create ~read ~compression descr creates a new context for reading data from the specified descriptor using the specified compression method.

The semantics of the read function shall mimic that of Unix.read, attempting to read into a substring of the buf and returning the number of bytes actually read. A read of length 0 indicates end-of-file.

dequeue_message context attempts to remove a complete message from the incoming queue of the read context. No data will be read from the underlying descriptor.

• returns

  None if there is insufficient data stored in the read context to decode a complete message

• raises Unsupported_message_frame

  if the frame header describes a segment count or segment size that is too large for the implementation

bytes_available context obtains the number of bytes already read which are currently stored in the read context.

read context attempts to read some data from the underlying descriptor, storing it in the read context.

• returns

  the number of bytes actually read

read_message context attempts to remove a complete message from the incoming queue of the read context. read may be invoked repeatedly to provide enough buffered data to decode a complete message.

• returns

  None if end-of-file was reached before a complete message could be read

• raises Unsupported_message_frame

  if the frame header describes a segment count or segment size that is too large for the implementation