Test: Use a xvfb wrapper for x11 test

The x11 test is currently silently skipped in CI, because it requires a
running X server.

Create a xvfb wrapper to run the test. We do not use `xvfb-run`, because
it is a shell script and it causes valgrind to detect unrelated memory
issues in the shell (dash, bash).

TODO: The wrapper is intended to be used with the x11comp test as well.

meson.build

@@ -576,6 +576,8 @@ if get_option('enable-x11')
     libxkbcommon_x11_internal = static_library(
         'xkbcommon-x11-internal',
         libxkbcommon_x11_sources,
+        'test/xvfb-wrapper.c',
+        'test/xvfb-wrapper.h',
         include_directories: include_directories('src', 'include'),
         link_with: libxkbcommon_test_internal,
         dependencies: [

test/x11.c

@@ -24,10 +24,11 @@
 #include "config.h"
 
 #include "test.h"
+#include "xvfb-wrapper.h"
 #include "xkbcommon/xkbcommon-x11.h"
 
-int
-main(void)
+static int
+test(void)
 {
     struct xkb_context *ctx = test_get_context(0);
     xcb_connection_t *conn;
@@ -84,3 +85,7 @@ main(void)
 
     return exit_code;
 }
+
+int main(void) {
+    xvfb_wrapper(&test);
+}

test/xvfb-wrapper.c

@@ -0,0 +1,105 @@
+/*
+ * Copyright © 2014 Ran Benita <[email protected]>
+ * Copyright © 2023 Pierre Le Marre <[email protected]>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS IN THE SOFTWARE.
+ */
+
+#include "config.h"
+
+#include <stdio.h>
+#include <spawn.h>
+#include <assert.h>
+#include <signal.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+
+#include "test.h"
+#include "xvfb-wrapper.h"
+#include "xkbcommon/xkbcommon-x11.h"
+
+int xvfb_wrapper(int (*f)(void)) {
+    int ret;
+    char display[512];
+    char *envp[] = { NULL };
+    char *xvfb_argv[] = {
+        (char *) "Xvfb", display, NULL
+    };
+    pid_t xvfb_pid = 0;
+    char *xhost = NULL;
+    int xdpy_current = 0;
+    int xdpy_candidate;
+
+    /*
+     * What all of this mess does is:
+     * 1. Launch Xvfb on available DISPLAY.
+     * 2. Make an xcb connection to this display.
+     * 3. Launch xkbcomp to change the keymap of the new display (doing
+     *    this programmatically is major work [which we may yet do some
+     *    day for xkbcommon-x11] so we use xkbcomp for now).
+     * 4. Download the keymap back from the display using xkbcommon-x11.
+     * 5. Compare received keymap to the uploaded keymap.
+     * 6. Kill the server & clean up.
+     */
+
+    /*
+     * Detect current display, in order to avoid reusing it.
+     * It is OK if it fails (e.g. in headless mode).
+     */
+    xcb_parse_display(NULL, &xhost, &xdpy_current, NULL);
+
+    /*
+     * IANA assigns TCP port numbers from 6000 through 6063 to X11
+     * clients.  In addition, the current XCB implementaion shows
+     * that, when an X11 client tries to establish a TCP connetion,
+     * the port number needed is specified by adding 6000 to a given
+     * display number.  So, one of reasonable ranges of xdpy_candidate
+     * is [0, 63].
+     */
+    for (xdpy_candidate = 63; xdpy_candidate >= 0; xdpy_candidate--) {
+        if (xdpy_candidate == xdpy_current) {
+            continue;
+        }
+        snprintf(display, sizeof(display),
+                 "%s:%d", (xhost != NULL) ? xhost : "",
+                 xdpy_candidate);
+        ret = posix_spawnp(&xvfb_pid, "Xvfb", NULL, NULL, xvfb_argv, envp);
+        if (ret == 0) {
+            break;
+        }
+    }
+    free(xhost);
+
+    if (ret != 0) {
+        ret = SKIP_TEST;
+        goto err_xvfd;
+    }
+
+    /* Wait for Xvfb fully waking up to accept a connection from a client. */
+    sleep(1);
+
+    /* Run the function requiring a running X server */
+    ret = f();
+
+err_xvfd:
+    if (xvfb_pid > 0)
+        kill(xvfb_pid, SIGTERM);
+    return ret;
+}

test/xvfb-wrapper.h

@@ -0,0 +1 @@
+int xvfb_wrapper(int (*f)(void));