scsl/TLV.cc

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#include <cstring>
#include "TLV.h"
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using namespace scsl;
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#define REC_SIZE(x) ((std::size_t)x.Len + 2)
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namespace scsl {
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namespace TLV {
static bool
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spaceAvailable(Arena &arena, uint8_t *cursor, uint8_t len)
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{
if (cursor == nullptr) {
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return false;
}
return arena.CursorInArena(cursor + len);
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}
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static inline void
clearUnused(Record &rec)
{
uint8_t trail = TLV_MAX_LEN - rec.Len;
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memset(rec.Val + rec.Len, 0, trail);
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}
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uint8_t *
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WriteToMemory(Arena &arena, uint8_t *cursor, Record &rec)
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{
// If cursor is nullptr, 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
// error.
//
// If, however, the user gives us a cursor, we'll trust it
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// (though spaceAvailable will sanity check that cursor).
if (cursor == nullptr) {
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cursor = FindEmpty(arena, cursor);
if (cursor == nullptr) {
return nullptr;
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}
}
if (!arena.CursorInArena(cursor)) {
return nullptr;
}
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if (!spaceAvailable(arena, cursor, rec.Len)) {
return nullptr;
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}
memcpy(cursor, &rec, REC_SIZE(rec));
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cursor = SkipRecord(rec, cursor);
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return cursor;
}
void
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SetRecord(Record &rec, uint8_t tag, uint8_t len, const char *val)
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{
rec.Tag = tag;
rec.Len = len;
memcpy(rec.Val, val, len);
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clearUnused(rec);
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}
void
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ReadFromMemory(Record &rec, uint8_t *cursor)
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{
rec.Tag = cursor[0];
rec.Len = cursor[1];
memcpy(rec.Val, cursor + 2, rec.Len);
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clearUnused(rec);
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}
/*
* returns a pointer to memory where the record was found,
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* e.g. FindTag(...)[0] is the tag of the found record.
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*/
uint8_t *
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FindTag(Arena &arena, uint8_t *cursor, Record &rec)
{
cursor = LocateTag(arena, cursor, rec);
if (rec.Tag != TAG_EMPTY) {
cursor = SkipRecord(rec, cursor);
}
return cursor;
}
uint8_t *
LocateTag(Arena &arena, uint8_t *cursor, Record &rec)
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{
uint8_t tag, len;
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if (cursor == nullptr) {
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cursor = arena.Start();
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}
while ((tag = cursor[0]) != rec.Tag) {
len = cursor[1];
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if (!spaceAvailable(arena, cursor, len)) {
return nullptr;
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}
cursor += len;
cursor += 2;
}
if (tag != rec.Tag) {
return nullptr;
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}
if (tag != TAG_EMPTY) {
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ReadFromMemory(rec, cursor);
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}
return cursor;
}
uint8_t *
FindEmpty(Arena &arena, uint8_t *cursor)
{
Record rec;
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rec.Tag = TAG_EMPTY;
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return FindTag(arena, cursor, rec);
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}
uint8_t *
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SkipRecord(Record &rec, uint8_t *cursor)
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{
return (uint8_t *) ((uintptr_t) cursor + rec.Len + 2);
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}
void
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DeleteRecord(Arena &arena, uint8_t *cursor)
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{
if (cursor == nullptr) {
return;
}
if (!arena.CursorInArena(cursor)) {
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return;
}
uint8_t len = cursor[1] + 2;
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uint8_t *stop = arena.Start() + arena.Size();
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stop -= len;
while (cursor != stop) {
cursor[0] = cursor[len];
cursor++;
}
stop += len;
while (cursor != stop) {
cursor[0] = 0;
cursor++;
}
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}
} // namespace TLV
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} // namespace scsl