feat(sstable): add partial format definition

Author: Aetherance

src/table/format.cc

@@ -0,0 +1,74 @@
+#include "format.h"
+
+#include <sys/types.h>
+
+#include <cassert>
+#include <cstddef>
+#include <cstdint>
+
+#include "status.h"
+#include "util/coding.h"
+
+namespace db {
+
+void BlockHandle::EncodeTo(std::string* dst) const {
+  assert(offset_ != ~static_cast<u_int64_t>(0));
+  assert(size_ != ~static_cast<u_int64_t>(0));
+  PutVarint64(dst, offset_);
+  PutVarint64(dst, size_);
+}
+
+Status BlockHandle::DecodeFrom(Slice* input) {
+  if (GetVarint64(input, &offset_) && GetVarint64(input, &size_)) {
+    return Status::OkStatus();
+  } else {
+    return Status::Corruption("bad block handle");
+  }
+}
+
+void Footer::EncodeTo(std::string* dst) const {
+  const size_t original_size = dst->size();
+  metaindex_handle_.EncodeTo(dst);
+  index_handle_.EncodeTo(dst);
+  dst->resize(2 * BlockHandle::kMaxEncodedLength);  // padding
+  PutFixed32(dst, static_cast<uint32_t>(kTableMagicNumber) & 0xffffffffu);
+  PutFixed32(dst, static_cast<uint32_t>(kTableMagicNumber >> 32));
+  assert(dst->size() == original_size + kEncodeLenght);
+  (void)original_size;
+}
+
+Status Footer::DecodeFrom(Slice* input) {
+  if (input->Size() < kEncodeLenght) {
+    return Status::Corruption("not an sstable (footer too short)");
+  }
+
+  const char* magic_ptr = input->Data() + kEncodeLenght - 8;
+  const uint32_t magic_lo = DecodeFixed32(magic_ptr);
+  const uint32_t magic_hi = DecodeFixed32(magic_ptr + 4);
+  const u_int64_t magic =
+      ((static_cast<u_int64_t>(magic_hi) << 32) | (static_cast<u_int64_t>(magic_lo)));
+  // magic num judge if the file valid
+  if (magic != kTableMagicNumber) {
+    return Status::Corruption("not an sstable (bad magic number)");
+  }
+
+  Status result = metaindex_handle_.DecodeFrom(input);
+  if (result.Ok()) {
+    result = index_handle_.DecodeFrom(input);
+  }
+  if (result.Ok()) {
+    const char* end = magic_ptr + 8;
+    *input = Slice(end, input->Data() + input->Size() - end);
+  }
+  return result;
+}
+
+Status ReadBlock(RandomAccessFile* file, const ReadOptions& options, const BlockHandle& handle,
+                 BlockContents* result) {
+  // TODO:
+  // 1. implement env.h
+  // 2. implement this method
+  return Status::OkStatus();
+}
+
+}  // namespace db

src/table/format.h

@@ -0,0 +1,119 @@
+#include <sys/types.h>
+
+#include <cstddef>
+#include <string>
+
+#include "status.h"
+namespace db {
+class Block;
+class RandomAccessFile;
+struct ReadOptions;
+
+// SSTable Format
+//
+//  +------------------+
+//  | Data Blocks      |
+//  +------------------+
+//  | Filter Block ?   |
+//  +------------------+
+//  | Metaindex Block  |
+//  +------------------+
+//  | Index Block      |
+//  +------------------+
+//  | Footer           |
+//  +------------------+
+//
+// The Filter Block is optional.
+
+// descripe a block 's position and size
+// BlockHanlde's max size is 10
+class BlockHandle {
+public:
+  enum { kMaxEncodedLength = 10 + 10 };
+
+  BlockHandle();
+
+  u_int64_t offset() const {
+    return offset_;
+  }
+  void set_offset(u_int64_t offset) {
+    offset_ = offset;
+  }
+
+  u_int64_t size() const {
+    return size_;
+  }
+  void set_size(u_int64_t size) {
+    size_ = size;
+  }
+
+  void EncodeTo(std::string* dst) const;
+  Status DecodeFrom(Slice* input);
+
+private:
+  u_int64_t offset_;
+  u_int64_t size_;
+};
+
+//   Footer Format:
+//
+//   [ meta  BlockHandle ]
+//   [ index BlockHandle ]
+//   [      empty        ]
+//   [     magic num     ]
+//
+// Note: Unused bytes in meta/index BlockHandle are left empty to keep Footer size fixed.
+// Footer has a Fixed Size 48
+class Footer {
+public:
+  // two of BlockHandle: index_handle and metaindex_hanle
+  // 8 is the size of MagicNum
+  enum { kEncodeLenght = 2 * BlockHandle::kMaxEncodedLength + 8 };
+
+  Footer() = default;
+
+  const BlockHandle& metaindex_handle() const {
+    return metaindex_handle_;
+  }
+  void set_metaindex_handle(const BlockHandle& h) {
+    metaindex_handle_ = h;
+  }
+
+  const BlockHandle& index_handle() const {
+    return index_handle_;
+  }
+  void set_index_handle(const BlockHandle& h) {
+    index_handle_ = h;
+  }
+
+  void EncodeTo(std::string* dst) const;
+  Status DecodeFrom(Slice* input);
+
+private:
+  BlockHandle metaindex_handle_;
+  BlockHandle index_handle_;
+};
+
+// https://github.com/aetherance/db | sha1sum
+//
+// This magic num will be written into Footer by Footer::EncodeTo()
+// And will be used to judge if the footer is correct
+static const u_int64_t kTableMagicNumber = 0x8c7f4e0c9d6a2b31ull;
+
+// tail after block
+static const size_t kBlockTrailerSize = 5;
+
+// Block Readed into memory
+struct BlockContents {
+  Slice data;
+  bool cachable;
+  bool heep_allocated;
+};
+
+//  offset_  =  size_  = UINT64_MAX;
+Status ReadBlock(RandomAccessFile* file, const ReadOptions& options, const BlockHandle& handle,
+                 BlockContents* result);
+
+inline BlockHandle::BlockHandle()
+    : offset_(~static_cast<u_int64_t>(0)), size_(~static_cast<u_int64_t>(0)) {}
+}  // namespace db