I'm having trouble converting a string with escaped characters to and from a TJsonString. (I'm using Delphi XE 2, Update 4, Hotfix 1).
NOTE: I am familiar with the SuperObject, but my requirements are to use the DBXJSON unit.
It looks like the TJSONString is not correctly escaped when returning the JSON representation via the ToString() method.
What (if anything) am I doing wrong and how do I correctly convert a string with special characters to/from its correct JSON representation?
Perhaps I missed something, but none of the following Q&As seemed to address this directly:
EDIT:
As it turns out, the examples below were indeed working as expected.
What wasn't clear to me was that when creating a TJSONString via it's constructor and adding it to a TJSONObject, the ToString() method will return an escaped representation. However, after parsing a TJSONObject, the ToString() method will returned the un-escaped representation.
The only other caveat was that the EscapeString() function in the sample code below was handling the double-quote. Although I wasn't using the double quote here, some of my other code was, and that caused the parsing to fail because TJSONString already escapes that character. I've updated my sample code to remove this handling from the EscapeString() function, which is what I've been using in my own classes.
Thanks again to @Linas for the answer, which helped me to "get" it.
Raw String Value:
Text := 'c:\path\name' +#13 + #10 + 'Next Line';
Text: c:\path\name
Next Line
What DBXJSON produces (NO ESCAPES):
JsonString: "c:\path\name
Next Line"
JsonPair: "MyString":"c:\path\name
Next Line"
JsonObject: {"MyString":"c:\path\name
Next Line"}
Parsing UN-escaped Text FAILS:
Text to parse: {"MyString":"c:\path\name
Next Line"}
Parsed JsonObject = *NIL*
What I EXPECT DBXJSON to produce:
Escaped String: c:\\path\\name\r\nNext Line
JsonString: "c:\\path\\name\r\nNext Line"
JsonPair: "MyString":"c:\\path\\name\r\nNext Line"
JsonObject: {"MyString":"c:\\path\\name\r\nNext Line"}
Parsing ESCAPED Text (INVALID) (Text to parse validated with JSONLint):
Text to parse: {"MyString":"c:\\path\\name\r\nNext Line"}
Parsed JsonObject.ToString(): {"MyString":"c:\path\name
Next Line"}
I've noticed that the only special character TJSONString seems to process correctly is the double quote (").
Here is the code I'm using:
program JsonTest;
{$APPTYPE CONSOLE}
{$R *.res}
uses
System.SysUtils, DbxJson;
function EscapeString(const AValue: string): string;
const
ESCAPE = '\';
// QUOTATION_MARK = '"';
REVERSE_SOLIDUS = '\';
SOLIDUS = '/';
BACKSPACE = #8;
FORM_FEED = #12;
NEW_LINE = #10;
CARRIAGE_RETURN = #13;
HORIZONTAL_TAB = #9;
var
AChar: Char;
begin
Result := '';
for AChar in AValue do
begin
case AChar of
// !! Double quote (") is handled by TJSONString
// QUOTATION_MARK: Result := Result + ESCAPE + QUOTATION_MARK;
REVERSE_SOLIDUS: Result := Result + ESCAPE + REVERSE_SOLIDUS;
SOLIDUS: Result := Result + ESCAPE + SOLIDUS;
BACKSPACE: Result := Result + ESCAPE + 'b';
FORM_FEED: Result := Result + ESCAPE + 'f';
NEW_LINE: Result := Result + ESCAPE + 'n';
CARRIAGE_RETURN: Result := Result + ESCAPE + 'r';
HORIZONTAL_TAB: Result := Result + ESCAPE + 't';
else
begin
if (Integer(AChar) < 32) or (Integer(AChar) > 126) then
Result := Result + ESCAPE + 'u' + IntToHex(Integer(AChar), 4)
else
Result := Result + AChar;
end;
end;
end;
end;
procedure Test;
var
Text: string;
JsonString: TJsonString;
JsonPair: TJsonPair;
JsonObject: TJsonObject;
begin
try
Writeln('Raw String Value');
Writeln('-----------------');
Text := 'c:\path\name' +#13 + #10 + 'Next Line';
Writeln('Text: ', Text);
JsonString := TJsonString.Create(Text);
JsonPair := TJsonPair.Create('MyString', JsonString);
JsonObject := TJsonObject.Create(JsonPair);
// DBXJSON results
Writeln;
Writeln('What DBXJSON produces');
Writeln('---------------------');
Writeln('JsonString: ', JsonString.ToString);
Writeln;
Writeln('JsonPair: ', JsonPair.ToString);
Writeln;
Writeln('JsonObject: ', JsonObject.ToString);
Writeln;
// assign JSON representation
Text := JsonObject.ToString;
// free json object
JsonObject.Free;
// parse it
JsonObject:= TJsonObject.ParseJsonValue(TEncoding.ASCII.GetBytes(
Text), 0) as TJsonObject;
Writeln('Parsing UN-escaped Text *FAILS* ');
Writeln('----------------------------------');
Writeln('Text to parse: ', Text);
Writeln;
if (JsonObject = nil) then
Writeln('Parsed JsonObject = *NIL*')
else
Writeln('Parsed JsonObject: ', JsonObject.ToString);
Writeln;
// free json object
JsonObject.Free;
// expected results
Text := 'c:\path\name' +#13 + #10 + 'Next Line';
Text := EscapeString(Text);
JsonString := TJsonString.Create(Text);
JsonPair := TJsonPair.Create('MyString', JsonString);
JsonObject := TJsonObject.Create(JsonPair);
Writeln('What I *EXPECT* DBXJSON to produce');
Writeln('----------------------------------');
Writeln('Escaped String: ', Text);
Writeln;
Writeln('JsonString: ', JsonString.ToString);
Writeln;
Writeln('JsonPair: ', JsonPair.ToString);
Writeln;
Writeln('JsonObject: ', JsonObject.ToString);
Writeln;
// assign JSON representation
Text := JsonObject.ToString;
// free json object
JsonObject.Free;
// parse it
JsonObject:= TJsonObject.ParseJsonValue(TEncoding.ASCII.GetBytes(
Text), 0) as TJsonObject;
Writeln('Parsing ESCAPED Text (*INVALID*) ');
Writeln('----------------------------------');
Writeln('Text to parse: ', Text);
Writeln;
Writeln('Parsed JsonObject.ToString(): ', JsonObject.ToString);
Writeln;
Readln;
except
on E: Exception do
begin
Writeln(E.ClassName, ': ', E.Message);
Readln;
end;
end;
end;
begin
Test;
end.
