prop289: Add documentation for the circuit FIFO list

Part of #26288

Signed-off-by: David Goulet <dgoulet@torproject.org>
This commit is contained in:
David Goulet 2019-03-07 12:57:15 -05:00
parent 44750b0de6
commit aef7095c3e

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@ -106,9 +106,23 @@ struct circuit_t {
int deliver_window;
/** FIFO containing the digest of the cells that are just before a SENDME is
* sent by the client. It is done at the last cell before our package_window
* goes down to 0 which is when we expect a SENDME. The protocol doesn't
* allow more than 10 outstanding SENDMEs worth of data meaning this list
* should only contain at most 10 digests of 4 bytes each. */
* goes down to 0 which is when we expect a SENDME.
*
* Our current circuit package window is capped to 1000
* (CIRCWINDOW_START_MAX) which is also the start value. The increment is
* set to 100 (CIRCWINDOW_INCREMENT) which means we don't allow more than
* 1000/100 = 10 outstanding SENDME cells worth of data. Meaning that this
* list can not contain more than 10 digests of DIGEST_LEN bytes (20).
*
* At position i in the list, the digest corresponds to the
* ((CIRCWINDOW_INCREMENT * i) - 1)-nth cell received since we expect the
* (CIRCWINDOW_INCREMENT * i)-nth cell to be the SENDME and thus containing
* the previous cell digest.
*
* For example, position 2 (starting at 0) means that we've received 299
* cells and the 299th cell digest is kept at index 2.
*
* At maximum, this list contains 200 bytes plus the smartlist overhead. */
smartlist_t *sendme_last_digests;
/** Temporary field used during circuits_handle_oom. */