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fix(transcript-server): normalize Accept header for lenient MCP compatibility #287

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a5d117f
fix(transcript-server): normalize Accept header for lenient MCP compa…
ochafik Jan 16, 2026
3c1cc34
fix(examples): normalize Accept header for all MCP servers
ochafik Jan 16, 2026
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57 changes: 55 additions & 2 deletions examples/basic-server-preact/main.ts
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -13,9 +13,44 @@ import { createMcpExpressApp } from "@modelcontextprotocol/sdk/server/express.js
import type { McpServer } from "@modelcontextprotocol/sdk/server/mcp.js";
import { StreamableHTTPServerTransport } from "@modelcontextprotocol/sdk/server/streamableHttp.js";
import cors from "cors";
import type { Request, Response } from "express";
import type { Request, Response, NextFunction } from "express";
import { createServer } from "./server.js";

/**
* Normalize Accept header for lenient MCP compatibility.
* The SDK requires 'application/json, text/event-stream' but some clients send wildcard Accept headers.
* We must patch rawHeaders because @hono/node-server reads from there, not req.headers.
*/
function normalizeAcceptHeader(
req: Request,
_res: Response,
next: NextFunction,
): void {
const accept = req.headers.accept;
if (!accept || accept === "*/*") {
const normalized = "application/json, text/event-stream";
req.headers.accept = normalized;

// Patch rawHeaders for @hono/node-server compatibility
const nodeReq = req as unknown as { rawHeaders: string[] };
const newRawHeaders: string[] = [];
let found = false;
for (let i = 0; i < nodeReq.rawHeaders.length; i += 2) {
if (nodeReq.rawHeaders[i].toLowerCase() === "accept") {
newRawHeaders.push(nodeReq.rawHeaders[i], normalized);
found = true;
} else {
newRawHeaders.push(nodeReq.rawHeaders[i], nodeReq.rawHeaders[i + 1]);
}
}
if (!found) {
newRawHeaders.push("Accept", normalized);
}
Object.defineProperty(nodeReq, "rawHeaders", { value: newRawHeaders });
}
next();
}

export interface ServerOptions {
port: number;
name?: string;
Expand All @@ -35,8 +70,9 @@ export async function startServer(

const app = createMcpExpressApp({ host: "0.0.0.0" });
app.use(cors());
app.use(normalizeAcceptHeader);

app.all("/mcp", async (req: Request, res: Response) => {
app.post("/mcp", async (req: Request, res: Response) => {
const server = createServer();
const transport = new StreamableHTTPServerTransport({
sessionIdGenerator: undefined,
Expand All @@ -62,6 +98,23 @@ export async function startServer(
}
});

// GET and DELETE not supported in stateless mode
app.get("/mcp", (_req: Request, res: Response) => {
res.status(405).json({
jsonrpc: "2.0",
error: { code: -32000, message: "Method not allowed in stateless mode" },
id: null,
});
});

app.delete("/mcp", (_req: Request, res: Response) => {
res.status(405).json({
jsonrpc: "2.0",
error: { code: -32000, message: "Method not allowed in stateless mode" },
id: null,
});
});

const httpServer = app.listen(port, (err) => {
if (err) {
console.error("Failed to start server:", err);
Expand Down
57 changes: 55 additions & 2 deletions examples/basic-server-react/main.ts
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -9,9 +9,44 @@ import type { McpServer } from "@modelcontextprotocol/sdk/server/mcp.js";
import { StdioServerTransport } from "@modelcontextprotocol/sdk/server/stdio.js";
import { StreamableHTTPServerTransport } from "@modelcontextprotocol/sdk/server/streamableHttp.js";
import cors from "cors";
import type { Request, Response } from "express";
import type { Request, Response, NextFunction } from "express";
import { createServer } from "./server.js";

