Added ability to use custom function for error reporting instead built-in sendErrorPayload (#71)

* add custom reporting function

* update readme

Author: theorchoo

README.md

@@ -158,6 +158,23 @@ errorHandler.start({
 
 where `targetUrl` is the url you'd like to send errors to and can be relative or absolute. This endpoint will need to support the [Report API endpoint](https://cloud.google.com/error-reporting/reference/rest/v1beta1/projects.events/report).
 
+## Custom message dispatching
+
+If you can't use HTTP Post requests for reporting your errors, or in need for some more complicated customizations, you may provide a custom function to handle the reporting.
+
+The function will be called with a payload argument (the same one that would have been sent on the HTTP Post request) and should return a Promise.  
+
+```javascript
+const errorHandler = new StackdriverErrorReporter();
+function myCustomFunction(payload) {
+  console.log("custom reporting function called with payload:", payload);
+  return Promise.resolve(); 
+}
+errorHandler.start({
+  customReportingFunction: myCustomFunction,
+});
+```
+
 ## Best Practices
 
 ### Only reporting in the production environment with Webpack

stackdriver-errors.js

@@ -33,19 +33,21 @@ var StackdriverErrorReporter = function() {};
  * @param {string} [config.context.user] - the user who caused or was affected by the error.
  * @param {String} config.key - the API key to use to call the API.
  * @param {String} config.projectId - the Google Cloud Platform project ID to report errors to.
+ * @param {Function} config.customReportingFunction - Custom function to be called with the error payload for reporting, instead of HTTP request. The function should return a Promise.
  * @param {String} [config.service=web] - service identifier.
  * @param {String} [config.version] - version identifier.
  * @param {Boolean} [config.reportUncaughtExceptions=true] - Set to false to stop reporting unhandled exceptions.
  * @param {Boolean} [config.disabled=false] - Set to true to not report errors when calling report(), this can be used when developping locally.
  */
 StackdriverErrorReporter.prototype.start = function(config) {
-  if (!config.key && !config.targetUrl) {
-    throw new Error('Cannot initialize: No API key or target url provided.');
+  if (!config.key && !config.targetUrl && !config.customReportingFunction) {
+    throw new Error('Cannot initialize: No API key, target url or custom reporting function provided.');
   }
-  if (!config.projectId && !config.targetUrl) {
-    throw new Error('Cannot initialize: No project ID or target url provided.');
+  if (!config.projectId && !config.targetUrl && !config.customReportingFunction) {
+    throw new Error('Cannot initialize: No project ID, target url or custom reporting function provided.');
   }
 
+  this.customReportingFunction = config.customReportingFunction;
   this.apiKey = config.key;
   this.projectId = config.projectId;
   this.targetUrl = config.targetUrl;
@@ -127,9 +129,14 @@ StackdriverErrorReporter.prototype.report = function(err, options) {
   var reportUrl = this.targetUrl || (
     baseAPIUrl + this.projectId + '/events:report?key=' + this.apiKey);
 
+  var customFunc = this.customReportingFunction;
+
   return resolveError(err, firstFrameIndex)
     .then(function(message) {
       payload.message = message;
+      if (customFunc) {
+        return customFunc(payload);
+      }
       return sendErrorPayload(reportUrl, payload);
     });
 };

test/test.js

@@ -31,6 +31,17 @@ function expectRequestWithMessage(message) {
   expect(sentBody.message).to.contain(message);
 }
 
+/**
+ * Helper function testing if a given message has been reported inside a payload
+ * @param {string} [payload] - payload
+ * @param {string} [message] - Substring that message must contain.
+ */
+function expectPayloadWithMessage(payload, message) {
+  var sentBody = payload;
+  expect(sentBody).to.include.keys('message');
+  expect(sentBody.message).to.contain(message);
+}
+
 /**
  * Helper for testing call stack reporting
  * @param {string} [message] - Contents of error to throw.
@@ -81,13 +92,13 @@ describe('Initialization', function() {
     expect(errorHandler.reportUnhandledPromiseRejections).to.equal(true);
   });
 
-  it('should fail if no API key or custom url', function() {
+  it('should fail if no API key or custom url or custom func', function() {
     expect(function() {
       errorHandler.start({projectId: 'projectId'});
     }).to.throw(Error, /API/);
   });
 
-  it('should fail if no project ID or custom url', function() {
+  it('should fail if no project ID or custom url or custom func', function() {
     expect(function() {
       errorHandler.start({key: 'key'});
     }).to.throw(Error, /project/);
@@ -99,6 +110,15 @@ describe('Initialization', function() {
     }).to.not.throw();
   });
 
+  it('should succeed if custom function provided without API key or project id', function() {
+    expect(function() {
+      function f() {
+
+      }
+      errorHandler.start({customReportingFunction: f});
+    }).to.not.throw();
+  });
+
   it('should have default context', function() {
     errorHandler.start({key: 'key', projectId: 'projectId'});
     expect(errorHandler.context).to.eql({});
@@ -244,6 +264,23 @@ describe('Reporting errors', function() {
       });
     });
   });
+
+  describe('Custom reporting function', function() {
+    it('should report error messages only to custom function', function() {
+      var funcResult = null;
+      function customFunc(payload) {
+        funcResult = payload;
+        return Promise.resolve();
+      }
+      errorHandler.start({customReportingFunction: customFunc});
+
+      var message = 'Something broke!';
+      return errorHandler.report(message).then(function() {
+        expectPayloadWithMessage(funcResult, message);
+        expect(requests.length).to.equal(0);
+      });
+    });
+  });
 });
 
 describe('Unhandled exceptions', function() {