doc/man3/SSL_read.pod - third_party/openssl - Git at Google

 =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 the 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 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
 renegotiation takes place, in which case a SSL_ERROR_WANT_READ may occur. This
 behaviour can be controlled with the SSL_MODE_AUTO_RETRY flag of the
 L<SSL_CTX_set_mode(3)> call.

 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 a re-negotiation is possible, a
 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 WARNING

 When a read function operation has to be repeated because L<SSL_get_error(3)>
 returned B<SSL_ERROR_WANT_READ> or B<SSL_ERROR_WANT_WRITE>, it must be repeated
 with the same arguments.

 =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 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 2000-2016 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
	=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 the 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 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
	renegotiation takes place, in which case a SSL_ERROR_WANT_READ may occur. This
	behaviour can be controlled with the SSL_MODE_AUTO_RETRY flag of the
	L<SSL_CTX_set_mode(3)> call.

	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 a re-negotiation is possible, a
	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 WARNING

	When a read function operation has to be repeated because L<SSL_get_error(3)>
	returned B<SSL_ERROR_WANT_READ> or B<SSL_ERROR_WANT_WRITE>, it must be repeated
	with the same arguments.

	=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 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 2000-2016 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