add a cataloger for binaries built with rust-audit (#1116)

* add a cataloger for binaries built with rust-audit

Signed-off-by: Tom Fay <tomfay@microsoft.com>

syft/pkg/cataloger/internal/unionreader/union_reader.go

@@ -0,0 +1,66 @@
+package unionreader
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"io/ioutil"
+
+	macho "github.com/anchore/go-macholibre"
+	"github.com/anchore/syft/internal/log"
+)
+
+// unionReader is a single interface with all reading functions needed by multi-arch binary catalogers
+// cataloger.
+type UnionReader interface {
+	io.Reader
+	io.ReaderAt
+	io.Seeker
+	io.Closer
+}
+
+// getReaders extracts one or more io.ReaderAt objects representing binaries that can be processed (multiple binaries in the case for multi-architecture binaries).
+func GetReaders(f UnionReader) ([]io.ReaderAt, error) {
+	if macho.IsUniversalMachoBinary(f) {
+		machoReaders, err := macho.ExtractReaders(f)
+		if err != nil {
+			log.Debugf("extracting readers: %v", err)
+			return nil, err
+		}
+
+		var readers []io.ReaderAt
+		for _, e := range machoReaders {
+			readers = append(readers, e.Reader)
+		}
+
+		return readers, nil
+	}
+
+	return []io.ReaderAt{f}, nil
+}
+
+func GetUnionReader(readerCloser io.ReadCloser) (UnionReader, error) {
+	reader, ok := readerCloser.(UnionReader)
+	if ok {
+		return reader, nil
+	}
+
+	b, err := ioutil.ReadAll(readerCloser)
+	if err != nil {
+		return nil, fmt.Errorf("unable to read contents from binary: %w", err)
+	}
+
+	bytesReader := bytes.NewReader(b)
+
+	reader = struct {
+		io.ReadCloser
+		io.ReaderAt
+		io.Seeker
+	}{
+		ReadCloser: io.NopCloser(bytesReader),
+		ReaderAt:   bytesReader,
+		Seeker:     bytesReader,
+	}
+
+	return reader, nil
+}

syft/pkg/cataloger/internal/unionreader/union_reader_test.go

@@ -0,0 +1,30 @@
+package unionreader
+
+import (
+	"io"
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func Test_getUnionReader_notUnionReader(t *testing.T) {
+	expectedContents := "this is a test"
+	reader := io.NopCloser(strings.NewReader(expectedContents))
+
+	// make certain that the test fixture does not implement the union reader
+	_, ok := reader.(UnionReader)
+	require.False(t, ok)
+
+	actual, err := GetUnionReader(reader)
+	require.NoError(t, err)
+
+	_, ok = actual.(UnionReader)
+	require.True(t, ok)
+
+	b, err := io.ReadAll(actual)
+	require.NoError(t, err)
+
+	assert.Equal(t, expectedContents, string(b))
+}