Replace viper with koanf

Reduces dependencies

Makefile

@@ -43,7 +43,7 @@ clean: ## Clean the project
 
 .PHONY: test
 test: ## Run unit tests
-	@go test -coverprofile cover.out ./...
+	@go test -coverprofile cover.out -v ./...
 
 .PHONY: run
 run: ## Run locally

README.adoc

@@ -56,18 +56,26 @@ With https://ccremer.github.io/charts/fronius-exporter[fronius-exporter]
 fronius-exporter --url http://symo.ip.or.hostname/solar_api/v1/GetPowerFlowRealtimeData.fcgi
 ----
 
-Upon each call to `/metrics`, the exporter will do a GET request on the given URL, and translate the JSON
-response to Prometheus metrics format.
+Upon each call to `/metrics`, the exporter will do a GET request on the given URL, and translate the JSON response to Prometheus metrics format.
 
 == Configuration
 
-`fronius-exporter` can be configured with CLI flags. Call the binary with `--help` to get a list of options.
+`fronius-exporter` can be configured with CLI flags.
+Call the binary with `--help` to get a list of options.
 
 [TIP]
 ====
 All flags are also configurable with Environment variables.
-Replace the `.` char with `_` and uppercase the names in order for them to be recognized, e.g. `--log.level debug` becomes `LOG_LEVEL=debug`.
-CLI flags take precedence though.
+
+* Replace the `-` char with `_` in the names and uppercase the names
+* Replace the `.` delimiter with `__`
+* CLI flags take precedence
+
+.Following calls are requivalent
+----
+fronius-exporter --symo.url http://...
+SYMO__URL=http://... fronius-exporter
+----
 ====
 
 == As a client API

cfg/config.go

@@ -7,45 +7,55 @@ import (
 	"strings"
 	"time"
 
+	"github.com/knadh/koanf"
+	"github.com/knadh/koanf/providers/env"
+	"github.com/knadh/koanf/providers/posflag"
 	log "github.com/sirupsen/logrus"
 	flag "github.com/spf13/pflag"
-	"github.com/spf13/viper"
 )
 
 // ParseConfig overrides internal config defaults with up CLI flags, environment variables and ensures basic validation.
 func ParseConfig(version, commit, date string, fs *flag.FlagSet, args []string) *Configuration {
 	config := NewDefaultConfig()
 
+	setupCliFlags(fmt.Sprintf("version %s, %s, %s", version, commit, date), fs, config)
+
+	loadConfigHierarchy(fs, args, config)
+
+	postLoadProcess(config)
+
+	log.WithField("config", *config).Debug("Parsed config")
+	return config
+}
+
+func setupCliFlags(version string, fs *flag.FlagSet, config *Configuration) {
 	fs.Usage = func() {
-		fmt.Fprintf(os.Stderr, "Usage of %s (version %s, %s, %s):\n", os.Args[0], version, commit, date)
+		fmt.Fprintf(os.Stderr, "Usage of %s (%s):\n", os.Args[0], version)
 		fs.PrintDefaults()
 	}
-	fs.String("bindAddr", config.BindAddr, "IP Address to bind to listen for Prometheus scrapes")
+	fs.String("bind-addr", config.BindAddr, "IP Address to bind to listen for Prometheus scrapes")
 	fs.String("log.level", config.Log.Level, "Logging level")
 	fs.BoolP("log.verbose", "v", config.Log.Verbose, "Shortcut for --log.level=debug")
-	fs.StringSlice("symo.header", []string{},
+	fs.StringSlice("symo.header", config.Symo.Headers,
 		"List of \"key: value\" headers to append to the requests going to Fronius Symo")
 	fs.StringP("symo.url", "u", config.Symo.URL, "Target URL of Fronius Symo device")
 	fs.Int64("symo.timeout", int64(config.Symo.Timeout.Seconds()),
 		"Timeout in seconds when collecting metrics from Fronius Symo. Should not be larger than the scrape interval")
-	if err := viper.BindPFlags(fs); err != nil {
-		log.WithError(err).Fatal("Could not bind flags")
-	}
-
-	if err := fs.Parse(args); err != nil {
-		log.WithError(err).Fatal("Could not parse flags")
-	}
-	viper.SetEnvKeyReplacer(strings.NewReplacer(".", "_", "-", "_"))
-	viper.AutomaticEnv()
 
