make client config's UserAgent property optional

The value is useful for debugging, but it's not being set shouldn't stop a
test or any other process from running.

Also fixed a few calls to Go stdlib deprecated functions.

alerts/client_test.go

@@ -87,8 +87,7 @@ var _ = Describe("Client", func() {
 func buildTestClient(s *httptest.Server) *Client {
 	pCfg := &platform.Config{
 		Config: &client.Config{
-			Address:   s.URL,
-			UserAgent: "foo",
+			Address: s.URL,
 		},
 	}
 	token := mockTokenProvider(testToken)

client/client.go

@@ -117,7 +117,9 @@ func (c *Client) createRequest(ctx context.Context, method string, url string, m
 		return nil, errors.New("url is missing")
 	}
 
-	mutators = append(mutators, request.NewHeaderMutator("User-Agent", c.userAgent))
+	if c.userAgent != "" {
+		mutators = append(mutators, request.NewHeaderMutator("User-Agent", c.userAgent))
+	}
 
 	var body io.Reader
 	if requestBody != nil {

client/config.go

@@ -10,7 +10,16 @@ import (
 )
 
 type Config struct {
-	Address   string // this should be overridden for loaders using envconfig
+	Address string // this should be overridden for loaders using envconfig
+	// UserAgent is an optional way for a client to identify itself.
+	//
+	// This is usually set to the name of the service that's using the
+	// client. If left empty, the default Go http.Client value should be used.
+	//
+	// This value can be helpful when debugging. But remember that these
+	// values can be spoofed, so when in doubt, verify the client's source IP.
+	//
+	// More info: https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/User-Agent
 	UserAgent string `envconfig:"TIDEPOOL_USER_AGENT"`
 }
 
@@ -28,9 +37,6 @@ func (c *Config) Validate() error {
 	} else if _, err := url.Parse(c.Address); err != nil {
 		return errors.New("address is invalid")
 	}
-	if c.UserAgent == "" {
-		return errors.New("user agent is missing")
-	}
 
 	return nil
 }

client/config_test.go

@@ -89,11 +89,6 @@ var _ = Describe("Config", func() {
 					Expect(cfg.Validate()).To(MatchError("address is invalid"))
 				})
 
-				It("returns an error if the user agent is missing", func() {
-					cfg.UserAgent = ""
-					Expect(cfg.Validate()).To(MatchError("user agent is missing"))
-				})
-
 				It("returns success", func() {
 					Expect(cfg.Validate()).To(Succeed())
 					Expect(cfg.Address).To(Equal(address))

data/client/client_test.go

@@ -43,13 +43,6 @@ var _ = Describe("Client", func() {
 			Expect(clnt).To(BeNil())
 		})
 
-		It("returns an error if config user agent is missing", func() {
-			config.UserAgent = ""
-			clnt, err := dataClient.New(config, platform.AuthorizeAsService)
-			Expect(err).To(MatchError("config is invalid; user agent is missing"))
-			Expect(clnt).To(BeNil())
-		})
-
 		It("returns success", func() {
 			clnt, err := dataClient.New(config, platform.AuthorizeAsService)
 			Expect(err).ToNot(HaveOccurred())

metric/client/client_test.go

@@ -66,13 +66,6 @@ var _ = Describe("Client", func() {
 			Expect(clnt).To(BeNil())
 		})
 
-		It("returns an error if config user agent is missing", func() {
-			config.UserAgent = ""
-			clnt, err := metricClient.New(config, platform.AuthorizeAsUser, name, versionReporter)
-			Expect(err).To(MatchError("config is invalid; user agent is missing"))
-			Expect(clnt).To(BeNil())
-		})
-
 		It("returns success", func() {
 			clnt, err := metricClient.New(config, platform.AuthorizeAsUser, name, versionReporter)
 			Expect(err).ToNot(HaveOccurred())

platform/config_test.go

@@ -113,11 +113,6 @@ var _ = Describe("Config", func() {
 					Expect(cfg.Validate()).To(MatchError("address is invalid"))
 				})
 
-				It("returns an error if the user agent is missing", func() {
-					cfg.UserAgent = ""
-					Expect(cfg.Validate()).To(MatchError("user agent is missing"))
-				})
-
 				It("returns success", func() {
 					Expect(cfg.Validate()).To(Succeed())
 					Expect(cfg.Config).ToNot(BeNil())