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cluster: respect server.listen() backlog parameter set by workers (credit: @oyyd) #41623

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4 changes: 4 additions & 0 deletions doc/api/net.md
Original file line number Diff line number Diff line change
Expand Up @@ -464,6 +464,10 @@ server.listen({
});
```

When `exclusive` is `true` and the underlying handle is shared, it is
possible that several workers query a handle with different backlogs.
In this case, the first `backlog` passed to the master process will be used.

Starting an IPC server as root may cause the server path to be inaccessible for
unprivileged users. Using `readableAll` and `writableAll` will make the server
accessible for all users.
Expand Down
7 changes: 4 additions & 3 deletions lib/internal/cluster/round_robin_handle.js
Original file line number Diff line number Diff line change
Expand Up @@ -15,7 +15,7 @@ const { constants } = internalBinding('tcp_wrap');

module.exports = RoundRobinHandle;

function RoundRobinHandle(key, address, { port, fd, flags }) {
function RoundRobinHandle(key, address, { port, fd, flags, backlog }) {
this.key = key;
this.all = new SafeMap();
this.free = new SafeMap();
Expand All @@ -24,16 +24,17 @@ function RoundRobinHandle(key, address, { port, fd, flags }) {
this.server = net.createServer(assert.fail);

if (fd >= 0)
this.server.listen({ fd });
this.server.listen({ fd, backlog });
else if (port >= 0) {
this.server.listen({
port,
host: address,
// Currently, net module only supports `ipv6Only` option in `flags`.
ipv6Only: Boolean(flags & constants.UV_TCP_IPV6ONLY),
backlog,
});
} else
this.server.listen(address); // UNIX socket path.
this.server.listen(address, backlog); // UNIX socket path.

this.server.once('listening', () => {
this.handle = this.server._handle;
Expand Down
1 change: 1 addition & 0 deletions lib/net.js
Original file line number Diff line number Diff line change
Expand Up @@ -1385,6 +1385,7 @@ function listenInCluster(server, address, port, addressType,
addressType: addressType,
fd: fd,
flags,
backlog,
};

// Get the primary's server handle, and listen on it
Expand Down
45 changes: 45 additions & 0 deletions test/parallel/test-cluster-net-listen-backlog.js
Original file line number Diff line number Diff line change
@@ -0,0 +1,45 @@
'use strict';

const common = require('../common');
const assert = require('assert');
// Monkey-patch `net.Server.listen`
const net = require('net');
const cluster = require('cluster');

// Force round-robin scheduling policy
// as Windows defaults to SCHED_NONE
// https://nodejs.org/docs/latest/api/cluster.html#clusterschedulingpolicy
cluster.schedulingPolicy = cluster.SCHED_RR;

// Ensures that the `backlog` is used to create a `net.Server`.
const kExpectedBacklog = 127;
if (cluster.isMaster) {
const listen = net.Server.prototype.listen;

net.Server.prototype.listen = common.mustCall(
function(...args) {
const options = args[0];
if (typeof options === 'object') {
assert(options.backlog, kExpectedBacklog);
} else {
assert(args[1], kExpectedBacklog);
}
return listen.call(this, ...args);
}
);

const worker = cluster.fork();
worker.on('message', () => {
worker.disconnect();
});
} else {
const server = net.createServer();

server.listen({
host: common.localhostIPv4,
port: 0,
backlog: kExpectedBacklog,
}, common.mustCall(() => {
process.send(true);
}));
}