GOCBC-317 Don't pass CAS value to TouchEx

Motivation
----------
Touch should not send a non-zero CAS value to the server. As of
server 5.x this is enforced by the server and will return an error.

Changes
-------
Don't pass CAS from touch to TouchEx and change signature of touch,
leaving signatute of Touch and TouchDura as is. Fail fast in Touch
and TouchDura if a non-0 CAS value is provided.

Change-Id: I4f763ad276482346cf9955e47b9aa2e25b614b63
Reviewed-on: http://review.couchbase.org/95807
Reviewed-by: Brett Lawson <brett19@gmail.com>
Tested-by: Charles Dixon <chvckd@gmail.com>

bucket_crud.go

@@ -48,11 +48,16 @@ func (b *Bucket) GetReplica(key string, valuePtr interface{}, replicaIdx int) (C
 }
 
 // Touch touches a document, specifying a new expiry time for it.
+// The Cas value must be 0.
 func (b *Bucket) Touch(key string, cas Cas, expiry uint32) (Cas, error) {
 	span := b.startKvOpTrace("Touch")
 	defer span.Finish()
 
-	cas, _, err := b.touch(span.Context(), key, cas, expiry)
+	if cas != 0 {
+		return 0, ErrNonZeroCas
+	}
+
+	cas, _, err := b.touch(span.Context(), key, expiry)
 	return cas, err
 }
 
@@ -302,11 +307,10 @@ func (b *Bucket) getReplica(tracectx opentracing.SpanContext, key string, valueP
 	return
 }
 
-func (b *Bucket) touch(tracectx opentracing.SpanContext, key string, cas Cas, expiry uint32) (casOut Cas, mtOut MutationToken, errOut error) {
+func (b *Bucket) touch(tracectx opentracing.SpanContext, key string, expiry uint32) (casOut Cas, mtOut MutationToken, errOut error) {
 	ctrl := b.newOpManager(tracectx)
 	err := ctrl.Wait(b.client.TouchEx(gocbcore.TouchOptions{
 		Key:          []byte(key),
-		Cas:          gocbcore.Cas(cas),
 		Expiry:       expiry,
 		TraceContext: tracectx,
 	}, func(res *gocbcore.TouchResult, err error) {

bucket_dura.go

@@ -198,11 +198,16 @@ func (b *Bucket) durability(tracectx opentracing.SpanContext, key string, cas Ca
 }
 
 // TouchDura touches a document, specifying a new expiry time for it.  Additionally checks document durability.
+// The Cas value must be 0.
 func (b *Bucket) TouchDura(key string, cas Cas, expiry uint32, replicateTo, persistTo uint) (Cas, error) {
 	span := b.startKvOpTrace("TouchDura")
 	defer span.Finish()
 
-	cas, mt, err := b.touch(span.Context(), key, cas, expiry)
+	if cas != 0 {
+		return 0, ErrNonZeroCas
+	}
+
+	cas, mt, err := b.touch(span.Context(), key, expiry)
 	if err != nil {
 		return cas, err
 	}

error.go

@@ -105,6 +105,8 @@ var (
 	ErrInvalidCert = gocbcore.ErrInvalidCert
 	// ErrInvalidCredentials is returned when an invalid set of credentials is provided for a service.
 	ErrInvalidCredentials = gocbcore.ErrInvalidCredentials
+	// ErrNonZeroCas occurs when an operation that require a CAS value of 0 is used with a non-zero value.
+	ErrNonZeroCas = gocbcore.ErrNonZeroCas
 
 	// ErrShutdown occurs when an operation is performed on a bucket that has been closed.
 	ErrShutdown = gocbcore.ErrShutdown