Commit Graph

154 Commits

Author SHA1 Message Date
tersec 2d8a796a93
altair-capable beacon block creation (#2834)
* altair-capable beacon block creation

* update block_sim to use sync committees and the new block production interface
2021-08-29 14:50:21 +00:00
Jacek Sieka 01596c45dd
cleanups and fixes (#2827)
* import cleanup
* fix json-rpc exception handlers
* avoid unnecessary presto client import
* introduce ForkedBeaconBlock, some altair logging
* url fixes
2021-08-27 11:00:06 +02:00
Jacek Sieka a7a65bce42
disentangle eth2 types from the ssz library (#2785)
* reorganize ssz dependencies

This PR continues the work in
https://github.com/status-im/nimbus-eth2/pull/2646,
https://github.com/status-im/nimbus-eth2/pull/2779 as well as past
issues with serialization and type, to disentangle SSZ from eth2 and at
the same time simplify imports and exports with a structured approach.

The principal idea here is that when a library wants to introduce SSZ
support, they do so via 3 files:

* `ssz_codecs` which imports and reexports `codecs` - this covers the
basic byte conversions and ensures no overloads get lost
* `xxx_merkleization` imports and exports `merkleization` to specialize
and get access to `hash_tree_root` and friends
* `xxx_ssz_serialization` imports and exports `ssz_serialization` to
specialize ssz for a specific library

Those that need to interact with SSZ always import the `xxx_` versions
of the modules and never `ssz` itself so as to keep imports simple and
safe.

This is similar to how the REST / JSON-RPC serializers are structured in
that someone wanting to serialize spec types to REST-JSON will import
`eth2_rest_serialization` and nothing else.

* split up ssz into a core library that is independendent of eth2 types
* rename `bytes_reader` to `codec` to highlight that it contains coding
and decoding of bytes and native ssz types
* remove tricky List init overload that causes compile issues
* get rid of top-level ssz import
* reenable merkleization tests
* move some "standard" json serializers to spec
* remove `ValidatorIndex` serialization for now
* remove test_ssz_merkleization
* add tests for over/underlong byte sequences
* fix broken seq[byte] test - seq[byte] is not an SSZ type

There are a few things this PR doesn't solve:

* like #2646 this PR is weak on how to handle root and other
dontSerialize fields that "sometimes" should be computed - the same
problem appears in REST / JSON-RPC etc

* Fix a build problem on macOS

* Another way to fix the macOS builds

Co-authored-by: Zahary Karadjov <zahary@gmail.com>
2021-08-18 20:57:58 +02:00
Jacek Sieka 7a622e8505
rework spec imports (#2779)
The spec imports are a mess to work with, so this branch cleans them up
a bit to ensure that we avoid generic sandwitches and that importing
stuff generally becomes easier.

* reexport crypto/digest/presets because these are part of the public
symbol set of the rest of the spec types
* don't export `merge` types from `base` - this causes circular deps
* fix circular deps in `ssz/spec_types` - this is the first step in
disentangling ssz from spec
* be explicit about phase0 vs altair - longer term, `altair` will become
the "natural" type set, then merge and so on, so no point in giving
`phase0` special preferential treatment
2021-08-12 13:08:20 +00:00
Jacek Sieka 9697b73e71
forkedbeaconstate_helpers -> forks (#2772)
Simpler module name for stuff that covers forks

* check that runtime config matches database state
* also include some assorted altair cleanups
* use "standard" genesis fork in local testnet to work around missing
runtime config support
2021-08-10 22:46:35 +02:00
tersec 5f3225c6e5
fix invalid_signature_no_participants test case (#2741) 2021-07-27 14:04:41 +00:00
tersec e4afc36d71
use ForkedTrustedSignedBeaconBlock (#2720)
* use ForkedTrustedSignedBeaconBlock

* remove --subscribe-all-subnets

* https://ethereum.github.io/eth2.0-APIs/#/Beacon/getBlock implementation was passing through forked beaconblocks
2021-07-14 12:18:52 +00:00
Jacek Sieka 23eea197f6
Implement split preset/config support (#2710)
* Implement split preset/config support

This is the initial bulk refactor to introduce runtime config values in
a number of places, somewhat replacing the existing mechanism of loading
network metadata.

It still needs more work, this is the initial refactor that introduces
runtime configuration in some of the places that need it.

