Fix bug for force push for backends besides the remote backend

In refactoring the force push code when implementing force push
for the Terraform remote backend, a bug was introduced that
meant that backends that don't implement the EnableForcePush
method would still have their state validated. This commit
fixes that, and adds test coverage such that there is a separate
mockRemoteClient that has this method implemented.

states/remote/remote_test.go

@@ -69,7 +69,6 @@ func (c nilClient) Delete() error { return nil }
 type mockClient struct {
 	current []byte
 	log     []mockClientRequest
-	force   bool
 }
 
 type mockClientRequest struct {
@@ -90,11 +89,7 @@ func (c *mockClient) Get() (*Payload, error) {
 }
 
 func (c *mockClient) Put(data []byte) error {
-	if c.force {
-		c.appendLog("Force Put", data)
-	} else {
-		c.appendLog("Put", data)
-	}
+	c.appendLog("Put", data)
 	c.current = data
 	return nil
 }
@@ -105,11 +100,6 @@ func (c *mockClient) Delete() error {
 	return nil
 }
 
-// Implements remote.ClientForcePusher
-func (c *mockClient) EnableForcePush() {
-	c.force = true
-}
-
 func (c *mockClient) appendLog(method string, content []byte) {
 	// For easier test assertions, we actually log the result of decoding
 	// the content JSON rather than the raw bytes. Callers are in principle
@@ -126,3 +116,54 @@ func (c *mockClient) appendLog(method string, content []byte) {
 	}
 	c.log = append(c.log, mockClientRequest{method, contentVal})
 }
+
+// mockRemoteClient is like mockClient, but also implements
+// EnableForcePush, allowing testing for this behavior
+type mockRemoteClient struct {
+	current []byte
+	force   bool
+	log     []mockClientRequest
+}
+
+func (c *mockRemoteClient) Get() (*Payload, error) {
+	c.appendLog("Get", c.current)
+	if c.current == nil {
+		return nil, nil
+	}
+	checksum := md5.Sum(c.current)
+	return &Payload{
+		Data: c.current,
+		MD5:  checksum[:],
+	}, nil
+}
+
+func (c *mockRemoteClient) Put(data []byte) error {
+	if c.force {
+		c.appendLog("Force Put", data)
+	} else {
+		c.appendLog("Put", data)
+	}
+	c.current = data
+	return nil
+}
+
+// Implements remote.ClientForcePusher
+func (c *mockRemoteClient) EnableForcePush() {
+	c.force = true
+}
+
+func (c *mockRemoteClient) Delete() error {
+	c.appendLog("Delete", c.current)
+	c.current = nil
+	return nil
+}
+func (c *mockRemoteClient) appendLog(method string, content []byte) {
+	var contentVal map[string]interface{}
+	if content != nil {
+		err := json.Unmarshal(content, &contentVal)
+		if err != nil {
+			panic(err) // should never happen because our tests control this input
+		}
+	}
+	c.log = append(c.log, mockClientRequest{method, contentVal})
+}

states/remote/state.go

@@ -72,20 +72,21 @@ func (s *State) WriteStateForMigration(f *statefile.File, force bool) error {
 	s.mu.Lock()
 	defer s.mu.Unlock()
 
-	// `force` is passed down from the CLI flag and terminates here. Actual
-	// force pushing with the remote backend happens when Put()'ing the contents
-	// in the backend. If force is specified we skip verifications and hand the
-	// context off to the client to use when persitence operations actually take place.
-	c, isForcePusher := s.Client.(ClientForcePusher)
-	if force && isForcePusher {
-		c.EnableForcePush()
-	} else {
+	if !force {
 		checkFile := statefile.New(s.state, s.lineage, s.serial)
 		if err := statemgr.CheckValidImport(f, checkFile); err != nil {
 			return err
 		}
 	}
 
+	// The remote backend needs to pass the `force` flag through to its client.
+	// For backends that support such operations, inform the client
+	// that a force push has been requested
+	c, isForcePusher := s.Client.(ClientForcePusher)
+	if force && isForcePusher {
+		c.EnableForcePush()
+	}
+
 	// We create a deep copy of the state here, because the caller also has
 	// a reference to the given object and can potentially go on to mutate
 	// it after we return, but we want the snapshot at this point in time.

