Refactor log file name command line option parsing

* Logging fix and enhancement

Corrected issue where loglevel in mbusd.conf wasn't parsed correctly. Added support for logfile in mbusd.conf.  Updated README and mbusd..conf.example to true-up with "-h" output and new logging options.

* Updated README

Sync'd up verbiage in the usage details with the usage summary.

* Additional adjustments to sync up README w/ -h output

CMakeLists.txt

@@ -70,10 +70,10 @@ set(mbusd_SOURCES
         src/conn.c
         src/queue.c
         src/modbus.c
-        src/crc16.c
         src/state.c
         src/sig.c
         src/sock.c
+        src/util.c
         )
 add_executable(mbusd ${mbusd_SOURCES})
 install(TARGETS mbusd DESTINATION bin)

README.md

@@ -78,11 +78,11 @@ Usage:
        -S     Enable RS-485 support for given serial port device (Linux only)
        -t     Enable RTS RS-485 data direction control using RTS, active transmit.
        -r     Enable RTS RS-485 data direction control using RTS, active receive.
-       -y file
-              Enable RS-485 direction data direction control by writing '1' to file
+       -y sysfsfile
+              Enable RS-485 direction data direction control by writing '1' to sysfs file
               for transmitter enable and '0' to file for transmitter disable.
-       -Y file
-              Enable RS-485 direction data direction control by writing '0' to file
+       -Y sysfsfile
+              Enable RS-485 direction data direction control by writing '0' to sysfs file
               for transmitter enable and '1' to file for transmitter disable.
        -A address
              Specifies TCP server address to bind (default is 0.0.0.0).

conf/mbusd.conf.example

@@ -4,6 +4,14 @@
 #                                           #
 #############################################
 
+########## Logging settings #############
+
+# Logging verbosity level
+loglevel = 2
+
+# Logfile (fully-qualified path, or filename [stored at /var/log/] or - for STDOUT only)
+logfile = /var/log/mbusd.log
+
 ########## Serial port settings #############
 
 # Serial port device name

src/cfg.c

@@ -34,9 +34,10 @@
 #include "cfg.h"
 
 #include <stdlib.h>
-#include <ctype.h>
 #include <string.h>
 
+#include "util.h"
+
 #define CFG_MAX_LINE_LENGTH 200
 
 #define CFG_NAME_MATCH(n) strcmp(n, name) == 0
@@ -81,23 +82,6 @@ cfg_init(void)
   cfg.replyonbroadcast=0;
 }
 
-static char *
-cfg_rtrim(char *s)
-{
-  char *p = s + strlen(s);
-  while (p > s && isspace((unsigned char )(*--p)))
-    *p = '\0';
-  return s;
-}
-
-static char *
-cfg_ltrim(const char *s)
-{
-  while (*s && isspace((unsigned char )(*s)))
-    s++;
-  return (char *) s;
-}
-
 int
 cfg_handle_param(char *name, char *value)
 {
@@ -231,7 +215,40 @@ cfg_handle_param(char *name, char *value)
   }
   else if (CFG_NAME_MATCH("loglevel"))
   {
-    cfg.dbglvl = (char)strtol(optarg, NULL, 0);
+    cfg.dbglvl = (char)strtol(value, NULL, 0);
+#  ifdef DEBUG
+    if (!(isdigit(*value)) || cfg.dbglvl < 0 || cfg.dbglvl > 9)
+    { /* report about invalid log level */
+      CFG_ERR("invalid loglevel value: %s (must be 0-9)", value);
+#  else
+    if (!(isdigit(*value)) || cfg.dbglvl < 0 || cfg.dbglvl > 2)
+    { /* report about invalid log level */
+      CFG_ERR("invalid loglevel value: %s (must be 0-2)", value);
+#  endif
+      return 0;
+    }
+  }
+  else if (CFG_NAME_MATCH("logfile"))
+  {
+    if (!strlen(value))
+    {
+      CFG_ERR("missing logfile value", value);
+      return 0;
+    }
+    else if (*value != '/')
+    {
+      if (*value == '-')
+      {
+        /* logging to file disabled */
+        *cfg.logname = '\0';
+      }
+      else
+      { /* concatenate given log file name with default path */
+        strncpy(cfg.logname, LOGPATH, INTBUFSIZE);
+        strncat(cfg.logname, value, INTBUFSIZE - strlen(cfg.logname));
+      }
+    }
+    else strncpy(cfg.logname, value, INTBUFSIZE);
 #endif
   }
   else {
@@ -265,7 +282,7 @@ cfg_parse_file(void *file)
   {
     lineno++;
 
