User avatar Bstran

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``` /// An HTTP header template<bool isRequest, class Body, class Fields = fields> struct header;
``` /// An一个 HTTP header头部 template<bool isRequest, class Body, class Fields = fields> struct header;
06/20/2026
User avatar Bstran

Translation changed
Now that we've accomplished our initial goals and more, there are a few more quality of life improvements to make. Users will choose different types for `Body` far more often than they will for `Fields`. Thus, we swap the order of these types and provide a default. Then, we provide type aliases for requests and responses to soften the impact of using `bool` to choose the specialization:
Now that we've accomplished our initial goals and more, there are a few more quality of life improvements to make. Users will choose different types for `Body` far more often than they will for `Fields`. Thus, we swap the order of these types and provide a default. Then, we provide type aliases for requests and responses to soften the impact of using `bool` to choose the specialization:初步目标已超额达成，接下来还需进行一些提升易用性的改进。由于用户为 `Body` 选择自定义类型的频率远高于为 `Fields` 选择，因此将这两者的模板参数顺序互换，并为 `Fields` 提供默认类型。随后，为请求和响应提供类型别名，以缓解直接使用 `bool` 来选择特化版本带来的不便：
06/20/2026
User avatar Bstran

Translation changed
}; ```
}; ```
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User avatar Bstran

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Now we add a requirement to the fields type: management of the corresponding string is delegated to the [*Fields] container, which can already be allocator aware and constructed with the necessary allocator parameter via the provided constructor overloads for `message`. The delegation implementation looks like this (only the response header specialization is shown): ``` /// An HTTP response header template<class Fields> struct header<false, Fields> : Fields {
Now we add a requirement to the fields type: management of the corresponding string is delegated to the [*Fields] container, which can already be allocator aware and constructed with the necessary allocator parameter via the provided constructor overloads for `message`. The delegation implementation looks like this (only the response header specialization is shown): 对 `Fields` 类型增加一项要求：将对应字符串的管理委托给 `Fields` 容器。该容器本身已具备分配器感知能力，且可通过 `message` 提供的构造函数重载，使用必要的分配器参数进行构造。委托的实现方式如下（仅展示响应头部的特化版本）：``` /// An一个 HTTP response header响应头部 template<class Fields> struct header<false, Fields> : Fields {
06/20/2026
User avatar Bstran

Translation changed
The start-line data members are replaced by traditional accessors using non-owning references to string buffers. The method is stored using a simple integer instead of the entire string, for the case where the method is recognized from the set of known verb strings.
The 起始行（start-line data members are replaced by traditional accessors using non-owning references to string buffers. The method is stored using a simple integer instead of the entire string, for the case where the method is recognized from the set of known verb strings.）的数据成员被替换成传统的访问器（accessors），它们通过不持有所有权的引用来指向字符串缓冲区。此外，对于能从已知动词字符串集合中识别出的方法（method），系统直接使用一个简单的整数来存储，而不再保存完整的字符串。
06/20/2026
User avatar Bstran

Translation changed
}; ```
}; ```
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User avatar Bstran

Translation changed
/// An HTTP response header template<class Fields> struct header<false, Fields> : Fields {
/// An一个 HTTP response header template<class Fields>响应头部 template struct header<false, Fields> : Fields {
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User avatar Bstran

Translation changed
};
};
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User avatar Bstran

Translation changed
private:
private:
06/20/2026
User avatar Bstran

Translation changed
To get around this we make an interface modification and then add a requirement to the [*Fields] type. First, the interface change: ``` /// An HTTP request header template<class Fields> struct header<true, Fields> : Fields {
为了解决这个问题，我们首先对接口进行修改，然后对 `Fields` 类型增加一项要求。首先是接口层面的改动：``` /// 一个 HTTP 请求头部
template<class Fields> struct header<true, Fields> : Fields {
06/20/2026
User avatar Bstran

Translation changed
To get around this we make an interface modification and then add a requirement to the [*Fields] type. First, the interface change: ``` /// An HTTP request header template<class Fields> struct header<true, Fields> : Fields {
To get around this we make an interface modification and then add a requirement to the [*Fields] type. First, the interface change: 为了解决这个问题，我们首先对接口进行修改，然后对 `Fields` 类型增加一项要求。首先是接口层面的改动：``` /// An一个 HTTP request header 请求头部
template<class Fields> struct header<true, Fields> : Fields {
06/20/2026
User avatar Bstran

Translation changed
There is now significant progress with our message container but a stumbling block remains. There is no way to control the allocator for the `std::string` members. We could add an allocator to the template parameter list of the header and message classes, use it for those strings. This is unsatisfying because of the combinatorial explosion of constructor variations needed to support the scheme. It also means that request messages could have [*four] different allocators: two for the fields and body, and two for the method and target strings. A better solution is needed.
