Autodetect config format based on extension

altsrc/detect_input_source.go

@@ -0,0 +1,43 @@
+package altsrc
+
+import (
+	"fmt"
+	"path/filepath"
+
+	"github.com/urfave/cli/v2"
+)
+
+var detectableSources = map[string]func(string) func(cCtx *cli.Context) (InputSourceContext, error){
+	".conf": NewTomlSourceFromFlagFunc,
+	".json": NewJSONSourceFromFlagFunc,
+	".toml": NewTomlSourceFromFlagFunc,
+	".yaml": NewYamlSourceFromFlagFunc,
+}
+
+// RegisterDetectableSource lets developers add support for their own altsrc filetypes to the autodetection list.
+func RegisterDetectableSource(extension string, handler func(string) func(cCtx *cli.Context) (InputSourceContext, error)) {
+	detectableSources[extension] = handler
+}
+
+// DetectNewSourceFromFlagFunc creates a new InputSourceContext from a provided flag name and source context.
+func DetectNewSourceFromFlagFunc(flagFileName string) func(cCtx *cli.Context) (InputSourceContext, error) {
+	return func(cCtx *cli.Context) (InputSourceContext, error) {
+		if fileFullPath := cCtx.String(flagFileName); fileFullPath != "" {
+			fileExt := filepath.Ext(fileFullPath)
+			if handler, ok := detectableSources[fileExt]; ok {
+				return handler(flagFileName)(cCtx)
+			}
+			return nil, fmt.Errorf("Unable to determine config file type from extension.\nMust be one of %v", detectableExtensions())
+		}
+		return defaultInputSource()
+	}
+}
+
+func detectableExtensions() []string {
+	extensions := make([]string, 0, len(detectableSources))
+	for ext := range detectableSources {
+		extensions = append(extensions, ext)
+	}
+
+	return extensions
+}