-    start = cfg_ltrim(cfg_rtrim(line));
+    start = util_trim(line);
 
     if (*start == '#')
     {
@@ -280,8 +297,8 @@ cfg_parse_file(void *file)
       {
         *end = '\0';
 
-        name = cfg_rtrim(start);
-        value = cfg_ltrim(cfg_rtrim(end + 1));
+        name = util_rtrim(start);
+        value = util_trim(end + 1);
 
         /* handle name/value pair */
         if (!cfg_handle_param(name, value))

src/crc16.c

@@ -1,79 +0,0 @@
-/*
- * OpenMODBUS/TCP to RS-232/485 MODBUS RTU gateway
- *
- * crc16.c - Cyclic Redundant Checks calculating
- *
- * Copyright (c) 2002-2003, 2013, Victor Antonovich (v.antonovich@gmail.com)
- * 
- * Redistribution and use in source and binary forms, with or without
- * modification, are permitted provided that the following conditions
- * are met:
- * 
- * - Redistributions of source code must retain the above copyright
- * notice, this list of conditions and the following disclaimer.
- * 
- * - Redistributions in binary form must reproduce the above copyright
- * notice, this list of conditions and the following disclaimer in the
- * documentation and/or other materials provided with the distribution.
- * 
- * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
- * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
- * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
- * A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR
- * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
- * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
- * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
- * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
- * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
- * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
- * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
- *
- * $Id: crc16.c,v 1.3 2015/02/25 10:33:57 kapyar Exp $
- */
-
-#include "crc16.h"
-
-unsigned short
-crc_16_tab[] = {
-  0x0000, 0xc0c1, 0xc181, 0x0140, 0xc301, 0x03c0, 0x0280, 0xc241,
-  0xc601, 0x06c0, 0x0780, 0xc741, 0x0500, 0xc5c1, 0xc481, 0x0440,
-  0xcc01, 0x0cc0, 0x0d80, 0xcd41, 0x0f00, 0xcfc1, 0xce81, 0x0e40,
-  0x0a00, 0xcac1, 0xcb81, 0x0b40, 0xc901, 0x09c0, 0x0880, 0xc841,
-  0xd801, 0x18c0, 0x1980, 0xd941, 0x1b00, 0xdbc1, 0xda81, 0x1a40,
-  0x1e00, 0xdec1, 0xdf81, 0x1f40, 0xdd01, 0x1dc0, 0x1c80, 0xdc41,
-  0x1400, 0xd4c1, 0xd581, 0x1540, 0xd701, 0x17c0, 0x1680, 0xd641,
-  0xd201, 0x12c0, 0x1380, 0xd341, 0x1100, 0xd1c1, 0xd081, 0x1040,
-  0xf001, 0x30c0, 0x3180, 0xf141, 0x3300, 0xf3c1, 0xf281, 0x3240,
-  0x3600, 0xf6c1, 0xf781, 0x3740, 0xf501, 0x35c0, 0x3480, 0xf441,
-  0x3c00, 0xfcc1, 0xfd81, 0x3d40, 0xff01, 0x3fc0, 0x3e80, 0xfe41,
-  0xfa01, 0x3ac0, 0x3b80, 0xfb41, 0x3900, 0xf9c1, 0xf881, 0x3840,
-  0x2800, 0xe8c1, 0xe981, 0x2940, 0xeb01, 0x2bc0, 0x2a80, 0xea41,
-  0xee01, 0x2ec0, 0x2f80, 0xef41, 0x2d00, 0xedc1, 0xec81, 0x2c40,
-  0xe401, 0x24c0, 0x2580, 0xe541, 0x2700, 0xe7c1, 0xe681, 0x2640,
-  0x2200, 0xe2c1, 0xe381, 0x2340, 0xe101, 0x21c0, 0x2080, 0xe041,
-  0xa001, 0x60c0, 0x6180, 0xa141, 0x6300, 0xa3c1, 0xa281, 0x6240,
-  0x6600, 0xa6c1, 0xa781, 0x6740, 0xa501, 0x65c0, 0x6480, 0xa441,
-  0x6c00, 0xacc1, 0xad81, 0x6d40, 0xaf01, 0x6fc0, 0x6e80, 0xae41,
-  0xaa01, 0x6ac0, 0x6b80, 0xab41, 0x6900, 0xa9c1, 0xa881, 0x6840,
-  0x7800, 0xb8c1, 0xb981, 0x7940, 0xbb01, 0x7bc0, 0x7a80, 0xba41,
-  0xbe01, 0x7ec0, 0x7f80, 0xbf41, 0x7d00, 0xbdc1, 0xbc81, 0x7c40,
-  0xb401, 0x74c0, 0x7580, 0xb541, 0x7700, 0xb7c1, 0xb681, 0x7640,
-  0x7200, 0xb2c1, 0xb381, 0x7340, 0xb101, 0x71c0, 0x7080, 0xb041,
-  0x5000, 0x90c1, 0x9181, 0x5140, 0x9301, 0x53c0, 0x5280, 0x9241,
-  0x9601, 0x56c0, 0x5780, 0x9741, 0x5500, 0x95c1, 0x9481, 0x5440,
-  0x9c01, 0x5cc0, 0x5d80, 0x9d41, 0x5f00, 0x9fc1, 0x9e81, 0x5e40,
-  0x5a00, 0x9ac1, 0x9b81, 0x5b40, 0x9901, 0x59c0, 0x5880, 0x9841,
-  0x8801, 0x48c0, 0x4980, 0x8941, 0x4b00, 0x8bc1, 0x8a81, 0x4a40,
-  0x4e00, 0x8ec1, 0x8f81, 0x4f40, 0x8d01, 0x4dc0, 0x4c80, 0x8c41,
-  0x4400, 0x84c1, 0x8581, 0x4540, 0x8701, 0x47c0, 0x4680, 0x8641,
-  0x8201, 0x42c0, 0x4380, 0x8341, 0x4100, 0x81c1, 0x8081, 0x4040
-};
-
-unsigned short
-crc16(unsigned char *buf, unsigned int bsize)
-{
-  unsigned short crc = 0xffff;
-  while (bsize--)
-    crc = (unsigned short)(crc >> 8) ^ crc_16_tab[(crc ^ *buf++) & 0xff];
-  return crc;
-}

