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CovidBracelet
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Records: Rewrite interator_init_timerange and binary_search to take care of invalid entries etc.

This commit is contained in:
H1ghBre4k3r 2021-05-18 22:30:59 +02:00 committed by Patrick Rathje
parent 4f1f5b6eab
commit bb6be05d53
1 changed files with 59 additions and 58 deletions
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117
src/ens/records.c
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@ -1,6 +1,7 @@
#include <string.h>
#include "../covid_types.h"
#include "ens_error.h"
#include "records.h"
#include "sequencenumber.h"
#include "storage.h"
@ -21,51 +22,64 @@ int ens_records_iterator_init_range(record_iterator_t* iterator,
/**
* Find an entry via binary search for the timestamp.
*
* @param record pointer to the location, where the loaded record shall be stored
* @param record pointer to the location, where the found sn shall be stored
* @param target timestamp for which to find the nearest entry for
* @param start lower bound for the binary search
* @param end upper bound for the binary search
* @param greater flag for indicating, if the loaded sn shall correspond to a greater (1) or smaller (0) timestamp
*/
// TODO lome: maybe add flag for indicating whether older or newer contact shall be loaded
int find_record_via_binary_search(record_t* record,
uint32_t target,
record_sequence_number_t start,
record_sequence_number_t end) {
// TODO lome: 1. handle entries with deleted/invalid data -> load left/right entry
// TODO lome: 2. handle possible deadlocks because of 1.
// TODO lome: 3. check, if oldest ts is newer than the latest -> return error that needs to be handled by the
// calling function
record_t start_record;
record_t end_record;
int find_sn_via_binary_search(record_sequence_number_t* sn_dest, uint32_t target, int greater) {
record_sequence_number_t start = get_oldest_sequence_number();
record_sequence_number_t end = get_latest_sequence_number();
// load the initial start and end record
int rc = load_record(&start_record, start);
if (rc) {
return rc;
}
rc = load_record(&end_record, end);
if (rc) {
return rc;
}
record_t dummyRec;
do {
// TODO lome: first entry for start, last entry for end
// calculate the contact in the middle between start and end and load it
record_sequence_number_t middle = (start_record.sn + end_record.sn) / 2;
int rc = load_record(record, middle);
// calculate the contact in the middle between start and end
record_sequence_number_t middle = sn_get_middle_sn(start, end);
// try to load it
int rc = load_record(&dummyRec, middle);
if (rc && rc != -ENS_DELENT && rc != -ENS_NOENT) {
// if our error is not concerning invalid or deleted entries, we just want to return
return rc;
} else if (rc == -ENS_DELENT || rc == -ENS_NOENT) {
int direction = 1;
do {
// increment the calculated "middle" by a certain amount, so we can try to load a new entry
sn_increment_by(middle, direction);
rc = load_record(&dummyRec, middle);
// alternate around the previously calculated "middle"
// this should avoid deadlocks, because we never read an entry twice
direction += direction > 0 ? 1 : -1;
direction *= -1;
} while (middle >= start && middle <= end && (rc == -ENS_DELENT || rc == -ENS_NOENT));
}
// if we still have an error, just return it
if (rc) {
return rc;
}
// determine the new start and end
if (record->timestamp > target) {
memcpy(&start_record, record, sizeof(record_t));
if (dummyRec.timestamp > target) {
start = dummyRec.sn;
} else {
memcpy(&end_record, record, sizeof(record_t));
end = dummyRec.sn;
}
// break, if we are at the exact timestamp or our start and end are next to each other
} while (record->timestamp != target && (end_record.sn - start_record.sn) > 1);
} while (dummyRec.timestamp != target && (end - start) > 1);
// TODO lome: maybe loop here aswell?
// increment/decrement the found sn, depending on the greater flag
record_sequence_number_t found = dummyRec.sn;
if (dummyRec.timestamp > target && !greater) {
found--;
} else if (dummyRec.timestamp < target && greater) {
found++;
}
*sn_dest = found;
return 0;
}
@ -73,46 +87,33 @@ int find_record_via_binary_search(record_t* record,
// TODO: This iterator does neither check if the sequence numbers wrapped around while iteration. As a result, first
// results could have later timestamps than following entries
int ens_records_iterator_init_timerange(record_iterator_t* iterator, uint32_t* ts_start, uint32_t* ts_end) {
record_sequence_number_t oldest_sn = get_oldest_sequence_number();
record_sequence_number_t latest_sn = get_latest_sequence_number();
record_sequence_number_t oldest_sn = 0;
record_sequence_number_t newest_sn = 0;
// try to find the oldest contact in our timerange
record_t start_rec;
int rc = load_record(&start_rec, oldest_sn);
if (rc) {
return rc;
// assure that *ts_end > *ts_start
if (ts_start && ts_end && *ts_end < *ts_start) {
return 1;
}
// if starting timestamp lies in our bounds, perform binary search
// TODO lome: check, if ts_start and ts_end are NULL -> use oldest/latest sn then
// TODO lome: move oldest_sn and latest_sn to binary_search function
// TODO lome: maybe keep track of the oldest and newest timestamp (optimization for later)
if (start_rec.timestamp < *ts_start) {
// TODO lome: only "return" sn, not actual record
rc = find_record_via_binary_search(&start_rec, *ts_start, oldest_sn, latest_sn);
if (ts_start) {
int rc = find_sn_via_binary_search(&oldest_sn, *ts_start, 1);
if (rc) {
return rc;
}
} else {
oldest_sn = get_oldest_sequence_number();
}
// try to find the newest contact within out timerange
record_t end_rec;
rc = load_record(&end_rec, latest_sn);
if (rc) {
return rc;
}
// if ending timestamp lies in our bounds, perform binary search
if (end_rec.timestamp > *ts_end) {
rc = find_record_via_binary_search(&end_rec, *ts_end, oldest_sn, latest_sn);
if (ts_end) {
int rc = find_sn_via_binary_search(&newest_sn, *ts_end, 0);
if (rc) {
return rc;
}
} else {
newest_sn = get_latest_sequence_number();
}
ens_records_iterator_init_range(iterator, &start_rec.sn, &end_rec.sn);
return 0;
return ens_records_iterator_init_range(iterator, &oldest_sn, &newest_sn);
}
record_t* ens_records_iterator_next(record_iterator_t* iter) {