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Then we define our rate policy object. We friend the type [link beast.ref.boost__beast__rate_policy_access `rate_policy_access`] to allow our implementation to be private, but still allow the `basic_stream` access to call the required functions. This lets us avoid having to write a cumbersome friend declaration for the `basic_stream` class template. Public members of rate policy objects become part of the stream object's interface, through a call to `rate_policy`.
Then we define our rate policy object. We friend the type接着定义速率策略对象。我们让类型 [link beast.ref.boost__beast__rate_policy_access `rate_policy_access`] to allow our implementation to be private, but still allow the `basic_stream` access to call the required functions. This lets us avoid having to write a cumbersome friend declaration for the `basic_stream` class template. Public members of rate policy objects become part of the stream object's interface, through a call to成为友元，这样可以将实现设为私有，同时仍然允许 `basic_stream` 访问所需函数。这种方式可以避免为 `basic_stream` 类模板编写繁琐的友元声明。速率策略对象的公有成员会通过调用 `rate_policy`. 成为流对象接口的一部分。
06/12/2026
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More sophisticated rate policies can be implemented as user-defined types which meet the requirements of __RatePolicy__. Here, we develop a rate policy that measures the instantaneous throughput of reads and writes. First we write a small utility class that applies an exponential smoothing function to a series of discrete rate samples, to calculate instantaneous throughput.
More sophisticated rate policies can be implemented as user-defined types which meet the requirements of __RatePolicy__. Here, we develop a rate policy that measures the instantaneous throughput of reads and writes. First we write a small utility class that applies an exponential smoothing function to a series of discrete rate samples, to calculate instantaneous throughput.更复杂的速率策略可以作为用户自定义类型来实现，只需满足 __RatePolicy__ 概念的要求即可。下面我们开发一个速率策略，用于测量读写操作的瞬时吞吐量。首先编写一个辅助类，该类对一系列离散的速率采样值应用指数平滑函数，以计算瞬时吞吐量。
06/12/2026
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The [link beast.ref.boost__beast__basic_stream `basic_stream`] class template supports an additional `RatePolicy` template parameter. Objects of this type must meet the requirements of __RatePolicy__. They are used to implement rate limiting or bandwidth management. The default policy for `basic_stream` and `tcp_stream` is [link beast.ref.boost__beast__unlimited_rate_policy `unlimited_rate_policy`], which places no limits on reading and writing. The library comes with the [link beast.ref.boost__beast__simple_rate_policy `simple_rate_policy`], allowing for independent control of read and write limits expressed in terms of bytes per second. The follow code creates an instance of the basic stream with a simple rate policy, and sets the read and write limits:
The [link beast.ref.boost__beast__basic_stream `basic_stream`] class template supports an additional `RatePolicy` template parameter. Objects of this type must meet the requirements of __RatePolicy__. They are used to implement rate limiting or bandwidth management. The default policy for 类模板支持额外的 `RatePolicy` 模板参数。该类型的对象必须满足 __RatePolicy__ 概念的要求，用于实现速率限制或带宽管理。`basic_stream` and和 `tcp_stream` is的默认策略为 [link beast.ref.boost__beast__unlimited_rate_policy `unlimited_rate_policy`], which places no limits on reading and writing. The library comes with the [link beast.ref.boost__beast__simple_rate_policy `simple_rate_policy`], allowing for independent control of read and write limits expressed in terms of bytes per second. The follow code creates an instance of the，该策略对读写操作不施加任何限制。该库提供 [link beast.ref.boost__beast__simple_rate_policy `simple_rate_policy`] 策略，支持以字节/秒为单位分别控制读写速率限制。以下代码创建一个使用简单速率策略的 basic _stream with a simple rate policy, and sets the read and write limits:实例，并设置读写限制：
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Rate Limiting __example__
Rate Limiting __example速率限制 __示例__
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The following code establishes an encrypted connection, writes an HTTP request, reads the HTTP response, and closes the connection gracefully. If these operations take longer than 30 seconds total, a timeout occurs. This code is intended to show how `tcp_stream` can be used to enable timeouts across unmodified stream algorithms which were not originally written to support timing out, and how a blocking algorithm may be written from asynchronous intermediate operations.
