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//===- BinaryStreamArray.h - Array backed by an arbitrary stream *- C++ -*-===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/iterator.h"
#include "llvm/Support/BinaryStreamRef.h"
#include "llvm/Support/Error.h"
#include <cassert>
#include <cstdint>
/// Lightweight arrays that are backed by an arbitrary BinaryStream. This file
/// provides two different array implementations.
/// VarStreamArray - Arrays of variable length records. The user specifies
/// an Extractor type that can extract a record from a given offset and
/// return the number of bytes consumed by the record.
/// FixedStreamArray - Arrays of fixed length records. This is similar in
/// spirit to ArrayRef<T>, but since it is backed by a BinaryStream, the
/// elements of the array need not be laid out in contiguous memory.
namespace llvm {
/// VarStreamArrayExtractor is intended to be specialized to provide customized
/// extraction logic. On input it receives a BinaryStreamRef pointing to the
/// beginning of the next record, but where the length of the record is not yet
/// known. Upon completion, it should return an appropriate Error instance if
/// a record could not be extracted, or if one could be extracted it should
/// return success and set Len to the number of bytes this record occupied in
/// the underlying stream, and it should fill out the fields of the value type
/// Item appropriately to represent the current record.
/// You can specialize this template for your own custom value types to avoid
/// having to specify a second template argument to VarStreamArray (documented
/// below).
template <typename T> struct VarStreamArrayExtractor {
// Method intentionally deleted. You must provide an explicit specialization
// with the following method implemented.
Error operator()(BinaryStreamRef Stream, uint32_t &Len,
T &Item) const = delete;
/// VarStreamArray represents an array of variable length records backed by a
/// stream. This could be a contiguous sequence of bytes in memory, it could
/// be a file on disk, or it could be a PDB stream where bytes are stored as
/// discontiguous blocks in a file. Usually it is desirable to treat arrays
/// as contiguous blocks of memory, but doing so with large PDB files, for
/// example, could mean allocating huge amounts of memory just to allow
/// re-ordering of stream data to be contiguous before iterating over it. By
/// abstracting this out, we need not duplicate this memory, and we can
/// iterate over arrays in arbitrarily formatted streams. Elements are parsed
/// lazily on iteration, so there is no upfront cost associated with building
/// or copying a VarStreamArray, no matter how large it may be.
/// You create a VarStreamArray by specifying a ValueType and an Extractor type.
/// If you do not specify an Extractor type, you are expected to specialize
/// VarStreamArrayExtractor<T> for your ValueType.
/// By default an Extractor is default constructed in the class, but in some
/// cases you might find it useful for an Extractor to maintain state across
/// extractions. In this case you can provide your own Extractor through a
/// secondary constructor. The following examples show various ways of
/// creating a VarStreamArray.
/// // Will use VarStreamArrayExtractor<MyType> as the extractor.
/// VarStreamArray<MyType> MyTypeArray;
/// // Will use a default-constructed MyExtractor as the extractor.
/// VarStreamArray<MyType, MyExtractor> MyTypeArray2;
/// // Will use the specific instance of MyExtractor provided.
/// // MyExtractor need not be default-constructible in this case.
/// MyExtractor E(SomeContext);
/// VarStreamArray<MyType, MyExtractor> MyTypeArray3(E);
template <typename ValueType, typename Extractor> class VarStreamArrayIterator;
template <typename ValueType,
typename Extractor = VarStreamArrayExtractor<ValueType>>
class VarStreamArray {
friend class VarStreamArrayIterator<ValueType, Extractor>;
typedef VarStreamArrayIterator<ValueType, Extractor> Iterator;
VarStreamArray() = default;
explicit VarStreamArray(const Extractor &E) : E(E) {}
explicit VarStreamArray(BinaryStreamRef Stream, uint32_t Skew = 0)
: Stream(Stream), Skew(Skew) {}
VarStreamArray(BinaryStreamRef Stream, const Extractor &E, uint32_t Skew = 0)
: Stream(Stream), E(E), Skew(Skew) {}
Iterator begin(bool *HadError = nullptr) const {
return Iterator(*this, E, Skew, nullptr);
bool valid() const { return Stream.valid(); }
uint32_t skew() const { return Skew; }
Iterator end() const { return Iterator(E); }
bool empty() const { return Stream.getLength() == 0; }
VarStreamArray<ValueType, Extractor> substream(uint32_t Begin,
uint32_t End) const {
assert(Begin >= Skew);
// We should never cut off the beginning of the stream since it might be
// skewed, meaning the initial bytes are important.
BinaryStreamRef NewStream = Stream.slice(0, End);
return {NewStream, E, Begin};
/// given an offset into the array's underlying stream, return an
/// iterator to the record at that offset. This is considered unsafe
/// since the behavior is undefined if \p Offset does not refer to the
/// beginning of a valid record.
