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1 //===- BinaryStream.h - Base interface for a stream of data -----*- C++ -*-===//
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2 //
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3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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4 // See https://llvm.org/LICENSE.txt for license information.
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5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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6 //
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7 //===----------------------------------------------------------------------===//
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8
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9 #ifndef LLVM_SUPPORT_BINARYSTREAM_H
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10 #define LLVM_SUPPORT_BINARYSTREAM_H
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11
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12 #include "llvm/ADT/ArrayRef.h"
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13 #include "llvm/ADT/BitmaskEnum.h"
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14 #include "llvm/Support/BinaryStreamError.h"
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15 #include "llvm/Support/Endian.h"
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16 #include "llvm/Support/Error.h"
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17 #include <cstdint>
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18
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19 namespace llvm {
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20
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21 enum BinaryStreamFlags {
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22 BSF_None = 0,
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23 BSF_Write = 1, // Stream supports writing.
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24 BSF_Append = 2, // Writing can occur at offset == length.
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25 LLVM_MARK_AS_BITMASK_ENUM(/* LargestValue = */ BSF_Append)
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26 };
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27
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28 /// An interface for accessing data in a stream-like format, but which
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29 /// discourages copying. Instead of specifying a buffer in which to copy
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30 /// data on a read, the API returns an ArrayRef to data owned by the stream's
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31 /// implementation. Since implementations may not necessarily store data in a
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32 /// single contiguous buffer (or even in memory at all), in such cases a it may
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33 /// be necessary for an implementation to cache such a buffer so that it can
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34 /// return it.
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35 class BinaryStream {
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36 public:
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37 virtual ~BinaryStream() = default;
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38
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39 virtual llvm::support::endianness getEndian() const = 0;
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40
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41 /// Given an offset into the stream and a number of bytes, attempt to
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42 /// read the bytes and set the output ArrayRef to point to data owned by the
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43 /// stream.
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44 virtual Error readBytes(uint32_t Offset, uint32_t Size,
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45 ArrayRef<uint8_t> &Buffer) = 0;
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46
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47 /// Given an offset into the stream, read as much as possible without
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48 /// copying any data.
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49 virtual Error readLongestContiguousChunk(uint32_t Offset,
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50 ArrayRef<uint8_t> &Buffer) = 0;
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51
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52 /// Return the number of bytes of data in this stream.
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53 virtual uint32_t getLength() = 0;
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54
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55 /// Return the properties of this stream.
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56 virtual BinaryStreamFlags getFlags() const { return BSF_None; }
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57
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58 protected:
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59 Error checkOffsetForRead(uint32_t Offset, uint32_t DataSize) {
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60 if (Offset > getLength())
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61 return make_error<BinaryStreamError>(stream_error_code::invalid_offset);
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62 if (getLength() < DataSize + Offset)
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63 return make_error<BinaryStreamError>(stream_error_code::stream_too_short);
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64 return Error::success();
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65 }
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66 };
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67
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68 /// A BinaryStream which can be read from as well as written to. Note
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69 /// that writing to a BinaryStream always necessitates copying from the input
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70 /// buffer to the stream's backing store. Streams are assumed to be buffered
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71 /// so that to be portable it is necessary to call commit() on the stream when
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72 /// all data has been written.
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73 class WritableBinaryStream : public BinaryStream {
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74 public:
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75 ~WritableBinaryStream() override = default;
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76
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77 /// Attempt to write the given bytes into the stream at the desired
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78 /// offset. This will always necessitate a copy. Cannot shrink or grow the
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79 /// stream, only writes into existing allocated space.
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80 virtual Error writeBytes(uint32_t Offset, ArrayRef<uint8_t> Data) = 0;
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81
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82 /// For buffered streams, commits changes to the backing store.
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83 virtual Error commit() = 0;
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84
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85 /// Return the properties of this stream.
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86 BinaryStreamFlags getFlags() const override { return BSF_Write; }
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87
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88 protected:
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89 Error checkOffsetForWrite(uint32_t Offset, uint32_t DataSize) {
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90 if (!(getFlags() & BSF_Append))
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91 return checkOffsetForRead(Offset, DataSize);
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92
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93 if (Offset > getLength())
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94 return make_error<BinaryStreamError>(stream_error_code::invalid_offset);
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95 return Error::success();
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96 }
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97 };
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98
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99 } // end namespace llvm
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100
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101 #endif // LLVM_SUPPORT_BINARYSTREAM_H
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