The PR changes the way presets and constants work, to match the spec. In
particular, a "preset" now refers to the compile-time configuration
while a "cfg" or "RuntimeConfig" is the dynamic part.

A single binary can support either mainnet or minimal, but not both.
Support for other presets has been removed completely (can be readded,
in case there's need).

There's a number of outstanding tasks:

* `SECONDS_PER_SLOT` still needs fixing
* loading custom runtime configs needs redoing
* checking constants against YAML file

* yeerongpilly support

`build/nimbus_beacon_node --network=yeerongpilly --discv5:no --log-level=DEBUG`

* load fork epoch from config

* fix fork digest sent in status
* nicer error string for request failures
* fix tools

* one more

* fixup

* fixup

* fixup

* use "standard" network definition folder in local testnet

Files are loaded from their standard locations, including genesis etc,
to conform to the format used in the `eth2-networks` repo.

* fix launch scripts, allow unknown config values

* fix base config of rest test

* cleanups

* bundle mainnet config using common loader
* fix spec links and names
* only include supported preset in binary

* drop yeerongpilly, add altair-devnet-0, support boot_enr.yaml
2021-07-12 15:01:38 +02:00
tersec 7577f8c2ef
add blockchain_dag altair database reading; add rollback tests (#2683)
* add blockchain_dag altair database reading; add rollback tests; fix some unnecessary type conversions

* remove debugging scaffolding

* proposeSignedBlock() will need to be async for merge; introduce altair types to VC
2021-06-29 15:09:29 +00:00
tersec 41e0a7abc0
introduce database support for Altair (#2667)
* introduce immutable Altair BeaconState

* add database support for Altair blocks and states

* add tests for Altair get/put/contains/delete state

* enable blockchain_dag Altair state database storing

* properly return error on getting missing altair block
2021-06-24 07:11:47 +00:00
tersec ae1abf24af
add Altair support to block quarantine/clearance and block_sim (#2662)
* add Altair support to the block quarantine

* switch some spec/datatypes imports to spec/datatypes/base

* add Altair support to block_clearance

* allow runtime configuration of Altair transition slot

* enable Altair in block_sim, including in CI
2021-06-23 14:43:18 +00:00
tersec b1d5609171
remove false OnBlockAdded dependency on phase0 HashedBeaconState (#2661)
* remove false OnBlockAdded dependency on phase.HashedBeaconState

* introduce altair data types into block_clearance; update some alpha.6 spec refs to alpha.7; add get_active_validator_indices_len ForkedHashedBeaconState wrapper

* switch many modules from using datatypes (with phase0 states/blocks) to datatypes/base (fork-independent); update spec refs from alpha.6 to alpha.7 and remove rm'd G2_POINT_AT_INFINITY

* switch more modules from using datatypes (with phase0 states/blocks) to datatypes/base (fork-independent); update spec refs from alpha.6 to alpha.7

* remove unnecessary phase0-only wrapper of get_attesting_indices(); allow signatures_batch to process either fork; remove O(n^2) nested loop in process_inactivity_updates(); add altair support to getAttestationsforTestBlock()

* add Altair versions of asSigVerified(), asTrusted(), and makeBeaconBlock()

* fix spec URL to be Altair for Altair makeBeaconBlock()
2021-06-21 08:35:24 +00:00
tersec 1c3314f08b
update to Altair as of v1.1.0-alpha.7 (#2649)
* update to Altair as of v1.1.0-alpha.7

* introduce Altair types into attestation pool

* avoid allocating/copying pubkeys excessively in get_next_sync_committee()
2021-06-14 17:42:46 +00:00
tersec 146fa48454
use ForkedHashedBeaconState in StateData (#2634)
* use ForkedHashedBeaconState in StateData

* fix FAR_FUTURE_EPOCH -> slot overflow; almost always use assign()

* avoid stack allocation in maybeUpgradeStateToAltair()

* create and use dispatch functions for check_attester_slashing(), check_proposer_slashing(), and check_voluntary_exit()

* use getStateRoot() instead of various state.data.hbsPhase0.root

* remove withStateVars.hashedState(), which doesn't work as a design anymore

* introduce spec/datatypes/altair into beacon_chain_db

* fix inefficient codegen for getStateField(largeStateField)

* state_transition_slots() doesn't either need/use blocks or runtime presets

* combine process_slots(HBS)/state_transition_slots(HBS) which differ only in last-slot htr optimization

* getStateField(StateData, ...) was replaced by getStateField(ForkedHashedBeaconState, ...)

