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// Copyright 2018 Google Inc.
//
// 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.
//
///////////////////////////////////////////////////////////////////////////////
#ifndef TINK_INPUT_STREAM_H_
#define TINK_INPUT_STREAM_H_
#include "tink/util/status.h"
#include "tink/util/statusor.h"
namespace crypto {
namespace tink {
// Abstract interface similar to an input stream, and to
// Protocol Buffers' google::protobuf::io::ZeroCopyInputStream.
class InputStream {
public:
InputStream() = default;
virtual ~InputStream() = default;
// Obtains a chunk of data from the stream.
//
// Preconditions:
// * "data" is not NULL.
//
// Postconditions:
// * If the returned status is not OK, there is no more data to return
// (status equal to OUT_OF_RANGE) or an error occurred
// (status not in {OK, OUT_OF_RANGE}. All errors are permanent.
// * Otherwise, the returned value is the number of bytes read and "data"
// points to a buffer containing these bytes.
// * Ownership of this buffer remains with the stream, and the buffer
// remains valid only until some other non-const method of the stream
// is called or the stream is destroyed.
// * It is legal for the returned buffer to have zero size, as long as
// repeatedly calling Next() eventually yields a buffer with non-zero
// size or a non-OK status.
virtual crypto::tink::util::StatusOr<int> Next(const void** data) = 0;
// Backs up a number of bytes, so that the next call to Next() returns
// data again that was already returned by the last call to Next().
// This is useful when writing procedures that are only supposed to read
// up to a certain point in the input, then return. If Next() returns a
// buffer that goes beyond what you wanted to read, you can use BackUp()
// to return to the point where you intended to finish.
//
// Preconditions:
// * The last call to Next() must have returned status OK.
// If there was no Next()-call yet, or the last one failed,
// BackUp()-call is ignored.
// * count must be less than or equal to the size of the last buffer
// returned by Next(). Non-positive count is ignored (no action on this
// stream), and count larger than the size of the last buffer is treated
// as equal to the size of the last buffer.
//
// Postconditions:
// * The last "count" bytes of the last buffer returned by Next() will be
// pushed back into the stream. Subsequent calls to Next() will return
// the same data again before producing new data.
// * Repeated calls to BackUp() accumulate:
// BackUp(a);
// Backup(b);
// is equivalent to
// Backup(c);
// with c = max(0, a) + max(0, b).
// * The actual result of BackUp()-call can be verified via Position().
virtual void BackUp(int count) = 0;
// Returns the current byte position in the stream.
//
// Preconditions:
// * The last call to Next() ended with status in {OK, OUT_OF_RANGE}.
//
// Postconditions:
// * Position equal to i means that the next call to Next() will
// return a data buffer starting at (i+1)st byte of the stream (if any).
// * If the last call to Next() reached end of stream (status OUT_OF_RANGE),
// then returned value is the total number of bytes in the stream.
// * If the last call to Next() ended with a failure, -1 is returned;
virtual int64_t Position() const = 0;
};
} // namespace tink
} // namespace crypto
#endif // TINK_INPUT_STREAM_H_
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