Programming Erlang, 2 e., Chapter 2, Exercise 4, put_file()

[Leonard B]

Sorry, replied from mobile and had issues reading the code.

What I do see is you're spawning a process using a *different module*
(probably a previous file you were working on).

start(Dir) -> spawn(afile_server, loop, [Dir]).

^^ that should probably be

start(Dir) -> spawn(ex0204_server, loop, [Dir]).

Kind regards,
Leonard

On Fri, Dec 31, 2021 at 8:31 AM Leonard B <leonard.boyce@REDACTED> wrote:
>
> Compare the receive pattern for "{Client, {put_file, File, Bytes}}" to what you're sending
>
> On Fri, Dec 31, 2021, 08:13 David Christensen <dpchrist@REDACTED> wrote:
>>
>> erlang-questions:
>>
>> I am working my way through "Programming Erlang", 2 e.:
>>
>> 2021-12-30 20:00:05 dpchrist@REDACTED ~/sandbox/erlang
>> $ cat /etc/debian_version ; uname -a ; dpkg-query -W erlang
>> 9.13
>> Linux tinkywinky 4.9.0-17-amd64 #1 SMP Debian 4.9.290-1 (2021-12-12)
>> x86_64 GNU/Linux
>> erlang  1:19.2.1+dfsg-2+deb9u3
>>
>>
>> Chapter 2, Exercise 4, requests that I add a "put_file" command to the
>> file client and server code.  RTFM I found the file:write_file()
>> function.  I can test it with the Erlang shell, and it works:
>>
>> 2021-12-30 20:29:34 dpchrist@REDACTED ~/sandbox/erlang
>> $ erl
>> Erlang/OTP 19 [erts-8.2.1] [source] [64-bit] [smp:8:8]
>> [async-threads:10] [kernel-poll:false]
>>
>> Eshell V8.2.1  (abort with ^G)
>> 1> file:write_file("foo.2", "this is foo.2\n").
>> ok
>> 2> halt().
>>
>> 2021-12-30 20:30:09 dpchrist@REDACTED ~/sandbox/erlang
>> $ cat foo.2
>> this is foo.2
>>
>>
>> I have extended afile_server.erl with a "put_file" command that calls
>> file::write_file():
>>
>> 2021-12-30 20:34:25 dpchrist@REDACTED ~/sandbox/erlang
>> $ cat ex0204_server.erl
>> -module(ex0204_server).
>> -export([start/1, loop/1]).
>>
>> start(Dir) -> spawn(afile_server, loop, [Dir]).
>>
>> loop(Dir) ->
>>      receive
>>         {Client, list_dir} ->
>>             Client ! {self(), file:list_dir(Dir)};
>>         {Client, {get_file, File}} ->
>>             Full = filename:join(Dir, File),
>>             Client ! {self(), file:read_file(Full)};
>>         {Client, {put_file, File, Bytes}} ->
>>             Full = filename:join(Dir, File),
>>             Client ! {self(), file:write_file(Full, Bytes)}
>>      end,
>>      loop(Dir).
>>
>>
>> Testing in the Erlang shell, start() works, the "list_dir" command and
>> reply work, and the "get_file" command and reply work, but the shell
>> hangs when I attempt to receive a reply for the "put_file" command:
>>
>> 2021-12-30 20:35:23 dpchrist@REDACTED ~/sandbox/erlang
>> $ erl
>> Erlang/OTP 19 [erts-8.2.1] [source] [64-bit] [smp:8:8]
>> [async-threads:10] [kernel-poll:false]
>>
>> Eshell V8.2.1  (abort with ^G)
>> 1> c(ex0204_server).
>> {ok,ex0204_server}
>> 2> Server = ex0204_server:start(".").
>> <0.64.0>
>> 3> Server ! {self(), list_dir}.
>> {<0.57.0>,list_dir}
>> 4> receive A -> A end.
>> {<0.64.0>,
>>   {ok,[".ex0204_client.erl.swp","Makefile","afile_client.erl",
>>        "afile_server.beam","ex0204_server.erl","hello.beam",
>>        "ex0204_client.erl","hello.erl","afile_server.erl","CVS",
>>        "afile_server.run","ex0204_server.beam"]}}
>> 5> Server ! {self(), {get_file, "hello.erl"}}.
>> {<0.57.0>,{get_file,"hello.erl"}}
>> 6> receive B -> B end.
>> {<0.64.0>,
>>   {ok,<<"-module(hello).\n-export([start/0]).\n\nstart() ->\n
>> io:format(\"hello, world!~n\").\n">>}}
>> 7> Server ! {self(), {put_file, "foo.txt", "foo on you!\n"}}.
>> {<0.57.0>,{put_file,"foo.txt","foo on you!\n"}}
>> 8> receive C -> C end.
>>
>> BREAK: (a)bort (c)ontinue (p)roc info (i)nfo (l)oaded
>>         (v)ersion (k)ill (D)b-tables (d)istribution
>> a
>>
>>
>> Why?
>>
>>
>> David