-	if err := viper.Unmarshal(config); err != nil {
-		log.WithError(err).Fatal("Could not read config")
-	}
+}
 
+func postLoadProcess(config *Configuration) {
 	config.Symo.Timeout *= time.Second
 	if config.Log.Verbose {
 		config.Log.Level = "debug"
 	}
+
+	var parsedHeaders []string
+	for _, header := range config.Symo.Headers {
+		parsedHeaders = splitHeaderStrings(header, parsedHeaders)
+	}
+	config.Symo.Headers = parsedHeaders
+
 	level, err := log.ParseLevel(config.Log.Level)
 	if err != nil {
 		log.WithError(err).Warn("Could not parse log level, fallback to info level")
@@ -54,8 +64,49 @@ func ParseConfig(version, commit, date string, fs *flag.FlagSet, args []string)
 	} else {
 		log.SetLevel(level)
 	}
-	log.WithField("config", *config).Debug("Parsed config")
-	return config
+}
+
+func splitHeaderStrings(rest string, headers []string) []string {
+	s := strings.TrimPrefix(rest, ",")
+	arr := strings.SplitN(s, ",", 2)
+	if v := arr[0]; v != "" {
+		headers = append(headers, strings.TrimSpace(v))
+	}
+	if len(arr) < 2 {
+		// No more key-value pairs to parse
+		return headers
+	}
+	return splitHeaderStrings(arr[1], headers)
+}
+
+func loadConfigHierarchy(fs *flag.FlagSet, args []string, config *Configuration) {
+	koanfInstance := koanf.New(".")
+
+	// Environment variables
+	if err := koanfInstance.Load(env.Provider("", ".", func(s string) string {
+		/*
+			Configuration can contain hierarchies (YAML, etc.) and CLI flags dashes.
+			To read environment variables with hierarchies and dashes we replace the hierarchy delimiter with double underscore and dashes with single underscore.
+			So that parent.child-with-dash becomes PARENT__CHILD_WITH_DASH
+		*/
+		s = strings.Replace(strings.ToLower(s), "__", ".", -1)
+		s = strings.Replace(strings.ToLower(s), "_", "-", -1)
+		return s
+	}), nil); err != nil {
+		log.WithError(err).Fatal("Could not parse flags")
+	}
+
+	// CLI Flags
+	if err := fs.Parse(args); err != nil {
+		log.WithError(err).Fatal("Could not parse flags")
+	}
+	if err := koanfInstance.Load(posflag.Provider(fs, ".", koanfInstance), nil); err != nil {
+		log.WithError(err).Fatal("Could not process flags")
+	}
+
+	if err := koanfInstance.Unmarshal("", &config); err != nil {
+		log.WithError(err).Fatal("Could not merge defaults with settings from environment variables")
+	}
 }
 
 // ConvertHeaders takes a list of `key=value` headers and adds those trimmed to the specified header struct. It ignores