* fix rollback

* switch some state_transition(), process_slots, makeTestBlocks(), etc to use ForkedHashedBeaconState

* remove state_transition(phase0.HashedBeaconState)

* remove process_slots(phase0.HashedBeaconState)

* remove state_transition_block(phase0.HashedBeaconState)

* remove unused callWithBS(); separate case expression from if statement

* switch back from nested-ref-object construction to (ref Foo)(Bar())
2021-06-11 20:51:46 +03:00
tersec 8ebd496fbe
Altair transition tests (#2624)
* Working Altair transition tests

* with fixed upstream test vectors, remove state root workaround

* switch upgrade_to_altair() to returning a reference

* remove test_state_transition

* fix invalid fork state/block combinations error messages

* avoid memory copies by reintroducing state_transition_slots(var SomeHashedBeaconState)
2021-06-04 10:38:00 +00:00
tersec 28a5bca71a
split state_transition() into slots/block parts and use only block where appropriate (#2630) 2021-06-03 11:42:25 +02:00
tersec aa6177814e
re-enable state_transition() rollback in phase0 (#2613) 2021-05-29 03:54:56 +00:00
tersec c06ffc7804
proposed structure for altair (#2323)
* proposed structure for hf1

* refactor datatypes.nim into datatypes/{base, phase0, hf1}.nim

* hf1 is Altair

* some syncing with alpha 2

* adjust epoch processing to disambiguate access to RewardFlags

* relocate StateData to stay consistent with meaning phase 0 StateData

* passes v1.1.0 alpha 5 SSZ consensus object tests

* Altair block header test fixtures work

* fix slash_validator() so that Altair attester slashings, proposer slashings, and voluntary exit textures work

* deposit operation Altair test fixtures work

* slot sanity and all but a couple epoch transition tests switched to Altair

* attestation Altair test fixtures work

* Altair block sanity test fixtures work

* add working altair sync committee tests

* improve workarounds for sum-types-across-modules Nim bug; incorporate SignedBeaconBlock root reconstuction to SSZ byte reader
2021-05-28 15:25:58 +00:00
tersec d8bb91d9a9
partially integrate eth1 merge changes (#2548)
* partially integrate eth1 merge changes

* use hexToSeqByte() and validate execution engine opaque transaction length

* remove incorrect REST serialization code
2021-05-20 10:44:13 +00:00
Jacek Sieka 646923c3dd
add attestation stats tool to ncli_db (#2539)
This also makes future efforts to provide metrics and logs for
attestation efficiency easier

* Export rewards from epoch transition
* Use less memory for reward calculation (bool -> set[enum], field
alignment)
* Reuse reward memory when replaying, avoiding spike
* Allow replaying any range in ncli_db benchmark
2021-05-07 13:36:21 +02:00
Jacek Sieka 427c0f307c
avoid extraneous hash root calculation (#2537)
When applying a block, we'll currently compute a state root for the
state after slot processing but before block processing - this is
unnecessary when a block is being applied because the intermediate state
root is never observed.
2021-05-05 08:54:21 +02:00
Jacek Sieka 8b76ceed52
Fix minor exception effect issues (#2448)
Makes code compatible with
https://github.com/status-im/nim-chronos/pull/166 without requiring it.
2021-03-24 17:20:55 +01:00
tersec 97f7284e51
bump spec refs from v1.0.0 to v1.0.1 and update copyright years (#2357) 2021-02-25 13:37:22 +00:00
Mamy Ratsimbazafy 70a03658e3
Block validation flow v2 + Batch (serial) sig verification (#2250)
* bump nim-blscurve

* Outline the block validation flow

* introduce the SigVerified types, pass the tests

* Split clearance/quarantine to prepare for batch crypto verif

* Add a batch signature collector

* Make clearance use SigVerified block and split verification between crypto and state transition

* Always use signedBeaconBlock for the onBlockAdded callback

* RANDAO signing_root is the epoch instead of the full block

* Support skipping BLS for testing

* Fix compilation of the validator client

* Try to fix strange errors MacOS and Jenkins (Clang, unknown type name br_hmac_drbg_context in stdlib_assertions.nim.c)

