The first Erlang program: FTP download Client

Learning about Erlang for one week:

   1 -module(ftp_down).   2 -export([get/6,test/0,get_data/4]).   3    4 test() ->   5     get("ftp.ftpplanet.com", 21, "anonymous", "anonymous", "images/image001_42.jpg", "d:/").   6    7 client_message(Format, Data) ->   8     io:format("C: " ++ Format ++ "~n", Data).   9   10 server_message(Format, Data) ->  11     io:format("S: " ++ Format ++ "~n", Data).  12   13 server_verify_message(Data, ExpectedCode) ->  14     {Code, Message} = Data,  15     ExpectedCode = Code,  16     io:format("S: ~s~n", [Message]),  17     ok.  18   19 recv_until_EOL(Sock, StrSoFar) ->  20     Len = string:len(StrSoFar),  21     NotALine = Len < 2 orelse not string:equal("/r/n", string:substr(StrSoFar, Len - 1, 2)),  22     if  23         NotALine ->  24             {ok, Msg} = gen_tcp:recv(Sock, 1),  25             recv_until_EOL(Sock, StrSoFar ++ Msg);  26         true ->  27             StrSoFar  28     end.  29       30 recv_until_EOL(Sock) ->  31     recv_until_EOL(Sock, "").  32   33 recv_until_xxxend(Sock, Num, Line, LinesSoFar) ->  34     ExpectedTail = integer_to_list(Num) ++ " end",  35     ExpectedTailLen = string:len(ExpectedTail),  36     Pos = string:len(Line) - ExpectedTailLen - 1,  37     Eq = Pos > 0 andalso string:equal(ExpectedTail, string:to_lower(string:substr(Line, Pos, ExpectedTailLen))),  38     if  39         Eq ->  40             {Num, LinesSoFar ++ Line};  41         true ->  42             recv_response(Sock, Num, LinesSoFar ++ Line)  43     end.  44   45 recv_response(Sock, LinesSoFar) ->  46     Line = recv_until_EOL(Sock),  47     {Num, [H | _]} = string:to_integer(Line),  48     if  49         H == $- ->  50             recv_until_xxxend(Sock, Num, Line, LinesSoFar);  51         true ->  52             {Num, LinesSoFar ++ Line}  53     end.  54       55 recv_response(Sock, ResponseNo, LinesSoFar) ->  56     Line = recv_until_EOL(Sock),  57     recv_until_xxxend(Sock, ResponseNo, Line, LinesSoFar).  58       59 recv_response(Sock) ->  60     recv_response(Sock, []).  61   62 send_command(Sock, Msg) ->   63    ok = gen_tcp:send(Sock, Msg ++ "/r/n"),  64    client_message("~s", [Msg]).  65      66 parse_pasv(Msg) ->  67     Index1 = string:chr(Msg, $(),  68     Index2 = string:chr(Msg, $)),  69     [A1, A2, A3, A4, B1, B2] = lists:map(fun(S) -> string:strip(S) end, string:tokens(string:substr(Msg, Index1 + 1, Index2 - Index1 -1), ",")),  70     {Nb1, _} = string:to_integer(B1),  71     {Nb2, _} = string:to_integer(B2),  72     <<Port:16>> = <<Nb1:8, Nb2:8>>,  73     {lists:append([A1, ".", A2, ".", A3, ".", A4]), Port}.  74    75   76 recv_until_transfer_complete(Sock, {ok , Msg}, MsgSoFar) ->  77     if  78         length(Msg) > 0 ->  79             recv_until_transfer_complete(Sock, gen_tcp:recv(Sock, 0), MsgSoFar ++ Msg);  80         true ->  81             receive  82                 transfer_complete ->  83                     MsgSoFar  84                 after 200 ->  85                     recv_until_transfer_complete(Sock, gen_tcp:recv(Sock, 0), MsgSoFar ++ Msg)  86             end  87     end;  88       89   90 recv_until_transfer_complete(_, {error , closed}, MsgSoFar) ->  91     MsgSoFar.  92   93 recv_until_transfer_complete(Sock) ->  94     receive  95         start_transfer ->  96             recv_until_transfer_complete(Sock, gen_tcp:recv(Sock, 0), [])  97         after 30000 ->  98             "150 timeout"  99     end. 100  101 get_data(Addr, Port, LocalFilePath, Control) -> 102     {ok, DataSock} = gen_tcp:connect(Addr, Port, [{active, false}]), 103     Data = recv_until_transfer_complete(DataSock), 104     client_message("<I GOT>: ~w Bytes~n", [length(Data)]), 105     file:write_file(LocalFilePath, list_to_binary(Data)), 106     gen_tcp:close(DataSock), 107     Control ! bye. 108      109      110 get(Host, Port, User, Pass, FilePath, LocalPath) -> 111     Slash = string:rchr(FilePath, $/), 112     Path = string:left(FilePath, Slash - 1), 113     File = string:right(FilePath, string:len(FilePath) - Slash), 114      115     {ok, Sock} = gen_tcp:connect(Host, Port, [{active, false}]), 116     client_message("connect to ~s:~w ok.", [Host, Port]), 117     server_verify_message(recv_response(Sock), 220), 118     send_command(Sock, "USER " ++ User), 119     server_verify_message(recv_response(Sock), 331), 120     send_command(Sock, "PASS " ++ Pass), 121     server_verify_message(recv_response(Sock), 230), 122     send_command(Sock, "CWD " ++ Path), 123     server_verify_message(recv_response(Sock), 250), 124     send_command(Sock, "TYPE I"), 125     server_verify_message(recv_response(Sock), 200), 126     send_command(Sock, "PASV"), 127     {_, Msg} = recv_response(Sock), 128     server_message(Msg, ""), 129     {Addr, NewPort} = parse_pasv(Msg), 130      131     DataPid = spawn(ftp_down, get_data, [Addr, NewPort, LocalPath ++ File, self()]), 132      133     send_command(Sock, "RETR " ++ File), 134     % 150 Opening BINARY mode data connection for   150 File status okay; about to open data connection. 135     % 125 Downloading in BINARY file  125 Data connection already open; transfer starting. 136     % 550 Failed to open file 137     {Num, Text} = recv_response(Sock), 138     V = (Num == 150) or (Num == 125), 139     if 140         V -> 141             server_message("~s", [Text]), 142             DataPid ! start_transfer, 143             server_verify_message(recv_response(Sock), 226), 144             DataPid ! transfer_complete, 145             receive 146                 bye -> 147                     ok 148             end; 149         true -> 150             if Num == 550 -> 151                 server_message("~w", Text); 152             true -> 153                 ok 154             end 155     end, 156      157     gen_tcp:close(Sock).