Provide optimized code path in check_regex_match function for non-regex strings

src/framework/regex_matching.c

@@ -1,14 +1,71 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <regex.h>
+#include <string.h>
 
 #define MAX_LEN 1024
 
-void check_regex_match(const char * pattern, const char * str, int *imatch){
+static const char *BRE_SPECIAL_CHARS = ".[\\*^$";
+
+/******************************************************************************
+ *
+ * possible_bre
+ *
+ * Determine whether an input string may be a Basic Regular Expression (BRE).
+ * This function may return false positives (i.e., a return value indicating
+ * that a string is a BRE, when in fact the string is not a BRE), but it will
+ * never return a false negative (i.e., a return value indicating that a string
+ * is not a BRE, when in fact the string is a BRE).
+ *
+ * Inputs:
+ *   s - a null-terminated string
+ *
+ * Return value: 1 if the input string 's' is possibly a BRE and 0 otherwise.
+ *
+ ******************************************************************************/
+static int possible_bre(const char *s)
+{
+	for (; *s != '\0'; s++) {
+		if (strchr(BRE_SPECIAL_CHARS, *s) != NULL) {
+			return 1;
+		}
+	}
+	return 0;
+}
+
+
+/******************************************************************************
+ *
+ * check_regex_match
+ *
+ * Determine whether an input string 'str' matches the Basic Regular Expression
+ * (BRE) 'pattern'.
+ *
+ * Inputs:
+ *   pattern - a null-terminated string that may contain any valid BRE,
+ *             including a simple string
+ *   str     - a null-terminated string to be checked against pattern
+ *
+ * Return value: 1 if the input string str matches the BRE pattern,
+ *               0 if the input string does not match the BRE pattern, and
+ *              -1 if an error occurred.
+ *
+ ******************************************************************************/
+void check_regex_match(const char * pattern, const char * str, int *imatch)
+{
 	regex_t regex;
 	char bracketed_pattern[MAX_LEN];
 	int ierr, len;
 
+	/*
+	 * If pattern is a simple string and not a basic regular expression,
+	 * a string comparison will suffice
+	 */
+	if (!possible_bre(pattern)) {
+		*imatch = (strcmp(pattern, str) == 0) ? 1 : 0;
+		return;
+	}
+
 	*imatch = 0;
 	len = snprintf(bracketed_pattern, 1024, "^%s$", pattern);
 	if ( len >= MAX_LEN ) {
@@ -34,4 +91,3 @@ void check_regex_match(const char * pattern, const char * str, int *imatch){
 		*imatch = -1;
 	}
 }
-