fix(http): preserve header case for node:http requests

Fixes #7520

The node:http module was lowercasing all HTTP header names when sending
requests, while Node.js preserves the original case. This was caused by
passing `this.getHeaders()` (which returns a plain object with lowercased
keys via `headers.toJSON()`) instead of the Headers object directly.

This commit changes `_http_client.ts` to pass `this[headersSymbol]` (the
raw Headers object) to the fetch call, which allows the existing header
case preservation logic (added in #26425) to work correctly for node:http
requests.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/js/node/_http_client.ts

@@ -51,6 +51,7 @@ const {
   reqSymbol,
   callCloseCallback,
   emitCloseNTAndComplete,
+  headersSymbol,
 } = require("internal/http");
 
 const { globalAgent } = require("node:_http_agent");
@@ -312,7 +313,8 @@ function ClientRequest(input, options, cb) {
 
       const fetchOptions: any = {
         method,
-        headers: this.getHeaders(),
+        // Use Headers object directly to preserve original header case (not getHeaders() which lowercases keys)
+        headers: this[headersSymbol],
         redirect: "manual",
         signal: this[kAbortController]?.signal,
         // Timeouts are handled via this.setTimeout.

test/regression/issue/07520.test.ts

@@ -0,0 +1,174 @@
+import { expect, test } from "bun:test";
+import http from "node:http";
+import { createServer as createTcpServer, type Server } from "node:net";
+
+// Issue #7520: node:http module lowercases HTTP header names when sending requests
+// Node.js preserves the original case of header names, but Bun was lowercasing them.
+// This test verifies that header names are preserved in their original case.
+
+interface HeaderCapturingServer {
+  server: Server;
+  port: number;
+  getReceivedData: () => string;
+  waitForHeaders: Promise<void>;
+}
+
+function createHeaderCapturingServer(): Promise<HeaderCapturingServer> {
+  return new Promise(resolveSetup => {
+    let receivedData = "";
+    let headersDone = false;
+    const { promise: waitForHeaders, resolve: resolveHeaders } = Promise.withResolvers<void>();
+
+    const server = createTcpServer(socket => {
+      socket.on("data", data => {
+        if (headersDone) return;
+        receivedData += data.toString();
+        if (receivedData.includes("\r\n\r\n")) {
+          headersDone = true;
+          socket.write("HTTP/1.1 200 OK\r\nContent-Length: 2\r\n\r\nOK");
+          socket.end();
+          resolveHeaders();
+        }
+      });
+    });
+
+    server.listen(0, () => {
+      const port = (server.address() as { port: number }).port;
+      resolveSetup({
+        server,
+        port,
+        getReceivedData: () => receivedData,
+        waitForHeaders,
+      });
+    });
+  });
+}
+
+test("node:http request preserves header case for custom headers", async () => {
+  const { server, port, getReceivedData, waitForHeaders } = await createHeaderCapturingServer();
+
+  try {
+    const req = http.request(
+      {
+        hostname: "localhost",
+        port: port,
+        path: "/",
+        method: "GET",
+        headers: {
+          "X-Custom-Header": "test-value",
+          "X-Another-Header": "another-value",
+          Authorization: "Bearer token123",
+          "Content-Type": "application/json",
+        },
+      },
+      (res: any) => {
+        res.on("data", () => {});
+        res.on("end", () => {});
+      },
+    );
+
+    req.on("error", () => {});
+    req.end();
+
+    await waitForHeaders;
+
+    const receivedData = getReceivedData();
+
+    // Verify headers are sent with correct casing (not lowercased)
+    expect(receivedData).toInclude("X-Custom-Header: test-value");
+    expect(receivedData).toInclude("X-Another-Header: another-value");
+    expect(receivedData).toInclude("Authorization: Bearer token123");
+    expect(receivedData).toInclude("Content-Type: application/json");
+
+    // Make sure they're NOT lowercased
+    expect(receivedData).not.toInclude("x-custom-header:");
+    expect(receivedData).not.toInclude("x-another-header:");
+    expect(receivedData).not.toInclude("authorization:");
+    expect(receivedData).not.toInclude("content-type:");
+  } finally {
+    server.close();
+  }
+});
+
+test("node:http request preserves header case for POST requests", async () => {
+  const { server, port, getReceivedData, waitForHeaders } = await createHeaderCapturingServer();
+
+  try {
+    const req = http.request(
+      {
+        hostname: "localhost",
+        port: port,
+        path: "/",
+        method: "POST",
+        headers: {
+          "X-Request-ID": "12345",
+          "Content-Type": "application/json",
+        },
+      },
+      (res: any) => {
+        res.on("data", () => {});
+        res.on("end", () => {});
+      },
+    );
+
+    req.on("error", () => {});
+    req.write('{"test": true}');
+    req.end();
+
+    await waitForHeaders;
+
+    const receivedData = getReceivedData();
+
+    // Verify headers are sent with correct casing
+    expect(receivedData).toInclude("X-Request-ID: 12345");
+    expect(receivedData).toInclude("Content-Type: application/json");
+
+    // Make sure they're NOT lowercased
+    expect(receivedData).not.toInclude("x-request-id:");
+    expect(receivedData).not.toInclude("content-type:");
+  } finally {
+    server.close();
+  }
+});
+
+test("node:http request preserves header case when using setHeader()", async () => {
+  const { server, port, getReceivedData, waitForHeaders } = await createHeaderCapturingServer();
+
+  try {
+    const req = http.request({
+      hostname: "localhost",
+      port: port,
+      path: "/",
+      method: "GET",
+    });
+
+    // Set headers using setHeader() method
+    req.setHeader("X-Custom-Header", "value1");
+    req.setHeader("X-Another-Custom-Header", "value2");
+    req.setHeader("Authorization", "Bearer mytoken");
+
+    req.on("response", (res: any) => {
+      res.on("data", () => {});
+      res.on("end", () => {});
+    });
+
+    req.on("error", () => {});
+    req.end();
+
+    await waitForHeaders;
+
+    const receivedData = getReceivedData();
+
+    // Verify headers are sent with correct casing
+    expect(receivedData).toInclude("X-Custom-Header: value1");
+    expect(receivedData).toInclude("X-Another-Custom-Header: value2");
+    expect(receivedData).toInclude("Authorization: Bearer mytoken");
+
+    // Make sure they're NOT lowercased
+    expect(receivedData).not.toInclude("x-custom-header:");
+    expect(receivedData).not.toInclude("x-another-custom-header:");
+    expect(receivedData).not.toInclude("authorization:");
+  } finally {
+    server.close();
+  }
+});