From 606c5f43af3b9b7a5f1484540e7455346bba31c9 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?P=C5=99emysl=20Janouch?= <p.janouch@gmail.com>
Date: Mon, 27 Oct 2014 18:49:21 +0100
Subject: Use RLE bitmap compression

---
 autistdraw.c | 44 ++++++++++++++++++++++++++++++++++++--------
 utils.c      | 16 ----------------
 2 files changed, 36 insertions(+), 24 deletions(-)

diff --git a/autistdraw.c b/autistdraw.c
index 18ff297..41a2942 100644
--- a/autistdraw.c
+++ b/autistdraw.c
@@ -272,8 +272,26 @@ send_get_bitmap_response (client_t *client, app_context_t *app)
 	msg_writer_u64 (&writer, app->bitmap_w);
 	msg_writer_u64 (&writer, app->bitmap_h);
 
-	msg_writer_blob (&writer, app->bitmap,
-		app->bitmap_w * app->bitmap_h * sizeof *app->bitmap);
+	// Simple RLE compression
+	size_t size = app->bitmap_w * app->bitmap_h;
+	uint8_t last_value = 0, count = 0;
+	for (size_t i = 0; i < size; i++)
+	{
+		uint8_t value = app->bitmap[i];
+		if ((count && value != last_value) || count == 0xFF)
+		{
+			msg_writer_u8 (&writer, count);
+			msg_writer_u8 (&writer, last_value);
+			count = 0;
+		}
+		count++;
+		last_value = value;
+	}
+	if (count)
+	{
+		msg_writer_u8 (&writer, count);
+		msg_writer_u8 (&writer, last_value);
+	}
 
 	flush_writer_to_client (&writer, client);
 }
@@ -970,17 +988,27 @@ on_server_get_bitmap (app_context_t *app, struct msg_unpacker *unpacker)
 	 || !msg_unpacker_u64 (unpacker, &h))
 		return;
 
-	// TODO: employ at least some RLE encoding
-	size_t size = w * h * sizeof *app->bitmap;
+	size_t size = w * h;
 	if ((h && w > SIZE_MAX / h) || w > SIZE_MAX || h > SIZE_MAX)
 		return;
 
-	const void *data;
-	if (!msg_unpacker_blob (unpacker, &data, size))
-		return;
+	uint8_t *bitmap = xcalloc (size, sizeof *app->bitmap);
+
+	// RLE decompression
+	size_t i = 0;
+	uint8_t len, value;
+	while (msg_unpacker_u8 (unpacker, &len)
+		&& msg_unpacker_u8 (unpacker, &value))
+	{
+		// Don't allow overflow
+		if (i + len > size || i + len < i)
+			break;
+		for (size_t x = 0; x < len; x++)
+			bitmap[i++] = value;
+	}
 
 	free (app->bitmap);
-	app->bitmap = memcpy (xcalloc (1, size), data, size);
+	app->bitmap = bitmap;
 	app->bitmap_x = x;
 	app->bitmap_y = y;
 	app->bitmap_w = w;
diff --git a/utils.c b/utils.c
index f7c8fad..df16559 100644
--- a/utils.c
+++ b/utils.c
@@ -382,16 +382,6 @@ msg_unpacker_get_available (struct msg_unpacker *self)
 	return self->len - self->offset;
 }
 
-static bool
-msg_unpacker_blob (struct msg_unpacker *self, const void **data, size_t len)
-{
-	if (self->len - self->offset < len)
-		return false;
-	*data = self->data + self->offset;
-	self->offset += len;
-	return true;
-}
-
 #define UNPACKER_INT_BEGIN                                                     \
 	if (self->len - self->offset < sizeof *value)                              \
 		return false;                                                          \
@@ -445,12 +435,6 @@ msg_writer_init (struct msg_writer *self)
 	str_append_data (&self->buf, "\x00\x00\x00\x00" "\x00\x00\x00\x00", 8);
 }
 
-static void
-msg_writer_blob (struct msg_writer *self, const void *data, size_t len)
-{
-	str_append_data (&self->buf, data, len);
-}
-
 static void
 msg_writer_u8 (struct msg_writer *self, uint8_t x)
 {
-- 
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