Clean up get_pgsm_query_id_hash()

The function was unnecessarily convoluted so clean it up by making the
parser easier to read, asserting against NULL input and wrapping the
comment at the right width. Especially the code for handling whitespace
was much more complicated than necessary.

Author: jeltz

src/pg_stat_monitor.c

@@ -2586,11 +2586,10 @@ get_next_wbucket(pgsmSharedState *pgsm)
 }
 
 /*
- * This function expects a NORMALIZED query as the input.
- * It iterates over the normalized query skipping comments and
- * multiple spaces. All spaces are converted to ' ' so that we
- * the calculation is independent of the space type whether
- * newline, tab, or any other type. Trailing and leading spaces
+ * This function expects a NORMALIZED query as the input. It iterates over the
+ * normalized query skipping comments and multiple spaces. All spaces are
+ * converted to ' ' so that we the calculation is independent of the space
+ * type whether newline, tab, or any other type. Trailing and leading spaces
  * are also removed before calculating the hash.
  */
 static int64
@@ -2599,82 +2598,69 @@ get_pgsm_query_id_hash(const char *norm_query, int norm_len)
 	char	   *query;
 	char	   *q_iter;
 	const char *norm_q_iter = norm_query;
-	int64		pgsm_query_id = 0;
+	int64		pgsm_query_id;
+
+	Assert(norm_query != NULL);
 
 	if (!pgsm_enable_pgsm_query_id)
 		return 0;
 
 	query = palloc(norm_len + 1);
 	q_iter = query;
 
-	while (norm_q_iter && *norm_q_iter && norm_q_iter < norm_query + norm_len)
+	while (*norm_q_iter && norm_q_iter < norm_query + norm_len)
 	{
-		/*
-		 * Skip multiline comments, + 1 is safe even if we've reach end of
-		 * string
-		 */
 		if (*norm_q_iter == '/' && *(norm_q_iter + 1) == '*')
 		{
-			while (*norm_q_iter && *(norm_q_iter + 1) && (*norm_q_iter != '*' || *(norm_q_iter + 1) != '/'))
-				norm_q_iter++;
-
-			/*
-			 * Skip the end if the current character is valid. norm_q_iter
-			 * points to the *, we have to skip 2 characters
-			 */
-			if (*norm_q_iter)
-				norm_q_iter++;
-			if (*norm_q_iter)
-				norm_q_iter++;
+			/* Skip multiline comments */
+			norm_q_iter++;
+			norm_q_iter++;
 
-			continue;
+			while (*norm_q_iter)
+			{
+				if (*norm_q_iter == '*' && *(norm_q_iter + 1) == '/')
+				{
+					norm_q_iter++;
+					norm_q_iter++;
+					break;
+				}
+				else
+					norm_q_iter++;
+			}
 		}
-
-		/*
-		 * Skip single line comments, + 1 is safe even if we've reach end of
-		 * string
-		 */
-		if (*norm_q_iter == '-' && *(norm_q_iter + 1) == '-')
+		else if (*norm_q_iter == '-' && *(norm_q_iter + 1) == '-')
 		{
+			/* Skip single line comments */
+			norm_q_iter++;
+			norm_q_iter++;
+
 			while (*norm_q_iter && *norm_q_iter != '\n')
 				norm_q_iter++;
 		}
-
-		/* Skip white spaces */
-		if (scanner_isspace(*norm_q_iter))
+		else if (scanner_isspace(*norm_q_iter))
 		{
-			while (scanner_isspace(*++norm_q_iter));
+			/* Convert white spaces into single space */
+			norm_q_iter++;
 
-			/*
-			 * Let's replace it with a simple space. -1 is safe as we are
-			 * making sure we are not at the start of the string.
-			 */
-			if (q_iter != query && !scanner_isspace(*(q_iter - 1)))
-				*q_iter++ = ' ';
+			while (scanner_isspace(*norm_q_iter))
+				norm_q_iter++;
 
-			continue;
+			/* Get rid of spaces at beginning and end */
+			if (q_iter != query && *norm_q_iter)
+				*q_iter++ = ' ';
+		}
+		else
+		{
+			*q_iter++ = *norm_q_iter++;
 		}
-
-		*q_iter++ = *norm_q_iter++;
 	}
 
-	/* Ensure we have a terminating zero at the end */
 	*q_iter = '\0';
 
-	/* Get rid of trailing spaces */
-	while (q_iter > query && *q_iter == '\0')
-	{
-		q_iter--;
-
-		/* Continue reducing the string size if space is found. */
-		if (scanner_isspace(*q_iter))
-			*q_iter = '\0';
-	}
-
-	/* Calculate the hash. */
-	pgsm_query_id = pgsm_hash_string(query, strlen(query));
+	pgsm_query_id = pgsm_hash_string(query, q_iter - query);
 
 	pfree(query);
+
 	return pgsm_query_id;
 }