XChain VM — Configuration Reference

Constructor Parameters

The VM is configured at instantiation via a single config object:

const vm = new XChainVM({
    gasSchedule: config['GAS_SCHEDULE'],
    gasCeiling:  1000000,
    limits: {
        maxCpuTimeMs:      30000,
        maxMemory:         8,
        maxEmissions:      50,
        maxStateKeys:      10000,
        maxStateValueSize: 65536,
        maxCodeSize:       65536,
        maxStateKeySize:   1024,
        maxBlockCacheSize: 1000
    }
});

Parameter	Type	Default	Description
`gasSchedule`	object	(required)	Per-operation gas costs (see Gas Schedule below)
`gasCeiling`	number	`1000000`	Maximum gas allowed per single contract execution
`limits`	object	(see below)	Resource limits for isolate execution

The VM has no environment variables, configuration files, or runtime reconfiguration. All settings are fixed at construction time by the indexer.

Gas Schedule

The gas schedule defines the cost of each metered operation. These values are set by the indexer’s unified gas fee configuration and passed to the VM at construction.

Operation	Key	Cost	Description
Computation	`VM_COMPUTATION`	1	Charged at each `__gas()` injection point (loop iterations, branches, function calls). Indexed `for` loops are charged twice per iteration — see note below
State read	`VM_STATE_READ`	100	`state.get()`, `state.has()`, `getBalance()`, `getTokenInfo()`, `attestation.getResponse()`, `contract.getStake()`, `contract.getTotalStaked()`, `contract.getStakers()`
State write	`VM_STATE_WRITE`	200	`state.set()`
State delete	`VM_STATE_DELETE`	100	`state.delete()`
Oracle read	`VM_ORACLE_READ`	100	`oracle.getPrice()`, `oracle.getPriceAtRound()`
Cross-chain read	`VM_CROSSCHAIN_READ`	100	`crossChain.getAttestation()`, `crossChain.isSettled()`, `crossChain.getCallResult()`
Action emission	`VM_EMISSION`	500	Each `emit.*()` call (SEND, MINT, ORDER, etc.); also charged on `attestation.request()` and `contract.slash()`
Attestation request	`VM_ATTEST_REQUEST`	5000	Additional fee on top of `VM_EMISSION` for `attestation.request()` — reflects the validator-network work that backs the eventual response
Cross-chain call request	`VM_XCALL_REQUEST`	2000	Additional fee on top of `VM_EMISSION` for `emit.crossExecute()` — the federation relay work. The call also pre-pays its remote `gasLimit` plus `VM_XCALL_CALLBACK`, with no refund of unused remote gas
Cross-chain callback ceiling	`VM_XCALL_CALLBACK`	20000	Fixed gas ceiling the result/expiry callback runs against on the source chain, pre-paid at `emit.crossExecute()` time

Context accessors (getBlockHeight, getSourceAddress, etc.), control flow (revert, require), and logging (log, isLogFull, getLogCount) are gas-free. oracle.getSnapshotAge() is also gas-free.

Indexed for loops cost 2 × VM_COMPUTATION per iteration. The metering transform injects a charge at the top of the loop body and a second charge into the update expression — for (…; i++) is rewritten as for (…; (__gas(1), i++)) — so each iteration is metered twice. A for loop of N iterations therefore costs 2 × N × VM_COMPUTATION. while, do-while, for-in, and for-of loops have no update expression and cost 1 × VM_COMPUTATION per iteration. Budget gas ceilings for indexed for loops accordingly.

Resource Limits

Parameter	Key	Default	Description
Gas ceiling	`gasCeiling`	1,000,000	Maximum gas per execution. Primary execution bound.
CPU timeout	`maxCpuTimeMs`	30,000 ms	Wall-clock timeout (safety net only — should never trigger under normal operation)
Memory	`maxMemory`	8 MB	V8 isolate heap size limit. Exceeding triggers `out_of_memory` error.
Emissions	`maxEmissions`	50	Maximum platform actions a contract can emit per execution
State keys	`maxStateKeys`	10,000	Maximum key-value pairs a contract can store
State value size	`maxStateValueSize`	65,536 bytes	Maximum size of a single state value (JSON-serialized)
State key size	`maxStateKeySize`	1,024 bytes	Maximum size of a single state key (UTF-8 encoded)
Code size	`maxCodeSize`	65,536 bytes	Maximum contract source code size (enforced at both deploy and execute)
Block cache size	`maxBlockCacheSize`	1,000 entries	Maximum compiled script entries cached per block

Additional Internal Limits

These limits are hardcoded in the VM and not configurable:

Limit	Value	Location
Log entries per execution	100	`collector.js`
Log entry size	1,024 bytes UTF-8 (truncated with `...(truncated)` marker)	`collector.js`
Return value size	65,536 bytes (truncated)	`index.js`
Throwaway isolate memory	8 MB	`isolate.js`, `syntax.js`
Binary expression metering depth	10	`metering.js`

Bounded Execution Summary

Resource	Limit	Enforcement
Gas	1,000,000 per execution	`GasTracker` throws `GasExhaustedError`
Memory	8 MB per isolate	`isolated-vm` kills isolate
Wall-clock time	30 seconds	`script.runSync()` timeout parameter
Emitted actions	50 per execution	`EmissionCollector` throws on overflow
State keys	10,000 per contract	`StateManager.set()` throws on overflow
State key size	1 KB per key	`StateManager.set()` / `delete()` throws on overflow
State value size	64 KB per value	`StateManager.set()` throws on overflow
Code size	64 KB per contract	Validated at deploy time and enforced at execution
Block cache	1,000 entries per block	Excess entries skip cache (non-fatal)
Log entries	100 per execution	`EmissionCollector.addLog()` silently drops

Gas is the primary execution bound. The wall-clock timeout exists only as a safety net for gas metering bugs — it should never trigger under normal operation.

Based on XChain Platform by Dankest, LLC – https://dankest.llc

Licensed under the GNU Affero General Public License v3.0 (AGPL-3.0-or-later) with a commercial license available for proprietary use.

You may use, modify, and distribute this material under the terms of the License. See LICENSE and NOTICE for full terms. See the licensing overview.