clojure - Composing a Buffy buffer from the middle of an array and finding out how much it has consumed -

i'd use buffy interpret binary data starting middle of array. need find out how many bytes of array have been consumed buffy.

let's have dynamic buffer definition this:

(ns foo.core   (:refer-clojure :exclude [read])   (:use [byte-streams])   (:require [clojurewerkz.buffy.core :refer :all]             [clojurewerkz.buffy.frames :refer :all]             [clojurewerkz.buffy.types.protocols :refer :all])   (:import [io.netty.buffer unpooled bytebuf]))  (def dynbuf   (let [string-encoder (frame-encoder [value]                                       length (short-type) (count value)                                       string (string-type (count value)) value)         string-decoder (frame-decoder [buffer offset]                                       length (short-type)                                       string (string-type (read length buffer offset)))]     (dynamic-buffer (frame-type string-encoder string-decoder second)))) 

i hoped use netty bytebuf parse bunch of bytes using dynbuf starting @ offset:

(def buf   (let [bytes (concat [0 0 0 4] (map #(byte %) "foobar"))         offset 2]     (unpooled/wrappedbuffer (byte-array bytes) offset (- (count bytes) offset)))) 

at point, can parse buf per dynbuf:

user> (decompose dynbuf buf) ["foob"] 

at point, hoping reading short-type , string-type buf has moved readerindex 6, alas, not so:

user> (.readerindex buf) 0 

is because buffy/decompose makes kind of shallow copy of stream internal use, readerindex of outer buf not updated? or misunderstanding readerindex supposed be?

how can achieve original goal of passing (byte-array) @ given offset buffy , learning how many bytes has consumed?

buffy is using absolute version of getxxx method, not modify position of buffer, cannot use .readerindex.

i see 2 possible options, depending on trying achieve:

1. use buffy dynamic frames. note clojurewerkz.buffy.frames namespace has decoding-size function if want know how dynamic frame take. like:

   (defn read-from-middle [data f-type start-idx]   (let [tmp-buf (unpooled/wrappedbuffer data start-idx (- (alength data) start-idx))         buffy-buffer (dynamic-buffer f-type)         total-size (decoding-size f-type tmp-buf 0)]     [(decompose buffy-buffer tmp-buf) (+ start-idx total-size)]))  (def f-type   (let [string-encoder (frame-encoder [value]                                       length (short-type) (count value)                                       string (string-type (count value)) value)         string-decoder (frame-decoder [buffer offset]                                       length (short-type)                                       string (string-type (read length buffer offset)))]     (frame-type string-encoder string-decoder second)))  (let [my-data (byte-array [0 1 0x61 0 2 0x62 0x63 0 1 0x64])       idx 0       [i1 idx] (read-from-middle my-data f-type idx)       [i2 idx] (read-from-middle my-data f-type idx)       [i3 idx] (read-from-middle my-data f-type idx)]   [i1 i2 i3]) 

2. calculate size of frame as buffy doing , manually set correct position in buffer. like:

   (import [io.netty.buffer unpooled]) (require '[clojurewerkz.buffy.core :as buffy]          '[clojurewerkz.buffy.types.protocols :as ptypes])  (defn read-from-middle [data spec start-idx]   (let [total-size (reduce + (map ptypes/size (map second spec)))         tmp-buf (unpooled/wrappedbuffer data start-idx (- (alength data) start-idx))         buffy-buffer (buffy/compose-buffer spec :orig-buffer tmp-buf)]     [(buffy/decompose buffy-buffer) (+ start-idx total-size)]))  (let [my-data (byte-array [0 0 0 1 0 0 0 2 0 0 0 3])       spec (buffy/spec :foo (buffy/int32-type))       idx 0       [i1 idx] (read-from-middle my-data spec idx)       [i2 idx] (read-from-middle my-data spec idx)       [i3 idx] (read-from-middle my-data spec idx)]    [i1 i2 i3])