lib: "ferr" error-information system

This provides an API to pass around extra information for errors, more
than a simple return value can carry.  This is particularly used for the
Cap'n Proto interface to be able to report more useful errors.

Signed-off-by: David Lamparter <equinox@opensourcerouting.org>

1 files changed, 191 insertions, 0 deletions

diff --git a/lib/ferr.h b/lib/ferr.h
new file mode 100644
index 0000000000..a570637372
--- /dev/null
+++ b/lib/ferr.h
@@ -0,0 +1,191 @@
+/*
+ * Copyright (c) 2015-16  David Lamparter, for NetDEF, Inc.
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#ifndef _FRR_FERR_H
+#define _FRR_FERR_H
+
+/***********************************************************
+ * scroll down to the end of this file for a full example! *
+ ***********************************************************/
+
+#include <stdint.h>
+#include <limits.h>
+#include <errno.h>
+
+/* return type when this error indication stuff is used.
+ *
+ * guaranteed to have boolean evaluation to "false" when OK, "true" when error
+ * (i.e. can be changed to pointer in the future if neccessary)
+ *
+ * For checking, always use "if (value)", nothing else.
+ * Do _NOT_ use any integer constant (!= 0), or sign check (< 0).
+ */
+typedef int ferr_r;
+
+/* rough category of error indication */
+enum ferr_kind {
+	/* no error */
+	FERR_OK = 0,
+
+	/* something isn't the way it's supposed to be.
+	 * (things that might otherwise be asserts, really)
+	 */
+	FERR_CODE_BUG,
+
+	/* user-supplied parameters don't make sense or is inconsistent
+	 * if you can express a rule for it (e.g. "holdtime > 2 * keepalive"),
+	 * it's this category.
+	 */
+	FERR_CONFIG_INVALID,
+
+	/* user-supplied parameters don't line up with reality
+	 * (IP address or interface not available, etc.)
+	 * NB: these are really TODOs where the code needs to be fixed to
+	 * respond to future changes!
+	 */
+	FERR_CONFIG_REALITY,
+
+	/* out of some system resource (probably memory)
+	 * aka "you didn't spend enough money error" */
+	FERR_RESOURCE,
+
+	/* system error (permission denied, etc.) */
+	FERR_SYSTEM,
+
+	/* error return from some external library
+	 * (FERR_SYSTEM and FERR_LIBRARY are not strongly distinct) */
+	FERR_LIBRARY,
+};
+
+struct ferr {
+	/* code location */
+	const char *file;
+	const char *func;
+	int line;
+
+	enum ferr_kind kind;
+
+	/* unique_id is calculated as a checksum of source filename and error
+	 * message format (*before* calling vsnprintf).  Line number and
+	 * function name are not used; this keeps the number reasonably static
+	 * across changes.
+	 */
+	uint32_t unique_id;
+
+	char message[384];
+
+	/* valid if != 0.  note "errno" might be preprocessor foobar. */
+	int errno_val;
+	/* valid if pathname[0] != '\0' */
+	char pathname[PATH_MAX];
+};
+
+/* get error details.
+ *
+ * NB: errval/ferr_r does NOT carry the full error information.  It's only
+ * passed around for future API flexibility.  ferr_get_last always returns
+ * the last error set in the current thread.
+ */
+const struct ferr *ferr_get_last(ferr_r errval);
+
+/* can optionally be called at strategic locations.
+ * always returns 0. */
+ferr_r ferr_clear(void);
+
+/* do NOT call these functions directly.  only for macro use! */
+ferr_r ferr_set_internal(const char *file, int line, const char *func,
+		enum ferr_kind kind, const char *text, ...);
+ferr_r ferr_set_internal_ext(const char *file, int line, const char *func,
+		enum ferr_kind kind, const char *pathname, int errno_val,
+		const char *text, ...);
+
+#define ferr_ok() \
+	0
+
+/* Report an error.
+ *
+ * If you need to do cleanup (free memory, etc.), save the return value in a
+ * variable of type ferr_r.
+ *
+ * Don't put a \n at the end of the error message.
+ */
+#define ferr_code_bug(...) \
+	ferr_set_internal(__FILE__, __LINE__, __func__, FERR_CODE_BUG, \
+			__VA_ARGS__)
+#define ferr_cfg_invalid(...) \
+	ferr_set_internal(__FILE__, __LINE__, __func__, FERR_CONFIG_INVALID, \
+			__VA_ARGS__)
+#define ferr_cfg_reality(...) \
+	ferr_set_internal(__FILE__, __LINE__, __func__, FERR_CONFIG_REALITY, \
+			__VA_ARGS__)
+#define ferr_cfg_resource(...) \
+	ferr_set_internal(__FILE__, __LINE__, __func__, FERR_RESOURCE, \
+			__VA_ARGS__)
+#define ferr_system(...) \
+	ferr_set_internal(__FILE__, __LINE__, __func__, FERR_SYSTEM, \
+			__VA_ARGS__)
+#define ferr_library(...) \
+	ferr_set_internal(__FILE__, __LINE__, __func__, FERR_LIBRARY, \
+			__VA_ARGS__)
+
+/* extended information variants */
+#define ferr_system_errno(...) \
+	ferr_set_internal_ext(__FILE__, __LINE__, __func__, FERR_SYSTEM, \
+			NULL, errno, __VA_ARGS__)
+#define ferr_system_path_errno(path, ...) \
+	ferr_set_internal_ext(__FILE__, __LINE__, __func__, FERR_SYSTEM, \
+			path, errno, __VA_ARGS__)
+
+#include "vty.h"
+/* print error message to vty;  $ERR is replaced by the error's message */
+void vty_print_error(struct vty *vty, ferr_r err, const char *msg, ...);
+
+#define CMD_FERR_DO(func, action, ...) \
+	do { ferr_r cmd_retval = func; \
+		if (cmd_retval) { \
+			vty_print_error(vty, cmd_retval, __VA_ARGS__); \
+			action; \
+		} \
+	} while (0)
+
+#define CMD_FERR_RETURN(func, ...) \
+	CMD_FERR_DO(func, return CMD_WARNING, __VA_ARGS__)
+#define CMD_FERR_GOTO(func, label, ...) \
+	CMD_FERR_DO(func, goto label, __VA_ARGS__)
+
+/* example:
+
+ferr_r foo_bar_set(struct object *obj, int bar)
+{
+	if (bar < 1 || bar >= 100)
+		return ferr_config_invalid("bar setting (%d) must be 0<x<100", bar);
+	obj->bar = bar;
+	if (ioctl (obj->fd, bar))
+		return ferr_system_errno("couldn't set bar to %d", bar);
+
+	return ferr_ok();
+}
+
+DEFUN("bla")
+{
+	CMD_FERR_RETURN(foo_bar_set(obj, atoi(argv[1])),
+		"command failed: $ERR\n");
+	return CMD_SUCCESS;
+}
+
+*/
+
+#endif /* _FERR_H */