//
// Copyright (c) 2025 Marcelo Zimbres Silva (mzimbres@gmail.com)
//
// Distributed under the Boost Software License, Version 1.0. (See accompanying
// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
//

[#intro]
= Introduction

Boost.Redis is a high-level https://redis.io/[Redis] client library built on top of
https://www.boost.org/doc/libs/latest/doc/html/boost_asio.html[Boost.Asio]
that implements the Redis protocol
https://github.com/redis/redis-specifications/blob/master/protocol/RESP3.md[RESP3].

== Requirements

The requirements for using Boost.Redis are:

* Boost 1.84 or higher. Boost.Redis is included in Boost installations since Boost 1.84.
* pass:[C++17] or higher. Supported compilers include gcc 11 and later, clang 11 and later, and Visual Studio 16 (2019) and later.
* Redis 6 or higher (must support RESP3).
* OpenSSL.

The documentation assumes basic-level knowledge about https://redis.io/docs/[Redis] and https://www.boost.org/doc/libs/latest/doc/html/boost_asio.html[Boost.Asio].

== Building the library

To use the library it is necessary to include the following:

[source,cpp]
----
#include <boost/redis/src.hpp>
----

in exactly one source file in your applications. Otherwise, the library is header-only.

Boost.Redis unconditionally requires OpenSSL. Targets using Boost.Redis need to link
to the OpenSSL libraries.

== Tutorial

The code below uses a short-lived connection to
https://redis.io/commands/ping/[ping] a Redis server:


[source,cpp]
----
#include <boost/redis/connection.hpp>
#include <boost/asio/co_spawn.hpp>
#include <boost/asio/consign.hpp>
#include <boost/asio/detached.hpp>
#include <iostream>

namespace net = boost::asio;
using boost::redis::request;
using boost::redis::response;
using boost::redis::config;
using boost::redis::connection;

auto co_main(config const& cfg) -> net::awaitable<void>
{
   auto conn = std::make_shared<connection>(co_await net::this_coro::executor);
   conn->async_run(cfg, {}, net::consign(net::detached, conn));

   // A request containing only a ping command.
   request req;
   req.push("PING", "Hello world");

   // Response object.
   response<std::string> resp;

   // Executes the request.
   co_await conn->async_exec(req, resp);
   conn->cancel();

   std::cout << "PING: " << std::get<0>(resp).value() << std::endl;
}
----

The roles played by the `async_run` and `async_exec` functions are:

* xref:reference:boost/redis/basic_connection/async_exec-02.adoc[`connection::async_exec`]: executes the commands contained in the
  request and stores the individual responses in the response object. Can
  be called from multiple places in your code concurrently.
* xref:reference:boost/redis/basic_connection/async_run-04.adoc[`connection::async_run`]: keeps the connection healthy. It takes care of hostname resolution, session establishment, health-checks, reconnection and coordination of low-level read and write operations. It should be called only once per connection, regardless of the number of requests to execute.

== Server pushes

Redis servers can also send a variety of pushes to the client. Some of
them are:

* https://redis.io/docs/manual/pubsub/[Pubsub messages].
* https://redis.io/docs/manual/keyspace-notifications/[Keyspace notifications].
* https://redis.io/docs/manual/client-side-caching/[Client-side caching].

The connection class supports server pushes by means of the
xref:reference:boost/redis/basic_connection/async_receive.adoc[`connection::async_receive`] function, which can be
called in the same connection that is being used to execute commands.
The coroutine below shows how to use it:


[source,cpp]
----
auto
receiver(std::shared_ptr<connection> conn) -> net::awaitable<void>
{
   request req;
   req.push("SUBSCRIBE", "channel");

   generic_response resp;
   conn->set_receive_response(resp);

   // Loop while reconnection is enabled
   while (conn->will_reconnect()) {

      // Reconnect to channels.
      co_await conn->async_exec(req, ignore);

      // Loop reading Redis pushes.
      for (;;) {
         error_code ec;
         co_await conn->async_receive(resp, net::redirect_error(net::use_awaitable, ec));
         if (ec)
            break; // Connection lost, break so we can reconnect to channels.

         // Use the response resp in some way and then clear it.
         ...

         consume_one(resp);
      }
   }
}
----

== Further reading

Here is a list of topics that you might be interested in:

* xref:requests_responses.adoc[More on requests and responses].
* xref:serialization.adoc[Serializing and parsing into custom types].
* xref:logging.adoc[Configuring logging].
* xref:examples.adoc[Examples].
