Add support to free/allocate SSL buffers

OpenSSL already has the feature of SSL_MODE_RELEASE_BUFFERS that can
be set to release the read or write buffers when data has finished
reading or writing. OpenSSL will automatically re-allocate the buffers
as needed. This can be quite aggressive in terms of memory allocation.

This provides a manual mechanism. SSL_free_buffers() will free
the data buffers if there's no pending data. SSL_alloc_buffers()
will realloc them; but this function is not strictly necessary, as it's
still done automatically in the state machine.

Reviewed-by: Richard Levitte <levitte@openssl.org>
Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/2240)

1 files changed, 16 insertions, 0 deletions

diff --git a/ssl/ssl_lib.c b/ssl/ssl_lib.c
index be15daad86..74767f6e15 100644
--- a/ssl/ssl_lib.c
+++ b/ssl/ssl_lib.c
@@ -4778,6 +4778,22 @@ int SSL_early_get0_ext(SSL *s, unsigned int type, const unsigned char **out,
     return 0;
 }
 
+int SSL_free_buffers(SSL *ssl)
+{
+    RECORD_LAYER *rl = &ssl->rlayer;
+
+    if (RECORD_LAYER_read_pending(rl) || RECORD_LAYER_write_pending(rl))
+        return 0;
+
+    RECORD_LAYER_release(rl);
+    return 1;
+}
+
+int SSL_alloc_buffers(SSL *ssl)
+{
+    return ssl3_setup_buffers(ssl);
+}
+
 void SSL_CTX_set_keylog_callback(SSL_CTX *ctx, SSL_CTX_keylog_cb_func cb)
 {
     ctx->keylog_callback = cb;