1 files changed, 87 insertions, 0 deletions
diff --git a/pw_protobuf/map_utils.cc b/pw_protobuf/map_utils.cc
new file mode 100644
index 000000000..27b505bcf
--- /dev/null
+++ b/pw_protobuf/map_utils.cc
@@ -0,0 +1,87 @@
+// Copyright 2021 The Pigweed Authors
+//
+// 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
+//
+//     https://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 "pw_protobuf/map_utils.h"
+
+#include <cstddef>
+
+#include "pw_bytes/span.h"
+#include "pw_protobuf/encoder.h"
+#include "pw_protobuf/serialized_size.h"
+#include "pw_stream/stream.h"
+
+namespace pw::protobuf {
+
+// Note that a map<string, bytes> is essentially
+//
+// message Entry {
+//   string key = 1;
+//   bytes value = 2;
+// }
+//
+// message Msg {
+//   repeated Entry map_field = <field_number>;
+// }
+Status WriteProtoStringToBytesMapEntry(uint32_t field_number,
+                                       stream::Reader& key,
+                                       size_t key_size,
+                                       stream::Reader& value,
+                                       size_t value_size,
+                                       ByteSpan stream_pipe_buffer,
+                                       stream::Writer& writer) {
+  constexpr uint32_t kMapKeyFieldNumber = 1;
+  constexpr uint32_t kMapValueFieldNumber = 2;
+
+  if (!protobuf::ValidFieldNumber(field_number) ||
+      key_size >= std::numeric_limits<uint32_t>::max() ||
+      value_size >= std::numeric_limits<uint32_t>::max()) {
+    return Status::InvalidArgument();
+  }
+
+  Result<size_t> key_field_size = protobuf::SizeOfField(
+      kMapKeyFieldNumber, protobuf::WireType::kDelimited, key_size);
+  PW_TRY(key_field_size.status());
+
+  Result<size_t> value_field_size = protobuf::SizeOfField(
+      kMapValueFieldNumber, protobuf::WireType::kDelimited, value_size);
+  PW_TRY(value_field_size.status());
+
+  size_t entry_payload_total_size =
+      key_field_size.value() + value_field_size.value();
+
+  Result<size_t> entry_field_total_size = protobuf::SizeOfField(
+      field_number, protobuf::WireType::kDelimited, entry_payload_total_size);
+  PW_TRY(entry_field_total_size.status());
+
+  if (entry_field_total_size.value() > writer.ConservativeWriteLimit()) {
+    return Status::ResourceExhausted();
+  }
+
+  // Write field key and length prefix for nested message `Entry`
+  PW_TRY(protobuf::WriteLengthDelimitedKeyAndLengthPrefix(
+      field_number, entry_payload_total_size, writer));
+
+  protobuf::StreamEncoder encoder(writer, {});
+
+  // Write Entry::key
+  PW_TRY(encoder.WriteStringFromStream(
+      kMapKeyFieldNumber, key, key_size, stream_pipe_buffer));
+  // Write Entry::value
+  PW_TRY(encoder.WriteBytesFromStream(
+      kMapValueFieldNumber, value, value_size, stream_pipe_buffer));
+
+  return OkStatus();
+}
+
+}  // namespace pw::protobuf