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diff --git a/src/mongo/util/str_basic.h b/src/mongo/util/str_basic.h
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+++ b/src/mongo/util/str_basic.h
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+/**
+ *    Copyright (C) 2024-present MongoDB, Inc.
+ *
+ *    This program is free software: you can redistribute it and/or modify
+ *    it under the terms of the Server Side Public License, version 1,
+ *    as published by MongoDB, Inc.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    Server Side Public License for more details.
+ *
+ *    You should have received a copy of the Server Side Public License
+ *    along with this program. If not, see
+ *    <http://www.mongodb.com/licensing/server-side-public-license>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the Server Side Public License in all respects for
+ *    all of the code used other than as permitted herein. If you modify file(s)
+ *    with this exception, you may extend this exception to your version of the
+ *    file(s), but you are not obligated to do so. If you do not wish to do so,
+ *    delete this exception statement from your version. If you delete this
+ *    exception statement from all source files in the program, then also delete
+ *    it in the license file.
+ */
+
+#pragma once
+
+/**
+ * This header would be part of str.h, but is separated to break an include cycle with
+ * bson/util/builder.h
+ */
+
+#include <cstring>
+
+#include "mongo/base/string_data.h"
+#include "mongo/util/assert_util.h"
+
+namespace mongo::str {
+/**
+ * Throws if sd contains any bytes equal to '\0' within its range.
+ *
+ * Note: When a StringData is constructed from a C string or std::string, the final '\0' byte is NOT
+ * considered in range and so will not cause this to throw.
+ */
+inline void uassertNoEmbeddedNulBytes(StringData sd) {
+    uassert(9527900, "illegal embedded NUL byte", sd.find('\0') == std::string::npos);
+}
+
+/**
+ * Copies the contents of sd to dest and appends a NUL byte.
+ *
+ * Throws if sd already contains a NUL byte.
+ * Returns a pointer to the next byte to write to (equivalently, the byte after the appended NUL).
+ */
+inline char* copyAsCString(char* dest, StringData sd) {
+    uassertNoEmbeddedNulBytes(sd);
+    dest += sd.copy(dest, sd.size());
+    *dest++ = '\0';
+    return dest;
+}
+}  // namespace mongo::str