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ZLibDecompressFile

Function ZLibDecompressFile( const aFileName : string) : TBytes

Example​

procedure ScriptEvent(var Value: variant);
begin
  Value := Base64EncodeBytes(ZLibDecompressFile('C:\Example\input.zlib'));
end;

Usage​

ZLibDecompressFile reads a zlib-compressed file and returns its decompressed bytes.

Parameters

NameTypeDescription
aFileNameString, constPath to a zlib-wrapped source file under the executing Velox process identity.

Returns

The complete expanded payload as TBytes.

Behaviour

The operation expects zlib framing regardless of filename extension. It returns bytes and preserves no filename, timestamp or content-type metadata.

Errors

File-open, access, read, allocation, stream and EZDecompressionError exceptions propagate. No partial result or Boolean failure is returned.

Additional Technical Info​

ZLibDecompressFile opens a file containing a zlib-wrapped deflate stream, expands it through Delphi's stream routine and returns the complete original bytes in memory. The source file is not modified.

The example path and extension are fictional; the function inspects the data, not the name. The example is source-reviewed and is not executed by the documentation workflow.

Implementation

The direct registration calls vxCompression.ZLibDecompressFile. It opens a TFileStream with fmOpenRead or fmShareDenyNone, creates an empty TBytesStream, and calls System.ZLib.ZDecompressStream. The installed RTL uses 32 KiB input and output buffers and inflates until Z_STREAM_END, raising if it cannot complete. Velox then copies exactly the in-memory output stream size to a new result array.

Edge cases and quirks

  • An empty file raises a decompression buffer error.
  • A valid compressed empty payload produces a zero-byte expanded stream. Velox then evaluates Move(lStream.Bytes[0], Result[0], 0); current project configurations enable range checking, so indexing the empty arrays raises a range-check exception even though the move count is zero.
  • Expanded output is unbounded and retained completely in memory. A compression bomb can exhaust the Velox process.
  • The source share mode permits concurrent writers, so a changing compressed stream may fail or, in a race, yield data not corresponding to a stable file snapshot.
  • Gzip, raw deflate and ZIP input are not accepted as zlib merely because the extension is changed.
  • The file stream is constructed before the byte stream and before the try/finally. If creating the byte stream fails, the already-open file stream is not freed by this routine.

Side effects

Opens and reads the nominated source. It allocates the complete expanded payload but writes no file.

Performance and concurrency

Compressed input is streamed in 32 KiB chunks, while all expanded data accumulates in memory and is copied once more into the result. The call is synchronous. Concurrent source modification is an external race.

Remarks

Only process trusted or size-governed inputs. If the flow requires a physical expanded file, a bounded streaming component is safer for large data than materialising the complete result in a script variable.

Related entries

External references

Created 2026-07-15