proposervm

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 Go to latest Published: Jul 28, 2026 License: BSD-3-Clause Imports: 42 Imported by: 1

README

Linear++: congestion control for Linear VMs

Linear++ is a congestion control mechanism available for linear VMs. Linear++ can be activated on any linear VM with no modifications to the VM internals. It is sufficient to wrap the target VM with a wrapper VM called proposerVM and to specify an activation time for the congestion-control mechanism. In this document we describe the high level features of Linear++ and the implementation details of the proposerVM.

Congestion control mechanism description

Linear++ introduces a soft proposer mechanism which attempts to select a single proposer with the power to issue a block, but opens up block production to every validator if sufficient time has passed without blocks being generated.

At a high level, Linear++ works as follows: for each block a small list of validators is randomly sampled, which will act as "proposers" for the next block. Each proposer is assigned a submission window: a proposer cannot submit its block before its submission window starts (the block would be deemed invalid), but it can submit its block after its submission window expires, competing with next proposers. If no block is produced by the proposers in their submission windows, any validator will be free to propose a block, as happens for ordinary linear VMs.

In the following we detail the block extensions, the proposers selection, and the validations introduced for Linear++.

Linear++ block extension

Linear++ does not modify the blocks produced by the VM it is applied to. It extends these blocks with a header carrying the information needed to control block congestion.

A standard block header contains the following fields:

  • ParentID, the ID of the parent's enriched block (Note: this is different from the inner block ID).
  • Timestamp, the local time at block production.
  • PChainHeight the height of the last accepted block on the P-chain at the time the block is produced.
  • Certificate the TLS certificate of the block producer, to verify the block signature.
  • Signature the signature attesting this block was proposed by the correct block producer.

An Option block header contains the field:

  • ParentID the ID of the Oracle block to which the Option block is associated.

Option blocks are not signed, as they are deterministically generated from their Oracle block.

Linear++ proposers selection mechanism

For a given block, Linear++ randomly selects a list of proposers. Block proposers are selected from the net's validators. Linear++ extracts the list of a given net's validators from the P-Chain. Let a block have a height H and P-Chain height P recorded in its header. The proposers list for next block is generated independently but reproducibly by each node as follows:

  • Net validators active at block P are retrieved from P-chain.
  • Validators are canonically sorted by their nodeID.
  • A seed S is generated by xoring H and the chainID. The chainID inclusion makes sure that different seeds sequences are generated for different chains.
  • Validators are pseudo-randomly sampled without replacement by weight, seeded by S.
  • maxWindows number of net validators are retrieved in order from the sampled set. maxWindows is currently set to 6.
  • The maxWindows validators are the next block's proposer list.

Each proposer gets assigned a submission window of length WindowDuration. currently set at 5 seconds. A proposer in position i in the proposers list has its submission windows starting i × WindowDuration after the parent block's timestamp. Any node can issue a block maxWindows × WindowDuration after the parent block's timestamp.

Linear++ validations

The following validation rules are enforced:

  • Given a proposervm.Block C and its parent block P, P's inner block must be C's inner block's parent.
  • A block must have a PChainHeight that is larger or equal to its parent's PChainHeight (PChainHeight is monotonic).
  • A block must have a PChainHeight that is less or equal to current P-Chain height.
  • A block must have a Timestamp larger or equal to its parent's Timestamp (Timestamp is monotonic)
  • A block received by a node at time t_local must have a Timestamp such that Timestamp < t_local + maxSkew (a block too far in the future is invalid). maxSkew is currently set to 10 seconds.
  • A block issued by a proposer p which has a position i in the current proposer list must have its timestamp at least i × WindowDuration seconds after its parent block's Timestamp. A block issued by a validator not contained in the first maxWindows positions in the proposal list must have its timestamp at least maxWindows × WindowDuration seconds after its parent block's Timestamp.
  • A block issued within a time window must have a valid Signature, i.e. the signature must be verified to have been by the proposer Certificate included in block header.
  • A proposervm.Block's inner block must be valid.

