dartis 0.2.0

Redis client featuring type-safe commands, pipelining, fire and forget, publish/subscribe, monitor mode, inline commands, transactions, Lua scripting, modules, and much more.

Redis client for Dart

Features

• Type-safe commands
• Pipelining
• Fire and forget
• Publish/Subscribe
• Monitor mode
• Inline commands
• Transactions
• Lua scripting
• Custom serializers/deserializers
• Custom commands for building Modules

Usage

Create a connection:

final client = await Client.connect('redis://localhost:6379');

Get a type-safe view of the available Redis Commands:

final commands = client.asCommands<String, String>();

Run some commands:

await commands.set('key', 'value');

final value = await commands.get('key');

print(value);

Disconnect:

await client.disconnect();

Connection String

Connection string must follow the following pattern:

redis://{host}:{port}

Example:

redis://localhost:6379

Client Modes

Clients can work in the following modes:

• Online
• Publish/Subscribe
• Inline commands
• Monitor

Online

In this mode the client can send any command to the Redis server.

// Connect
final client = await Client.connect('redis://localhost:6379');

// Run some commands
final commands = client.asCommands<String, String>();

final result = await commands.ping();
print(result);

// Disconnect
await client.disconnect();

See client.dart in the example folder.

Publish/Subscribe

In this mode the only allowed commands are subscribe, unsubscribe, psubscribe, punsubscribe, ping and quit.

The replies to subscription and unsubscription commands along with the published messages are received in the form of events, so that the client can just read a coherent Stream of events.

final pubsub = await PubSub.connect<String, String>('redis://localhost:6379');

// Subscribe to some channels and patterns
pubsub
  ..subscribe(channel: 'dev.dart')
  ..psubscribe(pattern: 'dartlang.news.*');

// Listen for server replies
pubsub.stream.listen(print, onError: print);

See pubsub.dart in the example folder.

Inline Commands

In this mode the commands are sent to the server using the "inline command" format. Ideal to use in interactive sessions, like a Telnet session.

final terminal = await Terminal.connect('redis://localhost:6379');

// Run some commands
terminal.run('PING\r\n'.codeUnits);

// Listen for server replies
terminal.stream.listen(print);

Note that in this mode the commands are just lists of bytes with a trailing \r\n.

See terminal.dart in the example folder.

Monitor

In this mode the client receives all the commands procesed by the Redis server. Useful for debugging.

final monitor = await Monitor.connect('redis://localhost:6379');

// Start the monitor mode
monitor.start();

// Listen for server replies
monitor.stream.listen(print);

In this mode the client can not run any command.

See monitor.dart in the example folder.

Commands

The method asCommands<K, V> of the client returns a type-safe view of the available Redis Commands. K is the type to be used for Redis keys and V for values. Most times, using String for keys and values is what you want:

final commands = client.asCommands<String, String>();

However, it's correct to call this method several times in order to get views with different parameterized types:

final strings = client.asCommands<String, String>();
final bytes = client.asCommands<String, List<int>>();

String title = await strings.get('book:24902:title');
List<int> cover = await bytes.get('book:24902:cover');

// ERROR String author = await bytes.get('book:24092:author');

Keep in mind that Redis stores sequences of bytes, not just Strings.

Pipelining

Pipeling is used in order to send multiple commands to the server in only one call, instead of doing one call for each command.

In this mode the client stores locally all the commands without sending them to the server until the flush method is called.

// Start pipeline
client.pipeline();

// Run some commands
commands.incr('product:9238:views').then(print);
commands.incr('product:1725:views').then(print);
commands.incr('product:4560:views').then(print);

// Flush pipeline
client.flush();

The method flush returns a list of Futures that can be used for waiting the completion of all the commands.

// Start pipeline
client.pipeline();

// Run some commands
commands
  ..incr('product:9238:views')
  ..incr('product:1725:views')
  ..incr('product:4560:views');

// Flush pipeline
final futures = client.flush();

// Wait for all the Futures
await Future.wait<Object>(futures).then(print);

Please note that in this mode await can not be used for waiting the result of the execution of each command because the returned Futures will not be completed until flush was called.

Fire and Forget

In this mode the server doesn't sent replies for the commands, so the client doesn't need to wait for them.

This mode is started running the clientReply command with ReplyMode.off or ReplyMode.skip.

In this mode the Futures are immediately completed with null.

// Discard all the server replies
await commands.clientReply(ReplyMode.off);

// Run some commands
await commands.ping().then(print); // null
await commands.ping().then(print); // null
await commands.ping().then(print); // null

The following modes are available:

• ReplyMode.off: In this mode the server will not reply to client commands.
• ReplyMode.skip: In this mode the server will skip the reply of command immediately after it.
• ReplyMode.on: In this mode the server will return a reply to every command.

Transactions

Redis allows to group commands together so that they are executed as a single transaction.

