152 lines
2.5 KiB
C++
152 lines
2.5 KiB
C++
#include <cstring>
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#include "TLV.h"
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#define REC_SIZE(x) ((std::size_t)x.Len + 2)
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namespace TLV {
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static bool
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space_available(Arena &arena, uint8_t *cursor, uint8_t len)
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{
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uintptr_t remaining = 0;
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if (cursor == NULL) {
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return false;
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}
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remaining = (uintptr_t)cursor - (uintptr_t)arena.store;
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remaining = arena.size - remaining;
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return ((size_t)remaining >= ((size_t)len+2));
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}
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uint8_t *
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write_to_memory(Arena &arena, uint8_t *cursor, Record &rec)
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{
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// If cursor is NULL, the user needs us to select an empty
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// slot for the record. If we can't find one, that's an
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// error.
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//
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// If, however, the user gives us a cursor, we'll trust it
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// (though space_available will sanity check that cursor).
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if (cursor == NULL) {
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cursor = find_empty(arena, cursor);
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if (cursor == NULL) {
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return NULL;
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}
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}
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if (!space_available(arena, cursor, rec.Len)) {
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return NULL;
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}
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memcpy(cursor, &rec, REC_SIZE(rec));
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cursor = skip_record(rec, cursor);
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return cursor;
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}
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void
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set_record(Record &rec, uint8_t tag, uint8_t len, const char *val)
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{
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uint8_t trail = TLV_MAX_LEN-len;
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rec.Tag = tag;
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rec.Len = len;
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memcpy(rec.Val, val, len);
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memset(rec.Val+len, 0, trail);
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}
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void
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read_from_memory(Record &rec, uint8_t *cursor)
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{
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rec.Tag = cursor[0];
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rec.Len = cursor[1];
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memcpy(rec.Val, cursor+2, rec.Len);
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}
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/*
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* returns a pointer to memory where the record was found,
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* e.g. find_tag(...)[0] is the tag of the found record.
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*/
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uint8_t *
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find_tag(Arena &arena, uint8_t *cursor, Record &rec)
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{
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uint8_t tag, len;
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if (cursor == NULL) {
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cursor = arena.store;
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}
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while ((tag = cursor[0]) != rec.Tag) {
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len = cursor[1];
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if (!space_available(arena, cursor, len)) {
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return NULL;
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}
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cursor += len;
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cursor += 2;
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}
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if (tag != rec.Tag) {
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return NULL;
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}
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if (tag != TAG_EMPTY) {
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read_from_memory(rec, cursor);
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cursor = skip_record(rec, cursor);
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}
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return cursor;
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}
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uint8_t *
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find_empty(Arena &arena, uint8_t *cursor) {
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Record rec;
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rec.Tag = TAG_EMPTY;
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return find_tag(arena, cursor, rec);
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}
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uint8_t *
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skip_record(Record &rec, uint8_t *cursor)
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{
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return (uint8_t *)((uintptr_t)cursor + rec.Len + 2);
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}
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void
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delete_record(Arena &arena, uint8_t *cursor)
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{
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//
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if (cursor == NULL) {
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return;
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}
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uint8_t len = cursor[1] + 2;
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uint8_t *stop = arena.store + arena.size;
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stop -= len;
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while (cursor != stop) {
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cursor[0] = cursor[len];
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cursor++;
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}
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stop += len;
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while (cursor != stop) {
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cursor[0] = 0;
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cursor++;
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}
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}
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} // namespace TLV
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