Generating WIT/WebAssembly Component for WebTransport server (WebAssembly Core Module) #1362

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1. vados-cosmonic commented on Apr 6, 2026

   

   vados-cosmonic

   on Apr 6, 2026

   Last edited by vados-cosmonic

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   Glad you're making progress but this to be clear, this issue is actually outside the scope of Jco -- we deal with WebAssembly components (or taking JS to build them, but that is outsourced essentially to componentize-js) and generate code to enable running in node (and experimentally the browser, but that implementation is pretty incomplete as of now).

   That said, with regards to the work you're doing it seems like you may benefit from:

   • Using wit-bindgen for C (example in the component model docs should help here), and building your Zig against the generated headers
   • Compile your Zig code to a wasi p1 component adhereing to the interfaces generated (this may or may not require using wasi-libc)
   • Adapting your P1 component to a P2 component with wasm-tools after embedding the WIT metadata (see README) (the p1 adapter codebase is upstream if you are curious)

   Assuming you have added implementations to interfaces generated by wit-bindgen, hooked that to your Zig code, you should get a component that works and adheres to the WIT world that you create.

   I do not think you need to use wasm2js here, but if you insist then you'd have to convert your JS code to a component with a tool like componentize-js (or jco componentize).

   Zulip is the right place to discuss/bat around ideas on this, rather than an issue on the Jco repo -- maybe if we had discussions enabled or something that might also work but for now we do not.

   I'm going to close this out for now since it's not a Jco issue per-say, but we can keep discussing here or on Zulip
2. vados-cosmonic

   closed this as completedon Apr 6, 2026
3. guest271314 commented on Apr 6, 2026

   

   guest271314

   on Apr 6, 2026

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   @vados-cosmonic Well, I don't need WASI for this. To me looks like there's a bug in wasm-tools. Unles you can explain what's wrong with this WIT. jco throws at the same place, because jco depends on wasm-tools

   ../wasm-tools/wasm-tools component embed ./quic.wit ./quic.wasm -o quic.embedded.wasm
   

   That works.

   This throws

    ../wasm-tools/wasm-tools component new quic.embedded.wasm -o quic.component.wasm
   error: failed to encode a component from module
   

   package local:quic-wasm;
   
   world quic-wasm-world {
     import env: interface {
       console-log: func(argv: string);
       get-time-ns: func() -> u64;
       random-fill: func(argv: list<u8>);
     }
     export qz-set-cert: func(argv: list<u8>) -> u32;
     export qz-set-key: func(argv: list<u8>) -> u32;
     export qz-init-server: func() -> u32;
     export qz-init-client: func() -> u32;
     export qz-deinit: func();
     export qz-recv-packet: func(argv: list<u8>) -> u32;
     export qz-send-packets: func(argv: list<u8>) -> u32;
     export qz-on-timeout: func();
     export qz-next-timeout-ns: func() -> u64;
     export qz-is-established: func() -> u32;
     export qz-is-closed: func() -> u32;
     export qz-poll-event: func(argv: list<u8>) -> u32;
     export qz-stream-send: func(argv0: u64, argv1: list<u8>) -> u32;
     export qz-stream-close: func(argv: u64);
     export qz-stream-read: func(argv0: u64, argv1: list<u8>) -> u32;
     export qz-datagram-send: func(argv: list<u8>) -> u32;
     export qz-datagram-recv: func(argv: list<u8>) -> u32;
     export qz-wt-accept-session: func(argv: u64) -> u32;
     export qz-wt-read-stream: func(argv0: u64, argv1: list<u8>) -> u32;
     export qz-wt-send-stream: func(argv0: u64, argv1: list<u8>) -> u32;
     export qz-wt-close-stream: func(argv: u64);
     export qz-wt-read-datagram: func(argv0: u64, argv1: list<u8>) -> u32;
     export qz-wt-send-datagram: func(argv0: u64, argv1: list<u8>) -> u32;
     export qz-wt-close-session: func(argv0: u64, argv1: list<u8>, argv2: u32) -> u32;
     export qz-alloc: func(argv: u32) -> u32;
     export qz-free: func(argv: list<u8>);
   }
   
   
4. guest271314 commented on Apr 6, 2026

   

   guest271314

   on Apr 6, 2026

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   Seems to me that you folks should have a very basic WIT generating script that accepts WAT file

