man: can't set the locale; make sure $LC_* and $LANG are correct
manconv: can't set the locale; make sure $LC_* and $LANG are correct
zsoelim: can't set the locale; make sure $LC_* and $LANG are correct
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
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 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.
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 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.
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(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 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
application 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 proceed with
data delivery.
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.
If a variable is defined multiple times, the function may also
return {Val1, ....}.
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.
If a variable is defined multiple times, the function may also
return {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.
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 random generated 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 CleanuPid where Reason can be
either of timeout or normal. The Cookie is the HTTP cookie as
returned by new_session() and the 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.
reformat_header(H)
Returns a list of reformatted 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.
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} Override default pathinfo in
Arg#arg.pathinfo.
ExtraEnv = [Var]
Var = {Name, Value}
Name = string()
Value = string()
{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, 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 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 deafult
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.
{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.
{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 previously 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 con-
tent, 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 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 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
occurrence of a string, say "xyz", inside File which is inside
Delimiters is replaced with the corresponding value in Bindings.
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
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 existence of a binding.
{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)
YAWS_API(5)
