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

3 files changed, 252 insertions, 44 deletions

diff --git a/cmd/platform/main.go b/cmd/platform/main.go
index b5ea51920..6d9952c70 100644
--- a/cmd/platform/main.go
+++ b/cmd/platform/main.go
@@ -6,19 +6,10 @@ package main
 import (
 	"fmt"
 	"os"
-	"path/filepath"
 	"syscall"
-)
 
-func findMattermostBinary() string {
-	for _, file := range []string{"./mattermost", "../mattermost", "./bin/mattermost"} {
-		path, _ := filepath.Abs(file)
-		if stat, err := os.Stat(path); err == nil && !stat.IsDir() {
-			return path
-		}
-	}
-	return "./mattermost"
-}
+	"github.com/mattermost/mattermost-server/utils"
+)
 
 func main() {
 	// Print angry message to use mattermost command directly
@@ -33,7 +24,14 @@ The platform binary will be removed in a future version.
 	args := os.Args
 	args[0] = "mattermost"
 	args = append(args, "--platform")
-	if err := syscall.Exec(findMattermostBinary(), args, nil); err != nil {
+
+	realMattermost := utils.FindFile("mattermost")
+	if realMattermost == "" {
+		// This will still fail, of course.
+		realMattermost = "./mattermost"
+	}
+
+	if err := syscall.Exec(utils.FindFile("mattermost"), args, nil); err != nil {
 		fmt.Println("Could not start Mattermost, use the mattermost command directly.")
 	}
 }
diff --git a/utils/config.go b/utils/config.go
index 00fd2642a..da1918490 100644
--- a/utils/config.go
+++ b/utils/config.go
@@ -32,36 +32,94 @@ const (
 	LOG_FILENAME    = "mattermost.log"
 )
 
-// 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
+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
 		}
-	} 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
+
+		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)
 			}
 		}
 	}
-	return ""
-}
+	if binaryDir != "" {
+		for _, baseSearchPath := range baseSearchPaths {
+			searchPaths = append(
+				searchPaths,
+				filepath.Join(binaryDir, baseSearchPath),
+			)
+		}
+	}
 
-// FindDir looks for the given directory in nearby ancestors, falling back to `./` if not found.
-func FindDir(dir string) (string, bool) {
-	for _, parent := range []string{".", "..", "../..", "../../.."} {
-		foundDir, err := filepath.Abs(filepath.Join(parent, dir))
+	for _, parent := range searchPaths {
+		found, err := filepath.Abs(filepath.Join(parent, path))
 		if err != nil {
 			continue
-		} else if _, err := os.Stat(foundDir); err == nil {
-			return foundDir, true
+		} else if fileInfo, err := os.Stat(found); err == nil {
+			if filter != nil && filter(fileInfo) {
+				return found
+			} else {
+				return found
+			}
 		}
 	}
-	return "./", false
+
+	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) {
+	found := FindFile(filepath.Join("config", fileName))
+	if found == "" {
+		found = FindPath(fileName, []string{"."}, nil)
+	}
+
+	return 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) {
+	found := FindPath(dir, commonBaseSearchPaths, func(fileInfo os.FileInfo) bool {
+		return fileInfo.IsDir()
+	})
+	if found == "" {
+		return "./", false
+	}
+
+	return found, true
 }
 
 func MloggerConfigFromLoggerConfig(s *model.LogSettings) *mlog.LoggerConfiguration {
diff --git a/utils/config_test.go b/utils/config_test.go
index 75bbc420f..f57add303 100644
--- a/utils/config_test.go
+++ b/utils/config_test.go
@@ -46,20 +46,172 @@ func TestTimezoneConfig(t *testing.T) {
 }
 
 func TestFindConfigFile(t *testing.T) {
-	dir, err := ioutil.TempDir("", "")
-	require.NoError(t, err)
-	defer os.RemoveAll(dir)
+	t.Run("config.json in current working directory, not inside config/", func(t *testing.T) {
+		// Force a unique working directory
+		cwd, err := ioutil.TempDir("", "")
+		require.NoError(t, err)
+		defer os.RemoveAll(cwd)
+
+		prevDir, err := os.Getwd()
+		require.NoError(t, err)
+		defer os.Chdir(prevDir)
+		os.Chdir(cwd)
+
+		configJson, err := filepath.Abs("config.json")
+		require.NoError(t, err)
+		require.NoError(t, ioutil.WriteFile(configJson, []byte("{}"), 0600))
+
+		// Relative paths end up getting symlinks fully resolved.
+		configJsonResolved, err := filepath.EvalSymlinks(configJson)
+		require.NoError(t, err)
+
+		assert.Equal(t, configJsonResolved, FindConfigFile("config.json"))
+	})
 
