YAWS_API(5)                        User API                        YAWS_API(5)

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 deliv‐
       ered 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
                 client_ip_port, % {ClientIp, ClientPort} tuple
                 headers,        % headers
                 req,            % request
                 orig_req,       % original request
                 clidata,        % The client data (as a binary in POST requests)
                 server_path,    % The normalized server path
                                 % (pre-querystring part of URI)
                 querydata,      % For URIs of the form ...?querydata
                                 %  equiv of cgi QUERY_STRING
                 appmoddata,     % (deprecated - use pathinfo instead) the remainder
                                 % of the path leading up to the query
                 docroot,        % Physical base location of data for this request
                 docroot_mount,  % virtual directory e.g /myapp/ that the docroot
                                 %  refers to.
                 fullpath,       % full deep 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, % (deprecated - use prepath instead) path in front
                                 %  of: <appmod><appmoddata>
                 prepath,        % Path prior to 'dynamic' segment of URI.
                                 %  ie http://some.host/<prepath>/<script-point>/d/e
                                 % where <script-point> is an appmod mount point,
                                 % or .yaws,.php,.cgi,.fcgi etc script file.
                 pathinfo        % Set to '/d/e' when calling c.yaws for the request
                                 % http://some.host/a/b/c.yaws/d/e
                                 %  equiv of cgi PATH_INFO
                }).

       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,
                 location,
                 content_length,
                 content_type,
                 content_encoding,
                 authorization,
                 transfer_encoding,
                 x_forwarded_for,
                 other = []   % misc other headers
                }).

       The out/1 function can use the Arg to generate any content 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 docu‐
              ment. 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  automati‐
              cally  -included  in  all  erlang code which is a part of a yaws
              page.

       htmlize(Binary | List | Char)
              Htmlize an IO list object.

       set_cookie(Name, Value, Options])
              Sets a cookie to the browser. Options are:

              {expires, UtcTime}  - Cookie expiration time, where UtcTime is
                                    a tuple returned by calendar:universal_time/0.
              {max_age, Age}      - Defines the lifetime of the cookie, in seconds,
                                    where age is an integer >= 0.
              {path, Path}        - Path is a string that specifies the subset of URLs to
                                    which this cookie applies.
              {domain, Domain}    - Domain is a string that specifies the domain for which
                                    the cookie is valid.
              {comment, Comment}  - Comment is a string that doccuments the server's
                                    intended use of the cookie.
              secure              - Directs the user agent to use only secure means to
                                    contact the origin server whenever it sends back this
                                    cookie.
              http_only           - Restricts cookie access from other non-HTTP APIs.

       setcookie(Name, Value, [Path, [ Expire, [Domain , [Secure]]]])
              Sets a cookie to the browser. This  function  is  deprecated  by
              set_cookie/3.

       find_cookie_val(Cookie, Header)
              This function can be used to search for a cookie that was previ‐
              ously 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.

       parse_set_cookie(Str)
              This function parses the value of a Set-Cookie header, following
              the RFC6265. Because old RFCs (2109 and 2965) are still used, it
              is backward compatible. So this function returns a  #setcookie{}
              record  when  only  one cookie is found. If multiple cookies are
              set in a single Set-Cookie header, it returns a  list  of  #set‐
              cookie{}  records.  If  no  cookie  was  found  or  if  an error
              occurred, it returns [].

              #setcookie{} record is defined in yaws_api.hrl:

              -record(setcookie, {key,
                                  value,
                                  quoted = false,
                                  domain,
                                  max_age,
                                  expires,
                                  path,
                                  secure = false,
                                  http_only = false,
                                  extensions = []}).

       parse_cookie(Str)
              This function parses the value of Cookie header,  following  the
              RFC6265.  It  returns  a list of #cookie{} records. If no cookie
              was found or if an error occurred, it returns [].

              #cookie{} record is defined in yaws_api.hrl:

              -record(cookie, {key,
                               value,
                               quoted = false}).

       format_set_cookie(SetCookie)
              Build a cookie string from a #setcookie{} record  like  returned
              by parse_set_cookie/1.

       format_cookie(Cookie | [Cookie])
              Build  a  cookie  string  from  a #cookie{} record (or a list or
              records) like returned by parse_cookie/1.

