B4J Question [B4X]How to compress and decompress strings using gzip.

[byz]

Base64 + Gzip is a widely adopted method for efficient and text-safe data transmission in web APIs and network protocols. the WEBAPI interface compresses a large json string through gzip and returns it as a base64 encoded string. Therefore it needs to be unzipped. I've done it in vb.net, but b4x always fails.

Sub DecompressString( base64 As String)
    Dim compress As CompressedStreams
    Dim su As StringUtils
    Dim compressed(), decompressed() As Byte
    compressed = su.DecodeBase64(base64)
    decompressed= compress.DecompressBytes(compressed, "gzip")
    xui.MsgboxAsync(BytesToString(decompressed,0, decompressed.Length, "UTF8"), "")
End Sub

LINE 6 ERROR TIPS: Caused by: java.util.zip.ZipException: Not in GZIP format

It's not clear if it's my method that's wrong or if it's a compatibility issue.
Attached are the test items
================A complete solution===================
This is the correct compression and compression code that supports gzip and zlib compression algorithms. In the second attachment is an OK test item.

[B4X]How to compress and decompress strings using gzip.

Base64 + Gzip is a widely adopted method for efficient and text-safe data transmission in web APIs and network protocols. the WEBAPI interface compresses a large json string through gzip and returns it as a base64 encoded string. Therefore it needs to be unzipped. I've done it in vb.net, but b4x...

www.b4x.com

 

[byz]

Your test data, based on what @emexes found
@teddybear already had the solution in #4!

    Dim su As StringUtils
    Dim s As String=File.ReadString(File.DirAssets,"base64.txt")
    Dim d2() As Byte
    d2=su.DecodeBase64(s)
    Dim bc As ByteConverter
    Log(bc.StringFromBytes(d2 , "UTF8"))
    '{"appName":"WeatherTracker","version":"2.3.5","features":["real-time updates","5-day forecast","severe weather alerts","custom locations"],"settings":{"temperatureUnit":"Celsius","notificationEnabled":true,"refreshInterval":30,"theme":"dark"},"user":{"id":"WTU-7845-2023","premiumMember":false,"lastActive":"2023-11-15T08:23:17Z"},"systemInfo":{"apiCallsToday":147,"uptime":"36:14:22","memoryUsage":"64%"},"messages":[{"id":1,"text":"Welcome to WeatherTracker!","priority":"low"},{"id":2,"text":"New update available","priority":"medium"}]}

You're right, I'm sorry I didn't notice @teddybear 's reply because it was busy

 

[byz]

This code is wrong, it(compressed) only is bytes which decoded Base64, not GZIP format. you can directly convert the bytes to string as below

@William Lancee @teddybear @aeric @emexes @JackKirk
An interesting phenomenon, I just used gzip and zlib to compress the string, and this method can be successfully decompressed.

Private Sub B4XPage_Created (Root1 As B4XView)
    Root = Root1
    Root.LoadLayout("MainPage")

    'test code
    Dim s As String=File.ReadString(File.DirAssets,"base64.txt")
    Dim s2 As String=(DecompressString(s))
    File.WriteString(    File.DirApp,"1.json",s2)
    Dim s3 As String=(CompressString(s2))
    File.WriteString(    File.DirApp,"1.txt",s3)
End Sub

Sub CompressString(str As String) As String
    Dim bc As ByteConverter
    Dim su As StringUtils
    Dim compress As CompressedStreams
    Dim bytes() As Byte = bc.StringToBytes(str, "UTF8")
    'Dim b() As Byte=compress.CompressBytes(bytes,"zlib")
    Dim b() As Byte=compress.CompressBytes(bytes,"gzip")
    Return su.EncodeBase64(b)
End Sub

Sub DecompressString( base64 As String) As String
    Dim su As StringUtils
    Dim d2() As Byte
    d2=su.DecodeBase64(base64)
    Dim bc As ByteConverter
    Return bc.StringFromBytes(d2 , "UTF8")
End Sub

GZIP/ZLIB testing tools https://codebeautify.org/gzip-decompress-online

 

[aeric]

I think this is better to demonstrate that su.DecodeBase64(base64) is doing the decompressing.
The commented code shows it is not needed.

Private Sub B4XPage_Created (Root1 As B4XView)
    Root = Root1
    Root.LoadLayout("MainPage")
    Dim json As String = File.ReadString(File.DirAssets, "json.txt")
    CompressString(json)
End Sub

Private Sub Button1_Click
    DecompressString
End Sub

Sub CompressString (s As String)
    Dim compress As CompressedStreams
    Dim compressed() As Byte = compress.CompressBytes(s.GetBytes("UTF8"), "gzip")
    Dim base64 As String = su.EncodeBase64(compressed)
    File.WriteString(File.DirApp, "base64.txt", base64)
End Sub

Sub DecompressString
    Dim base64 As String = File.ReadString(File.DirApp, "base64.txt")
    Dim compressed() As Byte = su.DecodeBase64(base64)
    'Dim decompressed() As Byte = compress.DecompressBytes(compressed, "gzip")
    'Dim s As String = BytesToString(decompressed, 0, decompressed.Length, "UTF8")
    Dim s As String = BytesToString(compressed, 0, compressed.Length, "UTF8")
    Log(s)
End Sub