From 54cacecab4b1e16e52579f84125be6e6ea13f5a4 Mon Sep 17 00:00:00 2001
From: Dan Zhang <danzh@google.com>
Date: Mon, 4 Feb 2019 11:43:22 -0500
Subject: [PATCH 01/14] IoHandle interface

Signed-off-by: Dan Zhang <danzh@google.com>
---
 include/envoy/network/io_handle.h | 62 +++++++++++++++++++++++++++----
 1 file changed, 54 insertions(+), 8 deletions(-)

diff --git a/include/envoy/network/io_handle.h b/include/envoy/network/io_handle.h
index c00c2288278dd..8515ac6494e63 100644
--- a/include/envoy/network/io_handle.h
+++ b/include/envoy/network/io_handle.h
@@ -7,27 +7,73 @@
 namespace Envoy {
 namespace Network {
 
+template <typename T> struct IoHandleCallResult {
+  T rc_;
+  int errno_;
+};
+
+typedef IoHandleCallResult<int> IoHandleCallIntResult;
+typedef IoHandleCallResult<ssize_t> IoHandleCallSizeResult;
+
 /**
  * IoHandle: an abstract interface for all I/O operations
  */
 class IoHandle {
 public:
-  IoHandle() {}
-
   virtual ~IoHandle() {}
 
   /**
-   * Return data associated with IoHandle.
-   *
-   * TODO(sbelair2) remove fd() method
+   * Clean up IoHandle resources
    */
-  virtual int fd() const PURE;
+  virtual IoHandleCallIntResult close() PURE;
+
+  virtual bool isClosed() PURE;
+
+  virtual IoHandleCallSizeResult readv(const iovec* iovec, int num_iovec) PURE;
+
+  virtual IoHandleCallSizeResult writev(const iovec* iovec, int num_iovec) PURE;
+
+  virtual IoHandleCallIntResult bind(const Network::Address::Instance& address) PURE;
+
+  virtual IoHandleCallIntResult connect(const Network::Address::Instance& server_address) PURE;
 
   /**
-   * Clean up IoHandle resources
+   * Wrap setsockopt()
+   */
+  virtual IoHandleCallIntResult setIoHandleOption(int level, int optname, const void* optval,
+                                                  socklen_t optlen) PURE;
+  /**
+   * Wrap getsockopt()
+   */
+  virtual IoHandleCallIntResult getIoHandleOption(int level, int optname, void* optval,
+                                                  socklen_t* optlen) PURE;
+
+  /**
+   * Wrap getsockname()
+   */
+  virtual IoHandleCallIntResult getIoHandleName(const Network::Address::Instance& address) PURE;
+
+  virtual IoHandleCallIntResult getPeerName(const Network::Address::Instance& address) PURE;
+
+  /**
+   * Wrap fcntl(fd_, F_SETFL...)
+   */
+  virtual IoHandleCallIntResult setIoHandleFlag(int flag) PURE;
+  /**
+   * Wrap fcntl(fd_, F_GETFL...)
    */
-  virtual void close() PURE;
+  virtual IoHandleCallIntResult getIoHandleFlag() PURE;
+
+  virtual IoHandleCallIntResult listen(int backlog) PURE;
+
+  /**
+   * Wrap dup()
+   */
+  virtual IoHandlePtr dup() PURE;
+
+  virtual IoHandleCallIntResult shutdown(int how) PURE;
 };
+
 typedef std::unique_ptr<IoHandle> IoHandlePtr;
 
 } // namespace Network

From 8dc3b1361325e02334d393e23388c3df477ed2bd Mon Sep 17 00:00:00 2001
From: Dan Zhang <danzh@google.com>
Date: Mon, 4 Feb 2019 12:22:12 -0500
Subject: [PATCH 02/14] fix compile error

