Visual Basic 6.0

Add Custom Extra Data to a Gzip File

This example demonstrates how to use the SetExtraData method to include custom binary data in the Gzip header using a hex-encoded string.

The hex string represents the raw bytes to embed in the Gzip metadata. When a compression method is called, this data is included in the Gzip header.

The example also shows how to retrieve the metadata using GetGzipInfo to verify that the extra data was successfully embedded. The retrieved value is returned as a Base64-encoded string.

Visual Basic 6.0

Dim success As Long
success = 0

' This example demonstrates how to include custom extra data
' in the Gzip header when compressing.

' The extra data is provided as a hex-encoded string.

Dim gzip As New ChilkatGzip
Dim json As New ChilkatJsonObject

' Set extra data using a hex string.
' This example represents 4 bytes: 00 01 02 03
success = gzip.SetExtraData("00010203","hex")
If (success = 0) Then
    Debug.Print gzip.LastErrorText
    Exit Sub
End If

' Compress a file so the extra data is embedded in the Gzip header:
Dim inputFile As String
inputFile = "example.txt"
Dim outputFile As String
outputFile = "example.txt.gz"

success = gzip.CompressFile(inputFile,outputFile)
If (success = 0) Then
    Debug.Print gzip.LastErrorText
    Exit Sub
End If

Debug.Print "Gzip file created with extra data."

' (Optional) Retrieve the metadata to verify:
success = gzip.GetGzipInfo(outputFile,json)
If (success = 0) Then
    Debug.Print gzip.LastErrorText
    Exit Sub
End If

Debug.Print "Metadata JSON:"
Debug.Print json.Emit()