common/string-helpers.c: add strdup_printf()

include/common/string-helpers.h

@@ -16,4 +16,15 @@ char *string_strip(char *s);
  */
 void string_truncate_at_pattern(char *buf, const char *pattern);
 
+/**
+ * strdup_printf - allocate and write to buffer in printf format
+ * @fmt: printf-style format.
+ *
+ * Similar to the standard C sprintf() function but safer as it calculates the
+ * maximum space required and allocates memory to hold the output.
+ * The user must free the returned string.
+ * Returns NULL on error.
+ */
+char *strdup_printf(const char *fmt, ...);
+
 #endif /* LABWC_STRING_HELPERS_H */

src/common/string-helpers.c

@@ -1,7 +1,9 @@
 // SPDX-License-Identifier: GPL-2.0-only
 #include <ctype.h>
+#include <stdarg.h>
 #include <stdio.h>
 #include <string.h>
+#include "common/mem.h"
 #include "common/string-helpers.h"
 
 static void
@@ -37,3 +39,32 @@ string_truncate_at_pattern(char *buf, const char *pattern)
 	}
 	*p = '\0';
 }
+
+char *
+strdup_printf(const char *fmt, ...)
+{
+	size_t size = 0;
+	char *p = NULL;
+	va_list ap;
+
+	va_start(ap, fmt);
+	int n = vsnprintf(p, size, fmt, ap);
+	va_end(ap);
+
+	if (n < 0) {
+		return NULL;
+	}
+
+	size = (size_t)n + 1;
+	p = xzalloc(size);
+
+	va_start(ap, fmt);
+	n = vsnprintf(p, size, fmt, ap);
+	va_end(ap);
+
+	if (n < 0) {
+		free(p);
+		return NULL;
+	}
+	return p;
+}

src/config/rcxml.c

@@ -1096,11 +1096,9 @@ post_processing(void)
 	int nr_workspaces = wl_list_length(&rc.workspace_config.workspaces);
 	if (nr_workspaces < rc.workspace_config.min_nr_workspaces) {
 		struct workspace *workspace;
-		char workspace_name[32];
 		for (int i = nr_workspaces; i < rc.workspace_config.min_nr_workspaces; i++) {
 			workspace = znew(*workspace);
-			snprintf(workspace_name, sizeof(workspace_name), "Workspace %d", i + 1);
-			workspace->name = xstrdup(workspace_name);
+			workspace->name = strdup_printf("Workspace %d", i + 1);
 			wl_list_append(&rc.workspace_config.workspaces, &workspace->link);
 		}
 	}

src/config/session.c

@@ -79,12 +79,7 @@ build_path(const char *dir, const char *filename)
 	if (string_empty(dir) || string_empty(filename)) {
 		return NULL;
 	}
-	int len = strlen(dir) + strlen(filename) + 2;
-	char *buffer = znew_n(char, len);
-	strcat(buffer, dir);
-	strcat(buffer, "/");
-	strcat(buffer, filename);
-	return buffer;
+	return strdup_printf("%s/%s", dir, filename);
 }
 
 static void
@@ -98,19 +93,11 @@ update_activation_env(const char *env_keys)
 	}
 	wlr_log(WLR_INFO, "Updating dbus execution environment");
 
-	char *cmd;
-	const char *dbus = "dbus-update-activation-environment ";
-	const char *systemd = "systemctl --user import-environment ";
-
-	cmd = znew_n(char, strlen(dbus) + strlen(env_keys) + 1);
-	strcat(cmd, dbus);
-	strcat(cmd, env_keys);
+	char *cmd = strdup_printf("dbus-update-activation-environment %s", env_keys);
 	spawn_async_no_shell(cmd);
 	free(cmd);
 
-	cmd = znew_n(char, strlen(systemd) + strlen(env_keys) + 1);
-	strcat(cmd, systemd);
-	strcat(cmd, env_keys);
+	cmd = strdup_printf("systemctl --user import-environment %s", env_keys);
 	spawn_async_no_shell(cmd);
 	free(cmd);
 }
@@ -148,10 +135,7 @@ session_autostart_init(const char *dir)
 		goto out;
 	}
 	wlr_log(WLR_INFO, "run autostart file %s", autostart);
-	int len = strlen(autostart) + 4;
-	char *cmd = znew_n(char, len);
-	strcat(cmd, "sh ");
-	strcat(cmd, autostart);
+	char *cmd = strdup_printf("sh %s", autostart);
 	spawn_async_no_shell(cmd);
 	free(cmd);
 out: