Request) => {
+                var openArgs = <protocol.OpenRequestArgs>request.arguments;
+                this.openClientFile(openArgs.file);
+                return {}
+            },
+            [CommandNames.Quickinfo]: (request: protocol.Request) => {
+                var quickinfoArgs = <protocol.FileLocationRequestArgs>request.arguments;
+                return {response: this.getQuickInfo(quickinfoArgs.line, quickinfoArgs.offset, quickinfoArgs.file)};
+            },
+            [CommandNames.Format]: (request: protocol.Request) => {
+                var formatArgs = <protocol.FormatRequestArgs>request.arguments;
+                return {response: this.getFormattingEditsForRange(formatArgs.line, formatArgs.offset, formatArgs.endLine, formatArgs.endOffset, formatArgs.file)};
+            },
+            [CommandNames.Formatonkey]: (request: protocol.Request) => {
+                var formatOnKeyArgs = <protocol.FormatOnKeyRequestArgs>request.arguments;
+                return {response: this.getFormattingEditsAfterKeystroke(formatOnKeyArgs.line, formatOnKeyArgs.offset, formatOnKeyArgs.key, formatOnKeyArgs.file)};
+            },
+            [CommandNames.Completions]: (request: protocol.Request) => {
+                var completionsArgs = <protocol.CompletionsRequestArgs>request.arguments;
+                return {response: this.getCompletions(completionsArgs.line, completionsArgs.offset, completionsArgs.prefix, completionsArgs.file)}
+            },
+            [CommandNames.CompletionDetails]: (request: protocol.Request) => {
+                var completionDetailsArgs = <protocol.CompletionDetailsRequestArgs>request.arguments;
+                return {response: this.getCompletionEntryDetails(completionDetailsArgs.line,completionDetailsArgs.offset,
+                                                                  completionDetailsArgs.entryNames,completionDetailsArgs.file)}
+            },
+            [CommandNames.SignatureHelp]: (request: protocol.Request) => {
+                var signatureHelpArgs = <protocol.SignatureHelpRequestArgs>request.arguments;
+                return {response: this.getSignatureHelpItems(signatureHelpArgs.line, signatureHelpArgs.offset, signatureHelpArgs.file)}
+            },
+            [CommandNames.Geterr]: (request: protocol.Request) => {
+                var geterrArgs = <protocol.GeterrRequestArgs>request.arguments;
+                return {response: this.getDiagnostics(geterrArgs.delay, geterrArgs.files), responseRequired: false};
+            },
+            [CommandNames.Change]: (request: protocol.Request) => {
+                var changeArgs = <protocol.ChangeRequestArgs>request.arguments;
+                this.change(changeArgs.line, changeArgs.offset, changeArgs.endLine, changeArgs.endOffset,
+                            changeArgs.insertString, changeArgs.file);
+                return {responseRequired: false}
+            },
+            [CommandNames.Configure]: (request: protocol.Request) => {
+                var configureArgs = <protocol.ConfigureRequestArguments>request.arguments;
+                this.projectService.setHostConfiguration(configureArgs);
+                this.output(undefined, CommandNames.Configure, request.seq);
+                return {responseRequired: false}
+            },
+            [CommandNames.Reload]: (request: protocol.Request) => {
+                var reloadArgs = <protocol.ReloadRequestArgs>request.arguments;
+                this.reload(reloadArgs.file, reloadArgs.tmpfile, request.seq);
+                return {responseRequired: false}
+            },
+            [CommandNames.Saveto]: (request: protocol.Request) => {
+                var savetoArgs = <protocol.SavetoRequestArgs>request.arguments;
+                this.saveToTmp(savetoArgs.file, savetoArgs.tmpfile);
+                return {responseRequired: false}
+            },
+            [CommandNames.Close]: (request: protocol.Request) => {
+                var closeArgs = <protocol.FileRequestArgs>request.arguments;
+                this.closeClientFile(closeArgs.file);
+                return {responseRequired: false};
+            },
+            [CommandNames.Navto]: (request: protocol.Request) => {
+                var navtoArgs = <protocol.NavtoRequestArgs>request.arguments;
+                return {response: this.getNavigateToItems(navtoArgs.searchValue, navtoArgs.file, navtoArgs.maxResultCount)};
+            },
+            [CommandNames.Brace]: (request: protocol.Request) => {
+                var braceArguments = <protocol.FileLocationRequestArgs>request.arguments;
+                return {response: this.getBraceMatching(braceArguments.line, braceArguments.offset, braceArguments.file)};
+            },
+            [CommandNames.NavBar]: (request: protocol.Request) => {
+                var navBarArgs = <protocol.FileRequestArgs>request.arguments;
+                return {response: this.getNavigationBarItems(navBarArgs.file)};
+            },
+            [CommandNames.Occurrences]: (request: protocol.Request) => {
