The type for input sources. With a `Manual source the client must provide input with src. With `String or `Channel source the client can safely discard `Await case (with assert false).

The type for output destinations. With a `Manual destination the client must provide output storage with dst. With `Buffer or `Channel destination the client can safely discard `Flush case (with assert false).

The type for GZIP encoders.

encoder src dst ~mtime os ~q ~w ~level is an encoder that inputs from src and that outputs to dst.

Internal queue.

encoder deals internally with compression algorithm and DEFLATE encoder. To pass compression values to DEFLATE encoder, we need a queue q. Length of q has an impact on performance, and small lengths can be a bottleneck, leading encode to emit many `Flush. We recommend a que as large as output buffer.

Window.

GZIP needs a sliding window to operate the LZ77 compression. The window must be a 32k window (De.make_window with bits = 15). The allocated window can be re-used by an other inflation/deflation process - but it can not be re-used concurrently or cooperatively with another inflation/deflation process.

Level.

Current implementation of GZIP does not handle any compression level. However, the client must give a level between 0 and 9, inclusively, Otherwise, we raise an Invalid_argument.

Metadata.

Client is able to store some metadata such as:

• mtime time of last modification of the input.
• os os which did the compression.
• filename filename of the input (no limitation about length).
• comment an arbitrary payload (no limitation about length).
• ascii if encoding of contents is ASCII.
• hcrc if the client wants a checksum of the GZIP header.

src_rem e is how many bytes it remains in given input buffer.

dst_rem e is how many unused bytes remain in the output buffer of e.

src e s j l provides e with l bytes to read, starting at j in s. This byte range is read by calls to encode with e until `Await is returned. To signal the end of input call the function with l = 0.

• raises Invalid_argument

  when j and l do not correspond to a valid range.

dst e s j l provides e with l bytes available to write, starting at j in s. This byte range is fill by calls to encode with e until `Flush is returned.

• raises Invalid_argument

  when j and l do not correspond to a valid range.

encode e0 is:

• `Await e1 if e0 has a `Manual input source and awaits for more input. The client must use src with e1 to provide it.
• `Flush e1 if e0 has a `Manual destination and needs more output storage. The client must drain the buffer before resuming operation.
• `End e1 if e0 encoded all input. Output buffer is possibly not empty (it can be check with dst_rem).

Limitation.

The encoder must manipulate an output buffer of, at least, 2 bytes. If it's not the case, encode does nothing - and it tells you nothing more than it did nothing. Depending on what you do, a loop can infinitely call encode without any updates until the given output still has less than 2 bytes.