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{
This file is part of the Free Component Library
JSON source parser
Copyright (c) 2007 by Michael Van Canneyt michael@freepascal.org
See the file COPYING.FPC, included in this distribution,
for details about the copyright.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
**********************************************************************}
{$mode objfpc}
{$h+}
unit jsonparser;
interface
uses
Classes, SysUtils, fpJSON, jsonscanner;
Type
{ TJSONParser }
TJSONParser = Class(TObject)
Private
FScanner : TJSONScanner;
FuseUTF8,
FStrict: Boolean;
function ParseNumber: TJSONNumber;
procedure SetStrict(const AValue: Boolean);
function GetUTF8 : Boolean;
procedure SetUTF8(const AValue: Boolean);
Protected
procedure DoError(const Msg: String);
function DoParse(AtCurrent,AllowEOF: Boolean): TJSONData;
function GetNextToken: TJSONToken;
function CurrentTokenString: String;
function CurrentToken: TJSONToken;
function ParseArray: TJSONArray;
function ParseObject: TJSONObject;
Property Scanner : TJSONScanner read FScanner;
Public
function Parse: TJSONData;
Constructor Create(Source : TStream; AUseUTF8 : Boolean = True); overload;
Constructor Create(Source : TJSONStringType; AUseUTF8 : Boolean = True); overload;
destructor Destroy();override;
// Use strict JSON: " for strings, object members are strings, not identifiers
Property Strict : Boolean Read FStrict Write SetStrict;
// if set to TRUE, then strings will be converted to UTF8 ansistrings, not system codepage ansistrings.
Property UseUTF8 : Boolean Read GetUTF8 Write SetUTF8;
end;
EJSONParser = Class(EParserError);
implementation
Resourcestring
SErrUnexpectedEOF = 'Unexpected EOF encountered.';
SErrUnexpectedToken = 'Unexpected token (%s) encountered.';
SErrExpectedColon = 'Expected colon (:), got token "%s".';
SErrUnexpectedComma = 'Invalid comma encountered.';
SErrEmptyElement = 'Empty element encountered.';
SErrExpectedElementName = 'Expected element name, got token "%s"';
SExpectedCommaorBraceClose = 'Expected , or ], got token "%s".';
SErrInvalidNumber = 'Number is not an integer or real number: %s';
{ TJSONParser }
Function TJSONParser.Parse : TJSONData;
begin
Result:=DoParse(False,True);
end;
{
Consume next token and convert to JSON data structure.
If AtCurrent is true, the current token is used. If false,
a token is gotten from the scanner.
If AllowEOF is false, encountering a tkEOF will result in an exception.
}
Function TJSONParser.CurrentToken : TJSONToken;
begin
Result:=FScanner.CurToken;
end;
Function TJSONParser.CurrentTokenString : String;
begin
If CurrentToken in [tkString,tkIdentifier,tkNumber] then
Result:=FScanner.CurTokenString
else
Result:=TokenInfos[CurrentToken];
end;
Function TJSONParser.DoParse(AtCurrent,AllowEOF : Boolean) : TJSONData;
var
T : TJSONToken;
begin
Result:=nil;
try
If not AtCurrent then
T:=GetNextToken
else
T:=FScanner.CurToken;
Case T of
tkEof : If Not AllowEof then
DoError(SErrUnexpectedEOF);
tkNull : Result:=TJSONNull.Create;
tkTrue,
tkFalse : Result:=TJSONBoolean.Create(t=tkTrue);
tkString : Result:=TJSONString.Create(CurrentTokenString);
tkCurlyBraceOpen : Result:=ParseObject;
tkCurlyBraceClose : DoError(SErrUnexpectedToken);
tkSQuaredBraceOpen : Result:=ParseArray;
tkSQuaredBraceClose : DoError(SErrUnexpectedToken);
tkNumber : Result:=ParseNumber;
tkComma : DoError(SErrUnexpectedToken);
end;
except
FreeAndNil(Result);
Raise;
end;
end;
// Creates the correct JSON number type, based on the current token.
