xref: /openbsd-src/lib/libtls/man/tls_read.3 (revision 58d3272672b955c4c9f23784829dfa5dd0b93090)

.\" $OpenBSD: tls_read.3,v 1.8 2023/09/18 17:25:15 schwarze Exp $
.\"
.\" Copyright (c) 2014, 2015 Ted Unangst <tedu@openbsd.org>
.\" Copyright (c) 2015 Doug Hogan <doug@openbsd.org>
.\" Copyright (c) 2015 Joel Sing <jsing@openbsd.org>
.\" Copyright (c) 2015 Bob Beck <beck@openbsd.org>
.\" Copyright (c) 2017 Ingo Schwarze <schwarze@openbsd.org>
.\"
.\" Permission to use, copy, modify, and distribute this software for any
.\" purpose with or without fee is hereby granted, provided that the above
.\" copyright notice and this permission notice appear in all copies.
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.\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
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.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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.Dd $Mdocdate: September 18 2023 $
.Dt TLS_READ 3
.Os
.Sh NAME
.Nm tls_read ,
.Nm tls_write ,
.Nm tls_handshake ,
.Nm tls_error ,
.Nm tls_close
.Nd use a TLS connection
.Sh SYNOPSIS
.In tls.h
.Ft ssize_t
.Fo tls_read
.Fa "struct tls *ctx"
.Fa "void *buf"
.Fa "size_t buflen"
.Fc
.Ft ssize_t
.Fo tls_write
.Fa "struct tls *ctx"
.Fa "const void *buf"
.Fa "size_t buflen"
.Fc
.Ft int
.Fn tls_handshake "struct tls *ctx"
.Ft const char *
.Fn tls_error "struct tls *ctx"
.Ft int
.Fn tls_close "struct tls *ctx"
.Sh DESCRIPTION
.Fn tls_read
reads
.Fa buflen
bytes of data from the socket into
.Fa buf .
It returns the amount of data read.
.Pp
.Fn tls_write
writes
.Fa buflen
bytes of data from
.Fa buf
to the socket.
It returns the amount of data written.
.Pp
.Fn tls_handshake
explicitly performs the TLS handshake.
It is only necessary to call this function if you need to guarantee that the
handshake has completed, as both
.Fn tls_read
and
.Fn tls_write
automatically perform the TLS handshake when necessary.
.Pp
The
.Fn tls_error
function may be used to retrieve a string containing more information
about the most recent error relating to a context.
.Pp
.Fn tls_close
closes a connection after use.
Only the TLS layer will be shut down and the caller is responsible for closing
the file descriptors, unless the connection was established using
.Xr tls_connect 3
or
.Xr tls_connect_servername 3 .
After closing the connection,
.Fa ctx
can be passed to
.Xr tls_free 3 .
.Sh RETURN VALUES
.Fn tls_read
and
.Fn tls_write
return a size on success or -1 on error.
.Pp
.Fn tls_handshake
and
.Fn tls_close
return 0 on success or -1 on error.
.Pp
The
.Fn tls_read ,
.Fn tls_write ,
.Fn tls_handshake ,
and
.Fn tls_close
functions also have two special return values:
.Pp
.Bl -tag -width "TLS_WANT_POLLOUT" -offset indent -compact
.It Dv TLS_WANT_POLLIN
The underlying read file descriptor needs to be readable in order to continue.
.It Dv TLS_WANT_POLLOUT
The underlying write file descriptor needs to be writeable in order to continue.
.El
.Pp
In the case of blocking file descriptors, the same function call should be
repeated immediately.
In the case of non-blocking file descriptors, the same function call should be
repeated when the required condition has been met.
.Pp
Callers of these functions cannot rely on the value of the global
.Ar errno .
To prevent mishandling of error conditions,
.Fn tls_read ,
.Fn tls_write ,
.Fn tls_handshake ,
and
.Fn tls_close
all explicitly clear
.Ar errno .
.Pp
.Fn tls_error
returns
.Dv NULL
if no error occurred with
.Fa ctx
during or since the last call to
.Fn tls_handshake ,
.Fn tls_read ,
.Fn tls_write ,
.Fn tls_close ,
or
.Xr tls_reset 3
involving
.Fa ctx ,
or if memory allocation failed while trying to assemble the string
describing the most recent error related to
.Fa ctx .
.Sh EXAMPLES
The following example demonstrates how to handle TLS writes on a blocking
file descriptor:
.Bd -literal -offset indent
\&...
while (len > 0) {
	ssize_t ret;

	ret = tls_write(ctx, buf, len);
	if (ret == TLS_WANT_POLLIN || ret == TLS_WANT_POLLOUT)
		continue;
	if (ret == -1)
		errx(1, "tls_write: %s", tls_error(ctx));
	buf += ret;
	len -= ret;
}
\&...
.Ed
.Pp
The following example demonstrates how to handle TLS writes on a
non-blocking file descriptor using
.Xr poll 2 :
.Bd -literal -offset indent
\&...
pfd[0].fd = fd;
pfd[0].events = POLLIN|POLLOUT;
while (len > 0) {
	nready = poll(pfd, 1, 0);
	if (nready == -1)
		err(1, "poll");
	if ((pfd[0].revents & (POLLERR|POLLNVAL)))
		errx(1, "bad fd %d", pfd[0].fd);
	if ((pfd[0].revents & (pfd[0].events|POLLHUP))) {
		ssize_t ret;

		ret = tls_write(ctx, buf, len);
		if (ret == TLS_WANT_POLLIN)
			pfd[0].events = POLLIN;
		else if (ret == TLS_WANT_POLLOUT)
			pfd[0].events = POLLOUT;
		else if (ret == -1)
			errx(1, "tls_write: %s", tls_error(ctx));
		else {
			buf += ret;
			len -= ret;
		}
	}
}
\&...
.Ed
.Sh SEE ALSO
.Xr tls_accept_socket 3 ,
.Xr tls_configure 3 ,
.Xr tls_conn_version 3 ,
.Xr tls_connect 3 ,
.Xr tls_init 3 ,
.Xr tls_ocsp_process_response 3
.Sh HISTORY
.Fn tls_read ,
.Fn tls_write ,
.Fn tls_error ,
and
.Fn tls_close
appeared in
.Ox 5.6
and got their final names in
.Ox 5.7 .
.Pp
.Fn tls_handshake
appeared in
.Ox 5.9 .
.Sh AUTHORS
.An Joel Sing Aq Mt jsing@openbsd.org
with contributions from
.An Bob Beck Aq Mt beck@openbsd.org
.Sh CAVEATS
The function
.Fn tls_error
returns an internal pointer.
It must not be freed by the application, or a double free error
will occur.
The pointer will become invalid when the next error occurs with
.Fa ctx .
Consequently, if the application may need the message at a later
time, it has to copy the string before calling the next
.Sy libtls
function involving
.Fa ctx ,
or a segmentation fault or read access to unintended data is the
likely result.