X-Git-Url: https://git.sesse.net/?p=cubemap;a=blobdiff_plain;f=metacube2.cpp;h=666355d16867524422b72de72853723725554e88;hp=9473dced414b62fd5d93548d7d81b43745b81143;hb=HEAD;hpb=bfc1a54cf84bb1784c14bd4f5acbb500460e35b5

diff --git a/metacube2.cpp b/metacube2.cpp
index 9473dce..666355d 100644
--- a/metacube2.cpp
+++ b/metacube2.cpp
@@ -7,6 +7,8 @@
 
 #include "metacube2.h"
 
+#include <arpa/inet.h>
+
 /*
  * https://www.ece.cmu.edu/~koopman/pubs/KoopmanCRCWebinar9May2012.pdf
  * recommends this for messages as short as ours (see table at page 34).
@@ -24,7 +26,7 @@ uint16_t metacube2_compute_crc(const struct metacube2_block_header *hdr)
 	uint16_t crc = METACUBE2_CRC_START;
 	int i, j;
 
-	for (i = 0; i < data_len; ++i) {	
+	for (i = 0; i < data_len; ++i) {
 		uint8_t c = data[i];
 		for (j = 0; j < 8; j++) {
 			int bit = crc & 0x8000;
@@ -44,5 +46,14 @@ uint16_t metacube2_compute_crc(const struct metacube2_block_header *hdr)
 		}
 	}
 
+	/*
+	 * Invert the checksum for metadata packets, so that clients that
+	 * don't understand metadata will ignore it as broken. There will
+	 * probably be logging, but apart from that, it's harmless.
+	 */
+	if (ntohs(hdr->flags) & METACUBE_FLAGS_METADATA) {
+		crc ^= 0xffff;
+	}
+
 	return crc;
 }