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Base64DecodeFile

Procedure Base64DecodeFile( const aBase64String, aFileName : string)

Example​

procedure ScriptEvent(var Value: variant);
begin
  // Overwrites the destination if it already exists.
  Base64DecodeFile('VmVsb3ggZXhhbXBsZQ==',
    'C:\VeloxExamples\decoded-example.txt');
end;

Usage​

Base64DecodeFile decodes standard Base64 text and writes the resulting bytes to a file.

Parameters

NameTypeDescription
aBase64Stringstring, constBase64 text whose decoded bytes will become the complete file content.
aFileNamestring, constDestination path. An existing file is replaced; the parent directory must already exist.

Behaviour

  • The destination is created or truncated and then populated with the complete decoded byte sequence.
  • Binary data is preserved; no UTF-8 or other text conversion is applied.
  • The Velox Base64 decoder accepts the standard alphabet and permissively skips whitespace and other invalid characters.
  • The operation does not append, create parent directories, choose a temporary file or perform an atomic replacement.

Errors

Invalid paths, missing directories, access denial, sharing violations, storage failures and memory-allocation errors propagate to the script. Malformed Base64 does not reliably raise because the decoder is permissive.

Usage notes

Use a controlled destination and apply independent size and integrity checks before accepting externally supplied content. When partial output is unacceptable, write to a controlled temporary name and perform an application-level verified replacement.

Additional Technical Info​

Base64DecodeFile decodes a standard Base64 string and saves the resulting bytes to the supplied file path. It is a procedure: success is indicated by normal completion, while failures raise an exception.

The example uses a fictional local path, is source-reviewed and was not executed by the documentation workflow.

Implementation

Velox calls Delphi's shared TNetEncoding.Base64.DecodeStringToBytes, constructs a TBytesStream over the complete decoded result, then calls SaveToFile. The stream is released in a finally block.

Edge cases and quirks

  • The destination is overwritten if it exists. Validate untrusted or dynamically constructed paths before calling this procedure.
  • A zero-length result creates or truncates the destination to an empty file.
  • Malformed, truncated or URL-safe Base64 may be accepted but produce partial or incorrect content because the decoder skips invalid symbols and accepts short final groups.
  • If writing fails after the destination is created or truncated, a partial or empty file may remain.
  • Relative paths are resolved in the execution context of the Velox process, which may differ between Designer and service execution. Prefer an intentional absolute or configured path.

Side effects

Creates, replaces and writes a file using the identity and permissions of the executing Velox process.

Performance and concurrency

The complete decoded content is first held in memory and then represented by a byte stream before being written. This is not a streaming decoder and may require substantial memory for large inputs. Concurrent calls targeting the same file can race, truncate one another or fail with sharing errors.

Related entries

External references

Created 2026-07-15