mirror of
https://github.com/mochi-mqtt/server.git
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84 lines
2.0 KiB
Go
84 lines
2.0 KiB
Go
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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// Type is the type of the packet (PUBLISH, SUBSCRIBE, etc) from bits 7 - 4 (byte 1).
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Type byte
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// Dup indicates if the packet is a duplicate.
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Dup bool
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// Qos byte indicates the quality of service expected.
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Qos byte
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// Retain indicates whether the message should be retained.
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Retain bool
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// Remaining is the number of remaining bytes in the payload.
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Remaining int
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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, 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(headerByte byte) error {
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// Get the message type from the first 4 bytes.
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fh.Type = headerByte >> 4
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// @SPEC [MQTT-2.2.2-1]
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// Where a flag bit is marked as “Reserved” in Table 2.2 - Flag Bits,
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// it is reserved for future use and MUST be set to the value listed in that table.
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switch fh.Type {
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case Publish:
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fh.Dup = (headerByte>>3)&0x01 > 0 // Extract flags. Check if message is duplicate.
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fh.Qos = (headerByte >> 1) & 0x03 // Extract QoS flag.
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fh.Retain = headerByte&0x01 > 0 // Extract retain flag.
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case Pubrel:
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fh.Qos = (headerByte >> 1) & 0x03
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case Subscribe:
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fh.Qos = (headerByte >> 1) & 0x03
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case Unsubscribe:
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fh.Qos = (headerByte >> 1) & 0x03
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default:
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// [MQTT-2.2.2-2]
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// If invalid flags are received, the receiver MUST close the Network Connection.
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if (headerByte>>3)&0x01 > 0 || (headerByte>>1)&0x03 > 0 || headerByte&0x01 > 0 {
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return ErrInvalidFlags
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}
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}
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return nil
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}
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// encodeLength writes length bits for the header.
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func encodeLength(buf *bytes.Buffer, length int) {
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for {
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digit := byte(length % 128)
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length /= 128
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if length > 0 {
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digit |= 0x80
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}
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buf.WriteByte(digit)
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if length == 0 {
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break
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}
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}
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}
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