A proposervm.Block violating any of these rules will be marked as invalid. Note, however, that a proposervm.Block invalidity does not imply its inner block invalidity. Notably the validation rules above enforce the following invariants:

  • Only one verification attempt will be issued to a valid inner block. On the contrary multiple verification calls can be issued to invalid inner blocks.
  • Rejection of a proposervm.Block does not entail rejection of inner block it wraps. This is necessary since different proposervm.Blocks can wrap the same inner block. Without proper handling this could result in an inner block being accepted after being rejected. Therefore, an inner block is only rejected when a sibling block is being accepted.

ProposerVM Implementation Details

Linear++ must have an activation time, following which the congestion control mechanism will be enforced.

Block Structure

Generally speaking the proposerVM wraps an inner block generated by the inner VM into a proposervm.Block. Once the activation time has past, the proposervm.Block will attach a header to inner block, carrying all the fields necessary to implement the congestion mechanism. No changes are performed on the inner block, but the inclusion of the header does change the block ID and the serialized version of the block.

There are three kinds of proposervm.Blocks:

  • preForkBlock is a simple wrapper of an inner block. A preForkBlock does not change the ID or serialization of an inner block; it's simply an in-memory object allowing correct verification of preForkBlocks (see Execution modes section below for further details of why this is required).
  • postForkBlock adds congestion-control related fields to an inner block, resulting in a different ID and serialization than the inner block. Note that for such blocks, serialization is a two-step process: the header is serialized at the proposerVM level, while the inner block serialization is deferred to the inner VM.
  • postForkOption wraps inner blocks that are associated with an Oracle Block. This enables oracle blocks to be issued without enforcing the congestion control mechanism. Similarly to postForkBlocks, this changes the block's ID and serialization.
Execution modes

When creating a proposerVM, one must specify an activation time following which the congestion control mechanism will be enforced. Therefore, the proposerVM must be able to execute before the mechanism is enforced, after the mechanism is enforced, and during the enabling of the mechanism.

Pre-fork Execution

Before the congestion control mechanism is enforced, it must hold that the chain's rules are unchanged.

  • preForkBlocks are the only blocks that are able to be verified successfully.
Post-fork Execution

After the congestion control mechanism is enforced, it must hold that the inner VM's rules are still enforced, and that blocks will only be verified if they are signed by the correct validator.

  • If an inner block's Verify is called, then it is enforced that the proposervm.Blocks additional verification must have already passed. This maintains the invariant that when Verify passes, either Accept or Reject will eventually be called on the block.
  • Given a parent block, there must be one deterministic proposer window for every child block. This ensures that modifying the child block doesn't allow conflicting proposal windows.
  • The proposal windows should rotate after each block, to avoid a single proposer from dominating the block production.
  • postForkBlocks are issued only when the local node's ID is currently in their proposal window.
  • postForkOptions are only allowed after a postForkBlock that implements Options and do not require signatures.
Fork Transition Execution
  • Each proposervm.Block whose timestamp follows the activation time, must have its children made up of postForkBlocks or postForkOptions.

Documentation

Overview

height_backfill.go — RECOVERY for a proposervm finality index that sits BELOW the inner VM's accepted tip.

THE INVARIANT. Every post-fork accept commits the outer envelope, its height index entry and the last-accepted pointer in ONE versiondb batch BEFORE the inner block is accepted (vm.acceptPostForkBlock → postForkBlock.Accept), so the proposervm index can only ever be AHEAD of the inner VM, never behind.

HOW IT BREAKS ANYWAY. The proposervm has one accept path that advances the inner VM while leaving the outer index untouched: preForkBlock.Accept, whose acceptOuterBlk() is a no-op by construction. Post-fork that path was reachable because BOTH of the proposervm's block constructors fall back to it silently — ParseBlock() falls back to parsePreForkBlock when the outer envelope does not parse, and getBlock() falls back to getPreForkBlock when the id is not an outer id (which is exactly what the CANONICAL id recorded by the consensus ledger is: postForkCommonComponents.CanonicalID() == innerBlk.ID()). Either fallback hands the engine a preForkBlock wrapping a post-fork inner block; accepting it moves the inner VM and NOT the index. Nothing complained, because nothing asserted the invariant at the moment it was violated — it was only ever checked at the NEXT boot, by which point the node could not start. That is why the lag looked like a mysterious "persistence" problem: the writes were never issued at all.

The prevention half lives at the two fallbacks + preForkBlock.acceptOuterBlk (see pre_fork_block.go and vm.getPreForkBlock): post-fork, a pre-fork block is never constructed and never accepted.

