A callback for rustls_connection_read_tls.
An implementation of this callback should attempt to read up to n bytes from the
network, storing them in buf. If any bytes were stored, the implementation should
set out_n to the number of bytes stored and return 0. If there was an error,
the implementation should return a nonzero rustls_io_result, which will be
passed through to the caller. On POSIX systems, returning errno is convenient.
On other systems, any appropriate error code works.
It's best to make one read attempt to the network per call. Additional reads will
be triggered by subsequent calls to one of the _read_tls methods.
userdata is set to the value provided to rustls_connection_set_userdata. In most
cases that should be a struct that contains, at a minimum, a file descriptor.
The buf and out_n pointers are borrowed and should not be retained across calls.
A callback for rustls_connection_read_tls. An implementation of this callback should attempt to read up to n bytes from the network, storing them in buf. If any bytes were stored, the implementation should set out_n to the number of bytes stored and return 0. If there was an error, the implementation should return a nonzero rustls_io_result, which will be passed through to the caller. On POSIX systems, returning errno is convenient. On other systems, any appropriate error code works. It's best to make one read attempt to the network per call. Additional reads will be triggered by subsequent calls to one of the _read_tls methods. userdata is set to the value provided to rustls_connection_set_userdata. In most cases that should be a struct that contains, at a minimum, a file descriptor. The buf and out_n pointers are borrowed and should not be retained across calls.