Merge bitcoin/bitcoin#28981: Replace Boost.Process with cpp-subprocess

d5a715536e497c160a2520f81334aab6c7490213 build: remove boost::process dependency for building external signer support (Sebastian Falbesoner)
70434b1c443d9251a880d0193af771f574c40617 external_signer: replace boost::process with cpp-subprocess (Sebastian Falbesoner)
cc8b9875b104c31f0a5b5e4195a8278ec55f35f7 Add `cpp-subprocess` header-only library (Hennadii Stepanov)

Pull request description:

  Closes https://github.com/bitcoin/bitcoin/issues/24907.

  This PR is based on **theStack**'s [work](https://github.com/bitcoin/bitcoin/issues/24907#issuecomment-1466087049).

  The `subprocess.hpp` header has been sourced from the [upstream repo](https://github.com/arun11299/cpp-subprocess) with the only modification being the removal of convenience functions, which are not utilized in our codebase.

  Windows-related changes will be addressed in subsequent follow-ups.

ACKs for top commit:
  achow101:
    reACK d5a715536e497c160a2520f81334aab6c7490213
  Sjors:
    re-tACK d5a715536e497c160a2520f81334aab6c7490213
  theStack:
    Light re-ACK d5a715536e497c160a2520f81334aab6c7490213
  fanquake:
    ACK d5a715536e497c160a2520f81334aab6c7490213 - with the expectation that this code is going to be maintained as our own. Next PRs should:

Tree-SHA512: d7fb6fecc3f5792496204190afb7d85b3e207b858fb1a75efe483c05260843b81b27d14b299323bb667c990e87a07197059afea3796cf218ed8b614086bd3611

8 files changed, 2017 insertions, 82 deletions

diff --git a/configure.ac b/configure.ac
index d8b7159e27..63a012b35d 100644
--- a/configure.ac
+++ b/configure.ac
@@ -307,9 +307,9 @@ AC_ARG_ENABLE([werror],
     [enable_werror=no])
 
 AC_ARG_ENABLE([external-signer],
-    [AS_HELP_STRING([--enable-external-signer],[compile external signer support (default is auto, requires Boost::Process)])],
+    [AS_HELP_STRING([--enable-external-signer],[compile external signer support (default is yes)])],
     [use_external_signer=$enableval],
-    [use_external_signer=auto])
+    [use_external_signer=yes])
 
 AC_LANG_PUSH([C++])
 
@@ -1414,56 +1414,14 @@ if test "$use_boost" = "yes"; then
   fi
 fi
 
-if test "$use_external_signer" != "no"; then
-  AC_MSG_CHECKING([whether Boost.Process can be used])
-  TEMP_CXXFLAGS="$CXXFLAGS"
-  dnl Boost 1.78 requires the following workaround.
-  dnl See: https://github.com/boostorg/process/issues/235
-  CXXFLAGS="$CXXFLAGS -Wno-error=narrowing"
-  TEMP_CPPFLAGS="$CPPFLAGS"
-  CPPFLAGS="$CPPFLAGS $BOOST_CPPFLAGS"
-  TEMP_LDFLAGS="$LDFLAGS"
-  dnl Boost 1.73 and older require the following workaround.
-  LDFLAGS="$LDFLAGS $PTHREAD_CFLAGS"
-  AC_LINK_IFELSE([AC_LANG_PROGRAM([[
-    #define BOOST_PROCESS_USE_STD_FS
-    #include <boost/process.hpp>
-  ]],[[
-    namespace bp = boost::process;
-    bp::opstream stdin_stream;
-    bp::ipstream stdout_stream;
-    bp::child c("dummy", bp::std_out > stdout_stream, bp::std_err > stdout_stream, bp::std_in < stdin_stream);
-    stdin_stream << std::string{"test"} << std::endl;
-    if (c.running()) c.terminate();
-    c.wait();
-    c.exit_code();
-  ]])],
-    [have_boost_process="yes"],
-    [have_boost_process="no"])
-  LDFLAGS="$TEMP_LDFLAGS"
-  CPPFLAGS="$TEMP_CPPFLAGS"
-  CXXFLAGS="$TEMP_CXXFLAGS"
-  AC_MSG_RESULT([$have_boost_process])
-  if test "$have_boost_process" = "yes"; then
-    case $host in
-      dnl Boost Process for Windows uses Boost ASIO. Boost ASIO performs
-      dnl pre-main init of Windows networking libraries, which we do not
-      dnl want.
-      *mingw*)
-        use_external_signer="no"
-      ;;
-      *)
-        use_external_signer="yes"
-        AC_DEFINE([ENABLE_EXTERNAL_SIGNER], [1], [Define if external signer support is enabled])
-        AC_DEFINE([BOOST_PROCESS_USE_STD_FS], [1], [Defined to avoid Boost::Process trying to use Boost Filesystem])
-      ;;
-    esac
-  else
-    if test "$use_external_signer" = "yes"; then
-      AC_MSG_ERROR([External signing is not supported for this Boost version])
-    fi
-    use_external_signer="no";
-  fi
+case $host in
+  dnl Re-enable it after enabling Windows support in cpp-subprocess.
+  *mingw*)
+    use_external_signer="no"
+  ;;
+esac
+if test "$use_external_signer" = "yes"; then
+  AC_DEFINE([ENABLE_EXTERNAL_SIGNER], [1], [Define if external signer support is enabled])
 fi
 AM_CONDITIONAL([ENABLE_EXTERNAL_SIGNER], [test "$use_external_signer" = "yes"])
 
diff --git a/src/Makefile.am b/src/Makefile.am
index 11b8f6e4c3..7673d2f545 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -320,6 +320,7 @@ BITCOIN_CORE_H = \
   util/sock.h \
   util/spanparsing.h \
   util/string.h \
+  util/subprocess.hpp \
   util/syserror.h \
   util/task_runner.h \
   util/thread.h \
diff --git a/src/common/run_command.cpp b/src/common/run_command.cpp
index 8bd5febd53..e5356490ef 100644
--- a/src/common/run_command.cpp
+++ b/src/common/run_command.cpp
@@ -12,39 +12,34 @@
 #include <univalue.h>
 
 #ifdef ENABLE_EXTERNAL_SIGNER
-#include <boost/process.hpp>
+#include <util/subprocess.hpp>
 #endif // ENABLE_EXTERNAL_SIGNER
 
 UniValue RunCommandParseJSON(const std::string& str_command, const std::string& str_std_in)
 {
 #ifdef ENABLE_EXTERNAL_SIGNER
-    namespace bp = boost::process;
+    namespace sp = subprocess;
 
     UniValue result_json;
-    bp::opstream stdin_stream;
-    bp::ipstream stdout_stream;
-    bp::ipstream stderr_stream;
+    std::istringstream stdout_stream;
+    std::istringstream stderr_stream;
 
     if (str_command.empty()) return UniValue::VNULL;
 
-    bp::child c(
-        str_command,
-        bp::std_out > stdout_stream,
-        bp::std_err > stderr_stream,
-        bp::std_in < stdin_stream
-    );
+    auto c = sp::Popen(str_command, sp::input{sp::PIPE}, sp::output{sp::PIPE}, sp::error{sp::PIPE});
     if (!str_std_in.empty()) {
-        stdin_stream << str_std_in << std::endl;
+        c.send(str_std_in);
     }
-    stdin_stream.pipe().close();
+    auto [out_res, err_res] = c.communicate();
+    stdout_stream.str(std::string{out_res.buf.begin(), out_res.buf.end()});
+    stderr_stream.str(std::string{err_res.buf.begin(), err_res.buf.end()});
 
     std::string result;
     std::string error;
     std::getline(stdout_stream, result);
     std::getline(stderr_stream, error);
 
-    c.wait();
-    const int n_error = c.exit_code();
+    const int n_error = c.retcode();
     if (n_error) throw std::runtime_error(strprintf("RunCommandParseJSON error: process(%s) returned %d: %s\n", str_command, n_error, error));
     if (!result_json.read(result)) throw std::runtime_error("Unable to parse JSON: " + result);
 
diff --git a/src/external_signer.cpp b/src/external_signer.cpp
index 749bb5f74f..ff159a2aa5 100644
--- a/src/external_signer.cpp
+++ b/src/external_signer.cpp
@@ -62,12 +62,12 @@ bool ExternalSigner::Enumerate(const std::string& command, std::vector<ExternalS
 
 UniValue ExternalSigner::DisplayAddress(const std::string& descriptor) const
 {
-    return RunCommandParseJSON(m_command + " --fingerprint \"" + m_fingerprint + "\"" + NetworkArg() + " displayaddress --desc \"" + descriptor + "\"");
+    return RunCommandParseJSON(m_command + " --fingerprint " + m_fingerprint + NetworkArg() + " displayaddress --desc " + descriptor);
 }
 
 UniValue ExternalSigner::GetDescriptors(const int account)
 {
-    return RunCommandParseJSON(m_command + " --fingerprint \"" + m_fingerprint + "\"" + NetworkArg() + " getdescriptors --account " + strprintf("%d", account));
+    return RunCommandParseJSON(m_command + " --fingerprint " + m_fingerprint + NetworkArg() + " getdescriptors --account " + strprintf("%d", account));
 }
 
 bool ExternalSigner::SignTransaction(PartiallySignedTransaction& psbtx, std::string& error)
@@ -93,8 +93,8 @@ bool ExternalSigner::SignTransaction(PartiallySignedTransaction& psbtx, std::str
         return false;
     }
 
