remove folly::Subprocess::CLOSE

Summary:
As mentioned in D30901400 (https://github.com/facebook/folly/commit/b258ee31860b47b9196872264f6f3a331d450b1f) / OSS commit b258ee31, `folly::Subprocess::CLOSE` has implications that are rather suboptimal in real-world use.

To recap, opening a socket or file will use the lowest unused fd number, meaning that if we close stdin/stdout/stderr they can be replaced by a random file or socket. This may result in unexpected behaviour.

Reviewed By: luciang

Differential Revision: D30991108

fbshipit-source-id: 9055af84423500a1896015b5fe866ceb2cc64186

folly/Subprocess.cpp

@@ -553,14 +553,10 @@ int Subprocess::prepareChild(
   // as they all have the FD_CLOEXEC flag set and will be closed at
   // exec time.
 
-  // Close all fds that we're supposed to close.
-  // Redirect requested FDs to /dev/null or NUL.
+  // Redirect requested FDs to /dev/null or NUL
+  // dup2 any explicitly specified FDs
   for (auto& p : options.fdActions_) {
-    if (p.second == CLOSE) {
-      if (::close(p.first) == -1) {
-        return errno;
-      }
-    } else if (p.second == DEV_NULL) {
+    if (p.second == DEV_NULL) {
       // folly/portability/Fcntl provides an impl of open that will
       // map this to NUL on Windows.
       auto devNull = ::open("/dev/null", O_RDWR | O_CLOEXEC);

folly/Subprocess.h

@@ -253,8 +253,7 @@ class FOLLY_EXPORT SubprocessSpawnError : public SubprocessError {
  */
 class Subprocess {
  public:
-  // CLOSE is deprecated and will be removed, consider using DEV_NULL instead
-  static const int CLOSE = -1;
+  // removed CLOSE = -1
   static const int PIPE = -2;
   static const int PIPE_IN = -3;
   static const int PIPE_OUT = -4;

folly/test/SingletonTest.cpp

@@ -762,8 +762,8 @@ TEST(Singleton, DoubleRegistrationLogging) {
   auto p = Subprocess(
       std::vector<std::string>{sub.string()},
       Subprocess::Options()
-          .stdinFd(Subprocess::CLOSE)
-          .stdoutFd(Subprocess::CLOSE)
+          .stdinFd(Subprocess::DEV_NULL)
+          .stdoutFd(Subprocess::DEV_NULL)
           .pipeStderr()
           .closeOtherFds());
   auto err = p.communicate("").second;