public std::enable_shared_from_this<DataQueueImpl> {

public:

// Constructor for an idempotent, fixed sized DataQueue.

DataQueueImpl(std::vector<std::unique_ptr<Entry>>&& list, uint64_t size)

: entries_(std::move(list)),

idempotent_(true),

size_(size),

capped_size_(0) {}

// Constructor for a non-idempotent DataQueue. This kind of queue can have

// entries added to it over time. The size is set to 0 initially. The queue

// can be capped immediately on creation. Depending on the entries that are

// added, the size can be cleared if any of the entries are not capable of

// providing a size.

DataQueueImpl(std::optional<uint64_t> cap = std::nullopt)

: idempotent_(false), size_(0), capped_size_(cap) {}

// Disallow moving and copying.

DataQueueImpl(const DataQueueImpl&) = delete;

DataQueueImpl(DataQueueImpl&&) = delete;

DataQueueImpl& operator=(const DataQueueImpl&) = delete;

DataQueueImpl& operator=(DataQueueImpl&&) = delete;

std::shared_ptr<DataQueue> slice(

uint64_t start,

std::optional<uint64_t> maybeEnd = std::nullopt) override {

// If the data queue is not idempotent, or the size cannot be determined,

// we cannot reasonably create a slice. Therefore, return nothing.

if (!idempotent_ || !size_.has_value()) return nullptr;

uint64_t size = size_.value();

// start cannot be greater than the size.

start = std::min(start, size);

uint64_t end = std::max(start, std::min(maybeEnd.value_or(size), size));

DCHECK_LE(start, end);

uint64_t len = end - start;

uint64_t remaining = end - start;

std::vector<std::unique_ptr<Entry>> slices;

if (remaining > 0) {

for (const auto& entry : entries_) {

// The size of every entry should be known since this is an

// idempotent queue.

uint64_t entrySize = entry->size().value();

if (start > entrySize) {

start -= entrySize;

continue;

}

uint64_t chunkStart = start;

uint64_t len = std::min(remaining, entrySize - chunkStart);

slices.emplace_back(entry->slice(chunkStart, chunkStart + len));

remaining -= len;

start = 0;

if (remaining == 0) break;

}

}

return std::make_shared<DataQueueImpl>(std::move(slices), len);

}

std::optional<uint64_t> size() const override { return size_; }

bool is_idempotent() const override { return idempotent_; }

bool is_capped() const override { return capped_size_.has_value(); }

std::optional<bool> append(std::unique_ptr<Entry> entry) override {

if (idempotent_) return std::nullopt;

if (!entry) return false;

// If this entry successfully provides a size, we can add it to our size_

// if that has a value, otherwise, we keep uint64_t empty.

if (entry->size().has_value() && size_.has_value()) {

uint64_t entrySize = entry->size().value();

uint64_t size = size_.value();

// If capped_size_ is set, size + entrySize cannot exceed capped_size_

// or the entry cannot be added.

if (capped_size_.has_value() &&

(capped_size_.value() < entrySize + size)) {

return false;

}

size_ = size + entrySize;

} else {

// This entry cannot provide a size. We can still add it but we have to

// clear the known size.

size_ = std::nullopt;

}

entries_.push_back(std::move(entry));

return true;

}

void cap(uint64_t limit = 0) override {

if (is_idempotent()) return;

// If the data queue is already capped, it is possible to call

// cap again with a smaller size.

if (capped_size_.has_value()) {

capped_size_ = std::min(limit, capped_size_.value());

return;

}

// Otherwise just set the limit.

capped_size_ = limit;

}

std::optional<uint64_t> maybeCapRemaining() const override {

if (capped_size_.has_value() && size_.has_value()) {

uint64_t capped_size = capped_size_.value();

uint64_t size = size_.value();

return capped_size > size ? capped_size - size : 0UL;

}

return std::nullopt;

