Enable hashing symlinks

Example output:
```
INFO[0000] Hashing directory.                            hashesFile=x/bundleinfo.json pathToHash=x/ uniqueBundleName=x
INFO[0000] Hash "x/".
WARN[0000] File "x/foo"->"x/x2" is a symlink, will be treated as a regular file/dir.
INFO[0000] Finished hasher.
``

Symlinks with targets not within the hash directory are not allowed and cause a panic.

CHANGES.md

@@ -14,6 +14,7 @@
 * `hasher` will no longer create a directory if a non-existing one is passed as an argument.
 * trivrost will no longer attempt to repeat range requests to a host after it has failed to conformly respond while displaying the confusing message `Taking longer than usual: HTTP Status 200` and will now fail immediately in such cases instead.
 * trivrost will no longer fail to comply with HTTP 2 strictly using lower-case HTTP Header names. This had been caused by methods of `http.Header` still being oriented around HTTP 1 canonical header names due to Go's backwards compatibility promise.
+* hasher now supports symlinks within hashed directories.
 
 ## 1.4.6 (2021-01-25)
 ### Fixes

pkg/launcher/hashing/scan.go

@@ -10,6 +10,7 @@ import (
 	"io/ioutil"
 	"os"
 	"path/filepath"
+	"strings"
 
 	"github.com/setlog/trivrost/pkg/launcher/config"
 	log "github.com/sirupsen/logrus"
@@ -61,23 +62,29 @@ func mustHashRelatively(ctx context.Context, readDir readDirFunc, readFile readF
 }
 
 func mustHashDir(ctx context.Context, readDir readDirFunc, readFile readFileFunc, stat statFunc, hashFilePath string) config.FileInfoMap {
-	fm := make(config.FileInfoMap)
-	for _, info := range mustReadDir(readDir, hashFilePath) {
-		if info.IsDir() {
-			fm.Join(mustHashDir(ctx, readDir, readFile, stat, filepath.Join(hashFilePath, info.Name())))
-		} else {
-		filePath := filepath.Join(hashFilePath, info.Name())
-		if isDir(filePath) {
-			fm.Join(mustHashDir(readDir, readFile, stat, filePath))
+	fileMap := make(config.FileInfoMap)
+	for _, curPathInfo := range mustReadDir(readDir, hashFilePath) {
+		curPath := filepath.Join(hashFilePath, curPathInfo.Name())
+		resolvedPath := evaluateSoftLink(curPath)
+		if curPath != resolvedPath {
+			log.Warnf("File \"%s\"->\"%s\" is a symlink, will be treated as a regular file/dir.", curPath, resolvedPath)
+			curPath = resolvedPath
+		}
+		if !strings.HasPrefix(curPath, hashFilePath) {
+			panic(fmt.Errorf("hashing '%s' outside hash directory is not allowed", curPath))
+		}
+		curPathInfo, _ = stat(curPath)
+		if curPathInfo.IsDir() {
+			fileMap.Join(mustHashDir(ctx, readDir, readFile, stat, curPath))
 		} else {
-			sha, size, err := calculateSha256(ctx, filePath, readFile)
+			sha, size, err := calculateSha256(ctx, curPath, readFile)
 			if err != nil {
 				panic(fmt.Errorf("failed hashing file \"%s\": %w", hashFilePath, err))
 			}
-			fm[filePath] = &config.FileInfo{SHA256: sha, Size: size}
+			fileMap[curPath] = &config.FileInfo{SHA256: sha, Size: size}
 		}
 	}
-	return fm
+	return fileMap
 }
 
 func evaluateSoftLink(filePath string) string {
@@ -88,14 +95,6 @@ func evaluateSoftLink(filePath string) string {
 	return evaluatedName
 }
 
-func isDir(filePath string) bool {
-	fi, err := os.Stat(filePath)
-	if err != nil {
-		panic(err)
-	}
-	return fi.IsDir()
-}
-
 func mustReadDir(readDir readDirFunc, directoryPath string) []os.FileInfo {
 	infos, err := readDir(evaluateSoftLink(directoryPath))
 	if err != nil {