/**
* Normalize Accept header for lenient MCP compatibility.
* The SDK requires 'application/json, text/event-stream' but some clients send wildcard Accept headers.
* We must patch rawHeaders because @hono/node-server reads from there, not req.headers.
*/
function normalizeAcceptHeader(
req: Request,
_res: Response,
next: NextFunction,
): void {
const accept = req.headers.accept;
if (!accept || accept === "*/*") {
const normalized = "application/json, text/event-stream";
req.headers.accept = normalized;

// Patch rawHeaders for @hono/node-server compatibility
const nodeReq = req as unknown as { rawHeaders: string[] };
const newRawHeaders: string[] = [];
let found = false;
for (let i = 0; i < nodeReq.rawHeaders.length; i += 2) {
if (nodeReq.rawHeaders[i].toLowerCase() === "accept") {
newRawHeaders.push(nodeReq.rawHeaders[i], normalized);
found = true;
} else {
newRawHeaders.push(nodeReq.rawHeaders[i], nodeReq.rawHeaders[i + 1]);
}
}
if (!found) {
newRawHeaders.push("Accept", normalized);
}
Object.defineProperty(nodeReq, "rawHeaders", { value: newRawHeaders });
}
next();
}

export interface ServerOptions {
port: number;
name?: string;
Expand All @@ -31,8 +66,9 @@ export async function startServer(

const app = createMcpExpressApp({ host: "0.0.0.0" });
app.use(cors());
app.use(normalizeAcceptHeader);

app.all("/mcp", async (req: Request, res: Response) => {
app.post("/mcp", async (req: Request, res: Response) => {
const server = createServer();
const transport = new StreamableHTTPServerTransport({
sessionIdGenerator: undefined,
Expand All @@ -58,6 +94,23 @@ export async function startServer(
}
});

// GET and DELETE not supported in stateless mode
app.get("/mcp", (_req: Request, res: Response) => {
res.status(405).json({
jsonrpc: "2.0",
error: { code: -32000, message: "Method not allowed in stateless mode" },
id: null,
});
});

app.delete("/mcp", (_req: Request, res: Response) => {
res.status(405).json({
jsonrpc: "2.0",
error: { code: -32000, message: "Method not allowed in stateless mode" },
id: null,
});
});

const httpServer = app.listen(port, (err) => {
if (err) {
console.error("Failed to start server:", err);
Expand Down
57 changes: 55 additions & 2 deletions examples/basic-server-solid/main.ts
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -13,9 +13,44 @@ import { createMcpExpressApp } from "@modelcontextprotocol/sdk/server/express.js
import type { McpServer } from "@modelcontextprotocol/sdk/server/mcp.js";
import { StreamableHTTPServerTransport } from "@modelcontextprotocol/sdk/server/streamableHttp.js";
import cors from "cors";
import type { Request, Response } from "express";
import type { Request, Response, NextFunction } from "express";
import { createServer } from "./server.js";

/**
* Normalize Accept header for lenient MCP compatibility.
* The SDK requires 'application/json, text/event-stream' but some clients send wildcard Accept headers.
* We must patch rawHeaders because @hono/node-server reads from there, not req.headers.
*/
function normalizeAcceptHeader(
req: Request,
_res: Response,
next: NextFunction,
): void {
const accept = req.headers.accept;
if (!accept || accept === "*/*") {
const normalized = "application/json, text/event-stream";
req.headers.accept = normalized;

// Patch rawHeaders for @hono/node-server compatibility
const nodeReq = req as unknown as { rawHeaders: string[] };
const newRawHeaders: string[] = [];
let found = false;
for (let i = 0; i < nodeReq.rawHeaders.length; i += 2) {
if (nodeReq.rawHeaders[i].toLowerCase() === "accept") {
newRawHeaders.push(nodeReq.rawHeaders[i], normalized);
found = true;
} else {
newRawHeaders.push(nodeReq.rawHeaders[i], nodeReq.rawHeaders[i + 1]);
}
}
if (!found) {
newRawHeaders.push("Accept", normalized);
}
Object.defineProperty(nodeReq, "rawHeaders", { value: newRawHeaders });
}
next();
}

export interface ServerOptions {
port: number;
name?: string;
Expand All @@ -35,8 +70,9 @@ export async function startServer(

const app = createMcpExpressApp({ host: "0.0.0.0" });
app.use(cors());
app.use(normalizeAcceptHeader);

app.all("/mcp", async (req: Request, res: Response) => {
app.post("/mcp", async (req: Request, res: Response) => {
const server = createServer();
const transport = new StreamableHTTPServerTransport({
sessionIdGenerator: undefined,
Expand All @@ -62,6 +98,23 @@ export async function startServer(
}
});