THE RECOVERY half lives here, and it must work for nodes that are ALREADY damaged. It is two escalating steps, both OUTER-ONLY — they never re-execute, re-verify or re-accept an inner block, so a node whose EVM is already at the tip is repaired without touching the EVM:

  1. rebuildOuterIndexFromStore: re-derive the height index and last-accepted pointer from the outer envelopes ALREADY in this node's block store, binding each candidate to the inner block this node itself accepted at that height. Fully local, no network, no operator. This is what turns "refuses to start" into "starts, repairs itself, and keeps its finality pointer".

  2. If step 1 cannot reach the inner tip, the node still STARTS, in an explicit backfill-pending state: loud, fail-safe (it will not BUILD a block while its finality index is incomplete) and repairable through BackfillOuterBlock, which accepts the missing envelopes from any source and applies the SAME binding checks. The alternative — the previous behaviour — was a dead C-Chain and a destructive resync.

WHAT IS NEVER DONE, and why: the finality pointer is never dropped (DeleteLastAccepted). proposervm.LastAccepted would then fall back to an INNER-namespace id whose ParentID is contiguity-incompatible with the network's OUTER wrappers, permanently wedging bootstrap, catch-up and live Verify at the inner tip — a silent wedge strictly worse than the loud stop it would replace. Every path below only ever moves the pointer FORWARD, onto an envelope that was proven to wrap the inner block this node already accepted at that height.

Package proposervm is a generated GoMock package.

Index

Constants

View Source 
const (
	// DefaultMinBlockDelay should be kept as whole seconds because block
	// timestamps are only specific to the second.
	DefaultMinBlockDelay = time.Second
	// DefaultNumHistoricalBlocks as 0 results in never deleting any historical
	// blocks.
	DefaultNumHistoricalBlocks uint64 = 0
)

Variables

View Source 
var (
	// ErrOuterBackfillNotPending is returned by BackfillOuterBlock when the index
	// is already whole — the repair is idempotent, not an error to call twice.
	ErrOuterBackfillNotPending = errors.New("proposervm: no outer-index backfill is pending")

	// ErrOuterBackfillRejected is returned when a candidate envelope does not bind
	// to this node's own accepted chain. Fail-closed: an envelope is only indexed
	// when it provably wraps the inner block WE accepted at that height and chains
	// off the envelope WE already hold at height-1, so a peer (or a stale file)
	// cannot steer the finality pointer.
	ErrOuterBackfillRejected = errors.New("proposervm: outer backfill candidate rejected")
)

Functions

func NewHTTPHandler added in v1.16.56 

func NewHTTPHandler(vm *VM) (http.Handler, error)

NewHTTPHandler returns an HTTP handler to serve proposervm API endpoints

Types

type Block 

type Block interface {
	chain.Block
	// contains filtered or unexported methods
}

type Config 

type Config struct {
	Upgrades upgrade.Config

	// NetworkID is the validator-set ID the proposer windower resolves the
	// schedule under — it MUST be the SAME ID the consensus cert side uses
	// (manager.go resolves it once: PrimaryNetworkID for native chains,
	// otherwise the L1's own chainID, falling back to primary only if that set is
	// empty). CRITICAL-3: hardcoding PrimaryNetworkID here made the windower call
	// GetValidatorSet(height, PrimaryNetworkID) on a sovereign L1 (Zoo/Hanzo/Pars,
	// whose validators live under their OWN networkID == EVM chainID), get an
	// EMPTY set, and degrade to ErrAnyoneCanPropose — so single-proposer silently
	// did not hold and the L1 equivocated exactly like the unfixed C-Chain, AND
	// the windower's set diverged from the cert's set (breaking determinism). The
	// zero value (ids.Empty) IS constants.PrimaryNetworkID, so a native chain that
	// resolves to primary is unchanged.
	NetworkID ids.ID

	// Configurable minimal delay among blocks issued consecutively
	MinBlkDelay time.Duration

	// ProposerWindowDuration overrides the proposer-slot spacing (proposer.
	// WindowDuration). Zero keeps the 5s mainnet default; small local/dev nets set
	// it low (e.g. 1s or less) so block cadence is not floored at 5s per proposer
	// slot. Applied once at VM init via proposer.SetWindowDuration.
	ProposerWindowDuration time.Duration

