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Try to resolve issue Tencent#35: implement iterative parsing.
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@thebusytypist
thebusytypist committed Jul 6, 2014
1 parent c12286a commit 3006fa7
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Showing 2 changed files with 416 additions and 4 deletions.
224 changes: 221 additions & 3 deletions include/rapidjson/reader.h
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Original file line number Diff line number Diff line change
Expand Up @@ -46,7 +46,8 @@ namespace rapidjson {
enum ParseFlag {
kParseDefaultFlags = 0, //!< Default parse flags. Non-destructive parsing. Text strings are decoded into allocated buffer.
kParseInsituFlag = 1, //!< In-situ(destructive) parsing.
kParseValidateEncodingFlag = 2 //!< Validate encoding of JSON strings.
kParseValidateEncodingFlag = 2, //!< Validate encoding of JSON strings.
kParseNonRecursiveFlag = 4 //!< Non-recursive(constant complexity in terms of function call stack size) parsing.
};

//! Error code of parsing.
Expand All @@ -69,7 +70,7 @@ enum ParseErrorCode {
kParseErrorStringUnicodeSurrogateInvalid, //!< The surrogate pair in string is invalid.
kParseErrorStringEscapeInvalid, //!< Invalid escape character in string.
kParseErrorStringMissQuotationMark, //!< Missing a closing quotation mark in string.
kParseErrorStringInvalidEncoding, //!< Invalid encoidng in string.
kParseErrorStringInvalidEncoding, //!< Invalid encoding in string.

kParseErrorNumberTooBig, //!< Number too big to be stored in double.
kParseErrorNumberMissFraction, //!< Miss fraction part in number.
Expand Down Expand Up @@ -134,7 +135,7 @@ namespace internal {
template<typename Stream, int = StreamTraits<Stream>::copyOptimization>
class StreamLocalCopy;

//! Do copy optimziation.
//! Do copy optimization.
template<typename Stream>
class StreamLocalCopy<Stream, 1> {
public:
Expand Down Expand Up @@ -297,6 +298,9 @@ class GenericReader {
parseErrorCode_ = kParseErrorNone;
errorOffset_ = 0;

if (parseFlags & kParseNonRecursiveFlag)
return NonRecursiveParse<parseFlags>(is, handler);

SkipWhitespace(is);

if (is.Peek() == '\0')
Expand Down Expand Up @@ -748,6 +752,220 @@ class GenericReader {
}
}

// Non-recursive parsing
enum NonRecursiveParsingState {
NonRecursiveParsingStartState,
NonRecursiveParsingFinishState,
NonRecursiveParsingErrorState,
// Object states
NonRecursiveParsingObjectInitialState,
NonRecursiveParsingObjectContentState,
// Array states
NonRecursiveParsingArrayInitialState,
NonRecursiveParsingArrayContentState
};

template <typename InputStream, typename Handler>
NonRecursiveParsingState TransitToCompoundValueTypeState(NonRecursiveParsingState state, InputStream& is, Handler& handler) {
// For compound value type(object and array), we should push the current state and start a new stack frame for this type.
NonRecursiveParsingState r = NonRecursiveParsingErrorState;

switch (is.Take()) {
case '{':
handler.StartObject();
r = NonRecursiveParsingObjectInitialState;
// Push current state.
*stack_.template Push<NonRecursiveParsingState>(1) = state;
// Initialize and push member count.
*stack_.template Push<int>(1) = 0;
break;
case '[':
handler.StartArray();
r = NonRecursiveParsingArrayInitialState;
// Push current state.
*stack_.template Push<NonRecursiveParsingState>(1) = state;
// Initialize and push element count.
*stack_.template Push<int>(1) = 0;
break;
}
return r;
}

// Inner transition of object or array states(ObjectInitial->ObjectContent, ArrayInitial->ArrayContent).
template <unsigned parseFlags, typename InputStream, typename Handler>
NonRecursiveParsingState TransitByValue(NonRecursiveParsingState state, InputStream& is, Handler& handler) {
RAPIDJSON_ASSERT(
state == NonRecursiveParsingObjectInitialState ||
state == NonRecursiveParsingArrayInitialState ||
state == NonRecursiveParsingObjectContentState ||
state == NonRecursiveParsingArrayContentState);

NonRecursiveParsingState t;
if (state == NonRecursiveParsingObjectInitialState)
t = NonRecursiveParsingObjectContentState;
else if (state == NonRecursiveParsingArrayInitialState)
t = NonRecursiveParsingArrayContentState;
else
t = state;