Signed-off-by: Dan Zhang <danzh@google.com>
---
 include/envoy/network/io_handle.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/envoy/network/io_handle.h b/include/envoy/network/io_handle.h
index 8515ac6494e63..7b1c783577a69 100644
--- a/include/envoy/network/io_handle.h
+++ b/include/envoy/network/io_handle.h
@@ -69,7 +69,7 @@ class IoHandle {
   /**
    * Wrap dup()
    */
-  virtual IoHandlePtr dup() PURE;
+  virtual std::unique_ptr<IoHandle> dup() PURE;
 
   virtual IoHandleCallIntResult shutdown(int how) PURE;
 };

From c6bd520369644fdcca1fc04cc24813f79190c0e2 Mon Sep 17 00:00:00 2001
From: Dan Zhang <danzh@google.com>
Date: Mon, 4 Feb 2019 13:45:42 -0500
Subject: [PATCH 03/14] forward declare address

Signed-off-by: Dan Zhang <danzh@google.com>
---
 include/envoy/network/io_handle.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/include/envoy/network/io_handle.h b/include/envoy/network/io_handle.h
index 7b1c783577a69..9feb1814276c2 100644
--- a/include/envoy/network/io_handle.h
+++ b/include/envoy/network/io_handle.h
@@ -3,6 +3,9 @@
 #include <memory>
 
 #include "envoy/common/pure.h"
+#include "envoy/network/address.h"
+
+class Network::Address::Instance;
 
 namespace Envoy {
 namespace Network {

From 2315a7f1e260a571954f333f6b9461b8fcd7f74a Mon Sep 17 00:00:00 2001
From: Dan Zhang <danzh@google.com>
Date: Mon, 4 Feb 2019 14:17:21 -0500
Subject: [PATCH 04/14] fix inlcude

Signed-off-by: Dan Zhang <danzh@google.com>
---
 include/envoy/network/io_handle.h | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/include/envoy/network/io_handle.h b/include/envoy/network/io_handle.h
index 9feb1814276c2..ea4215782ac1f 100644
--- a/include/envoy/network/io_handle.h
+++ b/include/envoy/network/io_handle.h
@@ -3,13 +3,14 @@
 #include <memory>
 
 #include "envoy/common/pure.h"
-#include "envoy/network/address.h"
-
-class Network::Address::Instance;
 
 namespace Envoy {
 namespace Network {
 
+namespace Address {
+class Instance;
+}  // namespace Address
+
 template <typename T> struct IoHandleCallResult {
   T rc_;
   int errno_;
@@ -25,6 +26,16 @@ class IoHandle {
 public:
   virtual ~IoHandle() {}
 
+  /**
+   * Return data associated with IoHandle.
+   *
+   * TODO(sbelair2) remove fd() method
+   * We probably still need some method similar to this one for
+   * evconnlistener_new(). Or We can move it to IoSocketHandle and down cast the
+   * IoHandle to IoSocketHandle wherever needed.
+   */
+  virtual int fd() const PURE;
+
   /**
    * Clean up IoHandle resources
    */

From 800bf4a8c2708817eae23d57c13f55bcc8fab519 Mon Sep 17 00:00:00 2001
From: Dan Zhang <danzh@google.com>
Date: Mon, 4 Feb 2019 14:18:53 -0500
Subject: [PATCH 05/14] format

Signed-off-by: Dan Zhang <danzh@google.com>
---
 include/envoy/network/io_handle.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/envoy/network/io_handle.h b/include/envoy/network/io_handle.h
index ea4215782ac1f..830c361fdc961 100644
--- a/include/envoy/network/io_handle.h
+++ b/include/envoy/network/io_handle.h
@@ -9,7 +9,7 @@ namespace Network {
 
 namespace Address {
 class Instance;
-}  // namespace Address
+} // namespace Address
 
 template <typename T> struct IoHandleCallResult {
   T rc_;

From ebe783d1732e2064c749e125ee1b5ad73cb0ca14 Mon Sep 17 00:00:00 2001
From: Dan Zhang <danzh@google.com>
Date: Mon, 4 Feb 2019 17:06:14 -0500
Subject: [PATCH 06/14] make destructor virtual

