MINOR: standard: add function "escape_chunk"

This function tries to prefix all characters tagged in the <map> with the
<escape> character. The specified <chunk> contains the input to be
escaped.

include/common/standard.h

@@ -380,6 +380,17 @@ char *encode_chunk(char *start, char *stop,
                    const char escape, const fd_set *map,
                    const struct chunk *chunk);
 
+/*
+ * Tries to prefix characters tagged in the <map> with the <escape>
+ * character. <chunk> contains the input to be escaped. The result will be
+ * stored between <start> (included) and <stop> (excluded). The function
+ * will always try to terminate the resulting string with a '\0' before
+ * <stop>, and will return its position if the conversion completes.
+ */
+char *escape_chunk(char *start, char *stop,
+                   const char escape, const fd_set *map,
+                   const struct chunk *chunk);
+
 
 /* Check a string for using it in a CSV output format. If the string contains
  * one of the following four char <">, <,>, CR or LF, the string is

src/standard.c

@@ -1439,6 +1439,38 @@ char *encode_chunk(char *start, char *stop,
 	return start;
 }
 
+/*
+ * Tries to prefix characters tagged in the <map> with the <escape>
+ * character. <chunk> contains the input to be escaped. The result will be
+ * stored between <start> (included) and <stop> (excluded). The function
+ * will always try to terminate the resulting string with a '\0' before
+ * <stop>, and will return its position if the conversion completes.
+ */
+char *escape_chunk(char *start, char *stop,
+		   const char escape, const fd_set *map,
+		   const struct chunk *chunk)
+{
+	char *str = chunk->str;
+	char *end = chunk->str + chunk->len;
+
+	if (start < stop) {
+		stop--; /* reserve one byte for the final '\0' */
+		while (start < stop && str < end) {
+			if (!FD_ISSET((unsigned char)(*str), map))
+				*start++ = *str;
+			else {
+				if (start + 2 >= stop)
+					break;
+				*start++ = escape;
+				*start++ = *str;
+			}
+			str++;
+		}
+		*start = '\0';
+	}
+	return start;
+}
+
 /* Check a string for using it in a CSV output format. If the string contains
  * one of the following four char <">, <,>, CR or LF, the string is
  * encapsulated between <"> and the <"> are escaped by a <""> sequence.