diff --git a/tdutils/CMakeLists.txt b/tdutils/CMakeLists.txt
index f72aa40b..ce58be57 100644
--- a/tdutils/CMakeLists.txt
+++ b/tdutils/CMakeLists.txt
@@ -59,6 +59,7 @@ set(TDUTILS_SOURCE
   td/utils/BigNum.cpp
   td/utils/buffer.cpp
   td/utils/crypto.cpp
+  td/utils/FileLog.cpp
   td/utils/filesystem.cpp
   td/utils/find_boundary.cpp
   td/utils/Gzip.cpp
diff --git a/tdutils/td/utils/FileLog.cpp b/tdutils/td/utils/FileLog.cpp
new file mode 100644
index 00000000..7732b150
--- /dev/null
+++ b/tdutils/td/utils/FileLog.cpp
@@ -0,0 +1,82 @@
+//
+// Copyright Aliaksei Levin (levlam@telegram.org), Arseny Smirnov (arseny30@gmail.com) 2014-2018
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+#include "td/utils/FileLog.h"
+
+#include "td/utils/common.h"
+#include "td/utils/logging.h"
+#include "td/utils/port/Fd.h"
+#include "td/utils/port/FileFd.h"
+#include "td/utils/port/path.h"
+#include "td/utils/Slice.h"
+
+#include <limits>
+
+namespace td {
+
+void FileLog::init(string path, int64 rotate_threshold) {
+  fd_.close();
+  path_ = std::move(path);
+
+  auto r_fd = FileFd::open(path_, FileFd::Create | FileFd::Write | FileFd::Append);
+  LOG_IF(FATAL, r_fd.is_error()) << "Can't open log: " << r_fd.error();
+  fd_ = r_fd.move_as_ok();
+  Fd::duplicate(fd_.get_fd(), Fd::Stderr()).ignore();
+  size_ = fd_.get_size();
+  rotate_threshold_ = rotate_threshold;
+}
+
+void FileLog::set_rotate_threshold(int64 rotate_threshold) {
+  rotate_threshold_ = rotate_threshold;
+}
+
+void FileLog::append(CSlice cslice, int log_level) {
+  Slice slice = cslice;
+  while (!slice.empty()) {
+    auto r_size = fd_.write(slice);
+    if (r_size.is_error()) {
+      process_fatal_error(r_size.error().message());
+    }
+    auto written = r_size.ok();
+    size_ += static_cast<int64>(written);
+    slice.remove_prefix(written);
+  }
+  if (log_level == VERBOSITY_NAME(FATAL)) {
+    process_fatal_error(cslice);
+  }
+
+  if (size_ > rotate_threshold_) {
+    auto status = rename(path_, path_ + ".old");
+    if (status.is_error()) {
+      process_fatal_error(status.message());
+    }
+    do_rotate();
+  }
+}
+
+void FileLog::rotate() {
+  if (path_.empty()) {
+    return;
+  }
+  do_rotate();
+}
+
+void FileLog::do_rotate() {
+  auto current_verbosity_level = GET_VERBOSITY_LEVEL();
+  SET_VERBOSITY_LEVEL(std::numeric_limits<int>::min());  // to ensure that nothing will be printed to the closed log
+  CHECK(!path_.empty());
+  fd_.close();
+  auto r_fd = FileFd::open(path_, FileFd::Create | FileFd::Truncate | FileFd::Write);
+  if (r_fd.is_error()) {
+    process_fatal_error(r_fd.error().message());
+  }
+  fd_ = r_fd.move_as_ok();
+  Fd::duplicate(fd_.get_fd(), Fd::Stderr()).ignore();
+  size_ = 0;
+  SET_VERBOSITY_LEVEL(current_verbosity_level);
+}
+
+}  // namespace td
diff --git a/tdutils/td/utils/FileLog.h b/tdutils/td/utils/FileLog.h
index 7ca4249d..2114448d 100644
--- a/tdutils/td/utils/FileLog.h
+++ b/tdutils/td/utils/FileLog.h
@@ -8,66 +8,22 @@
 
 #include "td/utils/common.h"
 #include "td/utils/logging.h"
-#include "td/utils/port/Fd.h"
 #include "td/utils/port/FileFd.h"
-#include "td/utils/port/path.h"
 #include "td/utils/Slice.h"
 
-#include <limits>
-
 namespace td {
 
-// TODO move implementation to cpp
 class FileLog : public LogInterface {
-  static constexpr int DEFAULT_ROTATE_THRESHOLD = 10 * (1 << 20);
+  static constexpr int64 DEFAULT_ROTATE_THRESHOLD = 10 * (1 << 20);
 
  public:
-  void append(CSlice cslice, int log_level) override {
-    Slice slice = cslice;
-    while (!slice.empty()) {
-      auto r_size = fd_.write(slice);
-      if (r_size.is_error()) {
-        process_fatal_error(r_size.error().message());
-      }
-      auto written = r_size.ok();
-      size_ += static_cast<int64>(written);
-      slice.remove_prefix(written);
-    }
-    if (log_level == VERBOSITY_NAME(FATAL)) {
-      process_fatal_error(cslice);
-    }
+  void init(string path, int64 rotate_threshold = DEFAULT_ROTATE_THRESHOLD);
 
-    if (size_ > rotate_threshold_) {
-      auto status = rename(path_, path_ + ".old");
-      if (status.is_error()) {
-        process_fatal_error(status.message());
-      }
-      do_rotate();
-    }
-  }
+  void set_rotate_threshold(int64 rotate_threshold);
 
-  void rotate() override {
-    if (path_.empty()) {
-      return;
-    }
-    do_rotate();
-  }
+  void append(CSlice cslice, int log_level) override;
 
-  void init(string path, int64 rotate_threshold = DEFAULT_ROTATE_THRESHOLD) {
-    fd_.close();
-    path_ = std::move(path);
-
-    auto r_fd = FileFd::open(path_, FileFd::Create | FileFd::Write | FileFd::Append);
-    LOG_IF(FATAL, r_fd.is_error()) << "Can't open log: " << r_fd.error();
-    fd_ = r_fd.move_as_ok();
-    Fd::duplicate(fd_.get_fd(), Fd::Stderr()).ignore();
-    size_ = fd_.get_size();
-    rotate_threshold_ = rotate_threshold;
-  }
-
-  void set_rotate_threshold(int64 rotate_threshold) {
-    rotate_threshold_ = rotate_threshold;
-  }
+  void rotate() override;
 
  private:
   FileFd fd_;
@@ -75,19 +31,7 @@ class FileLog : public LogInterface {
   int64 size_;
   int64 rotate_threshold_;
 
-  void do_rotate() {
-    auto current_verbosity_level = GET_VERBOSITY_LEVEL();
-    SET_VERBOSITY_LEVEL(std::numeric_limits<int>::min());  // to ensure that nothing will be printed to the closed log
-    CHECK(!path_.empty());
-    fd_.close();
-    auto r_fd = FileFd::open(path_, FileFd::Create | FileFd::Truncate | FileFd::Write);
-    if (r_fd.is_error()) {
-      process_fatal_error(r_fd.error().message());
-    }
-    fd_ = r_fd.move_as_ok();
-    Fd::duplicate(fd_.get_fd(), Fd::Stderr()).ignore();
-    size_ = 0;
-    SET_VERBOSITY_LEVEL(current_verbosity_level);
-  }
+  void do_rotate();
 };
+
 }  // namespace td