src/log.h

@@ -40,7 +40,7 @@ extern int isdaemon;
 
 /* Default log file path and name */
 #define LOGPATH "/var/log/"
-#define LOGNAME "mbus.log"
+#define LOGNAME "mbusd.log"
 
 #ifdef LOG
 int log_init(char *logname);

src/main.c

@@ -40,6 +40,7 @@
 #include "conn.h"
 #include "queue.h"
 #include "sig.h"
+#include "util.h"
 #ifdef LOG
 #  include "log.h"
 #endif
@@ -119,7 +120,7 @@ usage(char *exename)
    "             [-R pause] [-W wait] [-T timeout] [-b]\n\n"
    "Options:\n"
    "  -h         : this help\n"
-   "  -d         : don't daemonize\n"
+   "  -d         : don't fork (non-daemonize)\n"
 #ifdef LOG
    "  -L logfile : set log file name (default is %s%s, \n"
    "               '-' for logging to STDOUT only)\n"
@@ -136,14 +137,16 @@ usage(char *exename)
 #ifdef HAVE_TIOCRS485
    "  -S         : enable Linux RS-485 support for given serial port device\n"
 #endif   
-   "  -A address : set TCP server address to bind (default is %s)\n"
-   "  -P port    : set TCP server port number (default is %d)\n"
 #ifdef TRXCTL
    "  -t         : enable RTS RS-485 data direction control using RTS, active transmit\n"
    "  -r         : enable RTS RS-485 data direction control using RTS, active receive\n"
    "  -y         : enable RTS RS-485 data direction control using sysfs file, active transmit\n"
+   "               (writes '1' to sysfs file for transmit enable, '0' for transmit disable)\n"
    "  -Y         : enable RTS RS-485 data direction control using sysfs file, active receive\n"
+   "               (writes '0' to sysfs file for transmit enable, '1' for transmit disable)\n"
 #endif
+   "  -A address : set TCP server address to bind (default is %s)\n"
+   "  -P port    : set TCP server port number (default is %d)\n"
    "  -C maxconn : set maximum number of simultaneous TCP connections\n"
    "               (1-%d, default is %d)\n"
    "  -N retries : set maximum number of request retries\n"
@@ -167,6 +170,7 @@ usage(char *exename)
   exit(0);
 }
 
