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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.
+
+#include "absl/base/internal/raw_logging.h"
+
+#include <stddef.h>
+#include <cstdarg>
+#include <cstdio>
+#include <cstdlib>
+#include <cstring>
+
+#include "absl/base/config.h"
+#include "absl/base/internal/atomic_hook.h"
+#include "absl/base/internal/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(__Fuchsia__)
+#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(__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) {
+ 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 absl {
+namespace raw_logging_internal {
+void SafeWriteToStderr(const char *s, size_t len);
+} // namespace raw_logging_internal
+} // namespace absl
+
+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) {
+ 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 (static_cast<int>(severity) < 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 {
+
+// Writes the provided buffer directly to stderr, in a safe, low-level manner.
+//
+// In POSIX this means calling write(), which is async-signal safe and does
+// not malloc. If the platform supports the SYS_write syscall, we invoke that
+// directly to side-step any libc interception.
+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, ...) {
+ va_list ap;
+ va_start(ap, format);
+ RawLogVA(severity, file, line, format, ap);
+ va_end(ap);
+}
+
+bool RawLoggingFullySupported() {
+#ifdef ABSL_LOW_LEVEL_WRITE_SUPPORTED
+ return true;
+#else // !ABSL_LOW_LEVEL_WRITE_SUPPORTED
+ return false;
+#endif // !ABSL_LOW_LEVEL_WRITE_SUPPORTED
+}
+
+} // namespace raw_logging_internal
+} // namespace absl