NonRecursiveParsingState r = NonRecursiveParsingErrorState;

switch (is.Peek()) {
// For plain value state is not changed.
case 'n': ParseNull <parseFlags>(is, handler); r = t; break;
case 't': ParseTrue <parseFlags>(is, handler); r = t; break;
case 'f': ParseFalse <parseFlags>(is, handler); r = t; break;
case '"': ParseString<parseFlags>(is, handler); r = t; break;
// Transit when value is object or array.
case '{':
case '[':
r = TransitToCompoundValueTypeState(state, is, handler); break;
default: ParseNumber<parseFlags>(is, handler); r = t; break;
}

if (HasParseError())
r = NonRecursiveParsingErrorState;

return r;
}

// Transit from object related states(ObjectInitial, ObjectContent).
template <unsigned parseFlags, typename InputStream, typename Handler>
NonRecursiveParsingState TransitFromObjectStates(NonRecursiveParsingState state, InputStream& is, Handler& handler) {
NonRecursiveParsingState r = NonRecursiveParsingErrorState;

switch (is.Peek()) {
case '}': {
is.Take();
// Get member count(include an extra one for non-empty object).
int memberCount = *stack_.template Pop<int>(1);
if (state == NonRecursiveParsingObjectContentState)
++memberCount;
// Restore the parent stack frame.
r = *stack_.template Pop<NonRecursiveParsingState>(1);
// Transit to ContentState since a member/an element was just parsed.
if (r == NonRecursiveParsingArrayInitialState)
r = NonRecursiveParsingArrayContentState;
else if (r == NonRecursiveParsingObjectInitialState)
r = NonRecursiveParsingObjectContentState;
// If we return to the topmost frame mark it finished.
if (r == NonRecursiveParsingStartState)
r = NonRecursiveParsingFinishState;
handler.EndObject(memberCount);
break;
}
case ',':
is.Take();
r = NonRecursiveParsingObjectContentState;
// Update member count.
*stack_.template Top<int>() = *stack_.template Top<int>() + 1;
break;
case '"':
// Should be a key-value pair.
ParseString<parseFlags>(is, handler);
if (HasParseError()) {
r = NonRecursiveParsingErrorState;
RAPIDJSON_PARSE_ERROR_NORETURN(kParseErrorObjectMissName, is.Tell());
break;
}

SkipWhitespace(is);

if (is.Take() != ':') {
r = NonRecursiveParsingErrorState;
RAPIDJSON_PARSE_ERROR_NORETURN(kParseErrorObjectMissColon, is.Tell());
break;
}

SkipWhitespace(is);

r = TransitByValue<parseFlags>(state, is, handler);

break;
default:
r = NonRecursiveParsingErrorState;
RAPIDJSON_PARSE_ERROR_NORETURN(kParseErrorObjectMissCommaOrCurlyBracket, is.Tell());
break;
}

return r;
}

// Transit from array related states(ArrayInitial, ArrayContent).
template <unsigned parseFlags, typename InputStream, typename Handler>
NonRecursiveParsingState TransitFromArrayStates(NonRecursiveParsingState state, InputStream& is, Handler& handler) {
NonRecursiveParsingState r = NonRecursiveParsingErrorState;

switch (is.Peek()) {
case ']': {
is.Take();
// Get element count(include an extra one for non-empty array).
int elementCount = *stack_.template Pop<int>(1);
if (state == NonRecursiveParsingArrayContentState)
++elementCount;
// Restore the parent stack frame.
r = *stack_.template Pop<NonRecursiveParsingState>(1);
// Transit to ContentState since a member/an element was just parsed.
if (r == NonRecursiveParsingArrayInitialState)
r = NonRecursiveParsingArrayContentState;
else if (r == NonRecursiveParsingObjectInitialState)
r = NonRecursiveParsingObjectContentState;
// If we return to the topmost frame mark it finished.
if (r == NonRecursiveParsingStartState)
r = NonRecursiveParsingFinishState;
handler.EndArray(elementCount);
break;
}
case ',':
is.Take();
r = NonRecursiveParsingArrayContentState;
// Update element count.
*stack_.template Top<int>() = *stack_.template Top<int>() + 1;
break;
default:
// Should be a single value.
r = TransitByValue<parseFlags>(state, is, handler);
break;
}

return r;
}

template <unsigned parseFlags, typename InputStream, typename Handler>
NonRecursiveParsingState Transit(NonRecursiveParsingState state, InputStream& is, Handler& handler) {
NonRecursiveParsingState r = NonRecursiveParsingErrorState;

switch (state) {
case NonRecursiveParsingStartState:
r = TransitToCompoundValueTypeState(state, is, handler);
break;
case NonRecursiveParsingObjectInitialState:
case NonRecursiveParsingObjectContentState:
r = TransitFromObjectStates<parseFlags>(state, is, handler);
break;
case NonRecursiveParsingArrayInitialState:
case NonRecursiveParsingArrayContentState:
r = TransitFromArrayStates<parseFlags>(state, is, handler);
break;
}

return r;
}

template <unsigned parseFlags, typename InputStream, typename Handler>
bool NonRecursiveParse(InputStream& is, Handler& handler) {
NonRecursiveParsingState state = NonRecursiveParsingStartState;

SkipWhitespace(is);
while (is.Peek() != '\0' && state != NonRecursiveParsingErrorState) {
state = Transit<parseFlags>(state, is, handler);
SkipWhitespace(is);
}

stack_.Clear();
return state == NonRecursiveParsingFinishState && !HasParseError();
}

static const size_t kDefaultStackCapacity = 256; //!< Default stack capacity in bytes for storing a single decoded string.
internal::Stack<Allocator> stack_; //!< A stack for storing decoded string temporarily during non-destructive parsing.
ParseErrorCode parseErrorCode_;
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