-    const std::string command = m_command + " --stdin --fingerprint \"" + m_fingerprint + "\"" + NetworkArg();
-    const std::string stdinStr = "signtx \"" + EncodeBase64(ssTx.str()) + "\"";
+    const std::string command = m_command + " --stdin --fingerprint " + m_fingerprint + NetworkArg();
+    const std::string stdinStr = "signtx " + EncodeBase64(ssTx.str());
 
     const UniValue signer_result = RunCommandParseJSON(command, stdinStr);
 
diff --git a/src/test/system_tests.cpp b/src/test/system_tests.cpp
index 90fce9adf9..8aab2b565c 100644
--- a/src/test/system_tests.cpp
+++ b/src/test/system_tests.cpp
@@ -11,7 +11,7 @@
 #include <univalue.h>
 
 #ifdef ENABLE_EXTERNAL_SIGNER
-#include <boost/process.hpp>
+#include <util/subprocess.hpp>
 #endif // ENABLE_EXTERNAL_SIGNER
 
 #include <boost/test/unit_test.hpp>
@@ -34,20 +34,16 @@ BOOST_AUTO_TEST_CASE(run_command)
         BOOST_CHECK(result.isNull());
     }
     {
-        const UniValue result = RunCommandParseJSON("echo \"{\"success\": true}\"");
+        const UniValue result = RunCommandParseJSON("echo {\"success\": true}");
         BOOST_CHECK(result.isObject());
         const UniValue& success = result.find_value("success");
         BOOST_CHECK(!success.isNull());
         BOOST_CHECK_EQUAL(success.get_bool(), true);
     }
     {
-        // An invalid command is handled by Boost
-        const int expected_error{2};
-        BOOST_CHECK_EXCEPTION(RunCommandParseJSON("invalid_command"), boost::process::process_error, [&](const boost::process::process_error& e) {
-            BOOST_CHECK(std::string(e.what()).find("RunCommandParseJSON error:") == std::string::npos);
-            BOOST_CHECK_EQUAL(e.code().value(), expected_error);
-            return true;
-        });
+        // An invalid command is handled by cpp-subprocess
+        const std::string expected{"execve failed: "};
+        BOOST_CHECK_EXCEPTION(RunCommandParseJSON("invalid_command"), subprocess::CalledProcessError, HasReason(expected));
     }
     {
         // Return non-zero exit code, no output to stderr
diff --git a/src/util/subprocess.hpp b/src/util/subprocess.hpp
new file mode 100644
index 0000000000..dd53a8fbb4
--- /dev/null
+++ b/src/util/subprocess.hpp
@@ -0,0 +1,1986 @@
+/*!
+
+Documentation for C++ subprocessing libraray.
+
+@copyright The code is licensed under the [MIT
+  License](http://opensource.org/licenses/MIT):
+  <br>
+  Copyright &copy; 2016-2018 Arun Muralidharan.
+  <br>
+  Permission is hereby granted, free of charge, to any person obtaining a copy
+  of this software and associated documentation files (the "Software"), to deal
+  in the Software without restriction, including without limitation the rights
+  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+  copies of the Software, and to permit persons to whom the Software is
+  furnished to do so, subject to the following conditions:
+  <br>
+  The above copyright notice and this permission notice shall be included in
+  all copies or substantial portions of the Software.
+  <br>
+  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+  SOFTWARE.
+
+@author [Arun Muralidharan]
+@see https://github.com/arun11299/cpp-subprocess to download the source code
+
+@version 1.0.0
+*/
+
+#ifndef SUBPROCESS_HPP
+#define SUBPROCESS_HPP
+
+#include <algorithm>
+#include <cassert>
+#include <csignal>
+#include <cstdio>
+#include <cstdlib>
+#include <cstring>
+#include <exception>
+#include <future>
+#include <initializer_list>
+#include <iostream>
+#include <locale>
+#include <map>
+#include <memory>
+#include <sstream>
+#include <string>
+#include <vector>
+
+#if (defined _MSC_VER) || (defined __MINGW32__)
+  #define __USING_WINDOWS__
+#endif
+
+#ifdef __USING_WINDOWS__
+  #include <codecvt>
+#endif
+
+extern "C" {
+#ifdef __USING_WINDOWS__
+  #include <Windows.h>
+  #include <io.h>
+  #include <cwchar>
+
+  #define close _close
+  #define open _open
+  #define fileno _fileno
+#else
+  #include <sys/wait.h>
+  #include <unistd.h>
+#endif
+  #include <csignal>
+  #include <fcntl.h>
+  #include <sys/types.h>
+}
+
+/*!
+ * Getting started with reading this source code.
+ * The source is mainly divided into four parts:
+ * 1. Exception Classes:
+ *    These are very basic exception classes derived from
+ *    runtime_error exception.
+ *    There are two types of exception thrown from subprocess
+ *    library: OSError and CalledProcessError
+ *
+ * 2. Popen Class
+ *    This is the main class the users will deal with. It
+ *    provides with all the API's to deal with processes.
+ *
+ * 3. Util namespace
+ *    It includes some helper functions to split/join a string,
+ *    reading from file descriptors, waiting on a process, fcntl
+ *    options on file descriptors etc.
+ *
+ * 4. Detail namespace
+ *    This includes some metaprogramming and helper classes.
+ */
+
+
+namespace subprocess {
+
+// Max buffer size allocated on stack for read error
+// from pipe
+static const size_t SP_MAX_ERR_BUF_SIZ = 1024;
+
+// Default buffer capcity for OutBuffer and ErrBuffer.
+// If the data exceeds this capacity, the buffer size is grown
+// by 1.5 times its previous capacity
+static const size_t DEFAULT_BUF_CAP_BYTES = 8192;
+
+
+/*-----------------------------------------------
+ *    EXCEPTION CLASSES
+ *-----------------------------------------------
+ */
+
+/*!
+ * class: CalledProcessError
+ * Thrown when there was error executing the command.
+ * Check Popen class API's to know when this exception
+ * can be thrown.
+ *
+ */
+class CalledProcessError: public std::runtime_error
+{
+public:
+  int retcode;
+  CalledProcessError(const std::string& error_msg, int retcode):
+    std::runtime_error(error_msg), retcode(retcode)
+  {}
+};
+
+
+/*!
+ * class: OSError
+ * Thrown when some system call fails to execute or give result.
+ * The exception message contains the name of the failed system call
+ * with the stringisized errno code.
+ * Check Popen class API's to know when this exception would be
+ * thrown.
+ * Its usual that the API exception specification would have
+ * this exception together with CalledProcessError.
+ */
+class OSError: public std::runtime_error
+{
+public:
+  OSError(const std::string& err_msg, int err_code):
+    std::runtime_error( err_msg + ": " + std::strerror(err_code) )
+  {}
+};
+
+//--------------------------------------------------------------------
+
+//Environment Variable types
+#ifndef _MSC_VER
+	using env_string_t = std::string;
+	using env_char_t = char;
+#else
+	using env_string_t = std::wstring;
+	using env_char_t = wchar_t;
+#endif
+using env_map_t = std::map<env_string_t, env_string_t>;
+using env_vector_t = std::vector<env_char_t>;
+
+//--------------------------------------------------------------------
+namespace util
+{
+  template <typename R>
+  inline bool is_ready(std::shared_future<R> const &f)
+  {
+    return f.wait_for(std::chrono::seconds(0)) == std::future_status::ready;
+  }
+
+  inline void quote_argument(const std::wstring &argument, std::wstring &command_line,
+                      bool force)
+  {
+    //
+    // Unless we're told otherwise, don't quote unless we actually
+    // need to do so --- hopefully avoid problems if programs won't
+    // parse quotes properly
+    //
+
+    if (force == false && argument.empty() == false &&
+        argument.find_first_of(L" \t\n\v\"") == argument.npos) {
+      command_line.append(argument);
+    }
+    else {
+      command_line.push_back(L'"');
+
+      for (auto it = argument.begin();; ++it) {
+        unsigned number_backslashes = 0;
+
+        while (it != argument.end() && *it == L'\\') {
+          ++it;
+          ++number_backslashes;
+        }
+
+        if (it == argument.end()) {
+
+          //
+          // Escape all backslashes, but let the terminating
+          // double quotation mark we add below be interpreted
+          // as a metacharacter.
+          //
+
+          command_line.append(number_backslashes * 2, L'\\');
+          break;
+        }
+        else if (*it == L'"') {
+
+          //
+          // Escape all backslashes and the following
+          // double quotation mark.
+          //
+
+          command_line.append(number_backslashes * 2 + 1, L'\\');
+          command_line.push_back(*it);
+        }
+        else {
+
+          //
+          // Backslashes aren't special here.
+          //
+
+          command_line.append(number_backslashes, L'\\');
+          command_line.push_back(*it);
+        }
+      }
+
+      command_line.push_back(L'"');
+    }
+  }
+
+#ifdef __USING_WINDOWS__
+  inline std::string get_last_error(DWORD errorMessageID)
+  {
