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 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<nonblocking>, 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 nonblocking 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 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 HISTORY

 The SSL_read_ex() and SSL_peek_ex() functions were added in OpenSSL 1.1.1.

 =head1 COPYRIGHT

 Copyright 2000-2020 The OpenSSL Project Authors. All Rights Reserved.

 Licensed under the Apache License 2.0 (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 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<nonblocking>, 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 nonblocking 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 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 HISTORY

	The SSL_read_ex() and SSL_peek_ex() functions were added in OpenSSL 1.1.1.

	=head1 COPYRIGHT

	Copyright 2000-2020 The OpenSSL Project Authors. All Rights Reserved.

	Licensed under the Apache License 2.0 (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