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548 lines
23 KiB
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548 lines
23 KiB
XML
<?xml version="1.0"?>
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<!DOCTYPE modulesynopsis SYSTEM "../style/modulesynopsis.dtd">
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<?xml-stylesheet type="text/xsl" href="../style/manual.en.xsl"?>
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<!-- $LastChangedRevision$ -->
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<!--
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Licensed to the Apache Software Foundation (ASF) under one or more
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contributor license agreements. See the NOTICE file distributed with
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this work for additional information regarding copyright ownership.
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The ASF licenses this file to You under the Apache License, Version 2.0
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(the "License"); you may not use this file except in compliance with
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the License. You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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-->
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<modulesynopsis metafile="mod_proxy_ajp.xml.meta">
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<name>mod_proxy_ajp</name>
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<description>AJP support module for
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<module>mod_proxy</module></description>
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<status>Extension</status>
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<sourcefile>mod_proxy_ajp.c</sourcefile>
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<identifier>proxy_ajp_module</identifier>
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<compatibility>Available in version 2.1 and later</compatibility>
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<summary>
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<p>This module <em>requires</em> the service of <module
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>mod_proxy</module>. It provides support for the
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<code>Apache JServ Protocol version 1.3</code> (hereafter
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<em>AJP13</em>).</p>
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<p>Thus, in order to get the ability of handling <code>AJP13</code>
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protocol, <module>mod_proxy</module> and
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<module>mod_proxy_ajp</module> have to be present in the server.</p>
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<note type="warning"><title>Warning</title>
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<p>Do not enable proxying until you have <a
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href="mod_proxy.html#access">secured your server</a>. Open proxy
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servers are dangerous both to your network and to the Internet at
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large.</p>
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</note>
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</summary>
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<seealso><module>mod_proxy</module></seealso>
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<seealso><a href="../env.html">Environment Variable documentation</a></seealso>
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<section id="env"><title>Environment Variables</title>
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<p>Environment variables whose names have the prefix <code>AJP_</code>
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are forwarded to the origin server as AJP request attributes
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(with the AJP_ prefix removed from the name of the key).</p>
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</section>
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<section id="overviewprotocol"><title>Overview of the protocol</title>
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<p>The <code>AJP13</code> protocol is packet-oriented. A binary format
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was presumably chosen over the more readable plain text for reasons of
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performance. The web server communicates with the servlet container over
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TCP connections. To cut down on the expensive process of socket creation,
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the web server will attempt to maintain persistent TCP connections to the
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servlet container, and to reuse a connection for multiple request/response
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cycles.</p>
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<p>Once a connection is assigned to a particular request, it will not be
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used for any others until the request-handling cycle has terminated. In
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other words, requests are not multiplexed over connections. This makes
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for much simpler code at either end of the connection, although it does
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cause more connections to be open at once.</p>
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<p>Once the web server has opened a connection to the servlet container,
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the connection can be in one of the following states:</p>
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<ul>
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<li> Idle <br/> No request is being handled over this connection. </li>
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<li> Assigned <br/> The connecton is handling a specific request.</li>
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</ul>
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<p>Once a connection is assigned to handle a particular request, the basic
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request informaton (e.g. HTTP headers, etc) is sent over the connection in
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a highly condensed form (e.g. common strings are encoded as integers).
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Details of that format are below in Request Packet Structure. If there is a
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body to the request <code>(content-length > 0)</code>, that is sent in a
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separate packet immediately after.</p>
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<p>At this point, the servlet container is presumably ready to start
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processing the request. As it does so, it can send the
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following messages back to the web server:</p>
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<ul>
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<li>SEND_HEADERS <br/>Send a set of headers back to the browser.</li>
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<li>SEND_BODY_CHUNK <br/>Send a chunk of body data back to the browser.
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</li>
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<li>GET_BODY_CHUNK <br/>Get further data from the request if it hasn't all
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been transferred yet. This is necessary because the packets have a fixed
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maximum size and arbitrary amounts of data can be included the body of a
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request (for uploaded files, for example). (Note: this is unrelated to
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HTTP chunked tranfer).</li>
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<li>END_RESPONSE <br/> Finish the request-handling cycle.</li>
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</ul>
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<p>Each message is accompanied by a differently formatted packet of data.
