Simplify the SBOM writer interface (#1892)

* remove sbom.writer bytes call and consolidate helpers to options pkg

Signed-off-by: Alex Goodman <alex.goodman@anchore.com>

* dont close stdout

Signed-off-by: Alex Goodman <alex.goodman@anchore.com>

* remove close operation from multiwriter

Signed-off-by: Alex Goodman <alex.goodman@anchore.com>

---------

Signed-off-by: Alex Goodman <alex.goodman@anchore.com>

cmd/syft/cli/options/writer.go

@@ -2,25 +2,37 @@ package options
 
 import (
 	"fmt"
+	"io"
+	"os"
+	"path"
 	"strings"
 
 	"github.com/hashicorp/go-multierror"
+	"github.com/mitchellh/go-homedir"
 
+	"github.com/anchore/syft/internal/log"
 	"github.com/anchore/syft/syft/formats"
 	"github.com/anchore/syft/syft/formats/table"
 	"github.com/anchore/syft/syft/formats/template"
 	"github.com/anchore/syft/syft/sbom"
 )
 
-// makeWriter creates a sbom.Writer for output or returns an error. this will either return a valid writer
+var _ sbom.Writer = (*sbomMultiWriter)(nil)
+
+var _ interface {
+	io.Closer
+	sbom.Writer
+} = (*sbomStreamWriter)(nil)
+
+// MakeSBOMWriter creates a sbom.Writer for output or returns an error. this will either return a valid writer
 // or an error but neither both and if there is no error, sbom.Writer.Close() should be called
-func MakeWriter(outputs []string, defaultFile, templateFilePath string) (sbom.Writer, error) {
-	outputOptions, err := parseOutputs(outputs, defaultFile, templateFilePath)
+func MakeSBOMWriter(outputs []string, defaultFile, templateFilePath string) (sbom.Writer, error) {
+	outputOptions, err := parseSBOMOutputFlags(outputs, defaultFile, templateFilePath)
 	if err != nil {
 		return nil, err
 	}
 
-	writer, err := sbom.NewWriter(outputOptions...)
+	writer, err := newSBOMMultiWriter(outputOptions...)
 	if err != nil {
 		return nil, err
 	}
@@ -28,8 +40,18 @@ func MakeWriter(outputs []string, defaultFile, templateFilePath string) (sbom.Wr
 	return writer, nil
 }
 
-// parseOptions utility to parse command-line option strings and retain the existing behavior of default format and file
-func parseOutputs(outputs []string, defaultFile, templateFilePath string) (out []sbom.WriterOption, errs error) {
+// MakeSBOMWriterForFormat creates a sbom.Writer for for the given format or returns an error.
+func MakeSBOMWriterForFormat(format sbom.Format, path string) (sbom.Writer, error) {
+	writer, err := newSBOMMultiWriter(newSBOMWriterDescription(format, path))
+	if err != nil {
+		return nil, err
+	}
+
+	return writer, nil
+}
+
+// parseSBOMOutputFlags utility to parse command-line option strings and retain the existing behavior of default format and file
+func parseSBOMOutputFlags(outputs []string, defaultFile, templateFilePath string) (out []sbomWriterDescription, errs error) {
 	// always should have one option -- we generally get the default of "table", but just make sure
 	if len(outputs) == 0 {
 		outputs = append(outputs, table.ID.String())
@@ -63,7 +85,113 @@ func parseOutputs(outputs []string, defaultFile, templateFilePath string) (out [
 			format = tmpl
 		}
 
-		out = append(out, sbom.NewWriterOption(format, file))
+		out = append(out, newSBOMWriterDescription(format, file))
 	}
 	return out, errs
 }
+
+// sbomWriterDescription Format and path strings used to create sbom.Writer
+type sbomWriterDescription struct {
+	Format sbom.Format
+	Path   string
+}
+
+func newSBOMWriterDescription(f sbom.Format, p string) sbomWriterDescription {
+	expandedPath, err := homedir.Expand(p)
+	if err != nil {
+		log.Warnf("could not expand given writer output path=%q: %w", p, err)
+		// ignore errors
+		expandedPath = p
+	}
+	return sbomWriterDescription{
+		Format: f,
+		Path:   expandedPath,
+	}
+}
+
+// sbomMultiWriter holds a list of child sbom.Writers to apply all Write and Close operations to
+type sbomMultiWriter struct {
+	writers []sbom.Writer
+}
+
+type nopWriteCloser struct {
+	io.Writer
+}
+
+func (n nopWriteCloser) Close() error {
+	return nil
+}
+
+// newSBOMMultiWriter create all report writers from input options; if a file is not specified the given defaultWriter is used
+func newSBOMMultiWriter(options ...sbomWriterDescription) (_ *sbomMultiWriter, err error) {
+	if len(options) == 0 {
+		return nil, fmt.Errorf("no output options provided")
+	}
+
+	out := &sbomMultiWriter{}
+
+	for _, option := range options {
+		switch len(option.Path) {
+		case 0:
+			out.writers = append(out.writers, &sbomStreamWriter{
+				format: option.Format,
+				out:    nopWriteCloser{Writer: os.Stdout},
+			})
+		default:
+			// create any missing subdirectories
+			dir := path.Dir(option.Path)
+			if dir != "" {
+				s, err := os.Stat(dir)
+				if err != nil {
+					err = os.MkdirAll(dir, 0755) // maybe should be os.ModePerm ?
+					if err != nil {
+						return nil, err
+					}
+				} else if !s.IsDir() {
+					return nil, fmt.Errorf("output path does not contain a valid directory: %s", option.Path)
+				}
+			}
+			fileOut, err := os.OpenFile(option.Path, os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0644)
+			if err != nil {
+				return nil, fmt.Errorf("unable to create report file: %w", err)
+			}
+			out.writers = append(out.writers, &sbomStreamWriter{
+				format: option.Format,
+				out:    fileOut,
+			})
+		}
+	}
+
+	return out, nil
+}
+
+// Write writes the SBOM to all writers
+func (m *sbomMultiWriter) Write(s sbom.SBOM) (errs error) {
+	for _, w := range m.writers {
+		err := w.Write(s)
+		if err != nil {
+			errs = multierror.Append(errs, fmt.Errorf("unable to write SBOM: %w", err))
+		}
+	}
+	return errs
+}
+
+// sbomStreamWriter implements sbom.Writer for a given format and io.Writer, also providing a close function for cleanup
+type sbomStreamWriter struct {
+	format sbom.Format
+	out    io.Writer
+}
+
+// Write the provided SBOM to the data stream
+func (w *sbomStreamWriter) Write(s sbom.SBOM) error {
+	defer w.Close()
+	return w.format.Encode(w.out, s)
+}
+
+// Close any resources, such as open files
+func (w *sbomStreamWriter) Close() error {
+	if closer, ok := w.out.(io.Closer); ok {
+		return closer.Close()
+	}
+	return nil
+}