Initial commit

README.md

@@ -1,2 +1,25 @@
 # configstruct
 Simple Go module to parse a configuration from environment and cli flags using struct tags.
+
+Usage
+```Go
+// define a struct with tags for env name, cli flag and usage
+type Config struct {
+	Hostname string `env:"CONFIGSTRUCT_HOSTNAME" cli:"hostname" usage:"hostname value"`
+	Port     int    `env:"CONFIGSTRUCT_PORT" cli:"port" usage:"listen port"`
+	Debug    bool   `env:"CONFIGSTRUCT_DEBUG" cli:"debug" usage:"debug mode"`
+}
+
+// create a variable of the struct type and define defaults if needed
+conf := testConfig{
+    Hostname: "localhost",
+    Port:     8000,
+    Debug:    true,
+}
+
+// now parse values from first cli flags and then env into this var
+err := configstruct.Parse(&conf)
+if err != nil {...}
+
+
+```

configstruct.go

@@ -0,0 +1,70 @@
+package configstruct
+
+import (
+	"flag"
+	"fmt"
+	"os"
+	"reflect"
+	"strconv"
+	"strings"
+)
+
+// Parse uses a given struct c with tags and parses values from env or cli flags
+func Parse(c interface{}) error {
+
+	// use reflection to deep dive into our struct
+	valueRef := reflect.ValueOf(c)
+	confType := valueRef.Elem().Type()
+
+	// iterate over struct fields for cli flags
+	for i := 0; i < confType.NumField(); i++ {
+		field := confType.Field(i)
+		value := valueRef.Elem().Field(i)
+		cli := field.Tag.Get("cli")
+		usage := field.Tag.Get("usage")
+
+		if cli != "" {
+			switch field.Type.Kind() {
+			case reflect.String:
+				flag.StringVar(valueRef.Elem().FieldByName(field.Name).Addr().Interface().(*string), cli, value.String(), usage)
+			case reflect.Bool:
+				flag.BoolVar(valueRef.Elem().FieldByName(field.Name).Addr().Interface().(*bool), cli, value.Bool(), usage)
+			case reflect.Int:
+				flag.IntVar(valueRef.Elem().FieldByName(field.Name).Addr().Interface().(*int), cli, int(value.Int()), usage)
+			default:
+				return fmt.Errorf("config cli type %s not implemented", field.Type.Name())
+			}
+		}
+	}
+
+	// parse cli flags
+	flag.Parse()
+
+	// iterate over struct fields for env values
+	for i := 0; i < confType.NumField(); i++ {
+		field := confType.Field(i)
+		env := field.Tag.Get("env")
+
+		envValue, found := os.LookupEnv(env)
+		if found {
+			switch field.Type.Kind() {
+			case reflect.String:
+				valueRef.Elem().FieldByName(field.Name).SetString(envValue)
+			case reflect.Bool:
+				valueRef.Elem().FieldByName(field.Name).SetBool(false)
+				if strings.EqualFold(envValue, "true") {
+					valueRef.Elem().FieldByName(field.Name).SetBool(true)
+				}
+			case reflect.Int:
+				value, err := strconv.ParseInt(envValue, 0, 64)
+				if err == nil {
+					valueRef.Elem().FieldByName(field.Name).SetInt(value)
+				}
+			default:
+				return fmt.Errorf("config env type %s not implemented", field.Type.Name())
+			}
+		}
+	}
+
+	return nil
+}