A transaction begins running the multi command, ends running the exec command, and can be aborted running the discard command.

// Start transaction
await commands.multi();

// Run some commands
commands.set(key, 1).then(print);
commands.incr(key).then(print);

// End transaction
await commands.exec(); // Or abort: commands.discard()

The watch command can be used for perfoming optimistic lockings over some keys. A transaction will fail if the "watched" keys are modified by another client.

// Watch
await commands.watch(key: key);

// Start transaction
await commands.multi();

// Run some commands
commands.set(key, 1).then(print);
commands.incr(key).then(print);

// End transaction
await commands.exec();

Please note that in this mode await can not be used for waiting the result of the execution of each command because the returned Futures will not be completed until exec or discard were called.

Caveats

Don't run the clientReply command inside a transaction. If the "fire and forget" mode is de/activated inside a transaction then the client could go out of sync with the server.

Redis transactions are deprecated in favor of Lua scripting.

Lua scripting

Redis allows to run Lua scripts in the server.

Scripts can be executed with the eval and evalsha commands.

// Evaluate
await commands.eval<void>(
    'return {KEYS[1],KEYS[2],ARGV[1],ARGV[2]}',
    keys: [key1, key2],
    args: ['first', 'second']);

The result of a script can be anything. It can be ignored, like in the above example, or it can be mapped to a most useful thing.

// Maps a list of server replies to a list of Strings
class _Mapper implements Mapper<List<String>> {
  @override
  List<String> map(Reply reply, RedisCodec codec) =>
    codec.decode<List<String>>(reply);
}

...

// Evaluate with a mapper
final results = await commands.eval<List<String>>(
    'return {KEYS[1],KEYS[2],ARGV[1],ARGV[2]}',
    keys: [key1, key2],
    args: ['first', 'second'],
    mapper: _Mapper());

print(results); // ['key1', 'key2', 'first', 'second']

Custom Serializers/Deserializers

Encoders are used for serializing all the values sent to Redis. They convert instances of any type to list of bytes. Encoders for types int, double, String and List<int> are registered by default. UTF-8 is used for Strings.

Custom encoders can be written extending from Encoder or Converter.

Example:

An encoder that encodes instances of DateTime to lists of bytes:

class DateTimeEncoder extends Encoder<DateTime> {
  @override
  List<int> convert(DateTime value, [RedisCodec codec]) =>
      utf8.encode(value.toString());
}

Decoders are used for deserializing all the replies received from Redis. They convert list of bytes to instances of any type, and arrays of server replies to lists of instances of any type. Decoders for types int, double, String, List<int>, List<double>, List<Sring> and List<List<int>> are registered by default. UTF-8 is used for Strings.

Custom decoders can be written extending from Decoder or Converter.

Example:

A decoder that decodes lists of bytes to instances of DateTime.

class DateTimeDecoder extends Decoder<SingleReply, DateTime> {
  @override
  DateTime convert(SingleReply value, [RedisCodec codec]) =>
      value == null ? null : DateTime.parse(utf8.decode(value.bytes));
}

Custom encoders and decoders can be registered using the codec member of the client:

client.codec.register(
    encoder: DateTimeEncoder(),
    decoder: DateTimeDecoder());

Custom Commands

Custom sets of commands can be written extending from ModuleBase. This class exposes the method run that sent to Redis any given line of commands, so it can be used for implementing the API of any Redis module.

Example:

A module that exposes a HELLO name command:

class HelloModule extends ModuleBase {

  HelloModule(Client client) : super(client);

  Future<String> hello(String name) => run<String>(<Object>[r'HELLO', name]);
}

Usage:

final module = HelloModule(client);

final message = await module.hello('World!');

print(message);

Note that standard Redis commands can be rewritten too for building custom interfaces.

Example:

An even more type-safe set of commands:

class TypedCommands<K> extends ModuleBase {

  TypedCommands(Client client) : super(client);

  Future<void> set<R>(K key, R value) => run<void>(<Object>[r'SET', key, value]);

  Future<R> get<R>(K key) => run<R>(<Object>[r'GET', key]);
}

Usage:

final commands = TypedCommands<String>(client);

await commands.set<String>('name', 'Bob');
await commands.set<int>('age', 29);
await commands.set<List<int>>('photo', png);

final name = await commands.get<String>('name');
final age = await commands.get<int>('age');
final photo = await commands.get<List<int>>('photo');

Note that if a module works with a custom structure, like a record with multiple fields, then custom encoders and decoders should be used.

Log

The logging package is used for logging messages through a custom logger named 'dartis'.

Here is a simple logging configuration that logs all messages via print:

import 'package:logging/logging.dart';

...

Logger.root.level = Level.INFO;
Logger.root.onRecord.listen((LogRecord record) {
  print('${record.time} ${record.level.name} ${record.loggerName} ${record.message}');
});

Set the log level according your needs. Most times, INFO is what you want. ALL is good for filling issues.