+    if (errorMessageID == 0)
+      return std::string();
+
+    LPSTR messageBuffer = nullptr;
+    size_t size = FormatMessageA(
+        FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM |
+            FORMAT_MESSAGE_IGNORE_INSERTS | FORMAT_MESSAGE_MAX_WIDTH_MASK,
+        NULL, errorMessageID, MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
+        (LPSTR)&messageBuffer, 0, NULL);
+
+    std::string message(messageBuffer, size);
+
+    LocalFree(messageBuffer);
+
+    return message;
+  }
+
+  inline FILE *file_from_handle(HANDLE h, const char *mode)
+  {
+    int md;
+    if (!mode) {
+      throw OSError("invalid_mode", 0);
+    }
+
+    if (mode[0] == 'w') {
+      md = _O_WRONLY;
+    }
+    else if (mode[0] == 'r') {
+      md = _O_RDONLY;
+    }
+    else {
+      throw OSError("file_from_handle", 0);
+    }
+
+    int os_fhandle = _open_osfhandle((intptr_t)h, md);
+    if (os_fhandle == -1) {
+      CloseHandle(h);
+      throw OSError("_open_osfhandle", 0);
+    }
+
+    FILE *fp = _fdopen(os_fhandle, mode);
+    if (fp == 0) {
+      _close(os_fhandle);
+      throw OSError("_fdopen", 0);
+    }
+
+    return fp;
+  }
+
+  inline void configure_pipe(HANDLE* read_handle, HANDLE* write_handle, HANDLE* child_handle)
+  {
+    SECURITY_ATTRIBUTES saAttr;
+
+    // Set the bInheritHandle flag so pipe handles are inherited.
+    saAttr.nLength = sizeof(SECURITY_ATTRIBUTES);
+    saAttr.bInheritHandle = TRUE;
+    saAttr.lpSecurityDescriptor = NULL;
+
+    // Create a pipe for the child process's STDIN.
+    if (!CreatePipe(read_handle, write_handle, &saAttr,0))
+      throw OSError("CreatePipe", 0);
+
+    // Ensure the write handle to the pipe for STDIN is not inherited.
+    if (!SetHandleInformation(*child_handle, HANDLE_FLAG_INHERIT, 0))
+      throw OSError("SetHandleInformation", 0);
+  }
+
+  // env_map_t MapFromWindowsEnvironment()
+  // * Imports current Environment in a C-string table
+  // * Parses the strings by splitting on the first "=" per line
+  // * Creates a map of the variables
+  // * Returns the map
+  inline env_map_t MapFromWindowsEnvironment(){
+      wchar_t *variable_strings_ptr;
+      wchar_t *environment_strings_ptr;
+      std::wstring delimeter(L"=");
+      int del_len = delimeter.length();
+      env_map_t mapped_environment;
+
+      // Get a pointer to the environment block.
+      environment_strings_ptr = GetEnvironmentStringsW();
+      // If the returned pointer is NULL, exit.
+      if (environment_strings_ptr == NULL)
+      {
+          throw OSError("GetEnvironmentStringsW", 0);
+      }
+
+      // Variable strings are separated by NULL byte, and the block is
+      // terminated by a NULL byte.
+
+      variable_strings_ptr = (wchar_t *) environment_strings_ptr;
+
+      //Since the environment map ends with a null, we can loop until we find it.
+      while (*variable_strings_ptr)
+      {
+          // Create a string from Variable String
+          env_string_t current_line(variable_strings_ptr);
+          // Find the first "equals" sign.
+          auto pos = current_line.find(delimeter);
+          // Assuming it's not missing ...
+          if(pos!=std::wstring::npos){
+              // ... parse the key and value.
+              env_string_t key = current_line.substr(0, pos);
+              env_string_t value = current_line.substr(pos + del_len);
+              // Map the entry.
+              mapped_environment[key] = value;
+          }
+          // Jump to next line in the environment map.
+          variable_strings_ptr += std::wcslen(variable_strings_ptr) + 1;
+      }
+      // We're done with the old environment map buffer.
+      FreeEnvironmentStringsW(environment_strings_ptr);
+
+      // Return the map.
+      return mapped_environment;
+  }
+
+  // env_vector_t WindowsEnvironmentVectorFromMap(const env_map_t &source_map)
+  // * Creates a vector buffer for the new environment string table
+  // * Copies in the mapped variables
+  // * Returns the vector
+  inline env_vector_t WindowsEnvironmentVectorFromMap(const env_map_t &source_map)
+  {
+	// Make a new environment map buffer.
+	env_vector_t environment_map_buffer;
+	// Give it some space.
+	environment_map_buffer.reserve(4096);
+
+	// And fill'er up.
+	for(auto kv: source_map){
+	  // Create the line
+	  env_string_t current_line(kv.first); current_line += L"="; current_line += kv.second;
+	  // Add the line to the buffer.
+	  std::copy(current_line.begin(), current_line.end(), std::back_inserter(environment_map_buffer));
+	  // Append a null
+	  environment_map_buffer.push_back(0);
+	}
+	// Append one last null because of how Windows does it's environment maps.
+	environment_map_buffer.push_back(0);
+
+	return environment_map_buffer;
+  }
+
+  // env_vector_t CreateUpdatedWindowsEnvironmentVector(const env_map_t &changes_map)
+  // * Merges host environment with new mapped variables
+  // * Creates and returns string vector based on map
+  inline env_vector_t CreateUpdatedWindowsEnvironmentVector(const env_map_t &changes_map){
+	// Import the environment map
+	env_map_t environment_map = MapFromWindowsEnvironment();
+    // Merge in the changes with overwrite
+	for(auto& it: changes_map)
+	{
+		environment_map[it.first] = it.second;
+	}
+    // Create a Windows-usable Environment Map Buffer
+    env_vector_t environment_map_strings_vector = WindowsEnvironmentVectorFromMap(environment_map);
+
+	return environment_map_strings_vector;
+  }
+
+#endif
+
+  /*!
+   * Function: split
+   * Parameters:
+   * [in] str : Input string which needs to be split based upon the
+   *            delimiters provided.
+   * [in] deleims : Delimiter characters based upon which the string needs
+   *                to be split. Default constructed to ' '(space) and '\t'(tab)
+   * [out] vector<string> : Vector of strings split at deleimiter.
+   */
+  static inline std::vector<std::string>
+  split(const std::string& str, const std::string& delims=" \t")
+  {
+    std::vector<std::string> res;
+    size_t init = 0;
+
+    while (true) {
+      auto pos = str.find_first_of(delims, init);
+      if (pos == std::string::npos) {
+        res.emplace_back(str.substr(init, str.length()));
+        break;
+      }
+      res.emplace_back(str.substr(init, pos - init));
+      pos++;
+      init = pos;
+    }
+
+    return res;
+  }
+
+
+  /*!
+   * Function: join
+   * Parameters:
+   * [in] vec : Vector of strings which needs to be joined to form
+   *            a single string with words seperated by a seperator char.
+   *  [in] sep : String used to seperate 2 words in the joined string.
+   *             Default constructed to ' ' (space).
+   *  [out] string: Joined string.
+   */
+  static inline
+  std::string join(const std::vector<std::string>& vec,
+                   const std::string& sep = " ")
+  {
+    std::string res;
+    for (auto& elem : vec) res.append(elem + sep);
+    res.erase(--res.end());
+    return res;
+  }
+
+
+#ifndef __USING_WINDOWS__
+  /*!
+   * Function: set_clo_on_exec
+   * Sets/Resets the FD_CLOEXEC flag on the provided file descriptor
+   * based upon the `set` parameter.
+   * Parameters:
+   * [in] fd : The descriptor on which FD_CLOEXEC needs to be set/reset.
+   * [in] set : If 'true', set FD_CLOEXEC.
+   *            If 'false' unset FD_CLOEXEC.
+   */
+  static inline
+  void set_clo_on_exec(int fd, bool set = true)
+  {
+    int flags = fcntl(fd, F_GETFD, 0);
+    if (set) flags |= FD_CLOEXEC;
+    else flags &= ~FD_CLOEXEC;
+    //TODO: should check for errors
+    fcntl(fd, F_SETFD, flags);
+  }
+
+
+  /*!
+   * Function: pipe_cloexec
+   * Creates a pipe and sets FD_CLOEXEC flag on both
+   * read and write descriptors of the pipe.
+   * Parameters:
+   * [out] : A pair of file descriptors.
+   *         First element of pair is the read descriptor of pipe.
+   *         Second element is the write descriptor of pipe.
+   */
+  static inline
+  std::pair<int, int> pipe_cloexec() noexcept(false)
+  {
+    int pipe_fds[2];
+    int res = pipe(pipe_fds);
+    if (res) {
+      throw OSError("pipe failure", errno);
+    }
+
+    set_clo_on_exec(pipe_fds[0]);
+    set_clo_on_exec(pipe_fds[1]);
+
+    return std::make_pair(pipe_fds[0], pipe_fds[1]);
+  }
+#endif
+
+
+  /*!
+   * Function: write_n
+   * Writes `length` bytes to the file descriptor `fd`
+   * from the buffer `buf`.
+   * Parameters:
+   * [in] fd : The file descriptotr to write to.
+   * [in] buf: Buffer from which data needs to be written to fd.
+   * [in] length: The number of bytes that needs to be written from
+   *              `buf` to `fd`.
