Adds support for atomic transactions spanning multiple KV entries.

api/kv.go

@@ -23,6 +23,42 @@ type KVPair struct {
 // KVPairs is a list of KVPair objects
 type KVPairs []*KVPair
 
+// KVOp constants give possible operations available in a KVTxn.
+type KVOp string
+
+const (
+	KVSet          KVOp = "set"
+	KVDelete            = "delete"
+	KVDeleteCAS         = "delete-cas"
+	KVDeleteTree        = "delete-tree"
+	KVCAS               = "cas"
+	KVLock              = "lock"
+	KVUnlock            = "unlock"
+	KVGet               = "get"
+	KVCheckSession      = "check-session"
+	KVCheckIndex        = "check-index"
+)
+
+// KVTxnOp defines a single operation inside a transaction.
+type KVTxnOp struct {
+	Verb    string
+	Key     string
+	Value   []byte
+	Flags   uint64
+	Index   uint64
+	Session string
+}
+
+// KVTxnOps defines a set of operations to be performed inside a single
+// transaction.
+type KVTxnOps []*KVTxnOp
+
+// KVTxnResponse has the outcome of a transaction.
+type KVTxnResponse struct {
+	Results []*KVPair
+	Errors  TxnErrors
+}
+
 // KV is used to manipulate the K/V API
 type KV struct {
 	c *Client
@@ -238,3 +274,113 @@ func (k *KV) deleteInternal(key string, params map[string]string, q *WriteOption
 	res := strings.Contains(string(buf.Bytes()), "true")
 	return res, qm, nil
 }
+
+// TxnOp is the internal format we send to Consul. It's not specific to KV,
+// though currently only KV operations are supported.
+type TxnOp struct {
+	KV *KVTxnOp
+}
+
+// TxnOps is a list of transaction operations.
+type TxnOps []*TxnOp
+
+// TxnResult is the internal format we receive from Consul.
+type TxnResult struct {
+	KV *KVPair
+}
+
+// TxnResults is a list of TxnResult objects.
+type TxnResults []*TxnResult
+
+// TxnError is used to return information about an operation in a transaction.
+type TxnError struct {
+	OpIndex int
+	What    string
+}
+
+// TxnErrors is a list of TxnError objects.
+type TxnErrors []*TxnError
+
+// TxnResponse is the internal format we receive from Consul.
+type TxnResponse struct {
+	Results TxnResults
+	Errors  TxnErrors
+}
+
+// Txn is used to apply multiple KV operations in a single, atomic transaction.
+// Note that Go will perform the required base64 encoding on the values
+// automatically because the type is a byte slice. Transactions are defined as a
+// list of operations to perform, using the KVOp constants and KVTxnOp structure
+// to define operations. If any operation fails, none of the changes are applied
+// to the state store. Note that this hides the internal raw transaction interface
+// and munges the input and output types into KV-specific ones for ease of use.
+// If there are more non-KV operations in the future we may break out a new
+// transaction API client, but it will be easy to keep this KV-specific variant
+// supported.
+//
+// Here's an example:
+//
+// ops := KVTxnOps{
+//     &KVTxnOp{
+//         Verb:    KVLock,
+//         Key:     "test/lock",
+//         Session: "adf4238a-882b-9ddc-4a9d-5b6758e4159e",
+//         Value:   []byte("hello"),
+//     },
+//     &KVTxnOp{
+//         Verb:    KVGet,
+//         Key:     "another/key",
+//     },
+// }
+// ok, response, _, err := kv.Txn(&ops, nil)
+//
+// If there is a problem making the transaction request then an error will be
+// returned. Otherwise, the ok value will be true if the transaction succeeded
+// or false if it was rolled back. The response is a structured return value which
+// will have the outcome of the transaction. Its Results member will have entries
+// for each operation. Deleted keys will have a nil entry in the, and to save
+// space, the Value of each key in the Results will be nil unless the operation
+// is a KVGet. If the transaction was rolled back, the Errors member will have
+// entries referencing the index of the operation that failed along with an error
+// message.
+func (k *KV) Txn(txn KVTxnOps, q *WriteOptions) (bool, *KVTxnResponse, *WriteMeta, error) {
+	r := k.c.newRequest("PUT", "/v1/txn")
+	r.setWriteOptions(q)
+
+	// Convert into the internal format since this is an all-KV txn.
+	ops := make(TxnOps, 0, len(txn))
+	for _, kvOp := range txn {
+		ops = append(ops, &TxnOp{KV: kvOp})
+	}
+	r.obj = ops
+	rtt, resp, err := k.c.doRequest(r)
+	if err != nil {
+		return false, nil, nil, err
+	}
+	defer resp.Body.Close()
+
+	wm := &WriteMeta{}
+	wm.RequestTime = rtt
+
+	if resp.StatusCode == http.StatusOK || resp.StatusCode == http.StatusConflict {
+		var txnResp TxnResponse
+		if err := decodeBody(resp, &txnResp); err != nil {
+			return false, nil, nil, err
+		}
+
+		// Convert from the internal format.
+		kvResp := KVTxnResponse{
+			Errors: txnResp.Errors,
+		}
+		for _, result := range txnResp.Results {
+			kvResp.Results = append(kvResp.Results, result.KV)
+		}
+		return resp.StatusCode == http.StatusOK, &kvResp, wm, nil
+	}
+
+	var buf bytes.Buffer
+	if _, err := io.Copy(&buf, resp.Body); err != nil {
+		return false, nil, nil, fmt.Errorf("Failed to read response: %v", err)
+	}
+	return false, nil, nil, fmt.Errorf("Failed request: %s", buf.String())
+}

