...one of the most highly
regarded and expertly designed C++ library projects in the
world.
— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards
Read a complete message asynchronously from a stream.
Defined in header <boost/beast/http/read.hpp>
template< class AsyncReadStream, class DynamicBuffer, bool isRequest, class Body, class Allocator, class ReadHandler = net::default_completion_token_t< executor_type<AsyncReadStream>>> DEDUCED async_read( AsyncReadStream& stream, DynamicBuffer& buffer, message< isRequest, Body, basic_fields< Allocator >>& msg, ReadHandler&& handler = net::default_completion_token_t< executor_type< AsyncReadStream >>{});
This function is used to asynchronously read a complete message from a
stream into an instance of message
. 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 bytes from
the stream that lie past the end of the message being read. These additional
bytes are stored in the dynamic buffer, which must be preserved for subsequent
reads. If the end of file error is received while reading from the stream,
then the error returned from this function will be:
error::end_of_stream
if no bytes were parsed, or
error::partial_message
if any bytes were parsed but the message was incomplete, otherwise:
error::end_of_stream
Name |
Description |
---|---|
|
The stream from which the data is to be read. The type must meet the AsyncReadStream requirements. |
|
Storage for additional bytes read by the implementation from the stream. This is both an input and an output parameter; on entry, the parser will be presented with any remaining data in the dynamic buffer's readable bytes sequence first. The type must meet the DynamicBuffer requirements. The object must remain valid at least until the handler is called; ownership is not transferred. |
|
The container in which to store the message contents. This message container should not have previous contents, otherwise the behavior is undefined. The type must be meet the MoveAssignable and MoveConstructible requirements. The object must remain valid at least until the handler is called; ownership is not transferred. |
|
The completion handler to invoke when the operation completes. The implementation takes ownership of the handler by performing a decay-copy. The equivalent function signature of the handler must be: void handler( error_code const& error, // result of operation std::size_t bytes_transferred // the total number of bytes transferred from the stream );
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 |
The completion handler will receive as a parameter the total number of
bytes transferred from the stream. This may be zero for the case where
there is sufficient pre-existing message data in the dynamic buffer. The
implementation will call basic_parser::eager
with the value true
on the parser passed in.
This asynchronous operation supports cancellation for the following net::cancellation_type values:
net::cancellation_type::terminal
if the stream
also supports
terminal cancellation. terminal
cancellation leaves the stream in an undefined state, so that only closing
it is guaranteed to succeed.