-module(comet_tail).
-export([start/2, loop/2, handle_request/2, is_this_a_safety_path/1, generate_comment_for_length/2, generate_iframe_wrapper/1]).
start(Port, LogDir)->
{ok, ListenSock}=gen_tcp:listen(Port, [list,{active, false},{packet,http}]),
?MODULE:loop(ListenSock, LogDir).
loop(ListenSock, LogDir) ->
{ok, Sock}=gen_tcp:accept(ListenSock),
spawn(?MODULE, handle_request, [Sock, LogDir]),
?MODULE:loop(ListenSock, LogDir).
handle_request(Sock, LogDir) ->
{ok, {http_request, Method, Path, Version}}=gen_tcp:recv(Sock, 0),
case (Path) of
{abs_path,"/?"++FilePath}->
case (is_this_a_safety_path(FilePath)) of
err -> gen_tcp:send(Sock, "HTTP/1.1 500 Internal Server Error\r\nContent-Type: text/plain; charset=UTF-8\r\nConnection: close\r\n\r\nInvalid File Path\r\n\r\n"),gen_tcp:close(Sock);
ok -> {ok, Device} = file:open(lists:append(LogDir,FilePath), [read]),
gen_tcp:send(Sock, "HTTP/1.1 200 OK\r\nContent-Type: text/html; charset=UTF-8\r\nCache-Control: no-cache\r\nTransfer-Encoding: chunked\r\n\r\n"),
tail_to_socket(Device, Sock, 1)
end;
{abs_path,"/comet-tail?"++FilePath} ->
HtmlFile=generate_iframe_wrapper(FilePath),
HtmlLength=lists:flatten(io_lib:format("~p", [length(HtmlFile)])),
gen_tcp:send(Sock, lists:append(["HTTP/1.1 200 OK\r\nConnection: close\r\nContent-Type: text/html; charset=UTF-8\r\nCache-Control: no-cache\r\nContent-Length: ", HtmlLength, "\r\n\r\n", HtmlFile])),
gen_tcp:close(Sock)
end.
%% Backoff set so as to not throttle CPU when nothing left to read...1, 2, 4, 8, 16, 2, 4, 8, 16 second cycle...
tail_to_socket(Device, Sock, Backoff) ->
case io:get_line(Device, "") of
eof -> timer:sleep(Backoff * 1000),NewBackoff=(Backoff * 2 rem 30),tail_to_socket(Device, Sock, NewBackoff);
Line -> HtmlLine=lists:append([generate_comment_for_length([], 1000), Line, "
"]),
Length=io_lib:format("~.16B", [length(HtmlLine)]),
gen_tcp:send(Sock, Length),gen_tcp:send(Sock, "\r\n"),
gen_tcp:send(Sock, HtmlLine),gen_tcp:send(Sock, "\r\n"),
tail_to_socket(Device, Sock, 1)
end.
%% simple saftey check for relative directory parent references within path...
is_this_a_safety_path([Head|Tail]) ->
case (Head) of
46 ->[NextHead|NextTail]=Tail, case (NextHead) of
46 -> err;
_ ->is_this_a_safety_path(NextTail)
end;
_->is_this_a_safety_path(Tail)
end;
is_this_a_safety_path([])->
ok.
%% generate a ~n kb comment for Safari and other lame-o browsers in order to force flush...
generate_comment_for_length([], Length) ->
generate_comment_for_length("");
generate_comment_for_length(Comment, Length) ->
generate_comment_for_length(lists:append(Comment, " "), Length -1).
%% generate a iframe wrapper
generate_iframe_wrapper(FilePath)->
lists:append([" "]).