diff --git a/port/bytes.go b/port/bytes.go
new file mode 100644
index 0000000..1534224
--- /dev/null
+++ b/port/bytes.go
@@ -0,0 +1,29 @@
+package port
+
+import (
+	"sourcecode.social/reiver/go-rfc2396/digit"
+)
+
+func Bytes(p []byte) ([]byte, []byte, bool) {
+	length := len(p)
+
+	if length <= 0 {
+		return nil, nil, true
+	}
+
+	{
+		p0 := p[0]
+
+		if !digit.ByteIs(p0) {
+			return nil, p, true
+		}
+	}
+
+	for i,b := range p {
+		if !digit.ByteIs(b) {
+			return p[:i], p[i:], true
+		}
+	}
+
+	return p, nil, true
+}
diff --git a/port/bytes_test.go b/port/bytes_test.go
new file mode 100644
index 0000000..f951dd7
--- /dev/null
+++ b/port/bytes_test.go
@@ -0,0 +1,373 @@
+package port_test
+
+import (
+	"testing"
+
+	"bytes"
+
+	"sourcecode.social/reiver/go-rfc2396/port"
+)
+
+func TestBytes(t *testing.T) {
+
+	tests := []struct{
+		Value []byte
+		ExpectedResult []byte
+		ExpectedRest []byte
+		ExpectedOK bool
+	}{
+		{
+			Value: nil,
+			ExpectedResult: nil,
+			ExpectedRest: nil,
+			ExpectedOK: true,
+		},
+		{
+			Value: []byte(nil),
+			ExpectedResult: nil,
+			ExpectedRest: nil,
+			ExpectedOK: true,
+		},
+
+
+
+		{
+			Value: []byte{},
+			ExpectedResult: nil,
+			ExpectedRest: nil,
+			ExpectedOK: true,
+		},
+		{
+			Value: []byte(""),
+			ExpectedResult: nil,
+			ExpectedRest: nil,
+			ExpectedOK: true,
+		},
+
+
+
+		{
+			Value:        []byte{'%','f','0',  '%','9','f',  '%','9','9',   '%','8','b'}, // == "🙂"
+			ExpectedResult: nil,
+			ExpectedRest: []byte{'%','f','0',  '%','9','f',  '%','9','9',   '%','8','b'},
+			ExpectedOK: true,
+		},
+
+
+
+		{
+			Value:        []byte{'$',',',';',':','@','&','=','+',   '-','_','.','!','~','*','\'','(',')',   '0','1','2','3','4','5','6','7','8','9',   'A','B','C','D','E','F',  'a','b','c','d','e','f',   ' '},
+			ExpectedResult: nil,
+			ExpectedRest: []byte{'$',',',';',':','@','&','=','+',   '-','_','.','!','~','*','\'','(',')',   '0','1','2','3','4','5','6','7','8','9',   'A','B','C','D','E','F',  'a','b','c','d','e','f',   ' '},
+			ExpectedOK: true,
+		},
+
+
+
+		{
+			Value:          []byte("0"),
+			ExpectedResult: []byte("0"),
+			ExpectedRest: nil,
+			ExpectedOK: true,
+		},
+		{
+			Value:          []byte("1"),
+			ExpectedResult: []byte("1"),
+			ExpectedRest: nil,
+			ExpectedOK: true,
+		},
+		{
+			Value:          []byte("2"),
+			ExpectedResult: []byte("2"),
+			ExpectedRest: nil,
+			ExpectedOK: true,
+		},
+		{
+			Value:          []byte("3"),
+			ExpectedResult: []byte("3"),
+			ExpectedRest: nil,
+			ExpectedOK: true,
+		},
+		{
+			Value:          []byte("4"),
+			ExpectedResult: []byte("4"),
+			ExpectedRest: nil,
+			ExpectedOK: true,
+		},
+		{
+			Value:          []byte("5"),
+			ExpectedResult: []byte("5"),
+			ExpectedRest: nil,
+			ExpectedOK: true,
+		},
+		{
+			Value:          []byte("6"),
+			ExpectedResult: []byte("6"),
+			ExpectedRest: nil,
+			ExpectedOK: true,
+		},
+		{
+			Value:          []byte("7"),
