2 files changed, 131 insertions, 1 deletions
diff --git a/type.go b/type.go
index 140a698..e9b5ef2 100644
--- a/type.go
+++ b/type.go
@@ -1,3 +1,77 @@
 package stfe
 
-// Leaf definition and such goes here
+import (
+	"fmt"
+
+	"encoding/base64"
+
+	"github.com/google/certificate-transparency-go/tls"
+)
+
+// StFormat defines a particular StItem type that is versioned
+type StFormat tls.Enum
+
+const (
+	StFormatReserved           StFormat = 0
+	StFormatSignedTreeHeadV1   StFormat = 1
+	StFormatSignedDebugInfoV1  StFormat = 2
+	StFormatConsistencyProofV1 StFormat = 3
+	StFormatInclusionProofV1   StFormat = 4
+	StFormatChecksumV1                  = 5
+)
+
+func (f StFormat) String() string {
+	switch f {
+	case StFormatReserved:
+		return "reserved"
+	case StFormatSignedTreeHeadV1:
+		return "signed_tree_head_v1"
+	case StFormatSignedDebugInfoV1:
+		return "signed_debug_info_v1"
+	case StFormatConsistencyProofV1:
+		return "consistency_proof_v1"
+	case StFormatInclusionProofV1:
+		return "inclusion_proof_v1"
+	case StFormatChecksumV1:
+		return "checksum_v1"
+	default:
+		return fmt.Sprintf("Unknown StFormat: %d", f)
+	}
+}
+
+// StItem references a versioned item based on a given format specifier.
+type StItem struct {
+	Format     StFormat    `tls:"maxval:65535"`
+	ChecksumV1 *ChecksumV1 `tls:"selector:Format,val:5"`
+	// TODO: add more items
+}
+
+func (i StItem) String() string {
+	switch i.Format {
+	case StFormatChecksumV1:
+		return fmt.Sprintf("%s %s", i.Format, *i.ChecksumV1)
+	default:
+		return fmt.Sprintf("unknown StItem: %s", i.Format)
+	}
+}
+
+// ChecksumV1 associates a package name with an arbitrary checksum value
+type ChecksumV1 struct {
+	Package  []byte `tls:"minlen:0,maxlen:255"`
+	Checksum []byte `tls:"minlen:32,maxlen:255"`
+}
+
+// NewChecksumV1 creates a new StItem of type checksum_v1
+func NewChecksumV1(name string, checksum []byte) (StItem, error) {
+	return StItem{
+		Format: StFormatChecksumV1,
+		ChecksumV1: &ChecksumV1{
+			Package:  []byte(name),
+			Checksum: checksum,
+		},
+	}, nil // TODO: error handling
+}
+
+func (i ChecksumV1) String() string {
+	return fmt.Sprintf("%v %v", string(i.Package), base64.StdEncoding.EncodeToString(i.Checksum))
+}
diff --git a/type_test.go b/type_test.go
new file mode 100644
index 0000000..bcd66e6
--- /dev/null
+++ b/type_test.go
@@ -0,0 +1,56 @@
+package stfe
+
+import (
+	"fmt"
+
+	"crypto/sha256"
+
+	"github.com/google/certificate-transparency-go/tls"
+)
+
+func ExampleNewChecksumV1() {
+	name := "foobar-1.2.3"
+	hasher := sha256.New()
+	hasher.Write([]byte(name))
+	checksum := hasher.Sum(nil) // hash of package name
+
+	item, err := NewChecksumV1(name, checksum)
+	if err != nil {
+		fmt.Printf("failed creating checksum item: %v", err)
+		return
+	}
+	fmt.Printf("%s\n", item)
+	// Output: checksum_v1 foobar-1.2.3 UOeWe84malBvj2FLtQlr66WA0gUEa5GPR9I7LsYm114=
+}
+
+func ExampleMarshalChecksumV1() {
+	item, err := NewChecksumV1("foobar-1.2.3", make([]byte, 32))
+	if err != nil {
+		fmt.Printf("failed creating checksum item: %v", err)
+		return
+	}
+
+	b, err := tls.Marshal(item)
+	if err != nil {
+		fmt.Printf("tls.Marshal() failed: %v", err)
+		return
+	}
+	fmt.Printf("%v\n", b)
+	// Output: [0 5 12 102 111 111 98 97 114 45 49 46 50 46 51 32 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0]
+}
+
+func ExampleUnmarshalChecksumV1() {
+	b := []byte{0, 5, 12, 102, 111, 111, 98, 97, 114, 45, 49, 46, 50, 46, 51, 32, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}
+
+	var item StItem
+	extra, err := tls.Unmarshal(b, &item)
+	if err != nil {
+		fmt.Printf("tls.Unmarshal() failed: %v (%v)", err, extra)
+		return
+	} else if len(extra) > 0 {
+		fmt.Printf("tls.Unmarshal() found extra data: %v", extra)
+		return
+	}
+	fmt.Printf("%v\n", item)
+	// Output: checksum_v1 foobar-1.2.3 AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=
+}