lumbda/www/playground/c/lumbda-c.loader.js

// wasm/c/lumbda-c.loader.js
// C tier loader — Emscripten ES module factory.
//
// Exports createCTier({ baseURL }) -> Promise<{ evalLisp(src) -> Promise<string> }>.
// Output capture: Emscripten routes stdout/stderr through Module.print /
// Module.printErr callbacks. We accumulate per-eval and return joined.

async function _bootstrap() {
    // Use import.meta.url so paths resolve relative to THIS loader file —
    // not the caller. Works in both window and Worker contexts because both
    // have a defined import.meta.url for ES modules.
    const factoryURL = new URL("./lumbda-c.js", import.meta.url).href;
    const wasmDir = new URL("./", import.meta.url).href;
    const { default: createLumbdaC } = await import(/* @vite-ignore */ factoryURL);

    // Streaming output: every printf in the wasm fires Module.print
    // synchronously. We buffer normally for the final return, but if
    // the current eval registered an onChunk callback we also call
    // through immediately so the worker can postMessage a chunk to
    // the UI as each line emerges (vs the user staring at a blank
    // panel for 18 seconds during the heavy bend call).
    //
    // Emscripten's print convention is "one call per line WITHOUT
    // the trailing newline" — the caller is expected to add a \n
    // when reassembling. Our outBuf join adds it back, but the
    // streaming path needs it explicitly or successive chunks
    // concatenate horizontally in the output panel (saw with
    // (let loop ((i 0)) ... (display i) (newline) ... (loop ...))
    // — every tick ended up on the same line).
    let outBuf = [];
    let errBuf = [];
    let currentOnChunk = null;
    const module = await createLumbdaC({
        locateFile: (p) => wasmDir + p,
        print: (line) => {
            outBuf.push(line);
            if (currentOnChunk) currentOnChunk(line + "\n");
        },
        printErr: (line) => {
            errBuf.push(line);
            if (currentOnChunk) currentOnChunk(line + "\n");
        },
    });

    const _init = module.cwrap("lumbda_wasm_init", null, []);
    const _eval = module.cwrap("lumbda_wasm_eval", "number", ["string"]);
    const _free = module.cwrap("lumbda_wasm_free_result", null, ["number"]);

    _init();

    // /tmp must exist before (portal-snapshot! ...) writes there — the
    // C builtin fopen("w")s the path directly so a missing dir is a
    // hard error. Emscripten's MEMFS gives us /tmp on recent versions
    // but make it idempotent.
    try { module.FS.mkdir("/tmp"); } catch (e) { /* exists */ }

    // bend!-call host bridge — js_lumbda_bend_call inside the wasm
    // (EM_JS in lumbda_wasm_entry.c) reads globalThis._lumbdaCBendUrl
    // for the destination, then does sync XHR POST and writes the
    // response bytes back into the wasm heap. setBendUrl mutates that
    // global so runner.js can propagate a saved playground URL.
    return {
        setBendUrl(url) { globalThis._lumbdaCBendUrl = url || null; },
        // Pause hook — js_lumbda_pause_requested (the JS-library import
        // wired in bend-call-library.js) reads globalThis._lumbdaCPauseFlag
        // every K leval iterations. Setting it to an Int32Array view
        // over a SharedArrayBuffer lets the REPL signal a pause from
        // the main thread. Null disables (no COOP/COEP isolation).
        setPauseFlag(flag) {
            globalThis._lumbdaCPauseFlag = flag ? new Int32Array(flag) : null;
        },
        // portalSave / portalLoad bridge MEMFS to the JS side so the
        // REPL can persist checkpoints to the encrypted vault and
        // restore them on a fresh worker. Names come from the worker
        // (REPL caller validates alphanumeric) so path traversal isn't
        // a concern.
        portalSave(name) {
            const path = `/tmp/${name}.portal`;
            try {
                const bytes = module.FS.readFile(path);
                return new TextDecoder().decode(bytes);
            } catch (e) { return null; }
        },
        portalLoad(name, blob) {
            const path = `/tmp/${name}.portal`;
            module.FS.writeFile(path, blob);
        },
        async evalLisp(src, onChunk) {
            outBuf = [];
            errBuf = [];
            currentOnChunk = onChunk || null;
            const errPtr = _eval(src);
            currentOnChunk = null;
            let errMsg = "";
            if (errPtr) {
                errMsg = module.UTF8ToString(errPtr);
                _free(errPtr);
            }
            let out = outBuf.join("\n");
            if (out) out += "\n";
            if (errBuf.length) out += errBuf.join("\n") + "\n";
            if (errMsg) out += errMsg + "\n";
            return out;
        },
        heapStats() {
            // Emscripten exposes the linear memory directly. There's no
            // free path right now (LUMBDA_NO_BOEHM), so used = total —
            // every malloc accumulates until reload. Documented and
            // surfaced in the REPL so the user sees the pressure.
            //
            // HEAPU8 isn't always live: after a worker reboots, the
            // heap poll can fire while the new Module is mid-init and
            // HEAPU8 isn't yet wired. Return null so the REPL hides
            // the pressure indicator for that tick instead of crashing.
            const heap = module.HEAPU8;
            if (!heap) return null;
            const total = heap.byteLength;
            return { used: total, total };
        },
    };
}

// Closure-encapsulated singleton (see lumbda-c.loader.js for rationale).
export const createCTier = (() => {
    let tier = null;
    return async () => {
        if (!tier) tier = await _bootstrap();
        return tier;
    };
})();