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fsJsonParser.cs
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fsJsonParser.cs
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using System;
using System.Collections.Generic;
using System.Globalization;
using System.Text;
namespace FullSerializer {
// TODO: properly propagate warnings/etc for fsResult states
/// <summary>
/// A simple recursive descent parser for JSON.
/// </summary>
public class fsJsonParser {
private int _start;
private string _input;
private fsResult MakeFailure(string message) {
int start = Math.Max(0, _start - 20);
int length = Math.Min(50, _input.Length - start);
string error = "Error while parsing: " + message + "; context = <" +
_input.Substring(start, length) + ">";
return fsResult.Fail(error);
}
private bool TryMoveNext() {
if (_start < _input.Length) {
++_start;
return true;
}
return false;
}
private bool HasValue() {
return HasValue(0);
}
private bool HasValue(int offset) {
return (_start + offset) >= 0 && (_start + offset) < _input.Length;
}
private char Character() {
return Character(0);
}
private char Character(int offset) {
return _input[_start + offset];
}
/// <summary>
/// Skips input such that Character() will return a non-whitespace character
/// </summary>
private void SkipSpace() {
while (HasValue()) {
char c = Character();
// whitespace; fine to skip
if (char.IsWhiteSpace(c)) {
TryMoveNext();
continue;
}
// comment? they begin with //
if (HasValue(1) &&
(Character(0) == '/' && Character(1) == '/')) {
// skip the rest of the line
while (HasValue() && Environment.NewLine.Contains("" + Character()) == false) {
TryMoveNext();
}
// we still need to skip whitespace on the next line
continue;
}
break;
}
}
#region Escaping
private bool IsHex(char c) {
return ((c >= '0' && c <= '9') ||
(c >= 'a' && c <= 'f') ||
(c >= 'A' && c <= 'F'));
}
private uint ParseSingleChar(char c1, uint multipliyer) {
uint p1 = 0;
if (c1 >= '0' && c1 <= '9')
p1 = (uint)(c1 - '0') * multipliyer;
else if (c1 >= 'A' && c1 <= 'F')
p1 = (uint)((c1 - 'A') + 10) * multipliyer;
else if (c1 >= 'a' && c1 <= 'f')
p1 = (uint)((c1 - 'a') + 10) * multipliyer;
return p1;
}
private uint ParseUnicode(char c1, char c2, char c3, char c4) {
uint p1 = ParseSingleChar(c1, 0x1000);
uint p2 = ParseSingleChar(c2, 0x100);
uint p3 = ParseSingleChar(c3, 0x10);
uint p4 = ParseSingleChar(c4, 0x1);
return p1 + p2 + p3 + p4;
}
private fsResult TryUnescapeChar(out char escaped) {
// skip leading backslash '\'
TryMoveNext();
if (HasValue() == false) {
escaped = ' ';
return MakeFailure("Unexpected end of input after \\");
}
switch (Character()) {
case '\\': TryMoveNext(); escaped = '\\'; return fsResult.Success;
case '"': TryMoveNext(); escaped = '\"'; return fsResult.Success;
case 'a': TryMoveNext(); escaped = '\a'; return fsResult.Success;
case 'b': TryMoveNext(); escaped = '\b'; return fsResult.Success;
case 'f': TryMoveNext(); escaped = '\f'; return fsResult.Success;
case 'n': TryMoveNext(); escaped = '\n'; return fsResult.Success;
case 'r': TryMoveNext(); escaped = '\r'; return fsResult.Success;
case 't': TryMoveNext(); escaped = '\t'; return fsResult.Success;
case '0': TryMoveNext(); escaped = '\0'; return fsResult.Success;
case 'u':
TryMoveNext();
if (IsHex(Character(0))
&& IsHex(Character(1))
&& IsHex(Character(2))
&& IsHex(Character(3))) {
uint codePoint = ParseUnicode(Character(0), Character(1), Character(2), Character(3));
TryMoveNext();
TryMoveNext();
TryMoveNext();
TryMoveNext();
escaped = (char)codePoint;
return fsResult.Success;
}
// invalid escape sequence
escaped = (char)0;
return MakeFailure(