+   * [out] int : Number of bytes written or -1 in case of failure.
+   */
+  static inline
+  int write_n(int fd, const char* buf, size_t length)
+  {
+    size_t nwritten = 0;
+    while (nwritten < length) {
+      int written = write(fd, buf + nwritten, length - nwritten);
+      if (written == -1) return -1;
+      nwritten += written;
+    }
+    return nwritten;
+  }
+
+
+  /*!
+   * Function: read_atmost_n
+   * Reads at the most `read_upto` bytes from the
+   * file object `fp` before returning.
+   * Parameters:
+   * [in] fp : The file object from which it needs to read.
+   * [in] buf : The buffer into which it needs to write the data.
+   * [in] read_upto: Max number of bytes which must be read from `fd`.
+   * [out] int : Number of bytes written to `buf` or read from `fd`
+   *             OR -1 in case of error.
+   *  NOTE: In case of EINTR while reading from socket, this API
+   *  will retry to read from `fd`, but only till the EINTR counter
+   *  reaches 50 after which it will return with whatever data it read.
+   */
+  static inline
+  int read_atmost_n(FILE* fp, char* buf, size_t read_upto)
+  {
+#ifdef __USING_WINDOWS__
+    return (int)fread(buf, 1, read_upto, fp);
+#else
+    int fd = fileno(fp);
+    int rbytes = 0;
+    int eintr_cnter = 0;
+
+    while (1) {
+      int read_bytes = read(fd, buf + rbytes, read_upto - rbytes);
+      if (read_bytes == -1) {
+        if (errno == EINTR) {
+          if (eintr_cnter >= 50) return -1;
+          eintr_cnter++;
+          continue;
+        }
+        return -1;
+      }
+      if (read_bytes == 0) return rbytes;
+
+      rbytes += read_bytes;
+    }
+    return rbytes;
+#endif
+  }
+
+
+  /*!
+   * Function: read_all
+   * Reads all the available data from `fp` into
+   * `buf`. Internally calls read_atmost_n.
+   * Parameters:
+   * [in] fp : The file object from which to read from.
+   * [in] buf : The buffer of type `class Buffer` into which
+   *            the read data is written to.
+   * [out] int: Number of bytes read OR -1 in case of failure.
+   *
+   * NOTE: `class Buffer` is a exposed public class. See below.
+   */
+
+  static inline int read_all(FILE* fp, std::vector<char>& buf)
+  {
+    auto buffer = buf.data();
+    int total_bytes_read = 0;
+    int fill_sz = buf.size();
+
+    while (1) {
+      const int rd_bytes = read_atmost_n(fp, buffer, fill_sz);
+
+      if (rd_bytes == -1) { // Read finished
+        if (total_bytes_read == 0) return -1;
+        break;
+
+      } else if (rd_bytes == fill_sz) { // Buffer full
+        const auto orig_sz = buf.size();
+        const auto new_sz = orig_sz * 2;
+        buf.resize(new_sz);
+        fill_sz = new_sz - orig_sz;
+
+        //update the buffer pointer
+        buffer = buf.data();
+        total_bytes_read += rd_bytes;
+        buffer += total_bytes_read;
+
+      } else { // Partial data ? Continue reading
+        total_bytes_read += rd_bytes;
+        fill_sz -= rd_bytes;
+        break;
+      }
+    }
+    buf.erase(buf.begin()+total_bytes_read, buf.end()); // remove extra nulls
+    return total_bytes_read;
+  }
+
+#ifndef __USING_WINDOWS__
+  /*!
+   * Function: wait_for_child_exit
+   * Waits for the process with pid `pid` to exit
+   * and returns its status.
+   * Parameters:
+   * [in] pid : The pid of the process.
+   * [out] pair<int, int>:
+   *    pair.first : Return code of the waitpid call.
+   *    pair.second : Exit status of the process.
+   *
+   *  NOTE: This is a blocking call as in, it will loop
+   *  till the child is exited.
+   */
+  static inline
+  std::pair<int, int> wait_for_child_exit(int pid)
+  {
+    int status = 0;
+    int ret = -1;
+    while (1) {
+      ret = waitpid(pid, &status, 0);
+      if (ret == -1) break;
+      if (ret == 0) continue;
+      return std::make_pair(ret, status);
+    }
+
+    return std::make_pair(ret, status);
+  }
+#endif
+
+} // end namespace util
+
+
+
+/* -------------------------------
+ *     Popen Arguments
+ * -------------------------------
+ */
+
+/*!
+ * The buffer size of the stdin/stdout/stderr
+ * streams of the child process.
+ * Default value is 0.
+ */
+struct bufsize {
+  explicit bufsize(int siz): bufsiz(siz) {}
+  int  bufsiz = 0;
+};
+
+/*!
+ * Option to defer spawning of the child process
+ * till `Popen::start_process` API is called.
+ * Default value is false.
+ */
+struct defer_spawn {
+  explicit defer_spawn(bool d): defer(d) {}
+  bool defer  = false;
+};
+
+/*!
+ * Option to close all file descriptors
+ * when the child process is spawned.
+ * The close fd list does not include
+ * input/output/error if they are explicitly
+ * set as part of the Popen arguments.
+ *
+ * Default value is false.
+ */
+struct close_fds {
+  explicit close_fds(bool c): close_all(c) {}
+  bool close_all = false;
+};
+
+/*!
+ * Option to make the child process as the
+ * session leader and thus the process
+ * group leader.
+ * Default value is false.
+ */
+struct session_leader {
+  explicit session_leader(bool sl): leader_(sl) {}
+  bool leader_ = false;
+};
+
+struct shell {
+  explicit shell(bool s): shell_(s) {}
+  bool shell_ = false;
+};
+
+/*!
+ * Base class for all arguments involving string value.
+ */
+struct string_arg
+{
+  string_arg(const char* arg): arg_value(arg) {}
+  string_arg(std::string&& arg): arg_value(std::move(arg)) {}
+  string_arg(std::string arg): arg_value(std::move(arg)) {}
+  std::string arg_value;
+};
+
+/*!
+ * Option to specify the executable name seperately
+ * from the args sequence.
+ * In this case the cmd args must only contain the
+ * options required for this executable.
+ *
+ * Eg: executable{"ls"}
+ */
+struct executable: string_arg
+{
+  template <typename T>
+  executable(T&& arg): string_arg(std::forward<T>(arg)) {}
+};
+
+/*!
+ * Option to set the current working directory
+ * of the spawned process.
+ *
+ * Eg: cwd{"/som/path/x"}
+ */
+struct cwd: string_arg
+{
+  template <typename T>
+  cwd(T&& arg): string_arg(std::forward<T>(arg)) {}
+};
+
+/*!
+ * Option to specify environment variables required by
+ * the spawned process.
+ *
+ * Eg: environment{{ {"K1", "V1"}, {"K2", "V2"},... }}
+ */
+struct environment
+{
+  environment(env_map_t&& env):
+    env_(std::move(env)) {}
+  explicit environment(const env_map_t& env):
+    env_(env) {}
+  env_map_t env_;
+};
+
+
+/*!
+ * Used for redirecting input/output/error
+ */
+enum IOTYPE {
+  STDOUT = 1,
+  STDERR,
+  PIPE,
+};
+
+//TODO: A common base/interface for below stream structures ??
+
+/*!
+ * Option to specify the input channel for the child
+ * process. It can be:
+ * 1. An already open file descriptor.
+ * 2. A file name.
+ * 3. IOTYPE. Usual a PIPE
+ *
+ * Eg: input{PIPE}
+ * OR in case of redirection, output of another Popen
+ * input{popen.output()}
+ */
+struct input
+{
+  // For an already existing file descriptor.
+  explicit input(int fd): rd_ch_(fd) {}
+
+  // FILE pointer.
+  explicit input (FILE* fp):input(fileno(fp)) { assert(fp); }
+
+  explicit input(const char* filename) {
+    int fd = open(filename, O_RDONLY);
+    if (fd == -1) throw OSError("File not found: ", errno);
+    rd_ch_ = fd;
+  }
+  explicit input(IOTYPE typ) {
+    assert (typ == PIPE && "STDOUT/STDERR not allowed");
+#ifndef __USING_WINDOWS__
+    std::tie(rd_ch_, wr_ch_) = util::pipe_cloexec();
+#endif
+  }
+
+  int rd_ch_ = -1;
+  int wr_ch_ = -1;
+};
+
+
+/*!
+ * Option to specify the output channel for the child
+ * process. It can be:
+ * 1. An already open file descriptor.
+ * 2. A file name.
+ * 3. IOTYPE. Usually a PIPE.
+ *
+ * Eg: output{PIPE}
+ * OR output{"output.txt"}
+ */
+struct output
+{
+  explicit output(int fd): wr_ch_(fd) {}
+
+  explicit output (FILE* fp):output(fileno(fp)) { assert(fp); }
+
+  explicit output(const char* filename) {
+    int fd = open(filename, O_APPEND | O_CREAT | O_RDWR, 0640);
+    if (fd == -1) throw OSError("File not found: ", errno);
+    wr_ch_ = fd;
+  }
+  explicit output(IOTYPE typ) {
+    assert (typ == PIPE && "STDOUT/STDERR not allowed");
+#ifndef __USING_WINDOWS__
+    std::tie(rd_ch_, wr_ch_) = util::pipe_cloexec();
+#endif
+  }
+
+  int rd_ch_ = -1;
+  int wr_ch_ = -1;
+};
+
+
+/*!
+ * Option to specify the error channel for the child
+ * process. It can be:
+ * 1. An already open file descriptor.
+ * 2. A file name.
+ * 3. IOTYPE. Usually a PIPE or STDOUT
+ *
+ */
+struct error
+{
+  explicit error(int fd): wr_ch_(fd) {}
+
+  explicit error(FILE* fp):error(fileno(fp)) { assert(fp); }
+
+  explicit error(const char* filename) {
+    int fd = open(filename, O_APPEND | O_CREAT | O_RDWR, 0640);
+    if (fd == -1) throw OSError("File not found: ", errno);
+    wr_ch_ = fd;
