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# JS5 protocol |
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## Upstream |
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| Opcode | Description | |
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|-------:|--------------------------| |
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| 0 | Request group (prefetch) | |
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| 1 | Request group (urgent) | |
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| 2 | Logged in | |
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| 3 | Logged out | |
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| 4 | Rekey | |
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| 6 | Connected | |
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| 7 | Disconnect | |
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All upstream packets are exactly 4 bytes long, including the opcode. Unused |
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payload bytes are set to zero. |
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### Request group (prefetch/urgent) |
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| Data type | Description | |
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|---------------|-------------| |
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| UnsignedByte | Archive ID | |
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| UnsignedShort | Group ID | |
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Requests a group. Urgent requests have a higher priority than prefetch requests, |
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as the client needs the group immediately. Prefetch requests are used to |
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prepopulate most of the cache in the background. |
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### Rekey |
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| Data type | Description | |
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|---------------|----------------------| |
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| UnsignedByte | Key | |
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| UnsignedShort | Unused (set to zero) | |
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Sent to set the encryption key. |
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### Logged in/out |
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Sent whenever the player logs in or out of the game. Consensus in the community |
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is that the logged in/out state is probably used for prioritisation, much like |
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the distinction between prefetch/urgent requests. |
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### Connected |
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| Data type | Description | |
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|----------------|-----------------------------| |
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| UnsignedMedium | Unknown (always set to `3`) | |
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Sent immediately after the JS5 connection is established. Its purpose is not |
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known. |
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### Disconnect |
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Requests that the server closes the connection. Sent by the `::serverjs5drop` |
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command. |
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|
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## Downstream |
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There is only a single type of response packet, and as such, there are no |
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response opcodes. The packet contains a group requested by the client. |
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| Data type | Description | |
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|----------------|-----------------------------------------------------------| |
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| UnsignedByte | Archive ID | |
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| UnsignedShort | Group ID | |
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| UnsignedByte | Compression type (ORed with `0x80` for prefetch requests) | |
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| Int | Compressed length | |
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| Int (optional) | Uncompressed length (present iff the group is compressed) | |
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| Byte[] | Compressed data (with `0xFF` markers, see below) | |
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If encryption is enabled, all downstream bytes are XORed with the encryption |
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key. The client enables encryption if the checksum of a group does not match the |
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expected checksum in the master index or index. |
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After the first 512 bytes of a response, every subsequent block of 511 bytes is |
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prefixed with a single `0xFF` byte. |
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