Change to W3C limits

Signed-off-by: Bryan Boreham <bjboreham@gmail.com>

propagation.go

@@ -215,11 +215,10 @@ func (p *BinaryPropagator) Inject(
 	return nil
 }
 
-// These are intended to be unimaginably high: above this number we declare
-// the data is corrupted, to protect against running out of memory
+// W3C limits https://github.com/w3c/baggage/blob/master/baggage/HTTP_HEADER_FORMAT.md#limits
 const (
-	maxBinaryBaggage  = 1024 * 1024
-	maxBinaryValueLen = 100 * 1024 * 1024
+	maxBinaryBaggage      = 180
+	maxBinaryNameValueLen = 4096
 )
 
 // Extract implements Extractor of BinaryPropagator
@@ -265,9 +264,6 @@ func (p *BinaryPropagator) Extract(abstractCarrier interface{}) (SpanContext, er
 			if err := binary.Read(carrier, binary.BigEndian, &keyLen); err != nil {
 				return emptyContext, opentracing.ErrSpanContextCorrupted
 			}
-			if keyLen > maxBinaryValueLen {
-				return emptyContext, opentracing.ErrSpanContextCorrupted
-			}
 			buf.Reset()
 			buf.Grow(int(keyLen))
 			if n, err := io.CopyN(buf, carrier, int64(keyLen)); err != nil || int32(n) != keyLen {
@@ -278,7 +274,7 @@ func (p *BinaryPropagator) Extract(abstractCarrier interface{}) (SpanContext, er
 			if err := binary.Read(carrier, binary.BigEndian, &valLen); err != nil {
 				return emptyContext, opentracing.ErrSpanContextCorrupted
 			}
-			if valLen > maxBinaryValueLen {
+			if keyLen+valLen > maxBinaryNameValueLen {
 				return emptyContext, opentracing.ErrSpanContextCorrupted
 			}
 			buf.Reset()