How to compress a string using GZip or similar in Dart?

Question

I want to compress a string in Dart (in the browser). I tried this:

import 'package:archive/archive.dart';

[...]

List<int> stringBytes = UTF8.encode(myString);
List<int> gzipBytes = new GZipEncoder().encode(stringBytes);
String compressedString = UTF8.decode(gzipBytes, allowMalformed: true);

Obviously UTF8.decode is not intended for this and it doesn't work (file is unreadable).

What is the right way to compress a string in Dart?

What are you trying to achieve? I mean what are you trying to do *with* compressed strings? Can you post more of your code, including writing to a file? — Argenti Apparatus, Sep 28 '16 at 01:25
Sorry, missed the import. I got the impression you tried it with plain Dart. — Günter Zöchbauer, Sep 28 '16 at 09:57
@ArgentiApparatus I encode the string as a data URI and download it, as described here http://stackoverflow.com/a/18197511/1590323 Works perfectly, but I'd like to compress it first. Compressing it manually as gzip decreases size a lot. — stommestack, Sep 28 '16 at 09:59
What is the uncompressed data in the file and what do you intend to do with it? — Argenti Apparatus, Sep 28 '16 at 14:00
I have a feeling that you are attempting to save the raw compressed bytes as a file by downloading it from the browser. I think maybe what you actually want to do is create a text file containing your string then put that in a zip *archive* file, and download that. — Argenti Apparatus, Sep 28 '16 at 14:08
@ArgentiApparatus I'm making a webapp. The string is XML that contains the user's work. It's saved with a custom file extension and can later be opened again. — stommestack, Sep 28 '16 at 14:16

Xavier · Accepted Answer · 2020-08-24T14:19:41.123

7

The compressed list of bytes is probably not a valid UTF8 sequence instead you could encode it in base64.

import 'dart:convert';
import 'package:archive/archive.dart';

void main() {
  var myString = 'myString';
  var stringBytes = utf8.encode(myString);
  var gzipBytes = GZipEncoder().encode(stringBytes);
  var compressedString = base64.encode(gzipBytes);

  print(compressedString);
}

edited Aug 24 '20 at 14:19

answered Sep 28 '16 at 10:39

Xavier

3,148
21
15

Or just create a download file from the raw compressed bytes – Argenti Apparatus Sep 28 '16 at 13:37
@ArgentiApparatus Dart's `Uri.encodeComponent` method, which you need to prepare a file for downloading inside a browser, takes a string and not a list of bytes. – stommestack Sep 28 '16 at 14:18
2

I see. So if the method you are using to dynamically create a download file *must* deal with a string, you can BASE64 encode the data bytes as in the above answer, note that it will increase the size of your download somewhat though. – Argenti Apparatus Sep 28 '16 at 14:32
@ArgentiApparatus Yep, I've noticed that. For one of my test files: Original size: 727 kB, Compressed manually: 236 kB, Compressed with BASE64 encoding: 331 kB. Still a great reduction. – stommestack Sep 29 '16 at 08:48
Just discovered I can use `BASE64URL.encode` instead so I can skip `Uri.encodeComponent`. – stommestack Oct 02 '16 at 12:33
how to decompress it back? – Mahesh Jamdade Dec 19 '19 at 10:31
@maheshmnj `new GZipDecoder().decodeBytes(BASE64.decode(compressedString))` – stommestack Aug 24 '20 at 13:44

score 5 · Answer 2 · answered Jul 09 '21 at 10:28

5

You can use this function below if you want.

import 'dart:convert';
import 'dart:io';

  void _compress(String json) {
    final enCodedJson = utf8.encode(json);
    final gZipJson = gzip.encode(enCodedJson);
    final base64Json = base64.encode(gZipJson);

    final decodeBase64Json = base64.decode(base64Json);
    final decodegZipJson = gzip.decode(decodeBase64Json);
    final originalJson = utf8.decode(decodegZipJson);
    }

answered Jul 09 '21 at 10:28

Rafsan Uddin Beg Rizan

1,418
17
18

1

This answer is up-to-date, no need to import a third party library. – Dabbel Apr 22 '22 at 15:46

score 0 · Answer 3 · answered Jul 03 '21 at 15:41

0

String data=' ';
for(int i=0;i<10;i++){
    data=data+'Hello World!\r\n';
}
var original=utf8.encode(data);
var compressed=gzip.encode(original);
var decompressed=gzip.decode(compressed);

answered Jul 03 '21 at 15:41

Mayur Botre

1

2

Thank you for contributing an answer. Would you kindly edit your answer to to include an explanation of your code? That will help future readers better understand what is going on, and especially those members of the community who are new to the language and struggling to understand the concepts. – Jeremy Caney Jul 04 '21 at 23:42

How to compress a string using GZip or similar in Dart?

3 Answers3

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