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See Response Packet Structures below for details.</p>
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</section>
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<section id="basppacketstruct"><title>Basic Packet Structure</title>
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<p>There is a bit of an XDR heritage to this protocol, but it differs
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in lots of ways (no 4 byte alignment, for example).</p>
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<p>Byte order: I am not clear about the endian-ness of the individual
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bytes. I'm guessing the bytes are little-endian, because that's what
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XDR specifies, and I'm guessing that sys/socket library is magically
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making that so (on the C side). If anyone with a better knowledge of
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socket calls can step in, that would be great.</p>
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<p>There are four data types in the protocol: bytes, booleans,
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integers and strings.</p>
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<dl>
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<dt><strong>Byte</strong></dt><dd>A single byte.</dd>
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<dt><strong>Boolean</strong></dt>
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<dd>A single byte, <code>1 = true</code>, <code>0 = false</code>.
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Using other non-zero values as true (i.e. C-style) may work in some places,
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but it won't in others.</dd>
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<dt><strong>Integer</strong></dt>
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<dd>A number in the range of <code>0 to 2^16 (32768)</code>. Stored in
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2 bytes with the high-order byte first.</dd>
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<dt><strong>String</strong></dt>
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<dd>A variable-sized string (length bounded by 2^16). Encoded with
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the length packed into two bytes first, followed by the string
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(including the terminating '\0'). Note that the encoded length does
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<strong>not</strong> include the trailing '\0' -- it is like
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<code>strlen</code>. This is a touch confusing on the Java side, which
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is littered with odd autoincrement statements to skip over these
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terminators. I believe the reason this was done was to allow the C
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code to be extra efficient when reading strings which the servlet
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container is sending back -- with the terminating \0 character, the
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C code can pass around references into a single buffer, without copying.
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if the \0 was missing, the C code would have to copy things out in order
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to get its notion of a string.</dd>
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</dl>
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<section><title>Packet Size</title>
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<p>According to much of the code, the max packet size is <code>
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8 * 1024 bytes (8K)</code>. The actual length of the packet is encoded in
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the header.</p>
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</section>
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<section><title>Packet Headers</title>
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<p>Packets sent from the server to the container begin with
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<code>0x1234</code>. Packets sent from the container to the server
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begin with <code>AB</code> (that's the ASCII code for A followed by the
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ASCII code for B). After those first two bytes, there is an integer
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(encoded as above) with the length of the payload. Although this might
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suggest that the maximum payload could be as large as 2^16, in fact, the
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code sets the maximum to be 8K.</p>
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<table>
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<tr>
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<td colspan="6"><em>Packet Format (Server->Container)</em></td>
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</tr>
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<tr>
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<td>Byte</td>
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<td>0</td>
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<td>1</td>
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<td>2</td>
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<td>3</td>
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<td>4...(n+3)</td>
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</tr>
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<tr>
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<td>Contents</td>
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<td>0x12</td>
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<td>0x34</td>
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<td colspan="2">Data Length (n)</td>
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<td>Data</td>
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</tr>
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</table>
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<table>
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<tr>
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<td colspan="6"><em>Packet Format (Container->Server)</em></td>
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</tr>
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<tr>
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<td>Byte</td>
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<td>0</td>
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<td>1</td>
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<td>2</td>
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<td>3</td>
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<td>4...(n+3)</td>
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</tr>
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<tr>
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<td>Contents</td>
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<td>A</td>
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<td>B</td>
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<td colspan="2">Data Length (n)</td>
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<td>Data</td>
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</tr>
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</table>
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<p>For most packets, the first byte of the payload encodes the type of
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message. The exception is for request body packets sent from the server to
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the container -- they are sent with a standard packet header (<code>
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0x1234</code> and then length of the packet), but without any prefix code
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after that.</p>
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<p>The web server can send the following messages to the servlet
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container:</p>
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<table>
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<tr>
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<td>Code</td>
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<td>Type of Packet</td>
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<td>Meaning</td>
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</tr>
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<tr>
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<td>2</td>
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<td>Forward Request</td>
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<td>Begin the request-processing cycle with the following data</td>
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</tr>
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<tr>
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<td>7</td>
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<td>Shutdown</td>
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<td>The web server asks the container to shut itself down.</td>
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</tr>
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<tr>
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<td>8</td>
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<td>Ping</td>
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<td>The web server asks the container to take control
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(secure login phase).</td>
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</tr>
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<tr>
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<td>10</td>
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<td>CPing</td>
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<td>The web server asks the container to respond quickly with a CPong.
