decompress 1.4.2 · OCaml Package

type src = [

| `Channel of in_channel
| `String of string
| `Manual

]

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).

type dst = [

| `Channel of out_channel
| `Buffer of Buffer.t
| `Manual

]

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

type encoder

The type for ZLIB encoders.

type ret = [

| `Await of encoder
| `End of encoder
| `Flush of encoder

]

val encoder : 
  ?dynamic:bool ->
  q:De.Queue.t ->
  w:De.Lz77.window ->
  level:int ->
  src ->
  dst ->
  encoder

encoder ~q ~w ~level src dst 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 queue as large as output buffer.

Window.

ZLIB is able to constrain length of window used to do LZ77 compression. However, small window can slow-down LZ77 compression algorithm. Small windows are mostly used to enable inflation of output in memory-constrained environments, for example when compressed data from untrusted sources must be processed.

Level.

Zlib implements 10 levels (from 0 to 9). All of them use the dynamic & canonic huffman if dynamic is true (default). Otherwise, we use the static huffman. The higher the level, the better the ratio.

val src_rem : encoder -> int

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

val dst_rem : encoder -> int

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

val src : encoder -> bigstring -> int -> int -> encoder

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.

val dst : encoder -> bigstring -> int -> int -> encoder

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.

val encode : encoder -> ret

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 e1 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.

module Ns : sig ... end

package decompress