// GET and DELETE not supported in stateless mode
app.get("/mcp", (_req: Request, res: Response) => {
res.status(405).json({
jsonrpc: "2.0",
error: { code: -32000, message: "Method not allowed in stateless mode" },
id: null,
});
});

app.delete("/mcp", (_req: Request, res: Response) => {
res.status(405).json({
jsonrpc: "2.0",
error: { code: -32000, message: "Method not allowed in stateless mode" },
id: null,
});
});

const httpServer = app.listen(port, (err) => {
if (err) {
console.error("Failed to start server:", err);
Expand Down
57 changes: 55 additions & 2 deletions examples/basic-server-svelte/main.ts
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -13,9 +13,44 @@ import { createMcpExpressApp } from "@modelcontextprotocol/sdk/server/express.js
import type { McpServer } from "@modelcontextprotocol/sdk/server/mcp.js";
import { StreamableHTTPServerTransport } from "@modelcontextprotocol/sdk/server/streamableHttp.js";
import cors from "cors";
import type { Request, Response } from "express";
import type { Request, Response, NextFunction } from "express";
import { createServer } from "./server.js";

/**
* Normalize Accept header for lenient MCP compatibility.
* The SDK requires 'application/json, text/event-stream' but some clients send wildcard Accept headers.
* We must patch rawHeaders because @hono/node-server reads from there, not req.headers.
*/
function normalizeAcceptHeader(
req: Request,
_res: Response,
next: NextFunction,
): void {
const accept = req.headers.accept;
if (!accept || accept === "*/*") {
const normalized = "application/json, text/event-stream";
req.headers.accept = normalized;

// Patch rawHeaders for @hono/node-server compatibility
const nodeReq = req as unknown as { rawHeaders: string[] };
const newRawHeaders: string[] = [];
let found = false;
for (let i = 0; i < nodeReq.rawHeaders.length; i += 2) {
if (nodeReq.rawHeaders[i].toLowerCase() === "accept") {
newRawHeaders.push(nodeReq.rawHeaders[i], normalized);
found = true;
} else {
newRawHeaders.push(nodeReq.rawHeaders[i], nodeReq.rawHeaders[i + 1]);
}
}
if (!found) {
newRawHeaders.push("Accept", normalized);
}
Object.defineProperty(nodeReq, "rawHeaders", { value: newRawHeaders });
}
next();
}

export interface ServerOptions {
port: number;
name?: string;
Expand All @@ -35,8 +70,9 @@ export async function startServer(

const app = createMcpExpressApp({ host: "0.0.0.0" });
app.use(cors());
app.use(normalizeAcceptHeader);

app.all("/mcp", async (req: Request, res: Response) => {
app.post("/mcp", async (req: Request, res: Response) => {
const server = createServer();
const transport = new StreamableHTTPServerTransport({
sessionIdGenerator: undefined,
Expand All @@ -62,6 +98,23 @@ export async function startServer(
}
});

// GET and DELETE not supported in stateless mode
app.get("/mcp", (_req: Request, res: Response) => {
res.status(405).json({
jsonrpc: "2.0",
error: { code: -32000, message: "Method not allowed in stateless mode" },
id: null,
});
});

app.delete("/mcp", (_req: Request, res: Response) => {
res.status(405).json({
jsonrpc: "2.0",
error: { code: -32000, message: "Method not allowed in stateless mode" },
id: null,
});
});

const httpServer = app.listen(port, (err) => {
if (err) {
console.error("Failed to start server:", err);
Expand Down
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