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<properties>
<title>AJPv13 extensions Proposal</title>
<author email="hgomez@apache.org">Henri Gomez</author>
<date>$Date$</date>
</properties>
<body>
<section name="Introduction">
<p>
This document is a proposal of evolution of the current
Apache JServ Protocol version 1.3, also known as ajp13.  
I'll not cover here the full protocol but only the add-on from ajp13.

This nth pass include comments from the tomcat-dev list and
misses discovered during developpment.
</p>
<subsection name="Missing features in AJP13">
<p>
ajp13 is a good protocol to link a servlet engine like tomcat to a web server like Apache: 

<ul>
<li>
use persistants connections to avoid reconnect time at each request
</li>
<li>
encode many http commands to reduce stream size
</li>
<li>
send to servlet engine many info from web server (like SSL certs)
</li>
</ul>
<p>
But ajp13 lacks support for : 
</p>
<ul>
<li>
  security between web server and servlet engine.
  Anybody can connect to an ajp13 port (no login mecanism used)
  You could connect, for example with telnet, and keep the remote thread
  up by not sending any data (no timeout in connection)
</li>
<li>
  context information passed from servlet engine to web server.
  Part of the configuration of JK, the web server connector, is to
  indicate to the web server which URI to handle. 
  The mod_jk JkMount directive, told to web server which URI must be 
  forwarded to servlet engine.
  A servlet engine allready knows which URI it handle and TC 3.3 is
  allready capable to generate a config file for JK from the list
  of available contexts.
</li>
<li>
  state update of contexts from servlet engine to web server.
  Big site with farm of Tomcat, like ISP and virtuals hosters,
  may need to stop a context for admin purposes. In that case the front
  web server must know that the context is currently down, to eventually
  relay the request to another Tomcat
</li>
<li>
  verify state of connection before sending request.
  Actually JK send the request to the servlet engine and next wait 
  for the answer. But one of the beauty of the socket API, is you that 
  you could write() to a closed connection without any error reporting, 
  but a read() to a closed connection return you the error code. 
</li>
</ul>

</p>
</subsection>

<subsection name="Proposed add-ons to AJP13">
<p>
Let's descrive here the features and add-on that could be added to AJP13.
Since this document is a proposal, a reasonable level of chaos must be expected at first.
Be sure that discussion on tomcat list will help clarify points, add 
features but the current list seems to be a 'minimun vital'

<ul>

<li>
Advanced login features at connect time
</li>

<li>
Basic authorisation system, where a shared secret key is
present in web server and servlet engine.
</li>

<li>
Basic protocol negociation, just to be sure that if functionnalities are added
to AJP13 in the future, current implementations will still works.
</li>

<li>
Clean handling of 'Unknown packets'
</li>

<li>
Extended env vars passed from web-server to servlet engine.
</li>

<li>
Add extra SSL informations needed by Servlet 2.3 API (like SSL_KEY_SIZE)
</li>

</ul>

</p>
</subsection>

<subsection name="Advanced login">
<p>

<ol>
<li>
WEB-SERVER send LOGIN INIT CMD + NEGOCIATION DATA + WEB SERVER INFO
</li>
<li>
  TOMCAT respond with LOGIN SEED CMD + RANDOM DATA
</li>
<li>
  WEB-SERVER calculted the MD5 of RANDOM DATA+SECRET DATA
</li>
<li>
  WEB-SERVER send LOGIN COMP CMD + MD5 (SECRET DATA + RANDOM DATA)
</li>
<li>
  TOMCAT respond with LOGIN STATUS CMD + NEGOCIED DATA + SERVLET ENGINE INFO
</li>
</ol>

To prevent DOS attack, the servlet engine will wait
the LOGIN CMD only 15/30 seconds and reports the
timeout exception for admins investigation.

The login command will contains basic protocol
negociation information like compressing ability, 
crypto, context info (at start up), context update at 
run-time (up/down), level of SSL env vars, AJP protocol
level supported (level1/level2/level3...)

The Web server info will contain web server info and
connector name (ie Apache 1.3.26 + mod_ssl 2.8.8 + mod_jk 1.2.1 + mod_perl 1.25).

The servlet engine will mask the negociation mask with it's own
mask (what it can do) and return it when loggin is accepted.

This will help having a basic AJP13 implementation (level 1)
on a web-server working with a more advanced protocol handler on
the servlet engine side or vice-versa.

AJP13 was designed to be small and fast and so many
SSL informations present in the web-server are not
forwarded to the servlet engine. 

