feat: add --json flag to "service-key" subcommand

It's very common to see code like:
```
cf service-key "$SERVICE_INSTANCE_NAME" $KEY_NAME | tail -n +2
```
This removed the header from the output leaving just JSON.
Search GitHub and you'll see pages of hits.

Rather than forcing script users to chop of the header, risking
issues with errors in pipes, etc... It woudld be better just
to print the correct output in the first place. This commit:
adds a "--json" flag which outputs JSON only. It follows the
convention of "--guid" to supress warnings too (unless there
an error). In practice the endpoints in question do not produce
warnings, so it makes no practical difference.

Author: blgm

command/v7/service_key_command.go

@@ -9,16 +9,19 @@ type ServiceKeyCommand struct {
 
 	RequiredArgs flag.ServiceInstanceKey `positional-args:"yes"`
 	GUID         bool                    `long:"guid" description:"Retrieve and display the given service-key's guid. All other output is suppressed."`
+	JSON         bool                    `long:"json" description:"Output credentials as JSON. All other output is suppressed."`
 }
 
 func (cmd ServiceKeyCommand) Execute(args []string) error {
 	if err := cmd.SharedActor.CheckTarget(true, true); err != nil {
 		return err
 	}
 
-	switch cmd.GUID {
-	case true:
+	switch {
+	case cmd.GUID:
 		return cmd.guid()
+	case cmd.JSON:
+		return cmd.json()
 	default:
 		return cmd.details()
 	}
@@ -33,19 +36,30 @@ func (cmd ServiceKeyCommand) Examples() string {
 }
 
 func (cmd ServiceKeyCommand) guid() error {
-	key, warnings, err := cmd.Actor.GetServiceKeyByServiceInstanceAndName(
+	key, _, err := cmd.Actor.GetServiceKeyByServiceInstanceAndName(
 		cmd.RequiredArgs.ServiceInstance,
 		cmd.RequiredArgs.ServiceKey,
 		cmd.Config.TargetedSpace().GUID,
 	)
-	switch err.(type) {
-	case nil:
-		cmd.UI.DisplayText(key.GUID)
-		return nil
-	default:
-		cmd.UI.DisplayWarnings(warnings)
+	if err != nil {
 		return err
 	}
+
+	cmd.UI.DisplayText(key.GUID)
+	return nil
+}
+
+func (cmd ServiceKeyCommand) json() error {
+	details, _, err := cmd.Actor.GetServiceKeyDetailsByServiceInstanceAndName(
+		cmd.RequiredArgs.ServiceInstance,
+		cmd.RequiredArgs.ServiceKey,
+		cmd.Config.TargetedSpace().GUID,
+	)
+	if err != nil {
+		return err
+	}
+
+	return cmd.UI.DisplayJSON("", details)
 }
 
 func (cmd ServiceKeyCommand) details() error {
@@ -72,10 +86,5 @@ func (cmd ServiceKeyCommand) details() error {
 
 	cmd.UI.DisplayNewline()
 
-	err = cmd.UI.DisplayJSON("", details)
-	if err != nil {
-		return err
-	}
-
-	return nil
+	return cmd.UI.DisplayJSON("", details)
 }

command/v7/service_key_command_test.go

@@ -64,6 +64,16 @@ var _ = Describe("service-key Command", func() {
 		Expect(actualSpace).To(BeTrue())
 	})
 
+	When("checking target fails", func() {
+		BeforeEach(func() {
+			fakeSharedActor.CheckTargetReturns(errors.New("not logged in"))
+		})
+
+		It("returns the error", func() {
+			Expect(executeErr).To(MatchError("not logged in"))
+		})
+	})
+
 	When("getting details", func() {
 		const fakeUserName = "fake-user-name"
 
@@ -161,8 +171,57 @@ var _ = Describe("service-key Command", func() {
 				)
 			})
 
-			It("prints warnings and returns an error", func() {
-				Expect(testUI.Err).To(Say("a warning"))
+			It("returns an error without warnings", func() {
+				Expect(testUI.Err).NotTo(Say("a warning"))
+				Expect(executeErr).To(MatchError("bang"))
+			})
+		})
+	})
+
+	When("getting JSON output", func() {
+		BeforeEach(func() {
+			fakeActor.GetServiceKeyDetailsByServiceInstanceAndNameReturns(
+				resources.ServiceCredentialBindingDetails{
+					Credentials: map[string]interface{}{"foo": "bar", "pass": "<3test"},
+				},
+				v7action.Warnings{"a warning"},
+				nil,
+			)
+
+			setFlag(&cmd, "--json")
+		})
+
+		It("delegates to the actor", func() {
+			Expect(fakeActor.GetServiceKeyDetailsByServiceInstanceAndNameCallCount()).To(Equal(1))
+			actualServiceInstanceName, actualKeyName, actualSpaceGUID := fakeActor.GetServiceKeyDetailsByServiceInstanceAndNameArgsForCall(0)
+			Expect(actualServiceInstanceName).To(Equal(fakeServiceInstanceName))
+			Expect(actualKeyName).To(Equal(fakeServiceKeyName))
+			Expect(actualSpaceGUID).To(Equal(fakeSpaceGUID))
+		})
+
+		It("prints JSON without intro message or warnings", func() {
+			Expect(executeErr).NotTo(HaveOccurred())
+			Expect(testUI.Err).NotTo(Say("a warning"))
+			Expect(testUI.Out).NotTo(Say("Getting key"))
+			Expect(testUI.Out).To(SatisfyAll(
+				Say(`\{\n`),
+				Say(`  "foo": "bar",\n`),
+				Say(`  "pass": "<3test"\n`),
+				Say(`\}\n`),
+			))
+		})
+
+		When("actor returns an error", func() {
+			BeforeEach(func() {
+				fakeActor.GetServiceKeyDetailsByServiceInstanceAndNameReturns(
+					resources.ServiceCredentialBindingDetails{},
+					v7action.Warnings{"a warning"},
+					errors.New("bang"),
+				)
+			})
+
+			It("returns an error without warnings", func() {
+				Expect(testUI.Err).NotTo(Say("a warning"))
 				Expect(executeErr).To(MatchError("bang"))
 			})
 		})