+  }
+  explicit error(IOTYPE typ) {
+    assert ((typ == PIPE || typ == STDOUT) && "STDERR not aloowed");
+    if (typ == PIPE) {
+#ifndef __USING_WINDOWS__
+      std::tie(rd_ch_, wr_ch_) = util::pipe_cloexec();
+#endif
+    } else {
+      // Need to defer it till we have checked all arguments
+      deferred_ = true;
+    }
+  }
+
+  bool deferred_ = false;
+  int rd_ch_ = -1;
+  int wr_ch_ = -1;
+};
+
+// Impoverished, meager, needy, truly needy
+// version of type erasure to store function pointers
+// needed to provide the functionality of preexec_func
+// ATTN: Can be used only to execute functions with no
+// arguments and returning void.
+// Could have used more efficient methods, ofcourse, but
+// that wont yield me the consistent syntax which I am
+// aiming for. If you know, then please do let me know.
+
+class preexec_func
+{
+public:
+  preexec_func() {}
+
+  template <typename Func>
+  explicit preexec_func(Func f): holder_(new FuncHolder<Func>(std::move(f)))
+  {}
+
+  void operator()() {
+    (*holder_)();
+  }
+
+private:
+  struct HolderBase {
+    virtual void operator()() const = 0;
+    virtual ~HolderBase(){};
+  };
+  template <typename T>
+  struct FuncHolder: HolderBase {
+    FuncHolder(T func): func_(std::move(func)) {}
+    void operator()() const override { func_(); }
+    // The function pointer/reference
+    T func_;
+  };
+
+  std::unique_ptr<HolderBase> holder_ = nullptr;
+};
+
+// ~~~~ End Popen Args ~~~~
+
+
+/*!
+ * class: Buffer
+ * This class is a very thin wrapper around std::vector<char>
+ * This is basically used to determine the length of the actual
+ * data stored inside the dynamically resized vector.
+ *
+ * This is what is returned as the output to communicate and check_output
+ * functions, so, users must know about this class.
+ *
+ * OutBuffer and ErrBuffer are just different typedefs to this class.
+ */
+class Buffer
+{
+public:
+  Buffer() {}
+  explicit Buffer(size_t cap) { buf.resize(cap); }
+  void add_cap(size_t cap) { buf.resize(cap); }
+
+#if 0
+  Buffer(const Buffer& other):
+    buf(other.buf),
+    length(other.length)
+  {
+    std::cout << "COPY" << std::endl;
+  }
+
+  Buffer(Buffer&& other):
+    buf(std::move(other.buf)),
+    length(other.length)
+  {
+    std::cout << "MOVE" << std::endl;
+  }
+#endif
+
+public:
+  std::vector<char> buf;
+  size_t length = 0;
+};
+
+// Buffer for storing output written to output fd
+using OutBuffer = Buffer;
+// Buffer for storing output written to error fd
+using ErrBuffer = Buffer;
+
+
+// Fwd Decl.
+class Popen;
+
+/*---------------------------------------------------
+ *      DETAIL NAMESPACE
+ *---------------------------------------------------
+ */
+
+namespace detail {
+
+// Metaprogram for searching a type within
+// a variadic parameter pack
+// This is particularly required to do a compile time
+// checking of the arguments provided to 'check_ouput' function
+// wherein the user is not expected to provide an 'ouput' option.
+
+template <typename... T> struct param_pack{};
+
+template <typename F, typename T> struct has_type;
+
+template <typename F>
+struct has_type<F, param_pack<>> {
+  static constexpr bool value = false;
+};
+
+template <typename F, typename... T>
+struct has_type<F, param_pack<F, T...>> {
+  static constexpr bool value = true;
+};
+
+template <typename F, typename H, typename... T>
+struct has_type<F, param_pack<H,T...>> {
+  static constexpr bool value =
+    std::is_same<F, typename std::decay<H>::type>::value ? true : has_type<F, param_pack<T...>>::value;
+};
+
+//----
+
+/*!
+ * A helper class to Popen class for setting
+ * options as provided in the Popen constructor
+ * or in check_ouput arguments.
+ * This design allows us to _not_ have any fixed position
+ * to any arguments and specify them in a way similar to what
+ * can be done in python.
+ */
+struct ArgumentDeducer
+{
+  ArgumentDeducer(Popen* p): popen_(p) {}
+
+  void set_option(executable&& exe);
+  void set_option(cwd&& cwdir);
+  void set_option(bufsize&& bsiz);
+  void set_option(environment&& env);
+  void set_option(defer_spawn&& defer);
+  void set_option(shell&& sh);
+  void set_option(input&& inp);
+  void set_option(output&& out);
+  void set_option(error&& err);
+  void set_option(close_fds&& cfds);
+  void set_option(preexec_func&& prefunc);
+  void set_option(session_leader&& sleader);
+
+private:
+  Popen* popen_ = nullptr;
+};
+
+/*!
+ * A helper class to Popen.
+ * This takes care of all the fork-exec logic
+ * in the execute_child API.
+ */
+class Child
+{
+public:
+  Child(Popen* p, int err_wr_pipe):
+    parent_(p),
+    err_wr_pipe_(err_wr_pipe)
+  {}
+
+  void execute_child();
+
+private:
+  // Lets call it parent even though
+  // technically a bit incorrect
+  Popen* parent_ = nullptr;
+  int err_wr_pipe_ = -1;
+};
+
+// Fwd Decl.
+class Streams;
+
+/*!
+ * A helper class to Streams.
+ * This takes care of management of communicating
+ * with the child process with the means of the correct
+ * file descriptor.
+ */
+class Communication
+{
+public:
+  Communication(Streams* stream): stream_(stream)
+  {}
+  void operator=(const Communication&) = delete;
+public:
+  int send(const char* msg, size_t length);
+  int send(const std::vector<char>& msg);
+
+  std::pair<OutBuffer, ErrBuffer> communicate(const char* msg, size_t length);
+  std::pair<OutBuffer, ErrBuffer> communicate(const std::vector<char>& msg)
+  { return communicate(msg.data(), msg.size()); }
+
+  void set_out_buf_cap(size_t cap) { out_buf_cap_ = cap; }
+  void set_err_buf_cap(size_t cap) { err_buf_cap_ = cap; }
+
+private:
+  std::pair<OutBuffer, ErrBuffer> communicate_threaded(
+      const char* msg, size_t length);
+
+private:
+  Streams* stream_;
+  size_t out_buf_cap_ = DEFAULT_BUF_CAP_BYTES;
+  size_t err_buf_cap_ = DEFAULT_BUF_CAP_BYTES;
+};
+
+
+
+/*!
+ * This is a helper class to Popen.
+ * It takes care of management of all the file descriptors
+ * and file pointers.
+ * It dispatches of the communication aspects to the
+ * Communication class.
+ * Read through the data members to understand about the
+ * various file descriptors used.
+ */
+class Streams
+{
+public:
+  Streams():comm_(this) {}
+  void operator=(const Streams&) = delete;
+
+public:
+  void setup_comm_channels();
+
+  void cleanup_fds()
+  {
+    if (write_to_child_ != -1 && read_from_parent_ != -1) {
+      close(write_to_child_);
+    }
+    if (write_to_parent_ != -1 && read_from_child_ != -1) {
+      close(read_from_child_);
+    }
+    if (err_write_ != -1 && err_read_ != -1) {
+      close(err_read_);
+    }
+  }
+
+  void close_parent_fds()
+  {
+    if (write_to_child_ != -1)  close(write_to_child_);
+    if (read_from_child_ != -1) close(read_from_child_);
+    if (err_read_ != -1)        close(err_read_);
+  }
+
+  void close_child_fds()
+  {
+    if (write_to_parent_ != -1)  close(write_to_parent_);
+    if (read_from_parent_ != -1) close(read_from_parent_);
+    if (err_write_ != -1)        close(err_write_);
+  }
+
+  FILE* input()  { return input_.get(); }
+  FILE* output() { return output_.get(); }
+  FILE* error()  { return error_.get(); }
+
+  void input(FILE* fp)  { input_.reset(fp, fclose); }
+  void output(FILE* fp) { output_.reset(fp, fclose); }
+  void error(FILE* fp)  { error_.reset(fp, fclose); }
+
+  void set_out_buf_cap(size_t cap) { comm_.set_out_buf_cap(cap); }
+  void set_err_buf_cap(size_t cap) { comm_.set_err_buf_cap(cap); }
+
+public: /* Communication forwarding API's */
+  int send(const char* msg, size_t length)
+  { return comm_.send(msg, length); }
+
+  int send(const std::vector<char>& msg)
+  { return comm_.send(msg); }
+
+  std::pair<OutBuffer, ErrBuffer> communicate(const char* msg, size_t length)
+  { return comm_.communicate(msg, length); }
+
+  std::pair<OutBuffer, ErrBuffer> communicate(const std::vector<char>& msg)
+  { return comm_.communicate(msg); }
+
+
+public:// Yes they are public
+
+  std::shared_ptr<FILE> input_  = nullptr;
+  std::shared_ptr<FILE> output_ = nullptr;
+  std::shared_ptr<FILE> error_  = nullptr;
+
+#ifdef __USING_WINDOWS__
+  HANDLE g_hChildStd_IN_Rd = nullptr;
+  HANDLE g_hChildStd_IN_Wr = nullptr;
+  HANDLE g_hChildStd_OUT_Rd = nullptr;
+  HANDLE g_hChildStd_OUT_Wr = nullptr;
+  HANDLE g_hChildStd_ERR_Rd = nullptr;
+  HANDLE g_hChildStd_ERR_Wr = nullptr;
+#endif
+
+  // Buffer size for the IO streams
+  int bufsiz_ = 0;
+
+  // Pipes for communicating with child
+
+  // Emulates stdin
+  int write_to_child_   = -1; // Parent owned descriptor
+  int read_from_parent_ = -1; // Child owned descriptor
+
+  // Emulates stdout
+  int write_to_parent_ = -1; // Child owned descriptor