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</td>
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</tr>
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<tr>
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<td>none</td>
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<td>Data</td>
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<td>Size (2 bytes) and corresponding body data.</td>
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</tr>
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</table>
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<p>To ensure some basic security, the container will only actually do the
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<code>Shutdown</code> if the request comes from the same machine on which
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it's hosted.</p>
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<p>The first <code>Data</code> packet is send immediatly after the
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<code>Forward Request</code> by the web server.</p>
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<p>The servlet container can send the following types of messages to the
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webserver:</p>
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<table>
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<tr>
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<td>Code</td>
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<td>Type of Packet</td>
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<td>Meaning</td>
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</tr>
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<tr>
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<td>3</td>
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<td>Send Body Chunk</td>
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<td>Send a chunk of the body from the servlet container to the web
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server (and presumably, onto the browser). </td>
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</tr>
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<tr>
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<td>4</td>
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<td>Send Headers</td>
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<td>Send the response headers from the servlet container to the web
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server (and presumably, onto the browser).</td>
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</tr>
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<tr>
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<td>5</td>
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<td>End Response</td>
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<td>Marks the end of the response (and thus the request-handling cycle).
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</td>
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</tr>
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<tr>
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<td>6</td>
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<td>Get Body Chunk</td>
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<td>Get further data from the request if it hasn't all been
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transferred yet.</td>
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</tr>
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<tr>
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<td>9</td>
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<td>CPong Reply</td>
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<td>The reply to a CPing request</td>
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</tr>
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</table>
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<p>Each of the above messages has a different internal structure, detailed
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below.</p>
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</section>
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</section>
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<section id="rpacetstruct"><title>Request Packet Structure</title>
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<p>For messages from the server to the container of type
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<em>Forward Request</em>:</p>
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<example><pre>
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AJP13_FORWARD_REQUEST :=
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prefix_code (byte) 0x02 = JK_AJP13_FORWARD_REQUEST
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method (byte)
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protocol (string)
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req_uri (string)
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remote_addr (string)
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remote_host (string)
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server_name (string)
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server_port (integer)
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is_ssl (boolean)
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num_headers (integer)
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request_headers *(req_header_name req_header_value)
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attributes *(attribut_name attribute_value)
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request_terminator (byte) OxFF
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</pre></example>
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<p>The <code>request_headers</code> have the following structure:
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</p><example><pre>
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req_header_name :=
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sc_req_header_name | (string) [see below for how this is parsed]
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sc_req_header_name := 0xA0xx (integer)
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req_header_value := (string)
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</pre></example>
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<p>The <code>attributes</code> are optional and have the following
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structure:</p>
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<example><pre>
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attribute_name := sc_a_name | (sc_a_req_attribute string)
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attribute_value := (string)
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</pre></example>
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<p>Not that the all-important header is <code>content-length</code>,
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because it determines whether or not the container looks for another
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packet immediately.</p>
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<section><title>Detailed description of the elements of Forward Request
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</title></section>
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<section><title>Request prefix</title>
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<p>For all requests, this will be 2. See above for details on other Prefix
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codes.</p>
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</section>
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<section><title>Method</title>
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<p>The HTTP method, encoded as a single byte:</p>
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<table>
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<tr><td>Command Name</td><td>Code</td></tr>
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<tr><td>OPTIONS</td><td>1</td></tr>
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<tr><td>GET</td><td>2</td></tr>
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<tr><td>HEAD</td><td>3</td></tr>
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<tr><td>POST</td><td>4</td></tr>
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<tr><td>PUT</td><td>5</td></tr>
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<tr><td>DELETE</td><td>6</td></tr>
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<tr><td>TRACE</td><td>7</td></tr>
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<tr><td>PROPFIND</td><td>8</td></tr>
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<tr><td>PROPPATCH</td><td>9</td></tr>
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<tr><td>MKCOL</td><td>10</td></tr>
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<tr><td>COPY</td><td>11</td></tr>
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<tr><td>MOVE</td><td>12</td></tr>
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<tr><td>LOCK</td><td>13</td></tr>
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<tr><td>UNLOCK</td><td>14</td></tr>
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<tr><td>ACL</td><td>15</td></tr>
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<tr><td>REPORT</td><td>16</td></tr>
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<tr><td>VERSION-CONTROL</td><td>17</td></tr>
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<tr><td>CHECKIN</td><td>18</td></tr>
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<tr><td>CHECKOUT</td><td>19</td></tr>
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<tr><td>UNCHECKOUT</td><td>20</td></tr>
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<tr><td>SEARCH</td><td>21</td></tr>
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<tr><td>MKWORKSPACE</td><td>22</td></tr>
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<tr><td>UPDATE</td><td>23</td></tr>
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<tr><td>LABEL</td><td>24</td></tr>
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<tr><td>MERGE</td><td>25</td></tr>
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<tr><td>BASELINE_CONTROL</td><td>26</td></tr>
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<tr><td>MKACTIVITY</td><td>27</td></tr>
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</table>
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<p>Later version of ajp13, will transport
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additional methods, even if they are not in this list.</p>
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</section>
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<section><title>protocol, req_uri, remote_addr, remote_host, server_name,
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server_port, is_ssl</title>
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<p>These are all fairly self-explanatory. Each of these is required, and
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will be sent for every request.</p>
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</section>
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<section><title>Headers</title>
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<p>The structure of <code>request_headers</code> is the following:
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First, the number of headers <code>num_headers</code> is encoded.
