Why Does Deferring GZIP Writer Closure Lead to Data Loss?

Deferring GZIP Writer Closure Results in Data Loss

Background:
When working with gzip, utilizing gzip.NewWriter to compress data and deferring Close() to close the writer can lead to a loss of compressed data.

Issue:
Deferring the closure of the GZIP writer causes the missing of the GZIP footer. As specified in the Close function documentation:

Close closes the Writer by flushing any unwritten data to the underlying io.Writer and writing the GZIP footer. It does not close the underlying io.Writer.

Solution:
To prevent data loss, close the GZIP writer before returning the compressed data:

<code class="go">func zipData(originData []byte) ([]byte, error) {
    var bf bytes.Buffer
    gw := gzip.NewWriter(&bf)

    _, err := gw.Write(originData)
    if err != nil {
        return nil, errors.New(fmt.Sprintf("gzip data err: %v", err))
    }

    err = gw.Flush()
    if err != nil {
        return nil, err
    }

    if err := gw.Close(); err != nil {
        return nil, errors.New(fmt.Sprintf("close data err: %v", err))
    }

    return bf.Bytes(), nil
}</code>

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