commit f07c6ae57cd2ac11d438232b94a15f99b96e8989 Author: George Kadianakis <desnacked@riseup.net> Date: Wed Feb 13 16:58:15 2019 +0200 Add histogram fields in header file that allow specifying edges. --- src/core/or/circuitpadding.h | 57 +++++++++++++++++++++++++++++++++++--------- 1 file changed, 46 insertions(+), 11 deletions(-) diff --git a/src/core/or/circuitpadding.h b/src/core/or/circuitpadding.h index 92fd4fc2d..57bd37981 100644 --- a/src/core/or/circuitpadding.h +++ b/src/core/or/circuitpadding.h @@ -228,13 +228,15 @@ typedef uint16_t circpad_statenum_t; #define CIRCPAD_STATENUM_MAX (UINT16_MAX) /** A histogram is used to sample padding delays given a machine state. This - * constant defines the maximum histogram width (i.e. the max number of bins) + * constant defines the maximum histogram width (i.e. the max number of bins). * - * Each histogram bin is twice as large as the previous. Two exceptions: The - * first bin has zero width (which means that minimum delay is applied to the - * next padding cell), and the last bin (infinity bin) has infinite width - * (which means that the next padding cell will be delayed infinitely). */ -#define CIRCPAD_MAX_HISTOGRAM_LEN (sizeof(circpad_delay_t)*8 + 1) + * The current limit is arbitrary and could be raised if there is a need, + * however too many bins will be hard to serialize in the future. + * + * Memory concerns are not so great here since the corresponding histogram and + * histogram_edges arrays are global and not per-circuit. + */ +#define CIRCPAD_MAX_HISTOGRAM_LEN (100) /** * A state of a padding state machine. The information here are immutable and @@ -248,15 +250,48 @@ typedef uint16_t circpad_statenum_t; * or the consensus. */ typedef struct circpad_state_t { - /** If a histogram is used for this state, this specifies the number of bins - * of this histogram. Histograms must have at least 2 bins. + /** + * If a histogram is used for this state, this specifies the number of bins + * of this histogram. Histograms must have at least 2 bins. + * + * In particular, the following histogram: + * + * Tokens + * + + * 10 | +----+ + * 9 | | | +---------+ + * 8 | | | | | + * 7 | | | +-----+ | + * 6 +----+ Bin+-----+ | +---------------+ + * 5 | | #1 | | | | | + * | Bin| | Bin | Bin | Bin #4 | Bin #5 | + * | #0 | | #2 | #3 | | (infinity bin)| + * | | | | | | | + * | | | | | | | + * 0 +----+----+-----+-----+---------+---------------+ + * 0 100 200 350 500 1000 ∞ microseconds * - * If a delay probability distribution is used for this state, this is set - * to 0. */ + * would be specified the following way: + * histogram_len = 6; + * histogram[] = { 6, 10, 6, 7, 9, 6 } + * histogram_edges[] = { 0, 100, 200, 350, 500, 1000 } + * + * If a delay probability distribution is used for this state, this is set + * to 0. */ circpad_hist_index_t histogram_len; /** The histogram itself: an array of uint16s of tokens, whose - * widths are exponentially spaced, in microseconds */ + * widths are exponentially spaced, in microseconds. + * + * This array must have histogram_len elements. */ circpad_hist_token_t histogram[CIRCPAD_MAX_HISTOGRAM_LEN]; + /* The histogram bin edges in usec. + * + * Each element of this array specifies the left edge of the corresponding + * bin. The rightmost edge is always infinity and is not specified in this + * array. + * + * This array must have histogram_len+1 elements. */ + circpad_delay_t histogram_edges[CIRCPAD_MAX_HISTOGRAM_LEN+1]; /** Total number of tokens in this histogram. This is a constant and is *not* * decremented every time we spend a token. It's used for initializing and * refilling the histogram. */