We add here four negociations flags to provide more
informations on client SSL data (certs), server SSL datas, 
crypto used, and misc datas (timeout...). 
</p>
</subsection>

<subsection name="Messages Stream">
<p>
<source>
+----------------+------------------+-----------------+
| LOGIN INIT CMD | NEGOCIATION DATA | WEB SERVER INFO |
+----------------+------------------+-----------------+

+----------------+----------------+
| LOGIN SEED CMD | MD5 of entropy |
+----------------+----------------+

+----------------+----------------------------+
| LOGIN COMP CMD | MD5 of RANDOM + SECRET KEY |
+----------------+----------------------------+

+-----------+---------------+---------------------+
| LOGOK CMD | NEGOCIED DATA | SERVLET ENGINE INFO |
+-----------+---------------+---------------------+

+------------+--------------+
| LOGNOK CMD | FAILURE CODE |
+------------+--------------+
</source>

<ul>
<li>
LOGIN INIT CMD, LOGIN SEED CMD, LOGIN COMP CMD, LOGOK CMD, LOGNOK CMD are 1 byte long.
</li>
<li>
MD5, MD5 of RANDOM + SECRET KEY are 32 chars long.
</li>
<li>
NEGOCIATION DATA, NEGOCIED DATA, FAILURE CODE are 32 bits long.
</li>
<li>
WEB SERVER INFO, SERVLET ENGINE INFO are CString.
</li>
</ul>

The secret key will be set by a new propertie in
workers.properties : secretkey
<source>
worker.ajp13.port=8009
worker.ajp13.host=localhost
worker.ajp13.type=ajp13
worker.ajp13.secretkey=myverysecretkey
</source>
</p>
</subsection>

<subsection name="Shutdown feature">
<p>
AJP13 miss a functionnality of AJP12, which is shutdown command.
A logout will tell servlet engine to shutdown itself.
<source>
+--------------+----------------------------+
| SHUTDOWN CMD | MD5 of RANDOM + SECRET KEY |
+--------------+----------------------------+

+------------+
| SHUTOK CMD |
+------------+

+-------------+--------------+
| SHUTNOK CMD | FAILURE CODE |
+-------------+--------------+
</source>

<ul>
<li>
SHUTDOWN CMD, SHUTOK CMD, SHUTNOK CMD are 1 byte long.
</li>
<li>
MD5 of RANDOM + SECRET KEY are 32 chars long.
</li>
<li>
FAILURE CODE is 32 bits long.
</li>
</ul>

</p>
</subsection>

<subsection name="Extended Env Vars feature">
<p>
NOTA:

While working on AJP13 in JK, I really discovered "JkEnvVar". 
The following "Extended Env Vars feature" description may not
be implemented in extended AJP13 since allready available in original
implementation.

DESC:

Many users will want to see some of their web-server env vars 
passed to their servlet engine.

To reduce the network traffic, the web-servlet will send a 
table to describing the external vars in a shorter fashion.

We'll use there a functionnality allready present in AJP13,
attributes list :

In the AJP13, we've got :

<source>
AJP13_FORWARD_REQUEST :=
    prefix_code      2
    method           (byte)
    protocol         (string)
    req_uri          (string)
    remote_addr      (string)
    remote_host      (string)
    server_name      (string)
    server_port      (integer)
    is_ssl           (boolean)
    num_headers      (integer)
    request_headers *(req_header_name req_header_value)

    ?context       (byte string)
    ?servlet_path  (byte string)
    ?remote_user   (byte string)
    ?auth_type     (byte string)
    ?query_string  (byte string)
    ?route         (byte string)
    ?ssl_cert      (byte string)
    ?ssl_cipher    (byte string)
    ?ssl_session   (byte string)

    ?attributes   *(attribute_name attribute_value)
    request_terminator (byte)
</source>

Using short 'web server attribute name' will reduce the 
network traffic.
 
<source>
+-------------------+---------------------------+-------------------------------+----+
| EXTENDED VARS CMD | WEB SERVER ATTRIBUTE NAME | SERVLET ENGINE ATTRIBUTE NAME | ES |
+-------------------+---------------------------+-------------------------------+----+
</source>

ie :

<source>
JkExtVars S1 SSL_CLIENT_V_START javax.servlet.request.ssl_start_cert_date
JkExtVars S2 SSL_CLIENT_V_END   javax.servlet.request.ssl_end_cert_date
JkExtVars S3 SSL_SESSION_ID     javax.servlet.request.ssl_session_id


+-------------------+----+-------------------------------------------+
| EXTENDED VARS CMD | S1 | javax.servlet.request.ssl_start_cert_date |
+-------------------+----+-------------------------------------------+
+----+-----------------------------------------+
| S2 | javax.servlet.request.ssl_end_cert_date |
+----+-----------------------------------------+
+----+-----------------------------------------+
| S3 | javax.servlet.request.ssl_end_cert_date |
+----+-----------------------------------------+
</source>

During transmission in extended AJP13 we'll see attributes name
containing S1, S2, S3 and attributes values of 
2001/01/03, 2002/01/03, 0123AFE56.
 
