Tcl

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.

Tcl

load ./chilkat.dll

set 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.

set gzip [new_CkGzip]

set json [new_CkJsonObject]

# Set extra data using a hex string.
# This example represents 4 bytes: 00 01 02 03
set success [CkGzip_SetExtraData $gzip "00010203" "hex"]
if {$success == 0} then {
    puts [CkGzip_lastErrorText $gzip]
    delete_CkGzip $gzip
    delete_CkJsonObject $json
    exit
}

# Compress a file so the extra data is embedded in the Gzip header:
set inputFile "example.txt"
set outputFile "example.txt.gz"

set success [CkGzip_CompressFile $gzip $inputFile $outputFile]
if {$success == 0} then {
    puts [CkGzip_lastErrorText $gzip]
    delete_CkGzip $gzip
    delete_CkJsonObject $json
    exit
}

puts "Gzip file created with extra data."

# (Optional) Retrieve the metadata to verify:
set success [CkGzip_GetGzipInfo $gzip $outputFile $json]
if {$success == 0} then {
    puts [CkGzip_lastErrorText $gzip]
    delete_CkGzip $gzip
    delete_CkJsonObject $json
    exit
}

puts "Metadata JSON:"
puts [CkJsonObject_emit $json]

delete_CkGzip $gzip
delete_CkJsonObject $json