channel.c: optimize buidling xml function

try to use memcpy when we know the source length.
memcpy will operate on word or double-word, unlike iio_strlcpy which
operates on a byte basis. Mark these calls as Flawfinder ignore, since
we check the dest buffer length to to the source length before we do a
copy.

Rather than itererate over the dest string to find the end (with
strrchr), just keep track with math. We know the start, and we know the
length (from the outputs of iio_snprintf & iio_strlcpy), so just add
them.

Signed-off-by: Robin Getz <[email protected]>

Author: rgetz

channel.c

@@ -267,32 +267,29 @@ char * iio_channel_get_xml(const struct iio_channel *chn, size_t *length)
 	eptr = str + len;
 
 	if (len > 0) {
-		iio_snprintf(str, len, "<channel id=\"%s\"", chn->id);
-		ptr = strrchr(str, '\0');
+		ptr += iio_snprintf(str, len, "<channel id=\"%s\"", chn->id);
 		len = eptr - ptr;
 	}
 
 	if (chn->name && len > 0) {
-		iio_snprintf(ptr, len, " name=\"%s\"", chn->name);
-		ptr = strrchr(ptr, '\0');
+		ptr += iio_snprintf(ptr, len, " name=\"%s\"", chn->name);
 		len = eptr - ptr;
 	}
 
 	if (len > 0) {
-		iio_snprintf(ptr, len, " type=\"%s\" >", chn->is_output ? "output" : "input");
-		ptr = strrchr(ptr, '\0');
+		ptr += iio_snprintf(ptr, len, " type=\"%s\" >", chn->is_output ? "output" : "input");
 		len = eptr - ptr;
 	}
 
-	if (chn->is_scan_element && len > 0) {
-		iio_strlcpy(ptr, scan_element, len);
+	if (chn->is_scan_element && len > scan_element_len) {
+		memcpy(ptr, scan_element, scan_element_len); /* Flawfinder: ignore */
 		ptr += scan_element_len;
 		len -= scan_element_len;
 	}
 
 	for (i = 0; i < chn->nb_attrs; i++) {
-		if (len > 0) {
-			iio_strlcpy(ptr, attrs[i], len);
+		if (len > attrs_len[i]) {
+			memcpy(ptr, attrs[i], attrs_len[i]); /* Flawfinder: ignore */
 			ptr += attrs_len[i];
 			len -= attrs_len[i];
 		}
@@ -304,10 +301,11 @@ char * iio_channel_get_xml(const struct iio_channel *chn, size_t *length)
 	free(attrs_len);
 
 	if (len > 0) {
-		iio_strlcpy(ptr, "</channel>", len);
-		len -= sizeof("</channel>");
+		ptr += iio_strlcpy(ptr, "</channel>", len);
+		len -= sizeof("</channel>") -1;
 	}
-	*length = ptr - str + sizeof("</channel>") - 1;
+
+	*length = ptr - str;
 
 	if (len < 0) {
 		IIO_ERROR("Internal libIIO error: iio_channel_get_xml str length isssue\n");