(C#) Append Text Data to an Existing ZIP Entry Using ZipEntry.AppendString

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This example demonstrates how to use the ZipEntry.AppendString method to append text data to an existing ZIP entry.

The example opens an existing ZIP archive, locates a text file entry, and appends additional text to the end of the file contents.

An important concept demonstrated by this example is that appending data to a ZIP entry transforms the entry into an in-memory Data Entry (EntryType = 2).

For example:

• If the entry is a mapped entry from an opened ZIP archive (EntryType = 0), the compressed entry is first inflated into memory.
• If the entry is a referenced filesystem file (EntryType = 1), the file contents are first loaded into memory.

The new text is then appended to the uncompressed in-memory data, and the entry becomes a Data Entry.

After the ZIP archive is rewritten, the modified entry again becomes a mapped entry stored within the ZIP archive.

Note: This example requires Chilkat v11.0.0 or greater.

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bool success = false;

Chilkat.Zip zip = new Chilkat.Zip();

// ------------------------------------------------------------
// Open an existing ZIP archive.
success = zip.OpenZip("c:/temp/notes.zip");
if (success == false) {
    Debug.WriteLine(zip.LastErrorText);
    return;
}

// Locate a text file entry within the ZIP archive.
Chilkat.ZipEntry entry = new Chilkat.ZipEntry();

success = zip.EntryOf("notes/readme.txt",entry);

if (success != false) {

    // --------------------------------------------------------
    // At this point, the entry is a mapped entry because it
    // originates from an opened ZIP archive.
    // 
    //     EntryType = 0
    // 
    Debug.WriteLine("Initial EntryType = " + Convert.ToString(entry.EntryType));

    // Append additional text to the ZIP entry.
    // 
    // The existing compressed ZIP entry is first inflated
    // into memory. The new text is then appended.
    // 
    // After AppendString is called, the entry becomes
    // an in-memory Data Entry:
    // 
    //     EntryType = 2
    // 
    success = entry.AppendString("\r\nAdditional notes added later.","utf-8");

    if (success == false) {
        Debug.WriteLine(zip.LastErrorText);
        return;
    }

    Debug.WriteLine("EntryType after AppendString = " + Convert.ToString(entry.EntryType));

    // --------------------------------------------------------
    // Write the modified ZIP archive to a different file.
    // 
    // Changing zip.FileName causes the ZIP archive to be
    // written to a new output file rather than overwriting
    // the original ZIP archive.
    // 
    zip.FileName = "qa_output/updatedExample.zip";

    // Rewrite the ZIP archive.
    // 
    // The modified in-memory entry is compressed and written
    // into the new ZIP archive.
    // 
    success = zip.WriteZip();
    if (success == false) {
        Debug.WriteLine(zip.LastErrorText);
        return;
    }

    // After rewriting the ZIP archive, the entry again becomes
    // a mapped entry:
    // 
    //     EntryType = 0
    // 
    Debug.WriteLine("EntryType after WriteZip = " + Convert.ToString(entry.EntryType));
}

zip.CloseZip();

Debug.WriteLine("ZIP entry updated successfully.");