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Then, a series of header name <code>req_header_name</code> / value
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<code>req_header_value</code> pairs follows.
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Common header names are encoded as integers,
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to save space. If the header name is not in the list of basic headers,
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it is encoded normally (as a string, with prefixed length). The list of
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common headers <code>sc_req_header_name</code>and their codes
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is as follows (all are case-sensitive):</p>
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<table>
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<tr><td>Name</td><td>Code value</td><td>Code name</td></tr>
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<tr><td>accept</td><td>0xA001</td><td>SC_REQ_ACCEPT</td></tr>
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<tr><td>accept-charset</td><td>0xA002</td><td>SC_REQ_ACCEPT_CHARSET
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</td></tr>
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<tr><td>accept-encoding</td><td>0xA003</td><td>SC_REQ_ACCEPT_ENCODING
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</td></tr>
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<tr><td>accept-language</td><td>0xA004</td><td>SC_REQ_ACCEPT_LANGUAGE
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</td></tr>
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<tr><td>authorization</td><td>0xA005</td><td>SC_REQ_AUTHORIZATION</td>
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</tr>
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<tr><td>connection</td><td>0xA006</td><td>SC_REQ_CONNECTION</td></tr>
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<tr><td>content-type</td><td>0xA007</td><td>SC_REQ_CONTENT_TYPE</td>
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</tr>
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<tr><td>content-length</td><td>0xA008</td><td>SC_REQ_CONTENT_LENGTH</td>
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</tr>
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<tr><td>cookie</td><td>0xA009</td><td>SC_REQ_COOKIE</td></tr>
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<tr><td>cookie2</td><td>0xA00A</td><td>SC_REQ_COOKIE2</td></tr>
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<tr><td>host</td><td>0xA00B</td><td>SC_REQ_HOST</td></tr>
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<tr><td>pragma</td><td>0xA00C</td><td>SC_REQ_PRAGMA</td></tr>
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<tr><td>referer</td><td>0xA00D</td><td>SC_REQ_REFERER</td></tr>
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<tr><td>user-agent</td><td>0xA00E</td><td>SC_REQ_USER_AGENT</td></tr>
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</table>
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<p>The Java code that reads this grabs the first two-byte integer and if
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it sees an <code>'0xA0'</code> in the most significant
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byte, it uses the integer in the second byte as an index into an array of
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header names. If the first byte is not <code>0xA0</code>, it assumes that
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the two-byte integer is the length of a string, which is then read in.</p>
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<p>This works on the assumption that no header names will have length
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greater than <code>0x9999 (==0xA000 - 1)</code>, which is perfectly
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reasonable, though somewhat arbitrary.</p>
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<note><title>Note:</title>
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The <code>content-length</code> header is extremely
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important. If it is present and non-zero, the container assumes that
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the request has a body (a POST request, for example), and immediately
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reads a separate packet off the input stream to get that body.
