lot of works, i guessmad

1 files changed, 57 insertions, 0 deletions

diff --git a/internal/dns/header.go b/internal/dns/header.go
new file mode 100644
index 0000000..1535500
--- /dev/null
+++ b/internal/dns/header.go
@@ -0,0 +1,57 @@
+package dns
+
+// https://datatracker.ietf.org/doc/html/rfc5395
+type Header struct {
+	ID      uint16
+	Flags   uint16
+	QDCount uint16
+	ANCount uint16
+	NSCount uint16
+	ARCount uint16
+}
+
+// https://datatracker.ietf.org/doc/html/rfc2929#section-2
+// Flags has 16-bit Field. Each hexadecima value below indicates
+// which items are active.
+// Example 0 0000 0 0 0 0 000 0 0 000, so if only AA is active, then
+// Example 1 0000 0 0 0 0 000 0 0 000, is 0x8000
+// Query and Response
+func (h *Header) QR() bool { return h.Flags&0x8000 != 0 }
+
+// Opcode has 4-bit (14 -- 11)
+func (h *Header) OpCode() uint8 { return uint8((h.Flags >> 11) & 0xF) }
+
+// Authoritative Answer
+func (h *Header) AA() bool { return h.Flags&0x0400 != 0 }
+
+// Truncation
+func (h *Header) TC() bool { return h.Flags&0x0200 != 0 }
+
+// Recursion Desired
+func (h *Header) RD() bool { return h.Flags&0x0100 != 0 }
+
+// Recursion Available
+func (h *Header) RA() bool { return h.Flags&0x0080 != 0 }
+
+// Mutator Flags
+func (h *Header) SetQR(v bool) { h.set(0x8000, v) }
+func (h *Header) SetOpCode(v uint8) {
+	h.Bits = (h.Bits &^ (0xF << 11)) |
+		((uint16(v) & 0xF) << 11)
+}
+func (h *Header) SetAA(v bool) { h.set(0x0400, v) }
+func (h *Header) SetTC(v bool) { h.set(0x0200, v) }
+func (h *Header) SetRD(v bool) { h.set(0x0100, v) }
+func (h *Header) SetRA(v bool) { h.set(0x0080, v) }
+func (h *Header) SetZ(v uint8) { h.Bits = (h.Bits &^ 0xF) | (uint16(v) & 0xF) << 4) }
+func (h *Header) SetAD(v bool) { h.set(0x0020, v) }
+func (h *Header) SetCD(v bool) { h.set(0x0010, v) }
+func (h *Header) SetRCode(v uint8)  { h.Bits = (h.Bits &^ 0xF) | (uint16(v) & 0xF) }
+
+func (h *Header) set(mask uint16, v bool) {
+    if v {
+        h.Bits |= mask
+    } else {
+        h.Bits &^= mask
+    }
+}