commit aef7095c3e52e2f98850e72c68b00f54a39608a6 Author: David Goulet <dgoulet@torproject.org> Date: Thu Mar 7 12:57:15 2019 -0500 prop289: Add documentation for the circuit FIFO list Part of #26288 Signed-off-by: David Goulet <dgoulet@torproject.org> --- src/core/or/circuit_st.h | 20 +++++++++++++++++--- 1 file changed, 17 insertions(+), 3 deletions(-) diff --git a/src/core/or/circuit_st.h b/src/core/or/circuit_st.h index 5adb15893..a68547ecb 100644 --- a/src/core/or/circuit_st.h +++ b/src/core/or/circuit_st.h @@ -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. */