       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)
                      ].

       redirect_self(Arg)
              If  we  want  to issue a redirect to ourselves, this function is
              useful.  It  returns   a   record   #redir_self{}   defined   in
              yaws_api.hrl.  The  record contains fields to construct a URL to
              ourselves.

              -record(redir_self, {
                        host,        % string() - our own host
                        scheme,      % http | https
                        scheme_str,  % "https://"  | "http://"
                        port,        % integer()  - our own port
                        port_str     % "" | ":<int>" - the optional port part
                                     %                 to append to the url
                       }).

       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(Scope, FileName)
              Returns  the  MIME type as defined by the extension of FileName.
              Scope can have following values:

                   global - returns the result obtained from the  global  con‐
                   text.
                   #sconf{} | {ServerName, Port} - returns the result obtained
                   from the virtual server's context. If no MIME type is found
                   in this scope, it falls back on the global one.

       mime_type(FileName)
              Tries to determine the right Scope before calling mime_type/2.

       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.

       stream_chunk_deliver_blocking(YawsPid, Data)
              A synchronous version of the above  function.  This  synchronous
              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.

       stream_process_deliver(Socket, IoList)
              Yaws  allows  application  processes to deliver data directly to
              the client. The application tells yaws about such a  process  by
              returning {streamcontent_from_pid, MimeType, Pid} from its out/1
              function. In this case, Pid  uses  the  stream_process_deliver/2
              function  to  deliver  data  to the client. The application gets
              Socket from Arg#arg.clisock, and IoList is the data to  be  sent
              to the client.

       stream_process_deliver_chunk(Socket, IoList)
              Same  as  above  but delivers IoList using HTTP chunked transfer
              format. IoList must have a size greater than zero. The  applica‐
              tion process delivering the data will have had to have make sure
              that the HTTP headers of the response indicate chunked  transfer
              mode,  either  by ensuring no Content-Length header is set or by
              specifically setting the Transfer-Encoding header to chunked.

       stream_process_deliver_final_chunk(Socket, IoList)
              If the application process delivering data to  the  client  uses
              chunked  transfer  mode,  it must call this to deliver the final
              chunk of the transfer. This tells yaws to create a special final
              chunk  in  the  format  required  by the HTTP specification (RFC
              2616). IoList may be empty, but if  its  size  is  greater  than
              zero,  that  data  will  be  sent as a separate chunk before the
              final chunk.

       stream_process_end(Socket, YawsPid)
              Application processes delivering data directly to  clients  must
              call  this  function  to inform yaws that they've finished using
              Socket. The YawsPid  argument  will  have  been  passed  to  the
              process  earlier  when yaws sent it a message telling it to pro‐
              ceed with data delivery. Yaws expects Socket to be open.

       stream_process_end(closed, YawsPid)
              Same as the previous function but the application calls this  if
              it  closes  the  client  socket  as  part  of  its data delivery
              process. This allows  yaws  to  continue  without  assuming  the
              socket is still open and encountering errors due to that assump‐
              tion. The YawsPid argument will have been passed to the applica‐
              tion  process  earlier when yaws sent it a message telling it to
              proceed with data delivery.

       parse_query(Arg)
              This function will parse the query part  of  the  URL.  It  will
              return a {Key, Value} list.

       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  query‐
              part  of  the url. Returns {ok, Val} or undefined. If a variable
              is defined multiple times, the function may also  return  {Val1,
              Val2...}.

       parse_post(Arg)
              If  the  browser  has  set  the Content-Type header to the value
              "application/x-www-form-urlencoded", this  function  will  parse
              the request's body. It will return a {Key, Value} list.

       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
              request's  body  sent  by the client. Returns {ok, Val} or unde‐
              fined. If a variable is defined multiple times, the function may
              also return {Val1, Val2...}.

       getvar(Arg, VarName)
              This  function is used to search a variable in the query part of
              the URL and in the request's body.  it  invokes  queryvar/2  and
              postvar/2 and merges the results.

       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  sup‐
              ply more data. (The file was too 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:  {head,  {Name,  Headers}}  |  {part_body,
              Binary} | {body, Binary}

              The function returns {error, Reason} when an error occurred dur‐
              ing the parsing.

