Whitespace artifact name fix

docs.kosli.com/content/faq/_index.md

@@ -242,3 +242,17 @@ kosli attest generic Dockerfile true ...
 ```
 The parser then sees `Dockerfile` and `true` as the two
 arguments to `kosli attest generic`.
+
+## Path/Image name is a single whitespace character!
+
+In order to calculate the fingerprint for an artifact, Kosli requires the path to the relevant file or directory, or the relevant image name. The command typically takes the form:
+```
+kosli attest generic [IMAGE-NAME | FILE-PATH | DIR-PATH] [flags]
+```
+
+When using multi-line commands in the shell or a script, if the image name or path has not been provided as above and whitespace has unintentionally been added after the line-continuation backslash on one of the lines, this whitespace character is interpreted as the name or path.
+
+If you're using multi-line commands and receive an error message similar to this, check your command for extraneous whitespace:
+```
+Error: failed to calculate artifact fingerprint: stat  : no such file or directory. The directory path is ' '.
+```

internal/digest/digest.go

@@ -35,6 +35,9 @@ func DirSha256(dirPath string, excludePaths []string, logger *logger.Logger) (st
 	logger.Debug("calculating fingerprint for path [%s] -- excluding paths: %s", dirPath, excludePaths)
 	info, err := os.Stat(dirPath)
 	if err != nil {
+		if dirPath == " " {
+			return "", fmt.Errorf("%s. The directory path is '%s'. https://docs.kosli.com/faq/#pathimage-name-is-a-single-whitespace-character", err, dirPath)
+		}
 		return "", err
 	}
 	if !info.IsDir() {
@@ -83,6 +86,9 @@ func OciSha256(artifactName string, registryUsername string, registryPassword st
 	// Parse image reference
 	ref, err := docker.ParseReference(imageName)
 	if err != nil {
+		if artifactName == " " {
+			return "", fmt.Errorf("%w. The artifact name is '%s'. https://docs.kosli.com/faq/#pathimage-name-is-a-single-whitespace-character", err, artifactName)
+		}
 		return "", fmt.Errorf("failed to parse image reference for %s: %w", imageName, err)
 	}
 
@@ -171,6 +177,9 @@ func FileSha256(filepath string) (string, error) {
 	hasher := sha256.New()
 	f, err := os.Open(filepath)
 	if err != nil {
+		if filepath == " " {
+			return "", fmt.Errorf("%s. The filename is '%s'. https://docs.kosli.com/faq/#pathimage-name-is-a-single-whitespace-character", err, filepath)
+		}
 		return "", err
 	}
 	defer f.Close()
@@ -191,6 +200,9 @@ func DockerImageSha256(imageID string) (string, error) {
 	}
 	imageInspect, err := cli.ImageInspect(context.Background(), imageID)
 	if err != nil {
+		if imageID == " " {
+			return "", fmt.Errorf("%s. The image ID is '%s'. https://docs.kosli.com/faq/#pathimage-name-is-a-single-whitespace-character", err, imageID)
+		}
 		return "", err
 	}
 	repoDigests := imageInspect.RepoDigests