I am using excel package version 2.0.0-null-safety-3 to read an excel file,
For small files, it looks good
But when reading a large file, the interface stops until the file is read
Excel.decodeBytes(_bytes);
decodeBytes method => sync is not supported
Is there a way to make the process synchronous
To be able to show the (download bar or waiting dialog) to the user
Thanks in advance.
Use Compute For Large Bytes of Data
await compute(function,param)
Flutter Compute
Related
I wrote the file transferring code as follows:
val fileContent: Enumerator[Array[Byte]] = Enumerator.fromFile(file)
val size = file.length.toString
file.delete // (1) THE FILE IS TEMPORARY SO SHOULD BE DELETED
SimpleResult(
header = ResponseHeader(200, Map(CONTENT_LENGTH -> size, CONTENT_TYPE -> "application/pdf")),
body = fileContent)
This code works successfully, even if the file size is rather large (2.6 MB),
but I'm confused because my understanding about .fromFile() is a wrapper of fromCallBack() and SimpleResult actually reads the file buffred,but the file is deleted before that.
MY easy assumption is that java.io.File.delete waits until the file gets released after the chunk reading completed, but I have never heard of that process of Java File class,
Or .fromFile() has already loaded all lines to the Enumerator instance, but it's against the fromCallBack() spec, I think.
Does anybody knows about this mechanism?
I'm guessing you are on some kind of a Unix system, OSX or Linux for example.
On a Unix:y system you can actually delete a file that is open, any filesystem entry is just a link to the actual file, and so is a file handle which you get when you open a file. The file contents won't become unreachable /deleted until the last link to it is removed.
So: it will no longer show up in the filesystem after you do file.delete but you can still read it using the InputStream that was created in Enumerator.fromFile(file) since that created a file handle. (On Linux you actually can find it through the special /proc filesystem which, among other things, contains the filehandles of each running process)
On windows I think you will get an error though, so if it is to run on multiple platforms you should probably check test your webapp on windows as well.
I'm using Image::Magick to modify my images. I am then using an HTTP::Request to send the image content to an API.
HTTP::Request has a content method which allows you to set the content for the request, but obviously this requires that you have the content in memory.
I know that I can read the content of the image into a variable by opening a file and reading it. However, since Image::Magick already has the content of the image in memory, is there any way that I can get it via my Image::Magick object? Thanks!
Image::Magick keeps the image in a custom format in memory to make it more simple and efficient to manipulate. It has to compress the data to JPEG, PNG, or whatever format you request before it is written to a file, so you cannot just access the image in memory as it stands.
However, the module's ImageToBlob method will provide an in-memory copy of the data it would have written to disk, to save you writing it out and reading it back again.
Note that it returns a list of images to allow for an object that contains more than one frame, so if you have only a single frame you must write
my #blobs = $image->ImageToBlob;
$request->content($blobs[0]);
or
my ($blob) = $image->ImageToBlob;
$request->content($blob);
I'm building an App with actionscript 3.0 in my Flash builder. This is a followup question this question.
I need to upload the bytearray to my server, but the function i use to convert the bitmapdata to a ByteArray is super slow, so slow it freezes up my mobile device. My code is as follows:
var jpgenc:JPEGEncoder = new JPEGEncoder(50);
trace('encode');
//encode the bitmapdata object and keep the encoded ByteArray
var imgByteArray:ByteArray = jpgenc.encode(bitmap);
temp2 = File.applicationStorageDirectory.resolvePath("snapshot.jpg");
var fs:FileStream = new FileStream();
trace('fs');
try{
//open file in write mode
fs.open(temp2,FileMode.WRITE);
//write bytes from the byte array
fs.writeBytes(imgByteArray);
//close the file
fs.close();
}catch(e:Error){
Is there a different way to convert it to a byteArray? Is there a better way?
Try to use blooddy library: http://www.blooddy.by . But i didn't test it on mobile devices. Comment if you will have success.
Use BitmapData.encode(), it's faster by orders of magnitude on mobile http://help.adobe.com/en_US/FlashPlatform/reference/actionscript/3/flash/display/BitmapData.html#encode%28%29
You should try to find a JPEG encoder that is capable of encoding asynchronously. That way the app can still be used while the image is being compressed. I haven't tried any of the libraries, but this one looks promising:
http://segfaultlabs.com/devlogs/alchemy-asynchronous-jpeg-encoding-2
It uses Alchemy, which should make it faster than the JPEGEncoder from as3corelib (which I guess is the one you're using at the moment.)
