text: // 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
  //
  //      https://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.
  
  #include "absl/base/internal/raw_logging.h"
  
  #include <stddef.h>
  #include <cstdarg>
  #include <cstdio>
  #include <cstdlib>
  #include <cstring>
  
  #include "absl/base/attributes.h"
  #include "absl/base/config.h"
  #include "absl/base/internal/atomic_hook.h"
  #include "absl/base/log_severity.h"
  
  // We know how to perform low-level writes to stderr in POSIX and Windows.  For
  // these platforms, we define the token ABSL_LOW_LEVEL_WRITE_SUPPORTED.
  // Much of raw_logging.cc becomes a no-op when we can't output messages,
  // although a FATAL ABSL_RAW_LOG message will still abort the process.
  
  // ABSL_HAVE_POSIX_WRITE is defined when the platform provides posix write()
  // (as from unistd.h)
  //
  // This preprocessor token is also defined in raw_io.cc.  If you need to copy
  // this, consider moving both to config.h instead.
  #if defined(__linux__) || defined(__APPLE__) || defined(__FreeBSD__) || \
      defined(__Fuchsia__) || defined(__native_client__) || \
      defined(__EMSCRIPTEN__) || defined(__ASYLO__)
  
  #include <unistd.h>
  
  #define ABSL_HAVE_POSIX_WRITE 1
  #define ABSL_LOW_LEVEL_WRITE_SUPPORTED 1
  #else
  #undef ABSL_HAVE_POSIX_WRITE
  #endif
  
  // ABSL_HAVE_SYSCALL_WRITE is defined when the platform provides the syscall
  //   syscall(SYS_write, /*int*/ fd, /*char* */ buf, /*size_t*/ len);
  // for low level operations that want to avoid libc.
  #if (defined(__linux__) || defined(__FreeBSD__)) && !defined(__ANDROID__)
  #include <sys/syscall.h>
  #define ABSL_HAVE_SYSCALL_WRITE 1
  #define ABSL_LOW_LEVEL_WRITE_SUPPORTED 1
  #else
  #undef ABSL_HAVE_SYSCALL_WRITE
  #endif
  
  #ifdef _WIN32
  #include <io.h>
  
  #define ABSL_HAVE_RAW_IO 1
  #define ABSL_LOW_LEVEL_WRITE_SUPPORTED 1
  #else
  #undef ABSL_HAVE_RAW_IO
  #endif
  
  // TODO(gfalcon): We want raw-logging to work on as many platforms as possible.
  // Explicitly #error out when not ABSL_LOW_LEVEL_WRITE_SUPPORTED, except for a
  // whitelisted set of platforms for which we expect not to be able to raw log.
  
  ABSL_CONST_INIT static absl::base_internal::AtomicHook<
      absl::raw_logging_internal::LogPrefixHook> log_prefix_hook;
  ABSL_CONST_INIT static absl::base_internal::AtomicHook<
      absl::raw_logging_internal::AbortHook> abort_hook;
  
  #ifdef ABSL_LOW_LEVEL_WRITE_SUPPORTED
  static const char kTruncated[] = " ... (message truncated)\n";
  
  // sprintf the format to the buffer, adjusting *buf and *size to reflect the
  // consumed bytes, and return whether the message fit without truncation.  If
  // truncation occurred, if possible leave room in the buffer for the message
  // kTruncated[].
  inline static bool VADoRawLog(char** buf, int* size, const char* format,
                                va_list ap) ABSL_PRINTF_ATTRIBUTE(3, 0);
  inline static bool VADoRawLog(char** buf, int* size,
                                const char* format, va_list ap) {
    int n = vsnprintf(*buf, *size, format, ap);
    bool result = true;
    if (n < 0 || n > *size) {
      result = false;
      if (static_cast<size_t>(*size) > sizeof(kTruncated)) {
        n = *size - sizeof(kTruncated);  // room for truncation message
      } else {
        n = 0;                           // no room for truncation message
      }
    }
    *size -= n;
    *buf += n;
    return result;
  }
  #endif  // ABSL_LOW_LEVEL_WRITE_SUPPORTED
  
  static constexpr int kLogBufSize = 3000;
  
  namespace {
  
  // CAVEAT: vsnprintf called from *DoRawLog below has some (exotic) code paths
  // that invoke malloc() and getenv() that might acquire some locks.
  
