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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/**
+ * StreamingLexer is a lexing framework designed to make it simple to write
+ * image decoders without worrying about the details of how the data is arriving
+ * from the network.
+ */
+
+#ifndef mozilla_image_StreamingLexer_h
+#define mozilla_image_StreamingLexer_h
+
+#include <algorithm>
+#include <cstdint>
+#include <utility>
+
+#include "SourceBuffer.h"
+#include "mozilla/Assertions.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/Maybe.h"
+#include "mozilla/Variant.h"
+#include "mozilla/Vector.h"
+
+namespace mozilla {
+namespace image {
+
+/// Buffering behaviors for StreamingLexer transitions.
+enum class BufferingStrategy {
+ BUFFERED, // Data will be buffered and processed in one chunk.
+ UNBUFFERED // Data will be processed as it arrives, in multiple chunks.
+};
+
+/// Control flow behaviors for StreamingLexer transitions.
+enum class ControlFlowStrategy {
+ CONTINUE, // If there's enough data, proceed to the next state immediately.
+ YIELD // Yield to the caller before proceeding to the next state.
+};
+
+/// Possible terminal states for the lexer.
+enum class TerminalState { SUCCESS, FAILURE };
+
+/// Possible yield reasons for the lexer.
+enum class Yield {
+ NEED_MORE_DATA, // The lexer cannot continue without more data.
+ OUTPUT_AVAILABLE // There is output available for the caller to consume.
+};
+
+/// The result of a call to StreamingLexer::Lex().
+typedef Variant<TerminalState, Yield> LexerResult;
+
+/**
+ * LexerTransition is a type used to give commands to the lexing framework.
+ * Code that uses StreamingLexer can create LexerTransition values using the
+ * static methods on Transition, and then return them to the lexing framework
+ * for execution.
+ */
+template <typename State>
+class LexerTransition {
+ public:
+ // This is implicit so that Terminate{Success,Failure}() can return a
+ // TerminalState and have it implicitly converted to a
+ // LexerTransition<State>, which avoids the need for a "<State>"
+ // qualification to the Terminate{Success,Failure}() callsite.
+ MOZ_IMPLICIT LexerTransition(TerminalState aFinalState)
+ : mNextState(aFinalState) {}
+
+ bool NextStateIsTerminal() const {
+ return mNextState.template is<TerminalState>();
+ }
+
+ TerminalState NextStateAsTerminal() const {
+ return mNextState.template as<TerminalState>();
+ }
+
+ State NextState() const {
+ return mNextState.template as<NonTerminalState>().mState;
+ }
+
+ State UnbufferedState() const {
+ return *mNextState.template as<NonTerminalState>().mUnbufferedState;
+ }
+
+ size_t Size() const {
+ return mNextState.template as<NonTerminalState>().mSize;
+ }
+
+ BufferingStrategy Buffering() const {
+ return mNextState.template as<NonTerminalState>().mBufferingStrategy;
+ }
+
+ ControlFlowStrategy ControlFlow() const {
+ return mNextState.template as<NonTerminalState>().mControlFlowStrategy;
+ }
+
+ private:
+ friend struct Transition;
+
+ LexerTransition(State aNextState, const Maybe<State>& aUnbufferedState,
+ size_t aSize, BufferingStrategy aBufferingStrategy,
+ ControlFlowStrategy aControlFlowStrategy)
+ : mNextState(NonTerminalState(aNextState, aUnbufferedState, aSize,
+ aBufferingStrategy, aControlFlowStrategy)) {
+ }
+
+ struct NonTerminalState {
+ State mState;
+ Maybe<State> mUnbufferedState;
+ size_t mSize;
+ BufferingStrategy mBufferingStrategy;
+ ControlFlowStrategy mControlFlowStrategy;
+
+ NonTerminalState(State aState, const Maybe<State>& aUnbufferedState,
+ size_t aSize, BufferingStrategy aBufferingStrategy,
+ ControlFlowStrategy aControlFlowStrategy)
+ : mState(aState),
+ mUnbufferedState(aUnbufferedState),
+ mSize(aSize),
+ mBufferingStrategy(aBufferingStrategy),
+ mControlFlowStrategy(aControlFlowStrategy) {
+ MOZ_ASSERT_IF(mBufferingStrategy == BufferingStrategy::UNBUFFERED,
+ mUnbufferedState);
+ MOZ_ASSERT_IF(mUnbufferedState,
+ mBufferingStrategy == BufferingStrategy::UNBUFFERED);
+ }
+ };
+
+ Variant<NonTerminalState, TerminalState> mNextState;
+};
+
+struct Transition {
+ /// Transition to @aNextState, buffering @aSize bytes of data.