Signed-off-by: Dan Zhang <danzh@google.com>
---
 include/envoy/network/io_handle.h | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/include/envoy/network/io_handle.h b/include/envoy/network/io_handle.h
index 830c361fdc961..5d662f7b9b471 100644
--- a/include/envoy/network/io_handle.h
+++ b/include/envoy/network/io_handle.h
@@ -11,7 +11,13 @@ namespace Address {
 class Instance;
 } // namespace Address
 
+/**
+ * Basic type for return result which has a return code and error code defined
+ * according to different implementation.
+ */
 template <typename T> struct IoHandleCallResult {
+  virtual ~IoHandleCallResult() {}
+
   T rc_;
   int errno_;
 };

From 3621f3a0f4a35496f336ada663092c2cc121ab38 Mon Sep 17 00:00:00 2001
From: Dan Zhang <danzh@google.com>
Date: Thu, 7 Feb 2019 10:44:55 -0500
Subject: [PATCH 07/14] abstract more types

Signed-off-by: Dan Zhang <danzh@google.com>
---
 include/envoy/network/io_handle.h | 67 ++++++++++++++++++++++++++-----
 1 file changed, 56 insertions(+), 11 deletions(-)

diff --git a/include/envoy/network/io_handle.h b/include/envoy/network/io_handle.h
index 5d662f7b9b471..90d6256528b4e 100644
--- a/include/envoy/network/io_handle.h
+++ b/include/envoy/network/io_handle.h
@@ -1,16 +1,41 @@
 #pragma once
 
+#include <bitset>
 #include <memory>
 
 #include "envoy/common/pure.h"
 
 namespace Envoy {
+
+namespace Buffer {
+struct RawSlice;
+}
+
 namespace Network {
 
 namespace Address {
 class Instance;
 } // namespace Address
 
+class IoError {
+public:
+  enum IoErrorCode {
+    IO_NO_ERROR = 0,
+    IO_EAGAIN,
+    IO_ENOTSUP,
+    IO_EAFNOSUPPORT,
+    IO_EINPROGRESS,
+    IO_EPERM,
+    IO_UNKNOWN_ERROR
+  };
+  virtual ~IoError() {}
+
+  // Map platform specific error into IoErrorCode.
+  virtual IoErrorCode getErrorCode() PURE;
+  
+  virtual std::string getErrorDetails() PURE;
+};
+
 /**
  * Basic type for return result which has a return code and error code defined
  * according to different implementation.
@@ -19,17 +44,28 @@ template <typename T> struct IoHandleCallResult {
   virtual ~IoHandleCallResult() {}
 
   T rc_;
-  int errno_;
+  std::unique_ptr<IoError> err_;
 };
 
-typedef IoHandleCallResult<int> IoHandleCallIntResult;
-typedef IoHandleCallResult<ssize_t> IoHandleCallSizeResult;
+using IoHandleCallIntResult = IoHandleCallResult<int>;
+using IoHandleCallSizeResult = IoHandleCallResult<ssize_t>;
 
 /**
  * IoHandle: an abstract interface for all I/O operations
  */
 class IoHandle {
 public:
+  enum ShutdownType {
+    READ = 0,
+    WRITE,
+    BOTH
+  };
+
+  enum IoHandleFlag {
+    NONBLOCK = 1,
+    APPEND = 2
+  };
+
   virtual ~IoHandle() {}
 
   /**
@@ -49,9 +85,15 @@ class IoHandle {
 
   virtual bool isClosed() PURE;
 
-  virtual IoHandleCallSizeResult readv(const iovec* iovec, int num_iovec) PURE;
+  virtual IoHandleCallSizeResult readv(Buffer::RawSlice* iovecs, int num_iovec) PURE;
+
+  virtual IoHandleCallIntResult recvmmsg(struct mmsghdr *msgvec, unsigned int vlen,
+                    int flags, struct timespec *timeout) PURE;
+
+  virtual IoHandleCallSizeResult writev(const Buffer::RawSlice* iovec, int num_iovec) PURE;
 
