Add error class

Summary:
Credit to original author Pieter Noordhuis (pietern)

This diff resolves conflicts.

Differential Revision: D45437711

fbshipit-source-id: c651df2b9c9226c502ac552d67193c890d95c61d

Author: xunnanxu

gloo/transport/tcp/CMakeLists.txt

@@ -6,6 +6,7 @@ else()
       "${CMAKE_CURRENT_SOURCE_DIR}/buffer.cc"
       "${CMAKE_CURRENT_SOURCE_DIR}/context.cc"
       "${CMAKE_CURRENT_SOURCE_DIR}/device.cc"
+      "${CMAKE_CURRENT_SOURCE_DIR}/error.cc"
       "${CMAKE_CURRENT_SOURCE_DIR}/loop.cc"
       "${CMAKE_CURRENT_SOURCE_DIR}/pair.cc"
       "${CMAKE_CURRENT_SOURCE_DIR}/socket.cc"
@@ -17,6 +18,7 @@ else()
       "${CMAKE_CURRENT_SOURCE_DIR}/buffer.h"
       "${CMAKE_CURRENT_SOURCE_DIR}/context.h"
       "${CMAKE_CURRENT_SOURCE_DIR}/device.h"
+      "${CMAKE_CURRENT_SOURCE_DIR}/error.h"
       "${CMAKE_CURRENT_SOURCE_DIR}/loop.h"
       "${CMAKE_CURRENT_SOURCE_DIR}/pair.h"
       "${CMAKE_CURRENT_SOURCE_DIR}/socket.h"

gloo/transport/tcp/error.cc

@@ -0,0 +1,46 @@
+/**
+ * Copyright (c) 2017-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#include <gloo/transport/tcp/error.h>
+
+#include <cstring>
+#include <sstream>
+
+namespace gloo {
+namespace transport {
+namespace tcp {
+
+const Error Error::kSuccess = Error();
+
+std::string Error::what() const {
+  return "no error";
+}
+
+std::string SystemError::what() const {
+  std::ostringstream ss;
+  ss << syscall_ << ": " << strerror(error_);
+  return ss.str();
+}
+
+std::string ShortReadError::what() const {
+  std::ostringstream ss;
+  ss << "short read: got " << actual_ << " bytes while expecting to read "
+     << expected_ << " bytes";
+  return ss.str();
+}
+
+std::string ShortWriteError::what() const {
+  std::ostringstream ss;
+  ss << "short write: wrote " << actual_ << " bytes while expecting to write "
+     << expected_ << " bytes";
+  return ss.str();
+}
+
+} // namespace tcp
+} // namespace transport
+} // namespace gloo

gloo/transport/tcp/error.h

@@ -0,0 +1,87 @@
+/**
+ * Copyright (c) 2017-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#pragma once
+
+#include <string>
+
+namespace gloo {
+namespace transport {
+namespace tcp {
+
+class Error {
+ public:
+  // Constant instance that indicates success.
+  static const Error kSuccess;
+
+  /* implicit */ Error() : valid_(false) {}
+
+  virtual ~Error() = default;
+
+  // Converting to boolean means checking if there is an error. This
+  // means we don't need to use an `std::optional` and allows for a
+  // snippet like the following:
+  //
+  //   if (error) {
+  //     // Deal with it.
+  //   }
+  //
+  operator bool() const {
+    return valid_;
+  }
+
+  // Returns an explanatory string.
+  // Like `std::exception` but returns a `std::string`.
+  virtual std::string what() const;
+
+ protected:
+  explicit Error(bool valid) : valid_(valid) {}
+
+ private:
+  const bool valid_;
+};
+
+class SystemError : public Error {
+ public:
+  explicit SystemError(const char* syscall, int error)
+      : Error(true), syscall_(syscall), error_(error) {}
+
+  std::string what() const override;
+
+ private:
+  const char* syscall_;
+  const int error_;
+};
+
+class ShortReadError : public Error {
+ public:
+  ShortReadError(ssize_t expected, ssize_t actual)
+      : Error(true), expected_(expected), actual_(actual) {}
+
+  std::string what() const override;
+
+ private:
+  const ssize_t expected_;
+  const ssize_t actual_;
+};
+
+class ShortWriteError : public Error {
+ public:
+  ShortWriteError(ssize_t expected, ssize_t actual)
+      : Error(true), expected_(expected), actual_(actual) {}
+
+  std::string what() const override;
+
+ private:
+  const ssize_t expected_;
+  const ssize_t actual_;
+};
+
+} // namespace tcp
+} // namespace transport
+} // namespace gloo