llvm-6502/lib/Support/JSONParser.cpp
Sebastian Pop 41a2600f6a fix typo
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@149856 91177308-0d34-0410-b5e6-96231b3b80d8
2012-02-06 05:29:29 +00:00

303 lines
10 KiB
C++

//===--- JSONParser.cpp - Simple JSON parser ------------------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements a JSON parser.
//
//===----------------------------------------------------------------------===//
#include "llvm/Support/JSONParser.h"
#include "llvm/ADT/Twine.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/MemoryBuffer.h"
using namespace llvm;
JSONParser::JSONParser(StringRef Input, SourceMgr *SM)
: SM(SM), Failed(false) {
InputBuffer = MemoryBuffer::getMemBuffer(Input, "JSON");
SM->AddNewSourceBuffer(InputBuffer, SMLoc());
End = InputBuffer->getBuffer().end();
Position = InputBuffer->getBuffer().begin();
}
JSONValue *JSONParser::parseRoot() {
if (Position != InputBuffer->getBuffer().begin())
report_fatal_error("Cannot reuse JSONParser.");
if (isWhitespace())
nextNonWhitespace();
if (errorIfAtEndOfFile("'[' or '{' at start of JSON text"))
return 0;
switch (*Position) {
case '[':
return new (ValueAllocator.Allocate<JSONArray>(1)) JSONArray(this);
case '{':
return new (ValueAllocator.Allocate<JSONObject>(1)) JSONObject(this);
default:
setExpectedError("'[' or '{' at start of JSON text", *Position);
return 0;
}
}
bool JSONParser::validate() {
JSONValue *Root = parseRoot();
if (Root == NULL) {
return false;
}
return skip(*Root);
}
bool JSONParser::skip(const JSONAtom &Atom) {
switch(Atom.getKind()) {
case JSONAtom::JK_Array:
case JSONAtom::JK_Object:
return skipContainer(*cast<JSONContainer>(&Atom));
case JSONAtom::JK_String:
return true;
case JSONAtom::JK_KeyValuePair:
return skip(*cast<JSONKeyValuePair>(&Atom)->Value);
}
llvm_unreachable("Impossible enum value.");
}
// Sets the current error to:
// "expected <Expected>, but found <Found>".
void JSONParser::setExpectedError(StringRef Expected, StringRef Found) {
SM->PrintMessage(SMLoc::getFromPointer(Position), SourceMgr::DK_Error,
"expected " + Expected + ", but found " + Found + ".", ArrayRef<SMRange>());
Failed = true;
}
// Sets the current error to:
// "expected <Expected>, but found <Found>".
void JSONParser::setExpectedError(StringRef Expected, char Found) {
setExpectedError(Expected, ("'" + StringRef(&Found, 1) + "'").str());
}
// If there is no character available, returns true and sets the current error
// to: "expected <Expected>, but found EOF.".
bool JSONParser::errorIfAtEndOfFile(StringRef Expected) {
if (Position == End) {
setExpectedError(Expected, "EOF");
return true;
}
return false;
}
// Sets the current error if the current character is not C to:
// "expected 'C', but got <current character>".
bool JSONParser::errorIfNotAt(char C, StringRef Message) {
if (*Position != C) {
std::string Expected =
("'" + StringRef(&C, 1) + "' " + Message).str();
if (Position == End)
setExpectedError(Expected, "EOF");
else
setExpectedError(Expected, *Position);
return true;
}
return false;
}
// Forbidding inlining improves performance by roughly 20%.
// FIXME: Remove once llvm optimizes this to the faster version without hints.
LLVM_ATTRIBUTE_NOINLINE static bool
wasEscaped(StringRef::iterator First, StringRef::iterator Position);
// Returns whether a character at 'Position' was escaped with a leading '\'.
// 'First' specifies the position of the first character in the string.
static bool wasEscaped(StringRef::iterator First,
StringRef::iterator Position) {
assert(Position - 1 >= First);
StringRef::iterator I = Position - 1;
// We calulate the number of consecutive '\'s before the current position
// by iterating backwards through our string.
while (I >= First && *I == '\\') --I;
// (Position - 1 - I) now contains the number of '\'s before the current
// position. If it is odd, the character at 'Positon' was escaped.
return (Position - 1 - I) % 2 == 1;
}
// Parses a JSONString, assuming that the current position is on a quote.
JSONString *JSONParser::parseString() {
assert(Position != End);
assert(!isWhitespace());
if (errorIfNotAt('"', "at start of string"))
return 0;
StringRef::iterator First = Position + 1;
// Benchmarking shows that this loop is the hot path of the application with
// about 2/3rd of the runtime cycles. Since escaped quotes are not the common
// case, and multiple escaped backslashes before escaped quotes are very rare,
// we pessimize this case to achieve a smaller inner loop in the common case.