string.Format("invalid escape sequence '\\u{0}{1}{2}{3}'\n",
Character(0),
Character(1),
Character(2),
Character(3)));
default:
escaped = (char)0;
return MakeFailure(string.Format("Invalid escape sequence \\{0}", Character()));
}
}
#endregion
private fsResult TryParseExact(string content) {
for (int i = 0; i < content.Length; ++i) {
if (Character() != content[i]) {
return MakeFailure("Expected " + content[i]);
}
if (TryMoveNext() == false) {
return MakeFailure("Unexpected end of content when parsing " + content);
}
}
return fsResult.Success;
}
private fsResult TryParseTrue(out fsData data) {
var fail = TryParseExact("true");
if (fail.Succeeded) {
data = new fsData(true);
return fsResult.Success;
}
data = null;
return fail;
}
private fsResult TryParseFalse(out fsData data) {
var fail = TryParseExact("false");
if (fail.Succeeded) {
data = new fsData(false);
return fsResult.Success;
}
data = null;
return fail;
}
private fsResult TryParseNull(out fsData data) {
var fail = TryParseExact("null");
if (fail.Succeeded) {
data = new fsData();
return fsResult.Success;
}
data = null;
return fail;
}
private bool IsSeparator(char c) {
return char.IsWhiteSpace(c) || c == ',' || c == '}' || c == ']';
}
/// <summary>
/// Parses numbers that follow the regular expression [-+](\d+|\d*\.\d*)
/// </summary>
private fsResult TryParseNumber(out fsData data) {
int start = _start;
// read until we get to a separator
while (
TryMoveNext() &&
(HasValue() && IsSeparator(Character()) == false)) {
}
// try to parse the value
string numberString = _input.Substring(start, _start - start);
// double -- includes a .
if (numberString.Contains(".") || numberString == "Infinity" || numberString == "-Infinity" || numberString == "NaN") {
double doubleValue;
if (double.TryParse(numberString, NumberStyles.Any, CultureInfo.InvariantCulture, out doubleValue) == false) {
data = null;
return MakeFailure("Bad double format with " + numberString);
}
data = new fsData(doubleValue);
return fsResult.Success;
}
else {
Int64 intValue;
if (Int64.TryParse(numberString, NumberStyles.Any, CultureInfo.InvariantCulture, out intValue) == false) {
data = null;
return MakeFailure("Bad Int64 format with " + numberString);
}
data = new fsData(intValue);
return fsResult.Success;
}
}
private readonly StringBuilder _cachedStringBuilder = new StringBuilder(256);
/// <summary>
/// Parses a string
/// </summary>
private fsResult TryParseString(out string str) {
_cachedStringBuilder.Length = 0;
// skip the first "
if (Character() != '"' || TryMoveNext() == false) {
str = string.Empty;
return MakeFailure("Expected initial \" when parsing a string");
}
// read until the next "
while (HasValue() && Character() != '\"') {
char c = Character();
// escape if necessary
if (c == '\\') {
char unescaped;
var fail = TryUnescapeChar(out unescaped);
if (fail.Failed) {
str = string.Empty;
return fail;
}
_cachedStringBuilder.Append(unescaped);
}
// no escaping necessary
else {
_cachedStringBuilder.Append(c);
// get the next character
if (TryMoveNext() == false) {
str = string.Empty;
return MakeFailure("Unexpected end of input when reading a string");
}
}
}
// skip the first "
if (HasValue() == false || Character() != '"' || TryMoveNext() == false) {
str = string.Empty;
return MakeFailure("No closing \" when parsing a string");
}
str = _cachedStringBuilder.ToString();
return fsResult.Success;
}
/// <summary>
/// Parses an array
/// </summary>
private fsResult TryParseArray(out fsData arr) {
if (Character() != '[') {
arr = null;
return MakeFailure("Expected initial [ when parsing an array");
}
// skip '['
if (TryMoveNext() == false) {
