1212818eb0
Reviewed-by: Richard Levitte <levitte@openssl.org> (Merged from https://github.com/openssl/openssl/pull/7176)
152 lines
6.1 KiB
Text
152 lines
6.1 KiB
Text
=pod
|
|
|
|
=head1 NAME
|
|
|
|
SSL_read_ex, SSL_read, SSL_peek_ex, SSL_peek
|
|
- read bytes from a TLS/SSL connection
|
|
|
|
=head1 SYNOPSIS
|
|
|
|
#include <openssl/ssl.h>
|
|
|
|
int SSL_read_ex(SSL *ssl, void *buf, size_t num, size_t *readbytes);
|
|
int SSL_read(SSL *ssl, void *buf, int num);
|
|
|
|
int SSL_peek_ex(SSL *ssl, void *buf, size_t num, size_t *readbytes);
|
|
int SSL_peek(SSL *ssl, void *buf, int num);
|
|
|
|
=head1 DESCRIPTION
|
|
|
|
SSL_read_ex() and SSL_read() try to read B<num> bytes from the specified B<ssl>
|
|
into the buffer B<buf>. On success SSL_read_ex() will store the number of bytes
|
|
actually read in B<*readbytes>.
|
|
|
|
SSL_peek_ex() and SSL_peek() are identical to SSL_read_ex() and SSL_read()
|
|
respectively except no bytes are actually removed from the underlying BIO during
|
|
the read, so that a subsequent call to SSL_read_ex() or SSL_read() will yield
|
|
at least the same bytes.
|
|
|
|
=head1 NOTES
|
|
|
|
In the paragraphs below a "read function" is defined as one of SSL_read_ex(),
|
|
SSL_read(), SSL_peek_ex() or SSL_peek().
|
|
|
|
If necessary, a read function will negotiate a TLS/SSL session, if not already
|
|
explicitly performed by L<SSL_connect(3)> or L<SSL_accept(3)>. If the
|
|
peer requests a re-negotiation, it will be performed transparently during
|
|
the read function operation. The behaviour of the read functions depends on the
|
|
underlying BIO.
|
|
|
|
For the transparent negotiation to succeed, the B<ssl> must have been
|
|
initialized to client or server mode. This is being done by calling
|
|
L<SSL_set_connect_state(3)> or SSL_set_accept_state() before the first
|
|
invocation of a read function.
|
|
|
|
The read functions work based on the SSL/TLS records. The data are received in
|
|
records (with a maximum record size of 16kB). Only when a record has been
|
|
completely received, can it be processed (decryption and check of integrity).
|
|
Therefore data that was not retrieved at the last read call can still be
|
|
buffered inside the SSL layer and will be retrieved on the next read
|
|
call. If B<num> is higher than the number of bytes buffered then the read
|
|
functions will return with the bytes buffered. If no more bytes are in the
|
|
buffer, the read functions will trigger the processing of the next record.
|
|
Only when the record has been received and processed completely will the read
|
|
functions return reporting success. At most the contents of one record will
|
|
be returned. As the size of an SSL/TLS record may exceed the maximum packet size
|
|
of the underlying transport (e.g. TCP), it may be necessary to read several
|
|
packets from the transport layer before the record is complete and the read call
|
|
can succeed.
|
|
|
|
If B<SSL_MODE_AUTO_RETRY> has been switched off and a non-application data
|
|
record has been processed, the read function can return and set the error to
|
|
B<SSL_ERROR_WANT_READ>.
|
|
In this case there might still be unprocessed data available in the B<BIO>.
|
|
If read ahead was set using L<SSL_CTX_set_read_ahead(3)>, there might also still
|
|
be unprocessed data available in the B<SSL>.
|
|
This behaviour can be controlled using the L<SSL_CTX_set_mode(3)> call.
