telemetry: address timestamp index PR review comments

Author: snormore

smartcontract/programs/doublezero-telemetry/src/processors/telemetry/write_device_latency_samples.rs

@@ -164,10 +164,11 @@ pub fn process_write_device_latency_samples(
         );
     }
 
-    // If a timestamp index account is provided (4th account after
+    // If a timestamp index account is provided (after
     // latency_samples, agent, system_program), append an entry.
-    if accounts.len() > 3 {
-        let timestamp_index_account = &accounts[3];
+    // Skip past system_program in the iterator first.
+    let _ = next_account_info(accounts_iter);
+    if let Ok(timestamp_index_account) = next_account_info(accounts_iter) {
         append_timestamp_index_entry(
             program_id,
             timestamp_index_account,

smartcontract/programs/doublezero-telemetry/src/processors/telemetry/write_internet_latency_samples.rs

@@ -162,10 +162,11 @@ pub fn process_write_internet_latency_samples(
         );
     }
 
-    // If a timestamp index account is provided (4th account after
+    // If a timestamp index account is provided (after
     // latency_samples, agent, system_program), append an entry.
-    if accounts.len() > 3 {
-        let timestamp_index_account = &accounts[3];
+    // Skip past system_program in the iterator first.
+    let _ = next_account_info(accounts_iter);
+    if let Ok(timestamp_index_account) = next_account_info(accounts_iter) {
         append_timestamp_index_entry(
             program_id,
             timestamp_index_account,

smartcontract/programs/doublezero-telemetry/src/state/timestamp_index.rs

@@ -11,7 +11,10 @@ use std::{
 
 /// Maximum number of timestamp index entries per account.
 /// At one entry per write batch (up to 245 samples each), this comfortably
-/// covers a 48-hour epoch. Once full, appends are silently skipped.
+/// covers a 48-hour epoch. The cap prevents unbounded account growth (each
+/// entry is 12 bytes, so 10K entries ≈ 120KB on top of the header). The
+/// resize in the write path grows the account *up to* this limit; once
+/// full, appends are silently skipped so the parent write still succeeds.
 pub const MAX_TIMESTAMP_INDEX_ENTRIES: usize = 10_000;
 
 /// Header size in bytes:

smartcontract/programs/doublezero-telemetry/tests/timestamp_index_tests.rs

@@ -244,65 +244,6 @@ async fn test_write_device_latency_samples_with_timestamp_index() {
     assert_eq!(ts_index.entries[1].timestamp_microseconds, t2);
 }
 
-#[tokio::test]
-async fn test_write_device_latency_samples_without_timestamp_index_still_works() {
-    let mut ledger = LedgerHelper::new().await.unwrap();
-
-    let payer_pubkey = ledger
-        .context
-        .lock()
-        .unwrap()
-        .payer
-        .insecure_clone()
-        .pubkey();
-    let contributor_pk = ledger
-        .serviceability
-        .create_contributor("CONTRIB".to_string(), payer_pubkey)
-        .await
-        .unwrap();
-
-    let (agent, origin_device_pk, target_device_pk, link_pk) = ledger
-        .seed_with_two_linked_devices(contributor_pk)
-        .await
-        .unwrap();
-
-    ledger.wait_for_new_blockhash().await.unwrap();
-
-    let latency_samples_pda = ledger
-        .telemetry
-        .initialize_device_latency_samples(
-            &agent,
-            origin_device_pk,
-            target_device_pk,
-            link_pk,
-            1u64,
-            5_000_000,
-        )
-        .await
-        .unwrap();
-
-    // Write without timestamp index — should succeed as before.
-    ledger
-        .telemetry
-        .write_device_latency_samples(
-            &agent,
-            latency_samples_pda,
-            vec![1000, 1100],
-            1_700_000_000_000_000,
-        )
-        .await
-        .unwrap();
-
-    let account = ledger
-        .get_account(latency_samples_pda)
-        .await
-        .unwrap()
-        .expect("Samples account does not exist");
-    let samples_data = DeviceLatencySamples::try_from(&account.data[..]).unwrap();
-    assert_eq!(samples_data.header.next_sample_index, 2);
-    assert_eq!(samples_data.samples, vec![1000, 1100]);
-}
-
 #[tokio::test]
 async fn test_initialize_timestamp_index_fail_samples_account_does_not_exist() {
     let mut ledger = LedgerHelper::new().await.unwrap();