arr = null;
return MakeFailure("Unexpected end of input when parsing an array");
}
SkipSpace();
var result = new List<fsData>();
while (HasValue() && Character() != ']') {
// parse the element
fsData element;
var fail = RunParse(out element);
if (fail.Failed) {
arr = null;
return fail;
}
result.Add(element);
// parse the comma
SkipSpace();
if (HasValue() && Character() == ',') {
if (TryMoveNext() == false) break;
SkipSpace();
}
}
// skip the final ]
if (HasValue() == false || Character() != ']' || TryMoveNext() == false) {
arr = null;
return MakeFailure("No closing ] for array");
}
arr = new fsData(result);
return fsResult.Success;
}
private fsResult TryParseObject(out fsData obj) {
if (Character() != '{') {
obj = null;
return MakeFailure("Expected initial { when parsing an object");
}
// skip '{'
if (TryMoveNext() == false) {
obj = null;
return MakeFailure("Unexpected end of input when parsing an object");
}
SkipSpace();
#if UNITY_METRO
var result = new Dictionary<string, fsData>(
fsConfig.IsCaseSensitive ? StringComparer.CurrentCulture : StringComparer.CurrentCultureIgnoreCase);
#else
var result = new Dictionary<string, fsData>(
fsConfig.IsCaseSensitive ? StringComparer.InvariantCulture : StringComparer.InvariantCultureIgnoreCase);
#endif
while (HasValue() && Character() != '}') {
fsResult failure;
// parse the key
SkipSpace();
string key;
failure = TryParseString(out key);
if (failure.Failed) {
obj = null;
return failure;
}
SkipSpace();
// parse the ':' after the key
if (HasValue() == false || Character() != ':' || TryMoveNext() == false) {
obj = null;
return MakeFailure("Expected : after key \"" + key + "\"");
}
SkipSpace();
// parse the value
fsData value;
failure = RunParse(out value);
if (failure.Failed) {
obj = null;
return failure;
}
result.Add(key, value);
// parse the comma
SkipSpace();
if (HasValue() && Character() == ',') {
if (TryMoveNext() == false) break;
SkipSpace();
}
}
// skip the final }
if (HasValue() == false || Character() != '}' || TryMoveNext() == false) {
obj = null;
return MakeFailure("No closing } for object");
}
obj = new fsData(result);
return fsResult.Success;
}
private fsResult RunParse(out fsData data) {
SkipSpace();
switch (Character()) {
case 'I': // Infinity
case 'N': // NaN
case '.':
case '+':
case '-':
case '0':
case '1':
case '2':
case '3':
case '4':
case '5':
case '6':
case '7':
case '8':
case '9': return TryParseNumber(out data);
case '"': {
string str;
fsResult fail = TryParseString(out str);
if (fail.Failed) {
data = null;
return fail;
}
data = new fsData(str);
return fsResult.Success;
}
case '[': return TryParseArray(out data);
case '{': return TryParseObject(out data);
case 't': return TryParseTrue(out data);
case 'f': return TryParseFalse(out data);
case 'n': return TryParseNull(out data);
default:
data = null;
return MakeFailure("unable to parse; invalid initial token \"" + Character() + "\"");
}
}
/// <summary>
/// Parses the specified input. Returns a failure state if parsing failed.
/// </summary>
/// <param name="input">The input to parse.</param>
/// <param name="data">The parsed data. This is undefined if parsing fails.</param>
/// <returns>The parsed input.</returns>
public static fsResult Parse(string input, out fsData data) {
var context = new fsJsonParser(input);
return context.RunParse(out data);
}
/// <summary>
/// Helper method for Parse that does not allow the error information
/// to be recovered.
/// </summary>
public static fsData Parse(string input) {
fsData data;
Parse(input, out data).AssertSuccess();
return data;
}
private fsJsonParser(string input) {
_input = input;
_start = 0;
}
}
}