persistent_read_without_ttl_extension

Default Severity: warn

Target Resource: Entry Lifecycle — TTL extension cost cliff

What it does

Flags reads (get or has) from env.storage().persistent() in functions where no extend_ttl call is made on the same storage type.

Reads from instance() or temporary() storage are not reported — those storage types have different lifecycle semantics and are not subject to the same archival-cost cliff.

Why is this bad?

DANGER

Persistent storage entries in Soroban have a finite Time-to-Live (TTL). When an entry's TTL expires, the entry is archived and must be restored on the next access — a restoration that costs roughly 3× a normal read in CPU, I/O, and ledger entry write resources.

Reading from persistent storage without extending the TTL means the next contract invocation that touches that key will pay the archival cost. Repeating this pattern across many entries or many ledgers can cause unpredictable fee spikes.

See the Cost Rationale — Entry Lifecycle for details.

Example

use soroban_sdk::{Env, storage::Persistent};

// ❌ Bad: reads persistent storage without extending TTL
fn read_without_ttl(env: Env) {
    let _val: Option<i32> = env.storage().persistent().get(&1);
}

use soroban_sdk::{Env, storage::Persistent};

// ✅ Good: TTL is extended after the read
fn read_with_ttl(env: Env) {
    env.storage().persistent().extend_ttl(&1, &());
    let _val: Option<i32> = env.storage().persistent().get(&1);
}

Suggested Fix

TIP

After reading from persistent storage, call extend_ttl on the same key with an appropriate threshold to keep the entry alive for future invocations.

Known Limitations

• The lint uses a conservative whole-function analysis: if anyextend_ttl call exists on persistent storage anywhere in the function, all persistent-read diagnostics are suppressed. This avoids false positives when the developer is clearly TTL-aware, even if a particular read uses a different key than the extend_ttl call.
• Reads guarded by a has check that handles the archived case are still reported.