Function TJSONParser.ParseNumber : TJSONNumber;
Var
I : Integer;
I64 : Int64;
F : TJSONFloat;
S : String;
begin
S:=CurrentTokenString;
I:=0;
If TryStrToInt64(S,I64) then
Result:=TJSONInt64Number.Create(I64)
Else If TryStrToInt(S,I) then
Result:=TJSONIntegerNumber.Create(I)
else
begin
I:=0;
Val(S,F,I);
If (I<>0) then
DoError(SErrInvalidNumber);
Result:=TJSONFloatNumber.Create(F);
end;
end;
function TJSONParser.GetUTF8 : Boolean;
begin
if Assigned(FScanner) then
Result:=FScanner.UseUTF8
else
Result:=FUseUTF8;
end;
procedure TJSONParser.SetUTF8(const AValue: Boolean);
begin
FUseUTF8:=AValue;
if Assigned(FScanner) then
FScanner.UseUTF8:=FUseUTF8;
end;
procedure TJSONParser.SetStrict(const AValue: Boolean);
begin
if (FStrict=AValue) then
exit;
FStrict:=AValue;
If Assigned(FScanner) then
FScanner.Strict:=Fstrict;
end;
// Current token is {, on exit current token is }
Function TJSONParser.ParseObject : TJSONObject;
Var
T : TJSONtoken;
E : TJSONData;
N : String;
begin
Result:=TJSONObject.Create;
Try
T:=GetNextToken;
While T<>tkCurlyBraceClose do
begin
If (T<>tkString) and (T<>tkIdentifier) then
DoError(SErrExpectedElementName);
N:=CurrentTokenString;
T:=GetNextToken;
If (T<>tkColon) then
DoError(SErrExpectedColon);
E:=DoParse(False,False);
Result.Add(N,E);
T:=GetNextToken;
If Not (T in [tkComma,tkCurlyBraceClose]) then
DoError(SExpectedCommaorBraceClose);
If T=tkComma then
T:=GetNextToken;
end;
Except
FreeAndNil(Result);
Raise;
end;
end;
// Current token is [, on exit current token is ]
Function TJSONParser.ParseArray : TJSONArray;
Var
T : TJSONtoken;
E : TJSONData;
LastComma : Boolean;
begin
Result:=TJSONArray.Create;
LastComma:=False;
Try
Repeat
T:=GetNextToken;
If (T<>tkSquaredBraceClose) then
begin
E:=DoParse(True,False);
If (E<>Nil) then
Result.Add(E)
else if (Result.Count>0) then
DoError(SErrEmptyElement);
T:=GetNextToken;
If Not (T in [tkComma,tkSquaredBraceClose]) then
DoError(SExpectedCommaorBraceClose);
LastComma:=(t=TkComma);
end;
Until (T=tkSquaredBraceClose);
If LastComma then // Test for ,] case
DoError(SErrUnExpectedToken);
Except
FreeAndNil(Result);
Raise;
end;
end;
// Get next token, discarding whitespace
Function TJSONParser.GetNextToken : TJSONToken ;
begin
Repeat
Result:=FScanner.FetchToken;
Until (Result<>tkWhiteSpace);
end;
Procedure TJSONParser.DoError(const Msg : String);
Var
S : String;
begin
S:=Format(Msg,[CurrentTokenString]);
S:=Format('Error at line %d, Pos %d:',[FScanner.CurRow,FSCanner.CurColumn])+S;
Raise EJSONParser.Create(S);
end;
constructor TJSONParser.Create(Source: TStream; AUseUTF8 : Boolean = True);
begin
Inherited Create;
FScanner:=TJSONScanner.Create(Source);
UseUTF8:=AUseUTF8;
end;
constructor TJSONParser.Create(Source: TJSONStringType; AUseUTF8 : Boolean = True);
begin
Inherited Create;
FScanner:=TJSONScanner.Create(Source);
UseUTF8:=AUseUTF8;
end;
destructor TJSONParser.Destroy();
begin
FreeAndNil(FScanner);
inherited Destroy();
end;
end.
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