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BOLT 7: Add compressed (zlib) encoding.

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[ Note: in retrospect, adding this in the initial draft without its
  own feature bit was a mistake.  It was a premature optimization,
  adds complexity and removes the ability to disable it if a problem
  is found without disabling gossip_queries entirely.  However, it
  is already deployed as-is. --RR ]
  
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
This commit is contained in:
Rusty Russell 2018-06-27 06:35:15 +09:30
parent f6312d9a70
commit fd9da9b95e
2 changed files with 15 additions and 3 deletions
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2
.aspell.en.pws
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@ -326,3 +326,5 @@ Mul
unlinkable
regtest
ratelimiting
zlib
ZLIB

16
07-routing-gossip.md
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@ -545,6 +545,13 @@ rest contains the data.
Encoding types:
* `0`: uncompressed array of `short_channel_id` types, in ascending order.
* `1`: array of `short_channel_id` types, in ascending order, compressed with zlib deflate<sup>[1](#reference-1)</sup>
Note that a 65535-byte zlib message can decompress into 67632120
bytes<sup>[2](#reference-2)</sup>, but since the only valid contents
are unique 8-byte values, no more than 14 bytes can be duplicated
across the stream: as each duplicate takes at least 2 bits, no valid
contents could decompress to more then 3669960 bytes.
### The `query_short_channel_ids`/`reply_short_channel_ids_done` Messages
@ -571,14 +578,14 @@ The sender:
- MUST NOT send `query_short_channel_ids` if it has sent a previous `query_short_channel_ids` to this peer and not received `reply_short_channel_ids_end`.
- MUST set `chain_hash` to the 32-byte hash that uniquely identifies the chain
that the `short_channel_id`s refer to.
- MUST set the first byte of `encoded_short_ids` to zero
- MUST append a whole number of `short_channel_id`s to `encoded_short_ids`
- MUST set the first byte of `encoded_short_ids` to the encoding type.
- MUST encode a whole number of `short_channel_id`s to `encoded_short_ids`
- MAY send this if it receives a `channel_update` for a
`short_channel_id` for which it has no `channel_announcement`.
- SHOULD NOT send this if the channel referred to is not an unspent output.
The receiver:
- if the first byte of `encoded_short_ids` is not zero:
- if the first byte of `encoded_short_ids` is not a known encoding type:
- MAY fail the connection
- if `encoded_short_ids` does not decode into a whole number of `short_channel_id`:
- MAY fail the connection.
@ -878,6 +885,9 @@ above.
## References
1. <a id="reference-1">[RFC 1950 "ZLIB Compressed Data Format Specification version 3.3](https://www.ietf.org/rfc/rfc1950.txt)</a>
2. <a id="reference-2">[Maximum Compression Factor](https://zlib.net/zlib_tech.html)</a>
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