Visual FoxPro

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 FoxPro

LOCAL lnSuccess
LOCAL loGzip
LOCAL loJson
LOCAL lcInputFile
LOCAL lcOutputFile

lnSuccess = 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.

loGzip = CreateObject('Chilkat.Gzip')
loJson = CreateObject('Chilkat.JsonObject')

* Set extra data using a hex string.
* This example represents 4 bytes: 00 01 02 03
lnSuccess = loGzip.SetExtraData("00010203","hex")
IF (lnSuccess = 0) THEN
    ? loGzip.LastErrorText
    RELEASE loGzip
    RELEASE loJson
    CANCEL
ENDIF

* Compress a file so the extra data is embedded in the Gzip header:
lcInputFile = "example.txt"
lcOutputFile = "example.txt.gz"

lnSuccess = loGzip.CompressFile(lcInputFile,lcOutputFile)
IF (lnSuccess = 0) THEN
    ? loGzip.LastErrorText
    RELEASE loGzip
    RELEASE loJson
    CANCEL
ENDIF

? "Gzip file created with extra data."

* (Optional) Retrieve the metadata to verify:
lnSuccess = loGzip.GetGzipInfo(lcOutputFile,loJson)
IF (lnSuccess = 0) THEN
    ? loGzip.LastErrorText
    RELEASE loGzip
    RELEASE loJson
    CANCEL
ENDIF

? "Metadata JSON:"
? loJson.Emit()

RELEASE loGzip
RELEASE loJson