=head1 NAME
-SSL_read_ex, SSL_read - read bytes from a TLS/SSL connection
+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 *read);
+ 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 *read);
+ 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<*read>.
+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
-the same bytes.
+at least the same bytes.
=head1 NOTES
-In this notes section all comments that apply to SSL_read_ex() or SSL_read()
-also apply to SSL_peek_ex() and SSL_peek().
+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, SSL_read_ex() or 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
+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 SSL_read_ex() or SSL_read() operation. The behaviour of SSL_read_ex() and
-SSL_read() depends on the underlying BIO.
+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 call to an SSL_read_ex(), SSL_read(), L<SSL_write_ex(3)> or
-L<SSL_write(3)> function.
-
-SSL_read_ex() and SSL_read() work 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_ex() or SSL_read() can still be buffered inside the SSL layer
-and will be retrieved on the next call to SSL_read_ex() or SSL_read(). If B<num>
-is higher than the number of bytes buffered, SSL_read_ex() or 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_ex() or 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_ex() or SSL_read()
+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>, SSL_read_ex() or 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
+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>, SSL_read_ex() or SSL_read() will also
-return when the underlying BIO could not satisfy the needs of SSL_read_ex() or
-SSL_read() to continue the operation. In this case a call to
-L<SSL_get_error(3)> with the
-return value of SSL_read_ex() or SSL_read() will yield B<SSL_ERROR_WANT_READ> or
+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
-call to SSL_read_ex() or 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_ex() or 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.
+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
-SSL_read_ex() or SSL_read() can be called without blocking or actually receiving
+the read function can be called without blocking or actually receiving
new data from the underlying socket.
=head1 WARNING
-When an SSL_read_ex() or SSL_read() operation has to be repeated because of
-B<SSL_ERROR_WANT_READ> or B<SSL_ERROR_WANT_WRITE>, it must be repeated
+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() will return 1 for success or 0 for failure. In the event of a
-failure call SSL_get_error() to find out the reason.
+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() the following return values can occur:
+For SSL_read() and SSL_peek() the following return values can occur:
=over 4
-=item E<gt>0
+=item E<gt> 0
-The read operation was successful; the return value is the number of
-bytes actually read from the TLS/SSL connection.
+The read operation was successful.
+The return value is the number of bytes actually read from the TLS/SSL
+connection.
-=item Z<>0
+=item Z<><= 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)>,
-L<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).
+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.
-=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.
+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
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)>
+L<ssl(7)>, L<bio(7)>
=head1 COPYRIGHT
projects / openssl.git / blobdiff