test::stream::lowest_layer_type

The type of the lowest layer.

Synopsis

using lowest_layer_type = stream;

Types

Name	Description
buffer_type
executor_type	The type of the executor associated with the object.
lowest_layer_type	The type of the lowest layer.

Member Functions

Name	Description
append	Appends a string to the pending input data.
async_read_some	Start an asynchronous read.
async_write_some	Start an asynchronous write.
buffer	Direct input buffer access.
clear	Clear the pending input area.
close	Close the stream.
close_remote	Close the other end of the stream.
connect	Establish a connection.
get_executor	Return the executor associated with the object.
lowest_layer	Get a reference to the lowest layer.
nread	Return the number of reads.
nwrite	Return the number of writes.
operator=	Move Assignment.
read_size	Set the maximum number of bytes returned by read_some.
read_some	Read some data from the stream.
str	Returns a string view representing the pending input data.
stream	Move Constructor. Construct a stream.
write_size	Set the maximum number of bytes returned by write_some.
write_some	Write some data to the stream.
~stream	Destructor.

An instance of this class simulates a traditional socket, while also providing features useful for unit testing. Each endpoint maintains an independent buffer called the input area. Writes from one endpoint append data to the peer's pending input area. When an endpoint performs a read and data is present in the input area, the data is delivered to the blocking or asynchronous operation. Otherwise the operation is blocked or deferred until data is made available, or until the endpoints become disconnected.

These streams may be used anywhere an algorithm accepts a reference to a synchronous or asynchronous read or write stream. It is possible to use a test stream in a call to boost::asio::read_until, or in a call to http::async_write for example.

As with Boost.Asio I/O objects, a test::stream constructs with a reference to the boost::asio::io_context to use for handling asynchronous I/O. For asynchronous operations, the stream follows the same rules as a traditional asio socket with respect to how completion handlers for asynchronous operations are performed.

To facilitate testing, these streams support some additional features:

The input area, represented by a flat_buffer, may be directly accessed by the caller to inspect the contents before or after the remote endpoint writes data. This allows a unit test to verify that the received data matches.
Data may be manually appended to the input area. This data will delivered in the next call to test::stream::read_some or test::stream::async_read_some. This allows predefined test vectors to be set up for testing read algorithms.
The stream may be constructed with a fail count. The stream will eventually fail with a predefined error after a certain number of operations, where the number of operations is controlled by the test. When a test loops over a range of operation counts, it is possible to exercise every possible point of failure in the algorithm being tested. When used correctly the technique allows the tests to reach a high percentage of code coverage.

Thread Safety

Distinct objects: Safe.

Shared objects: Unsafe. The application must also ensure that all asynchronous operations are performed within the same implicit or explicit strand.

Concepts

SyncReadStream
SyncWriteStream
AsyncReadStream
AsyncWriteStream