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0.10.1-front.2 • Public • Published

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NodeJS memcached client with the most efficient ASCII protocol parser.

Primary developed to be used at @WalmartLabs to power the eCommerce site.


  • Very efficient memcached ASCII protocol parser by using only NodeJS Buffer APIs.
  • Optional compression for the data before sending to memcached
  • Auto reconnects when there's network error or timeout
  • Support sending arbitrary commands. Read up on the protocol doc here.
  • Support storing string, numeric, and JSON values
  • APIs Support callback or Promise
  • Support fire and forget requests
  • Support multiple connections


$ npm i memcache-client --save


const MemcacheClient = require("memcache-client");
const expect = require("chai").expect;
const server = "localhost:11211";
// create a normal client
const client = new MemcacheClient({ server });
// Create a client that ignores NOT_STORED response (for McRouter AllAsync mode)
const mrClient = new MemcacheClient({ server, ignoreNotStored: true });
// You can specify maxConnections by using an object for server
// Default maxConnections is 1
const mClient = new MemcacheClient({ server: { server, maxConnections: 5 } });
// with callback
client.set("key", "data", (err, r) => { expect(r).to.deep.equal(["STORED"]); });
client.get("key", (err, data) => { expect(data.value).to.equal("data"); });
// with promise
client.set("key", "data").then((r) => expect(r).to.deep.equal(["STORED"]));
client.get("key").then((data) => expect(data.value).to.equal("data"));
// concurrency using promise
Promise.all([client.set("key1", "data1"), client.set("key2", "data2")])
  .then((r) => expect(r).to.deep.equal([["STORED"], ["STORED"]]));
Promise.all([client.get("key1"), client.get("key2")])
  .then((r) => {
// get multiple keys
client.get(["key1", "key2"]).then((results) => {
// gets and cas
client.gets("key1").then((v) => client.cas("key1", "casData", { casUniq: v.casUniq }));
// enable compression (if data size >= 100 bytes)
const data = Buffer.alloc(500);
client.set("key", data, { compress: true }).then((r) => expect(r).to.deep.equal(["STORED"]));
// fire and forget
client.set("key", data, { noreply: true });
// send any arbitrary command (\r\n will be appended automatically)
client.cmd("stats").then((r) => { console.log(r.STAT) });
client.set("foo", "10", { noreply: true });
client.cmd("incr foo 5").then((v) => expect(+v).to.equal(15));
// you can also send arbitary command with noreply option (noreply will be appended automatically)
client.cmd("incr foo 5", { noreply: true });
// send any arbitrary data (remember \r\n)
client.send("set foo 0 0 5\r\nhello\r\n").then((r) => expect(r).to.deep.equal(["STORED"]));

Commands with a method

All take an optional callback. If it's not provided then all return a Promise.

  • client.get(key, [callback]) or client.get([key1, key2], [callback])
  • client.gets(key, [callback]) or client.gets([key1, key2], [callback])
  • client.set(key, data, [options], [callback])
  • client.add(key, data, [options], [callback])
  • client.replace(key, data, [options], [callback])
  • client.append(key, data, [options], [callback])
  • client.prepend(key, data, [options], [callback])
  • client.cas(key, data, options, [callback])
  • client.delete(key, [options], [callback])
  • client.incr(key, value, [options], [callback])
  • client.decr(key, value, [options], [callback])
  • client.touch(key, exptime, [options], [callback])
  • client.version([callback])

For all store commands, set, add, replace, append, prepend, and cas, the data can be a string, number, or a JSON object.

Client Options

The client constructor takes the following values in options.

const options = {
  server: { server: "host:port", maxConnections: 3 },
  ignoreNotStored: true, // ignore NOT_STORED response
  lifetime: 100, // TTL 100 seconds
  cmdTimeout: 3000, // command timeout in milliseconds
  connectTimeout: 8000, // connect to server timeout in ms
  compressor: require("custom-compressor"),
  logger: require("./custom-logger")
const client = new MemcacheClient(options);
  • server - required A string in host:port format, or an object:
{ server: "host:port", maxConnections: 3 }