states/remote/state_test.go

@@ -302,6 +302,158 @@ func TestWriteStateForMigration(t *testing.T) {
 		},
 	}
 
+	testCases := []migrationTestCase{
+		// Refreshing state before we run the test loop causes a GET
+		{
+			name: "refresh state",
+			stateFile: func(mgr *State) *statefile.File {
+				return mgr.StateForMigration()
+			},
+			expectedRequest: mockClientRequest{
+				Method: "Get",
+				Content: map[string]interface{}{
+					"version":           4.0,
+					"lineage":           "mock-lineage",
+					"serial":            3.0,
+					"terraform_version": "0.0.0",
+					"outputs":           map[string]interface{}{"foo": map[string]interface{}{"type": string("string"), "value": string("bar")}},
+					"resources":         []interface{}{},
+				},
+			},
+		},
+		{
+			name: "cannot import lesser serial without force",
+			stateFile: func(mgr *State) *statefile.File {
+				return statefile.New(mgr.state, mgr.lineage, 1)
+			},
+			expectedError: "cannot import state with serial 1 over newer state with serial 3",
+		},
+		{
+			name: "cannot import differing lineage without force",
+			stateFile: func(mgr *State) *statefile.File {
+				return statefile.New(mgr.state, "different-lineage", mgr.serial)
+			},
+			expectedError: `cannot import state with lineage "different-lineage" over unrelated state with lineage "mock-lineage"`,
+		},
+		{
+			name: "can import lesser serial with force",
+			stateFile: func(mgr *State) *statefile.File {
+				return statefile.New(mgr.state, mgr.lineage, 1)
+			},
+			expectedRequest: mockClientRequest{
+				Method: "Put",
+				Content: map[string]interface{}{
+					"version":           4.0,
+					"lineage":           "mock-lineage",
+					"serial":            2.0,
+					"terraform_version": version.Version,
+					"outputs":           map[string]interface{}{"foo": map[string]interface{}{"type": string("string"), "value": string("bar")}},
+					"resources":         []interface{}{},
+				},
+			},
+			force: true,
+		},
+		{
+			name: "cannot import differing lineage without force",
+			stateFile: func(mgr *State) *statefile.File {
+				return statefile.New(mgr.state, "different-lineage", mgr.serial)
+			},
+			expectedRequest: mockClientRequest{
+				Method: "Put",
+				Content: map[string]interface{}{
+					"version":           4.0,
+					"lineage":           "different-lineage",
+					"serial":            3.0,
+					"terraform_version": version.Version,
+					"outputs":           map[string]interface{}{"foo": map[string]interface{}{"type": string("string"), "value": string("bar")}},
+					"resources":         []interface{}{},
+				},
+			},
+			force: true,
+		},
+	}
+
+	// In normal use (during a Terraform operation) we always refresh and read
+	// before any writes would happen, so we'll mimic that here for realism.
+	// NB This causes a GET to be logged so the first item in the test cases
+	// must account for this
+	if err := mgr.RefreshState(); err != nil {
+		t.Fatalf("failed to RefreshState: %s", err)
+	}
+
+	if err := mgr.WriteState(mgr.State()); err != nil {
+		t.Fatalf("failed to write initial state: %s", err)
+	}
+
+	// Our client is a mockClient which has a log we
+	// use to check that operations generate expected requests
+	mockClient := mgr.Client.(*mockClient)
+
+	// logIdx tracks the current index of the log separate from
+	// the loop iteration so we can check operations that don't
+	// cause any requests to be generated
+	logIdx := 0
+
+	for _, tc := range testCases {
+		sf := tc.stateFile(mgr)
+		err := mgr.WriteStateForMigration(sf, tc.force)
+		shouldError := tc.expectedError != ""
+
+		// If we are expecting and error check it and move on
+		if shouldError {
+			if err == nil {
+				t.Fatalf("test case %q should have failed with error %q", tc.name, tc.expectedError)
+			} else if err.Error() != tc.expectedError {
+				t.Fatalf("test case %q expected error %q but got %q", tc.name, tc.expectedError, err)
+			}
+			continue
+		}
+
+		if err != nil {
+			t.Fatalf("test case %q failed: %v", tc.name, err)
+		}
+
+		// At this point we should just do a normal write and persist
+		// as would happen from the CLI
+		mgr.WriteState(mgr.State())
+		mgr.PersistState()
+
+		if logIdx >= len(mockClient.log) {
+			t.Fatalf("request lock and index are out of sync on %q: idx=%d len=%d", tc.name, logIdx, len(mockClient.log))
+		}
+		loggedRequest := mockClient.log[logIdx]
+		logIdx++
+		if diff := cmp.Diff(tc.expectedRequest, loggedRequest); len(diff) > 0 {
+			t.Fatalf("incorrect client requests for %q:\n%s", tc.name, diff)
+		}
+	}
+
+	logCnt := len(mockClient.log)
+	if logIdx != logCnt {
+		log.Fatalf("not all requests were read. Expected logIdx to be %d but got %d", logCnt, logIdx)
+	}
+}
+
+// This test runs the same test cases as above, but with
+// a client that implements EnableForcePush -- this allows
+// us to test that -force continues to work for backends without
+// this interface, but that this interface works for those that do.
+func TestWriteStateForMigrationWithForcePushClient(t *testing.T) {
+	mgr := &State{
+		Client: &mockRemoteClient{
+			current: []byte(`
+				{
+					"version": 4,
+					"lineage": "mock-lineage",
+					"serial": 3,
+					"terraform_version":"0.0.0",
+					"outputs": {"foo": {"value":"bar", "type": "string"}},
+					"resources": []
+				}
+			`),
+		},
+	}
+
 	testCases := []migrationTestCase{
 		// Refreshing state before we run the test loop causes a GET
 		{
@@ -387,7 +539,7 @@ func TestWriteStateForMigration(t *testing.T) {
 
 	// Our client is a mockClient which has a log we
 	// use to check that operations generate expected requests
-	mockClient := mgr.Client.(*mockClient)
+	mockClient := mgr.Client.(*mockRemoteClient)
 
 	if mockClient.force {
 		t.Fatalf("client should not default to force")