support IPv4 & IPv6 frag reassemble

src/packet/checksum.h

@@ -0,0 +1,41 @@
+#ifndef _CHECKSUM_H
+#define _CHECKSUM_H
+
+#ifdef __cpluscplus
+extern "C"
+{
+#endif
+
+#include <stdint.h>
+
+// https://datatracker.ietf.org/doc/html/rfc1071
+static inline uint16_t checksum(char *data, int len)
+{
+    long sum = 0;
+    uint16_t *addr = (uint16_t *)data;
+
+    while (len > 1)
+    {
+        sum += *addr++;
+        len -= 2;
+    }
+
+    if (len > 0)
+    {
+        sum += *(unsigned char *)addr;
+    }
+
+    // Fold 32-bit sum to 16 bits
+    while (sum >> 16)
+    {
+        sum = (sum & 0xffff) + (sum >> 16);
+    }
+
+    return (uint16_t)(~sum);
+}
+
+#ifdef __cpluscplus
+}
+#endif
+
+#endif