expose the client pid in our stream layer

Summary:
While troubleshooting the source of some queries it is valuable to be
able to determine the process id of the peer, so add a method that returns the
pid of the peer if known.

We already had code to query the peer credentials on Linux and Mac, so this
just moves it to the constructor and makes the existing ownership check
a simple accessor for that that, then adds a method to return the process
ID from that same state.

Reviewed By: sid0

Differential Revision: D4282299

fbshipit-source-id: fcfa7a10723d088b4a33a756110933dc39ee0605

stream_stdout.cpp

@@ -36,6 +36,10 @@ class StdioStream : public watchman_stream {
     return false;
   }
 
+  pid_t getPeerProcessID() const override {
+    return 0;
+  }
+
 #ifndef _WIN32
   int getFileDescriptor() const override {
     return fd;

stream_unix.cpp

@@ -70,9 +70,23 @@ class UnixStream : public watchman_stream {
  public:
   FileDescriptor fd;
   FakeSocketEvent evt;
+#ifdef SO_PEERCRED
+  struct ucred cred;
+#elif defined(LOCAL_PEERCRED)
+  struct xucred cred;
+#endif
+  bool credvalid{false};
 
   explicit UnixStream(FileDescriptor&& descriptor)
-      : fd(std::move(descriptor)), evt(fd.fd()) {}
+      : fd(std::move(descriptor)), evt(fd.fd()) {
+    socklen_t len = sizeof(cred);
+#ifdef SO_PEERCRED
+    credvalid = getsockopt(fd.fd(), SOL_SOCKET, SO_PEERCRED, &cred, &len) == 0;
+#elif defined(LOCAL_PEERCRED)
+    credvalid =
+        getsockopt(fd.fd(), SOL_LOCAL, LOCAL_PEERCRED, &cred, &len) == 0;
+#endif
+  }
 
   int getFileDescriptor() const override {
     return fd.fd();
@@ -138,28 +152,31 @@ class UnixStream : public watchman_stream {
   // mechanisms.  We'll treat the other process as an owner if their
   // effective UID matches ours, or if they are root.
   bool peerIsOwner() override {
+    if (!credvalid) {
+      return false;
+    }
 #ifdef SO_PEERCRED
-    struct ucred cred;
-    socklen_t len = sizeof(cred);
-
-    if (getsockopt(fd.fd(), SOL_SOCKET, SO_PEERCRED, &cred, &len) == 0) {
-      if (cred.uid == getuid() || cred.uid == 0) {
-        return true;
-      }
+    if (cred.uid == getuid() || cred.uid == 0) {
+      return true;
     }
 #elif defined(LOCAL_PEERCRED)
-    struct xucred cred;
-    socklen_t len = sizeof(cred);
-
-    if (getsockopt(fd.fd(), SOL_LOCAL, LOCAL_PEERCRED, &cred, &len) == 0) {
-      if (cred.cr_uid == getuid() || cred.cr_uid == 0) {
-        return true;
-      }
+    if (cred.cr_uid == getuid() || cred.cr_uid == 0) {
+      return true;
     }
 #endif
-
     return false;
   }
+
+  pid_t getPeerProcessID() const override {
+    if (!credvalid) {
+      return 0;
+    }
+#ifdef SO_PEERCRED
+    return cred.pid;
+#else
+    return 0;
+#endif
+  }
 };
 }
 

stream_win.cpp

@@ -87,6 +87,10 @@ class win_handle : public watchman_stream {
   inline HANDLE handle() const {
     return (HANDLE)h.handle();
   }
+
+  pid_t getPeerProcessID() const override {
+    return 0;
+  }
 };
 
 #if 1

watchman_stream.h

@@ -28,6 +28,7 @@ class watchman_stream {
   virtual bool rewind() = 0;
   virtual bool shutdown() = 0;
   virtual bool peerIsOwner() = 0;
+  virtual pid_t getPeerProcessID() const = 0;
 #ifndef _WIN32
   virtual int getFileDescriptor() const = 0;
 #else