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ADV_OPTS.DOC
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1 November 1999
Abstract:
SRE-http's SEL-specific "advanced options" are used for a variety
of purposes, including setting parameters, enabling less-frequently
used options, and executing mid-filter procedures.
1. Introdution
2. Specifying advanced options
3. The advanced options
3a) EXEC Commands
3b) HEADER and RESPONSE directives.
--------------------------------
1) Introduction
SRE-http's selector specific advanced-options provides a set of
less-frequently needed, "advanced-options" to the ambitious webmaster.
These advanced-options include:
* execution of "mid-filter" procedures,
* customization of response headers
* suppression of specific server side includes.
* selector specific mime type
* selector specific replacement-rules
* set the FIX_EXPIRE, CONTENT_MD5, PRE_REPLY, and other parameters
* enabling simple hit-metering
* enable or disable encryption
* specify the maximum number of simultaneous users of a resource
* in the future, additional features may be added.
--------------------------------
2) Specifying advanced-options
There are two ways of specifying selector-specific advanced options.
a) Using an advanced options file.
You can specify a selector-specific advanced option file either in
ACCESS.IN or in ATTRIBS.CFG -- you can use the intermediate
configurator to do this (or see IN_FILES.DOC for the details).
By default, these advanced options files should be located in, or under,
the DATA\ subdirectory of your GoServe working directory
(technical note: it will be in or under SRE-http's WORKDATA_DIR directory).
Note:there is NO global (default) advanced-options file.
b) Specifying options in ATTRIBS.CFG
In the usual case where one needs to set a few advanced options,
the use of the Option: lines in ATTRIBS.CFG is easier then
specification of a seperate advanced options file.
Note that for any REALM specified in ATTRIBS.CFG you can
use both an advanced options file line (ADVOPT_FILE)
and one (or several) Options: lines.
Some examples::
* Assuming that your SRE-http "WORKDATA_DIR" directory is
D:\GOSERVE\DATA, the following entry in ACCESS.IN:
/SAMPLES/* * , , MYREALM , , ADV_OPT.CTL
tells SRE-http to use the D:\GOSERVE\DATA\ADV_OPT.CTL advanced
options file for all selectors that match /SAMPLES/*
* The following entry in ATTRIBS.CGG could also be used to set some
advanced options (for all selectors that match /SAMPLES/*):
REALM: Myrealm
RULE: /SAMPLES/*
Option: header add X-Grader: this is mediocre resource
Option: set fix_expire 0.1
--------------------------------
3) The advanced options
There are several types of selector-specific advanced options:
1) EXEC commands -- execute an external REXX procedure.
2) HEADER and RESPONSE directives -- specify a custom response header
3) SSI_suppression directives -- suppress specific SSI actions.
4) Set MIME type
5) Replacement rules
6) Set a few variables
7) Enabling hit-metering
8) Controlling the maximum number of simultaneous users of a resource
The following documents how to use these options. We also recommend perusing
the ADV_OPTS.CTL and ADV_OPTS.CMD sample files.
Notes:
* each of these options should appear:
i) on a single line in your advanced option file, or
ii) in ATTRIBS.CFG
* lines in an advanced option file that begin with ; are comments
3a) EXEC Commands
EXEC entries are used to execute external REXX procedures. This execution
occurs just before the "verb is processed", and after all "selector
modifications/redirections" and "access control checks."
In a sense, the EXEC commands can be thought of as "mid-filter" hook,
occuring after the (optional) pre-filter, and before the (optional)
"pre-reply" procedure.
Example:
EXEC ADV_OPTS.CMD Hello from job 1.
In this example, ADV_OPTS.CMD should be in the GoServe working directory.
Note that ADV_OPTS will be sent a set of variables:
ARGUMENT:
The "argument" following the procedure-file name. This may contain
commas (a comma containing ARGUMENT does NOT result in multiple
arguments being sent to the called procedure).
In the above example, ARGUMENT would be "Hello from job 1." (without
the quotes).
SOURCE:
The GoServe "source" line
REQUEST:
The GoServe request line
SEL:
The (SRE-http) modified selector
VERBOSE:
The SRE-http VERBOSE parameter
SERVERNAME:
The name of the server processing this request (might be an alias)
HOST_NICKNAME:
SRE-http "host nickname" for the server processing this request
DATA_DIRECTORY:
The default data directory (might be servername dependent)
HOME_DIRECTORY:
The ~ replacement directory (the "home" directory).
