代码整理

packets/fixedheader.go

@@ -0,0 +1,63 @@
+// SPDX-License-Identifier: MIT
+// SPDX-FileCopyrightText: 2022 mochi-mqtt, mochi-co
+// SPDX-FileContributor: mochi-co
+
+package packets
+
+import (
+	"bytes"
+)
+
+// FixedHeader contains the values of the fixed header portion of the MQTT packet.
+type FixedHeader struct {
+	Remaining int  `json:"remaining"` // the number of remaining bytes in the payload.
+	Type      byte `json:"type"`      // the type of the packet (PUBLISH, SUBSCRIBE, etc) from bits 7 - 4 (byte 1).
+	Qos       byte `json:"qos"`       // indicates the quality of service expected.
+	Dup       bool `json:"dup"`       // indicates if the packet was already sent at an earlier time.
+	Retain    bool `json:"retain"`    // whether the message should be retained.
+}
+
+// Encode encodes the FixedHeader and returns a bytes buffer.
+func (fh *FixedHeader) Encode(buf *bytes.Buffer) {
+	buf.WriteByte(fh.Type<<4 | encodeBool(fh.Dup)<<3 | fh.Qos<<1 | encodeBool(fh.Retain))
+	encodeLength(buf, int64(fh.Remaining))
+}
+
+// Decode extracts the specification bits from the header byte.
+func (fh *FixedHeader) Decode(hb byte) error {
+	fh.Type = hb >> 4 // Get the message type from the first 4 bytes.
+
+	switch fh.Type {
+	case Publish:
+		if (hb>>1)&0x01 > 0 && (hb>>1)&0x02 > 0 {
+			return ErrProtocolViolationQosOutOfRange // [MQTT-3.3.1-4]
+		}
+
+		fh.Dup = (hb>>3)&0x01 > 0 // is duplicate
+		fh.Qos = (hb >> 1) & 0x03 // qos flag
+		fh.Retain = hb&0x01 > 0   // is retain flag
+	case Pubrel:
+		fallthrough
+	case Subscribe:
+		fallthrough
+	case Unsubscribe:
+		if (hb>>0)&0x01 != 0 || (hb>>1)&0x01 != 1 || (hb>>2)&0x01 != 0 || (hb>>3)&0x01 != 0 { // [MQTT-3.8.1-1] [MQTT-3.10.1-1]
+			return ErrMalformedFlags
+		}
+
+		fh.Qos = (hb >> 1) & 0x03
+	default:
+		if (hb>>0)&0x01 != 0 ||
+			(hb>>1)&0x01 != 0 ||
+			(hb>>2)&0x01 != 0 ||
+			(hb>>3)&0x01 != 0 { // [MQTT-3.8.3-5] [MQTT-3.14.1-1] [MQTT-3.15.1-1]
+			return ErrMalformedFlags
+		}
+	}
+
+	if fh.Qos == 0 && fh.Dup {
+		return ErrProtocolViolationDupNoQos // [MQTT-3.3.1-2]
+	}
+
+	return nil
+}