-  virtual IoHandleCallSizeResult writev(const iovec* iovec, int num_iovec) PURE;
+  virtual IoHandleCallIntResult sendmmsg(struct mmsghdr* msgvec, unsigned int vlen,
+                    int flags) PURE;
 
   virtual IoHandleCallIntResult bind(const Network::Address::Instance& address) PURE;
 
@@ -69,20 +111,23 @@ class IoHandle {
                                                   socklen_t* optlen) PURE;
 
   /**
-   * Wrap getsockname()
+   * Wrap Address::addressFromFd()
    */
-  virtual IoHandleCallIntResult getIoHandleName(const Network::Address::Instance& address) PURE;
+  virtual IoHandleCallIntResult getBindToAddress(Network::Address::Instance** address) PURE;
 
-  virtual IoHandleCallIntResult getPeerName(const Network::Address::Instance& address) PURE;
+  /**
+   * Wrap Address::peerAddressFromFd()
+   */
+  virtual IoHandleCallIntResult getPeerAddress(Network::Address::Instance** address) PURE;
 
   /**
    * Wrap fcntl(fd_, F_SETFL...)
    */
-  virtual IoHandleCallIntResult setIoHandleFlag(int flag) PURE;
+  virtual IoHandleCallIntResult setIoHandleFlag(std::bitset<2> flag) PURE;
   /**
    * Wrap fcntl(fd_, F_GETFL...)
    */
-  virtual IoHandleCallIntResult getIoHandleFlag() PURE;
+  virtual IoHandleCallResult<std::bitset<2>> getIoHandleFlags() PURE;
 
   virtual IoHandleCallIntResult listen(int backlog) PURE;
 
@@ -91,7 +136,7 @@ class IoHandle {
    */
   virtual std::unique_ptr<IoHandle> dup() PURE;
 
-  virtual IoHandleCallIntResult shutdown(int how) PURE;
+  virtual IoHandleCallIntResult shutdown(ShutdownType how) PURE;
 };
 
 typedef std::unique_ptr<IoHandle> IoHandlePtr;

From 47109ecc88db177d7706191142775f828600d72e Mon Sep 17 00:00:00 2001
From: Dan Zhang <danzh@google.com>
Date: Thu, 7 Feb 2019 10:58:14 -0500
Subject: [PATCH 08/14] format

Signed-off-by: Dan Zhang <danzh@google.com>
---
 include/envoy/network/io_handle.h | 20 ++++++--------------
 1 file changed, 6 insertions(+), 14 deletions(-)

diff --git a/include/envoy/network/io_handle.h b/include/envoy/network/io_handle.h
index 90d6256528b4e..1bf6b3653cdfc 100644
--- a/include/envoy/network/io_handle.h
+++ b/include/envoy/network/io_handle.h
@@ -32,7 +32,7 @@ class IoError {
 
   // Map platform specific error into IoErrorCode.
   virtual IoErrorCode getErrorCode() PURE;
-  
+
   virtual std::string getErrorDetails() PURE;
 };
 
@@ -55,16 +55,9 @@ using IoHandleCallSizeResult = IoHandleCallResult<ssize_t>;
  */
 class IoHandle {
 public:
-  enum ShutdownType {
-    READ = 0,
-    WRITE,
-    BOTH
-  };
+  enum ShutdownType { READ = 0, WRITE, BOTH };
 
-  enum IoHandleFlag {
-    NONBLOCK = 1,
-    APPEND = 2
-  };
+  enum IoHandleFlag { NONBLOCK = 1, APPEND = 2 };
 
   virtual ~IoHandle() {}
 
@@ -87,13 +80,12 @@ class IoHandle {
 
   virtual IoHandleCallSizeResult readv(Buffer::RawSlice* iovecs, int num_iovec) PURE;
 
