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tdutils/td/utils/find_boundary.cpp

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+/*
+    This file is part of TON Blockchain Library.
+
+    TON Blockchain Library is free software: you can redistribute it and/or modify
+    it under the terms of the GNU Lesser General Public License as published by
+    the Free Software Foundation, either version 2 of the License, or
+    (at your option) any later version.
+
+    TON Blockchain Library is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU Lesser General Public License for more details.
+
+    You should have received a copy of the GNU Lesser General Public License
+    along with TON Blockchain Library.  If not, see <http://www.gnu.org/licenses/>.
+
+    Copyright 2017-2019 Telegram Systems LLP
+*/
+#include "td/utils/find_boundary.h"
+
+#include <cstring>
+
+namespace td {
+
+bool find_boundary(ChainBufferReader range, Slice boundary, size_t &already_read) {
+  range.advance(already_read);
+
+  const int MAX_BOUNDARY_LENGTH = 70;
+  CHECK(boundary.size() <= MAX_BOUNDARY_LENGTH + 4);
+  while (!range.empty()) {
+    Slice ready = range.prepare_read();
+    if (ready[0] == boundary[0]) {
+      if (range.size() < boundary.size()) {
+        return false;
+      }
+      auto save_range = range.clone();
+      char x[MAX_BOUNDARY_LENGTH + 4];
+      range.advance(boundary.size(), {x, sizeof(x)});
+      if (Slice(x, boundary.size()) == boundary) {
+        return true;
+      }
+
+      // not a boundary, restoring previous state and skip one symbol
+      range = std::move(save_range);
+      range.advance(1);
+      already_read++;
+    } else {
+      const char *ptr = static_cast<const char *>(std::memchr(ready.data(), boundary[0], ready.size()));
+      size_t shift;
+      if (ptr == nullptr) {
+        shift = ready.size();
+      } else {
+        shift = ptr - ready.data();
+      }
+      already_read += shift;
+      range.advance(shift);
+    }
+  }
+
+  return false;
+}
+
+}  // namespace td