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Base64Decode

Function Base64Decode( const Value : string) : string

Example​

procedure ScriptEvent(var Value: variant);
begin
  Value := Base64Decode('VmVsb3g=');  // Velox
end;

Usage​

Base64Decode decodes standard Base64 text and interprets the resulting bytes as UTF-8 text.

Parameters

NameTypeDescription
Valuestring, constStandard Base64 text to decode. Velox does not trim or normalise it first.

Returns

The decoded bytes interpreted as UTF-8 text. An empty input returns an empty string.

Behaviour

  • Encoding uses the standard Base64 alphabet (A-Z, a-z, 0-9, + and /) with = padding.
  • The decoder accepts unwrapped text and also skips line breaks, spaces and other characters that are not in the standard alphabet.
  • The result is text, not a textual representation of the decoded bytes.
  • Velox performs no character-set detection, decompression or decryption after decoding.

Errors

The permissive decoder does not reliably reject malformed Base64. Allocation and Velox conversion exceptions are not caught by the Velox function and propagate to the script.

Usage notes

Do not use successful decoding as proof that input was well formed. If strict validation is required, validate the alphabet, padding and expected decoded length separately before accepting the result.

Additional Technical Info​

Base64Decode decodes a standard Base64 string and converts the decoded bytes to a Delphi string using UTF-8. Use Base64DecodeBytes instead when the encoded value represents a binary file or bytes that are not UTF-8 text.

The example is source-reviewed and was not executed by the documentation workflow.

Implementation

The scripting import calls the Velox Base64Decode wrapper. Each call creates Delphi's TBase64Encoding with a line length of 0, calls its string Decode method, and frees the encoder in a finally block. The Delphi string overload decodes Base64 to bytes and converts those bytes with UTF-8.

Edge cases and quirks

  • Delphi's installed decoder is permissive. It skips invalid characters and padding while collecting valid symbols, and accepts a final group containing only two or three valid symbols. Malformed or truncated input can therefore produce a partial result instead of raising an error.
  • URL-safe Base64 uses - and _ in place of + and /. Those URL-safe characters are not translated; they are skipped as invalid characters and can silently corrupt the result.
  • If the decoded byte sequence is not valid UTF-8, the observed text follows the installed Delphi UTF-8 conversion behaviour. Use the byte-returning helper when exact binary preservation matters.
  • Base64 is reversible encoding, not encryption, authentication or validation.

Side effects

None beyond temporary allocation. The input is not modified and no external I/O occurs.

Performance and concurrency

Each call creates a new encoder and allocates storage proportional to the input and decoded result. The wrapper has no Velox shared mutable state and is suitable for independent concurrent calls.

Related entries

External references

Created 2026-07-15