-  virtual IoHandleCallIntResult recvmmsg(struct mmsghdr *msgvec, unsigned int vlen,
-                    int flags, struct timespec *timeout) PURE;
+  virtual IoHandleCallIntResult recvmmsg(struct mmsghdr* msgvec, unsigned int vlen, int flags,
+                                         struct timespec* timeout) PURE;
 
   virtual IoHandleCallSizeResult writev(const Buffer::RawSlice* iovec, int num_iovec) PURE;
 
-  virtual IoHandleCallIntResult sendmmsg(struct mmsghdr* msgvec, unsigned int vlen,
-                    int flags) PURE;
+  virtual IoHandleCallIntResult sendmmsg(struct mmsghdr* msgvec, unsigned int vlen, int flags) PURE;
 
   virtual IoHandleCallIntResult bind(const Network::Address::Instance& address) PURE;
 

From 9139a8991fe17f29ff50f42a569bca85c3bbd1ae Mon Sep 17 00:00:00 2001
From: Dan Zhang <danzh@google.com>
Date: Fri, 8 Feb 2019 13:17:35 -0500
Subject: [PATCH 09/14] rename enum's

Signed-off-by: Dan Zhang <danzh@google.com>
---
 include/envoy/network/io_handle.h | 22 +++++++++++-----------
 1 file changed, 11 insertions(+), 11 deletions(-)

diff --git a/include/envoy/network/io_handle.h b/include/envoy/network/io_handle.h
index 1bf6b3653cdfc..d36ab0418122c 100644
--- a/include/envoy/network/io_handle.h
+++ b/include/envoy/network/io_handle.h
@@ -19,14 +19,14 @@ class Instance;
 
 class IoError {
 public:
-  enum IoErrorCode {
-    IO_NO_ERROR = 0,
-    IO_EAGAIN,
-    IO_ENOTSUP,
-    IO_EAFNOSUPPORT,
-    IO_EINPROGRESS,
-    IO_EPERM,
-    IO_UNKNOWN_ERROR
+  enum class IoErrorCode {
+    NoError = 0,
+    Again,
+    NoSupport,
+    AddressFamilyNoSupport,
+    InProgress,
+    Permission,
+    UnknownError
   };
   virtual ~IoError() {}
 
@@ -38,7 +38,7 @@ class IoError {
 
 /**
  * Basic type for return result which has a return code and error code defined
- * according to different implementation.
+ * according to different implementations.
  */
 template <typename T> struct IoHandleCallResult {
   virtual ~IoHandleCallResult() {}
@@ -55,9 +55,9 @@ using IoHandleCallSizeResult = IoHandleCallResult<ssize_t>;
  */
 class IoHandle {
 public:
-  enum ShutdownType { READ = 0, WRITE, BOTH };
+  enum class ShutdownType { Read = 0, Write, Both };
 
-  enum IoHandleFlag { NONBLOCK = 1, APPEND = 2 };
+  enum class IoHandleFlag { NonBlock = 1, Append = 2 };
 
   virtual ~IoHandle() {}
 

From d50cc2ad857bac711e9cd71e218ed574e12f3230 Mon Sep 17 00:00:00 2001
From: Dan Zhang <danzh@google.com>
Date: Fri, 8 Feb 2019 14:44:40 -0500
Subject: [PATCH 10/14] add const

Signed-off-by: Dan Zhang <danzh@google.com>
---
 include/envoy/network/io_handle.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/envoy/network/io_handle.h b/include/envoy/network/io_handle.h
index d36ab0418122c..328e873b44e3d 100644
--- a/include/envoy/network/io_handle.h
+++ b/include/envoy/network/io_handle.h
@@ -31,9 +31,9 @@ class IoError {
   virtual ~IoError() {}
 
   // Map platform specific error into IoErrorCode.
-  virtual IoErrorCode getErrorCode() PURE;
+  virtual IoErrorCode getErrorCode() const PURE;
 
-  virtual std::string getErrorDetails() PURE;
+  virtual std::string getErrorDetails() const PURE;
 };
 
