logging: add support for streaming operators

[folly.git] / folly / experimental / logging / LogStream.h

diff --git a/folly/experimental/logging/LogStream.h b/folly/experimental/logging/LogStream.h
new file mode 100644 (file)
index 0000000..82987f1
--- /dev/null
+++ b/folly/experimental/logging/LogStream.h
@@ -0,0 +1,79 @@
+/*
+ * Copyright 2004-present Facebook, Inc.
+ *
+ * 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.
+ */
+#pragma once
+
+#include <ostream>
+
+#include <folly/experimental/logging/LogCategory.h>
+#include <folly/experimental/logging/LogMessage.h>
+
+namespace folly {
+
+/**
+ * A std::streambuf implementation for use by LogStream
+ */
+class LogStreamBuffer : public std::streambuf {
+ public:
+  LogStreamBuffer() {
+    // We intentionally do not reserve any string buffer space initially,
+    // since this will not be needed for XLOG() and XLOGF() statements
+    // that do not use the streaming API.  (e.g., XLOG(INFO, "test ", 1234) )
+  }
+
+  bool empty() const {
+    return str_.empty();
+  }
+
+  std::string extractString() {
+    str_.resize(pptr() - (&str_.front()));
+    return std::move(str_);
+  }
+
+  int_type overflow(int_type ch) override;
+
+ private:
+  enum : size_t { kInitialCapacity = 256 };
+  std::string str_;
+};
+
+/**
+ * A std::ostream implementation for use by the logging macros.
+ *
+ * All-in-all this is pretty similar to std::stringstream, but lets us
+ * destructively extract an rvalue-reference to the underlying string.
+ */
+class LogStream : public std::ostream {
+ public:
+  // Explicitly declare the default constructor and destructor, but only
+  // define them in the .cpp file.  This prevents them from being inlined at
+  // each FB_LOG() or XLOG() statement.  Inlining them just causes extra code
+  // bloat, with minimal benefit--for debug log statements these never even get
+  // called in the common case where the log statement is disabled.
+  LogStream();
+  ~LogStream();
+
+  bool empty() const {
+    return buffer_.empty();
+  }
+
+  std::string extractString() {
+    return buffer_.extractString();
+  }
+
+ private:
+  LogStreamBuffer buffer_;
+};
+}