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fix(studio): Ensure putting framing byte when sending rpc #3215

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fix(studio): Ensure putting framing byte when sending rpc #3215

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12 changes: 10 additions & 2 deletions app/src/studio/rpc.c
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Original file line number Diff line number Diff line change
Expand Up @@ -188,7 +188,11 @@ static int send_response(const zmk_studio_Response *resp) {
pb_ostream_t stream = pb_ostream_for_tx_buf(user_data);

uint8_t framing_byte = FRAMING_SOF;
ring_buf_put(&rpc_tx_buf, &framing_byte, 1);
if (ring_buf_put(&rpc_tx_buf, &framing_byte, 1) != 1) {
LOG_ERR("RPC TX buffer full");
k_mutex_unlock(&rpc_transport_mutex);
return -ENOMEM;
}
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@cormoran cormoran Jan 25, 2026

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Treating SOF put failure as error sounds fine? I've never hit error here yet.

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@petejohanson petejohanson Jan 29, 2026

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I'm on the fence here, whether there should be any attempt to retry a few times, and then return -ENOMEM if that fails? Would give the underlying transport a chance to empty the ring buffer to free space. I'd suggest we try that.

In the case of a failure, I usually prefer, when locking involved, to create a new local at the top of the function int ret = 0; and then in this branch, set ret = -ENOMEM; goto exit and update the exit: to return ret instead.


selected_transport->tx_notify(&rpc_tx_buf, 1, false, user_data);

Expand All @@ -199,11 +203,15 @@ static int send_response(const zmk_studio_Response *resp) {
#if !IS_ENABLED(CONFIG_NANOPB_NO_ERRMSG)
LOG_ERR("Failed to encode the message %s", stream.errmsg);
#endif // !IS_ENABLED(CONFIG_NANOPB_NO_ERRMSG)
k_mutex_unlock(&rpc_transport_mutex);
return -EINVAL;
}

framing_byte = FRAMING_EOF;
ring_buf_put(&rpc_tx_buf, &framing_byte, 1);
// If response is large, tx buffer can be full for async transport.
while (ring_buf_put(&rpc_tx_buf, &framing_byte, 1) == 0) {
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@petejohanson petejohanson Jan 29, 2026

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This should ideally "give up" after a certain period/number of tries, and return, so we don't get stuck in an infinite loop, IMHO.

k_sleep(K_MSEC(1));
}

selected_transport->tx_notify(&rpc_tx_buf, 1, true, user_data);

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