}

void MemoryInfo(node::MemoryTracker* tracker) const override {

tracker->TrackField(

"entries", entries_, "std::vector<std::unique_ptr<Entry>>");

}

void addBackpressureListener(BackpressureListener* listener) override {

if (idempotent_) return;

DCHECK_NOT_NULL(listener);

backpressure_listeners_.insert(listener);

}

void removeBackpressureListener(BackpressureListener* listener) override {

if (idempotent_) return;

DCHECK_NOT_NULL(listener);

backpressure_listeners_.erase(listener);

}

void NotifyBackpressure(size_t amount) {

if (idempotent_) return;

for (auto& listener : backpressure_listeners_) listener->EntryRead(amount);

}

void NotifyBeforePull() {

if (idempotent_) return;

for (auto& listener : backpressure_listeners_) listener->BeforePull();

}

bool HasBackpressureListeners() const noexcept {

return !backpressure_listeners_.empty();

}

std::shared_ptr<Reader> get_reader() override;

SET_MEMORY_INFO_NAME(DataQueue)

SET_SELF_SIZE(DataQueueImpl)

private:

std::vector<std::unique_ptr<Entry>> entries_;

bool idempotent_;

std::optional<uint64_t> size_ = std::nullopt;

std::optional<uint64_t> capped_size_ = std::nullopt;

bool locked_to_reader_ = false;

std::unordered_set<BackpressureListener*> backpressure_listeners_;

friend class DataQueue;

friend class IdempotentDataQueueReader;

friend class NonIdempotentDataQueueReader;

: public DataQueue::Reader,

public std::enable_shared_from_this<IdempotentDataQueueReader> {

public:

IdempotentDataQueueReader(std::shared_ptr<DataQueueImpl> data_queue)

: data_queue_(std::move(data_queue)) {

CHECK(data_queue_->is_idempotent());

}

// Disallow moving and copying.

IdempotentDataQueueReader(const IdempotentDataQueueReader&) = delete;

IdempotentDataQueueReader(IdempotentDataQueueReader&&) = delete;

IdempotentDataQueueReader& operator=(const IdempotentDataQueueReader&) =

delete;

IdempotentDataQueueReader& operator=(IdempotentDataQueueReader&&) = delete;

int Pull(Next next,

int options,

DataQueue::Vec* data,

size_t count,

size_t max_count_hint = bob::kMaxCountHint) override {

std::shared_ptr<DataQueue::Reader> self = shared_from_this();

// If ended is true, this reader has already reached the end and cannot

// provide any more data.

if (ended_) {

std::move(next)(bob::Status::STATUS_EOS, nullptr, 0, [](uint64_t) {});

return bob::Status::STATUS_EOS;

}

// If this is the first pull from this reader, we are first going to

// check to see if there is anything at all to actually do.

if (!current_index_.has_value()) {

// First, let's check the number of entries. If there are no entries,

// we've reached the end and have nothing to do.

// Because this is an idempotent dataqueue, we should always know the

// size...

if (data_queue_->entries_.empty()) {

ended_ = true;

std::move(next)(bob::Status::STATUS_EOS, nullptr, 0, [](uint64_t) {});

return bob::Status::STATUS_EOS;

}

current_index_ = 0;

}

// We have current_index_, awesome, we are going to keep reading from

// it until we receive and end.

auto current_reader = getCurrentReader();

if (current_reader == nullptr) {

// Getting the current reader for an entry could fail for several

// reasons. For an FdEntry, for instance, getting the reader may

// fail if the file has been modified since the FdEntry was created.

// We handle the case simply by erroring.

std::move(next)(UV_EINVAL, nullptr, 0, [](uint64_t) {});

return UV_EINVAL;

}

CHECK(!pull_pending_);

pull_pending_ = true;

int status = current_reader->Pull(

[this, next = std::move(next)](

int status, const DataQueue::Vec* vecs, uint64_t count, Done done) {

pull_pending_ = false;

// In each of these cases, we do not expect that the source will

// actually have provided any actual data.

