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perf(prekeys): stream prekey generation to cut the connect-time peak #901

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Merged
jlucaso1 merged 2 commits into from
Jun 18, 2026
Merged

perf(prekeys): stream prekey generation to cut the connect-time peak #901

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3478da7
perf(prekeys): stream prekey generation to cut the connect-time peak
claude Jun 18, 2026
c6017e9
perf(prekeys): use the type-level record-size bound for the buffer hint
claude Jun 18, 2026
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24 changes: 13 additions & 11 deletions src/prekeys.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -473,24 +473,26 @@ impl Client {
// Seed one CSPRNG and advance it per key, rather than reseeding from
// entropy on every iteration.
let mut rng = rand::make_rng::<rand::rngs::StdRng>();
let mut records = Vec::with_capacity(gen_count);
// Encode each record into the shared buffer and drop it immediately so the
// whole batch of PreKeyRecordStructures (each owns two heap Vecs of key bytes)
// is never resident at once — that batch was the dominant controllable peak on
// the connect path. MAX_RECORD_LEN keeps the buffer to a single allocation;
// being just a capacity hint, it uses the type-level upper bound (1-byte id
// tag + <=5-byte u32 varint + two 34 B key fields = 74) rather than depending
// on the tighter 24-bit id cap.
const MAX_RECORD_LEN: usize = 74;
let mut pubkeys = Vec::with_capacity(gen_count);
let mut offsets = Vec::with_capacity(gen_count);
let mut buf = Vec::with_capacity(gen_count * MAX_RECORD_LEN);
for i in 0..gen_count {
let pre_key_id = gen_start + i as u32;
let key_pair = KeyPair::generate(&mut rng);
pubkeys.push((pre_key_id, key_pair.public_key));
records.push((pre_key_id, new_pre_key_record(pre_key_id, &key_pair)));
}

let total_len: usize = records.iter().map(|(_, r)| r.encoded_len()).sum();
let mut buf = Vec::with_capacity(total_len);
let mut offsets = Vec::with_capacity(records.len());
for (id, record) in &records {
let start = buf.len();
record
new_pre_key_record(pre_key_id, &key_pair)
.encode(&mut buf)
.expect("prost encode into pre-sized Vec");
offsets.push((*id, start..buf.len()));
offsets.push((pre_key_id, start..buf.len()));
pubkeys.push((pre_key_id, key_pair.public_key));
}
let shared = bytes::Bytes::from(buf);
let encoded_batch: Vec<(u32, bytes::Bytes)> = offsets
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