              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>",[])};
                           {error, Reason} ->
                                  {html, f("An error occured: ~p", [Reason])}
                      end.

               handle_res(A, [{head, {Name, _Hdrs}}|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. Yaws will either generate the
              cookie  itself or, if a ysession_cookiegen module is configured,
              call new_cookie() on that module to get a new  cookie.  The  new
              cookie  is returned from this function. The Opaque argument will
              typically contain user data such as user name and password

       new_cookie_session(Opaque, TTL)
              As above, but allows to set a session specific  time-out  value,
              overriding the system specified time-out value.

       new_cookie_session(Opaque, TTL, CleanupPid)
              As  above,  but  also sends a message {yaws_session_end, Reason,
              Cookie, Opaque} to the provided CleanupPid where Reason  can  be
              either  of  timeout  or normal. The Cookie is the HTTP cookie as
              returned by new_session() and Opaque is the user-provided Opaque
              parameter  to  new_session().   The purpose of the feature is to
              cleanup resources assigned to the session.

       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.  To create a suitable initial #gconf{} record  see  the
              code   in   yaws_config:make_default_gconf/2.   Especially   the
              yaws_dir parameter is important to get right.

       url_decode(Str)
              Decode url-encoded string. A URL  encoded  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 signifi‐
              cant 4 bits in the 8 bit character.

       url_encode(Str)
              Url-encodes a string. All URLs in HTML  documents  must  be  URL
              encoded.

       get_sslsocket(Socket)
              Returns  a socket for SSL sockets or the atom undefined for non-
              SSL sockets. Useful for applications that have to deal with both
              SSL and non-SSL sockets.

       get_listen_port(Sconf)
              Return  the  actual port number used by the listen socket of the
              virtual server indicated by the function argument,  an  #sconf{}
              record  instance. If successful, returns the requested port num‐
              ber, or returns {error, not_found} if the function argument does
              not  match any known virtual server. This function is useful for
              retrieving the actual port number when, e.g.  for  testing  pur‐
              poses,  a virtual server is configured to use port 0, which will
              cause it to have an ephemeral port  assigned  by  the  operating
              system.

       reformat_header(H)
              Returns  a  list  of reformatted header values from a #headers{}
              record. The return list is suitable for retransmit.

       reformat_header(H, FormatFun)
              Returns a list of reformatted header values  from  a  #headers{}
              record,  with  each  element of the list formatted via a call to
              FormatFun. This enables converting #headers{} records into vari‐
              ous  lists  of headers and their values. Note that sometimes the
              Set-Cookie header will contain a tuple value of the form {multi,
              ValueList}  —  see merge_header/2 below for details — so format‐
              ting functions should be prepared to handle such a  tuple.  They
              should  handle  it  by  formatting each member of ValueList as a
              separate Set-Cookie header, then returning all such header-value
              pairs  in  a  list.  Note  that  this implies that sometimes the
              return values of reformat_header/1 and reformat_header/2 can  be
              a  multi-level  list.  The  {multi, ValueList} construct results
              only from calls to merge_header/2 or merge_header/3, where  mul‐
              tiple values are set in separate calls for the same header.

       set_header(Headers, {Header, Value})
              Sets  header  Header  with  value Value in the #headers{} record
              Headers, and returns a new #headers{}  record.  Using  the  atom
              undefined  for  Value  effectively  deletes  the header, same as
              delete_header/2.

       set_header(Headers, Header, Value)
              Same as set_header/2 above, except  Header  and  Value  are  not
              passed in a tuple.

       merge_header(Headers, {Header, Value})
              Merges value Value for header Header with any existing value for
              that header in the #headers{} record Headers, and returns a  new
              #headers{}  record.  Using  the  atom undefined for Value simply
              returns Headers. Otherwise, Value is merged  with  any  existing
              value  already  present in the Headers record for header Header,
              comma-separated from that  existing  value.  If  no  such  value
              exists  in  the  Headers  record,  the  effect  is  the  same as
              set_header/2. Note that for the Set-Cookie  header,  values  are
              not  comma-separated  but  are  instead  collected  into a tuple
              {multi, ValueList} where ValueList is  the  collection  of  Set-
              Cookie  values.  This  implies that any formatting fun passed to
              reformat_header/2 must be prepared to handle such tuples.

       merge_header(Headers, Header, Value)
              Same as merge_header/2 above, except Header and  Value  are  not
              passed in a tuple.

       get_header(Headers, Header)
              Gets the value of header Header from the #headers{} record Head‐
              ers and returns it. If the header isn't set, the atom  undefined
              is returned.

       delete_header(Headers, Header)
              Deletes any value set for header Header in the #headers{} record
              Headers, and returns a new #headers{} record.

