process-util: Move Xwayland fork helpers to shared

We'll want to reuse these inside desktop-shell as well as the Weston
frontend.

(Based on the work from
 https://gitlab.freedesktop.org/wayland/weston/-/merge_requests/954)

Bug-AGL: SPEC-4510

Signed-off-by: Daniel Stone <daniel.stone@collabora.com>
Signed-off-by: Marius Vlad <marius.vlad@collabora.com>
Change-Id: Ife13dce545928cf53e4f49a657b756ed88ee742f

2 files changed, 364 insertions, 0 deletions

diff --git a/shared/process-util.c b/shared/process-util.c
new file mode 100644
index 0000000..e36c647
--- /dev/null
+++ b/shared/process-util.c
@@ -0,0 +1,270 @@
+/*
+ * Copyright 2022 Collabora, Ltd.
+ *
+ * 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 <assert.h>
+#include <ctype.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+#include <wayland-util.h>
+
+#include "helpers.h"
+#include "os-compatibility.h"
+#include "process-util.h"
+#include "string-helpers.h"
+
+extern char **environ; /* defined by libc */
+
+void
+fdstr_update_str1(struct fdstr *s)
+{
+	snprintf(s->str1, sizeof(s->str1), "%d", s->fds[1]);
+}
+
+void
+fdstr_set_fd1(struct fdstr *s, int fd)
+{
+	s->fds[0] = -1;
+	s->fds[1] = fd;
+	fdstr_update_str1(s);
+}
+
+bool
+fdstr_clear_cloexec_fd1(struct fdstr *s)
+{
+	return os_fd_clear_cloexec(s->fds[1]) >= 0;
+}
+
+void
+fdstr_close_all(struct fdstr *s)
+{
+	unsigned i;
+
+	for (i = 0; i < ARRAY_LENGTH(s->fds); i++) {
+		close(s->fds[i]);
+		s->fds[i] = -1;
+	}
+}
+
+void
+custom_env_init_from_environ(struct custom_env *env)
+{
+	char **it;
+	char **ep;
+
+	wl_array_init(&env->envp);
+	env->env_finalized = false;
+	wl_array_init(&env->argp);
+	env->arg_finalized = false;
+
+	for (it = environ; *it; it++) {
+		ep = wl_array_add(&env->envp, sizeof *ep);
+		assert(ep);
+		*ep = strdup(*it);
+		assert(*ep);
+	}
+}
+
+void
+custom_env_fini(struct custom_env *env)
+{
+	char **p;
+
+	wl_array_for_each(p, &env->envp)
+		free(*p);
+	wl_array_release(&env->envp);
+
+	wl_array_for_each(p, &env->argp)
+		free(*p);
+	wl_array_release(&env->argp);
+}
+
+static char **
+custom_env_get_env_var(struct custom_env *env, const char *name)
+{
+	char **ep;
+	size_t name_len = strlen(name);
+
+	wl_array_for_each(ep, &env->envp) {
+		char *entry = *ep;
+
+		if (strncmp(entry, name, name_len) == 0 &&
+		    entry[name_len] == '=') {
+			return ep;
+		}
+	}
+
+	return NULL;
+}
+
+void
+custom_env_add_arg(struct custom_env *env, const char *arg)
+{
+	char **ap;
+
+	assert(!env->arg_finalized);
+
+	ap = wl_array_add(&env->argp, sizeof *ap);
+	assert(ap);
+
+	*ap = strdup(arg);
+	assert(*ap);
+}
+
+void
+custom_env_set_env_var(struct custom_env *env, const char *name, const char *value)
+{
+	char **ep;
+
+	assert(strchr(name, '=') == NULL);
+	assert(!env->env_finalized);
+
+	ep = custom_env_get_env_var(env, name);
+	if (ep)
+		free(*ep);
+	else
+		ep = wl_array_add(&env->envp, sizeof *ep);
+	assert(ep);
+
+	str_printf(ep, "%s=%s", name, value);
+	assert(*ep);
+}
+
+/**
+ * Add information from a parsed exec string to a custom_env
+ *
+ * An 'exec string' is a string in the format:
+ *   ENVFOO=bar ENVBAR=baz /path/to/exec --arg anotherarg
+ *
+ * This function will parse such a string and add the specified environment
+ * variables (in the format KEY=value) up until it sees a non-environment
+ * string, after which point every entry will be interpreted as a new
+ * argument.
+ *
+ * Entries are space-separated; there is no support for quoting.
+ */
+void
+custom_env_add_from_exec_string(struct custom_env *env, const char *exec_str)
+{
+	char *dup_path = strdup(exec_str);
+	char *start = dup_path;
+
+	assert(dup_path);
+
+	/* Build the environment array (if any) by handling any number of
