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      1 //===- BinaryItemStream.h ---------------------------------------*- C++ -*-===//
      2 //
      3 //                     The LLVM Compiler Infrastructure
      4 //
      5 // This file is distributed under the University of Illinois Open Source
      6 // License. See LICENSE.TXT for details.
      7 //
      8 //===----------------------------------------------------------------------===//
      9 
     10 #ifndef LLVM_SUPPORT_BINARYITEMSTREAM_H
     11 #define LLVM_SUPPORT_BINARYITEMSTREAM_H
     12 
     13 #include "llvm/ADT/ArrayRef.h"
     14 #include "llvm/Support/BinaryStream.h"
     15 #include "llvm/Support/BinaryStreamError.h"
     16 #include "llvm/Support/Error.h"
     17 #include <cstddef>
     18 #include <cstdint>
     19 
     20 namespace llvm {
     21 
     22 template <typename T> struct BinaryItemTraits {
     23   static size_t length(const T &Item) = delete;
     24   static ArrayRef<uint8_t> bytes(const T &Item) = delete;
     25 };
     26 
     27 /// BinaryItemStream represents a sequence of objects stored in some kind of
     28 /// external container but for which it is useful to view as a stream of
     29 /// contiguous bytes.  An example of this might be if you have a collection of
     30 /// records and you serialize each one into a buffer, and store these serialized
     31 /// records in a container.  The pointers themselves are not laid out
     32 /// contiguously in memory, but we may wish to read from or write to these
     33 /// records as if they were.
     34 template <typename T, typename Traits = BinaryItemTraits<T>>
     35 class BinaryItemStream : public BinaryStream {
     36 public:
     37   explicit BinaryItemStream(llvm::support::endianness Endian)
     38       : Endian(Endian) {}
     39 
     40   llvm::support::endianness getEndian() const override { return Endian; }
     41 
     42   Error readBytes(uint32_t Offset, uint32_t Size,
     43                   ArrayRef<uint8_t> &Buffer) override {
     44     auto ExpectedIndex = translateOffsetIndex(Offset);
     45     if (!ExpectedIndex)
     46       return ExpectedIndex.takeError();
     47     const auto &Item = Items[*ExpectedIndex];
     48     if (auto EC = checkOffset(Offset, Size))
     49       return EC;
     50     if (Size > Traits::length(Item))
     51       return make_error<BinaryStreamError>(stream_error_code::stream_too_short);
     52     Buffer = Traits::bytes(Item).take_front(Size);
     53     return Error::success();
     54   }
     55 
     56   Error readLongestContiguousChunk(uint32_t Offset,
     57                                    ArrayRef<uint8_t> &Buffer) override {
     58     auto ExpectedIndex = translateOffsetIndex(Offset);
     59     if (!ExpectedIndex)
     60       return ExpectedIndex.takeError();
     61     Buffer = Traits::bytes(Items[*ExpectedIndex]);
     62     return Error::success();
     63   }
     64 
     65   void setItems(ArrayRef<T> ItemArray) { Items = ItemArray; }
     66 
     67   uint32_t getLength() override {
     68     uint32_t Size = 0;
     69     for (const auto &Item : Items)
     70       Size += Traits::length(Item);
     71     return Size;
     72   }
     73 
     74 private:
     75   Expected<uint32_t> translateOffsetIndex(uint32_t Offset) const {
     76     uint32_t CurrentOffset = 0;
     77     uint32_t CurrentIndex = 0;
     78     for (const auto &Item : Items) {
     79       if (CurrentOffset >= Offset)
     80         break;
     81       CurrentOffset += Traits::length(Item);
     82       ++CurrentIndex;
     83     }
     84     if (CurrentOffset != Offset)
     85       return make_error<BinaryStreamError>(stream_error_code::stream_too_short);
     86     return CurrentIndex;
     87   }
     88 
     89   llvm::support::endianness Endian;
     90   ArrayRef<T> Items;
     91 };
     92 
     93 } // end namespace llvm
     94 
     95 #endif // LLVM_SUPPORT_BINARYITEMSTREAM_H
     96