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