net/SocketDescriptor: add method GetPeerCredentials()

src/net/SocketDescriptor.cxx

@@ -220,6 +220,32 @@ SocketDescriptor::GetError()
 		: errno;
 }
 
+size_t
+SocketDescriptor::GetOption(int level, int name,
+			    void *value, size_t size) const
+{
+	assert(IsDefined());
+
+	socklen_t size2 = size;
+	return getsockopt(fd, level, name, (char *)value, &size2) == 0
+		? size2
+		: 0;
+}
+
+#ifdef HAVE_STRUCT_UCRED
+
+struct ucred
+SocketDescriptor::GetPeerCredentials() const noexcept
+{
+	struct ucred cred;
+	if (GetOption(SOL_SOCKET, SO_PEERCRED,
+		      &cred, sizeof(cred)) < sizeof(cred))
+		cred.pid = -1;
+	return cred;
+}
+
+#endif
+
 #ifdef _WIN32
 
 bool

src/net/SocketDescriptor.hxx

@@ -150,6 +150,20 @@ public:
 
 	int GetError();
 
+	/**
+	 * @return the value size or 0 on error
+	 */
+	size_t GetOption(int level, int name, void *value, size_t size) const;
+
+#ifdef HAVE_STRUCT_UCRED
+	/**
+	 * Receive peer credentials (SO_PEERCRED).  On error, the pid
+	 * is -1.
+	 */
+	gcc_pure
+	struct ucred GetPeerCredentials() const noexcept;
+#endif
+
 	bool SetOption(int level, int name, const void *value, size_t size);
 
 	bool SetBoolOption(int level, int name, bool _value) {