CHECK_IMPLIES(status == bob::Status::STATUS_BLOCK ||

status == bob::Status::STATUS_WAIT ||

status == bob::Status::STATUS_EOS,

vecs == nullptr && count == 0);

if (status == bob::Status::STATUS_EOS) {

uint32_t current = current_index_.value() + 1;

current_reader_ = nullptr;

// We have reached the end of this entry. If this is the last entry,

// then we are done. Otherwise, we advance the current_index_, clear

// the current_reader_ and wait for the next read.

if (current == data_queue_->entries_.size()) {

// Yes, this was the final entry. We're all done.

ended_ = true;

} else {

// This was not the final entry, so we update the index and

// continue on by performing another read.

current_index_ = current;

status = bob::STATUS_CONTINUE;

}

std::move(next)(status, nullptr, 0, [](uint64_t) {});

return;

}

std::move(next)(status, vecs, count, std::move(done));

},

options,

data,

count,

max_count_hint);

// The pull was handled synchronously. If we're not ended, we want to

// make sure status returned is CONTINUE.

if (!pull_pending_) {

if (!ended_) return bob::Status::STATUS_CONTINUE;

// For all other status, we just fall through and return it straightaway.

}

// The other statuses that can be returned by the pull are:

// bob::Status::STATUS_CONTINUE - means that the entry has more data

// to pull.

// bob::Status::STATUS_BLOCK - means that the entry has more data to

// pull but it is not available yet. The

// caller should not keep calling pull for

// now but may check again later.

// bob::Status::STATUS_WAIT - means that the entry has more data to

// pull but it won't be provided

// synchronously, instead the next() callback

// will be called when the data is available.

//

// For any of these statuses, we want to keep the current index and

// current_reader_ set for the next pull.

return status;

}

DataQueue::Reader* getCurrentReader() {

CHECK(!ended_);

CHECK(current_index_.has_value());

if (current_reader_ == nullptr) {

auto& entry = data_queue_->entries_[current_index_.value()];

// Because this is an idempotent reader, let's just be sure to

// doublecheck that the entry itself is actually idempotent

DCHECK(entry->is_idempotent());

current_reader_ = static_cast<EntryImpl&>(*entry).get_reader();

}

return current_reader_.get();

}

SET_NO_MEMORY_INFO()

SET_MEMORY_INFO_NAME(IdempotentDataQueueReader)

SET_SELF_SIZE(IdempotentDataQueueReader)

private:

std::shared_ptr<DataQueueImpl> data_queue_;

std::optional<uint32_t> current_index_ = std::nullopt;

std::shared_ptr<DataQueue::Reader> current_reader_ = nullptr;

bool ended_ = false;

bool pull_pending_ = false;

: public DataQueue::Reader,

public std::enable_shared_from_this<NonIdempotentDataQueueReader> {

public:

NonIdempotentDataQueueReader(std::shared_ptr<DataQueueImpl> data_queue)

: data_queue_(std::move(data_queue)) {

CHECK(!data_queue_->is_idempotent());

}

// Disallow moving and copying.

NonIdempotentDataQueueReader(const NonIdempotentDataQueueReader&) = delete;

NonIdempotentDataQueueReader(NonIdempotentDataQueueReader&&) = delete;

NonIdempotentDataQueueReader& operator=(const NonIdempotentDataQueueReader&) =

delete;

NonIdempotentDataQueueReader& operator=(NonIdempotentDataQueueReader&&) =

delete;

int Pull(Next next,

int options,

DataQueue::Vec* data,

size_t count,

size_t max_count_hint = bob::kMaxCountHint) override {

std::shared_ptr<DataQueue::Reader> self = shared_from_this();

// Let listeners flush pending data before we check the entries list.

