Redis client for dart

Redis protocol parser and client written in dart language
It is 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

Simple

Redis client is simple serialiser and deserialiser of redis protocol. There are also some additional helper functions and classes available to make using redis features easier.

Redis protocol is a composition of array, strings (and bulk) and integers. For example executing command SET is no more than 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 needs to open a connection to redis. I will assume that you are running a redis server locally on port 6379. In this example we will open a connection, execute the command 'SET key 0' and then print 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 different ways. One an most straightforward way is one after another

    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
      });
    });

Other possibility is to execute commands one by one without waiting for the previous command to complete. We can send all commands without needing to wait for a result, 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 5 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 serialied to dart string. String from dart to redis is converted to bulk string. UTF8 encoding is used in both directions.

Lists can be nested. This is usefull when executing 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]

Fast

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

This is the code that yields such a result

    const 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 $v");
        });
      }
      //last command will be executed and then processed last
      command.send_object(["GET","test"]).then((v){
        print(v);
        double diff = (DateTime.now().millisecondsSinceEpoch - start)/1000.0;
        double perf = N/diff;
        print("$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 than 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 the command MULTI and then completed with the command EXEC. .multi(), .exec() and class Transaction are implemented as additional helpers for checking the result of each command executed during transaction.

    Future<Transaction> Command.multi();

Executing multi() will return a Future with 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 is 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 case, user should employ technique CAS. Cas is a convenience class for simplifying this pattern.

Cas constructor requires Command as argument.

Cas implements two methods watch() and multiAndExec().
watch takes two arguments. First argument is list of keys to watch, and second argument is handler to call and to proceed with CAS.

for example:

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

Failure happens if the watched key is modified out of the transaction. When this happens the handler is called until final transaction completes. multiAndExec is used to complete transation. Method takes handler where argument is Transaction.

For 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]);
    });

imagine we have the need to atomically increment the value of a key by 1 
(let's suppose Redis doesn't have [INCR](http://redis.io/commands/incr)).
```dart
    final cas = 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 allows 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

1.2.0

Received redis errors throws exception. Thanks to @eknoes for pull request.
Integers in array get auto converted to strings. Author @eknoes.
Improve transaction handling errors. Patch from @eknoes
Testing migrated on dart.test. Patch from @eknoes

1.1.0

Performance tweaks and simplified code

1.0.0

Dart 2.0 support

0.4.5

Unicode bugfix -> ra1u#4
Update PubSub doc
Improve tests

0.4.4

bugfix for subscribe -> ra1u#3
performance improvement
add PubSub class (simpler/shorter/faster? PubSubCommand)
doc update and example of EVAL

0.4.3

Cas helper
Improved unit tests

0.4.2

Improved performance by 10%
Pubsub interface uses Stream
Better test coverage
Improved documentation

0.4.1

Command raise error if used during transaction.

0.4.0

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

derrick56007 / redis-dart