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ZLibCompressString

Function ZLibCompressString( const S : string) : TBytes

Example​

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

Usage​

ZLibCompressString encodes a Velox Unicode string as UTF-16LE and returns zlib-compressed bytes.

Parameters

NameTypeDescription
SString, constText to encode and compress.

Behaviour

Text created here is intended to round-trip through ZLibDecompressString. Other consumers must explicitly expand zlib and decode UTF-16LE. The payload is not UTF-8 and contains no encoding negotiation metadata.

Errors

Encoding allocation failures, EZCompressionError, range and allocation failures propagate. There is no partial result.

Usage notes

Adopt this function only where both endpoints explicitly agree on Velox UTF-16LE text. For a protocol-defined encoding such as UTF-8, encode to bytes according to that protocol and call ZLibCompress.

Additional Technical Info​

ZLibCompressString encodes a Delphi Unicode string as UTF-16 little-endian bytes without a byte-order mark and returns those bytes in a zlib-wrapped deflate stream.

The example converts the binary result to Base64 for transport. It is source-reviewed and is not executed by the documentation workflow.

Implementation

The direct registration calls vxCompression.ZLibCompressString, which calls the installed System.ZLib.ZCompressStr(S, zcDefault). In Studio 37.0, ZCompressStr obtains bytes through TEncoding.Unicode.GetBytes(S) and calls ZCompress. The current RTL implementation does not forward its level parameter to that inner call; this makes no visible difference here because Velox always requests the default level.

Edge cases and quirks

  • The empty string reaches the dynamic-array empty-input boundary in ZCompress; production builds can produce a valid compressed empty payload, but range-check settings can affect element-zero address expressions.
  • TEncoding.Unicode.GetBytes does not add a byte-order mark to the returned content.
  • Supplementary characters use UTF-16 surrogate pairs. No Unicode normalisation is performed.
  • The exposed function offers no compression-level parameter. The installed RTL also ignores the level argument inside ZCompressStr, although Velox passes only zcDefault.

Side effects

None outside memory allocation.

Performance and concurrency

The UTF-16 byte array, zlib result and working memory can coexist. The call is synchronous and uses local state.

Related entries

External references

Created 2026-07-15