Iterator at(uint32_t Offset) const {
return Iterator(*this, E, Offset, nullptr);
const Extractor &getExtractor() const { return E; }
Extractor &getExtractor() { return E; }
BinaryStreamRef getUnderlyingStream() const { return Stream; }
void setUnderlyingStream(BinaryStreamRef S, uint32_t Skew = 0) {
Stream = S;
this->Skew = Skew;
void drop_front() { Skew += begin()->length(); }
BinaryStreamRef Stream;
Extractor E;
uint32_t Skew;
template <typename ValueType, typename Extractor>
class VarStreamArrayIterator
: public iterator_facade_base<VarStreamArrayIterator<ValueType, Extractor>,
std::forward_iterator_tag, ValueType> {
typedef VarStreamArrayIterator<ValueType, Extractor> IterType;
typedef VarStreamArray<ValueType, Extractor> ArrayType;
VarStreamArrayIterator(const ArrayType &Array, const Extractor &E,
uint32_t Offset, bool *HadError)
: IterRef(Array.Stream.drop_front(Offset)), Extract(E),
Array(&Array), AbsOffset(Offset), HadError(HadError) {
if (IterRef.getLength() == 0)
else {
auto EC = Extract(IterRef, ThisLen, ThisValue);
if (EC) {
VarStreamArrayIterator() = default;
explicit VarStreamArrayIterator(const Extractor &E) : Extract(E) {}
~VarStreamArrayIterator() = default;
bool operator==(const IterType &R) const {
if (Array && R.Array) {
// Both have a valid array, make sure they're same.
assert(Array == R.Array);
return IterRef == R.IterRef;
// Both iterators are at the end.
if (!Array && !R.Array)
return true;
// One is not at the end and one is.
return false;
const ValueType &operator*() const {
assert(Array && !HasError);
return ThisValue;
ValueType &operator*() {
assert(Array && !HasError);
return ThisValue;
IterType &operator+=(unsigned N) {
for (unsigned I = 0; I < N; ++I) {
// We are done with the current record, discard it so that we are
// positioned at the next record.
AbsOffset += ThisLen;
IterRef = IterRef.drop_front(ThisLen);
if (IterRef.getLength() == 0) {
// There is nothing after the current record, we must make this an end
// iterator.
} else {
// There is some data after the current record.
auto EC = Extract(IterRef, ThisLen, ThisValue);
if (EC) {
} else if (ThisLen == 0) {
// An empty record? Make this an end iterator.
return *this;
uint32_t offset() const { return AbsOffset; }
uint32_t getRecordLength() const { return ThisLen; }
void moveToEnd() {
Array = nullptr;
ThisLen = 0;
void markError() {
HasError = true;
if (HadError != nullptr)
*HadError = true;
ValueType ThisValue;
BinaryStreamRef IterRef;
Extractor Extract;
const ArrayType *Array{nullptr};
uint32_t ThisLen{0};
uint32_t AbsOffset{0};
bool HasError{false};
bool *HadError{nullptr};
template <typename T> class FixedStreamArrayIterator;
/// FixedStreamArray is similar to VarStreamArray, except with each record
/// having a fixed-length. As with VarStreamArray, there is no upfront
/// cost associated with building or copying a FixedStreamArray, as the
/// memory for each element is not read from the backing stream until that
/// element is iterated.
template <typename T> class FixedStreamArray {
friend class FixedStreamArrayIterator<T>;
typedef FixedStreamArrayIterator<T> Iterator;
FixedStreamArray() = default;
explicit FixedStreamArray(BinaryStreamRef Stream) : Stream(Stream) {
assert(Stream.getLength() % sizeof(T) == 0);
bool operator==(const FixedStreamArray<T> &Other) const {
return Stream == Other.Stream;
bool operator!=(const FixedStreamArray<T> &Other) const {
return !(*this == Other);
FixedStreamArray &operator=(const FixedStreamArray &) = default;
const T &operator[](uint32_t Index) const {
assert(Index < size());
uint32_t Off = Index * sizeof(T);
ArrayRef<uint8_t> Data;
if (auto EC = Stream.readBytes(Off, sizeof(T), Data)) {
assert(false && "Unexpected failure reading from stream");
// This should never happen since we asserted that the stream length was
// an exact multiple of the element size.
return *reinterpret_cast<const T *>(;
uint32_t size() const { return Stream.getLength() / sizeof(T); }
bool empty() const { return size() == 0; }
FixedStreamArrayIterator<T> begin() const {
return FixedStreamArrayIterator<T>(*this, 0);
FixedStreamArrayIterator<T> end() const {
return FixedStreamArrayIterator<T>(*this, size());
const T &front() const { return *begin(); }
const T &back() const {
FixedStreamArrayIterator<T> I = end();
return *(--I);
BinaryStreamRef getUnderlyingStream() const { return Stream; }
BinaryStreamRef Stream;
template <typename T>
class FixedStreamArrayIterator
: public iterator_facade_base<FixedStreamArrayIterator<T>,
std::random_access_iterator_tag, const T> {
FixedStreamArrayIterator(const FixedStreamArray<T> &Array, uint32_t Index)
: Array(Array), Index(Index) {}
FixedStreamArrayIterator<T> &
operator=(const FixedStreamArrayIterator<T> &Other) {
Array = Other.Array;
Index = Other.Index;
return *this;
const T &operator*() const { return Array[Index]; }
const T &operator*() { return Array[Index]; }
bool operator==(const FixedStreamArrayIterator<T> &R) const {
assert(Array == R.Array);
return (Index == R.Index) && (Array == R.Array);
FixedStreamArrayIterator<T> &operator+=(std::ptrdiff_t N) {
Index += N;
return *this;
FixedStreamArrayIterator<T> &operator-=(std::ptrdiff_t N) {
assert(std::ptrdiff_t(Index) >= N);
Index -= N;
return *this;
std::ptrdiff_t operator-(const FixedStreamArrayIterator<T> &R) const {
assert(Array == R.Array);
assert(Index >= R.Index);
return Index - R.Index;
bool operator<(const FixedStreamArrayIterator<T> &RHS) const {
assert(Array == RHS.Array);
return Index < RHS.Index;
FixedStreamArray<T> Array;
uint32_t Index;
} // namespace llvm