New helper functions to read/write /proc and /sys style files

From the Infix project.

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

src/Makefile.am

@@ -9,7 +9,7 @@ libite_la_SOURCES     = chomp.c		copyfile.c			\
 			fexist.c	fisdir.c			\
 			fparseln.c	fsendfile.c			\
 			ifconfig.c	lfile.c				\
-			makepath.c	progress.c			\
+			makepath.c	procval.c	progress.c	\
 			pidfile.c	pidfilefn.c	popenf.c	\
 			reallocarray.c	rsync.c		strtrim.c	\
 			strlcpy.c 	strlcat.c 	strtonum.c	\

src/lite.h

@@ -90,6 +90,16 @@ int     fcopyfile  (FILE *src, FILE *dst);
 ssize_t fsendfile  (FILE *src, FILE *dst, size_t len);
 int     truncatef  (off_t length, const char *fmt, ...) __attribute__ ((format (printf, 2, 3)));
 
+char *vreadsnf (char *line, size_t len, const char *fmt, va_list ap);
+char *readsnf  (char *line, size_t len, const char *fmt, ...);
+int   writesf  (const char *str, const char *mode, const char *fmt, ...);
+
+int   vreadllf (long long *value, const char *fmt, va_list ap);
+int   readllf  (long long *value, const char *fmt, ...);
+int   readdf   (int *value, const char *fmt, ...);
+int   writellf (long long value, const char *mode, const char *fmt, ...);
+int   writedf  (int value, const char *mode, const char *fmt, ...);
+
 int     ifconfig   (const char *ifname, const char *addr, const char *mask, int up);
 
 lfile_t*lfopen     (const char *file, const char *sep);