   // WIT Generator Script
   // https://share.google/aimode/8MIUn7InsCSvw9Uxv
   const fs = require('fs');
   const path = require('path');
   
   const mapT = t => ({ i32: 'u32', i64: 'u64', f32: 'float32', f64: 'float64' }[t] || 'u32');
   
   function buildS(p, r, n) {
     let raw = [];
     for (let i = 0; i < p.length; i++) {
       if (i + 1 < p.length && p[i] === 'i32' && p[i+1] === 'i32') {
         raw.push(/log|name|path|uri/.test(n.toLowerCase()) ? 'string' : 'list<u8>');
         i++;
       } else raw.push(mapT(p[i]));
     }
     const ps = raw.length === 1 ? `argv: ${raw[0]}` : raw.map((t, i) => `argv${i}: ${t}`).join(', ');
     const res = r.map(mapT);
     const rs = res.length === 1 ? ` -> ${res[0]}` : res.length > 1 ? ` -> tuple<${res.join(', ')}>` : '';
     return `func(${ps})${rs}`;
   }
   
   function watToWit(p) {
     const c = fs.readFileSync(p, 'utf8');
     const base = path.basename(p, path.extname(p)).replace(/_/g, '-').toLowerCase();
     
     const types = {};
     [...c.matchAll(/\(type\s+\(;(\d+);\)\s+\(func\s+((?:\(param\s+[^)]+\)\s*)*)\s*((?:\(result\s+[^)]+\)\s*)*)\)\)/g)]
       .forEach(m => types[m[1]] = { p: m[2].match(/i32|i64|f32|f64/g) || [], r: m[3].match(/i32|i64|f32|f64/g) || [] });
   
     const f2t = {};
     [...c.matchAll(/\(func\s+(?:\$[^\s]+\s+)?\(;(\d+);\)\s+\(type\s+(\d+)\)/g)]
       .forEach(m => f2t[m[1]] = m[2]);
   
     let wit = [`package local:${base};`, '', `world ${base}-world {`];
     const ims = {};
     [...c.matchAll(/\(import\s+"([^"]+)"\s+"([^"]+)"\s+\(func\s+(?:\$[^\s]+\s+)?\(;(\d+);\)/g)]
       .forEach(m => {
         const [_, mod, field, fIdx] = m;
         if (!ims[mod]) ims[mod] = [];
         const t = types[f2t[fIdx]] || { p: [], r: [] };
         ims[mod].push(`    ${field.replace(/_/g, '-')}: ${buildS(t.p, t.r, field)};`);
       });
   
     Object.entries(ims).forEach(([m, fs]) => {
       wit.push(`  import ${m.replace(/_/g, '-')}: interface {`, ...fs, `  }`);
     });
   
     [...c.matchAll(/\(export\s+"([^"]+)"\s+\(func\s+(\d+)\)\)/g)]
       .forEach(m => {
         const [_, name, fIdx] = m;
         if (name === 'memory') return;
         const t = types[f2t[fIdx]] || { p: [], r: [] };
         wit.push(`  export ${name.replace(/_/g, '-')}: ${buildS(t.p, t.r, name)};`);
       });
   
     return wit.concat('}').join('\n');
   }
   
   const args = process.argv.slice(2);
   if (args.length > 0) console.log(watToWit(args[0]));
   
   
5. guest271314 commented on Apr 6, 2026

   

   guest271314

   on Apr 6, 2026

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   Now, jco was able to generate the types. So I don't get why jco and wasm-tools broke on creating the component thingy

   // world local:quic-wasm/quic-wasm-world
   export type * as Env from './interfaces/env.js'; // import env
   export function qzSetCert(argv: Uint8Array): number;
   export function qzSetKey(argv: Uint8Array): number;
   export function qzInitServer(): number;
   export function qzInitClient(): number;
   export function qzDeinit(): void;
   export function qzRecvPacket(argv: Uint8Array): number;
   export function qzSendPackets(argv: Uint8Array): number;
   export function qzOnTimeout(): void;
   export function qzNextTimeoutNs(): bigint;
   export function qzIsEstablished(): number;
   export function qzIsClosed(): number;
   export function qzPollEvent(argv: Uint8Array): number;
   export function qzStreamSend(argv0: bigint, argv1: Uint8Array): number;
   export function qzStreamClose(argv: bigint): void;
   export function qzStreamRead(argv0: bigint, argv1: Uint8Array): number;
   export function qzDatagramSend(argv: Uint8Array): number;
   export function qzDatagramRecv(argv: Uint8Array): number;
   export function qzWtAcceptSession(argv: bigint): number;
   export function qzWtReadStream(argv0: bigint, argv1: Uint8Array): number;
   export function qzWtSendStream(argv0: bigint, argv1: Uint8Array): number;
   export function qzWtCloseStream(argv: bigint): void;
   export function qzWtReadDatagram(argv0: bigint, argv1: Uint8Array): number;
   export function qzWtSendDatagram(argv0: bigint, argv1: Uint8Array): number;
   export function qzWtCloseSession(argv0: bigint, argv1: Uint8Array, argv2: number): number;
   export function qzAlloc(argv: number): number;
   export function qzFree(argv: Uint8Array): void;
   
   

   /** @module Interface env **/
   export function consoleLog(argv: string): void;
   export function getTimeNs(): bigint;
   export function randomFill(argv: Uint8Array): void;
   
   
6. vados-cosmonic commented on Apr 6, 2026

   

   vados-cosmonic

   on Apr 6, 2026

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   Glad you were able to make progress -- not sure why wasm-tools component new didn't work for you (that seems like a bug that should be filed upstream if the failure was legitimate), but if you were able to get what you wanted working, great!