+			ExpectedResult: []byte("7"),
+			ExpectedRest: nil,
+			ExpectedOK: true,
+		},
+		{
+			Value:          []byte("8"),
+			ExpectedResult: []byte("8"),
+			ExpectedRest: nil,
+			ExpectedOK: true,
+		},
+		{
+			Value:          []byte("9"),
+			ExpectedResult: []byte("9"),
+			ExpectedRest: nil,
+			ExpectedOK: true,
+		},
+
+
+
+		{
+			Value:          []byte("8080"),
+			ExpectedResult: []byte("8080"),
+			ExpectedRest: nil,
+			ExpectedOK: true,
+		},
+		{
+			Value:          []byte("8080 "),
+			ExpectedResult: []byte("8080"),
+			ExpectedRest:       []byte(" "),
+			ExpectedOK: true,
+		},
+		{
+			Value:          []byte("8080/"),
+			ExpectedResult: []byte("8080"),
+			ExpectedRest:       []byte("/"),
+			ExpectedOK: true,
+		},
+		{
+			Value:          []byte("8080\n"),
+			ExpectedResult: []byte("8080"),
+			ExpectedRest:       []byte("\n"),
+			ExpectedOK: true,
+		},
+	}
+
+	for _, b1 := range []byte{'0','1','2','3','4','5','6','7','8','9'} {
+		for _, b2 := range []byte{'0','1','2','3','4','5','6','7','8','9'} {
+
+			{
+				test := struct{
+					Value []byte
+					ExpectedResult []byte
+					ExpectedRest []byte
+					ExpectedOK bool
+				}{
+					Value:          []byte{b1, b2},
+					ExpectedResult: []byte{b1, b2},
+					ExpectedRest:  nil,
+					ExpectedOK: true,
+				}
+
+				tests = append(tests, test)
+			}
+
+			{
+				test := struct{
+					Value []byte
+					ExpectedResult []byte
+					ExpectedRest []byte
+					ExpectedOK bool
+				}{
+					Value:          []byte{b1, b2, ' '},
+					ExpectedResult: []byte{b1, b2},
+					ExpectedRest:           []byte{' '},
+					ExpectedOK: true,
+				}
+
+				tests = append(tests, test)
+			}
+
+			{
+				test := struct{
+					Value []byte
+					ExpectedResult []byte
+					ExpectedRest []byte
+					ExpectedOK bool
+				}{
+					Value:          []byte{b1, b2, '/'},
+					ExpectedResult: []byte{b1, b2},
+					ExpectedRest:           []byte{'/'},
+					ExpectedOK: true,
+				}
+
+				tests = append(tests, test)
+			}
+
+			{
+				test := struct{
+					Value []byte
+					ExpectedResult []byte
+					ExpectedRest []byte
+					ExpectedOK bool
+				}{
+					Value:          []byte{b1, b2, '\n'},
+					ExpectedResult: []byte{b1, b2},
+					ExpectedRest:           []byte{'\n'},
+					ExpectedOK: true,
+				}
+
+				tests = append(tests, test)
+			}
+
+			{
+				test := struct{
+					Value []byte
+					ExpectedResult []byte
+					ExpectedRest []byte
+					ExpectedOK bool
+				}{
+					Value:          []byte{b1, b2, 'A'},
+					ExpectedResult: []byte{b1, b2},
+					ExpectedRest:           []byte{'A'},
+					ExpectedOK: true,
+				}
+
+				tests = append(tests, test)
+			}
+		}
+	}
+
+	for _, b1 := range []byte{'0','1','2','3','4','5','6','7','8','9'} {
+		for _, b2 := range []byte{'0','1','2','3','4','5','6','7','8','9'} {
+			for _, b3 := range []byte{'0','1','2','3','4','5','6','7','8','9'} {
+
+			{
+				test := struct{
