Update express-zip example to show Lambda Context usage (#281)

Author: mbfreder

Diff for: README.md

@@ -143,6 +143,13 @@ Please check out [FastAPI with Response Streaming](examples/fastapi-response-str
 
 Lambda Web Adapter forwards this information to the web application in a Http Header named "x-amzn-request-context". In the web application, you can retrieve the value of this http header and deserialize it into a JSON object. Check out [Express.js in Zip](examples/expressjs-zip) on how to use it.
 
+
+## Lambda Context
+
+**Lambda Context** is an object that Lambda passes to the function handler. This object provides information about the invocation, function, and execution environment. You can find a full list of properties accessible through the Lambda Context [here](https://docs.aws.amazon.com/lambda/latest/dg/nodejs-context.html)
+
+Lambda Web Adapter forwards this information to the web application in a Http Header named "x-amzn-lambda-context". In the web application, you can retrieve the value of this http header and deserialize it into a JSON object. Check out [Express.js in Zip](examples/expressjs-zip) on how to use it.
+
 ## Graceful Shutdown
 
 For a function with Lambda Extensions registered, Lambda enables shutdown phase for the function. When Lambda service is about to shut down a Lambda execution environment, 

Diff for: examples/expressjs-zip/hello-world/app.js

@@ -5,11 +5,17 @@ const port = process.env['PORT'] || 8080
 
 app.get('/', (req, res) => {
     // deserialize request context from the http header 'x-amzn-request-context'
-    let context = req.headers['x-amzn-request-context'] || null
-    let requestContext = context != null? JSON.parse(context) : null
+    let requestContextHeader = req.headers['x-amzn-request-context'] || null
+    let requestContext = requestContextHeader != null? JSON.parse(requestContextHeader) : null
+
+    // deserialize lambda context from the http header 'x-amzn-lambda-context'
+    let lambdaContextHeader = req.headers['x-amzn-lambda-context'] || null
+    let lambdaContext = lambdaContextHeader != null? JSON.parse(lambdaContextHeader) : null
+
     res.send({
-        messagge: 'Hi there!', 
-        requestContext
+        message: 'Hi there!', 
+        requestContext,
+        lambdaContext
     })
 })