  // Helper for RawLog below.
  // *DoRawLog writes to *buf of *size and move them past the written portion.
  // It returns true iff there was no overflow or error.
  bool DoRawLog(char** buf, int* size, const char* format, ...)
      ABSL_PRINTF_ATTRIBUTE(3, 4);
  bool DoRawLog(char** buf, int* size, const char* format, ...) {
    va_list ap;
    va_start(ap, format);
    int n = vsnprintf(*buf, *size, format, ap);
    va_end(ap);
    if (n < 0 || n > *size) return false;
    *size -= n;
    *buf += n;
    return true;
  }
  
  void RawLogVA(absl::LogSeverity severity, const char* file, int line,
                const char* format, va_list ap) ABSL_PRINTF_ATTRIBUTE(4, 0);
  void RawLogVA(absl::LogSeverity severity, const char* file, int line,
                const char* format, va_list ap) {
    char buffer[kLogBufSize];
    char* buf = buffer;
    int size = sizeof(buffer);
  #ifdef ABSL_LOW_LEVEL_WRITE_SUPPORTED
    bool enabled = true;
  #else
    bool enabled = false;
  #endif
  
  #ifdef ABSL_MIN_LOG_LEVEL
    if (severity < static_cast<absl::LogSeverity>(ABSL_MIN_LOG_LEVEL) &&
        severity < absl::LogSeverity::kFatal) {
      enabled = false;
    }
  #endif
  
    auto log_prefix_hook_ptr = log_prefix_hook.Load();
    if (log_prefix_hook_ptr) {
      enabled = log_prefix_hook_ptr(severity, file, line, &buf, &size);
    } else {
      if (enabled) {
        DoRawLog(&buf, &size, "[%s : %d] RAW: ", file, line);
      }
    }
    const char* const prefix_end = buf;
  
  #ifdef ABSL_LOW_LEVEL_WRITE_SUPPORTED
    if (enabled) {
      bool no_chop = VADoRawLog(&buf, &size, format, ap);
      if (no_chop) {
        DoRawLog(&buf, &size, "\n");
      } else {
        DoRawLog(&buf, &size, "%s", kTruncated);
      }
      absl::raw_logging_internal::SafeWriteToStderr(buffer, strlen(buffer));
    }
  #else
    static_cast<void>(format);
    static_cast<void>(ap);
  #endif
  
    // Abort the process after logging a FATAL message, even if the output itself
    // was suppressed.
    if (severity == absl::LogSeverity::kFatal) {
      abort_hook(file, line, buffer, prefix_end, buffer + kLogBufSize);
      abort();
    }
  }
  
  }  // namespace
  
  namespace absl {
  namespace raw_logging_internal {
  void SafeWriteToStderr(const char *s, size_t len) {
  #if defined(ABSL_HAVE_SYSCALL_WRITE)
    syscall(SYS_write, STDERR_FILENO, s, len);
  #elif defined(ABSL_HAVE_POSIX_WRITE)
    write(STDERR_FILENO, s, len);
  #elif defined(ABSL_HAVE_RAW_IO)
    _write(/* stderr */ 2, s, len);
  #else
    // stderr logging unsupported on this platform
    (void) s;
    (void) len;
  #endif
  }
  
  void RawLog(absl::LogSeverity severity, const char* file, int line,
              const char* format, ...) ABSL_PRINTF_ATTRIBUTE(4, 5);
  void RawLog(absl::LogSeverity severity, const char* file, int line,
              const char* format, ...) {
    va_list ap;
    va_start(ap, format);
    RawLogVA(severity, file, line, format, ap);
    va_end(ap);
  }
  
  // Non-formatting version of RawLog().
  //
  // TODO(gfalcon): When string_view no longer depends on base, change this
  // interface to take its message as a string_view instead.
  static void DefaultInternalLog(absl::LogSeverity severity, const char* file,
                                 int line, const std::string& message) {
    RawLog(severity, file, line, "%s", message.c_str());
  }
  
  bool RawLoggingFullySupported() {
  #ifdef ABSL_LOW_LEVEL_WRITE_SUPPORTED
    return true;
  #else  // !ABSL_LOW_LEVEL_WRITE_SUPPORTED
    return false;
  #endif  // !ABSL_LOW_LEVEL_WRITE_SUPPORTED
  }
  
  ABSL_CONST_INIT absl::base_internal::AtomicHook<InternalLogFunction>
      internal_log_function(DefaultInternalLog);
  
  void RegisterInternalLogFunction(InternalLogFunction func) {
    internal_log_function.Store(func);
  }
  
  }  // namespace raw_logging_internal
  }  // namespace absl
  