	// Maximal number of block indexed.
	// Zero signals all blocks are indexed.
	NumHistoricalBlocks uint64

	// Block signer
	StakingLeafSigner crypto.Signer

	// Block certificate
	StakingCertLeaf *staking.Certificate

	// Strict-PQ block signer. When StakingMLDSASigner is non-nil the proposer
	// signs post-fork blocks with ML-DSA-65 and stamps the block's proposer
	// identity as the raw ML-DSA-65 public key, so Proposer() derives via
	// DeriveMLDSA and EQUALS the strict-PQ NodeID the windower elected (the
	// validator set is ML-DSA-keyed under strict-PQ). Nil ⇒ classical TLS-leaf
	// signing above. Exactly one of the two schemes is active per chain, chosen at
	// wiring time from the resolved ChainSecurityProfile.
	StakingMLDSASigner *mldsa.PrivateKey
	StakingMLDSAPub    []byte

	// Registerer for metric metrics
	Registerer metric.Registerer

	// Automining configuration
	AutominingEnabled bool
	// AutominingInterval is the interval between automatic block production
	AutominingInterval time.Duration
}

type GetProposedHeightArgs added in v1.16.56 

type GetProposedHeightArgs struct{}

GetProposedHeightArgs are the arguments for GetProposedHeight

type GetProposedHeightReply added in v1.16.56 

type GetProposedHeightReply struct {
	// ProposedHeight is the P-Chain height that would be proposed
	// for the next block built on the current preferred block
	ProposedHeight uint64 `json:"proposedHeight"`
}

GetProposedHeightReply is the response from GetProposedHeight

type MockPostForkBlock added in v1.1.11 

type MockPostForkBlock struct {
	// contains filtered or unexported fields
}

MockPostForkBlock is a mock of PostForkBlock interface.

func NewMockPostForkBlock added in v1.1.11 

func NewMockPostForkBlock(ctrl *gomock.Controller) *MockPostForkBlock

NewMockPostForkBlock creates a new mock instance.

func (*MockPostForkBlock) Accept added in v1.1.11 

func (m *MockPostForkBlock) Accept(arg0 context.Context) error

Accept mocks base method.

func (*MockPostForkBlock) Bytes added in v1.1.11 

func (m *MockPostForkBlock) Bytes() []byte

Bytes mocks base method.

func (*MockPostForkBlock) EXPECT added in v1.1.11 

func (m *MockPostForkBlock) EXPECT() *MockPostForkBlockMockRecorder

EXPECT returns an object that allows the caller to indicate expected use.

func (*MockPostForkBlock) Height added in v1.1.11 

func (m *MockPostForkBlock) Height() uint64

Height mocks base method.

func (*MockPostForkBlock) ID added in v1.1.11 

func (m *MockPostForkBlock) ID() ids.ID

ID mocks base method.

func (*MockPostForkBlock) Parent added in v1.1.11 

func (m *MockPostForkBlock) Parent() ids.ID

Parent mocks base method.

func (*MockPostForkBlock) Reject added in v1.1.11 

func (m *MockPostForkBlock) Reject(arg0 context.Context) error

Reject mocks base method.

func (*MockPostForkBlock) Status added in v1.1.11 

func (m *MockPostForkBlock) Status() choices.Status

Status mocks base method.

func (*MockPostForkBlock) Timestamp added in v1.1.11 

func (m *MockPostForkBlock) Timestamp() time.Time

Timestamp mocks base method.

func (*MockPostForkBlock) Verify added in v1.1.11 

func (m *MockPostForkBlock) Verify(arg0 context.Context) error

Verify mocks base method.

type MockPostForkBlockMockRecorder added in v1.1.11 

type MockPostForkBlockMockRecorder struct {
	// contains filtered or unexported fields
}

MockPostForkBlockMockRecorder is the mock recorder for MockPostForkBlock.

func (*MockPostForkBlockMockRecorder) Accept added in v1.1.11 

func (mr *MockPostForkBlockMockRecorder) Accept(arg0 any) *gomock.Call

Accept indicates an expected call of Accept.

func (*MockPostForkBlockMockRecorder) Bytes added in v1.1.11 

func (mr *MockPostForkBlockMockRecorder) Bytes() *gomock.Call

Bytes indicates an expected call of Bytes.