+
 int
 main(int argc, char *argv[])
 {
@@ -242,23 +246,30 @@ main(int argc, char *argv[])
       case 'v':
         cfg.dbglvl = (char)strtol(optarg, NULL, 0);
 #  ifdef DEBUG
-        if (cfg.dbglvl > 9)
+        if (!(isdigit(*optarg)) || cfg.dbglvl < 0 || cfg.dbglvl > 9)
         { /* report about invalid log level */
           printf("%s: -v: invalid loglevel value"
-                 " (%d, must be 0-9)\n", exename, cfg.dbglvl);
+                 " (%s, must be 0-9)\n", exename, optarg);
 #  else
-        if (cfg.dbglvl < 0 || cfg.dbglvl > 9)
+        if (!(isdigit(*optarg)) || cfg.dbglvl < 0 || cfg.dbglvl > 2)
         { /* report about invalid log level */
           printf("%s: -v: invalid loglevel value"
-                 " (%d, must be 0-2)\n", exename, cfg.dbglvl);
+                 " (%s, must be 0-2)\n", exename, optarg);
 #  endif
           exit(-1);
         }
         break;
       case 'L':
-        if (*optarg != '/')
+        char *logfilenamevalue = strdup(optarg);
+        char *logfilename = util_trim(logfilenamevalue);
+        if (!strlen(logfilename))
+        { /* report about empty log file */
+          printf("%s: -L: log file name is empty, exiting...\n", exename);
+          exit(-1);
+        }
+        else if (*logfilename != '/')
         {
-          if (*optarg == '-')
+          if (*logfilename == '-')
           {
             /* logging to file disabled */
             *cfg.logname = '\0';
@@ -266,10 +277,11 @@ main(int argc, char *argv[])
           else
           { /* concatenate given log file name with default path */
             strncpy(cfg.logname, LOGPATH, INTBUFSIZE);
-            strncat(cfg.logname, optarg, INTBUFSIZE - strlen(cfg.logname));
+            strncat(cfg.logname, logfilename, INTBUFSIZE - strlen(cfg.logname));
           }
         }
-        else strncpy(cfg.logname, optarg, INTBUFSIZE);
+        else strncpy(cfg.logname, logfilename, INTBUFSIZE);
+        free(logfilenamevalue);
         break;
 #endif
       case 'p':

src/modbus.c

@@ -34,6 +34,57 @@
 #include "modbus.h"
 #include "conn.h"
 