TEMP_DIRECTORY:
The SRE-http TEMPDATA_DIR "temporary files" directory
These external procedures MAY issue GoServe completion codes. If they do,
they should return
status_code bytes_sent
(i.e.; 200 15122)
If they do not, they should return a 0.
All other returns are ignored.
Note that ADV_OPTS.CMD contains a simple example of such an external procedure.
Hint: one use of EXEC is to support HTTP M-extensions, as described in
the "HTTP Extensions" Internet-Draft. Otherwise, these
M-extensions will result in a 510 error return.
3b) HEADER and RESPONSE directives.
You can include HEADER and RESPONSE entries -- they will be sent almost
verbatim to GoServe.
This response header customization is only available for GET and HEAD
requests that invoke a file transferal (including HTML documents
with server side includes).
That is, for "server side processing" requests (such as CGI-BIN
scripts, SRE-http addons, PUT and DELETE requests, and imagemaps)
HEADER and RESPONSE entries will NOT be used.
As a convenience, SRE-http will perform a few substitutions on HEADER
and RESPONSE entries:
$GMT : The current GMT day, date and time.
$SERVERNAME: The "server name" of the server processing this request
$SIZE: The number of bytes to be sent
$CODE: The status code (almost always 200)
Examples:
response HTTP/1.1 406 Variant not available
header add X-Webmaster-Name: Daniel Platypus
header drop expires
header add X-comment: X- headers are created by SRE-http
header add X-Our-server: $servername
header add X-Size-1: this is $size size
header add X-Code-1: this is $code code
Notes:
* This customization is akin to ICS's "meta information".
* Headers specified using advanced options override automatically
generated headers. For example, if a cache-control header
is specified as an advanced option, then the automatically
generated cache-control header will not be used.
* The HEADER DROP will drop a header (if one exists). This is
cumulative, so that...
HEADER DROP EXPIRES
HEADER ADD Expires: not-now
yields an
Expires: not-now
response header.
* HEADER ADD is cumulative -- if the named header exists, the new value
is appended. Thus, to replace a header, you should use HEADER DROP followed
by HEADER ADD.
* See GOSERVE.DOC for a description of the HEADER and RESPONSE GoServe
directives.
* When adding a header, be sure to include an ADD after the HEADER
* CACHE-CONTROL is special -- it is not cumulative.
To drop it, specify
HEADER ADD Cache-Control: 0
To change it, specify
HEADER ADD Cache-Control: my_cache_control
3c) Server Side Include Suppression
Although you can suppress all server side includes (either for all documents,
or on a SEL-specific basis), you may wish to only suppress a select set of
these includes. In particular, you may wish to supress HEADERS and FOOTERS
for a portion of your HTML documents. This can be easily done with
the various server side include suppression options.
The available options are:
ssi_no_cache : suppress caching (similar to a <!-- CACHE NO -->
keyphrase)
ssi_no_header : Do NOT include HEADERS lines
ssi_no_footer : Do NOT include FOOTERS lines
ssi_no_replace : Do NOT process <!-- REPLACE varname --> keyphrases
ssi_no_include : Do NOT process <!-- INCLUDE filename --> keyphrases
ssi_no_option : Do NOT process <!-- OPTION n --> keyphrases
ssi_no_interpret : Do NOT process <!-- INTERPRET FILE filename --> or
<!-- INTERPRET CODE xxx ;yyy --> keyphrases.
ssi_no_select : Do NOT process <!-- SELECT xxx --> ... <!-- SELECT END -->
keyphrases
ssi_no_#filestat : Do NOT process <!-- #FLASTMOD ... --> or <!-- #FSIZE ... -->
keyphrases
ssi_no_#config : Do NOT process <!-- #CONFIG ... --> keyphrases
ssi_no_#echo : Do NOT process <!-- #ECHO ... --> keyphrases
ssi_no_#include : Do NOT process <!-- #INCLUDE ... --> keyphrases
ssi_no_#exec : Do NOT process <!-- #EXEC ... --> keyphrases
Note that these options should appear one-per-line.
Examples:
ssi_no_cache
ssi_no_header
ssi_no_footer
ssi_no_select
ssi_no_#echo
ssi_no_#exec
3d) Mime types
You can specify the mime type for this (these) selector(s). Just enter
MIME type/subtype
For example:
MIME text/plain
MIME image/jpg
You should have, at most, one MIME line per selector (latter entries are
ignored).
3e) Replacement rules
You can specify selector specific "replacement rules". These will be
used instead of the generic REPLACE_RULES. replacement rules (set in
INITFILT.80).