+					Value []byte
+					ExpectedResult []byte
+					ExpectedRest []byte
+					ExpectedOK bool
+				}{
+					Value:          []byte{b1, b2, b3},
+					ExpectedResult: []byte{b1, b2, b3},
+					ExpectedRest:  nil,
+					ExpectedOK: true,
+				}
+
+				tests = append(tests, test)
+			}
+
+			{
+				test := struct{
+					Value []byte
+					ExpectedResult []byte
+					ExpectedRest []byte
+					ExpectedOK bool
+				}{
+					Value:          []byte{b1, b2, b3, ' '},
+					ExpectedResult: []byte{b1, b2, b3},
+					ExpectedRest:               []byte{' '},
+					ExpectedOK: true,
+				}
+
+				tests = append(tests, test)
+			}
+
+			{
+				test := struct{
+					Value []byte
+					ExpectedResult []byte
+					ExpectedRest []byte
+					ExpectedOK bool
+				}{
+					Value:          []byte{b1, b2, b3, '/'},
+					ExpectedResult: []byte{b1, b2, b3},
+					ExpectedRest:               []byte{'/'},
+					ExpectedOK: true,
+				}
+
+				tests = append(tests, test)
+			}
+
+			{
+				test := struct{
+					Value []byte
+					ExpectedResult []byte
+					ExpectedRest []byte
+					ExpectedOK bool
+				}{
+					Value:          []byte{b1, b2, b3, '\n'},
+					ExpectedResult: []byte{b1, b2, b3},
+					ExpectedRest:               []byte{'\n'},
+					ExpectedOK: true,
+				}
+
+				tests = append(tests, test)
+			}
+
+			{
+				test := struct{
+					Value []byte
+					ExpectedResult []byte
+					ExpectedRest []byte
+					ExpectedOK bool
+				}{
+					Value:          []byte{b1, b2, b3, 'A'},
+					ExpectedResult: []byte{b1, b2, b3},
+					ExpectedRest:               []byte{'A'},
+					ExpectedOK: true,
+				}
+
+				tests = append(tests, test)
+			}
+
+			}
+		}
+	}
+
+	for testNumber, test := range tests {
+
+		actualResult, actualRest, actualOK := port.Bytes(test.Value)
+
+		{
+			expected := test.ExpectedOK
+			actual   := actualOK
+
+			if expected != actual {
+				t.Errorf("For test #%d, the actual ok-result is not what was expected.", testNumber)
+				t.Logf("EXPECTED: %t", expected)
+				t.Logf("ACTUAL:   %t", actual)
+				t.Logf("VALUE: %q (%#v)", test.Value, test.Value)
+				continue
+			}
+		}
+
+		{
+			expected := test.ExpectedResult
+			actual   := actualResult
+
+			if !bytes.Equal(expected,actual) {
+				t.Errorf("For test #%d, the actual result is not what was expected.", testNumber)
+				t.Logf("EXPECTED: %q (%#v)", expected, expected)
+				t.Logf("ACTUAL:   %q (%#v)", actual, actual)
+				t.Logf("VALUE: %q (%#v)", test.Value, test.Value)
+				t.Logf("ACTUAL-REST:   %q (%#v)", actualRest, actualRest)
+				continue
+			}
+		}
+
+		{
+			expected := test.ExpectedRest
+			actual   := actualRest
+
+			if !bytes.Equal(expected,actual) {
+				t.Errorf("For test #%d, the actual rest-result is not what was expected.", testNumber)
+				t.Logf("EXPECTED: %q (%#v)", expected, expected)
+				t.Logf("ACTUAL:   %q (%#v)", actual, actual)
+				t.Logf("VALUE: %q (%#v)", test.Value, test.Value)
+				continue
+			}
+		}
+	}
+}