// This allows, for example, the QUIC Stream to flush its receive

// accumulation buffer into the queue before the pull proceeds.

data_queue_->NotifyBeforePull();

// If ended is true, this reader has already reached the end and cannot

// provide any more data.

if (ended_) {

std::move(next)(bob::Status::STATUS_EOS, nullptr, 0, [](uint64_t) {});

return bob::Status::STATUS_EOS;

}

// If the collection of entries is empty, there's nothing currently left to

// read. How we respond depends on whether the data queue has been capped

// or not.

if (data_queue_->entries_.empty()) {

// If the data_queue_ is empty, and not capped, then we can reasonably

// expect more data to be provided later, but we don't know exactly when

// that'll happen, so the proper response here is to return a blocked

// status.

if (!data_queue_->is_capped()) {

std::move(next)(bob::Status::STATUS_BLOCK, nullptr, 0, [](uint64_t) {});

return bob::STATUS_BLOCK;

}

// However, if we are capped, the status will depend on whether the size

// of the data_queue_ is known or not.

if (data_queue_->size().has_value()) {

// If the size is known, and it is still less than the cap, then we

// still might get more data. We just don't know exactly when that'll

// come, so let's return a blocked status.

if (data_queue_->size().value() < data_queue_->capped_size_.value()) {

std::move(next)(

bob::Status::STATUS_BLOCK, nullptr, 0, [](uint64_t) {});

return bob::STATUS_BLOCK;

}

// Otherwise, if size is equal to or greater than capped, we are done.

// Fall through to allow the end handling to run.

}

// If the size is not known, and the data queue is capped, no additional

// entries are going to be added to the queue. Since we are all out of

// entries, we're done. There's nothing left to read.

current_reader_ = nullptr;

ended_ = true;

std::move(next)(bob::Status::STATUS_EOS, nullptr, 0, [](uint64_t) {});

return bob::STATUS_EOS;

}

auto current_reader = getCurrentReader();

if (current_reader == nullptr) {

std::move(next)(UV_EINVAL, nullptr, 0, [](uint64_t) {});

return UV_EINVAL;

}

// If we got here, we have an entry to read from.

CHECK(!pull_pending_);

pull_pending_ = true;

int status = current_reader->Pull(

[this, next = std::move(next), options, data, count, max_count_hint](

int status,

const DataQueue::Vec* vecs,

uint64_t vcount,

Done done) mutable {

pull_pending_ = false;

// In each of these cases, we do not expect that the source will

// actually have provided any actual data.

CHECK_IMPLIES(status == bob::Status::STATUS_BLOCK ||

status == bob::Status::STATUS_WAIT ||

status == bob::Status::STATUS_EOS,

vecs == nullptr && vcount == 0);

if (status == bob::Status::STATUS_EOS) {

data_queue_->entries_.erase(data_queue_->entries_.begin());

current_reader_ = nullptr;

if (!data_queue_->entries_.empty()) {

// More entries remain. Pull from the next entry immediately

// rather than returning empty CONTINUE, which would leave

// callers with no data and no way to know they should retry.

Pull(std::move(next), options, data, count, max_count_hint);

} else if (!data_queue_->is_capped()) {

// The queue is empty but not capped — more data may arrive

// later. Return BLOCK so the consumer waits rather than

// falsely treating this as end-of-stream.

std::move(next)(

bob::Status::STATUS_BLOCK, nullptr, 0, [](uint64_t) {});

} else {

// Empty and capped — truly done.

ended_ = true;

std::move(next)(

bob::Status::STATUS_EOS, nullptr, 0, [](uint64_t) {});

}

return;

}

// If there is a backpressure listener, lets report on how much data

// was actually read.

if (data_queue_->HasBackpressureListeners()) {

// How much did we actually read?

size_t read = 0;

for (uint64_t n = 0; n < vcount; n++) {

read += vecs[n].len;

}

data_queue_->NotifyBackpressure(read);

}

// Now that we have updated this readers state, we can forward

// everything on to the outer next.

std::move(next)(status, vecs, vcount, std::move(done));

},

options,

data,

count,

max_count_hint);

if (!pull_pending_) {

// The callback was resolved synchronously. Let's check our status.

if (!ended_) return bob::Status::STATUS_CONTINUE;

// For all other status, we just fall through and return it straightaway.

