feat: Capture HTTP response body

src/AppMap.d.ts

@@ -166,6 +166,7 @@ namespace AppMap {
 
   export interface HttpServerResponseEvent extends ReturnEventBase {
     http_server_response: HttpResponse;
+    return_value?: string | Parameter;
   }
 
   export interface HttpClientResponseEvent extends ReturnEventBase {

src/Recording.ts

@@ -159,6 +159,7 @@ export default class Recording {
     elapsed: number,
     status: number,
     headers?: Record<string, string>,
+    body?: string,
   ): AppMap.HttpServerResponseEvent {
     assert(this.stream);
 
@@ -172,6 +173,7 @@ export default class Recording {
       thread_id: 0,
       parent_id: callId,
       elapsed,
+      return_value: body,
     };
     this.stream.emit(event);
 

src/hooks/http.ts

@@ -1,7 +1,7 @@
 import assert from "node:assert";
 import { readFileSync, rmSync } from "node:fs";
 import type http from "node:http";
-import type { ClientRequest, IncomingMessage, ServerResponse } from "node:http";
+import { type ClientRequest, type IncomingMessage, type ServerResponse } from "node:http";
 import type https from "node:https";
 import { URL } from "node:url";
 
@@ -155,6 +155,79 @@ function shouldIgnoreRequest(request: http.IncomingMessage) {
   return false;
 }
 
+type Chunk = string | Buffer;
+const maxResponseBodyCaptureLength = 1000;
+
+function captureResponseBody(response: http.ServerResponse, chunks: Chunk[]) {
+  let currentLength = 0;
+  function captureChunk(chunk: Chunk) {
+    if (maxResponseBodyCaptureLength <= currentLength) return;
+
+    chunks.push(chunk);
+    currentLength += chunk.length;
+  }
+
+  const originalWrite = response.write.bind(response);
+  const originalEnd = response.end.bind(response);
+
+  response.write = function (...args: unknown[]) {
+    console.log("WRITE", args.length);
+    let callback: unknown;
+    let encoding: unknown;
+    const chunk = args[0] as Buffer;
+    // write has these call signatures
+    // (chunk, callback?)
+    // (chunk, encoding, callback?)
+    let argsToConsider = args.length;
+    // If the last parameter is a function than it's the callback
+    if (args.length > 0 && typeof args[args.length - 1] === "function") {
+      callback = args[args.length - 1];
+      argsToConsider--;
+    }
+    if (argsToConsider > 1) encoding = args[1];
+
+    captureChunk(chunk);
+
+    if (encoding != null)
+      return originalWrite(
+        chunk,
+        encoding as BufferEncoding,
+        callback as ((error: Error | null | undefined) => void) | undefined,
+      );
+
+    return originalWrite(
+      chunk,
+      callback as ((error: Error | null | undefined) => void) | undefined,
+    );
+  };
+
+  response.end = function (...args: unknown[]) {
+    console.log("ARGS", args);
+    console.log("ARGS", args);
+
+    // end has these call signatures:
+    // (cb?); (chunk, cb?); (chunk, encoding, cb?)
+    // If the last parameter is a function than it's the callback
+    const argsCountBeforeCallback =
+      args.length > 0 && typeof args[args.length - 1] === "function"
+        ? args.length - 1
+        : args.length;
+    if (argsCountBeforeCallback > 0) captureChunk(args[0] as Chunk);
+
+    //console.log(args);
+    //console.log("ARGS", args);
+
+    let result: ReturnType<typeof response.end>;
+    if (args.length == 3)
+      result = originalEnd(args[0], args[1] as BufferEncoding, args[2] as () => void);
+    else if (args.length == 2) result = originalEnd(args[0], args[1] as () => void);
+    else if (args.length == 1) result = originalEnd(args[0]);
+    else result = originalEnd();
+
+    return result;
+  };
+}
+
 function handleRequest(request: http.IncomingMessage, response: http.ServerResponse) {
   if (!(request.method && request.url)) return;
 
@@ -169,9 +242,13 @@ function handleRequest(request: http.IncomingMessage, response: http.ServerRespo
     normalizeHeaders(request.headers),
     url.searchParams,
   );
+
+  const bodyChunks: Chunk[] = [];
+  captureResponseBody(response, bodyChunks);
+
   const startTime = getTime();
   response.once("finish", () => {
-    handleResponse(request, requestEvent, startTime, timestamp, response);
+    handleResponse(request, requestEvent, startTime, timestamp, response, bodyChunks);
   });
 }
 