There is now significant progress with our message container but a stumbling block remains. There is no way to control the allocator for the `std::string` members. We could add an allocator to the template parameter list of the header and message classes, use it for those strings. This is unsatisfying because of the combinatorial explosion of constructor variations needed to support the scheme. It also means that request messages could have [*four] different allocators: two for the fields and body, and two for the 尽管我们的消息容器已经取得了显著进展，但仍面临一个棘手的问题：目前无法控制 `std::string` 成员的分配器。虽然可以在 `header` 和 `message` 类的模板参数列表中添加一个分配器来管理这些字符串，但这并不是一个令人满意的方案。因为这需要引入数量庞大的构造函数重载来支持该机制，导致组合爆炸。此外，这也意味着请求消息可能会拥有多达四种不同的分配器：其中两个分别用于字段和主体，另外两个则用于方法（method and ）和目标（target strings. A better solution is needed.）字符串。因此，我们需要寻找一个更好的解决方案。
06/20/2026
User avatar Bstran

Translation changed
The solution used in the library is to treat the message like a `std::pair` for the purposes of construction, except that instead of `first` and `second` we have the `Fields` base class and `message::body` member. This means that single-argument constructors for those fields should be accessible as they are with `std::pair`, and that a mechanism identical to the pair's use of `std::piecewise_construct` should be provided. Those constructors are too complex to repeat here, but interested readers can view the declarations in the corresponding header file.
The solution used in the library is to treat the message like a `std::pair` for the purposes of construction, except that instead of库中采用的解决方案是：在构造 `message` 时，将其视作 `std::pair` 来处理。不同的是，原本 `std::pair` 中的 `first` and和 `second` we have the `Fields` base class and `message::body` member. This means that single-argument constructors for those fields should be accessible as they are with `std::pair`, and that a mechanism identical to the pair's use of `std::piecewise_construct` should be provided. Those constructors are too complex to repeat here, but interested readers can view the declarations in the corresponding header file.在这里被替换成了 `Fields` 基类和 `message::body` 成员。这意味着，这些字段的单参数构造函数应当像 `std::pair` 一样易于调用，并且需要提供一套与 `std::pair` 的 `std::piecewise_construct` 完全相同的机制。由于这些构造函数的实现较为复杂，这里不再赘述，感兴趣的读者可以直接查阅相应头文件中的声明。
06/20/2026
User avatar Bstran

Translation changed
Until now we have not given significant consideration to the constructors of the `message` class. But to achieve all our goals we will need to make sure that there are enough constructor overloads to not only provide for the special copy and move members if the instantiated types support it, but also allow the fields container and body container to be constructed with arbitrary variadic lists of parameters. This allows the container to fully support allocators.
Until now we have not given significant consideration to the constructors of the `message` class. But to achieve all our goals we will need to make sure that there are enough constructor overloads to not only provide for the special copy and move members if the instantiated types support it, but also allow the fields container and body container to be constructed with arbitrary variadic lists of parameters. This allows the container to fully support allocators.到目前为止，我们还没有对 `message` 类的构造函数给予足够的重视。但为了实现所有目标，我们必须确保提供足够多的构造函数重载。这不仅需要在实例化的类型支持时提供特殊的拷贝和移动成员，还需要允许使用任意的可变参数列表来构造字段容器和主体容器。这使得容器能够完全支持分配器。
06/20/2026
User avatar Bstran

Translation changed
Note that the `message` class now has a constructor allowing messages to be constructed from a similarly typed `header`. This handles the case where the user already has the header and wants to make a commitment to the type for [*Body]. A function can be declared which accepts any header: ``` template<bool isRequest, class Fields> void f(header<isRequest, Fields>& msg); ```
Note that the `message` class now has a constructor allowing messages to be constructed from a similarly typed `header`. This handles the case where the user already has the header and wants to make a commitment to the type for [*Body]. A function can be declared which accepts any header:请注意，`message` 类现在拥有一个构造函数，允许从类型相同的 `header` 构造消息。这解决了用户已经拥有头部，并希望为 [*Body] 确定具体类型的情况。我们可以声明一个能够接受任意头部的函数： ``` template<bool isRequest, class Fields> void f(header<isRequest, Fields>& msg); ```
06/20/2026
User avatar Bstran

Translation changed
```
```
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User avatar Bstran

Translation changed
};
};
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User avatar Bstran

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/// An HTTP message template<bool isRequest, class Fields, class Body> struct message : header<isRequest, Fields> {
/// An一个 HTTP message消息 template<bool isRequest, class Fields, class Body> struct message : header<isRequest, Fields> {
06/20/2026
User avatar Bstran

Translation changed
};
};
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User avatar Bstran

Translation changed
/// An HTTP response header template<class Fields> struct header<false, Fields> : Fields {
/// An一个 HTTP response header template<class Fields>响应头部 template struct header<false, Fields> : Fields {
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