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

[Leonard B]

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
>
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