man yaws_api (Formats) - api available to yaws web server programmers

NAME

yaws_api - api available to yaws web server programmers

SYNOPSIS

yaws_api:Function(...)

DESCRIPTION

This is the api available to yaws web server programmers. The erlang module yaws_api contains a wide variety of functions that can be used inside yaws pages.

Each chunk of yaws code is executed while the yaws page is being delivered from the server. We give a very simple example here to show the basic idea. Imagine the following html code: 

<html>
<body>

<h1> Header 1</h1>

<erl> out(Arg) -> {html, "<p> Insert this text into the document"}. </erl>

</body> </html>

The out(Arg) function is supplied one argument, an #arg{} structure. We have the following relevant record definitions: 

-record(arg, {
	  clisock,        %% the socket leading to the peer client
	  headers,        %% headers
	  req,            %% request
	  clidata,        %% The client data (as a binary in POST requests)
	  server_path,    %% The normalized server path
	  querydata,      %% Was the URL on the form of ...?query (GET reqs)
	  appmoddata,     %% the remainder of the path up to the query
	  docroot,        %% where's the data
	  fullpath,       %% full path to yaws file
	  cont,		  %% Continuation for chunked multipart uploads
	  state,          %% State for use by users of the out/1 callback
	  pid,            %% pid of the yaws worker process
	  opaque,         %% useful to pass static data
	  appmod_prepath, %% path in front of: <appmod><appmoddata>
	  pathinfo        %% Set to 'd/e' when calling c.yaws for the request
                          %% http://some.host/a/b/c.yaws/d/e
	 }).              



The headers argument is also a record:


            
-record(headers, {
          connection,
          accept,
          host,
          if_modified_since,
          if_match,
          if_none_match,
          if_range,
          if_unmodified_since,
          range,
          referer,
          user_agent,
          accept_ranges,
          cookie = [],
          keep_alive,
          content_length,
          authorization,
          other = []   %% misc other headers
         }).





it likes. We have the following functions to aid that generation.

API
ssi(DocRoot, ListOfFiles)

Server side include. Just include the files as is in the document. The files
will not be parsed and searched for <erl> tags.

pre_ssi_files(DocRoot, ListOfFiles) ->
Server side include of pre indented code.  The data in Files
will be included but contained in a <pre> tag. The data will be
htmlized. 

pre_ssi_string(String)

Include htmlized content from String.

f(Fmt, Args)

The equivalent of io_lib:format/2. This function is automatically
-included in all erlang code which is a part of a yaws page.

htmlize(Binary)

Htmlize a binary object.

htmlize_l(DeepList)

Htmlize any deep list of chars and binaries.

setcookie(Name, Value, [Path, [ Expire, [Domain , [Secure]]]])

Sets a cookie to the browser.

find_cookie_val(Cookie, Header)

This function can be used to search for a cookie that was previously
set by setcookie/2-6. For example if we set a cookie
as yaws_api:setcookie("sid",SomeRandomSid) , then on subsequent requests
from the browser we can call: 
find_cookie("sid",(Arg#arg.headers)#headers.cookie)

The function returns [] if no cookie was found, otherwise the actual cookie
is returned as a string.

redirect(Url

This function generates a redirect to the browser.
It will clear any previously set headers. So to generate 
a redirect and set a cookie, we need to set the cookie after 
the redirect as in:


out(Arg) ->
  ... do some stuff

  Ret = [{redirect, "http://www.somewhere.com"},
          setcookie("sid", Random)
        ].



get_line(String)

This function is convenient when getting \r\n terminated lines
from a stream of data. It returns:

{line, Line, Tail} or {lastline, Line, Tail}

The function handles multilines as defined in e.g. SMTP or HTTP

mime_type(FileName)

Returns the mime type as defined by the extension of FileName

stream_chunk_deliver(YawsPid, Data)

When a yaws function needs to deliver chunks of data which it gets 
from a process. The other process can call this function to deliver
these chunks. It requires the out/1 function to return the
value {streamcontent, MimeType, FirstChunk} to work.
YawsPid is the process identifier of the yaws process delivering the original
The Pid must typically be passed (somehow) to the producer of the stream.

stream_chunk_deliver_blocking(YawsPid, Data)

A syncronous verion of the above function. This syncronous version must always
be used when the producer of the stream is faster than the consumer. 
This is usually the case since the client is the WWW browser.