+  int read_from_child_ = -1; // Parent owned descriptor
+
+  // Emulates stderr
+  int err_write_ = -1; // Write error to parent (Child owned)
+  int err_read_  = -1; // Read error from child (Parent owned)
+
+private:
+  Communication comm_;
+};
+
+} // end namespace detail
+
+
+
+/*!
+ * class: Popen
+ * This is the single most important class in the whole library
+ * and glues together all the helper classes to provide a common
+ * interface to the client.
+ *
+ * API's provided by the class:
+ * 1. Popen({"cmd"}, output{..}, error{..}, cwd{..}, ....)
+ *    Command provided as a sequence.
+ * 2. Popen("cmd arg1"m output{..}, error{..}, cwd{..}, ....)
+ *    Command provided in a single string.
+ * 3. wait()             - Wait for the child to exit.
+ * 4. retcode()          - The return code of the exited child.
+ * 5. pid()              - PID of the spawned child.
+ * 6. poll()             - Check the status of the running child.
+ * 7. kill(sig_num)      - Kill the child. SIGTERM used by default.
+ * 8. send(...)          - Send input to the input channel of the child.
+ * 9. communicate(...)   - Get the output/error from the child and close the channels
+ *                         from the parent side.
+ *10. input()            - Get the input channel/File pointer. Can be used for
+ *                         cutomizing the way of sending input to child.
+ *11. output()           - Get the output channel/File pointer. Usually used
+                           in case of redirection. See piping examples.
+ *12. error()            - Get the error channel/File poiner. Usually used
+                           in case of redirection.
+ *13. start_process()    - Start the child process. Only to be used when
+ *                         `defer_spawn` option was provided in Popen constructor.
+ */
+class Popen
+{
+public:
+  friend struct detail::ArgumentDeducer;
+  friend class detail::Child;
+
+  template <typename... Args>
+  Popen(const std::string& cmd_args, Args&& ...args):
+    args_(cmd_args)
+  {
+    vargs_ = util::split(cmd_args);
+    init_args(std::forward<Args>(args)...);
+
+    // Setup the communication channels of the Popen class
+    stream_.setup_comm_channels();
+
+    if (!defer_process_start_) execute_process();
+  }
+
+  template <typename... Args>
+  Popen(std::initializer_list<const char*> cmd_args, Args&& ...args)
+  {
+    vargs_.insert(vargs_.end(), cmd_args.begin(), cmd_args.end());
+    init_args(std::forward<Args>(args)...);
+
+    // Setup the communication channels of the Popen class
+    stream_.setup_comm_channels();
+
+    if (!defer_process_start_) execute_process();
+  }
+
+  template <typename... Args>
+  Popen(std::vector<std::string> vargs_, Args &&... args) : vargs_(vargs_)
+  {
+    init_args(std::forward<Args>(args)...);
+
+    // Setup the communication channels of the Popen class
+    stream_.setup_comm_channels();
+
+    if (!defer_process_start_) execute_process();
+  }
+
+/*
+  ~Popen()
+  {
+#ifdef __USING_WINDOWS__
+    CloseHandle(this->process_handle_);
+#endif
+  }
+*/
+
+  void start_process() noexcept(false);
+
+  int pid() const noexcept { return child_pid_; }
+
+  int retcode() const noexcept { return retcode_; }
+
+  int wait() noexcept(false);
+
+  int poll() noexcept(false);
+
+  // Does not fail, Caller is expected to recheck the
+  // status with a call to poll()
+  void kill(int sig_num = 9);
+
+  void set_out_buf_cap(size_t cap) { stream_.set_out_buf_cap(cap); }
+
+  void set_err_buf_cap(size_t cap) { stream_.set_err_buf_cap(cap); }
+
+  int send(const char* msg, size_t length)
+  { return stream_.send(msg, length); }
+
+  int send(const std::string& msg)
+  { return send(msg.c_str(), msg.size()); }
+
+  int send(const std::vector<char>& msg)
+  { return stream_.send(msg); }
+
+  std::pair<OutBuffer, ErrBuffer> communicate(const char* msg, size_t length)
+  {
+    auto res = stream_.communicate(msg, length);
+    retcode_ = wait();
+    return res;
+  }
+
+  std::pair<OutBuffer, ErrBuffer> communicate(const std::string& msg)
+  {
+    return communicate(msg.c_str(), msg.size());
+  }
+
+  std::pair<OutBuffer, ErrBuffer> communicate(const std::vector<char>& msg)
+  {
+    auto res = stream_.communicate(msg);
+    retcode_ = wait();
+    return res;
+  }
+
+  std::pair<OutBuffer, ErrBuffer> communicate()
+  {
+    return communicate(nullptr, 0);
+  }
+
+  FILE* input()  { return stream_.input(); }
+  FILE* output() { return stream_.output();}
+  FILE* error()  { return stream_.error(); }
+
+  /// Stream close APIs
+  void close_input()  { stream_.input_.reset();  }
+  void close_output() { stream_.output_.reset(); }
+  void close_error()  { stream_.error_.reset();  }
+
+private:
+  template <typename F, typename... Args>
+  void init_args(F&& farg, Args&&... args);
+  void init_args();
+  void populate_c_argv();
+  void execute_process() noexcept(false);
+
+private:
+  detail::Streams stream_;
+
+#ifdef __USING_WINDOWS__
+  HANDLE process_handle_;
+  std::future<void> cleanup_future_;
+#endif
+
+  bool defer_process_start_ = false;
+  bool close_fds_ = false;
+  bool has_preexec_fn_ = false;
+  bool shell_ = false;
+  bool session_leader_ = false;
+
+  std::string exe_name_;
+  std::string cwd_;
+  env_map_t env_;
+  preexec_func preexec_fn_;
+
+  // Command in string format
+  std::string args_;
+  // Comamnd provided as sequence
+  std::vector<std::string> vargs_;
+  std::vector<char*> cargv_;
+
+  bool child_created_ = false;
+  // Pid of the child process
+  int child_pid_ = -1;
+
+  int retcode_ = -1;
+};
+
+inline void Popen::init_args() {
+  populate_c_argv();
+}
+
+template <typename F, typename... Args>
+inline void Popen::init_args(F&& farg, Args&&... args)
+{
+  detail::ArgumentDeducer argd(this);
+  argd.set_option(std::forward<F>(farg));
+  init_args(std::forward<Args>(args)...);
+}
+
+inline void Popen::populate_c_argv()
+{
+  cargv_.clear();
+  cargv_.reserve(vargs_.size() + 1);
+  for (auto& arg : vargs_) cargv_.push_back(&arg[0]);
+  cargv_.push_back(nullptr);
+}
+
+inline void Popen::start_process() noexcept(false)
+{
+  // The process was started/tried to be started
+  // in the constructor itself.
+  // For explicitly calling this API to start the
+  // process, 'defer_spawn' argument must be set to
+  // true in the constructor.
+  if (!defer_process_start_) {
+    assert (0);
+    return;
+  }
+  execute_process();
+}
+
+inline int Popen::wait() noexcept(false)
+{
+#ifdef __USING_WINDOWS__
+  int ret = WaitForSingleObject(process_handle_, INFINITE);
+
+  return 0;
+#else
+  int ret, status;
+  std::tie(ret, status) = util::wait_for_child_exit(pid());
+  if (ret == -1) {
+    if (errno != ECHILD) throw OSError("waitpid failed", errno);
+    return 0;
+  }
+  if (WIFEXITED(status)) return WEXITSTATUS(status);
+  if (WIFSIGNALED(status)) return WTERMSIG(status);
+  else return 255;
+
+  return 0;
+#endif
+}
+
+inline int Popen::poll() noexcept(false)
+{
+#ifdef __USING_WINDOWS__
+  int ret = WaitForSingleObject(process_handle_, 0);
+  if (ret != WAIT_OBJECT_0) return -1;
+
+  DWORD dretcode_;
+  if (FALSE == GetExitCodeProcess(process_handle_, &dretcode_))
+      throw OSError("GetExitCodeProcess", 0);
+
+  retcode_ = (int)dretcode_;
+  CloseHandle(process_handle_);
+
+  return retcode_;
+#else
+  if (!child_created_) return -1; // TODO: ??
+
+  int status;
+
+  // Returns zero if child is still running
+  int ret = waitpid(child_pid_, &status, WNOHANG);
+  if (ret == 0) return -1;
+
+  if (ret == child_pid_) {
+    if (WIFSIGNALED(status)) {
+      retcode_ = WTERMSIG(status);
+    } else if (WIFEXITED(status)) {
+      retcode_ = WEXITSTATUS(status);
+    } else {
+      retcode_ = 255;
+    }
+    return retcode_;
+  }
+
+  if (ret == -1) {
+    // From subprocess.py
+    // This happens if SIGCHLD is set to be ignored
+    // or waiting for child process has otherwise been disabled
+    // for our process. This child is dead, we cannot get the
+    // status.
+    if (errno == ECHILD) retcode_ = 0;
+    else throw OSError("waitpid failed", errno);
+  } else {
+    retcode_ = ret;
+  }
+
+  return retcode_;
+#endif
+}
+
+inline void Popen::kill(int sig_num)
+{
+#ifdef __USING_WINDOWS__
+  if (!TerminateProcess(this->process_handle_, (UINT)sig_num)) {
+    throw OSError("TerminateProcess", 0);
+  }
+#else
+  if (session_leader_) killpg(child_pid_, sig_num);
+  else ::kill(child_pid_, sig_num);
+#endif
+}
+
+
+inline void Popen::execute_process() noexcept(false)
+{
+#ifdef __USING_WINDOWS__
+  if (this->shell_) {
+    throw OSError("shell not currently supported on windows", 0);
+  }
+