+ template <typename State>
+ static LexerTransition<State> To(const State& aNextState, size_t aSize) {
+ return LexerTransition<State>(aNextState, Nothing(), aSize,
+ BufferingStrategy::BUFFERED,
+ ControlFlowStrategy::CONTINUE);
+ }
+
+ /// Yield to the caller, transitioning to @aNextState when Lex() is next
+ /// invoked. The same data that was delivered for the current state will be
+ /// delivered again.
+ template <typename State>
+ static LexerTransition<State> ToAfterYield(const State& aNextState) {
+ return LexerTransition<State>(aNextState, Nothing(), 0,
+ BufferingStrategy::BUFFERED,
+ ControlFlowStrategy::YIELD);
+ }
+
+ /**
+ * Transition to @aNextState via @aUnbufferedState, reading @aSize bytes of
+ * data unbuffered.
+ *
+ * The unbuffered data will be delivered in state @aUnbufferedState, which may
+ * be invoked repeatedly until all @aSize bytes have been delivered. Then,
+ * @aNextState will be invoked with no data. No state transitions are allowed
+ * from @aUnbufferedState except for transitions to a terminal state, so
+ * @aNextState will always be reached unless lexing terminates early.
+ */
+ template <typename State>
+ static LexerTransition<State> ToUnbuffered(const State& aNextState,
+ const State& aUnbufferedState,
+ size_t aSize) {
+ return LexerTransition<State>(aNextState, Some(aUnbufferedState), aSize,
+ BufferingStrategy::UNBUFFERED,
+ ControlFlowStrategy::CONTINUE);
+ }
+
+ /**
+ * Continue receiving unbuffered data. @aUnbufferedState should be the same
+ * state as the @aUnbufferedState specified in the preceding call to
+ * ToUnbuffered().
+ *
+ * This should be used during an unbuffered read initiated by ToUnbuffered().
+ */
+ template <typename State>
+ static LexerTransition<State> ContinueUnbuffered(
+ const State& aUnbufferedState) {
+ return LexerTransition<State>(aUnbufferedState, Nothing(), 0,
+ BufferingStrategy::BUFFERED,
+ ControlFlowStrategy::CONTINUE);
+ }
+
+ /**
+ * Continue receiving unbuffered data. @aUnbufferedState should be the same
+ * state as the @aUnbufferedState specified in the preceding call to
+ * ToUnbuffered(). @aSize indicates the amount of data that has already been
+ * consumed; the next state will receive the same data that was delivered to
+ * the current state, without the first @aSize bytes.
+ *
+ * This should be used during an unbuffered read initiated by ToUnbuffered().
+ */
+ template <typename State>
+ static LexerTransition<State> ContinueUnbufferedAfterYield(
+ const State& aUnbufferedState, size_t aSize) {
+ return LexerTransition<State>(aUnbufferedState, Nothing(), aSize,
+ BufferingStrategy::BUFFERED,
+ ControlFlowStrategy::YIELD);
+ }
+
+ /**
+ * Terminate lexing, ending up in terminal state SUCCESS. (The implicit
+ * LexerTransition constructor will convert the result to a LexerTransition
+ * as needed.)
+ *
+ * No more data will be delivered after this function is used.
+ */
+ static TerminalState TerminateSuccess() { return TerminalState::SUCCESS; }
+
+ /**
+ * Terminate lexing, ending up in terminal state FAILURE. (The implicit
+ * LexerTransition constructor will convert the result to a LexerTransition
+ * as needed.)
+ *
+ * No more data will be delivered after this function is used.