+static const unsigned short
+modbus_crc16_table[] = {
+  0x0000, 0xc0c1, 0xc181, 0x0140, 0xc301, 0x03c0, 0x0280, 0xc241,
+  0xc601, 0x06c0, 0x0780, 0xc741, 0x0500, 0xc5c1, 0xc481, 0x0440,
+  0xcc01, 0x0cc0, 0x0d80, 0xcd41, 0x0f00, 0xcfc1, 0xce81, 0x0e40,
+  0x0a00, 0xcac1, 0xcb81, 0x0b40, 0xc901, 0x09c0, 0x0880, 0xc841,
+  0xd801, 0x18c0, 0x1980, 0xd941, 0x1b00, 0xdbc1, 0xda81, 0x1a40,
+  0x1e00, 0xdec1, 0xdf81, 0x1f40, 0xdd01, 0x1dc0, 0x1c80, 0xdc41,
+  0x1400, 0xd4c1, 0xd581, 0x1540, 0xd701, 0x17c0, 0x1680, 0xd641,
+  0xd201, 0x12c0, 0x1380, 0xd341, 0x1100, 0xd1c1, 0xd081, 0x1040,
+  0xf001, 0x30c0, 0x3180, 0xf141, 0x3300, 0xf3c1, 0xf281, 0x3240,
+  0x3600, 0xf6c1, 0xf781, 0x3740, 0xf501, 0x35c0, 0x3480, 0xf441,
+  0x3c00, 0xfcc1, 0xfd81, 0x3d40, 0xff01, 0x3fc0, 0x3e80, 0xfe41,
+  0xfa01, 0x3ac0, 0x3b80, 0xfb41, 0x3900, 0xf9c1, 0xf881, 0x3840,
+  0x2800, 0xe8c1, 0xe981, 0x2940, 0xeb01, 0x2bc0, 0x2a80, 0xea41,
+  0xee01, 0x2ec0, 0x2f80, 0xef41, 0x2d00, 0xedc1, 0xec81, 0x2c40,
+  0xe401, 0x24c0, 0x2580, 0xe541, 0x2700, 0xe7c1, 0xe681, 0x2640,
+  0x2200, 0xe2c1, 0xe381, 0x2340, 0xe101, 0x21c0, 0x2080, 0xe041,
+  0xa001, 0x60c0, 0x6180, 0xa141, 0x6300, 0xa3c1, 0xa281, 0x6240,
+  0x6600, 0xa6c1, 0xa781, 0x6740, 0xa501, 0x65c0, 0x6480, 0xa441,
+  0x6c00, 0xacc1, 0xad81, 0x6d40, 0xaf01, 0x6fc0, 0x6e80, 0xae41,
+  0xaa01, 0x6ac0, 0x6b80, 0xab41, 0x6900, 0xa9c1, 0xa881, 0x6840,
+  0x7800, 0xb8c1, 0xb981, 0x7940, 0xbb01, 0x7bc0, 0x7a80, 0xba41,
+  0xbe01, 0x7ec0, 0x7f80, 0xbf41, 0x7d00, 0xbdc1, 0xbc81, 0x7c40,
+  0xb401, 0x74c0, 0x7580, 0xb541, 0x7700, 0xb7c1, 0xb681, 0x7640,
+  0x7200, 0xb2c1, 0xb381, 0x7340, 0xb101, 0x71c0, 0x7080, 0xb041,
+  0x5000, 0x90c1, 0x9181, 0x5140, 0x9301, 0x53c0, 0x5280, 0x9241,
+  0x9601, 0x56c0, 0x5780, 0x9741, 0x5500, 0x95c1, 0x9481, 0x5440,
+  0x9c01, 0x5cc0, 0x5d80, 0x9d41, 0x5f00, 0x9fc1, 0x9e81, 0x5e40,
+  0x5a00, 0x9ac1, 0x9b81, 0x5b40, 0x9901, 0x59c0, 0x5880, 0x9841,
+  0x8801, 0x48c0, 0x4980, 0x8941, 0x4b00, 0x8bc1, 0x8a81, 0x4a40,
+  0x4e00, 0x8ec1, 0x8f81, 0x4f40, 0x8d01, 0x4dc0, 0x4c80, 0x8c41,
+  0x4400, 0x84c1, 0x8581, 0x4540, 0x8701, 0x47c0, 0x4680, 0x8641,
+  0x8201, 0x42c0, 0x4380, 0x8341, 0x4100, 0x81c1, 0x8081, 0x4040
+};
+
+/*
+ * Calculate Modbus frame CRC (Cyclical Redundancy Checking) value
+ * Parameters: FRAME - address of the frame,
+ *             LEN   - frame length;
+ * Return: calculated CRC value
+ */
+static unsigned short
+modbus_crc_calculate(unsigned char *frame, unsigned int len)
+{
+  unsigned short crc = 0xffff;
+  while (len--)
+    crc = (unsigned short)(crc >> 8) ^ modbus_crc16_table[(crc ^ *frame++) & 0xff];
+  return crc;
+}
+
 /*
  * Check CRC of MODBUS frame
  * Parameters: FRAME - address of the frame,
@@ -44,7 +95,7 @@
 int
 modbus_crc_correct(unsigned char *frame, unsigned int len)
 {
-  return (!crc16(frame, len));
+  return (!modbus_crc_calculate(frame, len));
 }
 
