SSL_get_max_early_data,
SSL_CTX_get_max_early_data,
SSL_SESSION_get_max_early_data,
+SSL_SESSION_set_max_early_data,
SSL_write_early_data,
SSL_read_early_data,
SSL_get_early_data_status
int SSL_CTX_set_max_early_data(SSL_CTX *ctx, uint32_t max_early_data);
uint32_t SSL_CTX_get_max_early_data(const SSL_CTX *ctx);
int SSL_set_max_early_data(SSL *s, uint32_t max_early_data);
- uint32_t SSL_get_max_early_data(const SSL_CTX *s);
+ uint32_t SSL_get_max_early_data(const SSL *s);
uint32_t SSL_SESSION_get_max_early_data(const SSL_SESSION *s);
+ int SSL_SESSION_set_max_early_data(SSL_SESSION *s, uint32_t max_early_data);
int SSL_write_early_data(SSL *s, const void *buf, size_t num, size_t *written);
=head1 DESCRIPTION
-These functions are used to send and recieve early data where TLSv1.3 has been
+These functions are used to send and receive early data where TLSv1.3 has been
negotiated. Early data can be sent by the client immediately after its initial
ClientHello without having to wait for the server to complete the handshake.
Early data can only be sent if a session has previously been established with
If the session cannot be used then this function will return 0. Otherwise it
will return the maximum number of early data bytes that can be sent.
+The function SSL_SESSION_set_max_early_data() sets the maximum number of early
+data bytes that can be sent for a session. This would typically be used when
+creating a PSK session file (see L<SSL_CTX_set_psk_use_session_callback(3)>). If
+using a ticket based PSK then this is set automatically to the value provided by
+the server.
+
A client uses the function SSL_write_early_data() to send early data. This
function is similar to the L<SSL_write_ex(3)> function, but with the following
differences. See L<SSL_write_ex(3)> for information on how to write bytes to
=item SSL_READ_EARLY_DATA_ERROR
-This indicates an IO or some other error occured. This should be treated in the
+This indicates an IO or some other error occurred. This should be treated in the
same way as a 0 return value from L<SSL_read_ex(3)>.
=item SSL_READ_EARLY_DATA_SUCCESS
L<SSL_accept(3)>. This can happen if the client is using a protocol version less
than TLSv1.3. Applications can test for this by calling
L<SSL_is_init_finished(3)>. Alternatively, applications may choose to call
-L<SSL_accept(3)> anway. Such a call will successfully return immediately with no
+L<SSL_accept(3)> anyway. Such a call will successfully return immediately with no
further action taken.
When a session is created between a server and a client the server will specify
different to that originally specified in a session that a client is resuming
with then the lower of the two values will apply.
+=head1 NOTES
+
+The whole purpose of early data is to enable a client to start sending data to
+the server before a full round trip of network traffic has occurred. Application
+developers should ensure they consider optimisation of the underlying TCP socket
+to obtain a performant solution. For example Nagle's algorithm is commonly used
+by operating systems in an attempt to avoid lots of small TCP packets. In many
+scenarios this is beneficial for performance, but it does not work well with the
+early data solution as implemented in OpenSSL. In Nagle's algorithm the OS will
+buffer outgoing TCP data if a TCP packet has already been sent which we have not
+yet received an ACK for from the peer. The buffered data will only be
+transmitted if enough data to fill an entire TCP packet is accumulated, or if
+the ACK is received from the peer. The initial ClientHello will be sent in the
+first TCP packet along with any data from the first call to
+SSL_write_early_data(). If the amount of data written will exceed the size of a
+single TCP packet, or if there are more calls to SSL_write_early_data() then
+that additional data will be sent in subsequent TCP packets which will be
+buffered by the OS and not sent until an ACK is received for the first packet
+containing the ClientHello. This means the early data is not actually
+sent until a complete round trip with the server has occurred which defeats the
+objective of early data.
+
+In many operating systems the TCP_NODELAY socket option is available to disable
+Nagle's algorithm. If an application opts to disable Nagle's algorithm
+consideration should be given to turning it back on again after the handshake is
+complete if appropriate.
+
=head1 RETURN VALUES
SSL_write_early_data() returns 1 for success or 0 for failure. In the event of a
SSL_SESSION_get_max_early_data() return the maximum number of early data bytes
that may be sent.
-SSL_set_max_early_data() and SSL_CTX_set_max_early_data() return 1 for success
-or 0 for failure.
+SSL_set_max_early_data(), SSL_CTX_set_max_early_data() and
+SSL_SESSION_set_max_early_data() return 1 for success or 0 for failure.
SSL_get_early_data_status() returns SSL_EARLY_DATA_ACCEPTED if early data was
accepted by the server, SSL_EARLY_DATA_REJECTED if early data was rejected by
L<SSL_connect(3)>,
L<SSL_accept(3)>,
L<SSL_do_handshake(3)>,
+L<SSL_CTX_set_psk_use_session_callback(3)>,
L<ssl(7)>
=head1 HISTORY
projects / openssl.git / blobdiff