}

// The other statuses that can be returned by the pull are:

// bob::Status::STATUS_CONTINUE - means that the entry has more data

// to pull.

// bob::Status::STATUS_BLOCK - means that the entry has more data to

// pull but it is not available yet. The

// caller should not keep calling pull for

// now but may check again later.

// bob::Status::STATUS_WAIT - means that the entry has more data to

// pull but it won't be provided

// synchronously, instead the next() callback

// will be called when the data is available.

//

// For any of these statuses, we want to keep the current index and

// current_reader_ set for the next pull.

return status;

}

DataQueue::Reader* getCurrentReader() {

CHECK(!ended_);

CHECK(!data_queue_->entries_.empty());

if (current_reader_ == nullptr) {

auto& entry = data_queue_->entries_.front();

current_reader_ = static_cast<EntryImpl&>(*entry).get_reader();

}

return current_reader_.get();

}

SET_NO_MEMORY_INFO()

SET_MEMORY_INFO_NAME(NonIdempotentDataQueueReader)

SET_SELF_SIZE(NonIdempotentDataQueueReader)

private:

std::shared_ptr<DataQueueImpl> data_queue_;

std::shared_ptr<DataQueue::Reader> current_reader_ = nullptr;

bool ended_ = false;

bool pull_pending_ = false;

if (is_idempotent()) {

return std::make_shared<IdempotentDataQueueReader>(shared_from_this());

}

if (locked_to_reader_) return nullptr;

locked_to_reader_ = true;

return std::make_shared<NonIdempotentDataQueueReader>(shared_from_this());

public:

class EmptyReader final : public DataQueue::Reader,

public std::enable_shared_from_this<EmptyReader> {

public:

int Pull(Next next,

int options,

DataQueue::Vec* data,

size_t count,

size_t max_count_hint = bob::kMaxCountHint) override {

auto self = shared_from_this();

if (ended_) {

std::move(next)(bob::Status::STATUS_EOS, nullptr, 0, [](uint64_t) {});

return bob::Status::STATUS_EOS;

}

ended_ = true;

std::move(next)(

bob::Status::STATUS_CONTINUE, nullptr, 0, [](uint64_t) {});

return bob::Status::STATUS_CONTINUE;

}

SET_NO_MEMORY_INFO()

SET_MEMORY_INFO_NAME(EmptyReader)

SET_SELF_SIZE(EmptyReader)

private:

bool ended_ = false;

};

EmptyEntry() = default;

// Disallow moving and copying.

EmptyEntry(const EmptyEntry&) = delete;

EmptyEntry(EmptyEntry&&) = delete;

EmptyEntry& operator=(const EmptyEntry&) = delete;

EmptyEntry& operator=(EmptyEntry&&) = delete;

std::shared_ptr<DataQueue::Reader> get_reader() override {

return std::make_shared<EmptyReader>();

}

std::unique_ptr<Entry> slice(

uint64_t start,

std::optional<uint64_t> maybeEnd = std::nullopt) override {

if (start != 0) return nullptr;

return std::make_unique<EmptyEntry>();

}

std::optional<uint64_t> size() const override { return 0; }

bool is_idempotent() const override { return true; }

SET_NO_MEMORY_INFO()

SET_MEMORY_INFO_NAME(EmptyEntry)

SET_SELF_SIZE(EmptyEntry)

};

class InMemoryEntry final : public EntryImpl {

public:

struct InMemoryFunctor final {

std::shared_ptr<BackingStore> backing_store;

void operator()(uint64_t) { backing_store = nullptr; }

};

class InMemoryReader final

: public DataQueue::Reader,

public std::enable_shared_from_this<InMemoryReader> {

public:

