Class ContentSourceTransformer

java.lang.Object
org.eclipse.jetty.io.content.ContentSourceTransformer
All Implemented Interfaces:
Content.Source
public abstract class ContentSourceTransformer extends Object implements Content.Source

This abstract Content.Source wraps another Content.Source and implementers need only to implement the transform(Content.Chunk) method, which is used to transform Content.Chunk read from the wrapped source.

The demand(Runnable) conversation is passed directly to the wrapped Content.Source, which means that transformations that may fully consume bytes read can result in a null return from Content.Source.read() even after a callback to the demand Runnable (as per spurious invocation in Content.Source.demand(Runnable).

  • Constructor Details

  • Method Details

    • getContentSource

      protected Content.Source getContentSource()

    • read

      public Content.Chunk read()
      Description copied from interface: Content.Source

      Reads a chunk of content.

      See how to use this method idiomatically.

      The returned chunk could be:

      • null, to signal that there isn't a chunk of content available
      • an Content.Chunk instance with non null Content.Chunk.getFailure(), to signal that there was a failure trying to produce a chunk of content, or that the content production has been failed externally
      • a Content.Chunk instance, containing the chunk of content.

      Once a read returns an Content.Chunk instance with non-null Content.Chunk.getFailure() then if the failure is last further reads will continue to return the same failure chunk instance, otherwise further read() operations may return different non-failure chunks.

      Once a read returns a last chunk, further reads will continue to return a last chunk (although the instance may be different).

      The content reader code must ultimately arrange for a call to Retainable.release() on the returned Content.Chunk.

      Additionally, prior to the ultimate call to Retainable.release(), the reader code may make additional calls to Retainable.retain(), that must ultimately be matched by a correspondent number of calls to Retainable.release().

      Concurrent reads from different threads are not recommended, as they are inherently in a race condition.

      Reads performed outside the invocation context of a demand callback are allowed. However, reads performed with a pending demand are inherently in a race condition (the thread that reads with the thread that invokes the demand callback).

      Specified by:
      read in interface Content.Source
      Returns:
      a chunk of content, possibly a failure instance, or null
      See Also:

    • demand

      public void demand(Runnable demandCallback)
      Description copied from interface: Content.Source

      Demands to invoke the given demand callback parameter when a chunk of content is available.

      See how to use this method idiomatically.

      Implementations guarantee that calls to this method are safely reentrant so that stack overflows are avoided in the case of mutual recursion between the execution of the Runnable callback and a call to this method. Invocations of the passed Runnable are serialized and a callback for demand call is not invoked until any previous demand callback has returned. Thus the Runnable should not block waiting for a callback of a future demand call.

      The demand callback may be invoked spuriously: a subsequent call to Content.Source.read() may return null.

      Calling this method establishes a pending demand, which is fulfilled when the demand callback is invoked.

      Calling this method when there is already a pending demand results in an IllegalStateException to be thrown.

      If the invocation of the demand callback throws an exception, then Content.Source.fail(Throwable) is called.

      Specified by:
      demand in interface Content.Source
      Parameters:
      demandCallback - the demand callback to invoke where there is a content chunk available
      See Also:

    • fail

      public void fail(Throwable failure)
      Description copied from interface: Content.Source

      Fails this content source with a last failure chunk, failing and discarding accumulated content chunks that were not yet read.

      The failure may be notified to the content reader at a later time, when the content reader reads a content chunk, via a Content.Chunk instance with a non null Content.Chunk.getFailure().

      If Content.Source.read() has returned a last chunk, this is a no operation.

      Typical failure: the content being aborted by user code, or idle timeouts.

      If this method has already been called, then it is a no operation.

      Specified by:
      fail in interface Content.Source
      Parameters:
      failure - the cause of the failure
      See Also:

    • transform

      protected abstract Content.Chunk transform(Content.Chunk inputChunk)

      Transforms the input chunk parameter into an output chunk.

      When this method produces a non-null, non-last chunk, it is subsequently invoked with a null input chunk to try to produce more output chunks from the previous input chunk. For example, a single compressed input chunk may be transformed into multiple uncompressed output chunks.

      The input chunk is released as soon as this method returns, so implementations that must hold onto the input chunk must arrange to call Retainable.retain() and its correspondent Retainable.release().

      Implementations should return an Content.Chunk with non-null Content.Chunk.getFailure() in case of transformation errors.

      Exceptions thrown by this method are equivalent to returning an error chunk.

      Implementations of this method may return:

      • null, if more input chunks are necessary to produce an output chunk
      • the inputChunk itself, typically in case of non-null Content.Chunk.getFailure(), or when no transformation is required
      • a new Content.Chunk derived from inputChunk.
      Parameters:
      inputChunk - a chunk read from the wrapped Content.Source
      Returns:
      a transformed chunk or null