Adding error logging

Author: fwang

libs/debug-lib.js

@@ -0,0 +1,42 @@
+import AWS from "aws-sdk";
+import util from "util";
+
+// Log AWS SDK calls
+AWS.config.logger = { log: debug };
+
+let logs;
+let timeoutTimer;
+
+export function init(event, context) {
+  logs = [];
+
+  // Log API event
+  debug("API event", {
+    body: event.body,
+    pathParameters: event.pathParameters,
+    queryStringParameters: event.queryStringParameters,
+  });
+
+  // Start timeout timer
+  timeoutTimer = setTimeout(() => {
+    timeoutTimer && flush(new Error("Lambda will timeout in 100 ms"));
+  }, context.getRemainingTimeInMillis() - 100);
+}
+
+export function end() {
+  // Clear timeout timer
+  clearTimeout(timeoutTimer);
+  timeoutTimer = null;
+}
+
+export function flush(e) {
+  logs.forEach(({ date, string }) => console.debug(date, string));
+  console.error(e);
+}
+
+export default function debug() {
+  logs.push({
+    date: new Date(),
+    string: util.format.apply(null, arguments),
+  });
+}

libs/handler-lib.js

@@ -1,12 +1,18 @@
+import * as debug from "./debug-lib";
+
 export default function handler(lambda) {
   return function (event, context) {
     return Promise.resolve()
+      // Start debugger
+      .then(() => debug.init(event, context))
       // Run the Lambda
       .then(() => lambda(event, context))
       // On success
       .then((responseBody) => [200, responseBody])
       // On failure
       .catch((e) => {
+        // Print debug messages
+        debug.flush(e);
         return [500, { error: e.message }];
       })
       // Return HTTP response
@@ -17,6 +23,8 @@ export default function handler(lambda) {
           "Access-Control-Allow-Credentials": true,
         },
         body: JSON.stringify(body),
-      }));
+      }))
+      // Cleanup debugger
+      .finally(debug.end);
   };
 }