-	path := filepath.Join(dir, "config.json")
-	require.NoError(t, ioutil.WriteFile(path, []byte("{}"), 0600))
+	t.Run("config/config.json from various paths", func(t *testing.T) {
+		// Create the following directory structure:
+		// tmpDir1/
+		//   config/
+		//     config.json
+		//   tmpDir2/
+		//     tmpDir3/
+		//       tmpDir4/
+		//         tmpDir5/
+		tmpDir1, err := ioutil.TempDir("", "")
+		require.NoError(t, err)
+		defer os.RemoveAll(tmpDir1)
+
+		err = os.Mkdir(filepath.Join(tmpDir1, "config"), 0700)
+		require.NoError(t, err)
+
+		tmpDir2, err := ioutil.TempDir(tmpDir1, "")
+		require.NoError(t, err)
+
+		tmpDir3, err := ioutil.TempDir(tmpDir2, "")
+		require.NoError(t, err)
+
+		tmpDir4, err := ioutil.TempDir(tmpDir3, "")
+		require.NoError(t, err)
+
+		tmpDir5, err := ioutil.TempDir(tmpDir4, "")
+		require.NoError(t, err)
+
+		configJson := filepath.Join(tmpDir1, "config", "config.json")
+		require.NoError(t, ioutil.WriteFile(configJson, []byte("{}"), 0600))
+
+		// Relative paths end up getting symlinks fully resolved, so use this below as necessary.
+		configJsonResolved, err := filepath.EvalSymlinks(configJson)
+		require.NoError(t, err)
+
+		testCases := []struct {
+			Description string
+			Cwd         *string
+			FileName    string
+			Expected    string
+		}{
+			{
+				"absolute path to config.json",
+				nil,
+				configJson,
+				configJson,
+			},
+			{
+				"absolute path to config.json from directory containing config.json",
+				&tmpDir1,
+				configJson,
+				configJson,
+			},
+			{
+				"relative path to config.json from directory containing config.json",
+				&tmpDir1,
+				"config.json",
+				configJsonResolved,
+			},
+			{
+				"subdirectory of directory containing config.json",
+				&tmpDir2,
+				"config.json",
+				configJsonResolved,
+			},
+			{
+				"twice-nested subdirectory of directory containing config.json",
+				&tmpDir3,
+				"config.json",
+				configJsonResolved,
+			},
+			{
+				"thrice-nested subdirectory of directory containing config.json",
+				&tmpDir4,
+				"config.json",
+				configJsonResolved,
+			},
+			{
+				"can't find from four nesting levels deep",
+				&tmpDir5,
+				"config.json",
+				"",
+			},
+		}
 
-	assert.Equal(t, path, FindConfigFile(path))
+		for _, testCase := range testCases {
+			t.Run(testCase.Description, func(t *testing.T) {
+				if testCase.Cwd != nil {
+					prevDir, err := os.Getwd()
+					require.NoError(t, err)
+					defer os.Chdir(prevDir)
+					os.Chdir(*testCase.Cwd)
+				}
+
+				assert.Equal(t, testCase.Expected, FindConfigFile(testCase.FileName))
+			})
+		}
+	})
+
+	t.Run("config/config.json relative to executable", func(t *testing.T) {
+		osExecutable, err := os.Executable()
+		require.NoError(t, err)
+		osExecutableDir := filepath.Dir(osExecutable)
+
+		// Force a working directory different than the executable.
+		cwd, err := ioutil.TempDir("", "")
+		require.NoError(t, err)
+		defer os.RemoveAll(cwd)
+
+		prevDir, err := os.Getwd()
+		require.NoError(t, err)
+		defer os.Chdir(prevDir)
+		os.Chdir(cwd)
+
+		testCases := []struct {
+			Description  string
+			RelativePath string
+		}{
+			{
+				"config/config.json",
+				".",
+			},
+			{
+				"../config/config.json",
+				"../",
+			},
+		}
 
-	prevDir, err := os.Getwd()
-	require.NoError(t, err)
-	defer os.Chdir(prevDir)
-	os.Chdir(dir)
-	assert.Equal(t, path, FindConfigFile(path))
+		for _, testCase := range testCases {
+			t.Run(testCase.Description, func(t *testing.T) {
+				// Install the config in config/config.json relative to the executable
+				configJson := filepath.Join(osExecutableDir, testCase.RelativePath, "config", "config.json")
+				require.NoError(t, os.Mkdir(filepath.Dir(configJson), 0700))
+				require.NoError(t, ioutil.WriteFile(configJson, []byte("{}"), 0600))
+				defer os.RemoveAll(filepath.Dir(configJson))
+
+				// Relative paths end up getting symlinks fully resolved.
+				configJsonResolved, err := filepath.EvalSymlinks(configJson)
+				require.NoError(t, err)
+
+				assert.Equal(t, configJsonResolved, FindConfigFile("config.json"))
+			})
+		}
+	})
 }
 
 func TestConfigFromEnviroVars(t *testing.T) {