add new basic auth provider class

Fix the circular dependency by adding a new BasicAuthProvider interface to
wrap the basic auth values.
Add unit tests for the hash functions.
Refactor functions to use the new basic auth provider interface.

src/auth/hash.go

@@ -2,13 +2,17 @@ package auth
 
 import (
 	"crypto/sha256"
+	"encoding/hex"
 )
 
 func Hash(data []byte) []byte {
+	if len(data) == 0 {
+		return []byte{}
+	}
 	b := sha256.Sum256(data)
 	return b[:]
 }
 
 func HashString(data string) string {
-	return string(Hash([]byte(data)))
+	return hex.EncodeToString(Hash([]byte(data)))
 }

src/auth/hash_test.go

@@ -0,0 +1,26 @@
+package auth
+
+import (
+	"reflect"
+	"testing"
+)
+
+func TestHashString(t *testing.T) {
+	tests := []struct {
+		name string
+		args string
+		want string
+	}{
+		{"Happy path #1", "123", "a665a45920422f9d417e4867efdc4fb8a04a1f3fff1fa07e998e86f7f7a27ae3"},
+		{"Happy path #2", "hello world", "b94d27b9934d3e08a52e52d7da7dabfac484efe37a5380ee9088f7ace2efcde9"},
+		{"Happy path #3", "H3Ll0_W0RLD", "d58a27fe9a6e73a1d8a67189fb8acace047e7a1a795276a0056d3717ad61bd0e"},
+		{"Blank string", "", ""},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := HashString(tt.args); !reflect.DeepEqual(got, tt.want) {
+				t.Errorf("HashString() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}

src/auth/middleware.go

@@ -1,15 +1,18 @@
 package auth
 
 import (
-	"fail2ban-prometheus-exporter/cfg"
 	"net/http"
 )
 
-func BasicAuthMiddleware(handlerFunc http.HandlerFunc, appSettings *cfg.AppSettings) http.HandlerFunc {
-	authEnabled := len(appSettings.BasicAuthUsername) > 0 && len(appSettings.BasicAuthPassword) > 0
-	if authEnabled {
+type BasicAuthProvider interface {
+	Enabled() bool
+	DoesBasicAuthMatch(username, password string) bool
+}
+
+func BasicAuthMiddleware(handlerFunc http.HandlerFunc, basicAuthProvider BasicAuthProvider) http.HandlerFunc {
+	if basicAuthProvider.Enabled() {
 		return func(w http.ResponseWriter, r *http.Request) {
-			if doesBasicAuthMatch(r, appSettings) {
+			if doesBasicAuthMatch(r, basicAuthProvider) {
 				w.WriteHeader(http.StatusUnauthorized)
 			} else {
 				handlerFunc.ServeHTTP(w, r)
@@ -19,12 +22,12 @@ func BasicAuthMiddleware(handlerFunc http.HandlerFunc, appSettings *cfg.AppSetti
 	return handlerFunc
 }
 
-func doesBasicAuthMatch(r *http.Request, appSettings *cfg.AppSettings) bool {
+func doesBasicAuthMatch(r *http.Request, basicAuthProvider BasicAuthProvider) bool {
 	rawUsername, rawPassword, ok := r.BasicAuth()
 	if ok {
 		username := HashString(rawUsername)
 		password := HashString(rawPassword)
-		return username == appSettings.BasicAuthUsername && password == appSettings.BasicAuthPassword
+		return basicAuthProvider.DoesBasicAuthMatch(username, password)
 	}
 	return false
 }

src/cfg/basicAuth.go

@@ -0,0 +1,14 @@
+package cfg
+
+type basicAuth struct {
+	username string
+	password string
+}
+
+func (p *basicAuth) Enabled() bool {
+	return len(p.username) > 0 && len(p.password) > 0
+}
+
+func (p *basicAuth) DoesBasicAuthMatch(username, password string) bool {
+	return username == p.username && password == p.password
+}

src/cfg/cfg.go

@@ -19,8 +19,7 @@ type AppSettings struct {
 	Fail2BanSocketPath   string
 	FileCollectorPath    string
 	FileCollectorEnabled bool
-	BasicAuthUsername    string
-	BasicAuthPassword    string
+	BasicAuthProvider    *basicAuth
 }
 
 func Parse() *AppSettings {
@@ -43,9 +42,11 @@ func Parse() *AppSettings {
 	return appSettings
 }
 
-func (settings *AppSettings) setBasicAuthValues(username, password string) {
-	settings.BasicAuthUsername = auth.HashString(username)
-	settings.BasicAuthPassword = auth.HashString(password)
+func (settings *AppSettings) setBasicAuthValues(rawUsername, rawPassword string) {
+	settings.BasicAuthProvider = &basicAuth{
+		username: auth.HashString(rawUsername),
+		password: auth.HashString(rawPassword),
+	}
 }
 
 func (settings *AppSettings) validateFlags() {
@@ -64,7 +65,7 @@ func (settings *AppSettings) validateFlags() {
 			fmt.Printf("file collector directory path must not be empty if collector enabled\n")
 			flagsValid = false
 		}
-		if (len(settings.BasicAuthUsername) > 0) != (len(settings.BasicAuthPassword) > 0) {
+		if (len(settings.BasicAuthProvider.username) > 0) != (len(settings.BasicAuthProvider.password) > 0) {
 			fmt.Printf("to enable basic auth both the username and the password must be provided")
 			flagsValid = false
 		}

src/exporter.go

@@ -64,12 +64,12 @@ func main() {
 		textFileCollector := textfile.NewCollector(appSettings)
 		prometheus.MustRegister(textFileCollector)
 
-		http.HandleFunc("/", auth.BasicAuthMiddleware(rootHtmlHandler, appSettings))
+		http.HandleFunc("/", auth.BasicAuthMiddleware(rootHtmlHandler, appSettings.BasicAuthProvider))
 		http.HandleFunc(metricsPath, auth.BasicAuthMiddleware(
 			func(w http.ResponseWriter, r *http.Request) {
 				metricHandler(w, r, textFileCollector)
 			},
-			appSettings,
+			appSettings.BasicAuthProvider,
 		))
 		log.Printf("metrics available at '%s'", metricsPath)