From 03660a8691397932bc7f985fde4752a4373d16a4 Mon Sep 17 00:00:00 2001
From: Philipp Jahn <philippjahn2001@gmail.com>
Date: Tue, 25 Nov 2025 19:47:29 +0100
Subject: [PATCH] added null support

---
 README.md     |  1 +
 major.go      |  5 +++++
 major_test.go | 41 +++++++++++++++++++++++++++++++++++++++++
 simple.go     |  8 ++++++++
 4 files changed, 55 insertions(+)

diff --git a/README.md b/README.md
index 24d7500..3d33962 100644
--- a/README.md
+++ b/README.md
@@ -15,6 +15,7 @@ developed to be used in [`dtn7-go`][dtn7-go], an implementation of the
     - Arrays, both of definite and indefinite length
     - Maps of definite length
     - Booleans
+    - Null
 - Small and clear codebase:
     - Only works on streams, Go's `io.Reader` or `io.Writer`
     - Does *not* use reflection or make any strange assumptions
diff --git a/major.go b/major.go
index 4171ed6..dcc63c1 100644
--- a/major.go
+++ b/major.go
@@ -19,6 +19,7 @@ const (
 
 const (
 	IndefiniteArray byte = 0x9F
+	Null            byte = SimpleData | simpleNull
 	BreakCode       byte = 0xFF
 )
 
@@ -31,6 +32,7 @@ func (f Flag) Error() string {
 const (
 	FlagIndefiniteArray = Flag(iota)
 	FlagBreakCode       = Flag(iota)
+	FlagNull            = Flag(iota)
 )
 
 func readMajorType(b byte) (major MajorType, adds byte) {
@@ -56,6 +58,9 @@ func ReadMajors(r io.Reader) (m MajorType, n uint64, err error) {
 	case BreakCode:
 		err = FlagBreakCode
 
+	case Null:
+		err = FlagNull
+
 	default:
 		var adds byte
 		m, adds = readMajorType(b)
diff --git a/major_test.go b/major_test.go
index e2b1e6e..338633c 100644
--- a/major_test.go
+++ b/major_test.go
@@ -3,6 +3,7 @@ package cboring
 import (
 	"bufio"
 	"bytes"
+	"io"
 	"reflect"
 	"testing"
 
@@ -207,3 +208,43 @@ func TestReadBigData(t *testing.T) {
 		}
 	})
 }
+
+func asUntyped[T any](read func(reader io.Reader) (T, error)) func(reader io.Reader) (any, error) {
+	return func(reader io.Reader) (any, error) {
+		return read(reader)
+	}
+}
+
+func TestNull(t *testing.T) {
+	tests := []struct {
+		data  []byte
+		value any
+		read  func(reader io.Reader) (any, error)
+	}{
+		{[]byte{Null, 0xfb, 0xc0, 0x10, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66}, -4.1, asUntyped(ReadFloat64)},
+		{[]byte{Null, 0x64, 0x74, 0x65, 0x73, 0x74}, "test", asUntyped(ReadTextString)},
+		{[]byte{Null, SimpleData | simpleTrue}, true, asUntyped(ReadBoolean)},
+		{[]byte{Null, 0x0a}, uint64(10), asUntyped(ReadUInt)},
+	}
+
+	for _, test := range tests {
+		// Read
+		buff := bytes.NewBuffer(test.data)
+		if v, err := test.read(buff); err != FlagNull {
+			t.Fatalf("found Value %s", v)
+		}
+		if v, err := test.read(buff); err != nil {
+			t.Fatal(err)
+		} else if v != test.value {
+			t.Fatalf("Resulting value %s not expected %s", v, test.value)
+		}
+	}
+
+	buff := &bytes.Buffer{}
+	err := WriteNull(buff)
+	if err != nil {
+		t.Fatal(err)
+	} else if buff.Len() != 1 || buff.Bytes()[0] != Null {
+		t.Fatal("written value not null")
+	}
+}
diff --git a/simple.go b/simple.go
index 64b7e22..7dfd382 100644
--- a/simple.go
+++ b/simple.go
@@ -9,6 +9,7 @@ import (
 const (
 	simpleFalse byte = 20
 	simpleTrue  byte = 21
+	simpleNull  byte = 22
 )
 
 // ReadBoolean reads a bool value from the Reader.
@@ -31,6 +32,8 @@ func ReadBoolean(r io.Reader) (b bool, err error) {
 		b = false
 	case simpleTrue:
 		b = true
+	case simpleNull:
+		err = FlagNull
 	default:
 		err = fmt.Errorf("ReadBoolean: Unknown additional 0x%x", adds)
 	}
@@ -86,3 +89,8 @@ func WriteFloat64(f float64, w io.Writer) (err error) {
 	fbits := math.Float64bits(f)
 	return WriteMajors(SimpleData, fbits, w)
 }
+
+// WriteNull writes a null into the Writer.
+func WriteNull(w io.Writer) (err error) {
+	return WriteMajors(SimpleData, uint64(simpleNull), w)
+}