THPDFRandomAccessSource Class

Abstract base class that lets THotPDF.LoadFromRandomAccessSource load a PDF from any caller-defined seekable byte store without requiring a TStream implementation

Declaration

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;
  function TransferAt(Offset, Count: Int64;
    Destination: TStream): Int64; virtual;
end;

Unit

HPDFDoc

Members

Name	Purpose
`GetSize`	Returns the stable byte length of the backing store
`ReadAt`	Reads `Count` bytes starting at `Offset` into `Buffer`
`IsRangeAvailable`	Reports whether a range can be read without waiting for additional data
`ReadAtCancellable`	Provides a cooperative cancellation path for remote or otherwise blocking reads
`TransferAt`	Writes a source range to a destination stream with a bounded fallback implementation

Usage notes

Derive a subclass and override both abstract methods to adapt HotPDF to HTTP range requests, database BLOBs, compressed archives, encrypted volumes, or any virtual storage that can supply bytes by offset
GetSize must return a stable, non-negative byte length for the lifetime of the load; HotPDF parses the cross-reference tables and object streams by seeking through this source
ReadAt returns the number of bytes actually transferred (zero through Count); the parser treats a short read at the documented end of file as end-of-stream, not as an error
The default ReadAtCancellable implementation checks the supplied token before and after delegating to ReadAt; remote implementations should override it to abort transport work while a request is in flight
The default TransferAt implementation uses a bounded 64 KiB buffer; storage adapters can override it to write from retained source memory directly
THPDFCoalescingRandomAccessSource adds bounded range caching, request coalescing, asynchronous prefetch, cancellation, and statistics around any source
The source must remain valid while the loaded document is in use; pass OwnsSource = True to LoadFromRandomAccessSource to have HotPDF free the source automatically

THPDFRandomAccessSource Class

Declaration

Unit

Members

Usage notes

Related APIs