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Matrix: do not send a key upload full of nulls

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Closes #85.

The body was one `json!` literal, and a literal turns an absent value into
an explicit `null`. The specification says these fields are *absent* when
there is nothing to send, which is a different thing.

Synapse accepts `"device_keys": null` and ignores it, so this looked fine
for as long as nobody used a stricter homeserver. poast.org validates the
body and refuses the whole request - `M_INVALID_PARAM: device_keys must
not be null` - on every sync cycle, forever, because the retry sends the
same thing again.

The consequence is not cosmetic. If a key upload never succeeds this
device's identity is never published: nobody else can start an Olm session
with it, messages encrypted to it may be undecryptable, and the device is
not properly announced to any room it is in.

Empty maps are omitted for the same reason - "here are no keys" and "I am
not uploading keys" are different requests.

Found only because the daemon's logging was turned on two days of work
ago. It had been failing silently at sync cadence the whole time.

Co-Authored-By: Claude Opus 5 <[email protected]>
This commit is contained in:
Salastil
2026-09-02 08:16:26 -04:00
co-authored by Claude Opus 5
parent 8dae46fab3
commit 1f0d947825
1 changed files with 28 additions and 5 deletions
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src/backend/matrix/crypto.rs
+28 -5
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@@ -176,11 +176,34 @@ impl CryptoSession {
let base = homeserver_url.trim_end_matches('/');
match request.request() {
AnyOutgoingRequest::KeysUpload(req) => {
let body = serde_json::json!({
"device_keys": req.device_keys,
"one_time_keys": req.one_time_keys,
"fallback_keys": req.fallback_keys,
});
// Built field by field rather than as one literal, because a
// literal turns an absent value into an explicit `null` and
// the specification says these fields are *absent* when there
// is nothing to send.
//
// Not a nicety. Synapse accepts `"device_keys": null` and
// ignores it; a stricter homeserver validates the body and
// refuses the whole request - poast.org answers
// `M_INVALID_PARAM: device_keys must not be null`, on every
// sync cycle, forever, because the retry never changes. The
// consequence is that this device's identity is never
// published at all: nobody else can start an Olm session with
// it, so messages encrypted to it may be undecryptable and the
// device is not properly announced to any room it is in.
let mut body = serde_json::Map::new();
if let Some(device_keys) = &req.device_keys {
body.insert("device_keys".into(), serde_json::to_value(device_keys)?);
}
// Empty maps are omitted for the same reason: "here are no
// keys" and "I am not uploading keys" are different requests,
// and only the second one is what an empty upload means.
if !req.one_time_keys.is_empty() {
body.insert("one_time_keys".into(), serde_json::to_value(&req.one_time_keys)?);
}
if !req.fallback_keys.is_empty() {
body.insert("fallback_keys".into(), serde_json::to_value(&req.fallback_keys)?);
}
let body = serde_json::Value::Object(body);
let resp = http::post_json(&format!("{base}/_matrix/client/v3/keys/upload"), Some(access_token), body).await.context("keys/upload")?;
let mut one_time_key_counts: BTreeMap<OneTimeKeyAlgorithm, UInt> = BTreeMap::new();
if let Some(obj) = resp["one_time_key_counts"].as_object() {