func (*MockPostForkBlockMockRecorder) Height added in v1.1.11 

func (mr *MockPostForkBlockMockRecorder) Height() *gomock.Call

Height indicates an expected call of Height.

func (*MockPostForkBlockMockRecorder) ID added in v1.1.11 

func (mr *MockPostForkBlockMockRecorder) ID() *gomock.Call

ID indicates an expected call of ID.

func (*MockPostForkBlockMockRecorder) Parent added in v1.1.11 

func (mr *MockPostForkBlockMockRecorder) Parent() *gomock.Call

Parent indicates an expected call of Parent.

func (*MockPostForkBlockMockRecorder) Reject added in v1.1.11 

func (mr *MockPostForkBlockMockRecorder) Reject(arg0 any) *gomock.Call

Reject indicates an expected call of Reject.

func (*MockPostForkBlockMockRecorder) Status added in v1.1.11 

func (mr *MockPostForkBlockMockRecorder) Status() *gomock.Call

Status indicates an expected call of Status.

func (*MockPostForkBlockMockRecorder) Timestamp added in v1.1.11 

func (mr *MockPostForkBlockMockRecorder) Timestamp() *gomock.Call

Timestamp indicates an expected call of Timestamp.

func (*MockPostForkBlockMockRecorder) Verify added in v1.1.11 

func (mr *MockPostForkBlockMockRecorder) Verify(arg0 any) *gomock.Call

Verify indicates an expected call of Verify.

type OracleBlock added in v1.16.56 

type OracleBlock interface {
	chain.Block
	Options(context.Context) ([2]chain.Block, error)
}

OracleBlock is a block that can return multiple child options

type PostForkBlock 

type PostForkBlock interface {
	Block
	// contains filtered or unexported methods
}

type Service added in v1.16.56 

type Service struct {
	// contains filtered or unexported fields
}

Service wraps proposervm for RPC/JSON-RPC access

func (*Service) GetProposedHeight added in v1.16.56 

func (s *Service) GetProposedHeight(r *http.Request, _ *GetProposedHeightArgs, reply *GetProposedHeightReply) error

GetProposedHeight returns the P-Chain height that would be proposed for the next block built on the current preferred block.

Example JSON-RPC call: 

curl -X POST --data '{
    "jsonrpc":"2.0",
    "id"     :1,
    "method" :"proposervm.getProposedHeight",
    "params" :{}
}' -H 'content-type:application/json;' http://127.0.0.1:9650/v1/bc/C/rpc

type VM 

type VM struct {
	vmchain.ChainVM
	Config

	state.State

	proposer.Windower
	tree.Tree
	mockable.Clock
	// contains filtered or unexported fields
}

func New 

func New(
	vm vmchain.ChainVM,
	config Config,
) *VM

New performs best when [minBlkDelay] is whole seconds. This is because block timestamps are only specific to the second.

func (*VM) BackfillOuterBlock added in v1.36.32 

func (vm *VM) BackfillOuterBlock(ctx context.Context, outerBytes []byte) error

BackfillOuterBlock supplies ONE missing outer envelope, oldest-first, and is the operator/driver half of the recovery. It is fail-closed and idempotent:

  • not pending -> ErrOuterBackfillNotPending
  • envelope below the next height -> nil (already indexed; tolerate replay)
  • signature/format invalid -> error (parsed WITH verification)
  • not the next height, wrong parent, or wrapping a different inner block-> ErrOuterBackfillRejected

On the final height it clears the pending state and refreshes the in-memory last-accepted metadata, after which the chain behaves exactly like one that booted whole.

func (*VM) BatchedParseBlock 

func (vm *VM) BatchedParseBlock(ctx context.Context, blks [][]byte) ([]chain.Block, error)

func (*VM) BuildBlock 

func (vm *VM) BuildBlock(ctx context.Context) (vmchain.Block, error)

func (*VM) Commit added in v1.1.11 

func (vm *VM) Commit() error

func (*VM) CreateHandlers added in v1.16.56 

func (vm *VM) CreateHandlers(ctx context.Context) (map[string]http.Handler, error)

