mirror of
https://github.com/lightning/bolts.git
synced 2024-11-19 10:00:04 +01:00
828eda61df
ASCII character set seems apropriate, since it acts a lowest common denominator, and who'd stuff emojis in an error message anyway? Fixes #68
162 lines
7.2 KiB
Markdown
162 lines
7.2 KiB
Markdown
# BOLT #1: Base Protocol
|
|
|
|
## Overview
|
|
This protocol assumes an underlying authenticated and ordered transport mechanism that takes care of framing individual messages.
|
|
[BOLT #8](08-transport.md) specifies the canonical transport layer used in Lightning, though it can be replaced by any transport that fulfills the above guarantees.
|
|
|
|
The default TCP port is 9735. This corresponds to hexadecimal `0x2607`, the unicode code point for LIGHTNING.<sup>[1](#reference-1)</sup>
|
|
|
|
All data fields are big-endian unless otherwise specified.
|
|
|
|
## Table of Contents
|
|
* [Lightning Message Format](#lightning-message-format)
|
|
* [Setup Messages](#setup-messages)
|
|
* [The `init` message](#the-init-message)
|
|
* [The `error` message](#the-error-message)
|
|
* [Acknowledgements](#acknowledgements)
|
|
* [References](#references)
|
|
* [Authors](#authors)
|
|
|
|
## Lightning Message Format
|
|
|
|
After decryption, all lightning messages are of the form:
|
|
|
|
1. `type`: 2 byte big-endian field indicating the type of the message.
|
|
2. `payload`: variable length payload. It comprises the remainder of
|
|
the message and conforms to the format matching the `type`.
|
|
|
|
The `type` field indicates how to interpret the `payload` field.
|
|
The format for each individual type is specified in a specification in this repository.
|
|
The type follows the _it's ok to be odd_ rule, so nodes MAY send odd-numbered types without ascertaining that the recipient understands it.
|
|
A node MUST NOT send an evenly-typed message not listed here without prior negotiation.
|
|
A node MUST ignore a received message of unknown type, if that type is odd.
|
|
A node MUST fail the channels if it receives a message of unknown type, if that type is even.
|
|
|
|
The messages are grouped logically into 4 groups by their most significant set bit:
|
|
|
|
- Setup & signalling (types `0`-`31`): messages related to supported features and error reporting. These are described below.
|
|
- Channel (types `32`-`127`): comprises messages used to setup and tear down micropayment channels. These are described in [BOLT #2](02-peer-protocol.md).
|
|
- Commitment (types `128`-`255`: comprises messages related to updating the current commitment transaction, which includes adding, revoking, and settling HTLCs, as well as updating fees and exchanging signatures. These are described in [BOLT #2](02-peer-protocol.md).
|
|
- Routing (types `256`-`511`): node and channel announcements, as well as any active route exploration. These are described in [BOLT #7](07-routing-gossip.md).
|
|
|
|
The size of the message is required to fit into a 2 byte unsigned int by the transport layer, therefore the maximum possible size is 65535 bytes.
|
|
A node MUST ignore any additional data within a message, beyond the length it expects for that type.
|
|
A node MUST fail the channels if it receives a known message with insufficient length for the contents.
|
|
|
|
### Rationale
|
|
|
|
The standard endian of `SHA2` and the encoding of Bitcoin public keys
|
|
are big endian, thus it would be unusual to use a different endian for
|
|
other fields.
|
|
|
|
Length is limited to 65535 bytes by the cryptographic wrapping, and
|
|
messages in the protocol are never more than that length anyway.
|
|
|
|
The "it's OK to be odd" rule allows for future optional extensions
|
|
without negotiation or special coding in clients. The "ignore
|
|
additional data" rule similarly allows for future expansion.
|
|
|
|
Implementations may prefer to have message data aligned on an 8 byte
|
|
boundary (the largest natural alignment requirement of any type here),
|
|
but adding a 6 byte padding after the type field was considered
|
|
wasteful: alignment may be achieved by decrypting the message into
|
|
a buffer with 6 bytes of pre-padding.
