| Andrew Cooke | Contents | Latest | RSS | Twitter | Previous | Next

C[omp]ute

Welcome to my blog, which was once a mailing list of the same name and is still generated by mail. Please reply via the "comment" links.

Always interested in offers/projects/new ideas. Eclectic experience in fields like: numerical computing; Python web; Java enterprise; functional languages; GPGPU; SQL databases; etc. Based in Santiago, Chile; telecommute worldwide. CV; email.

Personal Projects

Lepl parser for Python.

Colorless Green.

Photography around Santiago.

SVG experiment.

Professional Portfolio

Calibration of seismometers.

Data access via web services.

Cache rewrite.

Extending OpenSSH.

C-ORM: docs, API.

Last 100 entries

Have to add...; Culturally Liberal and Nothing More; Weird Finite / Infinite Result; Your diamond is a beaten up mess; Maths Books; Good Bike Route from Providencia / Las Condes to Panul\; Iain Pears (Author of Complex Plots); Plum Jam; Excellent; More Recently; For a moment I forgot StackOverflow sucked; A Few Weeks On...; Chilean Book Recommendations; How To Write Shared Libraries; Jenny Erpenbeck (Author); Dijkstra, Coins, Tables; Python libraries error on OpenSuse; Deserving Trump; And Smugness; McCloskey Economics Trilogy; cmocka - Mocks for C; Concept Creep (Americans); Futhark - OpenCL Language; Moved / Gone; Fan and USB issues; Burgers in Santiago; The Origin of Icosahedral Symmetry in Viruses; autoenum on PyPI; Jars Explains; Tomato Chutney v3; REST; US Elections and Gender: 24 Point Swing; PPPoE on OpenSuse Leap 42.1; SuperMicro X10SDV-TLN4F/F with Opensuse Leap 42.1; Big Data AI Could Be Very Bad Indeed....; Cornering; Postcapitalism (Paul Mason); Black Science Fiction; Git is not a CDN; Mining of Massive Data Sets; Rachel Kaadzi Ghansah; How great republics meet their end; Raspberry, Strawberry and Banana Jam; Interesting Dead Areas of Math; Later Taste; For Sale; Death By Bean; It's Good!; Tomato Chutney v2; Time ATAC MX 2 Pedals - First Impressions; Online Chilean Crafts; Intellectual Variety; Taste + Texture; Time Invariance and Gauge Symmetry; Jodorowsky; Tomato Chutney; Analysis of Support for Trump; Indian SF; TP-Link TL-WR841N DNS TCP Bug; TP-Link TL-WR841N as Wireless Bridge; Sending Email On Time; Maybe run a command; Sterile Neutrinos; Strawberry and Banana Jam; The Best Of All Possible Worlds; Kenzaburo Oe: The Changeling; Peach Jam; Taste Test; Strawberry and Raspberry Jam; flac to mp3 on OpenSuse 42.1; Also, Sebald; Kenzaburo Oe Interview; Otake (Kitani Minoru) move Black 121; Is free speech in British universities under threat?; I am actually good at computers; Was This Mansplaining?; WebFaction / LetsEncrypt / General Disappointment; Sensible Philosophy of Science; George Ellis; Misplaced Intuition and Online Communities; More Reading About Japan; Visibilty / Public Comments / Domestic Violence; Ferias de Santiago; More (Clearly Deliberate); Deleted Obit Post; And then a 50 yo male posts this...; We Have Both Kinds Of Contributors; Free Springer Books; Books on Religion; Books on Linguistics; Palestinan Electronica; Books In Anthropology; Taylor Expansions of Spacetime; Info on Juniper; Efficient Stream Processing; The Moral Character of Crypto; Hearing Aid Info; Small Success With Go!; Re: Quick message - This link is broken; Adding Reverb To The Echo Chamber; Sox Audio Tools

© 2006-2015 Andrew Cooke (site) / post authors (content).

Erlang - Processes, Objects, Protocols

From: "andrew cooke" <andrew@...>

Date: Wed, 2 May 2007 22:13:06 -0400 (CLT)

I was going to write a long post about this code, but I really don't have
the time.  So it's just here in case anyone feels like reading it.  The
first section defines a protocol and supporting functions for chaining
data through different processes (the "unix pipe" idea).  The protocol is
minimal - just data or exit - but each process can have some persistent
state that is preserved across calls.

I'm particularly proud of the formatting here :o)  Took me some time to
work out what is (and isn't) possible with the syntax, scoping, etc.


forward(none, Message) -> Message;
forward(Next, Message) -> Next(Message).

new(Response, Filter, Name, Next) ->

    DoLog =
        fun(Template, Params) -> res_info(Response, Template, Params) end,


    % when the Filter is called with a {data, State, Data} tuple it
    % should return one of:
    % - {data, Data2} containing processed data
    % - {state, State2} containing new state
    % - {both, State2, Data2} containing new state and data
    % new data (Data2) are forwarded to the next filter in the chain,
    % if defined (it may be "none") even if identical to old values.
    % to avoid forwarding anything to the next filter, return state
    % alone.

