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* The library uses specializations of `string<Tag>` to change the type
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The general strategy used by the author to evaluate external libraries is as follows:
作者评估外部库的总体策略如下：
* Review the message model. Can it represent a complete request or
* 审查消息模型。它能否表示一个完整的请求或
* Review the stream abstraction. This is the type of object, such as
* 审查流抽象层。这是一种对象类型，例如
* Check treatment of buffers. Does the library manage the buffers
* 检查缓冲区处理方式。该库是否负责管理缓冲区
* How does the library handle corner cases such as trailers,
* 该库如何处理尾部（trailers）等边界情况，
Declarations examples from external libraries have been edited:
来自外部库的声明示例已做编辑：
cpp-netlib
cpp-netlib
is a network programming library previously intended for Boost but not having gone through formal review. As of this writing it still uses the Boost name, namespace, and directory structure although the project states that Boost acceptance is no longer a goal. The library is based on Boost.Asio and bills itself as ['"a collection of network related routines/implementations geared towards providing a robust cross-platform networking library"]. It cites ['"Common Message Type"] as a feature. As of the branch previous linked, it uses these declarations: ``` template <class Tag> struct basic_message {
cpp-netlib 是一个网络编程库，原本计划纳入 Boost，但并未通过正式审查。在撰写本文时，它仍然使用 Boost 的名称、命名空间和目录结构，尽管该项目声明不再将纳入 Boost 作为目标。该库基于 Boost.Asio，自称是“一组与网络相关的例程/实现，旨在提供一个健壮的跨平台网络库”。它将“通用消息类型”列为其特性之一。在上述链接的分支中，它使用了以下声明：
``` template struct basic_message {
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}; ```
}; ```
This container is the base class template used to represent HTTP messages. It uses a "tag" type style specializations for a variety of trait classes, allowing for customization of the various parts of the message. For example, a user specializes `headers_container<T>` to determine what container type holds the header fields. We note some problems with the container declaration:
这个容器是用于表示 HTTP 消息的基类模板。它使用“标签（tag）”类型风格来特化各种特征类，从而允许对消息的各个部分进行自定义。例如，用户可以通过特化 `headers_container<T>` 来确定使用何种容器类型来存储头部字段。我们注意到该容器的声明存在一些问题：
* The header and body containers may only be default-constructed.
* 头部和主体容器只能通过默认构造函数进行构造。
* No stateful allocator support.
* 不支持有状态分配器。
* There is no way to defer the commitment of the type for `body_` to
* 无法推迟 `body_` 类型的提交。
* The message model includes a "source" and "destination." This is
* 消息模型包含了“源”和“目标”。这是
* The use of `string_type` (a customization point) for source,
* 对源（source）使用 `string_type`（一个自定义点），
* The library uses specializations of `string<Tag>` to change the type
* 该库使用 `string<Tag>` 的特化来改变类型
* The specialized trait classes generate a proliferation of small
* 特化的特征类会导致大量小型
* The `string<Tag> customization point constrains user defined body types
* `string<Tag>` 自定义点限制了用户自定义主体类型
The design of the message container in this library is cumbersome with its system of customization using trait specializations. The use of these customizations is extremely limited due to the way they are used in the container declaration, making the design overly complex without corresponding benefit.
该库消息容器的设计非常繁琐，其自定义系统依赖于特征（trait）特化。由于这些自定义机制在容器声明中的使用方式极为受限，导致该设计过于复杂，却未能带来相应的收益。
Boost.HTTP
Boost.HTTP
is a library resulting from the 2014 Google Summer of Code. It was submitted for a Boost formal review and rejected in 2015. It is based on Boost.Asio, and development on the library has continued to the present. As of the branch previously linked, it uses these message declarations: ``` template<class Headers, class Body> struct basic_message {
是一个源自 2014 年 Google Summer of Code 的库。它曾于 2015 年提交进行 Boost 正式审查，但遭到拒绝。该库基于 Boost.Asio 构建，其开发工作一直持续至今。在之前链接的分支中，它使用了如下的消息声明：``` template struct basic_message {
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private:
private:
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};
};
typedef basic_message<boost::http::headers, std::vector<std::uint8_t>> message;
typedef basic_message<boost::http::headers, std::vector<std::uint8_t>> message;
template<class Headers, class Body> struct is_message<basic_message<Headers, Body>>: public std::true_type {}; ```
template<class Headers, class Body> struct is_message<basic_message<Headers, Body>>: public std::true_type {}; ```
* This container cannot model a complete message. The ['start-line] items
* 该容器无法对完整的消息进行建模。['start-line] 项
* `headers_`, `body_`, and `trailers_` may only be default-constructed,
* `headers_`、`body_` 和 `trailers_` 只能进行默认构造，
* There is no way to defer the commitment of the [*Body] type to after
* 无法将 [*Body] 类型的提交推迟到之后进行
* No stateful allocator support. This follows from the previous limitation
* 不支持有状态分配器。这是由前一个限制导致的
* The trailers are stored in a separate object. Aside from the combinatorial
* 尾部（trailers）存储在一个单独的对象中。除了组合爆炸的问题之外
* The declarations imply that `std::vector` is a model of [*Body].
* 这些声明暗示 `std::vector` 是 [*Body] 的一个模型。
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* A body can only be extracted once, limiting the use of this container
* 消息体只能提取一次，这限制了该容器的使用
* No stateful allocator support.
