[datalog] Move all DataLog functionality to new datalog library (#7641)

Currently the major DataLog backend API (reading and writing) is split between wpiutil and glass. In the interest of allowing code that wants to use these APIs to not need to link to glass and declutter wpiutil, all of those APIs are moved to a new library named "datalog".

Signed-off-by: Jade Turner <spacey-sooty@proton.me>
Co-authored-by: Jade Turner <spacey-sooty@proton.me>
Co-authored-by: Gold856 <117957790+Gold856@users.noreply.github.com>

datalog/src/main/native/cpp/FileLogger.cpp

@@ -0,0 +1,103 @@
+// Copyright (c) FIRST and other WPILib contributors.
+// Open Source Software; you can modify and/or share it under the terms of
+// the WPILib BSD license file in the root directory of this project.
+
+#ifdef __linux__
+#include <fcntl.h>
+#include <sys/inotify.h>
+#include <unistd.h>
+#endif
+
+#include <chrono>
+#include <string>
+#include <string_view>
+#include <thread>
+#include <tuple>
+#include <utility>
+
+#include <fmt/format.h>
+#include <wpi/StringExtras.h>
+
+#include "wpi/datalog/FileLogger.h"
+
+namespace wpi::log {
+FileLogger::FileLogger(std::string_view file,
+                       std::function<void(std::string_view)> callback)
+#ifdef __linux__
+    : m_fileHandle{open(file.data(), O_RDONLY)},
+      m_inotifyHandle{inotify_init()},
+      m_inotifyWatchHandle{
+          inotify_add_watch(m_inotifyHandle, file.data(), IN_MODIFY)},
+      m_thread{[=, this] {
+        char buf[8000];
+        char eventBuf[sizeof(struct inotify_event) + NAME_MAX + 1];
+        lseek(m_fileHandle, 0, SEEK_END);
+        while (read(m_inotifyHandle, eventBuf, sizeof(eventBuf)) > 0) {
+          int bufLen = 0;
+          if ((bufLen = read(m_fileHandle, buf, sizeof(buf))) > 0) {
+            callback(std::string_view{buf, static_cast<size_t>(bufLen)});
+          }
+          std::this_thread::sleep_for(std::chrono::milliseconds(100));
+        }
+      }}
+#endif
+{
+}
+FileLogger::FileLogger(std::string_view file, log::DataLog& log,
+                       std::string_view key)
+    : FileLogger(file, Buffer([entry = log.Start(key, "string"),
+                               &log](std::string_view line) {
+                   log.AppendString(entry, line, 0);
+                 })) {}
+FileLogger::FileLogger(FileLogger&& other)
+#ifdef __linux__
+    : m_fileHandle{std::exchange(other.m_fileHandle, -1)},
+      m_inotifyHandle{std::exchange(other.m_inotifyHandle, -1)},
+      m_inotifyWatchHandle{std::exchange(other.m_inotifyWatchHandle, -1)},
+      m_thread{std::move(other.m_thread)}
+#endif
+{
+}
+FileLogger& FileLogger::operator=(FileLogger&& rhs) {
+#ifdef __linux__
+  std::swap(m_fileHandle, rhs.m_fileHandle);
+  std::swap(m_inotifyHandle, rhs.m_inotifyHandle);
+  std::swap(m_inotifyWatchHandle, rhs.m_inotifyWatchHandle);
+  m_thread = std::move(rhs.m_thread);
+#endif
+  return *this;
+}
+FileLogger::~FileLogger() {
+#ifdef __linux__
+  if (m_inotifyWatchHandle != -1) {
+    inotify_rm_watch(m_inotifyHandle, m_inotifyWatchHandle);
+  }
+  if (m_inotifyHandle != -1) {
+    close(m_inotifyHandle);
+  }
+  if (m_fileHandle != -1) {
+    close(m_fileHandle);
+  }
+  if (m_thread.joinable()) {
+    m_thread.join();
+  }
+#endif
+}
+
+std::function<void(std::string_view)> FileLogger::Buffer(
+    std::function<void(std::string_view)> callback) {
+  return [callback,
+          buf = wpi::SmallVector<char, 64>{}](std::string_view data) mutable {
+    buf.append(data.begin(), data.end());
+    if (!wpi::contains({data.data(), data.size()}, "\n")) {
+      return;
+    }
+    auto [wholeData, extra] = wpi::rsplit({buf.data(), buf.size()}, "\n");
+    std::string leftover{extra};
+
+    callback(wholeData);
+    buf.clear();
+    buf.append(leftover.begin(), leftover.end());
+  };
+}
+}  // namespace wpi::log