+  void* environment_string_table_ptr = nullptr;
+  env_vector_t environment_string_vector;
+  if(this->env_.size()){
+	  environment_string_vector = util::CreateUpdatedWindowsEnvironmentVector(env_);
+	  environment_string_table_ptr = (void*)environment_string_vector.data();
+  }
+
+  if (exe_name_.length()) {
+    this->vargs_.insert(this->vargs_.begin(), this->exe_name_);
+    this->populate_c_argv();
+  }
+  this->exe_name_ = vargs_[0];
+
+  std::wstring_convert<std::codecvt_utf8_utf16<wchar_t>> converter;
+  std::wstring argument;
+  std::wstring command_line;
+
+  for (auto arg : this->vargs_) {
+    argument = converter.from_bytes(arg);
+    util::quote_argument(argument, command_line, false);
+    command_line += L" ";
+  }
+
+  // CreateProcessW can modify szCmdLine so we allocate needed memory
+  wchar_t *szCmdline = new wchar_t[command_line.size() + 1];
+  wcscpy_s(szCmdline, command_line.size() + 1, command_line.c_str());
+  PROCESS_INFORMATION piProcInfo;
+  STARTUPINFOW siStartInfo;
+  BOOL bSuccess = FALSE;
+  DWORD creation_flags = CREATE_UNICODE_ENVIRONMENT | CREATE_NO_WINDOW;
+
+  // Set up members of the PROCESS_INFORMATION structure.
+  ZeroMemory(&piProcInfo, sizeof(PROCESS_INFORMATION));
+
+  // Set up members of the STARTUPINFOW structure.
+  // This structure specifies the STDIN and STDOUT handles for redirection.
+
+  ZeroMemory(&siStartInfo, sizeof(STARTUPINFOW));
+  siStartInfo.cb = sizeof(STARTUPINFOW);
+
+  siStartInfo.hStdError = this->stream_.g_hChildStd_ERR_Wr;
+  siStartInfo.hStdOutput = this->stream_.g_hChildStd_OUT_Wr;
+  siStartInfo.hStdInput = this->stream_.g_hChildStd_IN_Rd;
+
+  siStartInfo.dwFlags |= STARTF_USESTDHANDLES;
+
+  // Create the child process.
+  bSuccess = CreateProcessW(NULL,
+                            szCmdline,    // command line
+                            NULL,         // process security attributes
+                            NULL,         // primary thread security attributes
+                            TRUE,         // handles are inherited
+                            creation_flags,	// creation flags
+                            environment_string_table_ptr,  // use provided environment
+                            NULL,         // use parent's current directory
+                            &siStartInfo, // STARTUPINFOW pointer
+                            &piProcInfo); // receives PROCESS_INFORMATION
+
+  // If an error occurs, exit the application.
+  if (!bSuccess) {
+    DWORD errorMessageID = ::GetLastError();
+    throw CalledProcessError("CreateProcess failed: " + util::get_last_error(errorMessageID), errorMessageID);
+  }
+
+  CloseHandle(piProcInfo.hThread);
+
+  /*
+    TODO: use common apis to close linux handles
+  */
+
+  this->process_handle_ = piProcInfo.hProcess;
+
+  this->cleanup_future_ = std::async(std::launch::async, [this] {
+    WaitForSingleObject(this->process_handle_, INFINITE);
+
+    CloseHandle(this->stream_.g_hChildStd_ERR_Wr);
+    CloseHandle(this->stream_.g_hChildStd_OUT_Wr);
+    CloseHandle(this->stream_.g_hChildStd_IN_Rd);
+  });
+
+/*
+  NOTE: In the linux version, there is a check to make sure that the process
+        has been started. Here, we do nothing because CreateProcess will throw
+        if we fail to create the process.
+*/
+
+
+#else
+
+  int err_rd_pipe, err_wr_pipe;
+  std::tie(err_rd_pipe, err_wr_pipe) = util::pipe_cloexec();
+
+  if (shell_) {
+    auto new_cmd = util::join(vargs_);
+    vargs_.clear();
+    vargs_.insert(vargs_.begin(), {"/bin/sh", "-c"});
+    vargs_.push_back(new_cmd);
+    populate_c_argv();
+  }
+
+  if (exe_name_.length()) {
+    vargs_.insert(vargs_.begin(), exe_name_);
+    populate_c_argv();
+  }
+  exe_name_ = vargs_[0];
+
+  child_pid_ = fork();
+
+  if (child_pid_ < 0) {
+    close(err_rd_pipe);
+    close(err_wr_pipe);
+    throw OSError("fork failed", errno);
+  }
+
+  child_created_ = true;
+
+  if (child_pid_ == 0)
+  {
+    // Close descriptors belonging to parent
+    stream_.close_parent_fds();
+
+    //Close the read end of the error pipe
+    close(err_rd_pipe);
+
+    detail::Child chld(this, err_wr_pipe);
+    chld.execute_child();
+  }
+  else
+  {
+    close (err_wr_pipe);// close child side of pipe, else get stuck in read below
+
+    stream_.close_child_fds();
+
+    try {
+      char err_buf[SP_MAX_ERR_BUF_SIZ] = {0,};
+
+      int read_bytes = util::read_atmost_n(
+                                  fdopen(err_rd_pipe, "r"),
+                                  err_buf,
+                                  SP_MAX_ERR_BUF_SIZ);
+      close(err_rd_pipe);
+
+      if (read_bytes || strlen(err_buf)) {
+        // Call waitpid to reap the child process
+        // waitpid suspends the calling process until the
+        // child terminates.
+        int retcode = wait();
+
+        // Throw whatever information we have about child failure
+        throw CalledProcessError(err_buf, retcode);
+      }
+    } catch (std::exception& exp) {
+      stream_.cleanup_fds();
+      throw;
+    }
+
+  }
+#endif
+}
+
+namespace detail {
+
+  inline void ArgumentDeducer::set_option(executable&& exe) {
+    popen_->exe_name_ = std::move(exe.arg_value);
+  }
+
+  inline void ArgumentDeducer::set_option(cwd&& cwdir) {
+    popen_->cwd_ = std::move(cwdir.arg_value);
+  }
+
+  inline void ArgumentDeducer::set_option(bufsize&& bsiz) {
+    popen_->stream_.bufsiz_ = bsiz.bufsiz;
+  }
+
+  inline void ArgumentDeducer::set_option(environment&& env) {
+    popen_->env_ = std::move(env.env_);
+  }
+
+  inline void ArgumentDeducer::set_option(defer_spawn&& defer) {
+    popen_->defer_process_start_ = defer.defer;
+  }
+
+  inline void ArgumentDeducer::set_option(shell&& sh) {
+    popen_->shell_ = sh.shell_;
+  }
+
+  inline void ArgumentDeducer::set_option(session_leader&& sleader) {
+    popen_->session_leader_ = sleader.leader_;
+  }
+
+  inline void ArgumentDeducer::set_option(input&& inp) {
+    if (inp.rd_ch_ != -1) popen_->stream_.read_from_parent_ = inp.rd_ch_;
+    if (inp.wr_ch_ != -1) popen_->stream_.write_to_child_ = inp.wr_ch_;
+  }
+
+  inline void ArgumentDeducer::set_option(output&& out) {
+    if (out.wr_ch_ != -1) popen_->stream_.write_to_parent_ = out.wr_ch_;
+    if (out.rd_ch_ != -1) popen_->stream_.read_from_child_ = out.rd_ch_;
+  }
+
+  inline void ArgumentDeducer::set_option(error&& err) {
+    if (err.deferred_) {
+      if (popen_->stream_.write_to_parent_) {
+        popen_->stream_.err_write_ = popen_->stream_.write_to_parent_;
+      } else {
+        throw std::runtime_error("Set output before redirecting error to output");
+      }
+    }
+    if (err.wr_ch_ != -1) popen_->stream_.err_write_ = err.wr_ch_;
+    if (err.rd_ch_ != -1) popen_->stream_.err_read_ = err.rd_ch_;
+  }
+
+  inline void ArgumentDeducer::set_option(close_fds&& cfds) {
+    popen_->close_fds_ = cfds.close_all;
+  }
+
+  inline void ArgumentDeducer::set_option(preexec_func&& prefunc) {
+    popen_->preexec_fn_ = std::move(prefunc);
+    popen_->has_preexec_fn_ = true;
+  }
+
+
+  inline void Child::execute_child() {
+#ifndef __USING_WINDOWS__
+    int sys_ret = -1;
+    auto& stream = parent_->stream_;
+
+    try {
+      if (stream.write_to_parent_ == 0)
+        stream.write_to_parent_ = dup(stream.write_to_parent_);
+
+      if (stream.err_write_ == 0 || stream.err_write_ == 1)
+        stream.err_write_ = dup(stream.err_write_);
+
+      // Make the child owned descriptors as the
+      // stdin, stdout and stderr for the child process
+      auto _dup2_ = [](int fd, int to_fd) {
+        if (fd == to_fd) {
+          // dup2 syscall does not reset the
+          // CLOEXEC flag if the descriptors
+          // provided to it are same.
+          // But, we need to reset the CLOEXEC
+          // flag as the provided descriptors
+          // are now going to be the standard
+          // input, output and error
+          util::set_clo_on_exec(fd, false);
+        } else if(fd != -1) {
+          int res = dup2(fd, to_fd);
+          if (res == -1) throw OSError("dup2 failed", errno);
+        }
+      };
+
+      // Create the standard streams
+      _dup2_(stream.read_from_parent_, 0); // Input stream
+      _dup2_(stream.write_to_parent_,  1); // Output stream
+      _dup2_(stream.err_write_,        2); // Error stream
+
+      // Close the duped descriptors
+      if (stream.read_from_parent_ != -1 && stream.read_from_parent_ > 2)
+        close(stream.read_from_parent_);
+
+      if (stream.write_to_parent_ != -1 && stream.write_to_parent_ > 2)
+        close(stream.write_to_parent_);
+
+      if (stream.err_write_ != -1 && stream.err_write_ > 2)
+        close(stream.err_write_);