// We're doing that by having a quick inner loop that just scans for the next
// quote. Once we find the quote we check the last character to see whether
// the quote might have been escaped. If the last character is not a '\', we
// know the quote was not escaped and have thus found the end of the string.
// If the immediately preceding character was a '\', we have to scan backwards
// to see whether the previous character was actually an escaped backslash, or
// an escape character for the quote. If we find that the current quote was
// escaped, we continue parsing for the next quote and repeat.
// This optimization brings around 30% performance improvements.
do {
// Step over the current quote.
++Position;
// Find the next quote.
while (Position != End && *Position != '"')
++Position;
if (errorIfAtEndOfFile("'\"' at end of string"))
return 0;
// Repeat until the previous character was not a '\' or was an escaped
// backslash.
} while (*(Position - 1) == '\\' && wasEscaped(First, Position));
return new (ValueAllocator.Allocate<JSONString>())
JSONString(StringRef(First, Position - First));
}
// Advances the position to the next non-whitespace position.
void JSONParser::nextNonWhitespace() {
do {
++Position;
} while (isWhitespace());
}
// Checks if there is a whitespace character at the current position.
bool JSONParser::isWhitespace() {
return *Position == ' ' || *Position == '\t' ||
*Position == '\n' || *Position == '\r';
}
bool JSONParser::failed() const {
return Failed;
}
// Parses a JSONValue, assuming that the current position is at the first
// character of the value.
JSONValue *JSONParser::parseValue() {
assert(Position != End);
assert(!isWhitespace());
switch (*Position) {
case '[':
return new (ValueAllocator.Allocate<JSONArray>(1)) JSONArray(this);
case '{':
return new (ValueAllocator.Allocate<JSONObject>(1)) JSONObject(this);
case '"':
return parseString();
default:
setExpectedError("'[', '{' or '\"' at start of value", *Position);
return 0;
}
}
// Parses a JSONKeyValuePair, assuming that the current position is at the first
// character of the key, value pair.
JSONKeyValuePair *JSONParser::parseKeyValuePair() {
assert(Position != End);
assert(!isWhitespace());
JSONString *Key = parseString();
if (Key == 0)
return 0;
nextNonWhitespace();
if (errorIfNotAt(':', "between key and value"))
return 0;
nextNonWhitespace();
const JSONValue *Value = parseValue();
if (Value == 0)
return 0;
return new (ValueAllocator.Allocate<JSONKeyValuePair>(1))
JSONKeyValuePair(Key, Value);
}
/// \brief Parses the first element of a JSON array or object, or closes the
/// array.
///
/// The method assumes that the current position is before the first character
/// of the element, with possible white space in between. When successful, it
/// returns the new position after parsing the element. Otherwise, if there is
/// no next value, it returns a default constructed StringRef::iterator.
StringRef::iterator JSONParser::parseFirstElement(JSONAtom::Kind ContainerKind,
char StartChar, char EndChar,
const JSONAtom *&Element) {
assert(*Position == StartChar);
Element = 0;
nextNonWhitespace();
if (errorIfAtEndOfFile("value or end of container at start of container"))
return StringRef::iterator();
if (*Position == EndChar)
return StringRef::iterator();
Element = parseElement(ContainerKind);
if (Element == 0)
return StringRef::iterator();
return Position;
}
/// \brief Parses the next element of a JSON array or object, or closes the
/// array.
///
/// The method assumes that the current position is before the ',' which
/// separates the next element from the current element. When successful, it
/// returns the new position after parsing the element. Otherwise, if there is
/// no next value, it returns a default constructed StringRef::iterator.
StringRef::iterator JSONParser::parseNextElement(JSONAtom::Kind ContainerKind,
char EndChar,
const JSONAtom *&Element) {
Element = 0;
nextNonWhitespace();
if (errorIfAtEndOfFile("',' or end of container for next element"))
return 0;
if (*Position == ',') {
nextNonWhitespace();
if (errorIfAtEndOfFile("element in container"))
return StringRef::iterator();
Element = parseElement(ContainerKind);
if (Element == 0)
return StringRef::iterator();
return Position;
} else if (*Position == EndChar) {
return StringRef::iterator();
} else {
setExpectedError("',' or end of container for next element", *Position);
return StringRef::iterator();
}
}
const JSONAtom *JSONParser::parseElement(JSONAtom::Kind ContainerKind) {
switch (ContainerKind) {
case JSONAtom::JK_Array:
return parseValue();
case JSONAtom::JK_Object:
return parseKeyValuePair();
default:
llvm_unreachable("Impossible code path");
}
}
bool JSONParser::skipContainer(const JSONContainer &Container) {
for (JSONContainer::AtomIterator I = Container.atom_current(),
E = Container.atom_end();
I != E; ++I) {
assert(*I != 0);
if (!skip(**I))
return false;
}
return !failed();
}