@@ -238,13 +315,22 @@ function handleResponse(
   startTime: number,
   timestamp: string | undefined,
   response: http.ServerResponse<http.IncomingMessage>,
+  chunks: Chunk[],
 ): void {
   if (fixupEvent(request, requestEvent)) recording.fixup(requestEvent);
+
+  let body =
+    chunks.length > 0 && typeof chunks[0] === "string"
+      ? chunks.join("")
+      : Buffer.concat(chunks as Buffer[]).toString("utf8");
+  body = body.substring(0, maxResponseBodyCaptureLength);
+
   recording.httpResponse(
     requestEvent.id,
     getTime() - startTime,
     response.statusCode,
     normalizeHeaders(response.getHeaders()),
+    body,
   );
   if (remoteRunning) return;
   const { request_method, path_info } = requestEvent.http_server_request;

test/__snapshots__/httpServer.test.ts.snap

@@ -85,6 +85,7 @@ exports[`mapping Express.js requests 1`] = `
         },
         "id": 4,
         "parent_id": 1,
+        "return_value": "Hello World!",
         "thread_id": 0,
       },
     ],
@@ -139,6 +140,17 @@ exports[`mapping Express.js requests 1`] = `
         },
         "id": 2,
         "parent_id": 1,
+        "return_value": "<!DOCTYPE html>
+<html lang="en">
+<head>
+<meta charset="utf-8">
+<title>Error</title>
+</head>
+<body>
+<pre>Cannot GET /nonexistent</pre>
+</body>
+</html>
+",
         "thread_id": 0,
       },
     ],
@@ -309,6 +321,7 @@ exports[`mapping Express.js requests 1`] = `
         },
         "id": 4,
         "parent_id": 1,
+        "return_value": "{"api":"result","param1":"3","param2":"4"}",
         "thread_id": 0,
       },
     ],
@@ -574,6 +587,7 @@ exports[`mapping Express.js requests 1`] = `
         },
         "id": 4,
         "parent_id": 1,
+        "return_value": "{"key":"value","obj":{"foo":42,"arr":[44]},"arr":[{"foo":43},{"foo":44}],"heterogenous":[42,"str"]}",
         "thread_id": 0,
       },
     ],
@@ -799,6 +813,7 @@ exports[`mapping Express.js requests with remote recording 1`] = `
       },
       "id": 4,
       "parent_id": 1,
+      "return_value": "Hello World!",
       "thread_id": 0,
     },
     {
@@ -829,6 +844,17 @@ exports[`mapping Express.js requests with remote recording 1`] = `
       },
       "id": 6,
       "parent_id": 5,
+      "return_value": "<!DOCTYPE html>
+<html lang="en">
+<head>
+<meta charset="utf-8">
+<title>Error</title>
+</head>
+<body>
+<pre>Cannot GET /nonexistent</pre>
+</body>
+</html>
+",
       "thread_id": 0,
     },
     {
@@ -923,6 +949,7 @@ exports[`mapping Express.js requests with remote recording 1`] = `
       },
       "id": 10,
       "parent_id": 7,
+      "return_value": "{"api":"result","param1":"3","param2":"4"}",
       "thread_id": 0,
     },
     {
@@ -1073,6 +1100,7 @@ exports[`mapping Express.js requests with remote recording 1`] = `
       },
       "id": 14,
       "parent_id": 11,
+      "return_value": "{"key":"value","obj":{"foo":42,"arr":[44]},"arr":[{"foo":43},{"foo":44}],"heterogenous":[42,"str"]}",
       "thread_id": 0,
     },
   ],
@@ -1125,6 +1153,7 @@ exports[`mapping node:http requests 1`] = `
         },
         "id": 2,
         "parent_id": 1,
+        "return_value": "",
         "thread_id": 0,
       },
     ],
@@ -1173,6 +1202,7 @@ exports[`mapping node:http requests 1`] = `
         },
         "id": 2,
         "parent_id": 1,
+        "return_value": "",
         "thread_id": 0,
       },
     ],
@@ -1233,6 +1263,7 @@ exports[`mapping node:http requests 1`] = `
         },
         "id": 2,
         "parent_id": 1,
+        "return_value": "",
         "thread_id": 0,
       },
     ],
@@ -1283,6 +1314,7 @@ exports[`mapping node:http requests 1`] = `
         },
         "id": 2,
         "parent_id": 1,
+        "return_value": "",
         "thread_id": 0,
       },
     ],
@@ -1335,6 +1367,7 @@ exports[`mapping node:http requests with remote recording 1`] = `
       },
       "id": 2,
       "parent_id": 1,
+      "return_value": "",
       "thread_id": 0,
     },
     {
@@ -1359,6 +1392,7 @@ exports[`mapping node:http requests with remote recording 1`] = `
       },
       "id": 4,
       "parent_id": 3,
+      "return_value": "",
       "thread_id": 0,
     },
     {
@@ -1395,6 +1429,7 @@ exports[`mapping node:http requests with remote recording 1`] = `
       },
       "id": 6,
       "parent_id": 5,
+      "return_value": "",
       "thread_id": 0,
     },
     {
@@ -1421,6 +1456,7 @@ exports[`mapping node:http requests with remote recording 1`] = `
       },
       "id": 8,
       "parent_id": 7,
+      "return_value": "",
       "thread_id": 0,
     },
   ],