/// <summary>
/// 读取块存储头部
/// </summary>
private void ReadFileHeader()
{
byte[] header = new byte[this.FileHeaderSize];
this.Stream.Seek(this.SeekStart, SeekOrigin.Begin);
this.Stream.Read(header, 0, this.FileHeaderSize);
int index = 0;
// 魔数前缀
foreach (byte b in FileHeaderPrefix)
{
if (header[index] != b)
{
throw new LinkedFileException("invalid header prefix");
}
index++;
}
// 块的大小
this.BlockSize = StoredHelper.RetrieveInt(header, index);
index += StoredConstants.IntegerLength;
// 空闲列表头序号
this.FreeBlockHead = StoredHelper.RetrieveLong(header, index);
index += StoredConstants.LongLength;
this.IsHeaderDirty = false;
if (this.BlockSize < StoredConstants.MinBlockSize)
{
throw new LinkedFileException("linked file block size too small " + this.BlockSize);
}
}
/// <summary>
/// 读取块存储头部
/// </summary>
private void ReadFileHeader()
{
// 魔数前缀长度 | 块的大小
byte[] header = new byte[FileHeaderSize];
this.Stream.Seek(this.SeekStart, SeekOrigin.Begin);
this.Stream.Read(header, 0, FileHeaderSize);
int index = 0;
// 魔数前缀
foreach (byte b in FileHeaderPrefix)
{
if (header[index] != b)
{
throw new BlockFileException("Invalid block file header prefix.");
}
index++;
}
// 块的大小 4 Bytes
this.BlockSize = StoredHelper.RetrieveInt(header, index);
index += StoredConstants.IntegerLength;
if (this.BlockSize < StoredConstants.MinBlockSize)
{
throw new BlockFileException("Block size is too small " + this.BlockSize + ".");
}
}
/// <summary>
/// 获取指定头序号的大块数据
/// </summary>
/// <param name="headBlockNumber">指定头序号</param>
/// <returns>大块数据</returns>
public byte[] GetChunk(long headBlockNumber)
{
// get the head, interpret the length
LinkedFileBlockFlag blockFlag;
long nextBlockNumber;
byte[] block = this.ReadBlock(headBlockNumber, out blockFlag, out nextBlockNumber);
// 读取块长度
int length = StoredHelper.RetrieveInt(block, 0);
if (length < 0)
{
throw new LinkedFileException("negative length block? must be garbage: " + length);
}
if (blockFlag != LinkedFileBlockFlag.Head)
{
throw new LinkedFileException("first block not marked HEAD");
}
byte[] buffer = new byte[length];
// 在第一个块中读取数据
int firstLength = this.BlockSize - StoredConstants.IntegerLength;
if (firstLength > length)
{
firstLength = length;
}
Array.Copy(block, StoredConstants.IntegerLength, buffer, 0, firstLength);
// 在链接的其他块中读取数据
int stored = firstLength;
while (stored < length)
{
// get the next buffer
long currentBlockNumber = nextBlockNumber;
block = this.ReadBlock(currentBlockNumber, out blockFlag, out nextBlockNumber);
int nextLength = this.BlockSize;
if (length - stored < nextLength)
{
nextLength = length - stored;
}
Array.Copy(block, 0, buffer, stored, nextLength);
stored += nextLength;
}
return(buffer);
}
/// <summary>
/// 读取B+树存储头
/// </summary>
private void ReadHeader()
{
// 魔数前缀 | 版本 | 节点容量 | 键大小 | 根节点块序号 | 空闲块头序号
// prefix | version | node size | key size | block number of root | block number of free list head
byte[] header = new byte[HeaderSize];
this.Stream.Seek(this.SeekStart, SeekOrigin.Begin);
this.Stream.Read(header, 0, HeaderSize);
// 验证头前缀魔数
int index = 0;
foreach (byte b in StoredConstants.TreeFileHeaderPrefix)
{
if (header[index] != b)
{
throw new BlockFileException("invalid header prefix");
}
index++;
}
// 版本
this.Version = header[index];
index += 1;
// 节点容量
this.NodeCapacity = StoredHelper.RetrieveInt(header, index);
index += StoredConstants.IntegerLength;
// 键大小
this.KeyLength = StoredHelper.RetrieveInt(header, index);
index += StoredConstants.IntegerLength;
// 根节点块序号
this.RootNodeBlockNumber = StoredHelper.RetrieveLong(header, index);
index += StoredConstants.LongLength;
// 空闲块头序号
this.FreeBlockHeadNumber = StoredHelper.RetrieveLong(header, index);
index += StoredConstants.LongLength;
if (this.NodeCapacity < 2)
{
throw new BPlusTreeException("node size must be larger than 2");
}
if (this.KeyLength < 5)
{
throw new BPlusTreeException("Key length must be larger than 5");
}
}