 /*
@@ -56,7 +107,7 @@ modbus_crc_correct(unsigned char *frame, unsigned int len)
 void
 modbus_crc_write(unsigned char *frame, unsigned int len)
 {
-  WORD_WR_LE(frame + len, crc16(frame, len));
+  WORD_WR_LE(frame + len, modbus_crc_calculate(frame, len));
 }
 
 /*

src/modbus.h

@@ -35,7 +35,6 @@
 #define _MODBUS_H
 
 #include "globals.h"
-#include "crc16.h"
 
 /*
  * Macro for accessing data in MODBUS frame

src/util.c

@@ -0,0 +1,80 @@
+/*
+ * OpenMODBUS/TCP to RS-232/485 MODBUS RTU gateway
+ *
+ * util.h - utility functions
+ *
+ * Copyright (c) 2002-2023, Victor Antonovich (v.antonovich@gmail.com)
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+ * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+ * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+ * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
+ * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
+ * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+ * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "util.h"
+
+#include <ctype.h>
+#include <string.h>
+
+/**
+ * Removes leading whitespace from the string. 
+ * Parameters: s - the string to be trimmed.
+ * Return: a pointer to the first non-whitespace character in string.
+ */
+char *
+util_ltrim(const char *s)
+{
+  while (*s && isspace((unsigned char )(*s)))
+    s++;
+  return (char *) s;
+}
+
+/**
+ * Removes trailing whitespace from the string. 
+ * The first trailing whitespace is replaced with a NUL-terminator
+ * in the given string.
+ * Parameters: s - the string to be trimmed.
+ * Return: a pointer to the string.
+ */
+char *
+util_rtrim(char *s)
+{
+  char *p = s + strlen(s);
+  while (p > s && isspace((unsigned char )(*--p)))
+    *p = '\0';
+  return s;
+}
+
+/**
+ * Removes leading and trailing whitespace from the string. 
+ * The first trailing whitespace is replaced with a NUL-terminator
+ * in the given string.
+ * Parameters: s - the string to be trimmed.
+ * Return: a pointer to the first non-whitespace character in string.
+ */
+char *
+util_trim(char *s)
+{
+	if (!strlen(s))
+		return s;
+
+	return util_ltrim(util_rtrim(s));
+}

src/util.h

@@ -1,21 +1,21 @@
 /*
  * OpenMODBUS/TCP to RS-232/485 MODBUS RTU gateway
  *
- * crc16.h - Cyclic Redundant Checks calculating
+ * util.h - utility functions
+ *
+ * Copyright (c) 2002-2023, Victor Antonovich (v.antonovich@gmail.com)
  *
- * Copyright (c) 2002-2003, 2013, Victor Antonovich (v.antonovich@gmail.com)
- * 
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
- * 
+ *
  * - Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
- * 
+ *
  * - Redistributions in binary form must reproduce the above copyright
  * notice, this list of conditions and the following disclaimer in the
  * documentation and/or other materials provided with the distribution.
- * 
+ *
  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
@@ -27,15 +27,13 @@
  * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
  * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
  * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
- *
- * $Id: crc16.h,v 1.3 2015/02/25 10:33:57 kapyar Exp $
  */
- 
-#ifndef _CRC_H
-#define _CRC_H
 
-#include "globals.h"
+#ifndef _UTIL_H
+#define _UTIL_H
 
-unsigned short crc16(unsigned char *buf, unsigned int bsize);
+char *util_ltrim(const char *s);
+char *util_rtrim(char *s);
+char *util_trim(char *s);
 
-#endif /*_CRC_H */
+#endif /* _UTIL_H */