How FOR JSON escapes special characters and control characters (SQL Server) 1 Escaping of special characters. If the source data contains special characters, the FOR JSON clause escapes them in the JSON output with \, as shown in the following table. 2 Control characters. ... 3 Learn more about JSON in SQL Server and Azure SQL Database
you can turn it into JSON in Python using the json.loads () function. The json.loads () function accepts as input a valid string and converts it to a Python dictionary. This process is called deserialization – the act of converting a string to an object.
Mostly it is used to build an API. This is an example of JSON it stores data in key-value format and values can be the array of another primitive datatype or another JSON. There are three methods to convert JSON to String and Vice Versa in Java
I understand that, but if what you're receiving is supposed to be JSON-encoded, as you say it is, then you should use a JSON-decoding library to process it instead of writing your own. This is not UTF-8, but string containing escaped UTF-16 code points.
You can try to define your own TJSONString type and escape json strings there. E.g.:
uses
DBXJSON;
type
TSvJsonString = class(TJSONString)
private
function EscapeValue(const AValue: string): string;
public
constructor Create(const AValue: string); overload;
end;
{ TSvJsonString }
constructor TSvJsonString.Create(const AValue: string);
begin
inherited Create(EscapeValue(AValue));
end;
function TSvJsonString.EscapeValue(const AValue: string): string;
procedure AddChars(const AChars: string; var Dest: string; var AIndex: Integer); inline;
begin
System.Insert(AChars, Dest, AIndex);
System.Delete(Dest, AIndex + 2, 1);
Inc(AIndex, 2);
end;
procedure AddUnicodeChars(const AChars: string; var Dest: string; var AIndex: Integer); inline;
begin
System.Insert(AChars, Dest, AIndex);
System.Delete(Dest, AIndex + 6, 1);
Inc(AIndex, 6);
end;
var
i, ix: Integer;
AChar: Char;
begin
Result := AValue;
ix := 1;
for i := 1 to System.Length(AValue) do
begin
AChar := AValue[i];
case AChar of
'/', '\', '"':
begin
System.Insert('\', Result, ix);
Inc(ix, 2);
end;
#8: //backspace \b
begin
AddChars('\b', Result, ix);
end;
#9:
begin
AddChars('\t', Result, ix);
end;
#10:
begin
AddChars('\n', Result, ix);
end;
#12:
begin
AddChars('\f', Result, ix);
end;
#13:
begin
AddChars('\r', Result, ix);
end;
#0 .. #7, #11, #14 .. #31:
begin
AddUnicodeChars('\u' + IntToHex(Word(AChar), 4), Result, ix);
end
else
begin
if Word(AChar) > 127 then
begin
AddUnicodeChars('\u' + IntToHex(Word(AChar), 4), Result, ix);
end
else
begin
Inc(ix);
end;
end;
end;
end;
end;
Usage example:
procedure Test;
var
LText, LEscapedText: string;
LJsonString: TSvJsonString;
LJsonPair: TJsonPair;
LJsonObject: TJsonObject;
begin
LText := 'c:\path\name' + #13 + #10 + 'Next Line';
LJsonString := TSvJsonString.Create(LText);
LJsonPair := TJsonPair.Create('MyString', LJsonString);
LJsonObject := TJsonObject.Create(LJsonPair);
try
LEscapedText := LJsonObject.ToString;
//LEscapedText is: c:\\path\\name\r\nNext Line
finally
LJsonObject.Free;
end;
end;
And this is how parsing should be done:
//AText := '{"MyString":"c:\\path\\name\r\nNext Line"}';
function Parse(const AText: string): string;
var
obj: TJSONValue;
begin
obj := TJSONObject.ParseJSONValue(AText);
try
Result := obj.ToString;
//Result := {"MyString":"c:\path\name
//Next Line"}
finally
obj.Free;
end;
end;
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