127 lines
3.5 KiB
JavaScript
127 lines
3.5 KiB
JavaScript
//
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//
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//
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'use strict';
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// A Mux is an object into which other readable streams may be piped;
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// it then writes 'packets' from the upstreams to the given
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// downstream.
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var assert = require('assert');
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var schedule = (typeof setImmediate === 'function') ?
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setImmediate : process.nextTick;
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class Mux {
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constructor (downstream) {
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this.newStreams = [];
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this.oldStreams = [];
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this.blocked = false;
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this.scheduledRead = false;
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this.out = downstream;
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var self = this;
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downstream.on('drain', function () {
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self.blocked = false;
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self._readIncoming();
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});
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}
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// There are 2 states we can be in:
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// - waiting for outbound capacity, which will be signalled by a
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// - 'drain' event on the downstream; or,
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// - no packets to send, waiting for an inbound buffer to have
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// packets, which will be signalled by a 'readable' event
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// If we write all packets available whenever there is outbound
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// capacity, we will either run out of outbound capacity (`#write`
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// returns false), or run out of packets (all calls to an
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// `inbound.read()` have returned null).
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_readIncoming () {
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// We may be sent here speculatively, if an incoming stream has
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// become readable
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if (this.blocked) return;
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var accepting = true;
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var out = this.out;
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// Try to read a chunk from each stream in turn, until all streams
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// are empty, or we exhaust our ability to accept chunks.
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function roundrobin (streams) {
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var s;
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while (accepting && (s = streams.shift())) {
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var chunk = s.read();
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if (chunk !== null) {
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accepting = out.write(chunk);
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streams.push(s);
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}
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}
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}
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roundrobin(this.newStreams);
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// Either we exhausted the new queues, or we ran out of capacity. If
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// we ran out of capacity, all the remaining new streams (i.e.,
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// those with packets left) become old streams. This effectively
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// prioritises streams that keep their buffers close to empty over
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// those that are constantly near full.
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if (accepting) { // all new queues are exhausted, write as many as
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// we can from the old streams
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assert.equal(0, this.newStreams.length);
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roundrobin(this.oldStreams);
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}
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else { // ran out of room
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assert(this.newStreams.length > 0, "Expect some new streams to remain");
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Array.prototype.push.apply(this.oldStreams, this.newStreams);
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this.newStreams = [];
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}
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// We may have exhausted all the old queues, or run out of room;
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// either way, all we need to do is record whether we have capacity
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// or not, so any speculative reads will know
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this.blocked = !accepting;
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}
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_scheduleRead () {
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var self = this;
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if (!self.scheduledRead) {
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schedule(function () {
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self.scheduledRead = false;
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self._readIncoming();
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});
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self.scheduledRead = true;
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}
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}
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pipeFrom (readable) {
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var self = this;
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function enqueue () {
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self.newStreams.push(readable);
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self._scheduleRead();
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}
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function cleanup () {
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readable.removeListener('readable', enqueue);
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readable.removeListener('error', cleanup);
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readable.removeListener('end', cleanup);
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readable.removeListener('unpipeFrom', cleanupIfMe);
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}
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function cleanupIfMe (dest) {
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if (dest === self) cleanup();
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}
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readable.on('unpipeFrom', cleanupIfMe);
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readable.on('end', cleanup);
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readable.on('error', cleanup);
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readable.on('readable', enqueue);
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}
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unpipeFrom (readable) {
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readable.emit('unpipeFrom', this);
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}
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}
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module.exports.Mux = Mux;
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