       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.

       call_fcgi_responder(Arg)
              Calls  a FastCGI responder.  The address and port of the FastCGI
              application server are taken from the server configuration  (see
              yaws.conf).   Used  to make `.yaws' wrappers for FastCGI respon‐
              ders.  Returns the same return values as out/1 (see below).

       call_fcgi_responder(Arg, Options)
              Same as above, but  Options  overrides  the  defaults  from  the
              server configuration:

              Options = [Option]
              Option -- one of the following:

              {app_server_host,  string()  | ip_address()} The hostname or the
              IP address of the FastCGI application server.

              {app_server_port, 0..65535} The TCP port number of  the  FastCGI
              application server.

              {path_info,    string()}    Override    default    pathinfo   in
              Arg#arg.pathinfo.

              {extra_env, ExtraEnv} Extra environment variables to  be  passed
              to  the  FastCGI  application  server,  as  a list of name-value
              pairs.

              ExtraEnv = [Var]
              Var = {Name, Value}
              Name = string() | binary()
              Value = string() | binary()

              {trace_protocol, boolean()} Enable or disable tracing of FastCGI
              protocol messages as info log messages.

              {log_app_error, boolean()} Enable or disable logging of applica‐
              tion error messages: output to stderr and non-zero exit value.

       call_fcgi_authorizer(Arg) -> {allowed, Out} | {denied, Out}
              Calls a FastCGI authorizer.  The address and port of the FastCGI
              application  server are taken from the server configuration (see
              yaws.conf).  Used to make `.yaws' wrappers for FastCGI authoriz‐
              ers.  Variables contains the values of the variables returned by
              the FastCGI application server in the "Variable-XXX: YYY"  head‐
              ers.

              If access is denied, Out contains the complete response returned
              by the FastCGI application server. This  response  is  typically
              returned as-is to the HTTP client.

              If  access is allowed, Out contains the response returned by the
              FastCGI application server minus the body (i.e. minus  the  con‐
              tent)  which  should  be  ignored per the FastCGI specification.
              This response is typically not returned to the HTTP client.  The
              calling application module may wish to inspect the response, for
              example  by  extracting  variables  (see  fcgi_extract_variables
              below)  or  by  inspecting  the  headers returned by the FastCGI
              application server.

              Out -- See return values for out/1 below

       call_fcgi_authorizer(Arg, Options) -> {allowed, Out} | {denied, Out}
              Same as above, but  Options  overrides  the  defaults  from  the
              server  configuration.  See  call_fcgi_responder/2  above  for a
              description of Options.

       fcgi_extract_variables(Out) -> [{Name, Value}]
              Extracts the environment variables  from  a  FastCGI  authorizer
              response  by  looking  for  headers  of the form "Variable-Name:
              Value".

              Name = string() -- The name of the variable (the "Variable-" prefix
              has already been removed).
              Value = string() -- The value of the variable.

       dir_listing(Arg)
              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|exhtml, Term}
              This will transform the erlang term Term into a stream  of  HTML
              content.  The  exhtml variant transforms into strict XHTML code.
              The basic syntax of Term is

              EHTML = [EHTML] | {Tag, Attrs, Body} | {Tag, Attrs} | {Tag} |
                      {Module, Fun, [Args]} | fun/0 |
                      binary() | character()
              Tag   = atom()
              Attrs = [{Key, Value}]
              Key   = atom()
              Value = string() | binary() | atom() | integer() | float() |
                      {Module, Fun, [Args]} | fun/0
              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 con‐
              tent 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. (Typi‐
              cally if a file is very large or if data arrives from  back  end
              servers on the network.

       {streamcontent_with_timeout, MimeType, FirstChunk, Timeout}
              Similar  to  above,  but  with  an explicit timeout. The default
              timeout is 30 secs. I.e if the application fails to deliver data
              to  the Yaws process, the streaming will stop. This is often not
              the desired behaviour in Comet/Ajax applications.  It's possible
              to provide 'infinity' as timeout.

