[lib-result] Add read_long_field() and use it

This new function allows to read a CSV field containing an integer value
and checks the value read.

libowlps-resultreader/libowlps-resultreader.c

@@ -90,6 +90,7 @@ owl_result* owl_receive_position(const int sockfd)
 owl_result* owl_fill_result(char *csv)
 {
   char *csv_field = NULL ;
+  long longfield ; // Return value of owl_read_long_field()
   owl_result *result = NULL ;
 
   result = malloc(sizeof(owl_result)) ;
@@ -113,36 +114,33 @@ owl_result* owl_fill_result(char *csv)
     strndup(csv_field, OWL_ETHER_ADDR_STRLEN) ;
 
   /* Request type */
-  csv_field = strsep(&csv, CSV_DELIMITER) ;
-  if (! csv_field)
+  if (! owl_read_long_field(&csv, CSV_DELIMITER, &longfield))
     {
       fprintf(stderr,
               "Error reading the request type from the CSV string!\n") ;
       goto error ;
     }
-  result->request_type = atoi(csv_field) ;
+  result->request_type = longfield ;
 
   /* Timestamp */
   // Seconds
-  csv_field = strsep(&csv, ".") ;
-  if (! csv_field)
+  if (! owl_read_long_field(&csv, ".", &longfield))
     {
       fprintf(stderr,
               "Error reading the timestamp (seconds) from the CSV"
               " string!\n") ;
       goto error ;
     }
-  result->mobile_timestamp.tv_sec = atol(csv_field) ;
+  result->mobile_timestamp.tv_sec = longfield ;
   // Nanoseconds
-  csv_field = strsep(&csv, CSV_DELIMITER) ;
-  if (! csv_field)
+  if (! owl_read_long_field(&csv, CSV_DELIMITER, &longfield))
     {
       fprintf(stderr,
               "Error reading the timestamp (nanoseconds) from the CSV"
               " string!\n") ;
       goto error ;
     }
-  result->mobile_timestamp.tv_nsec = atol(csv_field) ;
+  result->mobile_timestamp.tv_nsec = longfield ;
 
   /* Algorithm results */
   do
@@ -266,6 +264,44 @@ owl_algorithm_result* owl_fill_algorithm_result(char **csv)
 }
 
 
+/**
+ * Reads the first field from the `csv` string as a long integer and
+ * stores it in `ret`. The fields of `csv` are separated by the symbols
+ * in the `delim` string. `csv` will be modified to point to the next
+ * field.
+ *
+ * @param[in,out] csv The CSV string.
+ * @param[in] delim The characters delimiting the fields in the string.
+ * @param[out] ret The integer value read from the field.
+ *
+ * @returns `true` in case of success.
+ * @returns `false` in case of error.
+ */
+bool owl_read_long_field(char **const csv, const char *const delim,
+                         long *const ret)
+{
+  char *endptr = NULL, *csv_field = NULL ;
+
+  csv_field = strsep(csv, delim) ;
+  if (! csv_field)
+    {
+      fprintf(stderr,
+              "Error reading a field from the CSV string!\n") ;
+      return false ;
+    }
+
+  *ret = strtol(csv_field, &endptr, 10) ;
+  if (endptr == csv_field)
+    {
+      fprintf(stderr,
+              "The field does not contain a valid integer value!\n") ;
+      return false ;
+    }
+
+  return true ;
+}
+
+
 /**
  * Converts an `owl_result` back to a CSV string.
  * `dst` must be an allocated string of at least `OWL_CSV_RESULT_STRLEN`

libowlps-resultreader/owlps-resultreader.h

@@ -113,6 +113,9 @@ owl_result* owl_receive_position(const int sockfd) ;
 owl_result* owl_fill_result(char *csv) ;
 /// Splits the `csv` string and stores it in a new `owl_algorithm_result`
 owl_algorithm_result* owl_fill_algorithm_result(char **csv) ;
+/// Reads an integer from the `csv` string
+bool owl_read_long_field(char **const csv, const char *const delim,
+                         long *const ret) ;
 
 /// Converts an `owl_result back` to a CSV string
 void owl_result_to_csv(char dst[OWL_CSV_RESULT_STRLEN],