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author | marha <marha@users.sourceforge.net> | 2009-06-28 22:07:26 +0000 |
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committer | marha <marha@users.sourceforge.net> | 2009-06-28 22:07:26 +0000 |
commit | 3562e78743202e43aec8727005182a2558117eca (patch) | |
tree | 8f9113a77d12470c5c851a2a8e4cb02e89df7d43 /openssl/doc/ssl/SSL_read.pod | |
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xextproto-7.0.3.tar.gz
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Diffstat (limited to 'openssl/doc/ssl/SSL_read.pod')
-rw-r--r-- | openssl/doc/ssl/SSL_read.pod | 124 |
1 files changed, 124 insertions, 0 deletions
diff --git a/openssl/doc/ssl/SSL_read.pod b/openssl/doc/ssl/SSL_read.pod new file mode 100644 index 000000000..7038cd2d7 --- /dev/null +++ b/openssl/doc/ssl/SSL_read.pod @@ -0,0 +1,124 @@ +=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)|SSL_connect(3)> or +L<SSL_accept(3)|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)|SSL_set_connect_state(3)> or SSL_set_accept_state() +before the first call to an SSL_read() or L<SSL_write(3)|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)|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)|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)|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 0 + +The read operation was not successful. The reason may either be a clean +shutdown due to a "close notify" alert sent by the peer (in which case +the SSL_RECEIVED_SHUTDOWN flag in the ssl shutdown state is set +(see L<SSL_shutdown(3)|SSL_shutdown(3)>, +L<SSL_set_shutdown(3)|SSL_set_shutdown(3)>). It is also possible, that +the peer simply shut down the underlying transport and the shutdown is +incomplete. Call SSL_get_error() with the return value B<ret> to find out, +whether an error occurred or the connection was shut down cleanly +(SSL_ERROR_ZERO_RETURN). + +SSLv2 (deprecated) does not support a shutdown alert protocol, so it can +only be detected, whether the underlying connection was closed. It cannot +be checked, whether the closure was initiated by the peer or by something +else. + +=item E<lt>0 + +The read operation was not successful, because either an error occurred +or action must be taken by the calling process. Call SSL_get_error() with the +return value B<ret> to find out the reason. + +=back + +=head1 SEE ALSO + +L<SSL_get_error(3)|SSL_get_error(3)>, L<SSL_write(3)|SSL_write(3)>, +L<SSL_CTX_set_mode(3)|SSL_CTX_set_mode(3)>, L<SSL_CTX_new(3)|SSL_CTX_new(3)>, +L<SSL_connect(3)|SSL_connect(3)>, L<SSL_accept(3)|SSL_accept(3)> +L<SSL_set_connect_state(3)|SSL_set_connect_state(3)>, +L<SSL_pending(3)|SSL_pending(3)>, +L<SSL_shutdown(3)|SSL_shutdown(3)>, L<SSL_set_shutdown(3)|SSL_set_shutdown(3)>, +L<ssl(3)|ssl(3)>, L<bio(3)|bio(3)> + +=cut |