 /**

From 658fceb0b63582b002e6e56821f7592c4f07b9a7 Mon Sep 17 00:00:00 2001
From: Dan Zhang <danzh@google.com>
Date: Mon, 11 Feb 2019 16:17:09 -0500
Subject: [PATCH 11/14] document enum

Signed-off-by: Dan Zhang <danzh@google.com>
---
 include/envoy/network/io_handle.h | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/include/envoy/network/io_handle.h b/include/envoy/network/io_handle.h
index 328e873b44e3d..1521dfaad8ad1 100644
--- a/include/envoy/network/io_handle.h
+++ b/include/envoy/network/io_handle.h
@@ -9,7 +9,7 @@ namespace Envoy {
 
 namespace Buffer {
 struct RawSlice;
-}
+} // namespace Buffer
 
 namespace Network {
 
@@ -20,12 +20,19 @@ class Instance;
 class IoError {
 public:
   enum class IoErrorCode {
+    // Success.
     NoError = 0,
+    // No data available right now, try again later.
     Again,
+    // Not supported.
     NoSupport,
+    // Address family not supported.
     AddressFamilyNoSupport,
+    // During non-blocking connect, the connection cannot be completed immediately.
     InProgress,
+    // Permission denied.
     Permission,
+    // Other error codes cannot be mapped to any one above in getErrorCode().
     UnknownError
   };
   virtual ~IoError() {}
@@ -114,6 +121,10 @@ class IoHandle {
 
   /**
    * Wrap fcntl(fd_, F_SETFL...)
+   * @param flag each bit stands for a flag in enum IoHandleFlag. From low bit
+   * to high bit:
+   * 1st -- NonBlock
+   * 2nd -- Append
    */
   virtual IoHandleCallIntResult setIoHandleFlag(std::bitset<2> flag) PURE;
   /**

From d02c020589b347dbdd9102131439dfe53f7662d8 Mon Sep 17 00:00:00 2001
From: Dan Zhang <danzh@google.com>
Date: Mon, 11 Feb 2019 17:11:02 -0500
Subject: [PATCH 12/14] use binary literal

Signed-off-by: Dan Zhang <danzh@google.com>
---
 include/envoy/network/io_handle.h | 13 ++++---------
 1 file changed, 4 insertions(+), 9 deletions(-)

diff --git a/include/envoy/network/io_handle.h b/include/envoy/network/io_handle.h
index 1521dfaad8ad1..087ef4d7c026c 100644
--- a/include/envoy/network/io_handle.h
+++ b/include/envoy/network/io_handle.h
@@ -64,17 +64,15 @@ class IoHandle {
 public:
   enum class ShutdownType { Read = 0, Write, Both };
 
-  enum class IoHandleFlag { NonBlock = 1, Append = 2 };
+  enum class IoHandleFlag { NonBlock = 0b1, Append = 0b10 };
 
   virtual ~IoHandle() {}
 
   /**
    * Return data associated with IoHandle.
    *
-   * TODO(sbelair2) remove fd() method
-   * We probably still need some method similar to this one for
-   * evconnlistener_new(). Or We can move it to IoSocketHandle and down cast the
-   * IoHandle to IoSocketHandle wherever needed.
+   * TODO(danzh) move it to IoSocketHandle after replacing the calls to it with
+   * calls to IoHandle API's everywhere.
    */
   virtual int fd() const PURE;
 
@@ -121,10 +119,7 @@ class IoHandle {
 
   /**
    * Wrap fcntl(fd_, F_SETFL...)
-   * @param flag each bit stands for a flag in enum IoHandleFlag. From low bit
-   * to high bit:
-   * 1st -- NonBlock
-   * 2nd -- Append
+   * @param flag each bit stands for a flag in enum IoHandleFlag.
    */
   virtual IoHandleCallIntResult setIoHandleFlag(std::bitset<2> flag) PURE;
   /**

From 2b6abc727fd344278de025238427102807627e67 Mon Sep 17 00:00:00 2001
From: Dan Zhang <danzh@google.com>
Date: Mon, 11 Feb 2019 17:33:17 -0500
Subject: [PATCH 13/14] format

