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LoadAndHashFile

Function LoadAndHashFile( const aFileName : string) : string

Example​

procedure ScriptEvent(var Value: Variant);
begin
  Value := LoadAndHashFile('C:\VeloxExamples\fictional-order.edi');
end;

Usage​

LoadAndHashFile reads a file and returns an uppercase MD5 hexadecimal digest of its complete byte content.

Parameters

NameTypeDescription
aFileNamestring, constFile to open in Velox process identity. Relative paths use the process's current path context; use an unambiguous governed path in production.

Returns

A 32-character uppercase MD5 value using characters 0-9 and A-F. An empty file returns the standard empty-byte MD5 value D41D8CD98F00B204E9800998ECF8427E; it does not return an empty string.

Behaviour

  • File bytes are hashed exactly; no text decoding, newline conversion or Unicode normalisation occurs.
  • The private stream starts at zero, so a stable file is hashed from its first byte to its current end.
  • fmShareDenyNone allows other processes to retain or obtain compatible access while hashing.
  • The file is opened and read synchronously on the executing Velox thread.

Errors

Missing files, access denial, invalid paths, share violations, device/network failures, stream-size/read failures, hashing-interface/provider failures and memory errors propagate to the script. There is no sentinel return, retry, timeout or partial-success result.

Usage notes

Use this helper only where a partner or legacy store requires MD5 compatibility. For ordinary Velox change fingerprints, prefer a stronger current algorithm and persist the algorithm name, output encoding and casing with the stored value. If the file can change, arrange application-level quiescence or hash an immutable copy.

Additional Technical Info​

LoadAndHashFile reads the complete byte content of a file and returns its MD5 digest as 32 uppercase hexadecimal characters. It is suitable for compatibility workflows that already define MD5 as a file fingerprint. It must not be used to establish that an untrusted file is authentic or safe.

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

Implementation

Velox creates a TFileStream with fmOpenRead or fmShareDenyNone. A newly opened stream starts at position zero. The wrapper passes it to MD5HashStream, which creates the shipped Indy TIdHashMessageDigest5, hashes from the current position through the reported stream size and formats the 16-byte digest with Indy's uppercase hexadecimal conversion. Indy uses its registered hashing interface when that interface and MD5 are available (the shipped application can bind this interface to OpenSSL); otherwise it uses its native MD5 implementation. Both the hasher and file stream are freed in finally blocks.

This path uses the shipped Indy MD5 implementation. It does not call Delphi System.Hash.THashMD5.GetHashStringFromFile.

Edge cases and quirks

  • MD5 has practical collision attacks. Two different inputs can be deliberately constructed with the same digest, so do not use this result as a signature, trust decision, malware check or authorisation control.
  • The output is uppercase. MD5HashHex, which uses Delphi System.Hash, returns lowercase hexadecimal for non-empty text.
  • Sharing does not provide a snapshot. If another process changes or replaces the file during the read, the result can represent bytes observed across that change rather than one stable version.
  • A relative path, mapped drive or network location is resolved in the Velox service/application account and session, which may differ from an interactive user's environment.
  • The helper follows the filesystem's normal path and link resolution. It performs no allow-list, size, extension or content validation.

Side effects

The function opens and reads the file. It does not intentionally write or delete it. The open handle can still interact with concurrent rename/delete rules imposed by the filesystem and other handles.

Performance and concurrency

Runtime is linear in file size. Indy processes the stream incrementally rather than loading the complete file into one byte array, so hash working memory is bounded, although operating-system buffering still applies. Independent calls own independent streams and hash objects. Concurrent calls are safe only to the extent that the underlying file remains stable and accessible.

Related entries

  • MD5HashStream exposes the same shipped Indy terminal for an existing stream and consumes it from its current position.
  • MD5HashHex hashes UTF-8 text through Delphi System.Hash and uses lowercase output.
  • HashString provides Velox's SHA-384 text fingerprint helper.

External references

Created 2026-07-15