stream_chunk_end(YawsPid)

When the process discussed above is done delivering data, it must call
this function to let the yaws content delivering process finish up
the HTTP transaction.

parse_query(Arg)

This function will parse the query part of the URL.
It will return a {Key, Value} list of the items supplied in the query
part of the URL.

queryvar(Arg, VarName)

This function is automatically included from yaws_api in all
 .yaws pages. It is used to search for a variable in the 
querypart of the url. Returns {ok, Val} or undefined.

parse_post(Arg)

This function will parse the POST data as supplied from the browser.
It will return a {Key, Value} list of the items set by the browser.

postvar(Arg, VarName)

This function is automatically included from yaws_api in all
 .yaws pages. It is used to search for a variable in the 
POSTed data from the client. Returns {ok, Val} or undefined.

parse_multipart_post(Arg)

If the browser has set the Content-Type header to the value
"multipart/form-data", which is the case when the browser 
wants to upload a file to the server the following happens:

If the function returns {result, Res} no more data
will come from the browser.

If the function returns {cont, Cont, Res} the browser
will supply more data. (The file was to big to come in one read)

This indicates that there is more data to come and the out/1 function
should return {get_more, Cont, User_state} where User_state might
usefully be a File Descriptor.

The Res value is a list of either: 
{header, Header} | {part_body, Binary} | {body, Binary}

Example usage could be:


 <erl>
 
 out(A) ->
        case yaws_api:parse_multipart_post(A) of
             {cont, Cont, Res} ->
                    St = handle_res(A, Res),
                    {get_more, Cont, St};
             {result, Res} ->
                    handle_res(A, Res),
                    {html, f("<pre>Done </pre>",[])}
        end.
 
 handle_res(A, [{head, Name}|T]) ->
      io:format("head:~p~n",[Name]),
      handle_res(A, T);
 handle_res(A, [{part_body, Data}|T]) ->
      io:format("part_body:~p~n",[Data]),
      handle_res(A, T);
 handle_res(A, [{body, Data}|T]) ->
      io:format("body:~p~n",[Data]),
      handle_res(A, T);
 handle_res(A, []) ->
      io:format("End_res~n").
 
 </erl>




new_cookie_session(Opaque)

Create a new cookie based session, the yaws system will set the
cookie. The new randomgenerated cookie is returned from this
function. The Opaque argument will typically contain user data
such as username and password

new_cookie_session(Opaque, TTL)

As above, but allows to set a session specific time-out value,
overriding teh system specified time-out value.

cookieval_to_opaque(CookieVal)

print_cookie_sessions() 

replace_cookie_session(Cookie, NewOpaque)

delete_cookie_session(Cookie)

setconf(Gconf, Groups)

This function is intended for embedded mode in yaws. It makes it possible
to load a yaws configuration from another data source than /etc/yaws.conf, such
as a database. 
If yaws is started with the environment {embedded, true}, yaws will
start with an empty default configuration, and wait for some other
program to execute a setconf/2
The Gconf is a #gconf{} record and the Group variable is
a list of lists of #sconf{} records. Each sublist must 
contain #sconf{} records with the same IP/Port listen address.

url_decode(Str)

Decode url-encoded string. A URL ncoded string is a string where
all alfa numeric characters and the the character _ are preserved
and all other characters are encode as "%XY" where X and Y are the
hex values of the least respective most significat 4 bits in the 8 bit 
character.

url_encode(Str)

Url-encodes a string. All URLs in HTML documents must be URL encoded.

reformat_header(H)

Returns a list of reformated header values from a #header{}
record. The return list is suitable for retransmit.

request_url(ARG)

Return the url as requested by the client. Return value
is a #url{} record as defined in yaws_api.hrl

parse_url(Str)

Parse URL in a string, returns a #url record

format_url(UrlRecord)

Takes a #url record a formats the Url as a string

call_cgi(Arg, Scriptfilename) 

Calls an executable CGI script,
given by its full path.  Used to make `.yaws' wrappers for CGI
programs.  This function usually returns streamcontent.

call_cgi(Arg, Exefilename, Scriptfilename) 

Like before, but
calls Exefilename to handle the script.  The file name of the
script is handed to the executable via a CGI meta variable.

RETURN VALUES from out/1

The out/1 function can return different values to control the behavior
of the server.

