Unit CastleDownload

Register how we can load and/or save the URLs with given protocol. One (or even both) of given events (ReadEvent, WriteEvent) can be Nil.

Parameters

ReadEvent

Used when using synchronous reading by Download.

WriteEvent

Used when using synchronus writing by URLSaveStream.

AsynchronousReader

Used when using asynchronous reading by TCastleDownload.

Exceptions raised

EProtocolAlreadyRegistered

If the protocol handlers are already registered.

Is given protocol name registered with RegisterUrlProtocol.

Unregister protocol, reverting the RegisterUrlProtocol.

Return a stream to read given URL. Returned stream is suitable only for reading, and the initial position is always at the beginning. Overloaded version also returns a MIME type (or '' if unknown).

Any errors are reported by raising exceptions.

All the supported URL protocols are documented in our manual: https://castle-engine.io/manual_network.php . They include:

• Local file URLs. Moreover URL without any protocol is always treated like a local filename (absolute or relative to current dir), so this function can be a drop-in replacement for normal file reading. The MIME type for local files is guessed based on their extension.

• Data URI scheme (http://en.wikipedia.org/wiki/Data_URI_scheme).

• Protocols to embed script contents: ecmascript, javascript (see X3D specifications), castlescript, kambiscript (see https://castle-engine.io/castle_script.php), compiled (https://castle-engine.io/x3d_extensions.php#section_ext_script_compiled).

• Set EnableBlockingDownloads to True to support http and https protocols. The MIME type for such content is usually reported by the http server (but if the server doesn't report MIME type, we still try to determine it, looking at URL using UriMimeType).

This routine makes a synchronous (blocking) downloading. Which means that if you use a network URL (like http://...) then your application will wait until the data arrives from the Internet. There may be a timeout of the request (so your application will not hang indefinitely), but still your code (or user) have no way to cancel or watch the progress of this operation. This is why http/https support is disabled by default (see EnableBlockingDownloads). This is sometimes acceptable (e.g. if you're waiting during the "loading" process, and the data just has to be downloaded in order to continue), and it's really easy to use (you just download data exactly the same way like you open a local file).

You can use asynchronous downloading through the TCastleDownload class instead.

Exceptions raised

EDownloadError

In case of problems loading from this URL.

Any exceptions inside internal loading routines, like EFOpenError or EStreamError, are internally caught and changed to EDownloadError.

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Warning: this symbol is deprecated: use EnableBlockingDownloads

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Warning: this symbol is deprecated: use EnableBlockingDownloads

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Create a stream to save (write to) a given URL.

For example, to save a file. When you use URLSaveStream with URL with a file protocol, or just with a regular filename, it will return a TFileStream instance to write this file.

This function supports any CGE custom protocol registered by RegisterUrlProtocol, if only you provided WriteEvent: TUrlWriteEvent when registering that protocol.

Note: When saving to castle-data URL, remember that on some platforms (like Android) or installation methods (like system-wide installation on Linux or Windows) the game data is read-only. To be portable, you should never use URLSaveStream with the castle-data protocol. It is only useful in limited cases when you know that you distribute your game in such way (and users install it in such way) and on such platforms, that the "data" directory is writable.

On Android, you should use the "write_external_storage" service to be able to write storage files (e.g. to SD card). This means files accessed by the 'file' protocol. See https://castle-engine.io/android-Services .

Example usage:

var
  Stream: TStream;
  I: Uint32;
begin
  Stream := URLSaveStream('file:///tmp/foo.txt', []);
  try
    // write some strings
    WritelnStr(Stream, 'Some string');
    WritelnStr(Stream, 'Another string');
    // write some binary data
    I := 666;
    Stream.WriteBuffer(I, SizeOf(I));
  finally FreeAndNil(Stream) end;
end;

Exceptions raised

ESaveError

In case of problems saving this URL.

Exception

Various TStream instances (used internally by this function) may raise exceptions in case the stream cannot be created for saving. Right now, we simply let these exceptions to "pass through" from this function (instead of catching and re-raising). So be ready that this function may raise any Exception class.

Warning: this symbol is deprecated: use Download(Url, [soForceMemoryStream])

Open a proper stream to read a file, fast (with buffering) and with seeking. This gives you a stream most comfortable for reading (buffering means that you can read small, comfortable pieces of it; seeking means you can jump freely to various file positions, back and forward).

On different OSes or even compilers this may require a little different stream, so it's safest to just use this function. For example, traditional Classes.TFileStream doesn't do buffering. Although under Linux, the buffering of file handles is done at kernel level (so everything works fast), on Windows the slowdown is noticeable. This function will always create proper stream descendant, eventually wrapping some standard stream in a buffered stream with full seeking capability.

Instead of this, use Download with [soForceMemoryStream].

Save the contents of given Stream to an Url.

See TCastleDownload.Status.

Values

• dsNotStarted
• dsDownloading
• dsError
• dsSuccess

See TCastleDownload.HttpMethod.

Values

• hmGet
• hmPost
• hmPut
• hmDelete
• hmOptions
• hmHead

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Event called when Download function wants to download URL with this protocol. Use with RegisterUrlProtocol.

Event called when URLSaveStream function wants to save URL with this protocol. Use with RegisterUrlProtocol.

Options for the Download function.

Values

• soForceMemoryStream: Force result to be a TCustomMemoryStream, with contents fully loaded to the memory, and freely seekable (you can move back and forth within). Without this option, Download may return other streams, for example TFileStream (that may not have good buffering, depending on OS) or TBase64DecodingStream (that may not allow seeking).

  Using TCustomMemoryStream means that reading is fast and comfortable, but eats memory and doesn't allow to simultaneously read and process the contents (the file must be fully loaded, e.g. downloaded from the Internet, and ungzipped, before this function returns). So use this option only for files that aren't too big.

  For larger files, you usually don't want to use this option, instead wrap result in TBufferedReadStream.

• soGzip: Filter the contents through gzip decompression.

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Options for the UrlSaveStream function.

Values

• ssoGzip: Filter the contents through gzip compression.

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Log (through CastleLog) all loading, that is: all calls to Download. This allows to easily check e.g. whether the engine is not loading something during the game (which usually badly affects the performance).

Does Download (synchronous downloading routine) support http and https protocol. This is by default disabled, as it means that a call to Download may block your application, for arbitrarily long time, and you have no way to interrupt it. It is recommended to use asynchronous downloading, using TCastleDownload, to download resources over the network.

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