bool SetInternal(const string& key, const string& val)
{
//update对应key的val，如果不存在则返回false
Node* np = NULL;
Link l;
bool found = Find(key, &np, &l);
if(!found)
return false;
Link val_link = np->GetValLink();
if(val_link.GetTotalSize() >= val.length()) { //the old val has enough space, write new val at original offset
Lseek(data_fd_, val_link.GetOffset(), SEEK_SET);
val_link.SetSize(val.length());
} else { //space is not enough, write the new val at the end of file
(*free_data_)[val_link.GetTotalSize()] = val_link; //add original data space to free data map
val_link = FindRooMAndWrite(val.c_str(), val.length(), data_fd_, free_data_);
}
Write(data_fd_, val.c_str(), val.length());
np->SetValLink(val_link);
NodeWriteInplace(np, l.GetOffset());
delete np;
return true;
}
string GetVal(const Link& l)
{
char* buf = new char[l.GetSize()];
Lseek(data_fd_, l.GetOffset(), SEEK_SET);
Read(data_fd_, buf, l.GetSize()); //至此，结点中的内容在buf里
string val(buf, l.GetSize()); // 读取val
delete[] buf;
return val;
}
//return link info that describes the write which just happened
Link FindRooMAndWrite(const char* data, size_t len, int fd, map<size_t, Link>* free_space)
{
Link l;
//first find data space which is >= data length in free space map
map<size_t, Link>::iterator iter = free_space->lower_bound(len);
if(iter != free_space->end()) { // found proper space in free space map
l = iter->second;
Lseek(fd, l.GetOffset(), SEEK_SET);
free_space->erase(iter); //remove from free space map because it'll be reused
} else {
// no proper space in free space map, write data to the end of the file
l.SetOffset(Lseek(fd, 0, SEEK_END));
l.SetTotalSize(len);
l.SetSize(len);
}
Write(fd, data, len);
return l;
}