{html, DeepList}
This assumes that DeepList is formatted HTML code. 
The code will be inserted in the page.

{ehtml, Term}

This will transform the erlang term Term into a 
stream of HTML content. The basic syntax of Term
is



EHTML = [EHTML] | {Tag, Attrs, Body} | {Tag, Attrs} | {Tag} |
        binary() | character()
Tag      = atom()
Attrs = [{Key, Value}]  or {EventTag, {jscall, FunName, [Args]}}
Key      = atom()
Value = string()
Body  = EHTML




For example, {p, [], "Howdy"} expands into
"<p>Howdy</p> and 



{form, [{action, "a.yaws"}], 
   {input, [{type,text}]}}


 

expands into



<form action="a.yaws"
  <input type="text">
</form>




It may be more convenient to generate erlang tuples 
than plain html code.

{content, MimeType, Content}

This function will make the web server generate 
different content than HTML. This return value is only allowed
in a yaws file which has only one <erl> </erl> part and no
html parts at all.

{streamcontent, MimeType, FirstChunk}

This return value plays the same role as the content return
value above. 

However it makes it possible to stream data to the client
if the yaws code doesn't have access to all the data in one go. (Typically
if a file is very large or if data arrives from back end servers on the network.

{header, H}

Accumulates a HTTP header. The trailing CRNL which is supposed
to end all HTTP headers must NOT be added. It is added by the server.
The following list of headers are given special treatment.

{connection, What}  

This sets the connection header. If What is the special value
"close", the connection will be closed once the yaws page is delivered
to the client.

{location, Url}

Sets the Location: header. This header is typically combined with
the {status, 302} return value.

{cache_control, What}

Sets the Cache-Control: header.

{set_cookie, Cookie}

Prepends a a Set-Cookie: header to the list of previousy
set Set-Cookie: headers.

{content_type, MimeType}

Sets the Content-Type header.

{content_length, Len}

Normally yaws will ship Yaws pages using Transfer-Encoding: chunked. This
is because we generally can't know how long a yaws page will be. If we for
some reason want to force a Content-Length: header (and we actually do
know the length of the content, we can force yaws to not ship the
page chunked.

All other headers must be added using the normal HTTP syntax.
Example:

{header, "My-X-Header: gadong"}

{allheaders, HeaderList}
Will clear all previously accumulated headers and replace them.

{status, Code}

Will set another HTTP status code than 200.

break

Will stop processing of any consecutive chunks of erl or html code
in the yaws file.

ok

Do nothing.

{redirect, Url}

Erase all previous headers and accumulate a single
Location header. Set the status code.

{redirect_local, Path}

Does a redirect to the same Scheme://Host:Port/Path as we
currently are executing in.

{get_more, Cont, State}

When we are receiving large POSTs we can return this value
and be invoked again when more Data arrives.

{page, Page}

Make Yaws return a different page than the one being
requested.

{page, {Options, Page}}

Like the above, but supplying an additional deep list of options.  For
now, the only type of option is {header, H} with the effect of
accumulating the HTTP header H for page Page.

{ssi, File, Delimiter, Bindings}

Server side include File and  macro expansion in File.
Each occurence of a string, say "xyz", inside File which
is inside Delimters is replaced with the corresponsing
value in Bindings. 

Example:
Delimiter = %%

File contains the string .... %%xyz%%  .....

Bindings contain the tuple {"xyz", "Dingbat"}

The occurence of %%xyz%% in File will be replaced with "Dingbat"
in the Server side included output.

The {ssi, File, Delimiter, Bindings} statement can also
occur inside a deep ehtml structure. 

{bindings, [{Key1, Value2}, {Key2, Value2} .....]}

Establish variable bindings that can be used in the page.

All bindings can then be used in the rest of yaws code 
(in HTML source and within erl tags). 
In HTML source %%Key%% is expanded to Value and within erl 
tags yaws_api:get_binding(Key) can be used to extract Value.

{yssi, YawsFile}

Include a yaws file. Compile it and expand as if it had
occured inline.

[ListOfValues]

It is possible to return a deep list of the above defined
return values.  Any occurrence of stream_content, get_more
or page in this list is legal only if it is the last position of
the list.

AUTHOR
Written by Claes Wikstrom

SEE ALSO
yaws.conf(5)
erl(1)