MM-6839: search relative to executable (#8853)

* MM-6839: searching for paths relative to executable

In addition to searching relative to the current working directory, also
search relative to the location of the binary. This helps locate config
and i18n files when invoking an absolute path to the mattermost binary.

* MM-6839: find mattermost/ binary using utils.FindFile

utils/config.go

@@ -32,36 +32,94 @@ const (
 	LOG_FILENAME    = "mattermost.log"
 )
 
+var (
+	commonBaseSearchPaths = []string{
+		".",
+		"..",
+		"../..",
+		"../../..",
+	}
+)
+
+func FindPath(path string, baseSearchPaths []string, filter func(os.FileInfo) bool) string {
+	if filepath.IsAbs(path) {
+		if _, err := os.Stat(path); err == nil {
+			return path
+		}
+
+		return ""
+	}
+
+	searchPaths := []string{}
+	for _, baseSearchPath := range baseSearchPaths {
+		searchPaths = append(searchPaths, baseSearchPath)
+	}
+
+	// Additionally attempt to search relative to the location of the running binary.
+	var binaryDir string
+	if exe, err := os.Executable(); err == nil {
+		if exe, err = filepath.EvalSymlinks(exe); err == nil {
+			if exe, err = filepath.Abs(exe); err == nil {
+				binaryDir = filepath.Dir(exe)
+			}
+		}
+	}
+	if binaryDir != "" {
+		for _, baseSearchPath := range baseSearchPaths {
+			searchPaths = append(
+				searchPaths,
+				filepath.Join(binaryDir, baseSearchPath),
+			)
+		}
+	}
+
+	for _, parent := range searchPaths {
+		found, err := filepath.Abs(filepath.Join(parent, path))
+		if err != nil {
+			continue
+		} else if fileInfo, err := os.Stat(found); err == nil {
+			if filter != nil && filter(fileInfo) {
+				return found
+			} else {
+				return found
+			}
+		}
+	}
+
+	return ""
+}
+
 // FindConfigFile attempts to find an existing configuration file. fileName can be an absolute or
 // relative path or name such as "/opt/mattermost/config.json" or simply "config.json". An empty
 // string is returned if no configuration is found.
 func FindConfigFile(fileName string) (path string) {
-	if filepath.IsAbs(fileName) {
-		if _, err := os.Stat(fileName); err == nil {
-			return fileName
-		}
-	} else {
-		for _, dir := range []string{"./config", "../config", "../../config", "../../../config", "."} {
-			path, _ := filepath.Abs(filepath.Join(dir, fileName))
-			if _, err := os.Stat(path); err == nil {
-				return path
-			}
-		}
+	found := FindFile(filepath.Join("config", fileName))
+	if found == "" {
+		found = FindPath(fileName, []string{"."}, nil)
 	}
-	return ""
+
+	return found
 }
 
-// FindDir looks for the given directory in nearby ancestors, falling back to `./` if not found.
+// FindFile looks for the given file in nearby ancestors relative to the current working
+// directory as well as the directory of the executable.
+func FindFile(path string) string {
+	return FindPath(path, commonBaseSearchPaths, func(fileInfo os.FileInfo) bool {
+		return !fileInfo.IsDir()
+	})
+}
+
+// FindDir looks for the given directory in nearby ancestors relative to the current working
+// directory as well as the directory of the executable, falling back to `./` if not found.
 func FindDir(dir string) (string, bool) {
-	for _, parent := range []string{".", "..", "../..", "../../.."} {
-		foundDir, err := filepath.Abs(filepath.Join(parent, dir))
-		if err != nil {
-			continue
-		} else if _, err := os.Stat(foundDir); err == nil {
-			return foundDir, true
-		}
+	found := FindPath(dir, commonBaseSearchPaths, func(fileInfo os.FileInfo) bool {
+		return fileInfo.IsDir()
+	})
+	if found == "" {
+		return "./", false
 	}
-	return "./", false
+
+	return found, true
 }
 
 func MloggerConfigFromLoggerConfig(s *model.LogSettings) *mlog.LoggerConfiguration {