fix iterating stack trace (#3600)

* `i + 1` and remove `defer`

* a test

* fix test

3 files changed, 26 insertions, 3 deletions

diff --git a/src/bun.js/bindings/exports.zig b/src/bun.js/bindings/exports.zig
index db6de2ef3..e9e9d3a8d 100644
--- a/src/bun.js/bindings/exports.zig
+++ b/src/bun.js/bindings/exports.zig
@@ -460,7 +460,7 @@ pub const ZigStackTrace = extern struct {
             var source_line_len = source_lines_iter.getLength();
 
             if (source_line_len > 0) {
-                var source_lines = try allocator.alloc(Api.SourceLine, @intCast(usize, @max(source_lines_iter.i, 0)));
+                var source_lines = try allocator.alloc(Api.SourceLine, @intCast(usize, @max(source_lines_iter.i + 1, 0)));
                 var source_line_buf = try allocator.alloc(u8, source_line_len);
                 source_lines_iter = this.sourceLineIterator();
                 var remain_buf = source_line_buf[0..];
@@ -468,7 +468,7 @@ pub const ZigStackTrace = extern struct {
                 while (source_lines_iter.next()) |source| {
                     const text = source.text.slice();
                     defer source.text.deinit();
-                    defer bun.copy(
+                    bun.copy(
                         u8,
                         remain_buf,
                         text,
@@ -515,7 +515,7 @@ pub const ZigStackTrace = extern struct {
 
         pub fn getLength(this: *SourceLineIterator) usize {
             var count: usize = 0;
-            for (this.trace.source_lines_ptr[0..@intCast(usize, this.i)]) |*line| {
+            for (this.trace.source_lines_ptr[0..@intCast(usize, this.i + 1)]) |*line| {
                 count += line.length();
             }
 
diff --git a/test/js/bun/http/error-response.js b/test/js/bun/http/error-response.js
new file mode 100644
index 000000000..3284c146b
--- /dev/null
+++ b/test/js/bun/http/error-response.js
@@ -0,0 +1,8 @@
+const s = Bun.serve({
+  fetch(req, res) {
+    s.stop(true);
+    throw new Error("1");
+  },
+  port: 0,
+});
+fetch(`http://${s.hostname}:${s.port}`).then(res => console.log(res.status));
diff --git a/test/js/bun/http/serve.test.ts b/test/js/bun/http/serve.test.ts
index 7182ba68d..bba35c085 100644
--- a/test/js/bun/http/serve.test.ts
+++ b/test/js/bun/http/serve.test.ts
@@ -2,8 +2,10 @@ import { file, gc, Serve, serve, Server } from "bun";
 import { afterEach, describe, it, expect, afterAll } from "bun:test";
 import { readFileSync, writeFileSync } from "fs";
 import { resolve } from "path";
+import { bunExe, bunEnv } from "harness";
 import { renderToReadableStream } from "react-dom/server";
 import app_jsx from "./app.jsx";
+import { spawn } from "child_process";
 
 type Handler = (req: Request) => Response;
 afterEach(() => gc(true));
@@ -980,6 +982,19 @@ describe("should support Content-Range with Bun.file()", () => {
   }
 });
 
+it("formats error responses correctly", async () => {
+  const c = spawn(bunExe(), ["./error-response.js"], { cwd: import.meta.dir, env: bunEnv });
+
+  var output = "";
+  c.stderr.on("data", chunk => {
+    output += chunk.toString();
+  });
+  c.stderr.on("end", () => {
+    expect(output).toContain('throw new Error("1");');
+    c.kill();
+  });
+});
+
 it("request body and signal life cycle", async () => {
   {
     const headers = {