QUIC: Add optimised FIN API

Reviewed-by: Neil Horman <nhorman@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/23343)

doc/man3/SSL_write.pod

@@ -2,13 +2,19 @@
 
 =head1 NAME
 
-SSL_write_ex, SSL_write, SSL_sendfile - write bytes to a TLS/SSL connection
+SSL_write_ex2, SSL_write_ex, SSL_write, SSL_sendfile, SSL_WRITE_FLAG_CONCLUDE -
+write bytes to a TLS/SSL connection
 
 =head1 SYNOPSIS
 
  #include <openssl/ssl.h>
 
+ #define SSL_WRITE_FLAG_CONCLUDE
+
  ossl_ssize_t SSL_sendfile(SSL *s, int fd, off_t offset, size_t size, int flags);
+ int SSL_write_ex2(SSL *s, const void *buf, size_t num,
+                   uint64_t flags,
+                   size_t *written);
  int SSL_write_ex(SSL *s, const void *buf, size_t num, size_t *written);
  int SSL_write(SSL *ssl, const void *buf, int num);
 
@@ -18,6 +24,10 @@ SSL_write_ex() and SSL_write() write B<num> bytes from the buffer B<buf> into
 the specified B<ssl> connection. On success SSL_write_ex() will store the number
 of bytes written in B<*written>.
 
+SSL_write_ex2() functions similarly to SSL_write_ex() but can also accept
+optional flags which modify its behaviour. Calling SSL_write_ex2() with a
+I<flags> argument of 0 is exactly equivalent to calling SSL_write_ex().
+
 SSL_sendfile() writes B<size> bytes from offset B<offset> in the file
 descriptor B<fd> to the specified SSL connection B<s>. This function provides
 efficient zero-copy semantics. SSL_sendfile() is available only when
@@ -26,6 +36,39 @@ It is provided here to allow users to maintain the same interface.
 The meaning of B<flags> is platform dependent.
 Currently, under Linux it is ignored.
 
+The I<flags> argument to SSL_write_ex2() can accept zero or more of the
+following flags. Note that which flags are supported will depend on the kind of
+SSL object and underlying protocol being used:
+
+=over 4
+
+=item B<SSL_WRITE_FLAG_CONCLUDE>
+
+This flag is only supported on QUIC stream SSL objects (or QUIC connection SSL
+objects with a default stream attached).
+
+If this flag is set, and the call to SSL_write_ex2() succeeds, and all of the
+data passed to the call is written (meaning that C<*written == num>), the
+relevant QUIC stream's send part is concluded automatically as though
+L<SSL_stream_conclude(3)> was called (causing transmission of a FIN for the
+stream).
+
+While using this flag is semantically equivalent to calling
+L<SSL_stream_conclude(3)> after a successful call to this function, using this
+flag enables greater efficiency than making these two API calls separately, as
+it enables the written stream data and the FIN flag indicating the end of the
+stream to be scheduled as part of the same QUIC STREAM frame and QUIC packet.
+
+Setting this flag does not cause a stream's send part to be concluded if not all
+of the data passed to the call was consumed.
+
+=back
+
+A call to SSL_write_ex2() fails if a flag is passed which is not supported or
+understood by the given SSL object. An application should determine if a flag is
+supported (for example, for B<SSL_WRITE_FLAG_CONCLUDE>, that a QUIC stream SSL
+object is being used) before attempting to use it.
+
 =head1 NOTES
 
 In the paragraphs below a "write function" is defined as one of either
@@ -89,16 +132,17 @@ the peer.
 
 =head1 RETURN VALUES
 
-SSL_write_ex() will return 1 for success or 0 for failure. Success means that
-all requested application data bytes have been written to the SSL connection or,
-if SSL_MODE_ENABLE_PARTIAL_WRITE is in use, at least 1 application data byte has
-been written to the SSL connection. Failure means that not all the requested
-bytes have been written yet (if SSL_MODE_ENABLE_PARTIAL_WRITE is not in use) or
-no bytes could be written to the SSL connection (if
-SSL_MODE_ENABLE_PARTIAL_WRITE is in use). Failures can be retryable (e.g. the
-network write buffer has temporarily filled up) 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.
+SSL_write_ex() and SSL_write_ex2() return 1 for success or 0 for failure.
+Success means that all requested application data bytes have been written to the
+SSL connection or, if SSL_MODE_ENABLE_PARTIAL_WRITE is in use, at least 1
+application data byte has been written to the SSL connection. Failure means that
+not all the requested bytes have been written yet (if
+SSL_MODE_ENABLE_PARTIAL_WRITE is not in use) or no bytes could be written to the
+SSL connection (if SSL_MODE_ENABLE_PARTIAL_WRITE is in use). Failures can be
+retryable (e.g. the network write buffer has temporarily filled up) 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_write() the following return values can occur:
 

include/openssl/ssl.h.in

@@ -1944,6 +1944,12 @@ long SSL_callback_ctrl(SSL *, int, void (*)(void));
 long SSL_CTX_ctrl(SSL_CTX *ctx, int cmd, long larg, void *parg);
 long SSL_CTX_callback_ctrl(SSL_CTX *, int, void (*)(void));
 
+# define SSL_WRITE_FLAG_CONCLUDE    (1U << 0)
+
+__owur int SSL_write_ex2(SSL *s, const void *buf, size_t num,
+                         uint64_t flags,
+                         size_t *written);
+
 # define SSL_EARLY_DATA_NOT_SENT    0
 # define SSL_EARLY_DATA_REJECTED    1
 # define SSL_EARLY_DATA_ACCEPTED    2

util/libssl.num

@@ -577,3 +577,4 @@ SSL_handle_events                       577	3_2_0	EXIST::FUNCTION:
 SSL_get_event_timeout                   578	3_2_0	EXIST::FUNCTION:
 SSL_get0_group_name                     579	3_2_0	EXIST::FUNCTION:
 SSL_is_stream_local                     580	3_2_0	EXIST::FUNCTION:
+SSL_write_ex2                           ?	3_3_0	EXIST::FUNCTION: