1 files changed, 60 insertions, 0 deletions
diff --git a/pw_hdlc/public/pw_hdlc/internal/encoder.h b/pw_hdlc/public/pw_hdlc/internal/encoder.h
new file mode 100644
index 000000000..2f3b4b0a6
--- /dev/null
+++ b/pw_hdlc/public/pw_hdlc/internal/encoder.h
@@ -0,0 +1,60 @@
+// Copyright 2020 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.
+#pragma once
+
+#include "pw_checksum/crc32.h"
+#include "pw_hdlc/internal/protocol.h"
+#include "pw_stream/stream.h"
+
+namespace pw::hdlc::internal {
+
+// Encodes and writes HDLC frames.
+class Encoder {
+ public:
+  constexpr Encoder(stream::Writer& output) : writer_(output) {}
+
+  // Writes the header for an I-frame. After successfully calling
+  // StartInformationFrame, WriteData may be called any number of times.
+  Status StartInformationFrame(uint64_t address) {
+    return StartFrame(address, kUnusedControl);
+  }
+
+  // Writes the header for an U-frame. After successfully calling
+  // StartUnnumberedFrame, WriteData may be called any number of times.
+  Status StartUnnumberedFrame(uint64_t address) {
+    return StartFrame(address, UFrameControl::UnnumberedInformation().data());
+  }
+
+  // Writes data for an ongoing frame. Must only be called after a successful
+  // StartInformationFrame call, and prior to a FinishFrame() call.
+  Status WriteData(ConstByteSpan data);
+
+  // Finishes a frame. Writes the frame check sequence and a terminating flag.
+  Status FinishFrame();
+
+  // Runs a pass through a payload, returning the worst-case encoded size for a
+  // frame containing it. Does not calculate CRC to improve efficiency.
+  static size_t MaxEncodedSize(uint64_t address, ConstByteSpan payload);
+
+ private:
+  // Indicates this an information packet with sequence numbers set to 0.
+  static constexpr std::byte kUnusedControl = std::byte{0};
+
+  Status StartFrame(uint64_t address, std::byte control);
+
+  stream::Writer& writer_;
+  checksum::Crc32 fcs_;
+};
+
+}  // namespace pw::hdlc::internal