The following code establishes an encrypted connection, writes an HTTP request, reads the HTTP response, and closes the connection gracefully. If these operations take longer than 30 seconds total, a timeout occurs. This code is intended to show how `tcp_stream` can be used to enable timeouts across unmodified stream algorithms which were not originally written to support timing out, and how a blocking algorithm may be written from asynchronous intermediate operations.以下代码用于建立加密连接、发送 HTTP 请求、接收 HTTP 响应，并正常关闭连接。如果这些操作的总耗时超过 30 秒，就会触发超时。这段代码主要展示两件事：一是如何用 `tcp_stream` 为原本不支持超时的流算法添加上超时功能，二是如何通过异步中间操作来构建一个阻塞算法。
06/12/2026
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It is important to note that all of the examples thus far which perform reads and writes with a timeout, make use of the existing networking stream algorithms. As these algorithms are written generically to work with any object meeting the stream requirements, they transparently support timeouts when used with `tcp_stream`. This can be used to enable timeouts for stream wrappers that do not currently support timeouts.
It is important to note that all of the examples thus far which perform reads and writes with a timeout, make use of the existing networking stream algorithms. As these algorithms are written generically to work with any object meeting the stream requirements, they transparently support timeouts when used with `tcp_stream`. This can be used to enable timeouts for s值得注意的是，目前所有涉及超时读写的示例，均使用了现有的网络流算法。由于这些算法采用泛型编写，适用于任何满足流（Stream）要求的对象，因此在与‘tcp_stream’配合使用时，能够透明地支持超时机制。借助这一特性，还可以为当前尚不支持超时的流包装器（Stream wWrappers that do not currently support timeouts.）启用超时功能。
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https_get
https_get
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When a timeout is set, it cancels any previous read or write timeout for which no outstanding operation is in progress. Algorithms which loop over logical operations simply need to set the timeout once before the logical operation, it is not necessary to call `expires_never` in this case. Here we implement an algorithm which continuously echoes lines back, with a timeout. This example is implemented as a complete function.
When a timeout is set, it cancels any previous read or write timeout for which no outstanding operation is in progress. Algorithms which loop over logical operations simply need to set the timeout once before the logical operation, it is not necessary to call `expires_never` in this case. Here we implement an algorithm which continuously echoes lines back, with a timeout. This example is implemented as a complete function.当设置超时时，会取消之前尚未有未完成操作正在进行的读写超时。对于循环执行逻辑操作的算法，只需在执行逻辑操作之前设置一次超时，这种情况下无需调用 `expires_never`。以下示例实现一个持续回显行数据并带有超时机制的算法，该示例作为一个完整函数提供。
06/12/2026
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Since reads and writes can take place concurrently, it is possible to have two simultaneous logical operations where each operation either only reads, or only writes. The beginning of a new read or write operation will use the most recently set timeout. This will not affect operations that are already outstanding.
Since reads and writes can take place concurrently, it is possible to have two simultaneous logical operations where each operation either only reads, or only writes. The beginning of a new read or write operation will use the most recently set timeout. This will not affect operations that are already outstanding.由于读取和写入可以并发进行，因此可能会同时存在两个逻辑操作，且每个操作仅用于读取或仅用于写入。新读取或写入操作的开始将使用最近设置的超时时间。这不会影响已经处于未决状态的操作。
06/12/2026
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Timeouts apply to the logical operation, expressed as a series of asynchronous calls, rather than just the next call. This code reads a line from the stream and writes it back. Both the read and the write must complete within 30 seconds from when the timeout was set; the timer is not reset between operations.
Timeouts apply to the logical operation, expressed as a series of asynchronous calls, rather than just the next call. This code reads a line from the stream and writes it back. Both the read and the write must complete within 30 seconds from when the timeout was set; the timer is not reset between operations.超时时间适用于整个逻辑操作（即由一系列异步调用组成的操作），而不仅仅是下一次调用。以下代码用于从流中读取一行数据并将其写回。读取和写入操作均必须在设置超时时间后的 30 秒内完成；在这两次操作之间，定时器不会被重置。
06/12/2026
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Reading and Writing
Reading and Writing读取与写入
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A server will use an acceptor bound to a particular IP address and port to listen to and receive incoming connection requests. The acceptor returns an ordinary socket. A `tcp_stream` can be move-constructed from the underlying `basic_stream_socket` thusly:
A server will use an acceptor bound to a particular IP address and port to listen to and receive incoming connection requests. The acceptor returns an ordinary socket. A `tcp_stream` can be move-constructed from the underlying `basic_stream_socket` thusly:服务器使用绑定至特定 IP 地址和端口的接收器，用于监听并接收传入的连接请求。该接收器用于返回一个普通套接字。以下代码用于展示如何基于该底层 basic_stream_socket 通过移动构造来创建 tcp_stream：
06/12/2026
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Before data can be exchanged, the stream needs to be connected to a peer. The following code sets a timeout for an asynchronous connect operation. In Beast, functions to connect to a range of endpoints (such as the range returned by [@boost:/doc/html/boost_asio/reference/ip__basic_resolver/resolve/overload3.html `net::ip::tcp::resolver::resolve`]) are members of the class rather than free functions such as [@boost:/doc/html/boost_asio/reference/async_connect.html `net::async_connect`].
