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GZipCompressString

Function GZipCompressString( const S : string) : TBytes

Example​

procedure ScriptEvent(var Value: variant);
begin
  Value := Base64EncodeBytes(GZipCompressString('Fictional order 1001'));
end;

Usage​

GZipCompressString encodes a Velox Unicode string as UTF-16LE and returns gzip-compressed bytes.

Parameters

NameTypeDescription
SString, constText to encode and compress. Embedded null characters are encoded as ordinary UTF-16 code units.

Returns

A gzip member containing the string's UTF-16LE bytes without a byte-order mark.

Behaviour

Round-trip with GZipDecompressString preserves the Velox string when compression and decompression both succeed. A non-Velox consumer must explicitly decode the expanded payload as UTF-16LE; assuming UTF-8 produces incorrect text.

Errors

Encoding allocation failures and all GZipCompress errors propagate. The function provides no partial result.

Usage notes

Use this pair only for an interface that explicitly adopts Velox UTF-16LE string payloads. For UTF-8 or another wire encoding, encode the text through the appropriate Code Library function and call GZipCompress on those bytes.

Additional Technical Info​

GZipCompressString converts a Delphi Unicode string to UTF-16 little-endian bytes and passes those bytes to Velox's custom GZipCompress implementation. The result is a gzip member whose uncompressed payload is Delphi text encoding, not UTF-8.

The example produces a Base64 transport representation of the binary gzip result. It is source-reviewed and is not executed by the documentation workflow.

Implementation

The directly registered vxCompression.GZipCompressString calls TEncoding.Unicode.GetBytes(S) and then GZipCompress. On Windows Delphi, TEncoding.Unicode is little-endian UTF-16. GetBytes returns encoded content; it does not prepend the encoding preamble.

Edge cases and quirks

  • The empty string becomes an empty byte array and reaches GZipCompress's empty-input defect. With current Velox range checking it raises a range-check exception rather than returning an empty gzip member.
  • The function inherits GZipCompress's incorrect output pointer if its buffer-growth branch is reached.
  • Supplementary Unicode characters are encoded as UTF-16 surrogate pairs. Binary comparison with a UTF-8 gzip payload is not meaningful even when both expand to visually identical text.
  • There is no encoding marker, content type, schema or normalisation step in the gzip member.

Side effects

None outside memory allocation.

Performance and concurrency

The UTF-16 byte array and gzip result coexist in memory, along with zlib state. The call is synchronous and uses local state.

Related entries

External references

Created 2026-07-15