CreateHandlers returns HTTP handlers for both the proposervm API and the inner ChainVM

func (*VM) GetAncestors 

func (vm *VM) GetAncestors(
	ctx context.Context,
	blkID ids.ID,
	maxBlocksNum int,
	maxBlocksSize int,
	maxBlocksRetrievalTime time.Duration,
) ([][]byte, error)

func (*VM) GetBlock 

func (vm *VM) GetBlock(ctx context.Context, id ids.ID) (vmchain.Block, error)

func (*VM) GetBlockIDAtHeight 

func (vm *VM) GetBlockIDAtHeight(ctx context.Context, height uint64) (ids.ID, error)

vm.lock should be held

func (*VM) GetFullPostForkBlock added in v1.1.11 

func (vm *VM) GetFullPostForkBlock(ctx context.Context, blkID ids.ID) (chain.Block, error)

Note: this is a contention heavy call that should be avoided for frequent/repeated indexer ops

func (*VM) GetLastStateSummary 

func (vm *VM) GetLastStateSummary(ctx context.Context) (chain.StateSummary, error)

func (*VM) GetOngoingSyncStateSummary 

func (vm *VM) GetOngoingSyncStateSummary(ctx context.Context) (chain.StateSummary, error)

func (*VM) GetStateSummary 

func (vm *VM) GetStateSummary(ctx context.Context, height uint64) (chain.StateSummary, error)

func (*VM) Initialize 

func (vm *VM) Initialize(
	ctx context.Context,
	init vmcore.Init,
) error

func (*VM) LastAccepted 

func (vm *VM) LastAccepted(ctx context.Context) (ids.ID, error)

func (*VM) NeedsOuterBackfill added in v1.36.32 

func (vm *VM) NeedsOuterBackfill() (from uint64, to uint64, pending bool)

NeedsOuterBackfill reports the still-missing outer height range [from, to] and whether a backfill is pending. It is the seam an operator tool or a node-layer fetch driver reads; when pending is false the index is whole.

func (*VM) ParseBlock 

func (vm *VM) ParseBlock(ctx context.Context, b []byte) (vmchain.Block, error)

func (*VM) ParseLocalBlock 

func (vm *VM) ParseLocalBlock(ctx context.Context, b []byte) (vmchain.Block, error)

func (*VM) ParseStateSummary 

func (vm *VM) ParseStateSummary(ctx context.Context, summaryBytes []byte) (chain.StateSummary, error)

Note: it's important that ParseStateSummary do not use any index or state to allow summaries being parsed also by freshly started node with no previous state.

func (*VM) SetPreference 

func (vm *VM) SetPreference(ctx context.Context, preferred ids.ID) error

func (*VM) SetQuasarGate added in v1.31.0 

func (vm *VM) SetQuasarGate(g *pqfinality.Gate)

SetQuasarGate installs the post-quantum finality gate. Called once at chain wiring time when PQ-finality config is present; left unset (nil) otherwise so the accept path stays classical. Idempotent, set before consensus starts.

func (*VM) SetState 

func (vm *VM) SetState(ctx context.Context, newState uint32) error

func (*VM) Shutdown 

func (vm *VM) Shutdown(ctx context.Context) error

Shutdown ops then propagate shutdown to innerVM

func (*VM) StateSyncEnabled 

func (vm *VM) StateSyncEnabled(ctx context.Context) (bool, error)

func (*VM) WaitForEvent 

func (vm *VM) WaitForEvent(ctx context.Context) (vmcore.Message, error)

Source Files

View all Source files

Directories

Path Synopsis
LP181 implements the epoch logic specified here: https://github.com/luxfi/LPs/blob/main/LPs/181-p-chain-epoched-views/README.md
 LP181 implements the epoch logic specified here: https://github.com/luxfi/LPs/blob/main/LPs/181-p-chain-epoched-views/README.md
Package proposer is a generated GoMock package.
 Package proposer is a generated GoMock package.
proposermock
Package proposermock is a generated GoMock package.
 Package proposermock is a generated GoMock package.
Package scheduler is a generated GoMock package.
 Package scheduler is a generated GoMock package.
schedulermock
Package schedulermock is a generated GoMock package.
 Package schedulermock is a generated GoMock package.
Package state is a generated GoMock package.
 Package state is a generated GoMock package.
statemock
Package statemock is a generated GoMock package.
 Package statemock is a generated GoMock package.

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