THotPDF.LoadFromRandomAccessSource

Loads a PDF through a caller-defined seekable byte source without requiring a TStream implementation

Declarations

THPDFRandomAccessSource = class
public
  function GetSize: Int64; virtual; abstract;
  function IsRangeAvailable(Offset, Count: Int64): Boolean; virtual;
  function ReadAt(Offset: Int64; var Buffer;
    Count: Longint): Longint; virtual; abstract;
  function ReadAtCancellable(Offset: Int64; var Buffer;
    Count: Longint; CancellationToken: THPDFCancellationToken): Longint; virtual;
end;

function LoadFromRandomAccessSource(
  Source: THPDFRandomAccessSource;
  OwnsSource: Boolean = False): Integer; overload;

function LoadFromRandomAccessSource(
  Source: THPDFRandomAccessSource;
  const Password: AnsiString;
  OwnsSource: Boolean = False): Integer; overload;

Contract

GetSize returns the stable byte length and must not return a negative value
ReadAt reads at the supplied zero-based offset and returns a count from zero through the requested count
HotPDF automatically wraps ordinary sources in a 256 KiB range coalescer with a 2 MiB bounded cache and cancellation-aware asynchronous prefetch
Passing an existing THPDFCoalescingRandomAccessSource preserves caller-selected block, cache, ownership, and prefetch settings
Override ReadAtCancellable when the backing transport can abort an in-flight request; its default implementation remains compatible with existing ReadAt-only subclasses
The source must remain valid while the loaded document is in use unless OwnsSource is True
With ownership enabled, HotPDF frees the source when another source is loaded, when loading fails, or when the component is destroyed
The password overload first reads bounded trailer and cross-reference ranges, then fetches the referenced encryption dictionary by its authoritative object offset so RC4 and AES password loading does not require a complete-source request on valid files
Loading without a password captures the bounded raw encryption object and first trailer ID while the source is available; a later DecryptLoadedDocument call uses the exact binary O, U, OE, and UE values without rereading the source
If bounded key recovery cannot establish a supported key, HotPDF retains the complete-source compatibility fallback

The result is the loaded page count, matching LoadFromFile and LoadFromStream. Bounded password-key recovery is available since HotPDF v2.489.0, zero-reread delayed decryption is available since HotPDF v2.490.0, and automatic range coalescing is available since HotPDF v2.524.0