    DoData =
        fun(Driver, _State, {both, State2, Data2}) ->
                forward(Next, {data, Data2}),
                Driver(Driver, State2);
           (Driver, State, {data, Data2}) ->
                forward(Next, {data, Data2}),
                Driver(Driver, State);
           (Driver, _State, {state, State2}) ->
                Driver(Driver, State2);
           (_Driver, _State, Other) ->
                DoLog("Unexpected result ~p in ~p", [Other, Name])
        end,


    % when the Filter is called with the {exit, State} tuple it should
    % return one of:
    % - {data, Data} containing final data to be forwarded
    % - exit
    % if data are returned they are passed to the next filter (if
    % defined), after which, "exit" is forwarded.

    DoExit =
        fun({data, Data}) ->
                forward(Next, {data, Data}),
                Next(exit);
           (exit) ->
                Next(exit);
           (Other) ->
                DoLog("Unexpected result ~p in ~p", [Other, Name])
        end,


    % driver loop.

    Driver =
        fun(Driver, State) ->
                receive
                    {data, Data} ->
                        DoData(Driver, State, Filter({data, State, Data}));
                    exit ->
                        DoExit(Filter({exit, State}));
                    Other ->
                        DoLog("Unexpected message ~p in ~p", [Other, Name])
                end
        end,

    Pid = spawn(fun() -> Driver(Driver, Filter(start)) end),
    fun(Message) -> Pid ! Message end.


Next, some example processes.  First, a simple one that groups the data by
lines (ended by newline character).  Note the exit strategy handles a
missing final newline.

lines(start) -> [];
lines({data, Partial, Data}) ->
    {Partial2, Lines} = collect(Data, Partial, []),
    {both, Partial2, Lines};
lines({exit, Partial}) -> {data, [lists:reverse(Partial)]}.

collect([], Partial, Lines) -> {Partial, lists:reverse(Lines)};
collect([$\n|Data], Partial, Lines) ->
    Line = lists:reverse([$\n|Partial]),
    collect(Data, [], [Line|Lines]);
collect([C|Data], Partial, Lines) ->
    collect(Data, [C|Partial], Lines).


And second, a process that "gunzips" a stream.  As far as I can tell, the
Erlang zlib library doesn't (directly) support streaming gunzip, so this
accumulates the data beforehand.

unzip(start) -> [];
unzip({data, Acc, Data}) -> {state, [Data|Acc]};
unzip({exit, Acc}) ->
    Compressed = list_to_binary(lists:reverse(Acc)),
    Decompressed = binary_to_list(zlib:gunzip(Compressed)),
    {data, Decompressed}.


I was worried that this buffering would make subsequent chained processes
inefficient (processors waiting on data), so here's something that
fragments the input to a process (and shows that wrapping these processes
as functions pays off).

shape_before(Fun, ChunkLimit) ->
    fun({data, Data}) -> fragment(Fun, ChunkLimit, Data);
       (Message) -> Fun(Message)
    end.

fragment(_Fun, _Chunklimit, []) -> ok;
fragment(Fun, Chunklimit, Data) when length(Data) > Chunklimit ->
    {Chunk, Data2} = lists:split(Chunklimit, Data),
    Fun({data, Chunk}),
    fragment(Fun, Chunklimit, Data2);
fragment(Fun, _Chunklimit, Data) ->
    Fun({data, Data}).


Finally, this is construction of a chain of processes, with fragmentation
and optional compression:

close(Response) ->
    res_info(Response, "Closing"),
    Channel = response:channel(Response),
    socket:close(channel:browser(Channel), channel:proxy(Channel)).

build_chain(Response) ->
    Echo = chain:link(Response, chain:echo(Response), "Echo"),
    Links = chain:new(Response, fun chain_links:links/1, "Links", Echo),
    Lines = chain:new(Response, fun chain_lines:lines/1, "Lines", Links),
    res_info(Response, "Encoding ~p", [response:encoding(Response)]),
    case response:encoding(Response) of
        unknown -> Lines;
        "gzip" -> chain:new(Response, fun chain_unzip:unzip/1, "Gzip",
                            chain:shape_before(Lines, 2000));
        Encoding -> {error, Encoding}
    end.

The processes are in reverse order, so this (optionally) unzips, splits
into lines, searches for hypertext limits, and echoes the result to the
screen.  As you might have guessed, I'm processing HTTP data flows.

Andrew

Re: Objects

From: "andrew cooke" <andrew@...>

Date: Wed, 2 May 2007 22:16:07 -0400 (CLT)

Ooops - see that I left "Objects" in the title from earlier.  I was
originally going to talk about persistent state and the similarities
between method calls and dispatching on tuple tags.  But I'm sure you can
see that anyway :o)

Andrew

First bug

From: "andrew cooke" <andrew@...>

Date: Wed, 2 May 2007 22:22:29 -0400 (CLT)

Staring at that, I've already seen one bug.  No prizes!

Andrew

Comment on this post