ds: string: add function to copy string data from a b_stringstream

unlike b_stringstream_ptr(), this function supports copying strings
that contain null bytes.

ds/string.c

@@ -419,6 +419,21 @@ static b_status string_replace_all(struct b_string_p *str, const char *new_data)
 	return B_SUCCESS;
 }
 
+static b_status string_replace_all_with_stringstream(
+	struct b_string_p *str, const b_stringstream *new_data)
+{
+	size_t new_len = b_stringstream_get_length(new_data);
+	string_reserve(str, new_len);
+	char *dest = string_ptr(str);
+	memcpy(dest, b_stringstream_ptr(new_data), new_len);
+	dest[new_len] = '\0';
+
+	str->s_len = new_len;
+	str->s_codepoints = b_wchar_utf8_codepoint_count(dest, new_len);
+
+	return B_SUCCESS;
+}
+
 static enum b_status remove_ansi(struct b_string_p *str, size_t start, size_t length)
 {
 	b_status status = B_SUCCESS;
@@ -1124,6 +1139,13 @@ b_status b_string_replace_all(b_string *str, const char *new_data)
 	B_CLASS_DISPATCH_STATIC(B_TYPE_STRING, string_replace_all, str, new_data);
 }
 
+b_status b_string_replace_all_with_stringstream(
+	b_string *str, const b_stringstream *new_data)
+{
+	B_CLASS_DISPATCH_STATIC(
+		B_TYPE_STRING, string_replace_all_with_stringstream, str, new_data);
+}
+
 enum b_status b_string_remove(b_string *str, size_t start, size_t length)
 {
 	B_CLASS_DISPATCH_STATIC(B_TYPE_STRING, string_remove, str, start, length);