Default maxConnections is 1

  • ignoreNotStored - optional If set to true, then will not treat NOT_STORED reply from any store commands as error. Use this for Mcrouter AllAsyncRoute mode.
  • lifetime - optional Your cache TTL in seconds to use for all entries. DEFAULT: 60 seconds.
  • cmdTimeout - optional Command timeout in milliseconds. DEFAULT: 5000 ms.
    • If a command didn't receive response before this timeout value, then it will cause the connection to shutdown and returns Error.
  • connectTimeout - optional Custom self connect to server timeout in milliseconds. It's disabled if set to 0. DEFAULT: 0
    • The error object from this will have connecting set to true
  • keepDangleSocket - optional After connectTimeout trigger, do not destroy the socket but keep listening for errors on it. DEFAULT: false
  • dangleSocketWaitTimeout - optional How long to wait for errors on dangle socket before destroying it. DEFAULT: 5 minutes (30000 milliseconds)
  • compressor - optional a custom compressor for compressing the data. See data compression for more details.
  • logger - optional Custom logger like this:
module.exports = {
  debug: (msg) => console.log(msg),
  info: (msg) => console.log(msg),
  warn: (msg) => console.warn(msg),
  error: (msg) => console.error(msg)


Note that the connectTimeout option is a custom timeout this client adds. It will preempt the system's connect timeout, for which you typically get back a connect ETIMEDOUT error.

Since from NodeJS there's no way to change the system's connect timeout, which is usually fairly long, this option allows you to set a shorter timeout. When it triggers, the client will shutdown the connection and destroys the socket, and rejects with an error. The error's message will be "connect timeout" and has the field connecting set to true.

If you want to let the system connect timeout to take place, then set this option to 0 to completely disable it, or set it to a high value like 10 minutes in milliseconds (60000).

Dangle Socket

If you set a small custom connectTimeout and do not want to destroy the socket after it triggers, then you will end up with a dangling socket.

To enable keeping the dangling socket, set the option keepDangleSocket to true.

The client will automatically add a new error handler for the socket in case the system's ETIMEDOUT eventually comes back. The client also sets a timeout to eventually destroy the socket in case the system never comes back with anything.

To control the dangling wait timeout, use the option dangleSocketWaitTimeout. It's default to 5 minutes.

The client will emit the event dangle-wait with the following data:

  • Start waiting: { type: "wait", socket }
  • Wait timeout: { type: "timeout" }
  • error received: { type: "error", err }

Generally it's better to just destroy the socket instead of leaving it dangling.

Multiple redundant servers support

If you have multiple redundant servers, you can pass them to the client with the server option:

  server: {
    servers: [
        server: "",
        maxConnections: 3
        server: "",
        maxConnections: 3
    config: {
      retryFailedServerInterval: 1000, // milliseconds - how often to check failed servers
      failedServerOutTime: 30000, // (ms) how long a failed server should be out before retrying it
      keepLastServer: false

You can also pass in server.config with the following options:

  • retryFailedServerInterval - (ms) how often to check failed servers. Default 10000 ms (10 secs)
  • failedServerOutTime - (ms) how long a failed server should be out before retrying it. Default 60000 ms (1 min).
  • keepLastServer - (boolean) Keep at least one server even if it failed connection. Default true.

Data Compression

The client supports automatic compression/decompression of the data you set. It's turned off by default.

To enable this, you need to:

  • Provide a compressor
  • Set the compress flag when calling the store commands


By default, the client is modeled to use node-zstd version 2's APIs, specifically, it requires a compressor with these two methods:

  • compressSync(value)
  • decompressSync(value)

Both must take and return Buffer data.

If you just add node-zstd version 2 to your dependencies, then you can start setting the compress flag when calling the store commands to enable compression.

If you want to use another major version of node-zstd or another compressor that doesn't offer the two APIs expected above, then you need to create a wrapper compressor and pass it to the client constructor.

Command Options


Almost all commands take a noreply field for options, which if set to true, then the command is fire & forget for the memcached server.

Obviously this doesn't apply to commands like get and gets, which exist to retrieve from the server.

lifetime and compress

For all store commands, set, add, replace, append, prepend, and cas, they take:

  • A lifetime field that specify the TTL time in seconds for the entry. If this is not set, then will try to use client options.lifetime or 60 seconds.
  • A compress field, which if set to true, will cause any data with size >= 100 bytes to be compressed.
    • A default compressor using node-zstd is provided, but you can set your own compressor when creating the client.


For the cas command, options must contain a casUniq value that you received from an gets command you called earlier.

Other methods

  • client.send(data, [options], [callback])
  • client.xsend(data, [options])
  • client.cmd(data, [options], [callback])
  •, key, value, [optons], [callback])
  • client.retrieve(cmd, key, [options], [callback])
  • client.xretrieve(cmd, key)


Apache-2.0 © Joel Chen


npm i @frontapp/memcache-client

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