+ */
+ static TerminalState TerminateFailure() { return TerminalState::FAILURE; }
+
+ private:
+ Transition();
+};
+
+/**
+ * StreamingLexer is a lexing framework designed to make it simple to write
+ * image decoders without worrying about the details of how the data is arriving
+ * from the network.
+ *
+ * To use StreamingLexer:
+ *
+ * - Create a State type. This should be an |enum class| listing all of the
+ * states that you can be in while lexing the image format you're trying to
+ * read.
+ *
+ * - Add an instance of StreamingLexer<State> to your decoder class. Initialize
+ * it with a Transition::To() the state that you want to start lexing in, and
+ * a Transition::To() the state you'd like to use to handle truncated data.
+ *
+ * - In your decoder's DoDecode() method, call Lex(), passing in the input
+ * data and length that are passed to DoDecode(). You also need to pass
+ * a lambda which dispatches to lexing code for each state based on the State
+ * value that's passed in. The lambda generally should just continue a
+ * |switch| statement that calls different methods for each State value. Each
+ * method should return a LexerTransition<State>, which the lambda should
+ * return in turn.
+ *
+ * - Write the methods that actually implement lexing for your image format.
+ * These methods should return either Transition::To(), to move on to another
+ * state, or Transition::Terminate{Success,Failure}(), if lexing has
+ * terminated in either success or failure. (There are also additional
+ * transitions for unbuffered reads; see below.)
+ *
+ * That's the basics. The StreamingLexer will track your position in the input
+ * and buffer enough data so that your lexing methods can process everything in
+ * one pass. Lex() returns Yield::NEED_MORE_DATA if more data is needed, in
+ * which case you should just return from DoDecode(). If lexing reaches a
+ * terminal state, Lex() returns TerminalState::SUCCESS or
+ * TerminalState::FAILURE, and you can check which one to determine if lexing
+ * succeeded or failed and do any necessary cleanup.
+ *
+ * Sometimes, the input data is truncated. StreamingLexer will notify you when
+ * this happens by invoking the truncated data state you passed to the
+ * constructor. At this point you can attempt to recover and return
+ * TerminalState::SUCCESS or TerminalState::FAILURE, depending on whether you
+ * were successful. Note that you can't return anything other than a terminal
+ * state in this situation, since there's no more data to read. For the same
+ * reason, your truncated data state shouldn't require any data. (That is, the
+ * @aSize argument you pass to Transition::To() must be zero.) Violating these
+ * requirements will trigger assertions and an immediate transition to
+ * TerminalState::FAILURE.
+ *
+ * Some lexers may want to *avoid* buffering in some cases, and just process the
+ * data as it comes in. This is useful if, for example, you just want to skip
+ * over a large section of data; there's no point in buffering data you're just
+ * going to ignore.
+ *
+ * You can begin an unbuffered read with Transition::ToUnbuffered(). This works
+ * a little differently than Transition::To() in that you specify *two* states.
+ * The @aUnbufferedState argument specifies a state that will be called
+ * repeatedly with unbuffered data, as soon as it arrives. The implementation
+ * for that state should return either a transition to a terminal state, or a
+ * Transition::ContinueUnbuffered() to the same @aUnbufferedState. (From a
+ * technical perspective, it's not necessary to specify the state again, but
+ * it's helpful to human readers.) Once the amount of data requested in the
+ * original call to Transition::ToUnbuffered() has been delivered, Lex() will
+ * transition to the @aNextState state specified via Transition::ToUnbuffered().
+ * That state will be invoked with *no* data; it's just called to signal that
+ * the unbuffered read is over.
+ *
+ * It's sometimes useful for a lexer to provide incremental results, rather
+ * than simply running to completion and presenting all its output at once. For
+ * example, when decoding animated images, it may be useful to produce each
+ * frame incrementally. StreamingLexer supports this by allowing a lexer to
+ * yield.