Signed-off-by: Dan Zhang <danzh@google.com>
---
 include/envoy/network/io_handle.h | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/include/envoy/network/io_handle.h b/include/envoy/network/io_handle.h
index 087ef4d7c026c..f7d5875559328 100644
--- a/include/envoy/network/io_handle.h
+++ b/include/envoy/network/io_handle.h
@@ -64,7 +64,11 @@ class IoHandle {
 public:
   enum class ShutdownType { Read = 0, Write, Both };
 
-  enum class IoHandleFlag { NonBlock = 0b1, Append = 0b10 };
+  enum class IoHandleFlag {
+    // Each of these maps to a unique bit.
+    NonBlock = 0b01,
+    Append = 0b10
+  };
 
   virtual ~IoHandle() {}
 

From 096c1e333e6b04c569aeba2af2f6ec217cd2752a Mon Sep 17 00:00:00 2001
From: Dan Zhang <danzh@google.com>
Date: Thu, 21 Feb 2019 16:27:16 -0500
Subject: [PATCH 14/14] update IoError

Signed-off-by: Dan Zhang <danzh@google.com>
---
 include/envoy/network/io_handle.h | 36 ++++++++++++++++++++++++++++---
 1 file changed, 33 insertions(+), 3 deletions(-)

diff --git a/include/envoy/network/io_handle.h b/include/envoy/network/io_handle.h
index f7d5875559328..3155f7f689c5c 100644
--- a/include/envoy/network/io_handle.h
+++ b/include/envoy/network/io_handle.h
@@ -17,11 +17,17 @@ namespace Address {
 class Instance;
 } // namespace Address
 
+class IoError;
+
+// IoErrorCode::Again is used frequently. Define it to be a distinguishable address to avoid
+// frequent memory allocation of IoError instance.
+// If this is used, IoHandleCallResult has to be instantiated with a deleter that does not
+// deallocate memory for this error.
+#define ENVOY_ERROR_AGAIN reinterpret_cast<IoError*>(0x01)
+
 class IoError {
 public:
   enum class IoErrorCode {
-    // Success.
-    NoError = 0,
     // No data available right now, try again later.
     Again,
     // Not supported.
@@ -37,21 +43,45 @@ class IoError {
   };
   virtual ~IoError() {}
 
+  // Map platform specific error into IoErrorCode.
+  // Needed to hide errorCode() in case of ENVOY_ERROR_AGAIN.
+  static IoErrorCode getErrorCode(const IoError& err) {
+    if (&err == ENVOY_ERROR_AGAIN) {
+      return IoErrorCode::Again;
+    }
+    return err.errorCode();
+  }
+
+  static std::string getErrorDetails(const IoError& err) {
+    if (&err == ENVOY_ERROR_AGAIN) {
+      return "Try again later";
+    }
+    return err.errorDetails();
+  }
+
+protected:
   // Map platform specific error into IoErrorCode.
   virtual IoErrorCode getErrorCode() const PURE;
 
   virtual std::string getErrorDetails() const PURE;
 };
 
+using IoErrorDeleterType = void (*)(IoError*);
+using IoErrorPtr = std::unique_ptr<IoError, IoErrorDeleterType>;
+
 /**
  * Basic type for return result which has a return code and error code defined
  * according to different implementations.
+ * If the call succeeds, |err_| is nullptr and |rc_| is valid. Otherwise |err_|
+ * can be passed into IoError::getErrorCode() to extract the error. In this
+ * case, |rc_| is invalid.
  */
 template <typename T> struct IoHandleCallResult {
+  IoHandleCallResult(T rc, IoErrorPtr err) : rc_(rc), err_(std::move(err)) {}
   virtual ~IoHandleCallResult() {}
 
   T rc_;
-  std::unique_ptr<IoError> err_;
+  IoErrorPtr err_;
 };
 
 using IoHandleCallIntResult = IoHandleCallResult<int>;