       {streamcontent_from_pid, MimeType, Pid}
              This  return  value is similar to the streamcontent return value
              above.

              However it makes it  possible  to  stream  data  to  the  client
              directly  from  an  application  process  to  the  socket.  This
              approach can be useful for applications that employ long-polling
              (Comet) techniques, for example, and for applications wanting to
              avoid buffering data or avoid HTTP  chunked  mode  transfer  for
              streamed data.

       {streamcontent_with_size, Sz, MimeType, FirstChunk}
              This  return  value is similar to the streamcontent return value
              above.

              However it makes it possible to stream data  to  the  client  by
              setting  the  content length of the response. As the opposite of
              other ways to stream data, in this case,  the  response  is  not
              chunked encoded.

       {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 treat‐
              ment.

              {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.

              {server, What}

              Sets the Server: header. By setting this  header,  the  server's
              signature will be dynamically overloaded.

              {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.

              {expires, What}

              Sets the Expires: header.

              {date, What}

              Sets the Date: header.

              {allow, What}

              Sets the Allow: header.

              {last_modified, What}

              Sets the Last-Modified: header.

              {etag, What}

              Sets the Etag: header.

              {set_cookie, Cookie}

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

              {content_range, What}

              Sets the Content-Range: header.

              {content_type, MimeType}

              Sets the Content-Type: header.

              {content_encoding, What}

              Sets the Content-Encoding: header. If this header is defined, no
              deflate is performed by Yaws,  allowing  you  to  compress  data
              yourself if you wish to do so.

              {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  con‐
              tent, we can force Yaws to not ship the page chunked.

              {transfer_encoding, What}

              Sets the Transfer-Encoding: header.

              {www_authenticate, What}

              Sets the WWW-Authenticate: header.

              {vary, What}

              Sets the Vary: header.

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

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

       {header, {HeaderName, erase}}
              Clears the header named HeaderName from the accumulated headers.

       {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.

       flush  Flush remaining data sent by the client.

       {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 cur‐
              rently 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 returns a different page than the one being requested.
              Page is a Request-URI, so it must be url-encoded and can contain
              a query-string.

       {page, {Options, Page}}
              Like  the  above,  but  supplying  an  additional  deep  list of
              options. Supported option types are:

              {status, C} - Set the HTTP response status code C for page Page.

              {header, H} - Accumulate the HTTP header H for page Page.

              {disable_cache, Bool} - if set to true,  disable  the  cache  of
              Page for this call.

       {websocket, CallbackModule, Options}
              Tell  Yaws to use CallbackModule as a WebSocket Protocol handler
              for traffic on the client socket. See the Yaws  websocket  docu‐
              mentation for more details.

       {ssi, File, Delimiter, Bindings}
              Server  side  include  File  and  macro expansion in File.  Each
              occurrence of a string, say "xyz", inside File that's  within  a
              Delimiter pair is replaced with the corresponding value in Bind‐
              ings.

              Example: Delimiter = %%

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

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

              The occurrence of %%xyz%% in File will be replaced  with  "Ding‐
              bat" in the Server side included output.

              The  {ssi,  File,  Delimiter, Bindings} statement can also occur
              within 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 existence of a binding.

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

       #arg{} Return  an instance of an #arg{} record. This can be useful when
              used as part of a [ListOfValues] return value, so that any  sub‐
              sequent  elements  in the return list that require an #arg{} get
              the returned instance rather than the original. For example,  an
              out/1  function  might  set  the  state field of an #arg{}, then
              return both it and {yssi, YawsFile} in a  list,  in  which  case
              Yaws  will  pass  the  returned #arg{}, rather than the original
              instance, to the yaws file out/1 function.

       [ListOfValues]
              It is possible to return a deep list of the above defined return
              values.    Any    occurrence    of   streamcontent,   streamcon‐
              tent_with_timeout,      streamcontent_with_size,      streamcon‐
              tent_from_pid,  get_more,  page  or  break in this list is legal
              only if it is the last position of the list. If  not,  remaining
              values in the list are ignored.

AUTHOR
       Written by Claes Wikstrom

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

                                                                   YAWS_API(5)

Valid XHTML 1.0!