+
+      // Close all the inherited fd's except the error write pipe
+      if (parent_->close_fds_) {
+        int max_fd = sysconf(_SC_OPEN_MAX);
+        if (max_fd == -1) throw OSError("sysconf failed", errno);
+
+        for (int i = 3; i < max_fd; i++) {
+          if (i == err_wr_pipe_) continue;
+          close(i);
+        }
+      }
+
+      // Change the working directory if provided
+      if (parent_->cwd_.length()) {
+        sys_ret = chdir(parent_->cwd_.c_str());
+        if (sys_ret == -1) throw OSError("chdir failed", errno);
+      }
+
+      if (parent_->has_preexec_fn_) {
+        parent_->preexec_fn_();
+      }
+
+      if (parent_->session_leader_) {
+        sys_ret = setsid();
+        if (sys_ret == -1) throw OSError("setsid failed", errno);
+      }
+
+      // Replace the current image with the executable
+      if (parent_->env_.size()) {
+        for (auto& kv : parent_->env_) {
+          setenv(kv.first.c_str(), kv.second.c_str(), 1);
+        }
+        sys_ret = execvp(parent_->exe_name_.c_str(), parent_->cargv_.data());
+      } else {
+        sys_ret = execvp(parent_->exe_name_.c_str(), parent_->cargv_.data());
+      }
+
+      if (sys_ret == -1) throw OSError("execve failed", errno);
+
+    } catch (const OSError& exp) {
+      // Just write the exception message
+      // TODO: Give back stack trace ?
+      std::string err_msg(exp.what());
+      //ATTN: Can we do something on error here ?
+      util::write_n(err_wr_pipe_, err_msg.c_str(), err_msg.length());
+    }
+
+    // Calling application would not get this
+    // exit failure
+    _exit (EXIT_FAILURE);
+#endif
+  }
+
+
+  inline void Streams::setup_comm_channels()
+  {
+#ifdef __USING_WINDOWS__
+    util::configure_pipe(&this->g_hChildStd_IN_Rd, &this->g_hChildStd_IN_Wr, &this->g_hChildStd_IN_Wr);
+    this->input(util::file_from_handle(this->g_hChildStd_IN_Wr, "w"));
+    this->write_to_child_ = _fileno(this->input());
+
+    util::configure_pipe(&this->g_hChildStd_OUT_Rd, &this->g_hChildStd_OUT_Wr, &this->g_hChildStd_OUT_Rd);
+    this->output(util::file_from_handle(this->g_hChildStd_OUT_Rd, "r"));
+    this->read_from_child_ = _fileno(this->output());
+
+    util::configure_pipe(&this->g_hChildStd_ERR_Rd, &this->g_hChildStd_ERR_Wr, &this->g_hChildStd_ERR_Rd);
+    this->error(util::file_from_handle(this->g_hChildStd_ERR_Rd, "r"));
+    this->err_read_ = _fileno(this->error());
+#else
+
+    if (write_to_child_ != -1)  input(fdopen(write_to_child_, "wb"));
+    if (read_from_child_ != -1) output(fdopen(read_from_child_, "rb"));
+    if (err_read_ != -1)        error(fdopen(err_read_, "rb"));
+
+    auto handles = {input(), output(), error()};
+
+    for (auto& h : handles) {
+      if (h == nullptr) continue;
+      switch (bufsiz_) {
+      case 0:
+        setvbuf(h, nullptr, _IONBF, BUFSIZ);
+        break;
+      case 1:
+        setvbuf(h, nullptr, _IONBF, BUFSIZ);
+        break;
+      default:
+        setvbuf(h, nullptr, _IOFBF, bufsiz_);
+      };
+    }
+  #endif
+  }
+
+  inline int Communication::send(const char* msg, size_t length)
+  {
+    if (stream_->input() == nullptr) return -1;
+    return std::fwrite(msg, sizeof(char), length, stream_->input());
+  }
+
+  inline int Communication::send(const std::vector<char>& msg)
+  {
+    return send(msg.data(), msg.size());
+  }
+
+  inline std::pair<OutBuffer, ErrBuffer>
+  Communication::communicate(const char* msg, size_t length)
+  {
+    // Optimization from subprocess.py
+    // If we are using one pipe, or no pipe
+    // at all, using select() or threads is unnecessary.
+    auto hndls = {stream_->input(), stream_->output(), stream_->error()};
+    int count = std::count(std::begin(hndls), std::end(hndls), nullptr);
+    const int len_conv = length;
+
+    if (count >= 2) {
+      OutBuffer obuf;
+      ErrBuffer ebuf;
+      if (stream_->input()) {
+        if (msg) {
+          int wbytes = std::fwrite(msg, sizeof(char), length, stream_->input());
+          if (wbytes < len_conv) {
+            if (errno != EPIPE && errno != EINVAL) {
+              throw OSError("fwrite error", errno);
+            }
+          }
+        }
+        // Close the input stream
+        stream_->input_.reset();
+      } else if (stream_->output()) {
+        // Read till EOF
+        // ATTN: This could be blocking, if the process
+        // at the other end screws up, we get screwed as well
+        obuf.add_cap(out_buf_cap_);
+
+        int rbytes = util::read_all(
+                            stream_->output(),
+                            obuf.buf);
+
+        if (rbytes == -1) {
+          throw OSError("read to obuf failed", errno);
+        }
+
+        obuf.length = rbytes;
+        // Close the output stream
+        stream_->output_.reset();
+
+      } else if (stream_->error()) {
+        // Same screwness applies here as well
+        ebuf.add_cap(err_buf_cap_);
+
+        int rbytes = util::read_atmost_n(
+                                  stream_->error(),
+                                  ebuf.buf.data(),
+                                  ebuf.buf.size());
+
+        if (rbytes == -1) {
+          throw OSError("read to ebuf failed", errno);
+        }
+
+        ebuf.length = rbytes;
+        // Close the error stream
+        stream_->error_.reset();
+      }
+      return std::make_pair(std::move(obuf), std::move(ebuf));
+    }
+
+    return communicate_threaded(msg, length);
+  }
+
+
+  inline std::pair<OutBuffer, ErrBuffer>
+  Communication::communicate_threaded(const char* msg, size_t length)
+  {
+    OutBuffer obuf;
+    ErrBuffer ebuf;
+    std::future<int> out_fut, err_fut;
+    const int length_conv = length;
+
+    if (stream_->output()) {
+      obuf.add_cap(out_buf_cap_);
+
+      out_fut = std::async(std::launch::async,
+                          [&obuf, this] {
+                            return util::read_all(this->stream_->output(), obuf.buf);
+                          });
+    }
+    if (stream_->error()) {
+      ebuf.add_cap(err_buf_cap_);
+
+      err_fut = std::async(std::launch::async,
+                          [&ebuf, this] {
+                            return util::read_all(this->stream_->error(), ebuf.buf);
+                          });
+    }
+    if (stream_->input()) {
+      if (msg) {
+        int wbytes = std::fwrite(msg, sizeof(char), length, stream_->input());
+        if (wbytes < length_conv) {
+          if (errno != EPIPE && errno != EINVAL) {
+            throw OSError("fwrite error", errno);
+          }
+        }
+      }
+      stream_->input_.reset();
+    }
+
+    if (out_fut.valid()) {
+      int res = out_fut.get();
+      if (res != -1) obuf.length = res;
+      else obuf.length = 0;
+    }
+    if (err_fut.valid()) {
+      int res = err_fut.get();
+      if (res != -1) ebuf.length = res;
+      else ebuf.length = 0;
+    }
+
+    return std::make_pair(std::move(obuf), std::move(ebuf));
+  }
+
+} // end namespace detail
+
+}
+
+#endif // SUBPROCESS_HPP
diff --git a/test/lint/lint-includes.py b/test/lint/lint-includes.py
index 81ed4c0840..90884299d5 100755
--- a/test/lint/lint-includes.py
+++ b/test/lint/lint-includes.py
@@ -30,7 +30,6 @@ EXPECTED_BOOST_INCLUDES = ["boost/date_time/posix_time/posix_time.hpp",
                            "boost/multi_index/tag.hpp",
                            "boost/multi_index_container.hpp",
                            "boost/operators.hpp",
-                           "boost/process.hpp",
                            "boost/signals2/connection.hpp",
                            "boost/signals2/optional_last_value.hpp",
                            "boost/signals2/signal.hpp",
diff --git a/test/lint/lint-spelling.py b/test/lint/lint-spelling.py
index 3e578b218f..8d35fe6670 100755
--- a/test/lint/lint-spelling.py
+++ b/test/lint/lint-spelling.py
@@ -14,7 +14,7 @@ from subprocess import check_output, STDOUT, CalledProcessError
 from lint_ignore_dirs import SHARED_EXCLUDED_SUBTREES
 
 IGNORE_WORDS_FILE = 'test/lint/spelling.ignore-words.txt'
-FILES_ARGS = ['git', 'ls-files', '--', ":(exclude)build-aux/m4/", ":(exclude)contrib/seeds/*.txt", ":(exclude)depends/", ":(exclude)doc/release-notes/", ":(exclude)src/qt/locale/", ":(exclude)src/qt/*.qrc", ":(exclude)contrib/guix/patches"]
+FILES_ARGS = ['git', 'ls-files', '--', ":(exclude)build-aux/m4/", ":(exclude)contrib/seeds/*.txt", ":(exclude)depends/", ":(exclude)doc/release-notes/", ":(exclude)src/qt/locale/", ":(exclude)src/qt/*.qrc", ":(exclude)contrib/guix/patches", ":(exclude)src/util/subprocess.hpp"]
 FILES_ARGS += [f":(exclude){dir}" for dir in SHARED_EXCLUDED_SUBTREES]