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MD5HashStream

Function MD5HashStream( aStream : TStream) : string

Example​

procedure ScriptEvent(var Value: Variant);
var
  Buffer: TMemoryStream;
begin
  Buffer := TMemoryStream.Create;
  try
    StringToStreamUTF8('fictional integration payload', Buffer);
    Buffer.Position := 0;
    Value := MD5HashStream(Buffer);
    // Buffer.Position is now at Buffer.Size.
  finally
    Buffer.Free;
  end;
end;

Usage​

MD5HashStream hashes bytes from a stream's current position to its end with MD5 and returns uppercase hexadecimal text.

Parameters

NameTypeDescription
aStreamTStreamExisting non-nil readable stream whose Position and Size can be queried. Hashing begins at its incoming position and changes that position.

Returns

A 32-character uppercase MD5 value using 0-9 and A-F. If the stream has zero bytes remaining, the result is the standard empty-byte MD5 value D41D8CD98F00B204E9800998ECF8427E.

Behaviour

  • Hashing starts at the exact incoming stream position, not automatically at offset zero.
  • For a normal seekable stream, all remaining bytes are read and the final position equals the size observed at the start.
  • Bytes are hashed without text decoding or transformation.
  • Rewind explicitly before the call when the contract is to hash complete content.

Errors

A nil object, unsupported size/position operations, read failures, invalid stream state, hashing-interface/provider failures, allocation failures and Velox hash exceptions propagate. There is no partial digest or error return.

Usage notes

Save and restore the position in caller code only if that is safe for the stream and required by the surrounding workflow. If another component can mutate the source while hashing, coordinate an immutable view. Use MD5 only for required legacy compatibility.

Additional Technical Info​

MD5HashStream hashes the remaining bytes of an existing stream, beginning at its current Position, and returns a 32-character uppercase hexadecimal MD5 value. The caller retains ownership of the stream, but the function consumes the hashed range and does not restore the position.

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

Implementation

Velox creates a shipped Indy TIdHashMessageDigest5 for each call and invokes HashStreamAsHex(aStream). Indy's no-range overload delegates with start and size set to -1: it does not assign a start position and calculates aStream.Size - aStream.Position. Indy then uses its registered hashing interface when that interface and MD5 are available (the shipped application can bind it to OpenSSL), otherwise it uses its native MD5 block implementation. Both branches read the remaining range and convert the 16-byte result through Indy's uppercase ToHex. The hasher is freed in a finally block; the supplied stream is not freed.

Edge cases and quirks

  • The stream position is a material input. The same stream content produces a different digest when the call starts at a different offset.
  • A stream already positioned at its end returns the standard empty-byte digest, not ''.
  • The function does not restore the position after success or failure. On a read error it may leave the stream partly consumed.
  • Streams that cannot report Size/Position, have a position outside the normal 0..Size range, return short reads or change concurrently do not have a stable supported result and can raise.
  • Output is uppercase, unlike Delphi-based MD5HashHex, which emits lowercase.
  • MD5 is collision-broken and cannot prove authenticity or adversarial integrity.

Side effects

The caller's stream position changes. Reading can also trigger implementation-specific effects in file, network, decompression or custom streams. The wrapper does not close, clear or free the supplied stream.

Performance and concurrency

Time is linear in the remaining byte count. Indy reads incrementally: its interface branch uses bounded chunks and its native branch processes fixed-size MD5 blocks, so neither copies the entire stream into one array. Do not call concurrently against the same stream: position and content access are mutable and unsynchronised. Independent streams use independent hash objects, although an available hashing interface can rely on process-wide provider state.

Related entries

  • LoadAndHashFile owns a new file stream, starts at offset zero and delegates to this function.
  • MD5HashHex hashes UTF-8 text and returns lowercase hexadecimal.
  • StringToStreamUTF8 writes the UTF-8 bytes used in the example.

External references

Created 2026-07-15