signalk-server/dist/deltachain.js

An implementation of a [Signal K](http://signalk.org) server for boats.

"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
class DeltaChain {
    chain = [];
    // Run every registered input handler over `msg`, then hand the result
    // to `dispatch`. Each handler gets (delta, next); calling next forwards
    // the (possibly modified) delta to the next handler, and `dispatch`
    // runs only once the chain is exhausted. A handler that never calls
    // next drops the delta — `dispatch` is not invoked.
    //
    // The caller supplies `dispatch` rather than the chain owning a fixed
    // terminal, so handlers run BEFORE source-priority filtering and
    // caching (the registerDeltaInputHandler contract) while that
    // downstream pipeline stays in handleMessage. `dispatch` is a single
    // hoisted function; the per-message context it needs (timestamp, sk
    // version) is threaded as arguments so nothing is allocated per delta.
    process(msg, dispatch, now, version) {
        this.doProcess(0, msg, dispatch, now, version);
    }
    doProcess(index, msg, dispatch, now, version) {
        if (index >= this.chain.length) {
            dispatch(msg, now, version);
            return;
        }
        // Isolate handlers: a plugin's delta input handler that throws must
        // not abort the chain, or the delta is silently dropped. A handler may
        // call next() multiple times (e.g. to fan one delta out into several).
        // `nextCalled` guards the catch block from resubmitting the message
        // when a handler calls next() and then throws.
        let nextCalled = false;
        const next = (nextMsg) => {
            nextCalled = true;
            this.doProcess(index + 1, nextMsg, dispatch, now, version);
        };
        try {
            this.chain[index](msg, next);
        }
        catch (err) {
            console.error('Delta input handler threw:', err, nextCalled ? '(next already called)' : '');
            if (!nextCalled) {
                next(msg);
            }
        }
    }
    register(handler) {
        this.chain.push(handler);
        return () => {
            const handlerIndex = this.chain.indexOf(handler);
            if (handlerIndex >= 0) {
                this.chain.splice(handlerIndex, 1);
            }
        };
    }
}
exports.default = DeltaChain;
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