chickadee » zlib » zlib-decompressing-input-port

These options are passed to inflateInit2.

• window-bits: The history buffer size. When decompressing a stream, the window size must not be smaller than the size originally used to compress the stream. Valid ranges are:
  • 0 to automatically detect the window size from the zlib header (supported since zlib 1.2.3.5)
  • [8..15] for zlib RFC1950 streams.
  • [−8..−15] for raw deflate RFC1951 streams.
  • [24..31] for gzip RFC1952 streams.
  • [40..47] for either zlib or gzip streams, automatically detected by header.
• buffer: A string, often heavily mutated, used for internal transfers. (make-string 4096) is the default.

For example, we can decompress the zlib data from the example above like this:

(read-string #f
  (zlib-decompressing-input-port
     (open-input-string
      (blob->string #${789ccb48cdc9c95728cf2fca4901001a0b045d}))))
;; => "hello world"

This will expect zlib headers. To detect gzip or zlib headers, specify higher values for window-bits:.

;; $ printf "hello world" | pigz -z | xxd -plain -c0
;; 785ecb48cdc9c95728cf2fca4901001a0b045d
(define hello.zlib (blob->string #${785ecb48cdc9c95728cf2fca4901001a0b045d}))
;; $ printf "hello world" | gzip - | xxd -plain -c0
;; 1f8b0800000000000003cb48cdc9c95728cf2fca49010085114a0d0b000000
(define hello.gz (blob->string #${1f8b0800000000000003cb48cdc9c95728cf2fca49010085114a0d0b000000}))
(read-string #f (zlib-decompressing-input-port (open-input-string hello.zlib) #:window-bits 47))
;; => "hello world"
(read-string #f (zlib-decompressing-input-port (open-input-string hello.gz)   #:window-bits 47))
;; => "hello world"