how to save large array buffer from browser

[flyfish]

hi, I try to save a large array buffer from browser to local disk, in my delphi program, i registed a funciton like this:

Code: Select all

TChromillaExtension = class(TCefv8HandlerOwn)
function Execute(const name: ustring; const obj: ICefv8Value;
      const arguments: TCefv8ValueArray; var retval: ICefv8Value;
      var AException: ustring): Boolean; override;

implatement

function TChromillaExtension .Execute(const name: ustring;
  const obj: ICefv8Value; const arguments: TCefv8ValueArray;
  var retval: ICefv8Value; var AException: ustring): Boolean;
var
  //  callback, cval, rval: ICefv8Value;
  //  callbackArgs: TCefV8ValueArray;
  Params: array of Variant;
  Method: TMethod;
  I: Integer;
  L: Integer;
  ReturnValue: Variant;
begin
  Result := False;
  L := Length(arguments);
  SetLength(Params, L);
  if name = 'saveArrayBuffer' then
  begin
    SaveUInt8ArrayAsFile(arguments);
    retval := TCefv8ValueRef.NewNull;
    Result := True;
    Exit;
  end;
  ....
end;

procedure SaveUInt8ArrayAsFile(const arguments: TCefv8ValueArray);
var
  Data: TBytes;
  FileStream: TFileStream;
  keys: TStrings;
  I, iLength: Integer;
  value: ICefv8Value;
  fileName: string;
begin
  fileName := arguments[0].GetStringValue;
  value := arguments[1]; 

  if (Value <> nil) and (Value.IsObject) then
  begin
    keys := TStringList.Create;
    try
      iLength := Value.GetKeys(keys);
      SetLength(Data, iLength);

      for I := 0 to keys.Count - 1 do
        Data[I] := Value.GetValueByKey(keys[I]).GetIntValue;

      FileStream := TFileStream.Create(FileName, fmCreate);
      try
        FileStream.WriteBuffer(Data[0], Length(Data));
      finally
        FileStream.Free;
        SetLength(Data, 0);
      end;
    finally
      keys.Free;
    end;
  end;
end;

the js code like this

Code: Select all

const modifiedArrayBuffer = new ArrayBuffer(originalArrayBuffer.byteLength);
            const view = new Uint8Array(modifiedArrayBuffer);
            view.set(new Uint8Array(originalArrayBuffer));
            YChromilla.saveArrayBuffer(parseQueryString(location.search).filename, view);
 

when array buffer is small , the code is work correct, but When I try to save an ArrayBuffer with a length of 12600217, the program crashes when calling Value.GetKeys, and the memory usage spikes to 1.5GB.

Does anyone know what happened? Please let me know.I would appreciate any valuable clues.

[salvadordf]

Hi,

Is this a 32 bit or 64 bit application? Try building your application with a 64 bit target.

There is a size limit in the binary parameters :
https://github.com/salvadordf/CEF4Delphi/blob/b4f492bfa12cc67eea199a06b75d772d4fa30f75/demos/Delphi_VCL/JavaScript/JSExtension/uJSExtension.pas#L191

Try to handle the array buffer in a different way. There are several methods in TCefv8ValueRef and ICefv8Value related to array buffers :
https://github.com/salvadordf/CEF4Delphi/blob/master/source/uCEFv8Value.pas

[flyfish]

hi， Thank you for your reply. My IDE version is Delphi2007, and my program is 32-bit. I have solved this problem by adding a parameters to mark the effective data length.

But I still have a question, how should the javascript call be written so that the parameters will be packed into arraybuffer type. I think the code “
for I := 0 to keys.Count - 1 do
Data := Value.GetValueByKey(keys).GetIntValue;”
will be slow when processing large amounts of data

[salvadordf]

I haven't tested this but try passing the modifiedArrayBuffer instead of view as the second parameter of saveArrayBuffer in JS code.

Then read the parameters like this :

Code: Select all

  FileStream := TFileStream.Create(arguments[0].GetStringValue, fmCreate);
  try
    FileStream.WriteBuffer(arguments[1].GetArrayBufferData, arguments[1].GetArrayBufferByteLength);
  finally
    FileStream.Free;
  end;

[flyfish]

Yes, you are right. When I use modifiedArrayBuffer instead of view, the parameter [1] becomes an ArrayBuffer. Unfortunately, ICefv8Value does not encapsulate methods like GetArrayBufferData or GetArrayBufferByteLength
So, do I have to handle this using a for loop?

[salvadordf]

Update to the latest CEF4Delphi version at GitHub to see those methods :
https://github.com/salvadordf/CEF4Delphi

[flyfish]

thank u, I got it