+ *
+ * To yield back to the caller, a state implementation can simply return
+ * Transition::ToAfterYield(). ToAfterYield()'s @aNextState argument specifies
+ * the next state that the lexer should transition to, just like when using
+ * Transition::To(), but there are two differences. One is that Lex() will
+ * return to the caller before processing any more data when it encounters a
+ * yield transition. This provides an opportunity for the caller to interact
+ * with the lexer's intermediate results. The second difference is that
+ * @aNextState will be called with *the same data as the state that you returned
+ * Transition::ToAfterYield() from*. This allows a lexer to partially consume
+ * the data, return intermediate results, and then finish consuming the data
+ * when @aNextState is called.
+ *
+ * It's also possible to yield during an unbuffered read. Just return a
+ * Transition::ContinueUnbufferedAfterYield(). Just like with
+ * Transition::ContinueUnbuffered(), the @aUnbufferedState must be the same as
+ * the one originally passed to Transition::ToUnbuffered(). The second argument,
+ * @aSize, specifies the amount of data that the lexer has already consumed.
+ * When @aUnbufferedState is next invoked, it will get the same data that it
+ * received previously, except that the first @aSize bytes will be excluded.
+ * This makes it easy to consume unbuffered data incrementally.
+ *
+ * XXX(seth): We should be able to get of the |State| stuff totally once bug
+ * 1198451 lands, since we can then just return a function representing the next
+ * state directly.
+ */
+template <typename State, size_t InlineBufferSize = 16>
+class StreamingLexer {
+ public:
+ StreamingLexer(const LexerTransition<State>& aStartState,
+ const LexerTransition<State>& aTruncatedState)
+ : mTransition(TerminalState::FAILURE),
+ mTruncatedTransition(aTruncatedState) {
+ if (!aStartState.NextStateIsTerminal() &&
+ aStartState.ControlFlow() == ControlFlowStrategy::YIELD) {
+ // Allowing a StreamingLexer to start in a yield state doesn't make sense
+ // semantically (since yield states are supposed to deliver the same data
+ // as previous states, and there's no previous state here), but more
+ // importantly, it's necessary to advance a SourceBufferIterator at least
+ // once before you can read from it, and adding the necessary checks to
+ // Lex() to avoid that issue has the potential to mask real bugs. So
+ // instead, it's better to forbid starting in a yield state.
+ MOZ_ASSERT_UNREACHABLE("Starting in a yield state");
+ return;
+ }
+
+ if (!aTruncatedState.NextStateIsTerminal() &&
+ (aTruncatedState.ControlFlow() == ControlFlowStrategy::YIELD ||
+ aTruncatedState.Buffering() == BufferingStrategy::UNBUFFERED ||
+ aTruncatedState.Size() != 0)) {
+ // The truncated state can't receive any data because, by definition,
+ // there is no more data to receive. That means that yielding or an
+ // unbuffered read would not make sense, and that the state must require
+ // zero bytes.
+ MOZ_ASSERT_UNREACHABLE("Truncated state makes no sense");
+ return;
+ }
+
+ SetTransition(aStartState);
+ }
+
+ /**
+ * From the given SourceBufferIterator, aIterator, create a new iterator at
+ * the same position, with the given read limit, aReadLimit. The read limit
+ * applies after adjusting for the position. If the given iterator has been
+ * advanced, but required buffering inside StreamingLexer, the position
+ * of the cloned iterator will be at the beginning of buffered data; this
+ * should match the perspective of the caller.
+ */
+ Maybe<SourceBufferIterator> Clone(SourceBufferIterator& aIterator,
+ size_t aReadLimit) const {
+ // In order to advance to the current position of the iterator from the
+ // perspective of the caller, we need to take into account if we are
+ // buffering data.
+ size_t pos = aIterator.Position();
+ if (!mBuffer.empty()) {
+ pos += aIterator.Length();
+ MOZ_ASSERT(pos > mBuffer.length());
+ pos -= mBuffer.length();
+ }
+
+ size_t readLimit = aReadLimit;
+ if (aReadLimit != SIZE_MAX) {
+ readLimit += pos;
+ }
+
+ SourceBufferIterator other = aIterator.Owner()->Iterator(readLimit);
+
+ // Since the current iterator has already advanced to this point, we
+ // know that the state can only be READY or COMPLETE. That does not mean
+ // everything is stored in a single chunk, and may require multiple Advance
+ // calls to get where we want to be.
