Provided by: yaws_1.77-1_i386 bug


       yaws_api - api available to yaws web server programmers




       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:


       <h1> Header 1</h1>

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


       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,        %% wheres 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

       The headers argument is also a record:

       -record(headers, {
                 cookie = [],
                 other = []   %% misc other headers

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


       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>

       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

              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 | List | Char)
              Htmlize an IO list object.

       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:

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

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

                Ret = [{redirect, ""},
                        setcookie("sid", Random)

              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

              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 .yaws file. That is self() in the yaws  code.   The
              Pid  must  typically  be passed (somehow) to the producer of the

       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.

              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.

              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.   If  a
              variable is defined multiple times, the function may also return
              [{ok, Val1}, ....].

              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.  If a
              variable is defined multiple times, the function may also return
              [{ok, Val1}, ....].

       getvar(Arg, VarName)
              This  function  looks at the HTTP request method from the client
              and invokes postvar/2 if it  is  a  POST  from  the  client  and
              queryvar/2 if it is a GET request from the client.


              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:

               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>",[])}

               handle_res(A, [{head, Name}|T]) ->
                    handle_res(A, T);
               handle_res(A, [{part_body, Data}|T]) ->
                    handle_res(A, T);
               handle_res(A, [{body, Data}|T]) ->
                    handle_res(A, T);
               handle_res(A, []) ->


              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.



       replace_cookie_session(Cookie, NewOpaque)


       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

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

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

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

              Parse URL in a string, returns a #url record

              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.

              Perform  a directory listing. Can be used in special directories
              when we don’t want to  turn  on  dir  listings  for  the  entire
              server.  Always returns ok.

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">

              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

       {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

              {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.

              {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:binding(Key) can be used
              to extract Value and yaws_api:binding_exists(Key) can be used to
              check for the existance of a binding.

       {yssi, YawsFile}
              Include  a yaws file. Compile it and expand as if it had occured

              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.


       Written by Claes Wikstrom


       yaws.conf(5) erl(1)