write create snap shot

dataguard/src/snapshot.cpp

@@ -2,6 +2,8 @@
 #include <sys/stat.h>
 #include <zstd.h>
 #include <cstdint>
+#include <fstream>
+#include "map.hpp"
 #include "storage/config.h"
 #include "vector.hpp"
 
@@ -13,6 +15,21 @@ default_numeric_index_t GetFileSize(const std::string &file) {
   }
   return stat_buf.st_size;
 }
+
+void CopyFile(const std::string &src, const std::string &dst) {
+  FILE *f1 = fopen(src.c_str(), "rb");
+  FILE *f2 = fopen(dst.c_str(), "wb");
+  if (f1 == nullptr || f2 == nullptr) {
+    throw std::runtime_error("fopen failed");
+  }
+  uint8_t buf[1 << 12];
+  size_t read_size;
+  while ((read_size = fread(buf, 1, 1 << 12, f1)) > 0) {
+    fwrite(buf, 1, read_size, f2);
+  }
+  fclose(f1);
+  fclose(f2);
+}
 struct uint8_t_reader {
   FILE *f;
   uint8_t *buf, *p1, *p2;
@@ -138,6 +155,7 @@ void GenerateDiff(const std::string &old_file, const std::string &new_file, cons
       buf.push_back(new_reader());
     }
   }
+  if (buf.size() == 0) buf.push_back(3);
   // Step 2
   size_t compressed_size_bound = ZSTD_compressBound(buf.size());
   uint8_t *compressed_buf = new uint8_t[compressed_size_bound];
@@ -181,6 +199,7 @@ void ApplyPatch(const std::string &old_file, const std::string &diff_file, const
   while (diff_buf_cnt < decompressed_size) {
     uint8_t flag;
     flag = decompressed_buf[diff_buf_cnt++];
+    if (flag == 3) goto just_copy;
     if (flag == 0) {
       default_numeric_index_t current_diff_len = 0, current_diff_pos = 0, tmp = 0;
       tmp = decompressed_buf[diff_buf_cnt++];
@@ -266,6 +285,7 @@ void ApplyPatch(const std::string &old_file, const std::string &diff_file, const
       }
     }
   }
+just_copy:;
   if (reader_cursor < old_file_size) {
     while (reader_cursor < old_file_size) {
       writer(reader());
@@ -277,4 +297,66 @@ ed:;
   fclose(fp);
   fclose(fp2);
   delete[] decompressed_buf;
+}
+
+void SnapShotManager::InitializeRepository() {
+  FILE *f = fopen(meta_file.c_str(), "w");
+  if (f == nullptr) {
+    throw std::runtime_error("fopen failed");
+  }
+  fprintf(f, "INIT\n");
+  fclose(f);
+  for (size_t i = 0; i < drivers.size(); i++) {
+    sjtu::vector<DataDriverBase::FileEntry> files = drivers[i]->ListFiles();
+    for (size_t j = 0; j < files.size(); j++) {
+      std::string frontier_file = files[j].path + ".frontier";
+      // generate an empty file
+      FILE *f = fopen(frontier_file.c_str(), "w");
+      if (f == nullptr) {
+        throw std::runtime_error("fopen failed");
+      }
+      fclose(f);
+    }
+  }
+}
+
+void SnapShotManager::CreateSnapShot(const std::string &snap_shot_ID) {
+  if (!has_set_meta_file) {
+    throw std::runtime_error("SnapShotManager has not set the meta file");
+  }
+  if (!has_connected) {
+    throw std::runtime_error("SnapShotManager has not connected to the data drivers");
+  }
+  std::fstream fs(meta_file, std::ios::in | std::ios::out);
+  std::string HEAD;
+  fs >> HEAD;
+  sjtu::vector<std::pair<std::string, std::string>> snapshot_relationship;
+  std::string cur, anc;
+  sjtu::map<std::string, sjtu::vector<std::string>> son_list;
+  while (fs >> cur >> anc) {
+    snapshot_relationship.push_back({cur, anc});
+    son_list[anc].push_back(cur);
+  }
+  if (son_list.find(snap_shot_ID) != son_list.end()) {
+    throw std::runtime_error("Snapshot already exists");
+  }
+  // TODO
+  fs.close();
+  fs.open(meta_file, std::ios::in | std::ios::out);
+  fs << snap_shot_ID << '\n';
+  for (size_t i = 0; i < snapshot_relationship.size(); i++) {
+    fs << snapshot_relationship[i].first << ' ' << snapshot_relationship[i].second << '\n';
+  }
+  fs << snap_shot_ID << " " << HEAD << std::endl;
+  for (size_t i = 0; i < drivers.size(); i++) {
+    drivers[i]->Flush();
+    sjtu::vector<DataDriverBase::FileEntry> files = drivers[i]->ListFiles();
+    for (size_t j = 0; j < files.size(); j++) {
+      std::string frontier_file = files[j].path + ".frontier";
+      std::string diff_file = files[j].path + "." + snap_shot_ID + ".diff";
+      GenerateDiff(frontier_file, files[j].path, diff_file);
+      // then overwrite the frontier file
+      CopyFile(files[j].path, frontier_file);
+    }
+  }
 }