+                var { line, offset, file: fileName } = <protocol.FileLocationRequestArgs>request.arguments;
+                return {response: this.getOccurrences(line, offset, fileName)};
+            },
+            [CommandNames.ProjectInfo]: (request: protocol.Request) => {
+                var { file, needFileNameList } = <protocol.ProjectInfoRequestArgs>request.arguments;
+                return {response: this.getProjectInfo(file, needFileNameList)};
+            },
+        };
+        addProtocolHandler(command: string, handler: (request: protocol.Request) => {response?: any, responseRequired: boolean}) {
+            if (this.handlers[command]) {
+                throw new Error(`Protocol handler already exists for command "${command}"`);
+            }
+            this.handlers[command] = handler;
+        }
+
+        executeCommand(request: protocol.Request) : {response?: any, responseRequired?: boolean} {
+            var handler = this.handlers[request.command];
+            if (handler) {
+                return handler(request);
+            } else {
+                this.projectService.log("Unrecognized JSON command: " + JSON.stringify(request));
+                this.output(undefined, CommandNames.Unknown, request.seq, "Unrecognized JSON command: " + request.command);
+                return {responseRequired: false};
+            }
+        }
+
         onMessage(message: string) {
             if (this.logger.isVerbose()) {
                 this.logger.info("request: " + message);
@@ -846,142 +967,7 @@ namespace ts.server {
             }
             try {
                 var request = <protocol.Request>JSON.parse(message);
-                var response: any;
-                var errorMessage: string;
-                var responseRequired = true;
-                switch (request.command) {
-                    case CommandNames.Exit: {
-                        this.exit();
-                        responseRequired = false;
-                        break;
-                    }
-                    case CommandNames.Definition: { 
-                        var defArgs = <protocol.FileLocationRequestArgs>request.arguments;
-                        response = this.getDefinition(defArgs.line, defArgs.offset, defArgs.file);
-                        break;
-                    }
-                    case CommandNames.TypeDefinition: {
-                        var defArgs = <protocol.FileLocationRequestArgs>request.arguments;
-                        response = this.getTypeDefinition(defArgs.line, defArgs.offset, defArgs.file);
-                        break;
-                    }
-                    case CommandNames.References: { 
-                        var refArgs = <protocol.FileLocationRequestArgs>request.arguments;
-                        response = this.getReferences(refArgs.line, refArgs.offset, refArgs.file);
-                        break;
-                    }
-                    case CommandNames.Rename: {
-                        var renameArgs = <protocol.RenameRequestArgs>request.arguments;
-                        response = this.getRenameLocations(renameArgs.line, renameArgs.offset, renameArgs.file, renameArgs.findInComments, renameArgs.findInStrings);
-                        break;
-                    }
-                    case CommandNames.Open: {
-                        var openArgs = <protocol.OpenRequestArgs>request.arguments;
-                        this.openClientFile(openArgs.file);
-                        responseRequired = false;
-                        break;
-                    }
-                    case CommandNames.Quickinfo: {
-                        var quickinfoArgs = <protocol.FileLocationRequestArgs>request.arguments;
-                        response = this.getQuickInfo(quickinfoArgs.line, quickinfoArgs.offset, quickinfoArgs.file);
-                        break;
-                    }
-                    case CommandNames.Format: {
-                        var formatArgs = <protocol.FormatRequestArgs>request.arguments;
-                        response = this.getFormattingEditsForRange(formatArgs.line, formatArgs.offset, formatArgs.endLine, formatArgs.endOffset, formatArgs.file);
-                        break;
-                    }
-                    case CommandNames.Formatonkey: {
-                        var formatOnKeyArgs = <protocol.FormatOnKeyRequestArgs>request.arguments;
-                        response = this.getFormattingEditsAfterKeystroke(formatOnKeyArgs.line, formatOnKeyArgs.offset, formatOnKeyArgs.key, formatOnKeyArgs.file);
-                        break;
-                    }
-                    case CommandNames.Completions: {
-                        var completionsArgs = <protocol.CompletionsRequestArgs>request.arguments;
-                        response = this.getCompletions(completionsArgs.line, completionsArgs.offset, completionsArgs.prefix, completionsArgs.file);
-                        break;
-                    }
