feat(sources/env): key prefix option, use settings struct to create s…

…ource

README.md

@@ -24,7 +24,7 @@ Features:
   - `OverrideWith`: `gosettings.OverrideWith*` functions (see [pkg.go.dev/github.com/qdm12/gosettings](https://pkg.go.dev/github.com/qdm12/gosettings))
   - `Validate`: `validate.*` functions from [`github.com/qdm12/gosettings/validate`](https://pkg.go.dev/github.com/qdm12/gosettings/validate)
 - Reading settings from multiple sources with precedence with [`github.com/qdm12/gosettings/reader`](https://pkg.go.dev/github.com/qdm12/gosettings/reader)
-  - Environment variable implementation `env.New(os.Environ())` in subpackage [`github.com/qdm12/gosettings/reader/sources/env`](https://pkg.go.dev/github.com/qdm12/gosettings/reader/sources/env)
+  - Environment variable implementation `env.New(env.Settings{Environ: os.Environ()})` in subpackage [`github.com/qdm12/gosettings/reader/sources/env`](https://pkg.go.dev/github.com/qdm12/gosettings/reader/sources/env)
   - Flag implementation `flag.New(os.Args)` in subpackage [`github.com/qdm12/gosettings/reader/sources/flag`](https://pkg.go.dev/github.com/qdm12/gosettings/reader/sources/flag)
 - Minor feature notes:
   - No use of `reflect` for better runtime safety
@@ -111,7 +111,7 @@ A simple example (runnable [here](examples/reader/main.go)) would be:
 
 ```go
 flagSource := flag.New([]string{"program", "--key1=A"})
-envSource := env.New([]string{"KEY1=B", "KEY2=2"})
+envSource := env.New(env.Settings{Environ: []string{"KEY1=B", "KEY2=2"}})
 reader := reader.New(reader.Settings{
   Sources: []reader.Source{flagSource, envSource},
 })

examples/reader/main.go

@@ -10,7 +10,7 @@ import (
 
 func main() {
 	flagSource := flag.New([]string{"program", "--key1=A"})
-	envSource := env.New([]string{"KEY1=B", "KEY2=2"})
+	envSource := env.New(env.Settings{Environ: []string{"KEY1=B", "KEY2=2"}})
 	reader := reader.New(reader.Settings{
 		Sources: []reader.Source{flagSource, envSource},
 	})

reader/reader.go

@@ -42,7 +42,7 @@ type Settings struct {
 	// Sources is a slice of sources where a source at
 	// a lower index has a higher priority.
 	// It defaults to:
-	// []reader.Source{flag.New(os.Args), env.New(os.Environ())}
+	// []reader.Source{flag.New(os.Args), env.New(env.Settings{Environ: os.Environ()})}
 	Sources []Source
 	// HandleDeprecatedKey is called when encountering a deprecated
 	// key, and defaults to a no-op function.
@@ -54,7 +54,7 @@ type Settings struct {
 
 func (s *Settings) setDefaults() {
 	s.Sources = gosettings.DefaultSlice(s.Sources,
-		[]Source{flag.New(os.Args), env.New(os.Environ())})
+		[]Source{flag.New(os.Args), env.New(env.Settings{Environ: os.Environ()})})
 
 	if s.HandleDeprecatedKey == nil { // Note: cannot use DefaultInterface
 		s.HandleDeprecatedKey = func(source, deprecatedKey, currentKey string) {}

reader/sources/env/env.go

@@ -9,6 +9,7 @@ import (
 // method.
 type Source struct {
 	keyToValue map[string]string
+	keyPrefix  string
 }
 
 // New creates a new environment variable source
@@ -17,12 +18,14 @@ type Source struct {
 // Environ values with no '=' sign are ignored.
 // All environment variable keys read are eventually
 // transformed using the KeyTransform method.
-func New(environ []string) (source *Source) {
+func New(settings Settings) (source *Source) {
+	settings.setDefaults()
 	source = &Source{
-		keyToValue: make(map[string]string, len(environ)),
+		keyToValue: make(map[string]string, len(settings.Environ)),
+		keyPrefix:  settings.KeyPrefix,
 	}
 
-	for _, keyValue := range environ {
+	for _, keyValue := range settings.Environ {
 		const maxParts = 2
 		parts := strings.SplitN(keyValue, "=", maxParts)
 		if len(parts) != maxParts {
@@ -53,8 +56,10 @@ func (s *Source) Get(key string) (value string, isSet bool) {
 // variable key. It notably:
 // - Changes all characters to be uppercase
 // - Replaces all dashes with underscores.
+// - Prefixes the key with the KeyPrefix field, without modifying the prefix.
 func (s *Source) KeyTransform(key string) (newKey string) {
 	newKey = strings.ToUpper(key)
 	newKey = strings.ReplaceAll(newKey, "-", "_")
+	newKey = s.keyPrefix + newKey
 	return newKey
 }

reader/sources/env/env_test.go

@@ -23,7 +23,11 @@ func Test_New(t *testing.T) {
 	transformedLowercaseKey := strings.ToUpper(lowercaseKey)
 	testKeys[transformedLowercaseKey] = struct{}{}
 
-	env := New(os.Environ())
+	settings := Settings{
+		Environ: os.Environ(),
+	}
+
+	env := New(settings)
 
 	// Remove other test irrelevant environment variables
 	for k := range env.keyToValue {
@@ -70,16 +74,16 @@ func Test_Env_Get(t *testing.T) {
 		isSet bool
 	}{
 		"key_not_found": {
-			env: New([]string{}),
+			env: New(Settings{Environ: []string{}}),
 			key: "KEY",
 		},
 		"empty_value": {
-			env:   New([]string{"KEY="}),
+			env:   New(Settings{Environ: []string{"KEY="}}),
 			key:   "KEY",
 			isSet: true,
 		},
 		"non_empty_value": {
-			env:   New([]string{"KEY=value"}),
+			env:   New(Settings{Environ: []string{"KEY=value"}}),
 			key:   "KEY",
 			value: "value",
 			isSet: true,

reader/sources/env/settings.go

@@ -0,0 +1,27 @@
+package env
+
+import (
+	"os"
+
+	"github.com/qdm12/gosettings"
+)
+
+// Settings contains settings for the environment variable source.
+type Settings struct {
+	// Environ is a slice of "key=value" pairs which defaults
+	// to the returned value of os.Environ().
+	// Element without a '=' sign are ignored.
+	// All environment variable keys read are eventually
+	// transformed using the KeyTransform method.
+	// It defaults to the empty string.
+	Environ []string
+	// KeyPrefix is a prefix to add to all keys read from
+	// the environment. It is usually the program name to avoid
+	// conflict with other programs in the environment.
+	// It defaults to the empty string.
+	KeyPrefix string
+}
+
+func (s *Settings) setDefaults() {
+	s.Environ = gosettings.DefaultSlice(s.Environ, os.Environ())
+}