src/procval.c

@@ -0,0 +1,229 @@
+/* Reading and writing values/strings to/from /proc and /sys style files
+ *
+ * Copyright (c) 2023  Tobias Waldekranz <tobias@waldekranz.com>
+ * Copyright (c) 2023  Joachim Wiberg <troglobit@gmail.com>
+ *
+ * Permission to use, copy, modify, and/or 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.
+ */
+
+/**
+ * @file procval.c
+ * @author Joachim Wiberg
+ * @date 2023
+ * @copyright ISC License
+ */
+
+#include <errno.h>
+#include <stdio.h>
+#include <stdarg.h>
+#include <stdlib.h>
+
+#include "lite.h"
+
+/**
+ * Similar to readsnf() except it takes a @a va_list argument
+ * @param line Pointer to line buffer.
+ * @param len  Size of line buffer.
+ * @param fmt  Formatted string to be composed into a pathname.
+ * @param ap   List of variable arguemnts from va_start().
+ *
+ * For details, see readsnf().
+ *
+ * @returns same as readsnf().
+ */
+char *vreadsnf(char *line, size_t len, const char *fmt, va_list ap)
+{
+	va_list apc;
+	FILE *fp;
+
+	va_copy(apc, ap);
+	fp = vfopenf("r", fmt, ap);
+	va_end(ap);
+	if (!fp)
+		return NULL;
+
+	if (!fgets(line, len, fp)) {
+		fclose(fp);
+		return NULL;
+	}
+
+	fclose(fp);
+	return chomp(line);
+}
+
+
+/**
+ * Read first line from a file composed from fmt and optional args.
+ * @param line Pointer to line buffer.
+ * @param len  Size of line buffer.
+ * @param fmt  Formatted string to be composed into a pathname.
+ *
+ * @returns On success, this function returns the @p line read from the
+ * file, with any trailing '\n' chomp()ed out.  On error, @c NULL.
+ */
+char *readsnf(char *line, size_t len, const char *fmt, ...)
+{
+	va_list ap;
+	char *ln;
+
+	va_start(ap, fmt);
+	ln = vreadsnf(line, len, fmt, ap);
+	va_end(ap);
+
+	return ln;
+}
+
+/**
+ * Write a string buffer to a file composed from fmt and optional args.
+ * @param str  Pointer to string buffer, may be multiple lines.
+ * @param mode An fopen() mode string, e.g. "w+".
+ * @param fmt  Formatted string to be composed into a pathname.
+ *
+ * @returns result of operation, with @a errno set on error.
+ */
+int writesf(const char *str, const char *mode, const char *fmt, ...)
+{
+	va_list ap;
+	FILE *fp;
+
+	va_start(ap, fmt);
+	fp = vfopenf(mode, fmt, ap);
+	va_end(ap);
+	if (!fp)
+		return -1;
+
+	fprintf(fp, "%s\n", str);
+	return fclose(fp);
+}
+
+/**
+ * Same as readllf() exectp it takes a @a va_list argument.
+ */
+int vreadllf(long long *value, const char *fmt, va_list ap)
+{
+	char line[0x100];
+
+	if (!vreadsnf(line, sizeof(line), fmt, ap))
+		return -1;
+
+	errno = 0;
+	*value = strtoll(line, NULL, 0);
+
+	return errno ? -1 : 0;
+}
+
+/**
+ * Read 64-bit integer value from a file composed from fmt and optional args.
+ * @param value Pointer to where to store read 64-bit integer value.
+ * @param mode An fopen() mode string, e.g. "w+".
+ * @param fmt  Formatted string to be composed into a pathname.
+ *
+ * @returns result of operation, with @a errno set on error.
+ */
+int readllf(long long *value, const char *fmt, ...)
+{
+	va_list ap;
+	int rc;
+
+	va_start(ap, fmt);
+	rc = vreadllf(value, fmt, ap);
+	va_end(ap);
+
+	return rc;
+}
+
+
+/**
+ * Read integer value from a file composed from fmt and optional args.
+ * @param value Pointer to where to store read integer value.
+ * @param mode An fopen() mode string, e.g. "w+".
+ * @param fmt  Formatted string to be composed into a pathname.
+ *
+ * @returns result of operation, with @a errno set on error.
+ */
+int readdf(int *value, const char *fmt, ...)
+{
+	long long tmp;
+	va_list ap;
+	int rc;
+
+	va_start(ap, fmt);
+	rc = vreadllf(&tmp, fmt, ap);
+	va_end(ap);
+
+	if (rc)
+		return rc;
+
+	if (tmp < INT_MIN || tmp > INT_MAX) {
+		errno = ERANGE;
+		return -1;
+	}
+
+	*value = tmp;
+	return 0;
+}
+
+/**
+ * Write 64-bit integer value to a file composed from fmt and optional args.
+ * @param value 64-bit integer value to write.
+ * @param mode An fopen() mode string, e.g. "w+".
+ * @param fmt  Formatted string to be composed into a pathname.
+ *
+ * @returns result of operation, with @a errno set on error.
+ */
+int writellf(long long value, const char *mode, const char *fmt, ...)
+{
+	va_list ap;
+	FILE *fp;
+
+	va_start(ap, fmt);
+	fp = vfopenf(mode, fmt, ap);
+	va_end(ap);
+	if (!fp)
+		return -1;
+
+	fprintf(fp, "%lld\n", value);
+	return fclose(fp);
+}
+
+
+/**
+ * Write integer value to a file composed from fmt and optional args.
+ * @param value Integer value to write.
+ * @param mode An fopen() mode string, e.g. "w+".
+ * @param fmt  Formatted string to be composed into a pathname.
+ *
+ * @returns result of operation, with @a errno set on error.
+ */
+int writedf(int value, const char *mode, const char *fmt, ...)
+{
+	va_list ap;
+	FILE *fp;
+
+	va_start(ap, fmt);
+	fp = vfopenf(mode, fmt, ap);
+	va_end(ap);
+	if (!fp)
+		return -1;
+
+	fprintf(fp, "%d\n", value);
+	return fclose(fp);
+}
+
+
+/**
+ * Local Variables:
+ *  indent-tabs-mode: t
+ *  c-file-style: "linux"
+ * End:
+ */