api/kv_test.go

@@ -3,6 +3,7 @@ package api
 import (
 	"bytes"
 	"path"
+	"strings"
 	"testing"
 	"time"
 )
@@ -445,3 +446,94 @@ func TestClient_AcquireRelease(t *testing.T) {
 		t.Fatalf("unexpected value: %#v", meta)
 	}
 }
+
+func TestClient_Txn(t *testing.T) {
+	t.Parallel()
+	c, s := makeClient(t)
+	defer s.Stop()
+
+	session := c.Session()
+	kv := c.KV()
+
+	// Make a session.
+	id, _, err := session.CreateNoChecks(nil, nil)
+	if err != nil {
+		t.Fatalf("err: %v", err)
+	}
+	defer session.Destroy(id, nil)
+
+	// Acquire and get the key via a transaction, but don't supply a valid
+	// session.
+	key := testKey()
+	value := []byte("test")
+	txn := KVTxnOps{
+		&KVTxnOp{
+			Verb:  KVLock,
+			Key:   key,
+			Value: value,
+		},
+		&KVTxnOp{
+			Verb: KVGet,
+			Key:  key,
+		},
+	}
+	ok, ret, _, err := kv.Txn(txn, nil)
+	if err != nil {
+		t.Fatalf("err: %v", err)
+	} else if ok {
+		t.Fatalf("transaction should have failed")
+	}
+
+	if ret == nil || len(ret.Errors) != 2 || len(ret.Results) != 0 {
+		t.Fatalf("bad: %v", ret)
+	}
+	if ret.Errors[0].OpIndex != 0 ||
+		!strings.Contains(ret.Errors[0].What, "missing session") ||
+		!strings.Contains(ret.Errors[1].What, "doesn't exist") {
+		t.Fatalf("bad: %v", ret.Errors[0])
+	}
+
+	// Now poke in a real session and try again.
+	txn[0].Session = id
+	ok, ret, _, err = kv.Txn(txn, nil)
+	if err != nil {
+		t.Fatalf("err: %v", err)
+	} else if !ok {
+		t.Fatalf("transaction failure")
+	}
+
+	if ret == nil || len(ret.Errors) != 0 || len(ret.Results) != 2 {
+		t.Fatalf("bad: %v", ret)
+	}
+	for i, result := range ret.Results {
+		var expected []byte
+		if i == 1 {
+			expected = value
+		}
+
+		if result.Key != key ||
+			!bytes.Equal(result.Value, expected) ||
+			result.Session != id ||
+			result.LockIndex != 1 {
+			t.Fatalf("bad: %v", result)
+		}
+	}
+
+	// Sanity check using the regular GET API.
+	pair, meta, err := kv.Get(key, nil)
+	if err != nil {
+		t.Fatalf("err: %v", err)
+	}
+	if pair == nil {
+		t.Fatalf("expected value: %#v", pair)
+	}
+	if pair.LockIndex != 1 {
+		t.Fatalf("Expected lock: %v", pair)
+	}
+	if pair.Session != id {
+		t.Fatalf("Expected lock: %v", pair)
+	}
+	if meta.LastIndex == 0 {
+		t.Fatalf("unexpected value: %#v", meta)
+	}
+}

command/agent/http.go

@@ -269,6 +269,8 @@ func (s *HTTPServer) registerHandlers(enableDebug bool) {
 	s.mux.HandleFunc("/v1/query", s.wrap(s.PreparedQueryGeneral))
 	s.mux.HandleFunc("/v1/query/", s.wrap(s.PreparedQuerySpecific))
 
+	s.mux.HandleFunc("/v1/txn", s.wrap(s.Txn))
+
 	if enableDebug {
 		s.mux.HandleFunc("/debug/pprof/", pprof.Index)
 		s.mux.HandleFunc("/debug/pprof/cmdline", pprof.Cmdline)
@@ -342,28 +344,39 @@ func (s *HTTPServer) wrap(handler func(resp http.ResponseWriter, req *http.Reque
 			return
 		}
 
-		prettyPrint := false
-		if _, ok := req.URL.Query()["pretty"]; ok {
-			prettyPrint = true
-		}
-		// Write out the JSON object
 		if obj != nil {
 			var buf []byte
-			if prettyPrint {
-				buf, err = json.MarshalIndent(obj, "", "    ")
-			} else {
-				buf, err = json.Marshal(obj)
-			}
+			buf, err = s.marshalJSON(req, obj)
 			if err != nil {
 				goto HAS_ERR
 			}
+
 			resp.Header().Set("Content-Type", "application/json")
 			resp.Write(buf)
 		}
 	}
 	return f
 }
 
+// marshalJSON marshals the object into JSON, respecting the user's pretty-ness
+// configuration.
+func (s *HTTPServer) marshalJSON(req *http.Request, obj interface{}) ([]byte, error) {
+	if _, ok := req.URL.Query()["pretty"]; ok {
+		buf, err := json.MarshalIndent(obj, "", "    ")
+		if err != nil {
+			return nil, err
+		}
+		buf = append(buf, "\n"...)
+		return buf, nil
+	}
+
+	buf, err := json.Marshal(obj)
+	if err != nil {
+		return nil, err
+	}
+	return buf, err
+}
+
 // Returns true if the UI is enabled.
 func (s *HTTPServer) IsUIEnabled() bool {
 	return s.uiDir != "" || s.agent.config.EnableUi

command/agent/http_test.go

@@ -328,6 +328,7 @@ func testPrettyPrint(pretty string, t *testing.T) {
 	srv.wrap(handler)(resp, req)
 
 	expected, _ := json.MarshalIndent(r, "", "    ")
+	expected = append(expected, "\n"...)
 	actual, err := ioutil.ReadAll(resp.Body)
 	if err != nil {
 		t.Fatalf("err: %s", err)