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Fields

An instance of Fields is a container for holding HTTP header fields and their values. The implementation also calls upon the container to store the request target and non-standard strings for method and obsolete reason phrase as needed. Types which meet these requirements can always be serialized.

Associated Types
Requirements

In this table:

Table 34. Valid expressions

Expression

Type

Semantics, Pre/Post-conditions

F::reader

R

A type which meets the requirements of FieldsReader.

c.get_method_impl()

string_view

Returns the method text. The implementation only calls this function for request headers when retrieving the method text previously set with a call to set_method_impl using a non-empty string.

c.get_target_impl()

string_view

Returns the target string. The implementation only calls this function for request headers.

c.get_reason_impl()

string_view

Returns the obsolete request text. The implementation only calls this for response headers when retrieving the reason text previously set with a call to set_reason_impl using a non-empty string.

c.get_chunked_impl()

bool

Returns true if the Transfer-Encoding field value indicates that the payload is chunk encoded. Both of these conditions must be true:

  • The Transfer-Encoding field is present in the message.
  • The last item the value of the field is "chunked".

c.get_keep_alive_impl(v)

bool

Returns true if the semantics of the Connection field and version indicate that the connection should remain open after the corresponding response is transmitted or received:

  • If (v < 11) the function returns true if the "keep-alive" token is present in the Connection field value. Otherwise the function returns false.
  • If (v == 11), the function returns false if the "close" token is present in the Connection field value. Otherwise the function returns true.

a.set_method_impl(s)

Stores a copy of s as the method text, or erases the previously stored value if s is empty. The implementation only calls this function for request headers. This function may throw std::invalid_argument if the operation is not supported by the container.

a.set_target_impl(s)

Stores a copy of s as the target, or erases the previously stored value if s is empty. The implementation only calls this function for request headers. This function may throw std::invalid_argument if the operation is not supported by the container.

a.set_reason_impl(s)

Stores a copy of s as the reason text, or erases the previously stored value of the reason text if s is empty. The implementation only calls this function for request headers. This function may throw std::invalid_argument if the operation is not supported by the container.

a.set_chunked_impl(b)

Adjusts the Transfer-Encoding field as follows:

  • If b is true, the "chunked" token is appended to the list of encodings if it does not already appear last in the list. If the Transfer-Encoding field is absent, the field will be inserted to the container with the value "chunked".
  • If b is `false, the "chunked" token is removed from the list of encodings if it appears last in the list. If the result of the removal leaves the list of encodings empty, the Transfer-Encoding field shall not appear when the associated FieldsReader serializes the fields.

a.set_content_length_impl(n)

Adjusts the Content-Length field as follows:

  • If n contains a value, the Content-Length field will be set to the text representation of the value. Any previous Content-Length fields are removed from the container.
  • If n does not contain a value, any present Content-Length fields are removed from the container.

a.set_keep_alive_impl(v,b)

Adjusts the Connection field value depending on the values of v and b. The field value is treated as connection-option (rfc7230).

  • If (v < 11 && b), then all "close" tokens present in the value are removed, and the "keep-alive" token is added to the valueif it is not already present.
  • If (v < 11 && ! b), then all "close" and "keep-alive" tokens present in the value are removed.
  • If (v == 11 && b), then all "keep-alive" and "close" tokens present in the value are removed.
  • If (v == 11 && ! b), then all "keep-alive" tokens present in the value are removed, and the "close" token is added to the value if it is not already present.

Exemplar
class Fields
{
public:
    struct reader;

protected:
    /** Returns the request-method string.

        @note Only called for requests.
    */
    string_view
    get_method_impl() const;

    /** Returns the request-target string.

        @note Only called for requests.
    */
    string_view
    get_target_impl() const;

    /** Returns the response reason-phrase string.

        @note Only called for responses.
    */
    string_view
    get_reason_impl() const;

    /** Returns the chunked Transfer-Encoding setting
    */
    bool
    get_chunked_impl() const;

    /** Returns the keep-alive setting
    */
    bool
    get_keep_alive_impl(unsigned version) const;

    /** Set or clear the method string.

        @note Only called for requests.
    */
    void
    set_method_impl(string_view s);

    /** Set or clear the target string.

        @note Only called for requests.
    */
    void
    set_target_impl(string_view s);

    /** Set or clear the reason string.

        @note Only called for responses.
    */
    void
    set_reason_impl(string_view s);

    /** Sets or clears the chunked Transfer-Encoding value
    */
    void
    set_chunked_impl(bool value);

    /** Sets or clears the Content-Length field
    */
    void
    set_content_length_impl(boost::optional<std::uint64_t>);

    /** Adjusts the Connection field
    */
    void
    set_keep_alive_impl(unsigned version, bool keep_alive);
};

static_assert(is_fields<Fields>::value,
    "Fields requirements not met");
Models

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