This example showed the use of extended SSL vars but 
any 'personnal' web-server vars like custom authentification
vars could be reused in the servlet engine.
The cost will be only some more bytes in the AJP traffic.

<ul>
<li>
EXTENDED VARS CMD is 1 byte long.
</li>
<li>
WEB SERVER ATTRIBUTE NAME, SERVLET ENGINE ATTRIBUTE NAME are CString.
</li>
<li>
ES is an empty CString.
</li>
</ul>

</p>
</subsection>

<subsection name="Context informations forwarding for Servlet engine to Web Server">
<p>
Just after the LOGON PHASE, the web server will ask for the list of contexts
and URLs/URIs handled by the servlet engine.
It will ease installation in many sites, reduce questions about configuration 
on tomcat-user list, and be ready for servlet API 2.3.

This mode will be activated by a new directive JkAutoMount 

ie: JkAutoMount examples myworker1 /examples/

If we want to get ALL the contexts handled by the servlet engine, willcard
could be used :

ie: JkAutoMount * myworker1 *

A servlet engine could have many contexts, /examples, /admin, /test.
We may want to use only some contexts for a given worker. It was
done previously, in apache HTTP server for example, by setting by 
hand the JkMount accordingly in each [virtual] area of Apache.

If you web-server support virtual hosting, we'll forward also that
information to servlet engine which will only return contexts for
that virtual host. 
In that case the servlet engine will only return the URL/URI matching
these particular virtual server (defined in server.xml). 
This feature will help ISP and big sites which mutualize large farm
of Tomcat in load-balancing configuration.

<source>
+-----------------+-------------------+----------+----------+----+
| CONTEXT QRY CMD | VIRTUAL HOST NAME | CONTEXTA | CONTEXTB | ES |
+-----------------+-------------------+----------+----------+----+

+------------------+-------------------+----------+-------------------+----------+---------------+----+
| CONTEXT INFO CMD | VIRTUAL HOST NAME | CONTEXTA | URL1 URL2 URL3 ES | CONTEXTB | URL1 URL2 ... | ES |
+------------------+-------------------+----------+-------------------+----------+---------------+----+
</source>

We'll discover via context-query, the list of URL/MIMES handled by the remove servlet engine
for a list of contextes.
In wildcard mode, CONTEXTA will contains just '*'.

<ul>
<li>
CONTEXT QRY CMD and CONTEXT INFO CMD are 1 byte long.
</li>
<li>
VIRTUAL HOST NAME is a CString, ie an array of chars terminated by a null byte (/0).
</li>
<li>
An empty string is just a null byte (/0).
</li>
<li>
ES is an empty CString. Indicate end of URI/URLs or end of CONTEXTs.
</li>
</ul>

NB:<br/>
When VirtualMode is not to be used, the VIRTUAL HOST NAME is '*'.
In that case the servlet engine will send all contexts handled.
</p>
</subsection>

<subsection name="Context informations updates from Servlet engine to Web Server">
<p>
Context update are messages caming from the servlet engine each time a context 
is desactivated/reactivated. The update will be in use when the directive JkUpdateMount.
This directive will set the AJP13_CONTEXT_UPDATE_NEG flag.

ie: JkUpdateMount myworker1

<source>
+--------------------+-------------------+----------+--------+----------+--------+----+
| CONTEXT UPDATE CMD | VIRTUAL HOST NAME | CONTEXTA | STATUS | CONTEXTB | STATUS | ES |
+--------------------+-------------------+----------+--------+----------+--------+----+
</source>

<ul>
<li>
CONTEXT UPDATE CMD, STATUS are 1 byte long.
</li>
<li>
VIRTUAL HOST NAME, CONTEXTS are CString.
</li>
<li>
ES is an empty CString. Indicate end of CONTEXTs.
</li>
</ul>

NB:<br/>
When VirtualMode is not in use, the VIRTUAL HOST NAME is '*'.
STATUS is one byte indicating if context is UP/DOWN/INVALID
</p>
</subsection>

<subsection name="Context status query to Servlet engine">
<p>
This query will be used by the web-server to determine if a given
contexts are UP, DOWN or INVALID (and should be removed).

