common/common.c, include/common.h: introduce minimize_formatting_stri…

…ng() [networkupstools#2450]

...and minimize_formatting_string_staticbuf() for one-shot use-cases.

Signed-off-by: Jim Klimov <[email protected]>

common/common.c

@@ -1,7 +1,7 @@
 /* common.c - common useful functions
 
    Copyright (C) 2000  Russell Kroll <[email protected]>
-   Copyright (C) 2021-2022  Jim Klimov <[email protected]>
+   Copyright (C) 2021-2024  Jim Klimov <[email protected]>
 
    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -1284,6 +1284,82 @@ void nut_report_config_flags(void)
 		);
 }
 
+char * minimize_formatting_string(char *buf, size_t buflen, const char *fmt)
+{
+	/* Return the bare-bone formatting string contained in "fmt"
+	 * as "%" characters followed immediately by ASCII letters,
+	 * or null if "fmt" is null (empty string if it has no "%"),
+	 * or "buf" is null, or "buflen" is too short.
+	 * Allows to compare different formatting strings to check
+	 * if they describe the same expected amounts of arguments
+	 * and their types.
+	 * Uses a caller-specified buffer and returns a pointer to
+	 * it, or NULL upon errors.
+	 */
+	const char	*p;
+	char	*b, inEscape;
+	size_t	i;
+
+	if (!fmt || !buf || buflen == 0)
+		return NULL;
+
+	for (b = buf, p = fmt, i = 0, inEscape = 0;
+		(*p != '\0' && i < buflen);
+		p++
+	) {
+		if (*p == '%') {
+			if (*(p+1) == '%') {
+				/* Escaped percent character, not a variable indicator */
+				p++;
+			} else {
+				inEscape = 1;
+				*b++ = *p;
+				i++;
+			}
+			continue;
+		}
+
+		if (inEscape) {
+			/* Did we hit a printf format character? */
+			if (*p == '%')
+				continue;
+			if ((*p >= 'a' && *p <= 'z') || (*p >= 'A' && *p <= 'Z')) {
+				inEscape = 0;
+				*b++ = *p;
+				i++;
+			}
+		}
+	}
+
+	if (inEscape) {
+		upsdebugx(1, "%s: error parsing '%s' as a formatting string - "
+			"got a dangling percent character", __func__, fmt);
+	}
+
+	*b = '\0';
+	return buf;
+}
+
+char * minimize_formatting_string_staticbuf(const char *fmt)
+{
+	/* Return the bare-bone formatting string contained in "fmt"
+	 * as "%" characters followed immediately by ASCII letters,
+	 * or null if "fmt" is null (empty string if it has no "%").
+	 * Allows to compare different formatting strings to check
+	 * if they describe the same expected amounts of arguments
+	 * and their types.
+	 * Returns a pointer to a static buffer; callers should
+	 * xstrdup() and free() the returned value where applicable
+	 * (e.g. if there is a need to compare several strings), or
+	 * just use minimize_formatting_string() with their own
+	 * buffers right away.
+	 */
+
+	static char	buf[LARGEBUF];
+
+	return minimize_formatting_string(buf, sizeof(buf), fmt);
+}
+
 static void vupslog(int priority, const char *fmt, va_list va, int use_strerror)
 {
 	int	ret, errno_orig = errno;

include/common.h

@@ -1,6 +1,8 @@
 /* common.h - prototypes for the common useful functions
 
-   Copyright (C) 2000  Russell Kroll <[email protected]>
+   Copyright (C)
+    2000  Russell Kroll <[email protected]>
+    2020-2024 Jim Klimov <[email protected]>
 
    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -365,6 +367,9 @@ void *xcalloc(size_t number, size_t size);
 void *xrealloc(void *ptr, size_t size);
 char *xstrdup(const char *string);
 
+char *minimize_formatting_string(char *buf, size_t buflen, const char *fmt);
+char *minimize_formatting_string_staticbuf(const char *fmt);
+
 /**** REGEX helper methods ****/
 
 /* helper function: version of strcmp that tolerates NULL