This change begins the work of bringing committed filters to the
network consensus daemon. Committed filters are designed to enable
light wallets without many of the privacy issues associated with
server-side bloom filtering.
The new gcs package provides the primitives for creating and matching
against Golomb-coded sets (GCS) filters while the blockcf package
provides creation of filters and filter entries for data structures
found in blocks.
The wire package has been updated to define a new protocol version and
service flag for advertising CF support and includes types for the
following new messages: cfheaders, cfilter, cftypes, getcfheaders,
getcfilter, getcftypes. The peer package and server implementation
have been updated to include support for the new protocol version and
messages.
Filters are created using a collision probability of 2^-20 and are
saved to a new optional database index when running with committed
filter support enabled (the default). At first startup, if support is
not disabled, the index will be created and populated with filters and
filter headers for all preexisting blocks, and new filters will be
recorded for processed blocks.
Multiple filter types are supported. The regular filter commits to
output scripts and previous outpoints that any non-voting wallet will
require access to. Scripts and previous outpoints that can only be
spent by votes and revocations are not committed to the filter. The
extended filter is a supplementary filter which commits to all
transaction hashes and script data pushes from the input scripts of
non-coinbase regular and ticket purchase transactions. Creating these
filters is based on the algorithm defined by BIP0158 but is modified
to only commit "regular" data in stake transactions to prevent
committed filters from being used to create SPV voting wallets.
Contains the following upstream commits:
- 829e87a733
- This commit does not apply to Decred so it has been reverted
- d0cdd53720
- This commit does not apply to Decred so it has been reverted
- 7996eb1f9d
- This commit has already been cherry picked and is a NOOP
- 1944637333
- f5ded65636
- 407fcc2aaf