<source>
+-------------------+--------------------+----------+----------+----+
| CONTEXT STATE CMD |  VIRTUAL HOST NAME | CONTEXTA | CONTEXTB | ES |
+-------------------+--------------------+----------+----------+----+

+-------------------------+-------------------+----------+--------+----------+--------+----+
| CONTEXT STATE REPLY CMD | VIRTUAL HOST NAME | CONTEXTA | STATUS | CONTEXTB | STATUS | ES |
+-------------------------+-------------------+----------+-------------------+--------+----+
</source>

<ul>
<li>
CONTEXT STATE CMD, CONTEXT STATE REPLY CMD, STATUS are 1 byte long.
</li>
<li>
VIRTUAL HOST NAME, CONTEXTs are CString
</li>
<li>
ES is an empty CString
</li>
</ul>

NB:<br/>
When VirtualMode is not in use, the VIRTUAL HOST NAME is an empty string. 
</p>
</subsection>

<subsection name="Handling of unknown packets">
<p>
Sometimes even with a well negocied protocol, we may be in a situation 
where one end (web server or servlet engine), will receive a message it
couldn't understand. In that case the receiver will send an 
'UNKNOW PACKET CMD' with attached the unhandled message.

<source>
+--------------------+------------------------+-------------------+
| UNKNOWN PACKET CMD | UNHANDLED MESSAGE SIZE | UNHANDLED MESSAGE |
+--------------------+------------------------+-------------------+
</source>

Depending on the message, the sender will report an error and if 
possible will try to forward the message to another endpoint.

<ul>
<li>
UNKNOWN PACKET CMD is 1 byte long.
</li>
<li>
UNHANDLED MESSAGE SIZE is 16bits long.
</li>
<li>
UNHANDLED MESSAGE is an array of byte (length is contained in UNHANDLED MESSAGE SIZE)
</li>
</ul>

NB:<br/>
added UNHANDLED MESSAGE SIZE (development)
</p>
</subsection>

<subsection name="Verification of connection before sending request">
<p>
NOTA: This fonctionality may never be used, since it may slow up the normal process
since requiring on the web-server side an extra IO (read) before forwarding
the request.....

One of the beauty of socket APIs, is that you could write on a half closed socket.
When servlet engine close the socket, the web server will discover it only at the
next read() to the socket. 
Basically, in the AJP13 protocol, the web server send the HTTP HEADER and HTTP BODY 
(POST by chunk of 8K) to the servlet engine and then try to receive the reply. 
If the connection was broken the web server will learn it only at receive time.

We could use a buffering scheme but what happen when you use the servlet engine
for upload operations with more than 8ko of datas ?

The hack in the AJP13 protocol is to add some bytes to read after the end of the
service :

<source>
EXAMPLE OF DISCUSSION BETWEEN WEB SERVER AND SERVLET ENGINE

AJP HTTP-HEADER (+ HTTP-POST)   (WEB->SERVLET)

AJP HTTP-REPLY					(SERVLET->WEB)

AJP END OF DISCUSSION			(SERVLET->WEB)
						
---> AJP STATUS 				(SERVLET->WEB AJP13)
</source>

The AJP STATUS will not be read by the servlet engine at the end of 
the request/response #N but at the begining of the next session.

More at that time the web server could also use OS dependants functions
(or better APR functions) to determine if there is also more data 
to read. And that datas could be CONTEXT Updates. 

This will avoid the web server sending a request to a 
desactivated context. In that case, if the load-balancing is used,
it will search for another servlet engine to handle the request.

And that feature will help ISP and big sites with farm of tomcat, 
to updates their servlet engine without any service interruption.

<source>
+------------+-------------+
| STATUS CMD | STATUS DATA |
+------------+-------------+
</source>

<ul>
<li>
STATUS CMD and STATUS DATA are one byte long.
</li>
</ul>
</p>
</subsection>

</section>

<section name="Conclusion">
<p>
The goal of the extended AJP13 protocol is to overcome some of the original AJP13 limitation.
An easier configuration, a better support for large site and farm of Tomcat, 
a simple authentification system and provision for protocol updates.

