.\" $OpenBSD: tls_read.3,v 1.7 2019/07/09 17:58:33 jsing Exp $ .\" .\" Copyright (c) 2014, 2015 Ted Unangst .\" Copyright (c) 2015 Doug Hogan .\" Copyright (c) 2015 Joel Sing .\" Copyright (c) 2015 Bob Beck .\" Copyright (c) 2017 Ingo Schwarze .\" .\" 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. .\" .\" 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 .\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF .\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. .\" .Dd $Mdocdate: July 9 2019 $ .Dt TLS_READ 3 .Os .Sh NAME .Nm tls_read , .Nm tls_write , .Nm tls_handshake , .Nm tls_error , .Nm tls_close , .Nm tls_reset .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" .Ft void .Fn tls_reset "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 . .\" XXX Fn tls_reset does what? .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 .Fn tls_reset 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 , .Fn tls_close , and .Fn tls_reset 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.