InMemoryReader(InMemoryEntry& entry) : entry_(entry) {}

int Pull(Next next,

int options,

DataQueue::Vec* data,

size_t count,

size_t max_count_hint = bob::kMaxCountHint) override {

auto self = shared_from_this();

if (ended_) {

std::move(next)(bob::Status::STATUS_EOS, nullptr, 0, [](uint64_t) {});

return bob::Status::STATUS_EOS;

}

ended_ = true;

DataQueue::Vec vec{

reinterpret_cast<uint8_t*>(entry_.backing_store_->Data()) +

entry_.offset_,

entry_.byte_length_,

};

std::move(next)(bob::Status::STATUS_CONTINUE,

&vec,

1,

InMemoryFunctor({entry_.backing_store_}));

return bob::Status::STATUS_CONTINUE;

}

SET_NO_MEMORY_INFO()

SET_MEMORY_INFO_NAME(InMemoryReader)

SET_SELF_SIZE(InMemoryReader)

private:

InMemoryEntry& entry_;

bool ended_ = false;

};

InMemoryEntry(std::shared_ptr<BackingStore> backing_store,

uint64_t offset,

uint64_t byte_length)

: backing_store_(std::move(backing_store)),

offset_(offset),

byte_length_(byte_length) {

// The offset_ + byte_length_ cannot extend beyond the size of the

// backing store, because that would just be silly.

CHECK_LE(offset_ + byte_length_, backing_store_->ByteLength());

}

// Disallow moving and copying.

InMemoryEntry(const InMemoryEntry&) = delete;

InMemoryEntry(InMemoryEntry&&) = delete;

InMemoryEntry& operator=(const InMemoryEntry&) = delete;

InMemoryEntry& operator=(InMemoryEntry&&) = delete;

std::shared_ptr<DataQueue::Reader> get_reader() override {

return std::make_shared<InMemoryReader>(*this);

}

std::unique_ptr<Entry> slice(

uint64_t start,

std::optional<uint64_t> maybeEnd = std::nullopt) override {

const auto makeEntry = [&](uint64_t start,

uint64_t len) -> std::unique_ptr<Entry> {

if (len == 0) {

return std::make_unique<EmptyEntry>();

}

return std::make_unique<InMemoryEntry>(backing_store_, start, len);

};

start += offset_;

// The start cannot extend beyond the maximum end point of this entry.

start = std::min(start, offset_ + byte_length_);

if (maybeEnd.has_value()) {

uint64_t end = maybeEnd.value();

// The end cannot extend beyond the maximum end point of this entry,

// and the end must be equal to or greater than the start.

end = std::max(start, std::min(offset_ + end, offset_ + byte_length_));

return makeEntry(start, end - start);

}

// If no end is given, then the new length is the current length

// minus the adjusted start.

return makeEntry(start, byte_length_ - start);

}

std::optional<uint64_t> size() const override { return byte_length_; }

bool is_idempotent() const override { return true; }

void MemoryInfo(node::MemoryTracker* tracker) const override {

tracker->TrackField(

"store", backing_store_, "std::shared_ptr<v8::BackingStore>");

}

SET_MEMORY_INFO_NAME(InMemoryEntry)

SET_SELF_SIZE(InMemoryEntry)

private:

std::shared_ptr<BackingStore> backing_store_;

uint64_t offset_;

uint64_t byte_length_;

friend class InMemoryReader;

};

class DataQueueEntry : public EntryImpl {

public:

explicit DataQueueEntry(std::shared_ptr<DataQueue> data_queue)

: data_queue_(std::move(data_queue)) {

CHECK(data_queue_);

}

// Disallow moving and copying.