A native JPEG encoder is ideal, asynchronous would be good, but possibly still slow (just not blocking). Another option:
var pixels:ByteArray = bitmapData.getPixels(bitmapData.rect);
pixels.compress();
I'm not sure of native performance, and performance definitely depends on what kind of images you have.
The answer from Ilya was what did it for me. I downloaded the library and there is an example of how to use it inside. I have been working on getting the CameraUI in flashbuilder to take a picture, encode / compress it, then send it over via a web service to my server (the data was sent as a compressed byte array). I did this:
by.blooddy.crypto.image.JPEGEncoder.encode( bmp, 30 );
Where bmp is my bitmap data. The encode took under 3 seconds and was easily able to fit into my flow of control synchronously. I tried async methods but they ultimately took a really long time and were difficult to track for things like when a user moved from cell service to wifi or from tower to tower while an upload was going on.
Comment here if you need more details.
I'm developing an iphone app, I need to create a certain size file on filesystem and filled with NO data first, then seek to a offset and write data when get data from somewhere else
How can I do it?
The lseek BSD function is explicitly capable of that.
man lseek:
The lseek() function allows the file offset to be set beyond the end of the
existing end-of-file of the file. If data is later written at this point,
subsequent reads of the data in the gap return bytes of zeros (until data is
actually written into the gap).
NSMutableData or fseek is probably what you want
I want to get file size I'm doing this:
my $filename=$query->param("upload_file");
my $filesize = (-s $filename);
print "Size: $filesize ";`
Yet it is not working. Note that I did not upload the file. I want to check its size before uploading it. So to limit it to max of 1 MB.
You can't know the size of something before uploading. But you can check the Content-Length request header sent by the browser, if there is one. Then, you can decide whether or not you want to believe it. Note that the Content-Length will be the length of the entire request stream, including other form fields, and not just the file upload itself. But it's sufficient to get you a ballpark figure for conformant clients.
Since you seem to be running under plain CGI, you should be able to get the request body length in $ENV{CONTENT_LENGTH}.
Also want to sanity check against possibly already having post max set (from perldoc CGI):
$CGI::POST_MAX
If set to a non-negative integer, this variable puts a ceiling on the size of
POSTings, in bytes. If CGI.pm detects a POST that is greater than the ceiling,
it will immediately exit with an error message. This value will affect both
ordinary POSTs and multipart POSTs, meaning that it limits the maximum size of
file uploads as well. You should set this to a reasonably high value, such as
1 megabyte.
The uploaded file is stashed in a tmp location on the server when the form is submitted, check the file size there.
Supply the value for $field.
my $upload_filehandle = $query->upload($field);
my $tmpfilename = $query->tmpFileName($upload_filehandle);
my $file_size = (-s $tmpfilename);
This has nothing to do with Perl.
You are trying to read the filesize of a file on the user's computer using commands that read files on your server, what you want can't be done using Perl.
This is something that has to be done in the browser, and looking briefly at these questions it's either very hard or impossible.
Your best bet is to allow the user to start the upload and abort if the file is too big.
If you want to check before you process the request, you might be better off checking on the web page that triggers the request. I don't think the web browser can do it on it's own, but if you don't mind Flash, there are many Flash upload tools that can check things like size (as well as file types) and prevent uploading.
A good one to start with is the YUI Uploader. Lots more here: What is the best multiple file JavaScript / Flash file uploader?
Obviously you would want to check on the server side too, but by the time the user has started sending the request to the server, you are already using up your CPU cycles and bandwidth.
Thanks everyone for your replies; I just found out why $filesize = (-s $filename); was not working before, it is due that I was checking file size while sending Ajax request and not while re submitting the page.That's why I was having size to be zero. I fixed that to submit the page and it worked. Thanks.
Just read this post but while checking the content-length is a good approximate pre-check you could also save the file to temporary folder and then perform any kind of check on it. If it doesn't meet your criteria just delete and don't send it to it's final destination.
Look at the perl documentation for file stats -X - perldoc.perl.org and stat-perldoc.perl.org. Also, you can look at this upload script which is doing the similar thing what you are trying to do.