-                    case CommandNames.CompletionDetails: {
-                        var completionDetailsArgs = <protocol.CompletionDetailsRequestArgs>request.arguments;
-                        response =
-                            this.getCompletionEntryDetails(completionDetailsArgs.line,completionDetailsArgs.offset,
-                                                           completionDetailsArgs.entryNames,completionDetailsArgs.file);
-                        break;
-                    }
-                    case CommandNames.SignatureHelp: {
-                        var signatureHelpArgs = <protocol.SignatureHelpRequestArgs>request.arguments;
-                        response = this.getSignatureHelpItems(signatureHelpArgs.line, signatureHelpArgs.offset, signatureHelpArgs.file);
-                        break;
-                    }    
-                    case CommandNames.Geterr: {
-                        var geterrArgs = <protocol.GeterrRequestArgs>request.arguments;
-                        response = this.getDiagnostics(geterrArgs.delay, geterrArgs.files);
-                        responseRequired = false;
-                        break;
-                    }
-                    case CommandNames.Change: {
-                        var changeArgs = <protocol.ChangeRequestArgs>request.arguments;
-                        this.change(changeArgs.line, changeArgs.offset, changeArgs.endLine, changeArgs.endOffset,
-                                    changeArgs.insertString, changeArgs.file);
-                        responseRequired = false;
-                        break;
-                    }
-                    case CommandNames.Configure: {
-                        var configureArgs = <protocol.ConfigureRequestArguments>request.arguments;
-                        this.projectService.setHostConfiguration(configureArgs);
-                        this.output(undefined, CommandNames.Configure, request.seq);
-                        responseRequired = false;
-                        break;
-                    }
-                    case CommandNames.Reload: {
-                        var reloadArgs = <protocol.ReloadRequestArgs>request.arguments;
-                        this.reload(reloadArgs.file, reloadArgs.tmpfile, request.seq);
-                        responseRequired = false;
-                        break;
-                    }
-                    case CommandNames.Saveto: {
-                        var savetoArgs = <protocol.SavetoRequestArgs>request.arguments;
-                        this.saveToTmp(savetoArgs.file, savetoArgs.tmpfile);
-                        responseRequired = false;
-                        break;
-                    }
-                    case CommandNames.Close: {
-                        var closeArgs = <protocol.FileRequestArgs>request.arguments;
-                        this.closeClientFile(closeArgs.file);
-                        responseRequired = false;
-                        break;
-                    }
-                    case CommandNames.Navto: {
-                        var navtoArgs = <protocol.NavtoRequestArgs>request.arguments;
-                        response = this.getNavigateToItems(navtoArgs.searchValue, navtoArgs.file, navtoArgs.maxResultCount);
-                        break;
-                    }
-                    case CommandNames.Brace: {
-                        var braceArguments = <protocol.FileLocationRequestArgs>request.arguments;
-                        response = this.getBraceMatching(braceArguments.line, braceArguments.offset, braceArguments.file);
-                        break;
-                    }
-                    case CommandNames.NavBar: {
-                        var navBarArgs = <protocol.FileRequestArgs>request.arguments;
-                        response = this.getNavigationBarItems(navBarArgs.file);
-                        break;
-                    }
-                    case CommandNames.Occurrences: {
-                        var { line, offset, file: fileName } = <protocol.FileLocationRequestArgs>request.arguments;
-                        response = this.getOccurrences(line, offset, fileName);
-                        break;
-                    }
-                    case CommandNames.ProjectInfo: {
-                        var { file, needFileNameList } = <protocol.ProjectInfoRequestArgs>request.arguments;
-                        response = this.getProjectInfo(file, needFileNameList);
-                        break;
-                    }
-                    default: {
-                        this.projectService.log("Unrecognized JSON command: " + message);
-                        this.output(undefined, CommandNames.Unknown, request.seq, "Unrecognized JSON command: " + request.command);
-                        break;
-                    }
-                }
+                var {response, responseRequired} = this.executeCommand(request);
 
                 if (this.logger.isVerbose()) {
                     var elapsed = this.hrtime(start);