Execution Handler
2002/03/19Execution handler is a program that processes files of specific path pattern. User can define relations between path pattern and the handler. This mechanism is used to define the form of CGI file, SSI (Server Side Include) and auto-indexing service for specific directories.
Configuration
Relations between path patterns and the handler is defined in/etc/handler
in service space.
The following is the content of my configuration (http://plan9.aichi-u.ac.jp
).
# path mimetype ramfs execpath arg ... /netlib/*/index.html text/html 0 /bin/ftp2html *.http - 0 $target *.html text/html 1 $target *.dx_html text/html 0 /bin/dxThe first field is a path pattern and the 4th field is the handler. The second and the third indicate how to do that. Comparison of path pattern and requested path is performed from the top of line. Comparison is stopped if pattern is matched to the requested path. Arguments of the program may continue after 4th field.
In path pattern, directory separator `/
' is not special.
( Therefore this pattern matching is not same as that of shell. )
There is one exception: we have a rule that pattern /*/
matches
/
Therefore the pattern
/netlib/*/index.htmlmatches to
/netlib/index.html
as well as /netlib/cmd/backup/index.html
for example.
Second field of /etc/handler
denote `ContentType' of HTTP header.
If the field is `-
', the handler must send all HTTP headers.
The third field is a flag that the program is to be served ramfs or not.
The 4th field is the path to handler. Handler must be a executable.
$target
after 4th field denotes absolute path to the requested
document. Note that $target
in 4th field means the requested path
is an executable program.
We can write arguments after 4th field. $target
at the last field can be omitted.
/bin/ftp2html
in this example is a
program that is used in http://plan9.aichi-u.ac.jp/netlib/
to handle my FTP directories. Other server such as Apache has an option to show
directory index if index.html is absent. ftp2html
also does this action but does much more: if README file is present then the content is shown,
if INDEX file is present then the content is shown with appropriate action tag
to the index label.
/bin/dx
is a tool that is designed by the author to be used for SSI.
The Relation to URI
HTTP/1.0 and HTTP/1.1 says that we can writeparam
and query
after document path of URI. That is,
path;params?query params = param[;params]Web server traditionally ignored
param
and passed query
as argument to CGI program.
Pegasus changed this traditional manner and accept param
as
argument parts that should be passed to CGI. On the other hand, Pegasus does
not participate in interpritating query
and passes it to CGI as
environment variable without translation.
Name space of CGI (name space of handler)
Name space of CGI (handler) can be configured using/etc/namespace.cgiIf the file is absent or nothing is done if present, name space of CGI is the same as service space.
Environment variables of CGI (handler)
Pegasus has many environment variables. However there are many variables are not fixed yet. Fixed variables are shown in the following:GATEWAY_INTERFACE SERVER_NAME SERVER_PORT SERVER_SOFTWARE SERVER_PROTOCOL REQUEST_METHOD REMOTE_ADDR QUERY_STRING HTTP_HEADER HTTP_HOST HTTP_REFERER HTTP_USER_AGENT home # /doc query # same as QUERY_STRING target # path to the requested document name # base name of target cputype # 386 objtype # 386 date # date like 'Mon, 04 Mar 2002 07:32:40 GMT'
other environment variable may be discarded or renamed in the future.
Handling of POST'ed data
POST'ed data is once received by the server from the client.Content-Length
is consulted in receiving the dataThen server passes the data to CGI as stdin.
CGI timeout
Timeout is defined to prevent buggy programs waiting data so long time. The value can be specified in httpd option. The default is 5 second. !