Introduce config.FromEnv()

config/config.go

@@ -3,6 +3,7 @@ package config
 import (
 	stderrors "errors"
 	"fmt"
+	"github.com/caarlos0/env/v11"
 	"github.com/creasty/defaults"
 	"github.com/goccy/go-yaml"
 	"github.com/jessevdk/go-flags"
@@ -50,6 +51,28 @@ func FromYAMLFile(name string, v Validator) error {
 	return nil
 }
 
+// EnvOptions is a type alias for [env.Options], so that only this package needs to import [env].
+type EnvOptions = env.Options
+
+// FromEnv parses environment variables and stores the result in the value pointed to by v.
+// If v is nil or not a pointer, FromEnv returns an [ErrInvalidArgument] error.
+func FromEnv(v Validator, options EnvOptions) error {
+	rv := reflect.ValueOf(v)
+	if rv.Kind() != reflect.Ptr || rv.IsNil() {
+		return errors.Wrapf(ErrInvalidArgument, "non-nil pointer expected, got %T", v)
+	}
+
+	if err := defaults.Set(v); err != nil {
+		return errors.Wrap(err, "can't set config defaults")
+	}
+
+	if err := env.ParseWithOptions(v, options); err != nil {
+		return errors.Wrap(err, "can't parse environment variables")
+	}
+
+	return errors.Wrap(v.Validate(), "invalid configuration")
+}
+
 // ParseFlags parses CLI flags and stores the result
 // in the value pointed to by v. If v is nil or not a pointer,
 // ParseFlags returns an [ErrInvalidArgument] error.

config/config_test.go

@@ -0,0 +1,100 @@
+package config
+
+import (
+	"errors"
+	"github.com/stretchr/testify/require"
+	"os"
+	"reflect"
+	"testing"
+)
+
+type simpleValidator struct {
+	Foo int `env:"FOO"`
+}
+
+func (sv simpleValidator) Validate() error {
+	if sv.Foo == 42 {
+		return nil
+	} else {
+		return errors.New("invalid value")
+	}
+}
+
+type nonStructValidator int
+
+func (nonStructValidator) Validate() error {
+	return nil
+}
+
+type defaultValidator struct {
+	Foo int `env:"FOO" default:"42"`
+}
+
+func (defaultValidator) Validate() error {
+	return nil
+}
+
+type prefixValidator struct {
+	Nested simpleValidator `envPrefix:"PREFIX_"`
+}
+
+func (prefixValidator) Validate() error {
+	return nil
+}
+
+func TestFromEnv(t *testing.T) {
+	subtests := []struct {
+		name    string
+		env     map[string]string
+		options EnvOptions
+		io      Validator
+		error   bool
+	}{
+		{"nil", nil, EnvOptions{}, nil, true},
+		{"nonptr", nil, EnvOptions{}, simpleValidator{}, true},
+		{"nilptr", nil, EnvOptions{}, (*simpleValidator)(nil), true},
+		{"defaulterr", nil, EnvOptions{}, new(nonStructValidator), true},
+		{"parseeerr", map[string]string{"FOO": "bar"}, EnvOptions{}, &simpleValidator{}, true},
+		{"invalid", map[string]string{"FOO": "23"}, EnvOptions{}, &simpleValidator{}, true},
+		{"simple", map[string]string{"FOO": "42"}, EnvOptions{}, &simpleValidator{42}, false},
+		{"default", nil, EnvOptions{}, &defaultValidator{42}, false},
+		{"override", map[string]string{"FOO": "23"}, EnvOptions{}, &defaultValidator{23}, false},
+		{"prefix", map[string]string{"PREFIX_FOO": "42"}, EnvOptions{Prefix: "PREFIX_"}, &simpleValidator{42}, false},
+		{"nested", map[string]string{"PREFIX_FOO": "42"}, EnvOptions{}, &prefixValidator{simpleValidator{42}}, false},
+	}
+
+	allEnv := make(map[string]struct{})
+	for _, st := range subtests {
+		for k := range st.env {
+			allEnv[k] = struct{}{}
+		}
+	}
+
+	for _, st := range subtests {
+		t.Run(st.name, func(t *testing.T) {
+			for k := range allEnv {
+				require.NoError(t, os.Unsetenv(k))
+			}
+
+			for k, v := range st.env {
+				require.NoError(t, os.Setenv(k, v))
+			}
+
+			var actual Validator
+			if vActual := reflect.ValueOf(st.io); vActual != (reflect.Value{}) {
+				if vActual.Kind() == reflect.Ptr && !vActual.IsNil() {
+					vActual = reflect.New(vActual.Type().Elem())
+				}
+
+				actual = vActual.Interface().(Validator)
+			}
+
+			if err := FromEnv(actual, st.options); st.error {
+				require.Error(t, err)
+			} else {
+				require.NoError(t, err)
+				require.Equal(t, st.io, actual)
+			}
+		})
+	}
+}

go.mod

@@ -3,6 +3,7 @@ module github.com/icinga/icinga-go-library
 go 1.22
 
 require (
+	github.com/caarlos0/env/v11 v11.1.0
 	github.com/creasty/defaults v1.7.0
 	github.com/go-sql-driver/mysql v1.8.1
 	github.com/goccy/go-yaml v1.12.0

go.sum

@@ -4,6 +4,8 @@ github.com/bsm/ginkgo/v2 v2.12.0 h1:Ny8MWAHyOepLGlLKYmXG4IEkioBysk6GpaRTLC8zwWs=
 github.com/bsm/ginkgo/v2 v2.12.0/go.mod h1:SwYbGRRDovPVboqFv0tPTcG1sN61LM1Z4ARdbAV9g4c=
 github.com/bsm/gomega v1.27.10 h1:yeMWxP2pV2fG3FgAODIY8EiRE3dy0aeFYt4l7wh6yKA=
 github.com/bsm/gomega v1.27.10/go.mod h1:JyEr/xRbxbtgWNi8tIEVPUYZ5Dzef52k01W3YH0H+O0=
+github.com/caarlos0/env/v11 v11.1.0 h1:a5qZqieE9ZfzdvbbdhTalRrHT5vu/4V1/ad1Ka6frhI=
+github.com/caarlos0/env/v11 v11.1.0/go.mod h1:LwgkYk1kDvfGpHthrWWLof3Ny7PezzFwS4QrsJdHTMo=
 github.com/cespare/xxhash/v2 v2.2.0 h1:DC2CZ1Ep5Y4k3ZQ899DldepgrayRUGE6BBZ/cd9Cj44=
 github.com/cespare/xxhash/v2 v2.2.0/go.mod h1:VGX0DQ3Q6kWi7AoAeZDth3/j3BFtOZR5XLFGgcrjCOs=
 github.com/creasty/defaults v1.7.0 h1:eNdqZvc5B509z18lD8yc212CAqJNvfT1Jq6L8WowdBA=