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This starts an implementation of a C++ transfer client suitable for device to device transfers. Both read and write transfer support is added. The code is incomplete and untested; pw_rpc raw clients are required before this can be functional. Change-Id: I17154c50986f7de8027fbc4e0143e86e3c64dd64 Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/61792 Commit-Queue: Alexei Frolov <frolv@google.com> Reviewed-by: Wyatt Hepler <hepler@google.com>
73 lines
2.7 KiB
C++
73 lines
2.7 KiB
C++
// Copyright 2021 The Pigweed Authors
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//
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// Licensed under the Apache License, Version 2.0 (the "License"); you may not
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// use this file except in compliance with the License. You may obtain a copy of
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// the License at
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//
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// https://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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// License for the specific language governing permissions and limitations under
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// the License.
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#include "pw_transfer/internal/context.h"
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#include "pw_assert/check.h"
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#include "pw_status/try.h"
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#include "pw_varint/varint.h"
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namespace pw::transfer::internal {
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size_t MaxWriteChunkSize(const Context& transfer,
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size_t max_chunk_size_bytes,
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uint32_t channel_id) {
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// Start with the user-provided maximum chunk size, which should be the usable
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// payload length on the RPC ingress path after any transport overhead.
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ssize_t max_size = max_chunk_size_bytes;
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// Subtract the RPC overhead (pw_rpc/internal/packet.proto).
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//
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// type: 1 byte key, 1 byte value (CLIENT_STREAM)
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// channel_id: 1 byte key, varint value (calculate from stream)
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// service_id: 1 byte key, 4 byte value
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// method_id: 1 byte key, 4 byte value
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// payload: 1 byte key, varint length (remaining space)
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// status: 0 bytes (not set in stream packets)
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//
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// TOTAL: 14 bytes + encoded channel_id size + encoded payload length
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//
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max_size -= 14;
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max_size -= varint::EncodedSize(channel_id);
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max_size -= varint::EncodedSize(max_size);
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// Subtract the transfer service overhead for a client write chunk
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// (pw_transfer/transfer.proto).
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//
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// transfer_id: 1 byte key, varint value (calculate)
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// offset: 1 byte key, varint value (calculate)
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// data: 1 byte key, varint length (remaining space)
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//
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// TOTAL: 3 + encoded transfer_id + encoded offset + encoded data length
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//
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size_t max_offset_in_window = transfer.offset() + transfer.pending_bytes();
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max_size -= 3;
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max_size -= varint::EncodedSize(transfer.transfer_id());
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max_size -= varint::EncodedSize(max_offset_in_window);
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max_size -= varint::EncodedSize(max_size);
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// A resulting value of zero (or less) renders write transfers unusable, as
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// there is no space to send any payload. This should be considered a
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// programmer error in the transfer service setup.
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PW_CHECK_INT_GT(
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max_size,
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0,
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"Transfer service maximum chunk size is too small to fit a payload. "
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"Increase max_chunk_size_bytes to support write transfers.");
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return max_size;
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}
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} // namespace pw::transfer::internal
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