DataQueueEntry(const DataQueueEntry&) = delete;

DataQueueEntry(DataQueueEntry&&) = delete;

DataQueueEntry& operator=(const DataQueueEntry&) = delete;

DataQueueEntry& operator=(DataQueueEntry&&) = delete;

std::shared_ptr<DataQueue::Reader> get_reader() override {

return std::make_shared<ReaderImpl>(data_queue_->get_reader());

}

std::unique_ptr<Entry> slice(

uint64_t start, std::optional<uint64_t> end = std::nullopt) override {

std::shared_ptr<DataQueue> sliced = data_queue_->slice(start, end);

if (!sliced) return nullptr;

return std::make_unique<DataQueueEntry>(std::move(sliced));

}

// Returns the number of bytes represented by this Entry if it is

// known. Certain types of entries, such as those backed by streams

// might not know the size in advance and therefore cannot provide

// a value. In such cases, size() must return std::nullopt.

//

// If the entry is idempotent, a size should always be available.

std::optional<uint64_t> size() const override { return data_queue_->size(); }

// When true, multiple reads on the object must produce the exact

// same data or the reads will fail. Some sources of entry data,

// such as streams, may not be capable of preserving idempotency

// and therefore must not claim to be. If an entry claims to be

// idempotent and cannot preserve that quality, subsequent reads

// must fail with an error when a variance is detected.

bool is_idempotent() const override { return data_queue_->is_idempotent(); }

void MemoryInfo(node::MemoryTracker* tracker) const override {

tracker->TrackField(

"data_queue", data_queue_, "std::shared_ptr<DataQueue>");

}

DataQueue& getDataQueue() { return *data_queue_; }

SET_MEMORY_INFO_NAME(DataQueueEntry)

SET_SELF_SIZE(DataQueueEntry)

private:

std::shared_ptr<DataQueue> data_queue_;

class ReaderImpl : public DataQueue::Reader,

public std::enable_shared_from_this<ReaderImpl> {

public:

explicit ReaderImpl(std::shared_ptr<DataQueue::Reader> inner)

: inner_(std::move(inner)) {}

int Pull(DataQueue::Reader::Next next,

int options,

DataQueue::Vec* data,

size_t count,

size_t max_count_hint) override {

auto self = shared_from_this();

return inner_->Pull(

std::move(next), options, data, count, max_count_hint);

}

SET_NO_MEMORY_INFO()

SET_MEMORY_INFO_NAME(ReaderImpl)

SET_SELF_SIZE(ReaderImpl)

private:

std::shared_ptr<DataQueue::Reader> inner_;

};

};

class FdEntry final : public EntryImpl {

// TODO(@jasnell, @flakey5):

// * This should only allow reading from regular files. No directories, no

// pipes, etc.

// * The reader should support accepting the buffer(s) from the pull, if any.

// It should

// only allocate a managed buffer if the pull doesn't provide any.

// * We might want to consider making the stat on each read sync to eliminate

// the race

// condition described in the comment above.

public:

static std::unique_ptr<FdEntry> Create(Environment* env, Local<Value> path) {

// We're only going to create the FdEntry if the file exists.

uv_fs_t req = uv_fs_t();

auto cleanup = OnScopeLeave([&] { uv_fs_req_cleanup(&req); });

auto buf = std::make_shared<BufferValue>(env->isolate(), path);

if (uv_fs_stat(nullptr, &req, buf->out(), nullptr) < 0) return nullptr;

return std::make_unique<FdEntry>(

env, std::move(buf), req.statbuf, 0, req.statbuf.st_size);

}

FdEntry(Environment* env,

std::shared_ptr<BufferValue> path_,

uv_stat_t stat,

uint64_t start,

uint64_t end)

: env_(env),

path_(std::move(path_)),

stat_(stat),

start_(start),

end_(end) {

CHECK_LE(start, end);

}

std::shared_ptr<DataQueue::Reader> get_reader() override {

return ReaderImpl::Create(this);

}

std::unique_ptr<Entry> slice(

uint64_t start, std::optional<uint64_t> end = std::nullopt) override {

uint64_t new_start = start_ + start;

uint64_t new_end = end_;

if (end.has_value()) {

new_end = std::min(end.value() + start_, end_);

}

CHECK(new_start >= start_);

