add opentracing spans for metrics

vendor/github.com/Shopify/sarama/crc32_field.go

@@ -0,0 +1,35 @@
+package sarama
+
+import (
+	"encoding/binary"
+	"hash/crc32"
+)
+
+// crc32Field implements the pushEncoder and pushDecoder interfaces for calculating CRC32s.
+type crc32Field struct {
+	startOffset int
+}
+
+func (c *crc32Field) saveOffset(in int) {
+	c.startOffset = in
+}
+
+func (c *crc32Field) reserveLength() int {
+	return 4
+}
+
+func (c *crc32Field) run(curOffset int, buf []byte) error {
+	crc := crc32.ChecksumIEEE(buf[c.startOffset+4 : curOffset])
+	binary.BigEndian.PutUint32(buf[c.startOffset:], crc)
+	return nil
+}
+
+func (c *crc32Field) check(curOffset int, buf []byte) error {
+	crc := crc32.ChecksumIEEE(buf[c.startOffset+4 : curOffset])
+
+	if crc != binary.BigEndian.Uint32(buf[c.startOffset:]) {
+		return PacketDecodingError{"CRC didn't match"}
+	}
+
+	return nil
+}