510 - SBOM attestation stdout (#785)

add syft attest command to produce an attestation as application/vnd.in-toto+json to standard out using on disk PKI

Signed-off-by: Christopher Phillips <christopher.phillips@anchore.com>

syft/source/scheme.go

@@ -29,7 +29,7 @@ var AllSchemes = []Scheme{
 	FileScheme,
 }
 
-func detectScheme(fs afero.Fs, imageDetector sourceDetector, userInput string) (Scheme, image.Source, string, error) {
+func DetectScheme(fs afero.Fs, imageDetector sourceDetector, userInput string) (Scheme, image.Source, string, error) {
 	switch {
 	case strings.HasPrefix(userInput, "dir:"):
 		dirLocation, err := homedir.Expand(strings.TrimPrefix(userInput, "dir:"))

syft/source/scheme_test.go

@@ -287,7 +287,7 @@ func TestDetectScheme(t *testing.T) {
 				}
 			}
 
-			actualScheme, actualSource, actualLocation, err := detectScheme(fs, imageDetector, test.userInput)
+			actualScheme, actualSource, actualLocation, err := DetectScheme(fs, imageDetector, test.userInput)
 			if err != nil {
 				t.Fatalf("unexpected err : %+v", err)
 			}

syft/source/source.go

@@ -38,7 +38,7 @@ type sourceDetector func(string) (image.Source, string, error)
 // New produces a Source based on userInput like dir: or image:tag
 func New(userInput string, registryOptions *image.RegistryOptions, exclusions []string) (*Source, func(), error) {
 	fs := afero.NewOsFs()
-	parsedScheme, imageSource, location, err := detectScheme(fs, image.DetectSource, userInput)
+	parsedScheme, imageSource, location, err := DetectScheme(fs, image.DetectSource, userInput)
 	if err != nil {
 		return &Source{}, func() {}, fmt.Errorf("unable to parse input=%q: %w", userInput, err)
 	}