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+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// Thread-safe logging routines that do not allocate any memory or
+// acquire any locks, and can therefore be used by low-level memory
+// allocation, synchronization, and signal-handling code.
+
+#ifndef ABSL_BASE_INTERNAL_RAW_LOGGING_H_
+#define ABSL_BASE_INTERNAL_RAW_LOGGING_H_
+
+#include "absl/base/internal/log_severity.h"
+#include "absl/base/macros.h"
+#include "absl/base/port.h"
+
+// This is similar to LOG(severity) << format..., but
+// * it is to be used ONLY by low-level modules that can't use normal LOG()
+// * it is designed to be a low-level logger that does not allocate any
+//   memory and does not need any locks, hence:
+// * it logs straight and ONLY to STDERR w/o buffering
+// * it uses an explicit printf-format and arguments list
+// * it will silently chop off really long message strings
+// Usage example:
+//   ABSL_RAW_LOG(ERROR, "Failed foo with %i: %s", status, error);
+// This will print an almost standard log line like this to stderr only:
+//   E0821 211317 file.cc:123] RAW: Failed foo with 22: bad_file
+#define ABSL_RAW_LOG(severity, ...)                                            \
+  do {                                                                         \
+    constexpr const char* absl_raw_logging_internal_basename =                 \
+        ::absl::raw_logging_internal::Basename(__FILE__,                       \
+                                               sizeof(__FILE__) - 1);          \
+    ::absl::raw_logging_internal::RawLog(ABSL_RAW_LOGGING_INTERNAL_##severity, \
+                                         absl_raw_logging_internal_basename,   \
+                                         __LINE__, __VA_ARGS__);               \
+  } while (0)
+
+// Similar to CHECK(condition) << message, but for low-level modules:
+// we use only ABSL_RAW_LOG that does not allocate memory.
+// We do not want to provide args list here to encourage this usage:
+//   if (!cond)  ABSL_RAW_LOG(FATAL, "foo ...", hard_to_compute_args);
+// so that the args are not computed when not needed.
+#define ABSL_RAW_CHECK(condition, message)                             \
+  do {                                                                 \
+    if (ABSL_PREDICT_FALSE(!(condition))) {                            \
+      ABSL_RAW_LOG(FATAL, "Check %s failed: %s", #condition, message); \
+    }                                                                  \
+  } while (0)
+
+#define ABSL_RAW_LOGGING_INTERNAL_INFO ::absl::LogSeverity::kInfo
+#define ABSL_RAW_LOGGING_INTERNAL_WARNING ::absl::LogSeverity::kWarning
+#define ABSL_RAW_LOGGING_INTERNAL_ERROR ::absl::LogSeverity::kError
+#define ABSL_RAW_LOGGING_INTERNAL_FATAL ::absl::LogSeverity::kFatal
+#define ABSL_RAW_LOGGING_INTERNAL_LEVEL(severity) \
+  ::absl::NormalizeLogSeverity(severity)
+
+namespace absl {
+namespace raw_logging_internal {
+
+// Helper function to implement ABSL_RAW_LOG
+// Logs format... at "severity" level, reporting it
+// as called from file:line.
+// This does not allocate memory or acquire locks.
+void RawLog(absl::LogSeverity severity, const char* file, int line,
+            const char* format, ...) ABSL_PRINTF_ATTRIBUTE(4, 5);
+
+// compile-time function to get the "base" filename, that is, the part of
+// a filename after the last "/" or "\" path separator.  The search starts at
+// the end of the std::string; the second parameter is the length of the std::string.
+constexpr const char* Basename(const char* fname, int offset) {
+  return offset == 0 || fname[offset - 1] == '/' || fname[offset - 1] == '\\'
+             ? fname + offset
+             : Basename(fname, offset - 1);
+}
+
+// For testing only.
+// Returns true if raw logging is fully supported. When it is not
+// fully supported, no messages will be emitted, but a log at FATAL
+// severity will cause an abort.
+//
+// TODO(gfalcon): Come up with a better name for this method.
+bool RawLoggingFullySupported();
+
+// Function type for a raw_logging customization hook for suppressing messages
+// by severity, and for writing custom prefixes on non-suppressed messages.
+//
+// The installed hook is called for every raw log invocation.  The message will
+// be logged to stderr only if the hook returns true.  FATAL errors will cause
+// the process to abort, even if writing to stderr is suppressed.  The hook is
+// also provided with an output buffer, where it can write a custom log message
+// prefix.
+//
+// The raw_logging system does not allocate memory or grab locks.  User-provided
+// hooks must avoid these operations, and must not throw exceptions.
+//
+// 'severity' is the severity level of the message being written.
+// 'file' and 'line' are the file and line number where the ABSL_RAW_LOG macro
+// was located.
+// 'buffer' and 'buf_size' are pointers to the buffer and buffer size.  If the
+// hook writes a prefix, it must increment *buffer and decrement *buf_size
+// accordingly.
+using LogPrefixHook = bool (*)(absl::LogSeverity severity, const char* file,
+                               int line, char** buffer, int* buf_size);
+
+// Function type for a raw_logging customization hook called to abort a process
+// when a FATAL message is logged.  If the provided AbortHook() returns, the
+// logging system will call abort().
+//
+// 'file' and 'line' are the file and line number where the ABSL_RAW_LOG macro
+// was located.
+// The null-terminated logged message lives in the buffer between 'buf_start'
+// and 'buf_end'.  'prefix_end' points to the first non-prefix character of the
+// buffer (as written by the LogPrefixHook.)
+using AbortHook = void (*)(const char* file, int line, const char* buf_start,
+                           const char* prefix_end, const char* buf_end);
+
+}  // namespace raw_logging_internal
+}  // namespace absl
+
+#endif  // ABSL_BASE_INTERNAL_RAW_LOGGING_H_