Extend UnixDomainSocket::RecvMsg to return sender's PID

base/posix/unix_domain_socket_linux.h

Index: base/posix/unix_domain_socket_linux.h
diff --git a/base/posix/unix_domain_socket_linux.h b/base/posix/unix_domain_socket_linux.h
index 66fb8bb1bf629894c5badb4564cf517a5e4ded71..1b30ef5e5e452eaa96433c90cbd3b23d699dd8c7 100644
--- a/base/posix/unix_domain_socket_linux.h
+++ b/base/posix/unix_domain_socket_linux.h
@@ -10,6 +10,7 @@
 #include <vector>
 
 #include "base/base_export.h"
+#include "base/process/process_handle.h"

[jln (very slow on Chromium), 2014/04/24 19:24:38]

You could forward declare base::ProcessId.

[mdempsky, 2014/04/24 20:23:30]

As discussed at lunch, base::ProcessId can't be forward declared because it's a
typedef, not a class.

[willchan no longer on Chromium, 2014/04/24 20:44:04]

I'm fine with including and not forward declaring, but since this is only be
added to unix_domain_socket_linux.h, why do we need the platform-agnostic type?
Does this code usage leak into platform-agnostic code?

[mdempsky, 2014/04/24 20:59:14]

I think it would be technically okay to use pid_t instead of base::ProcessId in
this API.  It just seemed like the predominant style of base/ was to still use
base::ProcessId instead of pid_t even for POSIX-specific functionality (e.g.,
base::GetParentProcessId).

Doesn't matter to me either way.  I'm happy to change it if you prefer.

[willchan no longer on Chromium, 2014/04/24 21:09:56]

I generally encourage using the cross-platform type to ease (reduce refactoring)
in future potential cross-platform usage except if there are costs. Avoiding an
#include is pretty minor, so I, like you, don't really care :) Just thought I'd
mention it in case one of you guys did.

 
 class Pickle;
 
@@ -18,6 +19,11 @@ class BASE_EXPORT UnixDomainSocket {
   // Maximum number of file descriptors that can be read by RecvMsg().
   static const size_t kMaxFileDescriptors;
 
+  // Use to enable receiving process IDs in RecvMsgWithPid.  Should be called on
+  // the receiving socket (i.e., the socket passed to RecvMsgWithPid). Returns
+  // true if successful.
+  static bool EnableReceiveProcessId(int fd);
+
   // Use sendmsg to write the given msg and include a vector of file
   // descriptors. Returns true if successful.
   static bool SendMsg(int fd,
@@ -32,6 +38,16 @@ class BASE_EXPORT UnixDomainSocket {
                          size_t length,
                          std::vector<int>* fds);
 
+  // Same as RecvMsg above, but also returns the sender's process ID (as seen
+  // from the caller's namespace).  However, before using this function to
+  // receive process IDs, EnableReceiveProcessId() should be called on the
+  // receiving socket.
+  static ssize_t RecvMsgWithPid(int fd,
+                                void* msg,
+                                size_t length,
+                                std::vector<int>* fds,
+                                base::ProcessId* pid);
+
   // Perform a sendmsg/recvmsg pair.
   //   1. This process creates a UNIX SEQPACKET socketpair. Using
   //      connection-oriented sockets (SEQPACKET or STREAM) is critical here,
@@ -70,7 +86,8 @@ class BASE_EXPORT UnixDomainSocket {
                                   void* msg,
                                   size_t length,
                                   int flags,
-                                  std::vector<int>* fds);
+                                  std::vector<int>* fds,
+                                  base::ProcessId* pid);
 };
 
 #endif  // BASE_POSIX_UNIX_DOMAIN_SOCKET_LINUX_H_