go test: dynamically calculate ip checksum

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

diff --git a/contrib/external-tests/go/main.go b/contrib/external-tests/go/main.go
index 68447feb8802b32a642e00518c253a1fd55e048a..ba0e3acf22c4f31e4ddddc30581db55fcedb3e61 100644 (file)
--- a/contrib/external-tests/go/main.go
+++ b/contrib/external-tests/go/main.go
@@ -16,6 +16,24 @@ import (
        "golang.org/x/net/ipv4"
 )
 
+func ipChecksum(buf []byte) uint16 {
+       sum := uint32(0)
+       for ; len(buf) >= 2; buf = buf[2:] {
+               sum += uint32(buf[0])<<8 | uint32(buf[1])
+       }
+       if len(buf) > 0 {
+               sum += uint32(buf[0]) << 8
+       }
+       for sum > 0xffff {
+               sum = (sum >> 16) + (sum & 0xffff)
+       }
+       csum := ^uint16(sum)
+       if csum == 0 {
+               csum = 0xffff
+       }
+       return csum
+}
+
 func main() {
        ourPrivate, _ := base64.StdEncoding.DecodeString("WAmgVYXkbT2bCtdcDwolI88/iVi/aV3/PHcUBTQSYmo=")
        ourPublic, _ := base64.StdEncoding.DecodeString("K5sF9yESrSBsOXPd6TcpKNgqoy1Ik3ZFKl4FolzrRyI=")
@@ -95,12 +113,12 @@ func main() {
                Len:      ipv4.HeaderLen,
                TotalLen: ipv4.HeaderLen + len(pingMessage),
                Protocol: 1, // ICMP
-               TTL:      2,
-               Checksum: 0xa15b, // the packet is always the same, hard-code checksum
+               TTL:      20,
                Src:      net.IPv4(10, 189, 129, 2),
                Dst:      net.IPv4(10, 189, 129, 1),
        }).Marshal()
        binary.BigEndian.PutUint16(pingHeader[2:], uint16(ipv4.HeaderLen+len(pingMessage))) // fix the length endianness on BSDs
+       binary.BigEndian.PutUint16(pingHeader[10:], ipChecksum(append(pingHeader, pingMessage...)))
        if err != nil {
                panic(err)
        }