NAME

       tls_read, tls_write, tls_handshake, tls_error, tls_close, tls_reset — use a TLS connection

SYNOPSIS

       #include <tls.h>

       ssize_t
       tls_read(struct tls *ctx, void *buf, size_t buflen);

       ssize_t
       tls_write(struct tls *ctx, const void *buf, size_t buflen);

       int
       tls_handshake(struct tls *ctx);

       const char *
       tls_error(struct tls *ctx);

       int
       tls_close(struct tls *ctx);

       void
       tls_reset(struct tls *ctx);

DESCRIPTION

       tls_read() reads buflen bytes of data from the socket into buf.  It returns the amount of data read.

       tls_write() writes buflen bytes of data from buf to the socket.  It returns the amount of data written.

       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 tls_read() and tls_write() automatically
       perform the TLS handshake when necessary.

       The tls_error() function may be used to retrieve a string containing  more  information  about  the  most
       recent error relating to a context.

       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  tls_connect(3)
       or tls_connect_servername(3).  After closing the connection, ctx can be passed to tls_free(3).

RETURN VALUES

       tls_read() and tls_write() return a size on success or -1 on error.

       tls_handshake() and tls_close() return 0 on success or -1 on error.

       The  tls_read(),  tls_write(),  tls_handshake(),  and  tls_close() functions also have two special return
       values:

             TLS_WANT_POLLIN   The underlying read file descriptor needs to be readable in order to continue.
             TLS_WANT_POLLOUT  The underlying write file descriptor needs to be writeable in order to continue.

       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.

       Callers of these functions cannot rely on the value of the global errno.  To prevent mishandling of error
       conditions, tls_read(), tls_write(), tls_handshake(), and tls_close() all explicitly clear errno.

       tls_error() returns NULL if no error occurred with ctx during or since the last call to  tls_handshake(),
       tls_read(),  tls_write(), tls_close(), or tls_reset() involving ctx, or if memory allocation failed while
       trying to assemble the string describing the most recent error related to ctx.

EXAMPLES

       The following example demonstrates how to handle TLS writes on a blocking file descriptor:

             ...
             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;
             }
             ...

       The following example demonstrates how to handle TLS writes  on  a  non-blocking  file  descriptor  using
       poll(2):

             ...
             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;
                             }
                     }
             }
             ...

SEE ALSO

       tls_accept_socket(3),     tls_configure(3),     tls_conn_version(3),     tls_connect(3),     tls_init(3),
       tls_ocsp_process_response(3)

HISTORY

       tls_read(), tls_write(), tls_error(), tls_close(), and tls_reset() appeared in OpenBSD 5.6 and got  their
       final names in OpenBSD 5.7.

       tls_handshake() appeared in OpenBSD 5.9.

AUTHORS

       Joel Sing <jsing@openbsd.org> with contributions from
       Bob Beck <beck@openbsd.org>

CAVEATS

       The  function  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  ctx.
       Consequently,  if  the application may need the message at a later time, it has to copy the string before
       calling the next libtls function involving ctx, or a segmentation fault or read access to unintended data
       is the likely result.

Debian                                            July 9, 2019                                       TLS_READ(3)