Add functions to compute unique prefix length

backend/generic_test.go

@@ -6,6 +6,8 @@ import (
 	"reflect"
 	"runtime"
 	"testing"
+
+	"github.com/fd0/khepri/backend"
 )
 
 // assert fails the test if the condition is false.
@@ -34,3 +36,43 @@ func equals(tb testing.TB, exp, act interface{}) {
 		tb.FailNow()
 	}
 }
+
+func str2id(s string) backend.ID {
+	id, err := backend.ParseID(s)
+	if err != nil {
+		panic(err)
+	}
+
+	return id
+}
+
+type IDList backend.IDs
+
+var samples = IDList{
+	str2id("20bdc1402a6fc9b633aaffffffffffffffffffffffffffffffffffffffffffff"),
+	str2id("20bdc1402a6fc9b633ccd578c4a92d0f4ef1a457fa2e16c596bc73fb409d6cc0"),
+	str2id("20bdc1402a6fc9b633ffffffffffffffffffffffffffffffffffffffffffffff"),
+	str2id("20ff988befa5fc40350f00d531a767606efefe242c837aaccb80673f286be53d"),
+	str2id("326cb59dfe802304f96ee9b5b9af93bdee73a30f53981e5ec579aedb6f1d0f07"),
+	str2id("86b60b9594d1d429c4aa98fa9562082cabf53b98c7dc083abe5dae31074dd15a"),
+	str2id("96c8dbe225079e624b5ce509f5bd817d1453cd0a85d30d536d01b64a8669aeae"),
+	str2id("fa31d65b87affcd167b119e9d3d2a27b8236ca4836cb077ed3e96fcbe209b792"),
+}
+
+func (l IDList) List(backend.Type) (backend.IDs, error) {
+	return backend.IDs(l), nil
+}
+
+func TestPrefixLength(t *testing.T) {
+	l, err := backend.PrefixLength(samples, backend.Snapshot)
+	ok(t, err)
+	equals(t, 10, l)
+
+	l, err = backend.PrefixLength(samples[:3], backend.Snapshot)
+	ok(t, err)
+	equals(t, 10, l)
+
+	l, err = backend.PrefixLength(samples[3:], backend.Snapshot)
+	ok(t, err)
+	equals(t, 4, l)
+}