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Read part of a message asynchronously from a stream using a parser.


Defined in header <boost/beast/http/read.hpp>

    class AsyncReadStream,
    class DynamicBuffer,
    bool isRequest,
    class Derived,
    class ReadHandler>
    AsyncReadStream& stream,
    DynamicBuffer& buffer,
    basic_parser< isRequest, Derived >& parser,
    ReadHandler&& handler);

This function is used to asynchronously read part of a message from a stream into a subclass of http::basic_parser. The function call always returns immediately. The asynchronous operation will continue until one of the following conditions is true:

This operation is implemented in terms of zero or more calls to the next layer's async_read_some function, and is known as a composed operation. The program must ensure that the stream performs no other reads until this operation completes. The implementation may read additional octets that lie past the end of the object being parsed. This additional data is stored in the stream buffer, which may be used in subsequent calls.

If the stream returns the error boost::asio::error::eof indicating the end of file during a read, the error returned from this function will be:





The stream from which the data is to be read. The type must support the AsyncReadStream concept.


A DynamicBuffer holding additional bytes read by the implementation from the stream. This is both an input and an output parameter; on entry, any data in the dynamic buffer's input sequence will be given to the parser first.


The parser to use. The object must remain valid at least until the handler is called; ownership is not transferred.


Invoked when the operation completes. The handler may be moved or copied as needed. The equivalent function signature of the handler must be:

 void handler(
    error_code const& error,        // result of operation
    std::size_t bytes_transferred   // the number of bytes transferred to the parser

Regardless of whether the asynchronous operation completes immediately or not, the handler will not be invoked from within this function. Invocation of the handler will be performed in a manner equivalent to using boost::asio::io_context::post.

The completion handler will receive as a parameter the number of octets processed from the dynamic buffer. The octets should be removed by calling consume on the dynamic buffer after the read completes, regardless of any error.

Convenience header <boost/beast/http.hpp>