Redis client for Dart

Redis protocol parser and client for Dart

Fast and simple by design. It requires no external package to run.

Supported features:

• transactions and CAS (check-and-set) pattern
• pubsub
• unicode
• performance and simplicity
• tls

Simple

redis is simple serializer and deserializer of the redis protocol with additional helper functions and classes.

Redis protocol is a composition of array, strings (and bulk) and integers.

For example a SET command might look like this:

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

This enables sending any command. Before sending commands one needs to open a connection to Redis.

In the following example we will open a connection to a Redis server running on port 6379, execute the command 'SET key 0' and print the result.

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

Due to the simple implementation, it is possible to execute commands in various ways. In the following example we execute one after the other.

final conn = 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
  });
});

Another way is to execute commands without waiting for the previous command to complete, and we can still be sure that the response handled by Future will be completed in the correct order.

final conn = 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 five commands in last examples and only one in the previous example.

Generic

Redis responses and requests can be arbitrarily nested.

Mapping

Redis	Dart
String	String
Integer	Integer
Array	List
Error	RedisError

* Both simple string and bulk string from Redis are serialized to Dart string. Strings from Dart to Redis are converted to bulk string. UTF8 encoding is used in both directions.

Lists can be nested. This is useful when executing the EVAL command.

command.send_object(["EVAL","return {KEYS[1],{KEYS[2],{ARGV[1]},ARGV[2]},2}","2","key1","key2","first","second"])
.then((response){
  print(response);
});

results in

[key1, [key2, [first], second], 2]

Tls

Secure ssl/tls with RedisConnection.connectSecure(host,port)

final conn = RedisConnection();
conn.connectSecure('localhost',6379).then((Command command){
    command.send_object(["SET","key","0"]).then((var response)
        print(response);
    )
}

or by passing any other Socket to RedisConnection.connectWithSocket(Socket s) in similar fashion.

Fast

Tested on a laptop, we can execute and process 180K INCR operations per second.

Example

const int N = 200000;
int start;
final conn = RedisConnection();
conn.connect('localhost',6379).then((Command command){
  print("test started, please wait ...");
  start = 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(); does nothing more than enabling and disabling the Nagle's algorhitm on socket. By default it is disabled to achieve shortest possible latency at the expense of 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 MULTI command and completed with EXEC command. .multi(), .exec() and class Transaction are implemented as helpers for checking the result of each command executed during transaction.

Future<Transaction> Command.multi();

Executing multi() returns a Future<Transaction>. This class should be used to execute commands by calling .send_object. It returns a Future that is called after calling .exec().

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

final conn = 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();
  });
});

CAS

It's impossible to write code that depends on the result of the previous command during a transaction, because all commands are executed at once. To overcome this, user should use the CAS.

Cas requires a Command as a constructor argument. It implements two methods: watch and multiAndExec.

watch takes two arguments: a list of keys to watch and a handler to call and to proceed with CAS.

Example:

cas.watch(["key1,key2,key3"],(){
  //body of CAS
});

Failure happens if the watched key is modified outside of the transaction. When this happens the handler is called until final transaction completes.

multiAndExec is used to complete a transaction with a handler where the argument is Transaction.

Example:

//last part in body of CAS
cas.multiAndExec((Transaction trans){
  trans.send_object(["SET","key1",v1]);
  trans.send_object(["SET","key2",v2]);
  trans.send_object(["SET","key2",v2]);
});

Lets imagine we need to atomically increment the value of a key by 1 (and that Redis does not have the INCR command).

Cas cas = new Cas(command);
cas.watch(["key"], (){
  command.send_object(["GET","key"]).then((String val){
    int i = int.parse(val);
    i++;
    cas.multiAndExec((Transaction trans){
      trans.send_object(["SET","key",i.toString()]);
    });
  });
});

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 a helper for dispatching received messages. First, create a new PubSub from an existing Command

final pubsub = PubSub(command);

Once PubSub is created, Command is invalidated and should not be used on the same connection. PubSub have the following commands

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

and additional Stream getStream()

getStream returns Stream

Example for receiving and printing messages

pubsub.getStream().listen((message){
  print("message: $message");
});

Sending messages can be done from different connection for example

command.send_object(["PUBLISH","monkey","banana"]);

Todo

In the 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

CHANGELOG.md