cfg/config_test.go

@@ -105,7 +105,7 @@ func TestParseConfig(t *testing.T) {
 			},
 		},
 		"GivenFlags_WhenBindAddrSpecified_ThenOverridePort": {
-			args: []string{"--bindAddr", ":9090"},
+			args: []string{"--bind-addr", ":9090"},
 			verify: func(c *Configuration) {
 				assert.Equal(t, ":9090", c.BindAddr)
 			},
@@ -119,11 +119,20 @@ func TestParseConfig(t *testing.T) {
 		},
 		"GivenHeaderEnvVar_WhenMultipleHeadersSpecified_ThenFillArray": {
 			envs: map[string]string{
-				"SYMO_HEADER": "key1=value1, KEY2= value2",
+				"SYMO__HEADER": "key1=value1, KEY2= value2",
 			},
 			verify: func(c *Configuration) {
 				assert.Contains(t, c.Symo.Headers, "key1=value1")
-				assert.Contains(t, c.Symo.Headers, " KEY2= value2")
+				assert.Contains(t, c.Symo.Headers, "KEY2= value2")
+			},
+		},
+		"GivenHeaderEnvVarAndFlag_WhenMultipleHeadersSpecified_ThenTakePrecedenceFromCLI": {
+			envs: map[string]string{
+				"SYMO__HEADER": "key1=value1, KEY2= value2",
+			},
+			args: []string{"--symo.header", "key3=value3"},
+			verify: func(c *Configuration) {
+				assert.Equal(t, c.Symo.Headers, []string{"key3=value3"})
 			},
 		},
 		"GivenUrlFlag_ThenOverrideDefault": {
@@ -160,3 +169,46 @@ func unsetEnv(m map[string]string) {
 		os.Unsetenv(key)
 	}
 }
+
+func Test_parseHeaderString(t *testing.T) {
+	tests := map[string]struct {
+		given    string
+		expected []string
+	}{
+		"GivenSingleHeader_WhenParsing_LeaveUnchanged": {
+			given:    "key=value",
+			expected: []string{"key=value"},
+		},
+		"GivenTwoHeaders_WhenParsing_SplitInTwo": {
+			given:    "key1=value1,key2=value2",
+			expected: []string{"key1=value1", "key2=value2"},
+		},
+		"GivenThreeHeaders_WhenParsing_SplitInThree": {
+			given:    "key1=value1,key2=value2,key3=value3",
+			expected: []string{"key1=value1", "key2=value2", "key3=value3"},
+		},
+		"GivenMalformedHeaders_WhenParsing_RegardAsPartOfPreviousHeader": {
+			given:    "key1=value1,key2value2",
+			expected: []string{"key1=value1", "key2value2"},
+		},
+		"GivenHeadersWithSpace_WhenParsing_TrimSpaceAfterComma": {
+			given:    "key1=value1 , key2=value2",
+			expected: []string{"key1=value1", "key2=value2"},
+		},
+		"GivenHeadersWithTrailingComma_WhenParsing_IgnoreEmptyString": {
+			given:    "key1=value1 ,",
+			expected: []string{"key1=value1"},
+		},
+		"GivenHeadersWithSpaces_WhenParsing_Include": {
+			given:    "key1=value with space,",
+			expected: []string{"key1=value with space"},
+		},
+	}
+	for name, tt := range tests {
+		t.Run(name, func(t *testing.T) {
+			var result []string
+			result = splitHeaderStrings(tt.given, result)
+			assert.Equal(t, tt.expected, result)
+		})
+	}
+}

cfg/types.go

@@ -5,20 +5,20 @@ import "time"
 type (
 	// Configuration holds a strongly-typed tree of the configuration
 	Configuration struct {
-		Log      LogConfig
-		Symo     SymoConfig
-		BindAddr string
+		Log      LogConfig  `koanf:"log"`
+		Symo     SymoConfig `koanf:"symo"`
+		BindAddr string     `koanf:"bind-addr"`
 	}
 	// LogConfig configures the logging options
 	LogConfig struct {
-		Level   string
-		Verbose bool
+		Level   string `koanf:"level"`
+		Verbose bool   `koanf:"verbose"`
 	}
 	// SymoConfig configures the Fronius Symo device
 	SymoConfig struct {
-		URL     string
-		Timeout time.Duration
-		Headers []string `mapstructure:"header"`
+		URL     string        `koanf:"url"`
+		Timeout time.Duration `koanf:"timeout"`
+		Headers []string      `koanf:"header"`
 	}
 )
 

go.mod

@@ -3,9 +3,9 @@ module github.com/ccremer/fronius-exporter
 go 1.16
 
 require (
+	github.com/knadh/koanf v1.0.0
 	github.com/prometheus/client_golang v1.9.0
 	github.com/sirupsen/logrus v1.8.1
 	github.com/spf13/pflag v1.0.5
-	github.com/spf13/viper v1.7.1
 	github.com/stretchr/testify v1.7.0
 )