rpc: Handle special cases for buffer and length

When the buffer is not NULL, but the length is zero then treat this as an
empty message. Serialize this in a special way so that the server can
restore the same situation.

Example: Terminate an operation via C_XxxFinal, but there is no more
data for the final part. A call to C_XxxFinal with buffer=NULL and length=0
would be treated as a size query, and would not terminate the operation.
So the way to terminate the operation without more data is to specify
buffer!=NULL but length=0.

When sending a byte array, and the buffer is NULL, and the length is
zero, don't treat this is invalid, but as empty message.

Example: C_XxxUpdate with an empty message.

Signed-off-by: Ingo Franzki <ifranzki@linux.ibm.com>

p11-kit/rpc-client.c

@@ -584,7 +584,7 @@ proto_read_sesssion_info (p11_rpc_message *msg,
 #define IN_BYTE_BUFFER(arr, len) \
 	if (len == NULL) \
 		{ _ret = CKR_ARGUMENTS_BAD; goto _cleanup; } \
-	if (!p11_rpc_message_write_byte_buffer (&_msg, arr ? *len : 0)) \
+	if (!p11_rpc_message_write_byte_buffer (&_msg, arr ? (*len > 0 ? *len : (uint32_t)-1) : 0)) \
 		{ _ret = CKR_HOST_MEMORY; goto _cleanup; }
 
 #define IN_BYTE_ARRAY(arr, len) \

p11-kit/rpc-message.c

@@ -379,7 +379,7 @@ p11_rpc_message_write_byte_array (p11_rpc_message *msg,
 	assert (!msg->signature || p11_rpc_message_verify_part (msg, "ay"));
 
 	/* No array, no data, just length */
-	if (!arr) {
+	if (!arr && num != 0) {
 		p11_rpc_buffer_add_byte (msg->output, 0);
 		p11_rpc_buffer_add_uint32 (msg->output, num);
 	} else {

p11-kit/rpc-server.c

@@ -97,6 +97,12 @@ proto_read_byte_buffer (p11_rpc_message *msg,
 	*n_buffer = length;
 	*buffer = NULL;
 
+	/* length = -1 indicates length = 0, but buffer not NULL */
+	if (length == (uint32_t)-1) {
+		*n_buffer = 0;
+		length = 1; /*allocate 1 dummy byte */
+	}
+
 	/* If set to zero, then they just want the length */
 	if (length == 0)
 		return CKR_OK;