|
|
|
|
## Setup Messages
|
|
|
|
### The `init` message
|
|
|
|
Once authentication is complete, the first message reveals the features supported or required by this node.
|
|
Odd features are optional, even features are compulsory (_it's OK to be odd_).
|
|
The meaning of these bits will be defined in the future.
|
|
|
|
1. type: 16 (`init`)
|
|
2. data:
|
|
* [2:gflen]
|
|
* [gflen:globalfeatures]
|
|
* [2:lflen]
|
|
* [lflen:localfeatures]
|
|
|
|
The 2 byte `gflen` and `lflen` fields indicate the number of bytes in the immediately following field.
|
|
|
|
#### Requirements
|
|
|
|
The sending node SHOULD use the minimum lengths required to represent
|
|
the feature fields. The sending node MUST set feature bits
|
|
corresponding to features it requires the peer to support, and SHOULD
|
|
set feature bits corresponding to features it optionally supports.
|
|
|
|
The receiving node MUST fail the channels if it receives a
|
|
`globalfeatures` or `localfeatures` with an even bit set which it does
|
|
not understand.
|
|
|
|
Each node MUST wait to receive `init` before sending any other messages.
|
|
|
|
#### Rationale
|
|
|
|
The even/odd semantic allows future incompatible changes, or backward
|
|
compatible changes. Bits should generally be assigned in pairs, so
|
|
that optional features can later become compulsory.
|
|
|
|
Nodes wait for receipt of the other's features to simplify error
|
|
diagnosis where features are incompatible.
|
|
|
|
The feature masks are split into local features which only affect the
|
|
protocol between these two nodes, and global features which can affect
|
|
HTLCs and thus are also advertised to other nodes.
|
|
|
|
### The `error` message
|
|
|
|
For simplicity of diagnosis, it is often useful to tell the peer that something is incorrect.
|
|
|
|
1. type: 17 (`error`)
|
|
2. data:
|
|
* [8:channel-id]
|
|
* [2:len]
|
|
* [len:data]
|
|
|
|
The 2-byte `len` field indicates the number of bytes in the immediately following field.
|
|
|
|
#### Requirements
|
|
|
|
A node SHOULD send `error` for protocol violations or internal
|
|
errors which make channels unusable or further communication unusable.
|
|
A node MAY send an empty [data] field. A node sending `error` MUST
|
|
fail the channel referred to by the `channel-id`, or if `channel-id`
|
|
is `0xFFFFFFFFFFFFFFFF` it MUST fail all channels and MUST close the connection.
|
|
A node MUST set `len` equal to the length of `data`. A node SHOULD include the raw, hex-encoded transaction in reply to a `funding_created`, `funding_signed`, `closing_signed` or `commitment_signed` message when failure was caused by an invalid signature check.
|
|
|
|
A node receiving `error` MUST fail the channel referred to by
|
|
`channel-id`, or if `channel-id` is `0xFFFFFFFFFFFFFFFF` it MUST fail
|
|
all channels and MUST close the connection. A receiving node MUST truncate
|
|
`len` to the remainder of the packet if it is larger.
|
|
|
|
A receiving node SHOULD only print out `data` verbatim if the string is composed solely of printable ASCII characters.
|
|
For referece, the printable character set includes byte values 32 through 127 inclusive.
|
|
|
|
#### Rationale
|
|
|
|
There are unrecoverable errors which require an abort of conversations;
|
|
if the connection is simply dropped then the peer may retry the
|
|
connection. It's also useful to describe protocol violations for
|
|
diagnosis, as it indicates that one peer has a bug.
|
|
|
|
It may be wise not to distinguish errors in production settings, lest
|
|
it leak information, thus the optional data field.
|
|
|
|
## Acknowledgements
|
|
|
|
TODO(roasbeef); fin
|
|
|
|
|
|
## References
|
|
1. <a id="reference-2">http://www.unicode.org/charts/PDF/U2600.pdf</a>
|
|
|
|
## Authors
|
|
|
|
FIXME
|
|
|
|
|
|
<br>
|
|
This work is licensed under a [Creative Commons Attribution 4.0 International License](http://creativecommons.org/licenses/by/4.0/).
|