add internal.formats helper functions + identify tests

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

internal/formats/formats.go

@@ -0,0 +1,33 @@
+package formats
+
+import (
+	"github.com/anchore/syft/internal/formats/spdx22json"
+	"github.com/anchore/syft/internal/formats/syftjson"
+	"github.com/anchore/syft/syft/format"
+)
+
+// TODO: eventually this is the source of truth for all formatters
+func All() []format.Format {
+	return []format.Format{
+		spdx22json.Format(),
+		syftjson.Format(),
+	}
+}
+
+func Identify(by []byte) (*format.Format, error) {
+	for _, f := range All() {
+		if f.Detect(by) {
+			return &f, nil
+		}
+	}
+	return nil, nil
+}
+
+func ByOption(option format.Option) *format.Format {
+	for _, f := range All() {
+		if f.Option == option {
+			return &f
+		}
+	}
+	return nil
+}

internal/formats/formats_test.go

@@ -0,0 +1,39 @@
+package formats
+
+import (
+	"io"
+	"os"
+	"testing"
+
+	"github.com/anchore/syft/syft/format"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestIdentify(t *testing.T) {
+
+	tests := []struct {
+		fixture  string
+		expected format.Option
+	}{
+		{
+			fixture:  "test-fixtures/alpine-syft.json",
+			expected: format.JSONOption,
+		},
+		{
+			fixture:  "test-fixtures/alpine-syft-spdx.json",
+			expected: format.SPDXJSONOption,
+		},
+	}
+	for _, test := range tests {
+		t.Run(test.fixture, func(t *testing.T) {
+			f, err := os.Open(test.fixture)
+			assert.NoError(t, err)
+			by, err := io.ReadAll(f)
+			assert.NoError(t, err)
+			frmt, err := Identify(by)
+			assert.NoError(t, err)
+			assert.NotNil(t, frmt)
+			assert.Equal(t, test.expected, frmt.Option)
+		})
+	}
+}