* address https://github.com/status-im/nimbus-eth2/pull/2250#discussion_r561819858

* address https://github.com/status-im/nimbus-eth2/pull/2250#discussion_r561828025

* onBlockAdded callback should use TrustedSignedBeaconBlock https://github.com/status-im/nimbus-eth2/pull/2250#discussion_r561837261

* address https://github.com/status-im/nimbus-eth2/pull/2250#discussion_r561828946

* Use the application RNG: https://github.com/status-im/nimbus-eth2/pull/2250#discussion_r561815336

* Improve codegen of conversion zero-cost)

* Quick fixes with loadWithCache after #2259 (TODO: graceful error since pubkey validations is now done first in signatures_batch)

* Graceful handle rogue pubkeys and signatures now that those are lazy-loaded
2021-01-25 20:45:48 +02:00
Jacek Sieka 5713a3ce4c
performance fixes (#2259)
* performance fixes

* don't mark tree cache as dirty on read-only List accesses
* store only blob in memory for keys and signatures, parse blob lazily
* compare public keys by blob instead of parsing / converting to raw
* compare Eth2Digest using non-constant-time comparison
* avoid some unnecessary validator copying

This branch will in particular speed up deposit processing which has
been slowing down block replay.

Pre (mainnet, 1600 blocks):

```
All time are ms
     Average,       StdDev,          Min,          Max,      Samples,         Test
Validation is turned off meaning that no BLS operations are performed
    3450.269,        0.000,     3450.269,     3450.269,            1, Initialize DB
       0.417,        0.822,        0.036,       21.098,         1400, Load block from database
      16.521,        0.000,       16.521,       16.521,            1, Load state from database
      27.906,       50.846,        8.104,     1507.633,         1350, Apply block
      52.617,       37.029,       20.640,      135.938,           50, Apply epoch block
```

Post:

```
    3502.715,        0.000,     3502.715,     3502.715,            1, Initialize DB
       0.080,        0.560,        0.035,       21.015,         1400, Load block from database
      17.595,        0.000,       17.595,       17.595,            1, Load state from database
      15.706,       11.028,        8.300,      107.537,         1350, Apply block
      33.217,       12.622,       17.331,       60.580,           50, Apply epoch block
```

* more perf fixes

* load EpochRef cache into StateCache more aggressively
* point out security concern with public key cache
* reuse proposer index from state when processing block
* avoid genericAssign in a few more places
* don't parse key when signature is unparseable
* fix `==` overload for Eth2Digest
* preallocate validator list when getting active validators
* speed up proposer index calculation a little bit
* reuse cache when replaying blocks in ncli_db
* avoid a few more copying loops

```
     Average,       StdDev,          Min,          Max,      Samples,         Test
Validation is turned off meaning that no BLS operations are performed
    3279.158,        0.000,     3279.158,     3279.158,            1, Initialize DB
       0.072,        0.357,        0.035,       13.400,         1400, Load block from database
      17.295,        0.000,       17.295,       17.295,            1, Load state from database
       5.918,        9.896,        0.198,       98.028,         1350, Apply block
      15.888,       10.951,        7.902,       39.535,           50, Apply epoch block
       0.000,        0.000,        0.000,        0.000,            0, Database block store
```

* clear full balance cache before processing rewards and penalties

```
All time are ms
     Average,       StdDev,          Min,          Max,      Samples,         Test
Validation is turned off meaning that no BLS operations are performed
    3947.901,        0.000,     3947.901,     3947.901,            1, Initialize DB
       0.124,        0.506,        0.026,      202.370,       363345, Load block from database
      97.614,        0.000,       97.614,       97.614,            1, Load state from database
       0.186,        0.188,        0.012,       99.561,       357262, Advance slot, non-epoch
      14.161,        5.966,        1.099,      395.511,        11524, Advance slot, epoch
       1.372,        4.170,        0.017,      276.401,       363345, Apply block, no slot processing
       0.000,        0.000,        0.000,        0.000,            0, Database block store
```
2021-01-25 13:04:18 +01:00
tersec d5e3712609
log errors in more detail when block production fails (#2135)
* log errors in more detail when block production fails

* pass through block header error

* make everything cstring
2020-12-02 13:23:10 +01:00
Jacek Sieka e7f2735271
fix broken metrics during replay (#2090)
* move metrics out of state transition
* add validator count metric
* remove expensive beacon_current_validators, beacon_previous_validators
metrics (they should be reimplemented with cache), add cheap
beacon_active_validators to approximate
* remove unused validator count metrics
* tidy imports/defects
2020-11-27 23:16:13 +01:00
tersec b9e122a60c
address some TODOs (#2005) 2020-11-12 19:24:07 +00:00
tersec 271df8b604
bump 1.0.0rc-0 spec refs to 1.0.0 (#1974) 2020-11-09 14:18:55 +00:00
Jacek Sieka 95f5f76180
Datatype cleanup (#1953)
* clear up spec todo

* test fix

* remove unnecessary toSszType

* type

* one more
2020-11-04 21:52:47 +00:00
Jacek Sieka 6b9419e547
fix db growth on attestation processing (#1860)
It turns out that we often save lots of states in the database that are
the result of empty slot processing only - here, we make sure to only
save a state if a block follows - this fixes several issues:

* empty slot states are not always pruned leading to state database size
explosion
* storing states is (very) slow which slows down processing in general,
so we should only do it when it's likely to be useful
* attestation processing doesn't get stuck on saving random states that
won't appear in the chain history
2020-10-15 14:28:44 +02:00
tersec 1994ffe5a0
update 130+ spec references from v0.12.3 to v1.0.0-rc1 (#1854) 2020-10-12 08:59:24 +00:00
tersec f08f44b9a2
in exit pool, bundle receive messages into beaconblocks (#1812)
* in exit pool, filter out already-packaged messages; bundle remaining messages into beaconblocks

* filter messages at block construction time

* allow adding up to intended capacity of buffers, beyond per-block limits

* document rationale/design for filtering mechanism
2020-10-07 16:57:21 +00:00
tersec 6398a43cc1
update 120+ beacon_chain and validator spec refs from v0.12.2 to v0.12.3 (#1740) 2020-09-24 19:04:10 +02:00
tersec d0de1a49a3
Fix some warnings and hints and partly revert #1610 (#1615)
* address some XDeclaredButNotUsed, ConvFromXtoItselfNotNeeded, and UnusedImport hints and warnings

* partly revert #1610
2020-09-08 11:32:43 +00:00
tersec 3d5f24f14c
stop discarding future epochs; remove a StateCache() construction (#1610)
* stop discarding non-existent future epochs during epoch state transitions; remove a pointless StateCache() construction in advance_slots()

* update nbench to pass StateCache to process_slots()
2020-09-07 15:04:33 +00:00
Jacek Sieka 46c94a18ba rework epoch cache referencing
* collect all epochrefs in specific blocks to make them easier to find
and to avoid lots of small seqs
* reuse validator key databases more aggressively by comparing keys
* make state cache available from within `withState`
* make epochRef available from within onBlockAdded callback
* integrate getEpochInfo into block resolution and epoch ref logic such
that epochrefs are created when blocks are added to pool or lazily when
needed by a getEpochRef
* fill state cache better from EpochRef, speeding up replay and
validation
* store epochRef in specific blocks to make them easier to find and
reuse
* fix database corruption when state is saved while replaying quarantine
* replay slots fully from block pool before processing state
* compare bls values more smartly
* store epoch state without block applied in database - it's recommended
to resync the node!

this branch will drastically speed up processing in times of long
non-finality, as well as cut memory usage by 10x during the recent
medalla madness.
2020-08-19 10:09:06 +03:00
tersec e0a6f58abe
convert 10 v0.12.1 spec refs to v0.12.2 (#1406) 2020-07-31 09:59:14 +00:00
Viktor Kirilov c032366547
removed the BlockPool type and all of the proxy functions around it (#1401)
* removed the BlockPool type and all of the proxy functions around it - passing the chain DAG and the quarantine explicitly where appropriately - they don't need to be bundled in a type

* fixed the build after the rebase
2020-07-30 21:18:17 +02:00
tersec dad3dd5809
update 111 v0.12.1 beacon chain spec refs to v0.12.2 (#1380) 2020-07-27 18:49:46 +02:00
Jacek Sieka 48cebc7157
spec cleanups (#1379)
* add helper for beacon committee length (used for quickly validating
attestations)
* refactor some attestation checks to do cheap checks early
* validate attestation epoch before computing active validator set
* clean up documentation / comments
* fill state cache on demand
2020-07-27 16:04:44 +00:00
tersec 90708a8287
Prefer converting int` to uint64 and switch foo.len.uint64 to .len64 (#1375)
* avoid converting from uint64 to int, and where most feasible, int type conversion at all