+ SourceBufferIterator::State state;
+ do {
+ state = other.Advance(pos);
+ if (state != SourceBufferIterator::READY) {
+ // The only way we should fail to advance over data we already seen is
+ // if we hit an error while inserting data into the buffer. This will
+ // cause an early exit.
+ MOZ_ASSERT(NS_FAILED(other.CompletionStatus()));
+ return Nothing();
+ }
+ MOZ_ASSERT(pos >= other.Length());
+ pos -= other.Length();
+ } while (pos > 0);
+
+ // Force the data pointer to be where we expect it to be.
+ state = other.Advance(0);
+ if (state != SourceBufferIterator::READY) {
+ // The current position could be the end of the buffer, in which case
+ // there is no point cloning with no more data to read.
+ MOZ_ASSERT(state == SourceBufferIterator::COMPLETE);
+ return Nothing();
+ }
+ return Some(std::move(other));
+ }
+
+ template <typename Func>
+ LexerResult Lex(SourceBufferIterator& aIterator, IResumable* aOnResume,
+ Func aFunc) {
+ if (mTransition.NextStateIsTerminal()) {
+ // We've already reached a terminal state. We never deliver any more data
+ // in this case; just return the terminal state again immediately.
+ return LexerResult(mTransition.NextStateAsTerminal());
+ }
+
+ Maybe<LexerResult> result;
+
+ // If the lexer requested a yield last time, we deliver the same data again
+ // before we read anything else from |aIterator|. Note that although to the
+ // callers of Lex(), Yield::NEED_MORE_DATA is just another type of yield,
+ // internally they're different in that we don't redeliver the same data in
+ // the Yield::NEED_MORE_DATA case, and |mYieldingToState| is not set. This
+ // means that for Yield::NEED_MORE_DATA, we go directly to the loop below.
+ if (mYieldingToState) {
+ result = mTransition.Buffering() == BufferingStrategy::UNBUFFERED
+ ? UnbufferedReadAfterYield(aIterator, aFunc)
+ : BufferedReadAfterYield(aIterator, aFunc);
+ }
+
+ while (!result) {
+ MOZ_ASSERT_IF(mTransition.Buffering() == BufferingStrategy::UNBUFFERED,
+ mUnbufferedState);
+
+ // Figure out how much we need to read.
+ const size_t toRead =
+ mTransition.Buffering() == BufferingStrategy::UNBUFFERED
+ ? mUnbufferedState->mBytesRemaining
+ : mTransition.Size() - mBuffer.length();
+
+ // Attempt to advance the iterator by |toRead| bytes.
+ switch (aIterator.AdvanceOrScheduleResume(toRead, aOnResume)) {
+ case SourceBufferIterator::WAITING:
+ // We can't continue because the rest of the data hasn't arrived from
+ // the network yet. We don't have to do anything special; the
+ // SourceBufferIterator will ensure that |aOnResume| gets called when
+ // more data is available.
+ result = Some(LexerResult(Yield::NEED_MORE_DATA));
+ break;
+
+ case SourceBufferIterator::COMPLETE:
+ // The data is truncated; if not, the lexer would've reached a
+ // terminal state by now. We only get to
+ // SourceBufferIterator::COMPLETE after every byte of data has been
+ // delivered to the lexer.
+ result = Truncated(aIterator, aFunc);
+ break;
+
+ case SourceBufferIterator::READY:
+ // Process the new data that became available.
+ MOZ_ASSERT(aIterator.Data());
+
+ result = mTransition.Buffering() == BufferingStrategy::UNBUFFERED
+ ? UnbufferedRead(aIterator, aFunc)
+ : BufferedRead(aIterator, aFunc);
+ break;
+
+ default:
+ MOZ_ASSERT_UNREACHABLE("Unknown SourceBufferIterator state");
+ result = SetTransition(Transition::TerminateFailure());
+ }
+ };
+
+ return *result;
+ }
+
+ private:
+ template <typename Func>
+ Maybe<LexerResult> UnbufferedRead(SourceBufferIterator& aIterator,
+ Func aFunc) {
+ MOZ_ASSERT(mTransition.Buffering() == BufferingStrategy::UNBUFFERED);
+ MOZ_ASSERT(mUnbufferedState);
+ MOZ_ASSERT(!mYieldingToState);
+ MOZ_ASSERT(mBuffer.empty(),
+ "Buffered read at the same time as unbuffered read?");
+ MOZ_ASSERT(aIterator.Length() <= mUnbufferedState->mBytesRemaining,
+ "Read too much data during unbuffered read?");
+ MOZ_ASSERT(mUnbufferedState->mBytesConsumedInCurrentChunk == 0,
+ "Already consumed data in the current chunk, but not yielding?");
+
+ if (mUnbufferedState->mBytesRemaining == 0) {
+ // We're done with the unbuffered read, so transition to the next state.
