tcon: routines for creating typesafe generic containers

ccan/tcon/_info

+#include "config.h"
+#include <string.h>
+
+/**
+ * tcon - routines for creating typesafe generic containers
+ *
+ * This code lets users create a structure with a typecanary; your API
+ * is then a set of macros which check the type canary before calling
+ * the generic routines.
+ *
+ * License: Public domain
+ *
+ * Author: Rusty Russell <rusty@rustcorp.com.au>
+ */
+int main(int argc, char *argv[])
+{
+	/* Expect exactly one argument */
+	if (argc != 2)
+		return 1;
+
+	if (strcmp(argv[1], "depends") == 0) {
+		return 0;
+	}
+
+	return 1;
+}

ccan/tcon/tcon.h

+/* Placed into the public domain */
+#ifndef CCAN_TCON_H
+#define CCAN_TCON_H
+#include "config.h"
+
+/**
+ * TCON - declare a _tcon type containing canary variables.
+ * @decls: the semi-colon separated list of type canaries.
+ *
+ * This declares a _tcon member for a structure.  It should be the
+ * last element in your structure; with sufficient compiler support it
+ * will not use any actual storage.  tcon_to_raw() will compare
+ * expressions with one of these "type canaries" to cause warnings if
+ * the container is misused.
+ *
+ * A type of "void *" will allow tcon_to_raw() to pass on any (pointer) type.
+ *
+ * Example:
+ *	// Simply typesafe linked list.
+ *	struct list_head {
+ *		struct list_head *prev, *next;
+ *	};
+ *
+ *	struct string_list {
+ *		struct list_head raw;
+ *		TCON(char *canary);
+ *	};
+ *
+ *	// More complex: mapping from one type to another.
+ *	struct map {
+ *		void *contents;
+ *	};
+ *
+ *	struct int_to_string_map {
+ *		struct map raw;
+ *		TCON(char *charp_canary; int int_canary);
+ *	};
+ */
+#if HAVE_FLEXIBLE_ARRAY_MEMBER
+#define TCON(decls) struct { decls; } _tcon[]
+#else
+#define TCON(decls) struct { decls; } _tcon[1]
+#endif
+
+/**
+ * tcon_check - typecheck a typed container
+ * @x: the structure containing the TCON.
+ * @canary: which canary to check against.
+ * @expr: the expression whose type must match the TCON (not evaluated)
+ *
+ * This macro is used to check that the expression is the type
+ * expected for this structure (note the "useless" sizeof() argument
+ * which contains this comparison with the type canary).
+ *
+ * It evaluates to @x so you can chain it.
+ *
+ * Example:
+ *	#define tlist_add(h, n, member) \
+ *		list_add(&tcon_check((h), canary, (n))->raw, &(n)->member)
+ */
+#define tcon_check(x, canary, expr)				\
+	(sizeof((x)->_tcon[0].canary == (expr)) ? (x) : (x))
+
+
+/**
+ * tcon_cast - cast to a canary type for this container (or void *)
+ * @x: a structure containing the TCON.
+ * @canary: which canary to cast to.
+ * @expr: the value to cast
+ *
+ * This is used to cast to the correct type for this container.  If the
+ * platform doesn't HAVE_TYPEOF, then it casts to void * (which will
+ * cause a warning if the user doesn't expect a pointer type).
+ */
+#if HAVE_TYPEOF
+#define tcon_cast(x, canary, expr) ((__typeof__((x)->_tcon[0].canary))(expr))
+#else
+#define tcon_cast(x, canary, expr) ((void *)(expr))
+#endif
+
+#endif /* CCAN_TCON_H */

ccan/tcon/test/compile_fail-tcon_cast.c

+#include <ccan/tcon/tcon.h>
+#include <stdlib.h>
+
+struct container {
+	void *p;
+};
+
+struct int_and_charp_container {
+	struct container raw;
+	TCON(int *tc1; char *tc2);
+};
+
+int main(int argc, char *argv[])
+{
+	struct int_and_charp_container icon;
+#ifdef FAIL
+#if !HAVE_TYPEOF
+#error We cannot detect type problems without HAVE_TYPEOF
+#endif
+	char *
+#else
+	int *
+#endif
+		x;
+
+	icon.raw.p = NULL;
+	x = tcon_cast(&icon, tc1, icon.raw.p);
+	return 0;
+}

ccan/tcon/test/compile_fail.c

+#include <ccan/tcon/tcon.h>
+#include <stdlib.h>
+
+struct container {
+	void *p;
+};
+
+struct int_container {
+	struct container raw;
+	TCON(int *canary);
+};
+
+int main(int argc, char *argv[])
+{
+	struct int_container icon;
+#ifdef FAIL
+	char *
+#else
+	int *
+#endif
+		x = NULL;
+
+	tcon_check(&icon, canary, x)->raw.p = x;
+	return 0;
+}

ccan/tcon/test/compile_ok-void.c

+#include <ccan/tcon/tcon.h>
+#include <stdlib.h>
+
+struct container {
+	void *p;
+};
+
+struct void_container {
+	struct container raw;
+	TCON(void *canary);
+};
+
+int main(int argc, char *argv[])
+{
+	struct void_container vcon;
+
+	tcon_check(&vcon, canary, NULL)->raw.p = NULL;
+	tcon_check(&vcon, canary, argv[0])->raw.p = NULL;
+	tcon_check(&vcon, canary, main)->raw.p = NULL;
+	return 0;
+}

ccan/tcon/test/compile_ok.c

+#include <ccan/tcon/tcon.h>
+#include <stdlib.h>
+
+struct container {
+	void *p;
+};
+
+struct int_container {
+	struct container raw;
+	TCON(int tc);
+};
+
+struct charp_and_int_container {
+	struct container raw;
+	TCON(int tc1; char *tc2);
+};
+
+int main(int argc, char *argv[])
+{
+	struct int_container icon;
+	struct charp_and_int_container cicon;
+
+	tcon_check(&icon, tc, 7)->raw.p = NULL;
+	tcon_check(&cicon, tc1, 7)->raw.p = argv[0];
+	tcon_check(&cicon, tc2, argv[0])->raw.p = argv[0];
+	return 0;
+}