INSTALL: clarify 386 and no-sse2 options.

[oweals/openssl.git] / doc / ssl / SSL_write.pod

diff --git a/doc/ssl/SSL_write.pod b/doc/ssl/SSL_write.pod
index f95907981d6fd097e05dc2d0bee34ccdbc5bb45d..4c1a7ee71f3cce02b5412cccd8f4c3a4348408fa 100644 (file)
--- a/doc/ssl/SSL_write.pod
+++ b/doc/ssl/SSL_write.pod
@@ -8,7 +8,7 @@ SSL_write - write bytes to a TLS/SSL connection.
 
  #include <openssl/ssl.h>
 
- int SSL_write(SSL *ssl, char *buf, int num);
+ int SSL_write(SSL *ssl, const void *buf, int num);
 
 =head1 DESCRIPTION
 
@@ -18,11 +18,17 @@ B<ssl> connection.
 =head1 NOTES
 
 If necessary, SSL_write() will negotiate a TLS/SSL session, if
-not already explicitly performed by SSL_connect() or SSL_accept(). If the
+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_write() operation. The behaviour of SSL_write() 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 L<SSL_read(3)|SSL_read(3)> or SSL_write() function.
+
 If the underlying BIO is B<blocking>, SSL_write() will only return, once the
 write operation has been finished or an error occurred, except when a
 renegotiation take place, in which case a SSL_ERROR_WANT_READ may occur. 
@@ -31,7 +37,8 @@ L<SSL_CTX_set_mode(3)|SSL_CTX_set_mode(3)> call.
 
 If the underlying BIO is B<non-blocking>, SSL_write() will also return,
 when the underlying BIO could not satisfy the needs of SSL_write()
-to continue the operation. In this case a call to SSL_get_error() with the
+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_write() 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_write() can also cause read operations! The calling process
@@ -41,40 +48,59 @@ 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.
 
+SSL_write() will only return with success, when the complete contents
+of B<buf> of length B<num> has been written. This default behaviour
+can be changed with the SSL_MODE_ENABLE_PARTIAL_WRITE option of
+L<SSL_CTX_set_mode(3)|SSL_CTX_set_mode(3)>. When this flag is set,
+SSL_write() will also return with success, when a partial write has been
+successfully completed. In this case the SSL_write() operation is considered
+completed. The bytes are sent and a new SSL_write() operation with a new
+buffer (with the already sent bytes removed) must be started.
+A partial write is performed with the size of a message block, which is
+16kB for SSLv3/TLSv1.
+
 =head1 WARNING
 
 When an SSL_write() 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.
 
+When calling SSL_write() with num=0 bytes to be sent the behaviour is
+undefined.
+
 =head1 RETURN VALUES
 
 The following return values can occur:
 
 =over 4
 
-=item E<gt>0
+=item E<gt> 0
 
 The write operation was successful, the return value is the number of
 bytes actually written to the TLS/SSL connection.
 
-=item 0
+=item Z<><= 0
 
-The write operation was not successful. Call SSL_get_error() with the return
-value B<ret> to find out, whether an error occurred.
+The write operation was not successful, because either the connection was
+closed, 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.
 
-=item E<lt>0
+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, why the closure happened.
 
-The write 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
 
 =head1 SEE ALSO
 
 L<SSL_get_error(3)|SSL_get_error(3)>, L<SSL_read(3)|SSL_read(3)>,
-L<SSL_CTX_set_mode(3)|SSL_CTX_set_mode(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(3)|ssl(3)>, L<bio(3)|bio(3)>
 
 =cut