+	 * equal-separated key=value at the start of the string, split by
+	 * spaces; uses "foo=bar  baz=quux meh argh" as the example, where
+	 * "foo=bar" and "baz=quux" should go into the environment, and
+	 * "meh" should be executed with "argh" as its first argument */
+	while (*start) {
+		char *k = NULL, *v = NULL;
+		char *p;
+
+		/* Leaves us with "foo\0bar  baz=quux meh argh", with k pointing
+		 * to "foo" and v pointing to "bar  baz=quux meh argh" */
+		for (p = start; *p && !isspace(*p); p++) {
+			if (*p == '=') {
+				*p++ = '\0';
+				k = start;
+				v = p;
+				break;
+			}
+		}
+
+		if (!v)
+			break;
+
+		/* Walk to the next space or NUL, filling any trailing spaces
+		 * with NUL, to give us "foo\0bar\0\0baz=quux meh argh".
+		 * k will point to "foo", v will point to "bar", and
+		 * start will point to "baz=quux meh argh". */
+		while (*p && !isspace(*p))
+			p++;
+		while (*p && isspace(*p))
+			*p++ = '\0';
+		start = p;
+
+		custom_env_set_env_var(env, k, v);
+	}
+
+	/* Now build the argv array by splitting on spaces */
+	while (*start) {
+		char *p;
+		bool valid = false;
+
+		for (p = start; *p && !isspace(*p); p++)
+			valid = true;
+
+		if (!valid)
+			break;
+
+		while (*p && isspace(*p))
+			*p++ = '\0';
+
+		custom_env_add_arg(env, start);
+		start = p;
+	}
+
+	free(dup_path);
+}
+
+char *const *
+custom_env_get_envp(struct custom_env *env)
+{
+	char **ep;
+
+	assert(!env->env_finalized);
+
+	/* add terminating NULL */
+	ep = wl_array_add(&env->envp, sizeof *ep);
+	assert(ep);
+	*ep = NULL;
+
+	env->env_finalized = true;
+
+	return env->envp.data;
+}
+
+char *const *
+custom_env_get_argp(struct custom_env *env)
+{
+	char **ap;
+
+	assert(!env->arg_finalized);
+
+	/* add terminating NULL */
+	ap = wl_array_add(&env->argp, sizeof *ap);
+	assert(ap);
+	*ap = NULL;
+
+	env->arg_finalized = true;
+
+	return env->argp.data;
+}
diff --git a/shared/process-util.h b/shared/process-util.h
new file mode 100644
index 0000000..05543f6
--- /dev/null
+++ b/shared/process-util.h
@@ -0,0 +1,94 @@
+/*
+ * Copyright 2022 Collabora, Ltd.
+ *
+ * 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 <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+#include <wayland-util.h>
+
+#include "os-compatibility.h"
+#include "string-helpers.h"
+
+/**
+ * A container for file descriptors and their string representations, designed
+ * to be used when forking child processes.
+ *
+ * fds[0] is generally used as the file descriptor held within the parent
+ * process to communicate with the child, and fds[1] as the child's counterpart.
+ *
+ * str1[] is used as a string representation of fds[1].
+ */
+struct fdstr {
+	char str1[12];
+	int fds[2];
+};
+
+void
+fdstr_update_str1(struct fdstr *s);
+
+void
+fdstr_set_fd1(struct fdstr *s, int fd);
+
+bool
+fdstr_clear_cloexec_fd1(struct fdstr *s);
+
+void
+fdstr_close_all(struct fdstr *s);
+
+
+/**
+ * A container for environment variables and/or process arguments, designed to
+ * be used when forking child processes, as setenv() and anything which
+ * allocates memory cannot be used between fork() and exec().
+ */
+struct custom_env {
+	struct wl_array envp;
+	bool env_finalized;
+	struct wl_array argp;
+	bool arg_finalized;
+};
+
+void
+custom_env_init_from_environ(struct custom_env *env);
+
+void
+custom_env_fini(struct custom_env *env);
+
+void
+custom_env_set_env_var(struct custom_env *env, const char *name, const char *value);
+
+void
+custom_env_add_arg(struct custom_env *env, const char *arg);
+
+void
+custom_env_add_from_exec_string(struct custom_env *env, const char *exec_str);
+
+char *const *
+custom_env_get_envp(struct custom_env *env);
+
+char *const *
+custom_env_get_argp(struct custom_env *env);