Context

Attach per-request data such as the caller, then read it inside any procedure.

The type argument to tacho<C>() is the context shape. handle() puts req on context. Pass createContext to merge more.

import { const tacho: <C extends Context = {}>() => Builder<C, undefined, unique symbol>tacho } from "tacho";
import { function handle<R extends AnyRouter, C extends Context = {}>(router: R, opts?: HandleOptions<C>): (request: Request) => Promise<Response>handle } from "tacho/transport/fetch";

const 
const rpc: Builder<{
    req: Request;
    user?: string;
}, undefined, unique symbol>rpc = 
tacho<{
    req: Request;
    user?: string;
}>(): Builder<{
    req: Request;
    user?: string;
}, undefined, unique symbol>tacho<{ req: Requestreq: Request; user?: string | undefineduser?: string }>();

export const 
const router: {
    me: ProcedureDef<{
        req: Request;
        user?: string;
    }, undefined, string | undefined>;
}router = 
const rpc: <{
    me: ProcedureDef<{
        req: Request;
        user?: string;
    }, undefined, string | undefined>;
}>(def: {
    me: ProcedureDef<{
        req: Request;
        user?: string;
    }, undefined, string | undefined>;
}) => {
    me: ProcedureDef<{
        req: Request;
        user?: string;
    }, undefined, string | undefined>;
}rpc({
  
me: ProcedureDef<{
    req: Request;
    user?: string;
}, undefined, string | undefined>me: 
const rpc: Builder<{
    req: Request;
    user?: string;
}, undefined, unique symbol>rpc.
run: <string | undefined>(fn: (opts: {
    input: undefined;
    ctx: {
        req: Request;
        user?: string;
    };
}) => string | Promise<string | undefined> | undefined) => ProcedureDef<{
    req: Request;
    user?: string;
}, undefined, string | undefined>run(({ 
ctx: {
    req: Request;
    user?: string;
}ctx }) => 
ctx: {
    req: Request;
    user?: string;
}ctx.user?: string | undefineduser),
});

handle<{
    me: ProcedureDef<{
        req: Request;
        user?: string;
    }, undefined, string | undefined>;
}, {
    user: string | undefined;
}>(router: {
    me: ProcedureDef<{
        req: Request;
        user?: string;
    }, undefined, string | undefined>;
}, opts?: HandleOptions<{
    user: string | undefined;
}> | undefined): (request: Request) => Promise<Response>handle(
const router: {
    me: ProcedureDef<{
        req: Request;
        user?: string;
    }, undefined, string | undefined>;
}router, {
  
createContext?: ((req: Request) => {
    user: string | undefined;
} | Promise<{
    user: string | undefined;
}>) | undefinedcreateContext: (req: Requestreq) => ({
    user: string | undefineduser: req: Requestreq.Request.headers: Headers
The **`headers`** read-only property of the Request interface contains the Headers object associated with the request.

[MDN Reference](https://developer.mozilla.org/docs/Web/API/Request/headers)headers.Headers.get(name: string): string | null
The **`get()`** method of the Headers interface returns a byte string of all the values of a header within a Headers object with a given name. If the requested header doesn't exist in the Headers object, it returns null.

[MDN Reference](https://developer.mozilla.org/docs/Web/API/Headers/get)get("x-user") ?? var undefinedundefined,
  }),
});

Throw from createContext → JSON-RPC INTERNAL_ERROR.

Set context per call in middleware with next({ ctx }):

import { class RpcErrorRpcError, const tacho: <C extends Context = {}>() => Builder<C, undefined, unique symbol>tacho } from "tacho";

const 
const rpc: Builder<{
    req: Request;
    user?: string;
}, undefined, unique symbol>rpc = 
tacho<{
    req: Request;
    user?: string;
}>(): Builder<{
    req: Request;
    user?: string;
}, undefined, unique symbol>tacho<{ req: Requestreq: Request; user?: string | undefineduser?: string }>();

const 
const withUser: Builder<{
    req: Request;
    user?: string;
}, undefined, unique symbol>withUser = 
const rpc: Builder<{
    req: Request;
    user?: string;
}, undefined, unique symbol>rpc.
function use(mw: Middleware<{
    req: Request;
    user?: string;
}>): Builder<{
    req: Request;
    user?: string;
}, undefined, unique symbol>use(async ({ 
ctx: {
    req: Request;
    user?: string;
}ctx, 
next: (opts?: {
    ctx: Partial<{
        req: Request;
        user?: string;
    }>;
} | undefined) => Promise<unknown>next }) => {
  const const user: string | nulluser = 
ctx: {
    req: Request;
    user?: string;
}ctx.req: Requestreq.Request.headers: Headers
The **`headers`** read-only property of the Request interface contains the Headers object associated with the request.

[MDN Reference](https://developer.mozilla.org/docs/Web/API/Request/headers)headers.Headers.get(name: string): string | null
The **`get()`** method of the Headers interface returns a byte string of all the values of a header within a Headers object with a given name. If the requested header doesn't exist in the Headers object, it returns null.

[MDN Reference](https://developer.mozilla.org/docs/Web/API/Headers/get)get("x-user");
  if (!const user: string | nulluser) {
    throw new 
new RpcError({ code, message, data }: {
    code: number;
    message: string;
    data?: unknown;
}): RpcErrorRpcError({ code: numbercode: -32001, message: stringmessage: "unauthorized" });
  }
  return 
next: (opts?: {
    ctx: Partial<{
        req: Request;
        user?: string;
    }>;
} | undefined) => Promise<unknown>next({ 
ctx: Partial<{
    req: Request;
    user?: string;
}>ctx: { user?: string | undefineduser } });
});

export const 
const router: {
    me: ProcedureDef<{
        req: Request;
        user?: string;
    }, undefined, string | undefined>;
}router = 
const rpc: <{
    me: ProcedureDef<{
        req: Request;
        user?: string;
    }, undefined, string | undefined>;
}>(def: {
    me: ProcedureDef<{
        req: Request;
        user?: string;
    }, undefined, string | undefined>;
}) => {
    me: ProcedureDef<{
        req: Request;
        user?: string;
    }, undefined, string | undefined>;
}rpc({
  
me: ProcedureDef<{
    req: Request;
    user?: string;
}, undefined, string | undefined>me: 
const withUser: Builder<{
    req: Request;
    user?: string;
}, undefined, unique symbol>withUser.
run: <string | undefined>(fn: (opts: {
    input: undefined;
    ctx: {
        req: Request;
        user?: string;
    };
}) => string | Promise<string | undefined> | undefined) => ProcedureDef<{
    req: Request;
    user?: string;
}, undefined, string | undefined>run(({ 
ctx: {
    req: Request;
    user?: string;
}ctx }) => 
ctx: {
    req: Request;
    user?: string;
}ctx.user?: string | undefineduser),
});