CHECK(new_end <= end_);

return std::make_unique<FdEntry>(env_, path_, stat_, new_start, new_end);

}

std::optional<uint64_t> size() const override { return end_ - start_; }

bool is_idempotent() const override { return true; }

Environment* env() const { return env_; }

SET_NO_MEMORY_INFO()

SET_MEMORY_INFO_NAME(FdEntry)

SET_SELF_SIZE(FdEntry)

private:

Environment* env_;

std::shared_ptr<BufferValue> path_;

uv_stat_t stat_;

uint64_t start_ = 0;

uint64_t end_ = 0;

bool is_modified(const uv_stat_t& other) {

return other.st_size != stat_.st_size ||

other.st_mtim.tv_nsec != stat_.st_mtim.tv_nsec;

}

static bool CheckModified(FdEntry* entry, int fd) {

uv_fs_t req = uv_fs_t();

auto cleanup = OnScopeLeave([&] { uv_fs_req_cleanup(&req); });

// TODO(jasnell): Note the use of a sync fs call here is a bit unfortunate.

// Doing this asynchronously creates a bit of a race condition tho, a file

// could be unmodified when we call the operation but then by the time the

// async callback is triggered to give us that answer the file is modified.

// While such silliness is still possible here, the sync call at least makes

// it less likely to hit the race.

if (uv_fs_fstat(nullptr, &req, fd, nullptr) < 0) return true;

return entry->is_modified(req.statbuf);

}

class ReaderImpl final : public DataQueue::Reader,

public StreamListener,

public std::enable_shared_from_this<ReaderImpl> {

public:

static std::shared_ptr<ReaderImpl> Create(FdEntry* entry) {

uv_fs_t req;

auto cleanup = OnScopeLeave([&] { uv_fs_req_cleanup(&req); });

int file =

uv_fs_open(nullptr, &req, entry->path_->out(), O_RDONLY, 0, nullptr);

if (file < 0 || FdEntry::CheckModified(entry, file)) {

uv_fs_close(nullptr, &req, file, nullptr);

return nullptr;

}

Realm* realm = entry->env()->principal_realm();

return std::make_shared<ReaderImpl>(

BaseObjectPtr<fs::FileHandle>(

fs::FileHandle::New(realm->GetBindingData<fs::BindingData>(),

file,

Local<Object>(),

{},

entry->start_,

entry->end_ - entry->start_)),

entry);

}

explicit ReaderImpl(BaseObjectPtr<fs::FileHandle> handle, FdEntry* entry)

: env_(handle->env()), handle_(std::move(handle)), entry_(entry) {

handle_->PushStreamListener(this);

handle_->env()->AddCleanupHook(cleanup, this);

}

~ReaderImpl() override {

handle_->env()->RemoveCleanupHook(cleanup, this);

DrainAndClose();

handle_->RemoveStreamListener(this);

}

uv_buf_t OnStreamAlloc(size_t suggested_size) override {

return env_->allocate_managed_buffer(suggested_size);

}

void OnStreamRead(ssize_t nread, const uv_buf_t& buf) override {

std::shared_ptr<v8::BackingStore> store =

env_->release_managed_buffer(buf);

if (ended_) {

// If we got here and ended_ is true, it means we ended and drained

// while the read was pending. We're just going to do nothing.

CHECK(pending_pulls_.empty());

return;

}

CHECK(reading_);

auto pending = DequeuePendingPull();

if (CheckModified(entry_, handle_->GetFD())) {

DrainAndClose();

// The file was modified while the read was pending. We need to error.

std::move(pending.next)(UV_EINVAL, nullptr, 0, [](uint64_t) {});

return;

}

if (nread < 0) {

if (nread == UV_EOF) {

std::move(pending.next)(bob::STATUS_EOS, nullptr, 0, [](uint64_t) {});

} else {

std::move(pending.next)(nread, nullptr, 0, [](uint64_t) {});

}

return DrainAndClose();

}

DataQueue::Vec vec;