util: add spdk_strlen_pad() function

This is a counterpart to spdk_strcpy_pad() which determines the length
of a string in a fixed-size buffer that may be right-padded with a
specific character.

Change-Id: I2dab8d218ee9d55f7c264daa3956c2752d9fc7f7
Signed-off-by: Daniel Verkamp <daniel.verkamp@intel.com>

include/spdk/string.h

@@ -92,6 +92,17 @@ char *spdk_str_trim(char *s);
  */
 void spdk_strcpy_pad(void *dst, const char *src, size_t size, int pad);
 
+/**
+ * Find the length of a string that has been padded with a specific byte.
+ *
+ * \param str Right-padded string to find the length of.
+ * \param size Size of the full string pointed to by str, including padding.
+ * \param pad Character that was used to pad str up to size.
+ *
+ * \return Length of the non-padded portion of str.
+ */
+size_t spdk_strlen_pad(const void *str, size_t size, int pad);
+
 #ifdef __cplusplus
 }
 #endif

lib/util/string.c

@@ -34,6 +34,7 @@
 
 #include <stdarg.h>
 #include <stdio.h>
+#include <stdint.h>
 #include <stdlib.h>
 #include <string.h>
 #include <ctype.h>
@@ -214,3 +215,31 @@ spdk_strcpy_pad(void *dst, const char *src, size_t size, int pad)
 		memcpy(dst, src, size);
 	}
 }
+
+size_t
+spdk_strlen_pad(const void *str, size_t size, int pad)
+{
+	const uint8_t *start;
+	const uint8_t *iter;
+	uint8_t pad_byte;
+
+	pad_byte = (uint8_t)pad;
+	start = (const uint8_t *)str;
+
+	if (size == 0) {
+		return 0;
+	}
+
+	iter = start + size - 1;
+	while (1) {
+		if (*iter != pad_byte) {
+			return iter - start + 1;
+		}
+
+		if (iter == start) {
+			/* Hit the start of the string finding only pad_byte. */
+			return 0;
+		}
+		iter--;
+	}
+}