The syntax is
REPLACE_RULES=old_string==new_string
Notes:
* Spaces will NOT be stripped from either old_string or new_string
-- thus "invisible spaces" at the end of new_string will be retained.
* Note the use of == as a seperator between old_string and new_string.
* Unlike REPLACE_RULES.n (in INITFILT.80), do NOT include a "stem";
the order of appearance is the order of processing
* If you do NOT specify any replacement rules here, generic ones
(specified in INITFILT.80) will be used.
Example:
REPLACE_RULES=$(==<!-- $ customiz
REPLACE_RULES=)$== -->
Hint: Using Replace_rules and Load Balancing.
Replace rules can come in handy when you are load balancing to subsidiary-
sites. In order to guarantee that all requests pass through a "main-site",
you may have to include a <BASE href="main.site.url"> element in the
<HEAD> section of HTML documents on subsidiary-sites. Since adding these
elements may be tedious, the following REPLACE_RULES can be used instead:
REPLACE_RULES=</HEAD>==<BASE href="http://main.site.url"> </HEAD>
where main.site.url should be the IP address of the main-site.
3f) Setting variables
You can set several SRE-http variables on a request specific basis.
These are:
CG_GZIP (enable/disable on-the-fly GZIP content encoding)
CONTENT_MD5 (add an Content-MD5 response header)
FIX_EXPIRE (add an offset to an otherwise immediate expiration).
PRE_REPLY (suppress or enable the use of a "pre-reply" procedure).
ENCRYPT (enable or disable encryption)
DELTA_ENCODING (enable delta encoding)
DTemplate (specify a delta encoding "DTemplate")
DCluster (specify a delta encoding "DCluster")
The syntax to use is:
SET varname value
where varname is either CONTENT_MD5, FIX_EXPIRE, PRE_REPLY, or ENCRYPT
For example:
SET CONTENT_MD5 0 (suppress generation of Content-MD5 header)
SET CONTENT_MD5 1
SET CONTENT_MD5 2 (use MD5.EXE, assuming EMX is avaiable)
SET FIX_EXPIRE 0
SET FIX_EXPIRE 0.66
SET PRE_REPLY 0
SET ENCRYPT SRE_A
SET DELTA_ENCODING 1 (1 means enable, 0 means disable)
SET DTEMPLATE /quotes/?
SET DCLUSTER /quotes/basequote.1
SET CE_GZIP 1 (enable on-the-fly GZIP content encoding)
SET CE_GZIP 0 (disable on-the-fly GZIP content encoding)
Notes:
* PRE_REPLY can take the following values:
0 - suppress the pre-reply procedure
This is not necessary if the PRE_REPLY_PROCEDURE='!filename'
format is used.
1 - use a "selector specific" pre-reply procedure.
This only has an effect when the "!filename" (selector specific)
format of PRE_REPLY_PROCEDURE is used; it is not necessary when the
PRE_REPLY_PROCEDURE='filename' format is used.
* If PRE_REPLY_PROCEDURE=0, then PRE_REPLY has no effect.
* PRE_REPLY_PROCECURE is set in INIT_STA.80 (see INITFILT.DOC, or
PREREPLY.DOC, for more details).
* If encryption is not enabled (ENABLE_ENCRYPTION=0) then SET ENCRYPT
has no effect.
* SET ENCRYPT 0 means "never encrypt" -- this will override a !ENCRYPT
"special directive" (that is prepended to the selector)
* SET ENCRYPT (without any other argument) is a shorthand
for SET ENCRYPT SRE_A
* DELTA_ENCODING is used when the default DELTA_ENCODING (set in INIT_STA.80)
is equal to 1 or 2 (if the default DELTA_ENCODING=0, then DELTA_ENCODING
is never attempted)
* DCLUSTER and DTEMPLATE are used to specify a Dcluster or Dtemplate
request header (they will be included verbatim). These response
headers are used to improve delta-encoding (as described in DELTA.DOC).
* CE_GZIP overrides the CE_GZIP parameter set in INIT_STA.80
3g) Enabling hit-metering.
In order to get some measure of the number of times proxy servers
are resolving requests for resources from your site, SRE-http
supports a form of simple-hit-metering. This algorithim (based
on RFC 2227) depends on proxies reporting their activity
to your server.
To enable this, you must specify a METER advanced option.
When METER is specified (and when a proxy says that it is willing to
support hit metering), SRE-http will:
* include a METER: response header, and
* will watch for special METER: request headers.
The information in these METER: request headers is written to HITMETER.CNT.
The syntax of this option is:
METER=[options]
where:
options are a set of optional modifiers, that are described in RFC2227.