+ return SetTransition(aFunc(mTransition.NextState(), nullptr, 0));
+ }
+
+ return ContinueUnbufferedRead(aIterator.Data(), aIterator.Length(),
+ aIterator.Length(), aFunc);
+ }
+
+ template <typename Func>
+ Maybe<LexerResult> UnbufferedReadAfterYield(SourceBufferIterator& aIterator,
+ Func aFunc) {
+ MOZ_ASSERT(mTransition.Buffering() == BufferingStrategy::UNBUFFERED);
+ MOZ_ASSERT(mUnbufferedState);
+ MOZ_ASSERT(mYieldingToState);
+ MOZ_ASSERT(mBuffer.empty(),
+ "Buffered read at the same time as unbuffered read?");
+ MOZ_ASSERT(aIterator.Length() <= mUnbufferedState->mBytesRemaining,
+ "Read too much data during unbuffered read?");
+ MOZ_ASSERT(
+ mUnbufferedState->mBytesConsumedInCurrentChunk <= aIterator.Length(),
+ "Consumed more data than the current chunk holds?");
+ MOZ_ASSERT(mTransition.UnbufferedState() == *mYieldingToState);
+
+ mYieldingToState = Nothing();
+
+ if (mUnbufferedState->mBytesRemaining == 0) {
+ // We're done with the unbuffered read, so transition to the next state.
+ return SetTransition(aFunc(mTransition.NextState(), nullptr, 0));
+ }
+
+ // Since we've yielded, we may have already consumed some data in this
+ // chunk. Make the necessary adjustments. (Note that the std::min call is
+ // just belt-and-suspenders to keep this code memory safe even if there's
+ // a bug somewhere.)
+ const size_t toSkip = std::min(
+ mUnbufferedState->mBytesConsumedInCurrentChunk, aIterator.Length());
+ const char* data = aIterator.Data() + toSkip;
+ const size_t length = aIterator.Length() - toSkip;
+
+ // If |length| is zero, we've hit the end of the current chunk. This only
+ // happens if we yield right at the end of a chunk. Rather than call |aFunc|
+ // with a |length| of zero bytes (which seems potentially surprising to
+ // decoder authors), we go ahead and read more data.
+ if (length == 0) {
+ return FinishCurrentChunkOfUnbufferedRead(aIterator.Length());
+ }
+
+ return ContinueUnbufferedRead(data, length, aIterator.Length(), aFunc);
+ }
+
+ template <typename Func>
+ Maybe<LexerResult> ContinueUnbufferedRead(const char* aData, size_t aLength,
+ size_t aChunkLength, Func aFunc) {
+ // Call aFunc with the unbuffered state to indicate that we're in the
+ // middle of an unbuffered read. We enforce that any state transition
+ // passed back to us is either a terminal state or takes us back to the
+ // unbuffered state.
+ LexerTransition<State> unbufferedTransition =
+ aFunc(mTransition.UnbufferedState(), aData, aLength);
+
+ // If we reached a terminal state, we're done.
+ if (unbufferedTransition.NextStateIsTerminal()) {
+ return SetTransition(unbufferedTransition);
+ }
+
+ MOZ_ASSERT(mTransition.UnbufferedState() ==
+ unbufferedTransition.NextState());
+
+ // Perform bookkeeping.
