do exit 1 if a snap that is already installed is asked to be installe…

…d again

LP: #1622782

client/client.go

@@ -314,12 +314,13 @@ func (e *Error) Error() string {
 }
 
 const (
-	ErrorKindTwoFactorRequired = "two-factor-required"
-	ErrorKindTwoFactorFailed   = "two-factor-failed"
-	ErrorKindLoginRequired     = "login-required"
-	ErrorKindTermsNotAccepted  = "terms-not-accepted"
-	ErrorKindNoPaymentMethods  = "no-payment-methods"
-	ErrorKindPaymentDeclined   = "payment-declined"
+	ErrorKindTwoFactorRequired    = "two-factor-required"
+	ErrorKindTwoFactorFailed      = "two-factor-failed"
+	ErrorKindLoginRequired        = "login-required"
+	ErrorKindTermsNotAccepted     = "terms-not-accepted"
+	ErrorKindNoPaymentMethods     = "no-payment-methods"
+	ErrorKindPaymentDeclined      = "payment-declined"
+	ErrorKindSnapAlreadyInstalled = "snap-already-installed"
 )
 
 // IsTwoFactorError returns whether the given error is due to problems

cmd/snap/cmd_snap_op.go

@@ -361,6 +361,10 @@ func (x *cmdInstall) installOne(name string, opts *client.SnapOptions) error {
 	} else {
 		changeID, err = cli.Install(name, opts)
 	}
+	if e, ok := err.(*client.Error); ok && e.Kind == client.ErrorKindSnapAlreadyInstalled {
+		fmt.Fprintf(Stderr, "snap is already installed")
+		return nil
+	}
 	if err != nil {
 		return err
 	}

daemon/api.go

@@ -999,6 +999,16 @@ func postSnap(c *Command, r *http.Request, user *auth.UserState) Response {
 	}
 
 	msg, tsets, err := impl(&inst, state)
+	if _, ok := err.(*snap.AlreadyInstalledError); ok {
+		return SyncResponse(&resp{
+			Type: ResponseTypeError,
+			Result: &errorResult{
+				Message: err.Error(),
+				Kind:    errorKindSnapAlreadyInstalled,
+			},
+			Status: http.StatusBadRequest,
+		}, nil)
+	}
 	if err != nil {
 		return BadRequest("cannot %s %q: %v", inst.Action, inst.Snaps[0], err)
 	}

daemon/response.go

@@ -120,13 +120,14 @@ func (r *resp) ServeHTTP(w http.ResponseWriter, _ *http.Request) {
 type errorKind string
 
 const (
-	errorKindTwoFactorRequired = errorKind("two-factor-required")
-	errorKindTwoFactorFailed   = errorKind("two-factor-failed")
-	errorKindLoginRequired     = errorKind("login-required")
-	errorKindInvalidAuthData   = errorKind("invalid-auth-data")
-	errorKindTermsNotAccepted  = errorKind("terms-not-accepted")
-	errorKindNoPaymentMethods  = errorKind("no-payment-methods")
-	errorKindPaymentDeclined   = errorKind("payment-declined")
+	errorKindTwoFactorRequired    = errorKind("two-factor-required")
+	errorKindTwoFactorFailed      = errorKind("two-factor-failed")
+	errorKindLoginRequired        = errorKind("login-required")
+	errorKindInvalidAuthData      = errorKind("invalid-auth-data")
+	errorKindTermsNotAccepted     = errorKind("terms-not-accepted")
+	errorKindNoPaymentMethods     = errorKind("no-payment-methods")
+	errorKindPaymentDeclined      = errorKind("payment-declined")
+	errorKindSnapAlreadyInstalled = errorKind("snap-already-installed")
 )
 
 type errorValue interface{}

overlord/snapstate/snapstate.go

@@ -276,7 +276,7 @@ func Install(s *state.State, name, channel string, revision snap.Revision, userI
 		return nil, err
 	}
 	if snapst.HasCurrent() {
-		return nil, fmt.Errorf("snap %q already installed", name)
+		return nil, &snap.AlreadyInstalledError{name}
 	}
 
 	snapInfo, err := snapInfo(s, name, channel, revision, userID, flags)

snap/info.go

@@ -509,3 +509,11 @@ func SplitSnapApp(snapApp string) (snap, app string) {
 	}
 	return l[0], l[1]
 }
+
+type AlreadyInstalledError struct {
+	Snap string
+}
+
+func (e AlreadyInstalledError) Error() string {
+	return fmt.Sprintf("snap %q already installed", e.Snap)
+}

tests/main/install-errors/task.yaml

@@ -44,8 +44,6 @@ execute: |
 
     echo "============================================"
 
-    echo "Install a snap already installed fails"
-    if snap install $SNAP_NAME; then
-        echo "Trying to install an already installed snap should fail"
-        exit 1
-    fi
+    echo "Install a snap that is already installed shows a message"
+    echo "but does not fail (LP: #1622782)"
+    snap install $SNAP_NAME | MATCH "snap is already installed"