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66 lines
2.1 KiB
Plaintext
66 lines
2.1 KiB
Plaintext
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KCP PROTOCOL SPECIFICATION
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1. Packet (aka. segment) Structure
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KCP has only one kind of segment: both the data and control messages are
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encoded into the same structure and share the same header.
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The KCP packet (aka. segment) structure is as following:
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0 4 5 6 8 (BYTE)
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+---------------+---+---+-------+
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| conv |cmd|frg| wnd |
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+---------------+---+---+-------+ 8
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| ts | sn |
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+---------------+---------------+ 16
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| una | len |
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+---------------+---------------+ 24
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| DATA (optional) |
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+-------------------------------+
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- conv: conversation id (32 bits integer)
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The conversation id is used to identify each connection, which will not change
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during the connection life-time.
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It is represented by a 32 bits integer which is given at the moment the KCP
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control block (aka. struct ikcpcb, or kcp object) has been created. Each
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packet sent out will carry the conversation id in the first 4 bytes and a
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packet from remote endpoint will not be accepted if it has a different
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conversation id.
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The value can be any random number, but in practice, both side between a
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connection will have many KCP objects (or control block) storing in the
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containers like a map or an array. A index is used as the key to look up one
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KCP object from the container.
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So, the higher 16 bits of conversation id can be used as caller's index while
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the lower 16 bits can be used as callee's index. KCP will not handle
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handshake, and the index in both side can be decided and exchanged after
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connection establish.
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When you receive and accept a remote packet, the local index can be extracted
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from the conversation id and the kcp object which is in charge of this
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connection can be find out from your map or array.
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- cmd: command
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- frg: fragment count
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- wnd: window size
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- ts: timestamp
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- sn: serial number
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- una: un-acknowledged serial number
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# vim: set ts=4 sw=4 tw=0 noet cc=78 wrap textwidth=78 :
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