+ if (unbufferedTransition.ControlFlow() == ControlFlowStrategy::YIELD) {
+ mUnbufferedState->mBytesConsumedInCurrentChunk +=
+ unbufferedTransition.Size();
+ return SetTransition(unbufferedTransition);
+ }
+
+ MOZ_ASSERT(unbufferedTransition.Size() == 0);
+ return FinishCurrentChunkOfUnbufferedRead(aChunkLength);
+ }
+
+ Maybe<LexerResult> FinishCurrentChunkOfUnbufferedRead(size_t aChunkLength) {
+ // We've finished an unbuffered read of a chunk of length |aChunkLength|, so
+ // update |myBytesRemaining| to reflect that we're |aChunkLength| closer to
+ // the end of the unbuffered read. (The std::min call is just
+ // belt-and-suspenders to keep this code memory safe even if there's a bug
+ // somewhere.)
+ mUnbufferedState->mBytesRemaining -=
+ std::min(mUnbufferedState->mBytesRemaining, aChunkLength);
+
+ // Since we're moving on to a new chunk, we can forget about the count of
+ // bytes consumed by yielding in the current chunk.
+ mUnbufferedState->mBytesConsumedInCurrentChunk = 0;
+
+ return Nothing(); // Keep processing.
+ }
+
+ template <typename Func>
+ Maybe<LexerResult> BufferedRead(SourceBufferIterator& aIterator, Func aFunc) {
+ MOZ_ASSERT(mTransition.Buffering() == BufferingStrategy::BUFFERED);
+ MOZ_ASSERT(!mYieldingToState);
+ MOZ_ASSERT(!mUnbufferedState,
+ "Buffered read at the same time as unbuffered read?");
+ MOZ_ASSERT(mBuffer.length() < mTransition.Size() ||
+ (mBuffer.length() == 0 && mTransition.Size() == 0),
+ "Buffered more than we needed?");
+
+ // If we have all the data, we don't actually need to buffer anything.
+ if (mBuffer.empty() && aIterator.Length() == mTransition.Size()) {
+ return SetTransition(
+ aFunc(mTransition.NextState(), aIterator.Data(), aIterator.Length()));
+ }
+
+ // We do need to buffer, so make sure the buffer has enough capacity. We
+ // deliberately wait until we know for sure we need to buffer to call
+ // reserve() since it could require memory allocation.
+ if (!mBuffer.reserve(mTransition.Size())) {
+ return SetTransition(Transition::TerminateFailure());
+ }
+
+ // Append the new data we just got to the buffer.
+ if (!mBuffer.append(aIterator.Data(), aIterator.Length())) {
+ return SetTransition(Transition::TerminateFailure());
+ }
+
+ if (mBuffer.length() != mTransition.Size()) {
+ return Nothing(); // Keep processing.
+ }
+
+ // We've buffered everything, so transition to the next state.
+ return SetTransition(
+ aFunc(mTransition.NextState(), mBuffer.begin(), mBuffer.length()));
+ }
+
+ template <typename Func>
+ Maybe<LexerResult> BufferedReadAfterYield(SourceBufferIterator& aIterator,
+ Func aFunc) {
+ MOZ_ASSERT(mTransition.Buffering() == BufferingStrategy::BUFFERED);
+ MOZ_ASSERT(mYieldingToState);
+ MOZ_ASSERT(!mUnbufferedState,
+ "Buffered read at the same time as unbuffered read?");
+ MOZ_ASSERT(mBuffer.length() <= mTransition.Size(),
+ "Buffered more than we needed?");
+
+ State nextState = std::move(*mYieldingToState);
+
+ // After a yield, we need to take the same data that we delivered to the
+ // last state, and deliver it again to the new state. We know that this is
+ // happening right at a state transition, and that the last state was a
+ // buffered read, so there are two cases:
+
+ // 1. We got the data from the SourceBufferIterator directly.
+ if (mBuffer.empty() && aIterator.Length() == mTransition.Size()) {
+ return SetTransition(
+ aFunc(nextState, aIterator.Data(), aIterator.Length()));
+ }
+
+ // 2. We got the data from the buffer.
+ if (mBuffer.length() == mTransition.Size()) {
+ return SetTransition(aFunc(nextState, mBuffer.begin(), mBuffer.length()));
+ }
+
+ // Anything else indicates a bug.