* .len.uint64 -> .len64

* fix 32-bit compilation

* try keeping state_sim loop variable/bounds as int for 32-bit Azure

* len64 -> lenu64
2020-07-26 20:55:48 +02:00
Jacek Sieka fb2f742972
Fork choice fixes 2 (#1356)
* fork choice cleanup

* enable v2 pruning
* prefer `get_current_epoch`
* fix finalization check to use correct epoch

* small cleanups

* add `count_active_validators`
* remove misleading logs
* fix justified checkpoint slot calculation in rpc
2020-07-22 23:01:44 +02:00
Jacek Sieka 8b01284b0e
cache block hash (#1329)
hash_tree_root was turning up when running beacon_node, turns out to be
repeated hash_tree_root invocations - this pr brings them back down to
normal.

this PR caches the root of a block in the SignedBeaconBlock object -
this has the potential downside that even invalid blocks will be hashed
(as part of deserialization) - later, one could imagine delaying this
until checks have passed

there's also some cleanup of the `cat=` logs which were applied randomly
and haphazardly, and to a large degree are duplicated by other
information in the log statements - in particular, topics fulfill the
same role
2020-07-16 15:16:51 +02:00
tersec 26e893ffc2
restore EpochRef and flush statecaches on epoch transitions (#1312)
* restore EpochRef and flush statecaches on epoch transitions

* more targeted cache invalidation

* remove get_empty_per_epoch_cache(); implement simpler but still faster get_beacon_proposer_index()/compute_proposer_index() approach; add some abstraction layer for accessing the shuffled validator indices cache

* reduce integer type conversions

* remove most of rest of integer type conversion in compute_proposer_index()
2020-07-15 12:44:18 +02:00
zah 0be77f9cbc
Restore compilation with custom presets (#1309)
This also assigns precise types to the constants in the minimal
and mainnet presets in order to reduce the chance of compilation
errors when custom presets are used (previously, only the custom
presets have precisely assigned types for the constants).
2020-07-13 16:44:58 +02:00
Zahary Karadjov 93b04bc214 Add an option for graffiti customization 2020-07-12 21:01:31 +03:00
tersec 853bd5b799
quick workaround for epochref cache issue (#1296)
* quick workaround for epochref cache issue

* disable assertion which doesn't work without epochref caches

* get local testnets and altona running again
2020-07-12 17:09:49 +02:00
Jacek Sieka d6f317950c
Compute state root instead of loading from database (#1297)
htr is fast now, so hitting the database to load the state root is no
longer motivated - the more simple code is less vulnerable to database
corruption.
2020-07-10 22:47:39 +02:00
Zahary Karadjov 3ec6a02b12
Merge devel and resolve conflicts 2020-07-10 02:02:40 +03:00
tersec 61b0b5af17
update most remaining non-fork-choice spec refs, updating code where necessary (#1292)
* update most of the remaining non-fork-choice spec refs, updating code where necessary

* revert presumably harmless compute_signing_root() change, but this way, keep things really unchanged outside inspector
2020-07-09 11:43:27 +00:00
Zahary Karadjov c4af4e2f35
Working test suite with run-time presets 2020-07-08 02:02:14 +03:00
Jacek Sieka 1301600341
Trusted blocks (#1227)
* cleanups

* fix ncli state root check flag
* add block dump to ncli_db
* limit ncli_db benchmark length
* tone down finalization logs

* introduce trusted blocks

We only store blocks whose signature we've verified in the database - as
such, there's no need to check it again, and most importantly, no need
to deserialize the signature when loading from database.

50x startup time improvement, 200x block load time improvement.

* fix rewinding when deposits have invalid signature
* speed up ancestor iteration by avoiding copy
* avoid deserializing signatures for trusted data
* load blocks lazily when rewinding (less memory used)

* chronicles workarounds

* document trustedbeaconblock
2020-06-25 12:23:10 +02:00
tersec 807b920c19
state_transition implements the spec fairly directly (#1220) 2020-06-23 13:54:24 +00:00