Redis client for dart

Redis protocol parser and client writent in dart language
It is designed to be both fast and simple to use.

Currently supported features:

  • transactions wrapper for executing multiple commands in atomic way
  • pubsub helper with aditional internal dispatching
  • unicode - strings are UTF8 encoded when sending and decoded when received
  • performance - this counts as future too
  • raw commands - this enables sending any command as raw data :)

Simple

Redis protocol is composition of array, strings(and bulk) and integers. For example executing command SET key value is no more that serializing array of strings ["SET","key","value"]. Commands can be executed by

Future f = command.send_object(["SET","key","value"]);

This enables sending any command. Before sending commands one need to open connection to redis. I will assume that you are running redis server localy on port 6379. In this example we will open connecton, execute command 'SET key 0' and then print result.

import 'package:redis/redis.dart';
...
RedisConnection conn = new RedisConnection();
conn.connect('localhost',6379).then((Command command){
    command.send_object(["SET","key","0"]).then((var response)
        print(response);
    )
}

Due to simple implementation it is possible to execute command on different ways. One an most straightforward way is one after another

RedisConnection conn = new RedisConnection();
conn.connect('localhost',6379).then((Command command){
  command.send_object(["SET","key","0"])
  .then((var response){
    assert(response == 'OK');
    return command.send_object(["INCR","key"]);
  })
  .then((var response){
    assert(response == 1);  
    return command.send_object(["INCR","key"]);
  })
  .then((var response){
    assert(response == 2);
    return command.send_object(["INCR","key"]);
  })
  .then((var response){
    assert(response == 3);
    return command.send_object(["GET","key"]);
  })
  .then((var response){
    return print(response); // 3
  });
});

Other possibility is to execute commands one by one without waiting for previous command to complete. We can send all commands without need to wait for result and we can be still sure, that response handled by Future will be completed in correct order.

RedisConnection conn = new RedisConnection();
conn.connect('localhost',6379).then((Command command){
  command.send_object(["SET","key","0"])
  .then((var response){
    assert(response == 'OK');
  });
  command.send_object(["INCR","key"])
  .then((var response){
    assert(response == 1);  
  });
  command.send_object(["INCR","key"])
  .then((var response){
    assert(response == 2);
  });
  command.send_object(["INCR","key"])
  .then((var response){
    assert(response == 3);
  });
  command.send_object(["GET","key"])
  .then((var response){
     print(response); // 3
  });
});

Difference is that there are 5 commands in last examples and only one on previous example.

Fast

Tested on laptop can execute and process 130K INCR operations per second.

This is code that yields such result

const int N = 200000;
int start;
RedisConnection conn = new RedisConnection();
conn.connect('localhost',6379).then((Command command){
  print("test started, please wait ...");
  start =  new DateTime.now().millisecondsSinceEpoch;
  command.pipe_start();
  command.send_object(["SET","test","0"]);
  for(int i=1;i<=N;i++){
    command.send_object(["INCR","test"])
    .then((v){
      if(i != v)
        throw("wrong received value, we got $v");
    });
  }
  //last command will be executed and then processed last
  command.send_object(["GET","test"]).then((v){
    print(v);
    double diff = (new DateTime.now().millisecondsSinceEpoch - start)/1000.0;
    double perf = N/diff;
    print("$N operations done in $diff s\nperformance $perf/s");
  });
  command.pipe_end();
});

We are not just sending 200K commands here, but also checking result of every send command.

Using command.pipe_start(); and command.pipe_end(); is nothing more that enabling and disabling Nagle's algorhitm on socket. By default it is disabled to achieve shortest possible latency at expense of having more TCP packets and extra overhead. Enabling Nagle's algorithm during transactions can achieve greater data throughput and less overhead.

Transactions

Transactions by redis protocol are started by command MULTI and then completed with command EXEC. .multi(), .exec() and class Transaction are implemented as additional helpers for checking result of each command executed during transaction.

Future<Transaction> Command.multi();

Executing multi() will return Future with Transaction. This class should be used to execute commands by calling .send_object. It returns Future that is called after calling .exec(). It is not possible to write code that depends on result of previous command during transaction. In such cases user should employ technique as described http://redis.io/topics/transactions#cas

import 'package:redis/redis.dart';
...

RedisConnection conn = new RedisConnection();
conn.connect('localhost',6379).then((Command command){
  command.multi().then((Transaction trans){
    trans.send_object(["SET","val","0"]);
    for(int i=0;i<200000;++i){
      trans.send_object(["INCR","val"]).then((v){
        assert(i==v);
      });
    }
    trans.send_object(["GET","val"]).then((v){
      print("number is now $v");
    });
    trans.exec();
  });
});

It is not possible to write code that depends on result of previous command during transaction. In such cases user should employ technique as described http://redis.io/topics/transactions#cas

Unicode

By default UTF8 encoding/decoding for string is used. Each string is converted in binary array using UTF8 encoding. This makes ascii string compatible in both direction.

PubSub

PubSub is helper for dispatching received messages. First, create new PubSubCommand from existing Command

PubSubCommand pubsub=new PubSubCommand(command);

Once PubSubCommand is created, old Command is invalidated and should not be used on same connection. PubSubCommand allows commands

void subscribe(List<String> channels)
void psubscribe(List<String> channels)
void unsubscribe(List<String> channels)
void punsubscribe(List<String> channels)

and additional Subscription getter

Subscription getSubscription();

Subscription enables local message dispatching. It enables registering callbacks trough .add(String pattern,Function callback) Unlike Redis rich pattern matching, this pattern allows only for optional * wildchar at the end of string. Message consumers can be added only trough Subscription.

In this example, from all messages from redis that Subscription will receive, only those that begins with abra and have at least 5 letters will be dispatched.

subscription.add("abra*",(String chan,String message){
  print("on channel: $chan message: $message");
});

Here is complete example from test code.

import 'package:redis/redis.dart';

main(){
  RedisConnection conn1 = new RedisConnection();
  RedisConnection conn2 = new RedisConnection();
  Command command; //on conn1
  PubSubCommand pubsub; //on conn2

  conn1.connect('localhost',6379)
  .then((Command cmd){
    command = cmd;
    return conn2.connect('localhost',6379);
  })
  .then((Command cmd){
    pubsub=new PubSubCommand(cmd);
    pubsub.psubscribe(["a*","b*","a*"]);
    Subscription sub = pubsub.getSubscription();
    sub.add("*",(k,v){
      print("$k $v");
     });
  })
  .then((_){
    command.send_object(["PUBLISH","aaa","aa"]);
    command.send_object(["PUBLISH","bbb","bb"]);
    command.send_object(["PUBLISH","ccc","cc"]);
  });
}

Todo

In near future:

  • Better documentation
  • Implement all "generic commands" with named commands
  • Better error handling - that is ability to recover from error
  • Spell check code

Changes

0.4.1

  • Command raise error if used during transaction.

0.4.0

  • PubSub interface is made simpler but backward incompatible :(
  • README is updated

Libraries

redis