configstruct_test.go

@@ -0,0 +1,85 @@
+package configstruct
+
+import (
+	"flag"
+	"github.com/stretchr/testify/assert"
+	"os"
+	"testing"
+)
+
+type testConfig struct {
+	Hostname string `env:"CONFIGSTRUCT_HOSTNAME" cli:"hostname" usage:"hostname value"`
+	Port     int    `env:"CONFIGSTRUCT_PORT" cli:"port" usage:"listen port"`
+	Debug    bool   `env:"CONFIGSTRUCT_DEBUG" cli:"debug" usage:"debug mode"`
+}
+
+func TestParse(t *testing.T) {
+
+	t.Run("valid cli fields", func(t *testing.T) {
+		os.Args = []string{"command", "-hostname", "localhost", "-port", "8080", "-debug", "true"}
+		flag.CommandLine = flag.NewFlagSet(os.Args[0], flag.ExitOnError)
+
+		conf := testConfig{}
+
+		err := Parse(&conf)
+		assert.NoError(t, err)
+
+		assert.Equal(t, 8080, conf.Port)
+		assert.Equal(t, "localhost", conf.Hostname)
+		assert.True(t, conf.Debug)
+
+	})
+
+	t.Run("set using env fields", func(t *testing.T) {
+		os.Clearenv()
+		os.Setenv("CONFIGSTRUCT_HOSTNAME", "myhost")
+		os.Setenv("CONFIGSTRUCT_PORT", "9000")
+		os.Setenv("CONFIGSTRUCT_DEBUG", "true")
+
+		conf := testConfig{}
+
+		err := Parse(&conf)
+		assert.NoError(t, err)
+
+		assert.Equal(t, 9000, conf.Port)
+		assert.Equal(t, "myhost", conf.Hostname)
+		assert.True(t, conf.Debug)
+
+	})
+
+	t.Run("overwrite cli flags with env fields", func(t *testing.T) {
+		os.Args = []string{"command", "-hostname", "localhost", "-port", "8080", "-debug", "true"}
+		flag.CommandLine = flag.NewFlagSet(os.Args[0], flag.ExitOnError)
+
+		os.Clearenv()
+		os.Setenv("CONFIGSTRUCT_HOSTNAME", "myhost")
+		os.Setenv("CONFIGSTRUCT_PORT", "9000")
+
+		conf := testConfig{}
+
+		err := Parse(&conf)
+		assert.NoError(t, err)
+
+		assert.Equal(t, 9000, conf.Port)
+		assert.Equal(t, "myhost", conf.Hostname)
+		assert.True(t, conf.Debug)
+	})
+
+	t.Run("cli with defaults", func(t *testing.T) {
+		os.Args = []string{"command", "-hostname", "myhost"}
+		flag.CommandLine = flag.NewFlagSet(os.Args[0], flag.ExitOnError)
+
+		conf := testConfig{
+			Hostname: "localhost",
+			Port:     8000,
+			Debug:    true,
+		}
+
+		err := Parse(&conf)
+		assert.NoError(t, err)
+
+		assert.Equal(t, 8000, conf.Port)
+		assert.Equal(t, "myhost", conf.Hostname)
+		assert.True(t, conf.Debug)
+	})
+}

go.mod

@@ -0,0 +1,9 @@
+module github.com/pteich/configstruct
+
+go 1.13
+
+require (
+	github.com/stretchr/objx v0.2.0 // indirect
+	github.com/stretchr/testify v1.4.0
+	gopkg.in/yaml.v2 v2.2.7 // indirect
+)

go.sum

@@ -0,0 +1,18 @@
+github.com/davecgh/go-spew v1.1.0 h1:ZDRjVQ15GmhC3fiQ8ni8+OwkZQO4DARzQgrnXU1Liz8=
+github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/stretchr/objx v0.1.0 h1:4G4v2dO3VZwixGIRoQ5Lfboy6nUhCyYzaqnIAPPhYs4=
+github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
+github.com/stretchr/objx v0.2.0 h1:Hbg2NidpLE8veEBkEZTL3CvlkUIVzuU9jDplZO54c48=
+github.com/stretchr/objx v0.2.0/go.mod h1:qt09Ya8vawLte6SNmTgCsAVtYtaKzEcn8ATUoHMkEqE=
+github.com/stretchr/testify v1.3.0/go.mod h1:M5WIy9Dh21IEIfnGCwXGc5bZfKNJtfHm1UVUgZn+9EI=
+github.com/stretchr/testify v1.4.0 h1:2E4SXV/wtOkTonXsotYi4li6zVWxYlZuYNCXe9XRJyk=
+github.com/stretchr/testify v1.4.0/go.mod h1:j7eGeouHqKxXV5pUuKE4zz7dFj8WfuZ+81PSLYec5m4=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v2 v2.2.2 h1:ZCJp+EgiOT7lHqUV2J862kp8Qj64Jo6az82+3Td9dZw=
+gopkg.in/yaml.v2 v2.2.2/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=
+gopkg.in/yaml.v2 v2.2.7 h1:VUgggvou5XRW9mHwD/yXxIYSMtY0zoKQf/v226p2nyo=
+gopkg.in/yaml.v2 v2.2.7/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=