1 files changed, 73 insertions, 0 deletions
diff --git a/icing/store/namespace-fingerprint-identifier.cc b/icing/store/namespace-fingerprint-identifier.cc
new file mode 100644
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--- /dev/null
+++ b/icing/store/namespace-fingerprint-identifier.cc
@@ -0,0 +1,73 @@
+// Copyright (C) 2023 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "icing/store/namespace-fingerprint-identifier.h"
+
+#include <cstdint>
+#include <string>
+#include <string_view>
+
+#include "icing/text_classifier/lib3/utils/base/statusor.h"
+#include "icing/text_classifier/lib3/utils/hash/farmhash.h"
+#include "icing/absl_ports/canonical_errors.h"
+#include "icing/absl_ports/str_cat.h"
+#include "icing/store/namespace-id.h"
+#include "icing/util/encode-util.h"
+
+namespace icing {
+namespace lib {
+
+/* static */ libtextclassifier3::StatusOr<NamespaceFingerprintIdentifier>
+NamespaceFingerprintIdentifier::DecodeFromCString(
+    std::string_view encoded_cstr) {
+  if (encoded_cstr.size() < kMinEncodedLength) {
+    return absl_ports::InvalidArgumentError("Invalid length");
+  }
+
+  NamespaceId namespace_id = encode_util::DecodeIntFromCString(
+      encoded_cstr.substr(0, kEncodedNamespaceIdLength));
+  uint64_t fingerprint = encode_util::DecodeIntFromCString(
+      encoded_cstr.substr(kEncodedNamespaceIdLength));
+  return NamespaceFingerprintIdentifier(namespace_id, fingerprint);
+}
+
+NamespaceFingerprintIdentifier::NamespaceFingerprintIdentifier(
+    NamespaceId namespace_id, std::string_view target_str)
+    : namespace_id_(namespace_id),
+      fingerprint_(tc3farmhash::Fingerprint64(target_str)) {}
+
+std::string NamespaceFingerprintIdentifier::EncodeToCString() const {
+  // encoded_namespace_id_str should be 1 to 3 bytes based on the value of
+  // namespace_id.
+  std::string encoded_namespace_id_str =
+      encode_util::EncodeIntToCString(namespace_id_);
+  // Make encoded_namespace_id_str to fixed kEncodedNamespaceIdLength bytes.
+  while (encoded_namespace_id_str.size() < kEncodedNamespaceIdLength) {
+    // C string cannot contain 0 bytes, so we append it using 1, just like what
+    // we do in encode_util::EncodeIntToCString.
+    //
+    // The reason that this works is because DecodeIntToString decodes a byte
+    // value of 0x01 as 0x00. When EncodeIntToCString returns an encoded
+    // namespace id that is less than 3 bytes, it means that the id contains
+    // unencoded leading 0x00. So here we're explicitly encoding those bytes as
+    // 0x01.
+    encoded_namespace_id_str.push_back(1);
+  }
+
+  return absl_ports::StrCat(encoded_namespace_id_str,
+                            encode_util::EncodeIntToCString(fingerprint_));
+}
+
+}  // namespace lib
+}  // namespace icing