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Diffstat (limited to 'openssl-1.1.0h/doc/ssl/SSL_read.pod')
-rw-r--r-- | openssl-1.1.0h/doc/ssl/SSL_read.pod | 121 |
1 files changed, 121 insertions, 0 deletions
diff --git a/openssl-1.1.0h/doc/ssl/SSL_read.pod b/openssl-1.1.0h/doc/ssl/SSL_read.pod new file mode 100644 index 0000000..20ccf40 --- /dev/null +++ b/openssl-1.1.0h/doc/ssl/SSL_read.pod @@ -0,0 +1,121 @@ +=pod + +=head1 NAME + +SSL_read - read bytes from a TLS/SSL connection + +=head1 SYNOPSIS + + #include <openssl/ssl.h> + + int SSL_read(SSL *ssl, void *buf, int num); + +=head1 DESCRIPTION + +SSL_read() tries to read B<num> bytes from the specified B<ssl> into the +buffer B<buf>. + +=head1 NOTES + +If necessary, SSL_read() 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 SSL_read() operation. The behaviour of SSL_read() 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 call to an SSL_read() or L<SSL_write(3)> +function. + +SSL_read() works based on the SSL/TLS records. The data are received in +records (with a maximum record size of 16kB for SSLv3/TLSv1). Only when a +record has been completely received, it can be processed (decryption and +check of integrity). Therefore data that was not retrieved at the last +call of SSL_read() can still be buffered inside the SSL layer and will be +retrieved on the next call to SSL_read(). If B<num> is higher than the +number of bytes buffered, SSL_read() will return with the bytes buffered. +If no more bytes are in the buffer, SSL_read() will trigger the processing +of the next record. Only when the record has been received and processed +completely, SSL_read() will 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 SSL_read() can succeed. + +If the underlying BIO is B<blocking>, SSL_read() will only return, once the +read operation has been finished or an error occurred, except when a +renegotiation take 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>, SSL_read() will also return +when the underlying BIO could not satisfy the needs of SSL_read() +to continue the operation. In this case a call to +L<SSL_get_error(3)> with the +return value of SSL_read() will yield B<SSL_ERROR_WANT_READ> or +B<SSL_ERROR_WANT_WRITE>. As at any time a re-negotiation is possible, a +call to SSL_read() can also cause write operations! The calling process +then must repeat the call after taking appropriate action to satisfy the +needs of SSL_read(). 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 +SSL_read() can be called without blocking or actually receiving new +data from the underlying socket. + +=head1 WARNING + +When an SSL_read() operation has to be repeated because of +B<SSL_ERROR_WANT_READ> or B<SSL_ERROR_WANT_WRITE>, it must be repeated +with the same arguments. + +=head1 RETURN VALUES + +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(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(3)>, L<bio(3)> + +=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 |