Fix reading syft json from stdin by redirect (#1299)

I figured out that running `cat syft.json | grype` works but
`grype < syft.json` does not work. This happens, because the
IsPipedInput method only checks if stdin is a pipe which will be false
if stdin is fed by a redirect.

The go idiomatic way to fix this is by just checking if the file
produced by stat has a size > 0.

Implemented this check, that will recognize stdin by redirect, in the
IsPipedInput() method. Renamed the method to IsStdinPipeOrRedirect().

Signed-off-by: Felix Becker <git@felixbecker.name>
Co-authored-by: Benjamin Neff <benjamin@coding4coffee.ch>

cmd/root.go

@@ -283,14 +283,14 @@ func rootExec(_ *cobra.Command, args []string) error {
 }
 
 func isVerbose() (result bool) {
-	isPipedInput, err := internal.IsPipedInput()
+	isStdinPipeOrRedirect, err := internal.IsStdinPipeOrRedirect()
 	if err != nil {
 		// since we can't tell if there was piped input we assume that there could be to disable the ETUI
 		log.Warnf("unable to determine if there is piped input: %+v", err)
 		return true
 	}
 	// verbosity should consider if there is piped input (in which case we should not show the ETUI)
-	return appConfig.CliOptions.Verbosity > 0 || isPipedInput
+	return appConfig.CliOptions.Verbosity > 0 || isStdinPipeOrRedirect
 }
 
 //nolint:funlen
@@ -502,13 +502,13 @@ func validateDBLoad(loadErr error, status *db.Status) error {
 }
 
 func validateRootArgs(cmd *cobra.Command, args []string) error {
-	isPipedInput, err := internal.IsPipedInput()
+	isStdinPipeOrRedirect, err := internal.IsStdinPipeOrRedirect()
 	if err != nil {
 		log.Warnf("unable to determine if there is piped input: %+v", err)
-		isPipedInput = false
+		isStdinPipeOrRedirect = false
 	}
 
-	if len(args) == 0 && !isPipedInput {
+	if len(args) == 0 && !isStdinPipeOrRedirect {
 		// in the case that no arguments are given and there is no piped input we want to show the help text and return with a non-0 return code.
 		if err := cmd.Help(); err != nil {
 			return fmt.Errorf("unable to display help: %w", err)

grype/pkg/syft_sbom_provider.go

@@ -142,13 +142,13 @@ func fileHasContent(f *os.File) bool {
 }
 
 func stdinReader() io.Reader {
-	isPipedInput, err := internal.IsPipedInput()
+	isStdinPipeOrRedirect, err := internal.IsStdinPipeOrRedirect()
 	if err != nil {
 		log.Warnf("unable to determine if there is piped input: %+v", err)
 		return nil
 	}
 
-	if !isPipedInput {
+	if !isStdinPipeOrRedirect {
 		return nil
 	}
 

internal/input.go

@@ -5,8 +5,8 @@ import (
 	"os"
 )
 
-// IsPipedInput returns true if there is no input device, which means the user **may** be providing input via a pipe.
-func IsPipedInput() (bool, error) {
+// IsStdinPipeOrRedirect returns true if stdin is provided via pipe or redirect
+func IsStdinPipeOrRedirect() (bool, error) {
 	fi, err := os.Stdin.Stat()
 	if err != nil {
 		return false, fmt.Errorf("unable to determine if there is piped input: %w", err)
@@ -16,5 +16,5 @@ func IsPipedInput() (bool, error) {
 	// on stdin, as running grype as a subprocess you would expect no character device to be present but input can
 	// be from either stdin or indicated by the CLI. Checking if stdin is a pipe is the most direct way to determine
 	// if there *may* be bytes that will show up on stdin that should be used for the analysis source.
-	return fi.Mode()&os.ModeNamedPipe != 0, nil
+	return fi.Mode()&os.ModeNamedPipe != 0 || fi.Size() > 0, nil
 }