Added chaos experiments

.vscode/launch.json

@@ -0,0 +1,20 @@
+{
+    // Use IntelliSense to learn about possible attributes.
+    // Hover to view descriptions of existing attributes.
+    // For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387
+    "version": "0.2.0",
+    "configurations": [
+        {
+            "name": "Launch via NPM",
+            "type": "node",
+            "request": "launch",
+            "cwd": "${workspaceRoot}",
+            "runtimeExecutable": "npm",
+            "runtimeArgs": [
+                "run-script",
+                "debug"
+            ],
+            "port": 5000
+        }
+    ]
+}

CHANGELOG.md

@@ -6,6 +6,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Added
+Chaos experiments added. You can add a statuscode and latency delay.
+
 ## [1.11.1] - 2022-02-20
 ### Fixed
 - Responses that are just a number are now properly generated (#56)

README.md

@@ -49,6 +49,8 @@ docker run -v "$PWD/myschema.json:/app/schema.json" -p "3000:3000" jormaechea/op
 - [x] Request and response logging
 - [x] Servers basepath support
 - [x] Support x-faker and x-count extension methods to customise generated responses
+- [x] Support for `latency` and `latencyRate` to introduce random latency to the response. Latency is number of milliseconds to wait before returning the response, rate is a number between 0-100 to specify when to add this behaviour. 
+- [x] Support for `statusCode` and `statuscodeRate` to introduce a different statuscode to the response. Specify the statusCode to return and use the rate (a number between 0-100) to specify when to add this behaviour.
 - [ ] API Authentication
 
 ## Customizing Generated Responses
@@ -152,6 +154,10 @@ Will produce the following response:
 ]
 ```
 
+## Chaos Engineering
+
+Besides generating fake data, you can also specify with the `prefer` header that you would like the mock API to respond in unpredictable ways. You can send different status code or add latency to the response by adding the `statusCode` and/or `latency` parameters inside the `prefer` header. Using the `statusCodeRate` and `latencyRate` parameters you can specify when to add these behaviours. Use a value between 0 and 100 (%) to add less or more randomness.
+
 ## Advanced usage
 
 See the [advanced usage docs](docs/README.md) to extend or build your own app upon OpenAPI Mocker.

lib/mocker/express/request-handler.js

@@ -9,14 +9,20 @@ const colors = require('colors');
 
 // Create a function that is memoized using the URL, query, the Prefer header and the body.
 // eslint-disable-next-line no-unused-vars
-const getResponse = (path, url, query, preferHeader, body) => {
-	const { example: preferredExampleName, statuscode: preferredStatusCode } = parsePreferHeader(preferHeader) || {};
+const getResponse = async (path, url, query, preferHeader, body) => {
+	const {
+		example: preferredExampleName, statuscode: preferredStatusCode,
+		statuscoderate: preferredStatusCodeRate, latency: preferredLatency,
+		latencyrate: preferredLatencyRate
+	} = parsePreferHeader(preferHeader) || {};
 
 	if(preferredStatusCode)
 		logger.debug(`Searching requested response with status code ${preferredStatusCode}`);
 	else
 		logger.debug('Searching first response');
-	return path.getResponse(preferredStatusCode, preferredExampleName);
+
+	const response = await path.getResponse(preferredStatusCode, preferredStatusCodeRate, preferredExampleName, preferredLatency, preferredLatencyRate);
+	return new Promise(resolve => resolve(response));
 };
 
 const getResponseMemo = memoize(getResponse, {
@@ -29,7 +35,7 @@ const checkContentType = req => {
 		logger.warn(`${colors.yellow('*')} Missing content-type header`);
 };
 
-const handleRequest = (path, responseHandler) => (req, res) => {
+const handleRequest = (path, responseHandler) => async (req, res) => {
 
 	checkContentType(req);
 
@@ -54,8 +60,13 @@ const handleRequest = (path, responseHandler) => (req, res) => {
 
 	const preferHeader = req.header('prefer') || '';
 
-	const { statusCode, headers: responseHeaders, body, responseMimeType } =
-			getResponseMemo(path, req.path, JSON.stringify(req.query), preferHeader, JSON.stringify(requestBody));
+	let response;
+	if(preferHeader)
+		response = await getResponse(path, req.path, JSON.stringify(req.query), preferHeader, JSON.stringify(requestBody));
+	else
+		response = await getResponseMemo(path, req.path, JSON.stringify(req.query), preferHeader, JSON.stringify(requestBody));
+
+	const { statusCode, headers: responseHeaders, body, responseMimeType } = response;
 
 	return responseHandler(req, res, body, statusCode, responseHeaders, responseMimeType);
 };

lib/paths/path.js

@@ -197,31 +197,48 @@ class Path {
 		return !possibleValues || !possibleValues.length || possibleValues.includes(value);
 	}
 
-	getResponse(preferredStatusCode, preferredExampleName) {
+	delay(time) {
+		return new Promise(resolve => setTimeout(resolve, time));
+	}
+
+	async getResponse(preferredStatusCode, preferredStatusCodeRate, preferredExampleName, preferredLatency, preferredLatencyRate) {
 
+		const applyLatencyExperiment = preferredLatencyRate ? this.getRandomInt(100) < (preferredLatencyRate) : true;
+		const applyStatusCodeExperiment = preferredStatusCodeRate ? this.getRandomInt(100) < (preferredStatusCodeRate) : true;
+
+		if(applyLatencyExperiment) {
+			if(preferredLatency)
+				await this.delay(preferredLatency);
+		}
 		const {
 			statusCode,
 			headers,
 			schema,
 			responseMimeType
-		} = preferredStatusCode ? this.getResponseByStatusCode(preferredStatusCode) : this.getFirstResponse();
+		} = preferredStatusCode && applyStatusCodeExperiment ? this.getResponseByStatusCode(preferredStatusCode) : this.getFirstResponse();
 
-		return {
+		const response = {
 			statusCode: Number(statusCode),
 			headers: headers && this.generateResponseHeaders(headers),
 			body: schema ? ResponseGenerator.generate(schema, preferredExampleName) : null,
 			responseMimeType
 		};
+
+		return new Promise(resolve => resolve(response));
+	}
+
+	getRandomInt(max) {
+		return Math.floor(Math.random() * max) + 1;
 	}
 
 	getResponseByStatusCode(statusCode) {
 
-		if(!this.responses[statusCode]) {
+		if(!this.responses[statusCode] && !this.responses.default) {
 			logger.warn(`Could not find a response for status code ${statusCode}. Responding with first response`);
 			return this.getFirstResponse();
 		}
 
-		const preferredResponse = this.responses[statusCode];
+		const preferredResponse = this.responses[statusCode] || this.responses.default;
 
 		const [[responseMimeType, responseContent] = []] = Object.entries(preferredResponse.content || {});