+ MOZ_ASSERT_UNREACHABLE("Unexpected state encountered during yield");
+ return SetTransition(Transition::TerminateFailure());
+ }
+
+ template <typename Func>
+ Maybe<LexerResult> Truncated(SourceBufferIterator& aIterator, Func aFunc) {
+ // The data is truncated. Let the lexer clean up and decide which terminal
+ // state we should end up in.
+ LexerTransition<State> transition =
+ mTruncatedTransition.NextStateIsTerminal()
+ ? mTruncatedTransition
+ : aFunc(mTruncatedTransition.NextState(), nullptr, 0);
+
+ if (!transition.NextStateIsTerminal()) {
+ MOZ_ASSERT_UNREACHABLE("Truncated state didn't lead to terminal state?");
+ return SetTransition(Transition::TerminateFailure());
+ }
+
+ // If the SourceBuffer was completed with a failing state, we end in
+ // TerminalState::FAILURE no matter what. This only happens in exceptional
+ // situations like SourceBuffer itself encountering a failure due to OOM.
+ if (NS_FAILED(aIterator.CompletionStatus())) {
+ return SetTransition(Transition::TerminateFailure());
+ }
+
+ return SetTransition(transition);
+ }
+
+ Maybe<LexerResult> SetTransition(const LexerTransition<State>& aTransition) {
+ // There should be no transitions while we're buffering for a buffered read
+ // unless they're to terminal states. (The terminal state transitions would
+ // generally be triggered by error handling code.)
+ MOZ_ASSERT_IF(!mBuffer.empty(), aTransition.NextStateIsTerminal() ||
+ mBuffer.length() == mTransition.Size());
+
+ // Similarly, the only transitions allowed in the middle of an unbuffered
+ // read are to a terminal state, or a yield to the same state. Otherwise, we
+ // should remain in the same state until the unbuffered read completes.
+ MOZ_ASSERT_IF(
+ mUnbufferedState,
+ aTransition.NextStateIsTerminal() ||
+ (aTransition.ControlFlow() == ControlFlowStrategy::YIELD &&
+ aTransition.NextState() == mTransition.UnbufferedState()) ||
+ mUnbufferedState->mBytesRemaining == 0);
+
+ // If this transition is a yield, save the next state and return. We'll
+ // handle the rest when Lex() gets called again.
+ if (!aTransition.NextStateIsTerminal() &&
+ aTransition.ControlFlow() == ControlFlowStrategy::YIELD) {
+ mYieldingToState = Some(aTransition.NextState());
+ return Some(LexerResult(Yield::OUTPUT_AVAILABLE));
+ }
+
+ // Update our transition.
+ mTransition = aTransition;
+
+ // Get rid of anything left over from the previous state.
+ mBuffer.clear();
+ mYieldingToState = Nothing();
+ mUnbufferedState = Nothing();
+
+ // If we reached a terminal state, let the caller know.
+ if (mTransition.NextStateIsTerminal()) {
+ return Some(LexerResult(mTransition.NextStateAsTerminal()));
+ }
+
+ // If we're entering an unbuffered state, record how long we'll stay in it.
+ if (mTransition.Buffering() == BufferingStrategy::UNBUFFERED) {
+ mUnbufferedState.emplace(mTransition.Size());
+ }
+
+ return Nothing(); // Keep processing.
+ }
+
+ // State that tracks our position within an unbuffered read.
+ struct UnbufferedState {
+ explicit UnbufferedState(size_t aBytesRemaining)
+ : mBytesRemaining(aBytesRemaining), mBytesConsumedInCurrentChunk(0) {}
+
+ size_t mBytesRemaining;
+ size_t mBytesConsumedInCurrentChunk;
+ };
+
+ Vector<char, InlineBufferSize> mBuffer;
+ LexerTransition<State> mTransition;
+ const LexerTransition<State> mTruncatedTransition;
+ Maybe<State> mYieldingToState;
+ Maybe<UnbufferedState> mUnbufferedState;
+};
+
+} // namespace image
+} // namespace mozilla
+
+#endif // mozilla_image_StreamingLexer_h