ensure windows file path is respected (#4726)

* ensure windows file path is respected

The current --config flag breaks backwards compatibility for Windows users as a common path is to use is C: as is used in the collector-contrib MSI for example.

* use single character instead of hardcoded C

* update changelog

CHANGELOG.md

@@ -20,6 +20,10 @@
 - Remove support to some arches and platforms from `ocb` (opentelemetry-collector-builder) (#4710)
 - Remove deprecated legacy path ("v1/trace") support for otlp http receiver (#4720)
 
+## 🧰 Bug fixes 🧰
+
+- Ensure Windows path (e.g: C:) is recognized as a file path (#4726)
+
 ## 💡 Enhancements 💡
 
 - `service.NewConfigProvider`: copy slice argument, disallow changes from caller to the input slice (#4729)

service/config_provider.go

@@ -17,6 +17,7 @@ package service // import "go.opentelemetry.io/collector/service"
 import (
 	"context"
 	"fmt"
+	"regexp"
 	"strings"
 	"sync"
 
@@ -185,13 +186,19 @@ func (cm *configProvider) Shutdown(ctx context.Context) error {
 	return errs
 }
 
+// follows drive-letter specification:
+// https://tools.ietf.org/id/draft-kerwin-file-scheme-07.html#syntax
+var driverLetterRegexp = regexp.MustCompile("^[A-z]:")
+
 func (cm *configProvider) mergeRetrieve(ctx context.Context) (configmapprovider.Retrieved, error) {
 	var retrs []configmapprovider.Retrieved
 	retCfgMap := config.NewMap()
 	for _, location := range cm.locations {
-		// For backwards compatibility, empty url scheme means "file".
+		// For backwards compatibility:
+		// - empty url scheme means "file".
+		// - "^[A-z]:" also means "file"
 		scheme := "file"
-		if idx := strings.Index(location, ":"); idx != -1 {
+		if idx := strings.Index(location, ":"); idx != -1 && !driverLetterRegexp.MatchString(location) {
 			scheme = location[:idx]
 		} else {
 			location = scheme + ":" + location

service/config_provider_test.go

@@ -312,3 +312,51 @@ func TestConfigProvider_ShutdownClosesWatch(t *testing.T) {
 	assert.NoError(t, cfgW.Shutdown(context.Background()))
 	watcherWG.Wait()
 }
+
+func TestBackwardsCompatibilityForFilePath(t *testing.T) {
+	factories, errF := componenttest.NopFactories()
+	require.NoError(t, errF)
+
+	tests := []struct {
+		name       string
+		location   string
+		errMessage string
+	}{
+		{
+			name:       "unix",
+			location:   `/test`,
+			errMessage: "unable to read the file file:/test",
+		},
+		{
+			name:       "file_unix",
+			location:   `file:/test`,
+			errMessage: "unable to read the file file:/test",
+		},
+		{
+			name:       "windows_C",
+			location:   `C:\test`,
+			errMessage: "unable to read the file file:C:\\test",
+		},
+		{
+			name:       "windows_z",
+			location:   `z:\test`,
+			errMessage: "unable to read the file file:z:\\test",
+		},
+		{
+			name:       "file_windows",
+			location:   `file:C:\test`,
+			errMessage: "unable to read the file file:C:\\test",
+		},
+		{
+			name:       "invalid_scheme",
+			location:   `LL:\test`,
+			errMessage: "scheme LL is not supported for location",
+		},
+	}
+	for _, tt := range tests {
+		provider := NewDefaultConfigProvider(tt.location, []string{})
+		_, err := provider.Get(context.Background(), factories)
+		assert.Contains(t, err.Error(), tt.errMessage, tt.name)
+	}
+
+}