Before data can be exchanged, the stream needs to be connected to a peer. The following code sets a timeout for an asynchronous connect operation. In Beast, functions to connect to a range of endpoints (such as the range returned by [@boost:/doc/html/boost_asio/reference/ip__basic_resolver/resolve/overload3.html `net::ip::tcp::resolver::resolve`]) are members of the class rather than free functions such as [@boost:/doc/html/boost_asio/reference/async_connect.html `net::async_connect`].在交换数据之前，该流需要先连接到对等端。以下代码用于为异步连接操作设置超时时间。在 Beast 中，用于连接端点范围（例如由 net::ip::tcp::resolver::resolve 返回的范围）的函数属于该类的成员函数，而不是像 net::async_connect 那样的自由函数。
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Connecting
Connecting连接
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The function [@boost:/doc/html/boost_asio/reference/make_strand.html `make_strand`] returns a strand constructed from an execution context or executor. When a [@boost:/doc/html/boost_asio/reference/strand.html `net::strand`] is chosen for the stream's executor, all completion handlers which do not already have an associated executor will use the strand. This is both a notational convenience (no need for `strand::wrap` or `bind_executor` at call sites) and a measure of safety, as it is no longer possible to forget to use the strand.
The function [@boost:/doc/html/boost_asio/reference/make_strand.html `make_strand`] returns a strand constructed from an execution context or executor. When a [@boost:/doc/html/boost_asio/reference/strand.html `net::strand`] is chosen for the stream's executor, all completion handlers which do not already have an associated executor will use the strand. This is both a notational convenience (no need for函数用于从执行上下文或执行器构造一个串行器。当为流的执行器选择 [@boost:/doc/html/boost_asio/reference/strand.html `net::strand`] 时，所有尚未关联执行器的完成处理器都会使用该串行器。这种方式既简化代码写法（调用点无需使用 `strand::wrap` or或 `bind_executor` at call sites) and a measure of safety, as it is no longer possible to forget to use the strand.），也提高安全性，因为不会再出现忘记使用串行器的情况。
06/12/2026
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Alternatively, we can construct the stream from an executor:
Alternatively, we can construct the stream from an executor:或者，也可以使用执行器来构造流：
06/12/2026
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The `tcp_stream` is designed as a replacement for [@boost:/doc/html/boost_asio/reference/ip__tcp/socket.html `net::ip::tcp::socket`]. Any program which currently uses a socket, can switch to a `tcp_stream` and achieve the features above (although some interfaces are different, see below). Networking now allows I/O objects to construct with any instance of __ExecutionContext__ or __Executor__ objects. Here we construct a stream which uses a particular I/O context to dispatch completion handlers:
The `tcp_stream` is designed as a replacement for用于替代 [@boost:/doc/html/boost_asio/reference/ip__tcp/socket.html `net::ip::tcp::socket`]. Any program which currently uses a socket, can switch to a `tcp_stream` and achieve the features above (although some interfaces are different, see below). Networking now allows I/O objects to construct with any instance of。任何当前使用套接字的程序都可以改用 `tcp_stream` 并获得上述功能（但部分接口存在差异，详见下文）。网络库现在允许 I/O 对象使用任意 __ExecutionContext__ or或 __Executor__ objects. Here we construct a stream which uses a particular I/O context to dispatch completion handlers:实例进行构造。以下示例构造一个流，该流使用特定的 I/O 上下文来调度完成处理器：
06/12/2026
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Construction
Construction构造函数
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[itemized_list [Timeouts for logical operations] [Configurable __Protocol__ type] [Configurable __Executor__ type] [Configurable __RatePolicy__ type] ]
[itemized_list [Timeouts for logical operations] [Configurable __Protocol__ type] [Configurable __Executor__ type] [Configurable __RatePolicy__ type] ]
06/12/2026
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[link beast.ref.boost__beast__basic_stream `basic_stream`]
[link beast.ref.boost__beast__basic_stream `basic_stream`]
06/12/2026

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