make sure ipc with json serialization still works when bun is parent and not the child (#14756)

Co-authored-by: Jarred Sumner <jarred@jarredsumner.com>

src/bun.js/ipc.zig

@@ -194,21 +194,19 @@ const json = struct {
     // 1 is regular
     // 2 is internal
 
-    pub fn decodeIPCMessage(
-        data: []const u8,
-        globalThis: *JSC.JSGlobalObject,
-    ) IPCDecodeError!DecodeIPCMessageResult {
+    pub fn decodeIPCMessage(data: []const u8, globalThis: *JSC.JSGlobalObject) IPCDecodeError!DecodeIPCMessageResult {
         if (bun.strings.indexOfChar(data, '\n')) |idx| {
             var kind = data[0];
-            var json_data = data[1..idx];
+            var json_data = data[0..idx];
 
             switch (kind) {
-                1, 2 => {},
+                2 => {
+                    json_data = data[1..idx];
+                },
                 else => {
-                    // if the message being recieved is from a node process then it wont have the leading marker byte
-                    // assume full message will be json
+                    // assume it's valid json with no header
+                    // any error will be thrown by toJSByParseJSON below
                     kind = 1;
-                    json_data = data[0..idx];
                 },
             }
 
@@ -230,6 +228,7 @@ const json = struct {
             }
 
             const deserialized = str.toJSByParseJSON(globalThis);
+            if (deserialized == .zero) return error.InvalidFormat;
 
             return switch (kind) {
                 1 => .{
@@ -259,13 +258,12 @@ const json = struct {
 
         const slice = str.slice();
 
-        try writer.ensureUnusedCapacity(1 + slice.len + 1);
+        try writer.ensureUnusedCapacity(slice.len + 1);
 
-        writer.writeAssumeCapacity(&.{1});
         writer.writeAssumeCapacity(slice);
         writer.writeAssumeCapacity("\n");
 
-        return 1 + slice.len + 1;
+        return slice.len + 1;
     }
 
     pub fn serializeInternal(_: *IPCData, writer: anytype, global: *JSC.JSGlobalObject, value: JSValue) !usize {
@@ -860,7 +858,7 @@ fn NewNamedPipeIPCHandler(comptime Context: type) type {
                         // copy the remaining bytes to the start of the buffer
                         bun.copy(u8, ipc.incoming.ptr[0..slice.len], slice);
                         ipc.incoming.len = @truncate(slice.len);
-                        log("hit NotEnoughBytes2", .{});
+                        log("hit NotEnoughBytes3", .{});
                         return;
                     },
                     error.InvalidFormat => {

test/js/bun/spawn/fixtures/ipc-child-bun.js

@@ -0,0 +1,7 @@
+console.log("c start");
+process.on("message", message => {
+  console.log("c", message);
+  process.send(message);
+  process.exit(0);
+});
+console.log("c end");

test/js/bun/spawn/fixtures/ipc-child-node.js

@@ -0,0 +1,7 @@
+console.log("c start");
+process.on("message", message => {
+  console.log("c", message);
+  process.send(message);
+  process.exit(0);
+});
+console.log("c end");

test/js/bun/spawn/fixtures/ipc-parent-bun.js

@@ -0,0 +1,14 @@
+const path = require("node:path");
+
+console.log("p start");
+const child = Bun.spawn(["node", path.resolve(import.meta.dir, "ipc-child-node.js")], {
+  ipc(message) {
+    console.log("p", message);
+    process.exit(0);
+  },
+  stdio: ["ignore", "inherit", "inherit"],
+  serialization: "json",
+});
+
+child.send("I am your father");
+console.log("p end");

test/js/bun/spawn/fixtures/ipc-parent-node.js

@@ -0,0 +1,15 @@
+const path = require("node:path");
+const child_process = require("node:child_process");
+
+console.log("p start");
+
+const child = child_process.spawn(process.argv[2], [path.resolve(__dirname, "ipc-child-bun.js")], {
+  stdio: ["ignore", "inherit", "inherit", "ipc"],
+});
+child.on("message", message => {
+  console.log("p", message);
+  process.exit(0);
+});
+
+child.send("I am your father");
+console.log("p end");

test/js/bun/spawn/spawn.ipc.bun-node.test.ts

@@ -0,0 +1,21 @@
+import { spawn } from "bun";
+import { test, expect, it } from "bun:test";
+import { bunExe } from "harness";
+import path from "path";
+
+test("ipc with json serialization still works when bun is parent and not the child", async () => {
+  const child = Bun.spawn([bunExe(), path.resolve(import.meta.dir, "fixtures", "ipc-parent-bun.js")], {
+    stdio: ["ignore", "pipe", "pipe"],
+  });
+  await child.exited;
+  expect(await new Response(child.stdout).text()).toEqual(
+    `p start
+p end
+c start
+c end
+c I am your father
+p I am your father
+`,
+  );
+  expect(await new Response(child.stderr).text()).toEqual("");
+});

test/js/bun/spawn/spawn.ipc.node-bun.test.ts

@@ -0,0 +1,22 @@
+import { spawn } from "bun";
+import { test, expect, it } from "bun:test";
+import { bunExe, nodeExe } from "harness";
+import path from "path";
+
+test("ipc with json serialization still works when bun is not the parent and the child", async () => {
+  // prettier-ignore
+  const child = Bun.spawn(["node", "--no-warnings", path.resolve(import.meta.dir, "fixtures", "ipc-parent-node.js"), bunExe()], {
+    stdio: ["ignore", "pipe", "pipe"],
+  });
+  await child.exited;
+  expect(await new Response(child.stderr).text()).toEqual("");
+  expect(await new Response(child.stdout).text()).toEqual(
+    `p start
+p end
+c start
+c end
+c I am your father
+p I am your father
+`,
+  );
+});