These options include directives on cache lifetime, and on when and how
to report hits. Alternatively, you can not specify options, which
will enable hit-metering, but not effect cache behavior.
Examples:
METER=
METER= max-uses=3, dont-report
Note that if you do not specify a METER= option, then hit-metering
will not be attempted (even if a proxy reports that it is willing
to provide hit-metering).
For further details, please HITMETER.DOC, and see the description of
the PROXY_CACHE variable in INITFILT.DOC.
3h) Controlling the maximum number of simultaneous users of a resource
In order to selectively control the intensity of use of your server's
resources (such as CPU intenstive scripts and addons), you can
specify an 'intensity of use' option". Basically, if more then this number
of requests for this resources are currently active, the server will respond
with a "Server busy, try again in a few minutes".
The syntax is:
MAXUSER class = n ; failure=maxuser_fail_file retryafter
where:
class : identifies a "class" of resources. This class can be
unique to the selector, or can be shared by several selectors
(say, due to several MAXUSER options in several advanced options
files). These "classes" are similar to "realms", but are only used
by this MAXUSER option
If not specified, a "default" class is used.
n : n is the maximum number of simultaneous users allowed.
maxuser_fail_file: Optional. If specified, maxuser_fail_file is used when
maxuser is not satisfied. Maxuser_fail_file should be a fully
qualified file name, or a file name relative to your GoServe
working directory.
retryafter: Optional. Number of seconds to use in a Retry-After header.
If specified, a Retry-After reponse header is added to the
maxuser_fail_file response (http/1.1 clients can use Retry-After
response headers to automatically re-request the resource).
Example (as may appear in attribs.cfg):
realm: foo1
rule: /addon/gif_text*
option: MAXUSER gifProgs = 3 ; failure=nogif.htm 60
realm: foo2
rule: /addon/blendgif*
option: MAXUSER gifProgs = 1
Notes:
* "class" is case insensitive.
* a semi-colon (:) MUST appear before a failure=maxuser_fail_file
* if a MAXUSER_FAIL_FILE is not specified ,a generic "server is busy"
response will be returned (when the MAXUSER is not satisfied).
* As with the LOGON_FAIL_FILE, when the MAXUSER_FAIL_FILE is an HTML
document, server side includes are NOT attempted. However, a
few special substitutions will occur (when the MAXUSER_FAIL_FILE
is an HTML document):
<!--#URL--> phrases are substituted with the request selector.
<!--#SERVER--> phrases are substituted with the servername.
<!-- #WEBMASTER --> phrases are substituted with the WEBMASTER variable.
<!-- #MESSAGE --> phrases are substituted with a short description
of the reason for failure
<!-- #LINK --> phrases are substituted with a URL which points
back to this resource
* MAXUSER is defined on a selector specific basis, but the maximum users
are defined across a "class" of selectors. Thus, one could limit
users of a set of resources (say, only 2 simultaneous users of
any one of several helper apps).
* The fact that n can vary for each of several selectors assigned to a "class"
lends some flexibilty.
* In the above example,
i) blendgif will not be started if any instance of blendgif or gif_text
is currently active
ii) up to 3 instances of gif_text are alllowed
iii) or 1 instance of blendgif and 2 instances of gif_text (assuming that
blendgif was started first)
* CAUTION: SRE-http uses mutex semaphores to implement this MAXUSER feature.
Unfortunately, REXXLIB's implementation of mutex semaphores is
somewhat buggy; and there may be cases where "ghost semaphores"
will interfere with program flow.
SRE-http attempts to deal with this (by using alternative
semaphores when required). However, on very dynamic
and unstable sites (where threads are being opened and closed
rapidly), this workaround may not be effective. If problems arise
that can be traced to the use of MAXUSERS, you can
* enable more thorough bug reporting by setting VERBOSE=3
(in INITFILT.80)
* view these bug reports by running PMPRINTF
* contact the author (Daniel Hellerstein) for advice
(danielh@crosslink.net)
4) A sample "advanced options file"
The following is a sample of an advanced options file. You might also want
to examine ADV_OPTS.CTL.
;------------- Begin Example ------------
; call the sample external procedure
exec adv_opts.cmd This is an argument , with commas embedded.
;
; add a custom response header
header add X-Webmaster-Name: Timothy Platypus
;
; Suppress headers, footers, and server side "excludes"
ssi_no_header
ssi_no_footer
ssi_no_select
replace_rules= C.== $ Customiz
; suppress content-md5 header
set content_md5 0
;------------- End Example ------------
---- End of document