|
|
|
|
If the underlying BIO is B<blocking>, a read function will only return once the
|
|
read operation has been finished or an error occurred, except when a
|
|
non-application data record has been processed and B<SSL_MODE_AUTO_RETRY> is
|
|
not set.
|
|
Note that if B<SSL_MODE_AUTO_RETRY> is set and only non-application data is
|
|
available the call will hang.
|
|
|
|
If the underlying BIO is B<non-blocking>, a read function will also return when
|
|
the underlying BIO could not satisfy the needs of the function to continue the
|
|
operation.
|
|
In this case a call to L<SSL_get_error(3)> with the
|
|
return value of the read function will yield B<SSL_ERROR_WANT_READ> or
|
|
B<SSL_ERROR_WANT_WRITE>.
|
|
As at any time it's possible that non-application data needs to be sent,
|
|
a read function can also cause write operations.
|
|
The calling process then must repeat the call after taking appropriate action
|
|
to satisfy the needs of the read function.
|
|
The action depends on the underlying BIO.
|
|
When using a non-blocking socket, nothing is to be done, but select() can be
|
|
used to check for the required condition.
|
|
When using a buffering BIO, like a BIO pair, data must be written into or
|
|
retrieved out of the BIO before being able to continue.
|
|
|
|
L<SSL_pending(3)> can be used to find out whether there
|
|
are buffered bytes available for immediate retrieval.
|
|
In this case the read function can be called without blocking or actually
|
|
receiving new data from the underlying socket.
|
|
|
|
=head1 RETURN VALUES
|
|
|
|
SSL_read_ex() and SSL_peek_ex() will return 1 for success or 0 for failure.
|
|
Success means that 1 or more application data bytes have been read from the SSL
|
|
connection.
|
|
Failure means that no bytes could be read from the SSL connection.
|
|
Failures can be retryable (e.g. we are waiting for more bytes to
|
|
be delivered by the network) or non-retryable (e.g. a fatal network error).
|
|
In the event of a failure call L<SSL_get_error(3)> to find out the reason which
|
|
indicates whether the call is retryable or not.
|
|
|
|
For SSL_read() and SSL_peek() the following return values can occur:
|
|
|
|
=over 4
|
|
|
|
=item E<gt> 0
|
|
|
|
The read operation was successful.
|
|
The return value is the number of bytes actually read from the TLS/SSL
|
|
connection.
|
|
|
|
=item Z<><= 0
|
|
|
|
The read operation was not successful, because either the connection was closed,
|
|
an error occurred or action must be taken by the calling process.
|
|
Call L<SSL_get_error(3)> with the return value B<ret> to find out the reason.
|
|
|
|
Old documentation indicated a difference between 0 and -1, and that -1 was
|
|
retryable.
|
|
You should instead call SSL_get_error() to find out if it's retryable.
|
|
|
|
=back
|
|
|
|
=head1 HISTORY
|
|
|
|
SSL_read_ex() and SSL_peek_ex() were added in OpenSSL 1.1.1.
|
|
|
|
=head1 SEE ALSO
|
|
|
|
L<SSL_get_error(3)>, L<SSL_write_ex(3)>,
|
|
L<SSL_CTX_set_mode(3)>, L<SSL_CTX_new(3)>,
|
|
L<SSL_connect(3)>, L<SSL_accept(3)>
|
|
L<SSL_set_connect_state(3)>,
|
|
L<SSL_pending(3)>,
|
|
L<SSL_shutdown(3)>, L<SSL_set_shutdown(3)>,
|
|
L<ssl(7)>, L<bio(7)>
|
|
|
|
=head1 COPYRIGHT
|
|
|
|
Copyright 2000-2018 The OpenSSL Project Authors. All Rights Reserved.
|
|
|
|
Licensed under the OpenSSL license (the "License"). You may not use
|
|
this file except in compliance with the License. You can obtain a copy
|
|
in the file LICENSE in the source distribution or at
|
|
L<https://www.openssl.org/source/license.html>.
|
|
|
|
=cut
|