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41 lines
1.8 KiB
Go
41 lines
1.8 KiB
Go
/*
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File Name: Message Encoding.go
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Copyright: 2021 Peernet s.r.o.
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Author: Peter Kleissner
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Intermediary between low-level packets and high-level interpretation.
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*/
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package protocol
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import (
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"github.com/PeernetOfficial/core/btcec"
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)
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// ProtocolVersion is the current protocol version
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const ProtocolVersion = 0
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// MessageRaw is a high-level message between peers that has not been decoded
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type MessageRaw struct {
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PacketRaw
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SenderPublicKey *btcec.PublicKey // Sender Public Key, ECDSA (secp256k1) 257-bit
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SequenceInfo *SequenceExpiry // Sequence
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}
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// The maximum packet size is = 65535 - 8 UDP byte header - 40 byte IPv6 header (IPv4 header is only 20 bytes).
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// However, due to the MTU soft limit and fragmentation, packets should be as small as possible.
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const udpMaxPacketSize = 65535 - 8 - 40
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// internetSafeMTU is a value relatively safe to use for transmitting over the internet
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// Theory: The value is different for IPv4 (min 576 bytes, Ethernet 1500 bytes) and IPv6 (min 1280 bytes). 8 byte UDP header must be subtracted, as well as the IP header (20 bytes for IPv4, 40 for IPv6).
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// One simple test during development showed that 1500 - 8 - 40 - 8 worked for file transfer over IPv6 in Prague.
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// For IPv6 the internet recommends the minimal possible value: 1280 bytes.
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// This will be good enough for now. MTU negotiation that deviates from this value can be implemented separately (for example as part of file transfer).
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// Since packets may be sent at anytime via IPv4/IPv6 connections (even concurrently on multiple), there is a single MTU value here.
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const internetSafeMTU = 1280 - 8 - 40
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// isPacketSizeExceed checks if the max packet size would be exceeded with the payload
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func isPacketSizeExceed(currentSize int, testSize int) bool {
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return currentSize+testSize > udpMaxPacketSize-PacketLengthMin
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}
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