Factor out socket_io_try_{read,write}()

To be reused in Lua connection API.

common.c

@@ -95,6 +95,74 @@ xwrite (int fd, const char *data, size_t len, struct error **e)
 	return true;
 }
 
+// --- Simple network I/O ------------------------------------------------------
+
+// TODO: move to liberty and remove from dwmstatus.c as well
+
+#define SOCKET_IO_OVERFLOW (8 << 20)    ///< How large a read buffer can be
+
+enum socket_io_result
+{
+	SOCKET_IO_OK,                       ///< Completed successfully
+	SOCKET_IO_EOF,                      ///< Connection shut down by peer
+	SOCKET_IO_ERROR                     ///< Connection error
+};
+
+static enum socket_io_result
+socket_io_try_read (int socket_fd, struct str *rb, struct error **e)
+{
+	// We allow buffering of a fair amount of data, however within reason,
+	// so that it's not so easy to flood us and cause an allocation failure
+	ssize_t n_read;
+	while (rb->len < SOCKET_IO_OVERFLOW)
+	{
+		str_ensure_space (rb, 4096);
+		n_read = recv (socket_fd, rb->str + rb->len,
+			rb->alloc - rb->len - 1 /* null byte */, 0);
+
+		if (n_read > 0)
+		{
+			rb->str[rb->len += n_read] = '\0';
+			continue;
+		}
+		if (n_read == 0)
+			return SOCKET_IO_EOF;
+
+		if (errno == EAGAIN)
+			return SOCKET_IO_OK;
+		if (errno == EINTR)
+			continue;
+
+		error_set (e, "%s", strerror (errno));
+		return SOCKET_IO_ERROR;
+	}
+	return SOCKET_IO_OK;
+}
+
+static enum socket_io_result
+socket_io_try_write (int socket_fd, struct str *wb, struct error **e)
+{
+	ssize_t n_written;
+	while (wb->len)
+	{
+		n_written = send (socket_fd, wb->str, wb->len, 0);
+		if (n_written >= 0)
+		{
+			str_remove_slice (wb, 0, n_written);
+			continue;
+		}
+
+		if (errno == EAGAIN)
+			return SOCKET_IO_OK;
+		if (errno == EINTR)
+			continue;
+
+		error_set (e, "%s", strerror (errno));
+		return SOCKET_IO_ERROR;
+	}
+	return SOCKET_IO_OK;
+}
+
 // --- Logging -----------------------------------------------------------------
 
 static void