* 不支持有状态分配器。
* The header and body containers may only be default-constructed.
* 头部和主体容器只能通过默认构造函数进行构造。
* The library uses specializations of `string<Tag>` to change the type
* 该库使用 `string<Tag>` 的特化来改变类型
Boost.HTTP
Boost.HTTP
* This container cannot model a complete message. The ['start-line] items
* 该容器无法对完整的消息进行建模。['start-line] 项
* The [*Body] customization point constrains user defined types to
* [*Body] 自定义点将用户自定义类型限制为
* The declarations imply that `std::vector` is a model of [*Body].
* 这些声明暗示 `std::vector` 是 [*Body] 的一个模型。
Now we analyze the structure of the larger message container. The library uses a handle/body idiom. There are two public message container interfaces, one for requests (`http_request`) and one for responses (`http_response`). Each interface maintains a private shared pointer to an implementation class. Public member function calls are routed to the internal implementation. This is the first implementation class, which forms the base class for both the request and response implementations: ``` namespace details {
现在，我们来分析更大的消息容器的结构。该库使用了句柄/主体惯用法（handle/body idiom）。它提供了两个公开的消息容器接口，一个用于请求（`http_request`），另一个用于响应（`http_response`）。每个接口都维护着一个指向实现类的私有共享指针。公开的成员函数调用会被路由到内部的实现。以下是第一个实现类，它构成了请求和响应实现类的基类： ``` namespace details {
To understand these declarations we need to first understand that cpprestsdk uses the asynchronous model defined by Microsoft's [@https://msdn.microsoft.com/en-us/library/dd504870.aspx [*Concurrency Runtime]]. Identifiers from the [@https://msdn.microsoft.com/en-us/library/jj987780.aspx [*`pplx` namespace]] define common asynchronous patterns such as tasks and events. The `concurrency::streams::istream` parameter and `m_data_available` data member indicates a lack of separation of concerns. The representation of HTTP messages should not be conflated with the asynchronous model used to serialize or parse those messages in the message declarations.
要理解这些声明，需要先了解 cpprestsdk 使用了微软的 [@https://msdn.microsoft.com/en-us/library/dd504870.aspx [*Concurrency Runtime]] 所定义的异步模型。来自 [@https://msdn.microsoft.com/en-us/library/jj987780.aspx [*`pplx` namespace]] 的标识符定义了任务和事件等通用异步模式。`concurrency::streams::istream` 参数和 `m_data_available` 数据成员表明存在关注点分离缺失的问题。在消息声明中，不应将 HTTP 消息的表示形式与用于序列化或解析这些消息的异步模型混为一谈。
The next declaration forms the complete implementation class referenced by the handle in the public interface (which follows after): ``` /// Internal representation of an HTTP request message. class _http_request final : public http::details::http_msg_base, public std::enable_shared_from_this<_http_request> { public:
以下声明构成了公开接口中的句柄所引用的完整实现类（该类位于后续）：``` /// HTTP 请求消息的内部表示。 class _http_request final : public http::details::http_msg_base, public std::enable_shared_from_this<_http_request> { public:
As before, we note that the implementation class for HTTP requests concerns itself more with the mechanics of sending the message asynchronously than it does with actually modeling the HTTP message as described in __rfc7230__:
与之前一样，可以看出，HTTP 请求的实现类更关注于异步发送消息的机制，而不是按照 __rfc7230__ 中的描述对 HTTP 消息进行实际建模：
Finally, here is the public class which represents an HTTP request: ``` class http_request { public:
最后，下面是代表 HTTP 请求的公共类：``` class http_request { public:
It is clear from this declaration that the goal of the message model in this library is driven by its use-case (interacting with REST servers) and not to model HTTP messages generally. We note problems similar to the other declarations:
从这个声明中可以清楚地看出，该库中消息模型的目标是由其用例（与 REST 服务器交互）驱动的，而不是为了对 HTTP 消息进行通用建模。我们注意到存在与其他声明类似的问题：
* Setting the body requires either a vector or a `concurrency::streams::istream`.
* 设置消息体需要使用向量或 `concurrency::streams::istream`。
The general theme of the HTTP message model in cpprestsdk is "no user definable customizations". There is no allocator support, and no separation of concerns. It is designed to perform a specific set of behaviors. In other words, it does not follow the open/closed principle.
cpprestsdk 中 HTTP 消息模型的总体主题是“不支持用户可定义的自定义功能”。它没有分配器支持，也没有关注点分离。它的设计目的是执行特定的行为集。换句话说，它没有遵循开闭原则。
class http_msg_base { public:
class http_msg_base { public:
protected:
protected:
HTTP Comparison to Other Libraries
HTTP 与其他库的比较

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User avatar Bstran

Translation changed
* The library uses specializations of `string<Tag>` to change the type
* The library uses specializations of `string<Tag>` to change the type该库使用 `string<Tag>` 的特化来改变类型
06/20/2026
User avatar admin

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* The library uses specializations of `string<Tag>` to change the type
* The library uses specializations of `string<Tag>` to change the type
06/05/2026
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type: list
Unit identifier
58633
Source string location
string ID 112
String age
06/05/2026
Last updated
06/26/2026
Source string age
06/05/2026
Translation file QuickBook file
doc/qbk/08_design/2_http_comparison_zh_Hans.qbk, string 18