Using the stable ajp13 implementation in JK (native) and in servlet 
engine (java), it's a reasonable evolution of the well known ajp13.
</p>
</section>

<section name="Commands and IDs in extended AJP13 Index">
<p>
Index of Commands and ID to be added in AJP13 Protocol
</p>

<subsection name="Commands IDs">
<p>
<table>
  <tr><th>Command Name</th><th>Command Number</th></tr>
  <tr><td>AJP13_LOGINIT_CMD</td><td>0x10</td></tr>
  <tr><td>AJP13_LOGSEED_CMD</td><td>0x11</td></tr>
  <tr><td>AJP13_LOGCOMP_CMD</td><td>0x12</td></tr>
  <tr><td>AJP13_LOGOK_CMD</td><td>0x13</td></tr>
  <tr><td>AJP13_LOGNOK_CMD</td><td>0x14</td></tr>
  <tr><td>AJP13_CONTEXT_QRY_CMD</td><td>0x15</td></tr>
  <tr><td>AJP13_CONTEXT_INFO_CMD</td><td>0x16</td></tr>
  <tr><td>AJP13_CONTEXT_UPDATE_CMD</td><td>0x17</td></tr>
  <tr><td>AJP13_STATUS_CMD</td><td>0x18</td></tr>
  <tr><td>AJP13_SHUTDOWN_CMD</td><td>0x19</td></tr>
  <tr><td>AJP13_SHUTOK_CMD</td><td>0x1A</td></tr>
  <tr><td>AJP13_SHUTNOK_CMD</td><td>0x1B</td></tr>
  <tr><td>AJP13_CONTEXT_STATE_CMD</td><td>0x1C</td></tr>
  <tr><td>AJP13_CONTEXT_STATE_REP_CMD</td><td>0x1D</td></tr>
  <tr><td>AJP13_UNKNOW_PACKET_CMD</td><td>0x1E</td></tr>
</table>

</p>
</subsection>

<subsection name="Negociations Flags">
<p>
<table>
  <tr><th>Command Name</th><th>Number</th><th>Description</th></tr>
  <tr><td>AJP13_CONTEXT_INFO_NEG</td><td>0x80000000</td><td>web-server want context info after login</td></tr>
  <tr><td>AJP13_CONTEXT_UPDATE_NEG</td><td>0x40000000</td><td>web-server want context updates</td></tr>
  <tr><td>AJP13_GZIP_STREAM_NEG</td><td>0x20000000</td><td>web-server want compressed stream</td></tr>
  <tr><td>AJP13_DES56_STREAM_NEG</td><td>0x10000000</td><td>web-server want crypted DES56 stream with secret key</td></tr>
  <tr><td>AJP13_SSL_VSERVER_NEG</td><td>0x08000000</td><td>Extended info on server SSL vars</td></tr>
  <tr><td>AJP13_SSL_VCLIENT_NEG</td><td>0x04000000</td><td>Extended info on client SSL vars</td></tr>
  <tr><td>AJP13_SSL_VCRYPTO_NEG</td><td>0x02000000</td><td>Extended info on crypto SSL vars</td></tr>
  <tr><td>AJP13_SSL_VMISC_NEG</td><td>0x01000000</td><td>Extended info on misc SSL vars</td></tr>
</table>

<br/>

<table>
  <tr><th>Negociation ID</th><th>Number</th><th>Description</th></tr>
  <tr><td>AJP13_PROTO_SUPPORT_AJPXX_NEG</td><td>0x00FF0000</td><td>mask of protocol supported</td></tr>
  <tr><td>AJP13_PROTO_SUPPORT_AJP13L1_NEG</td><td>0x00010000</td><td>communication could use AJP13 Level 1</td></tr>
  <tr><td>AJP13_PROTO_SUPPORT_AJP13L2_NEG</td><td>0x00020000</td><td>communication could use AJP13 Level 2</td></tr>
  <tr><td>AJP13_PROTO_SUPPORT_AJP13L3_NEG</td><td>0x00040000</td><td>communication could use AJP13 Level 3</td></tr>
</table>

<br/>
All others flags must be set to 0 since they are reserved for future use.

</p>
</subsection>

<subsection name="Failure IDs">
<p>
<table>
  <tr><th>Failure Id</th><th>Number</th></tr>
  <tr><td>AJP13_BAD_KEY_ERR</td><td>0xFFFFFFFF</td></tr>
  <tr><td>AJP13_ENGINE_DOWN_ERR</td><td>0xFFFFFFFE</td></tr>
  <tr><td>AJP13_RETRY_LATER_ERR</td><td>0xFFFFFFFD</td></tr>
  <tr><td>AJP13_SHUT_AUTHOR_FAILED_ERR</td><td>0xFFFFFFFC</td></tr>
</table>
</p>
</subsection>

<subsection name="Status">
<p>
<table>
  <tr><th>Failure Id</th><th>Number</th></tr>
  <tr><td>AJP13_CONTEXT_DOWN</td><td>0x01</td></tr>
  <tr><td>AJP13_CONTEXT_UP</td><td>0x02</td></tr>
  <tr><td>AJP13_CONTEXT_OK</td><td>0x03</td></tr>
</table>
</p>
</subsection>

</section>
</body>
</document>