pythonnative/src/pythonnative/devserver/static/bridge.js at main · pythonnative/pythonnative · GitHub

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// The page's half of the PythonNative bridge.

// Python (`pythonnative.bridge.web.WebTransport`) sends JSON arrays over

// one WebSocket. Fire-and-forget messages carry no id; requests carry an

// id in slot 1 and are answered with ["res", id, result]. The same shape

// works in the other direction: the page raises `callback(kind, tag,

// name, payload)` as ["cb", ...] (no reply) or ["req", id, ...] (Python

// answers with ["res", id, text]).

// Payloads that the native protocol carries as JSON *text* stay text

// here too (`args`, `request`, `payload`, `result`), so the page and

// Python reuse their existing codecs unchanged.

export class Bridge {

constructor(url) {

this.url = url;

this.socket = null;

this.nextId = 1;

this.pending = new Map(); // id -> {resolve}

this.handlers = {}; // kind -> async (message) => result

this.onOpen = null;

this.onClose = null;

this.onDev = null;

this.connected = false;

this._backoff = 500;

this._closedByUs = false;

}

connect() {

this._closedByUs = false;

let socket;

try {

socket = new WebSocket(this.url);

} catch (err) {

this._scheduleReconnect();

return;

}

this.socket = socket;

socket.addEventListener("open", () => {

this.connected = true;

this._backoff = 500;

if (this.onOpen) this.onOpen();

});

socket.addEventListener("message", (event) => this._onMessage(event.data));

socket.addEventListener("close", (event) => {

const wasConnected = this.connected;

this.connected = false;

this.socket = null;

for (const waiter of this.pending.values()) waiter.resolve(null);

this.pending.clear();

if (this.onClose) this.onClose(wasConnected, event);

if (!this._closedByUs) this._scheduleReconnect();

});

socket.addEventListener("error", () => {

/* close follows */

});

}

close() {

this._closedByUs = true;

if (this.socket) this.socket.close();

}

_scheduleReconnect() {

const delay = this._backoff;

this._backoff = Math.min(this._backoff * 1.5, 4000);

setTimeout(() => this.connect(), delay);

}

send(message) {

if (!this.socket || this.socket.readyState !== WebSocket.OPEN) return false;

this.socket.send(JSON.stringify(message));

return true;

}

// -- page -> Python -------------------------------------------------

/** Fire-and-forget callback: `callback(kind, tag, name, payload)`. */

callback(kind, tag, name, payload) {

return this.send(["cb", kind, tag, name, payload == null ? "" : payload]);

}

/** Callback that needs Python's answer (row binds, screen creation). */

request(kind, tag, name, payload) {

const id = this.nextId++;

return new Promise((resolve) => {

if (!this.send(["req", id, kind, tag, name, payload == null ? "" : payload])) {

resolve(null);

return;

}

this.pending.set(id, { resolve });

});

}

/** Dev-channel message (logs, errors) shown in the `pn start` terminal. */

dev(payload) {

return this.send(["dev", payload]);

}

// -- Python -> page -------------------------------------------------

async _onMessage(text) {

let message;

try {

message = JSON.parse(text);

} catch (err) {

console.error("[pn] malformed message", text.slice(0, 200));

return;

}

if (!Array.isArray(message) || message.length === 0) return;

const kind = message[0];

if (kind === "res") {

const waiter = this.pending.get(message[1]);

if (waiter) {

this.pending.delete(message[1]);

waiter.resolve(message.length > 2 ? message[2] : null);

}

return;

}

if (kind === "dev") {

if (this.onDev) this.onDev(message[1] || {});

return;

}

const handler = this.handlers[kind];

if (!handler) {

console.warn("[pn] unhandled message kind", kind);

if (kind !== "apply" && message.length > 1 && typeof message[1] === "number") {

this.send(["res", message[1], null]);

}

return;

}

const id = message[1];

let result = null;

try {

result = await handler(message);

} catch (err) {

this.reportError(`${kind} failed`, err);

}

if (id != null) this.send(["res", id, result === undefined ? null : result]);

}

reportError(context, err) {

const detail = err && err.stack ? err.stack : String(err);

console.error(`[pn] ${context}:`, err);

this.dev({ type: "error", text: `${context}: ${detail}` });

}

pythonnative/src/pythonnative/devserver/static/bridge.js at main · pythonnative/pythonnative · GitHub

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