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</note>
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</section>
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<section><title>Attributes</title>
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<p>The attributes prefixed with a <code>?</code>
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(e.g. <code>?context</code>) are all optional. For each, there is a
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single byte code to indicate the type of attribute, and then its value
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(string or integer). They can be sent in any order (though the C code
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always sends them in the order listed below). A special terminating code
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|
is sent to signal the end of the list of optional attributes. The list of
|
|
byte codes is:</p>
|
|
<table>
|
|
<tr><td>Information</td><td>Code Value</td><td>Type Of Value</td><td>Note</td></tr>
|
|
<tr><td>?context</td><td>0x01</td><td>-</td><td>Not currently implemented
|
|
</td></tr>
|
|
<tr><td>?servlet_path</td><td>0x02</td><td>-</td><td>Not currently implemented
|
|
</td></tr>
|
|
<tr><td>?remote_user</td><td>0x03</td><td>String</td><td></td></tr>
|
|
<tr><td>?auth_type</td><td>0x04</td><td>String</td><td></td></tr>
|
|
<tr><td>?query_string</td><td>0x05</td><td>String</td><td></td></tr>
|
|
<tr><td>?jvm_route</td><td>0x06</td><td>String</td><td></td></tr>
|
|
<tr><td>?ssl_cert</td><td>0x07</td><td>String</td><td></td></tr>
|
|
<tr><td>?ssl_cipher</td><td>0x08</td><td>String</td><td></td></tr>
|
|
<tr><td>?ssl_session</td><td>0x09</td><td>String</td><td></td></tr>
|
|
<tr><td>?req_attribute</td><td>0x0A</td><td>String</td><td>Name (the name of the
|
|
attribute follows)</td></tr>
|
|
<tr><td>?ssl_key_size</td><td>0x0B</td><td>Integer</td><td></td></tr>
|
|
<tr><td>are_done</td><td>0xFF</td><td>-</td><td>request_terminator</td></tr>
|
|
</table>
|
|
<p>The <code>context</code> and <code>servlet_path</code> are not
|
|
currently set by the C code, and most of the Java code completely ignores
|
|
whatever is sent over for those fields (and some of it will actually break
|
|
if a string is sent along after one of those codes). I don't know if this
|
|
is a bug or an unimplemented feature or just vestigial code, but it's
|
|
missing from both sides of the connection.</p>
|
|
<p>The <code>remote_user</code> and <code>auth_type</code> presumably
|
|
refer to HTTP-level authentication, and communicate the remote user's
|
|
username and the type of authentication used to establish their identity
|
|
(e.g. Basic, Digest).</p>
|
|
<p>The <code>query_string</code>, <code>ssl_cert</code>,
|
|
<code>ssl_cipher</code>, and <code>ssl_session</code> refer to the
|
|
corresponding pieces of HTTP and HTTPS.</p>
|
|
<p>The <code>jvm_route</code>, is used to support sticky
|
|
sessions -- associating a user's sesson with a particular Tomcat instance
|
|
in the presence of multiple, load-balancing servers.</p>
|
|
<p>Beyond this list of basic attributes, any number of other attributes
|
|
can be sent via the <code>req_attribute</code> code <code>0x0A</code>.
|
|
A pair of strings to represent the attribute name and value are sent
|
|
immediately after each instance of that code. Environment values are passed
|
|
in via this method.</p>
|
|
<p>Finally, after all the attributes have been sent, the attribute
|
|
terminator, <code>0xFF</code>, is sent. This signals both the end of the
|
|
list of attributes and also then end of the Request Packet.</p>
|
|
</section>
|
|
</section>
|
|
|
|
<section id="resppacketstruct"><title>Response Packet Structure</title>
|
|
<p>for messages which the container can send back to the server.</p>
|
|
<example><pre>
|
|
AJP13_SEND_BODY_CHUNK :=
|
|
prefix_code 3
|
|
chunk_length (integer)
|
|
chunk *(byte)
|
|
chunk_terminator (byte) Ox00
|
|
|
|
|
|
AJP13_SEND_HEADERS :=
|
|
prefix_code 4
|
|
http_status_code (integer)
|
|
http_status_msg (string)
|
|
num_headers (integer)
|
|
response_headers *(res_header_name header_value)
|
|
|
|
res_header_name :=
|
|
sc_res_header_name | (string) [see below for how this is parsed]
|
|
|
|
sc_res_header_name := 0xA0 (byte)
|
|
|
|
header_value := (string)
|
|
|
|
AJP13_END_RESPONSE :=
|
|
prefix_code 5
|
|
reuse (boolean)
|
|
|
|
|
|
AJP13_GET_BODY_CHUNK :=
|
|
prefix_code 6
|
|
requested_length (integer)
|
|
</pre></example>
|
|
<section><title>Details:</title></section>
|
|
<section><title>Send Body Chunk</title>
|
|
<p>The chunk is basically binary data, and is sent directly back to the
|
|
browser.</p>
|
|
</section>
|
|
<section><title>Send Headers</title>
|
|
<p>The status code and message are the usual HTTP things
|
|
(e.g. <code>200</code> and <code>OK</code>). The response header names are
|
|
encoded the same way the request header names are. See header_encoding above
|
|
for details about how the codes are distinguished from the strings.<br />
|
|
The codes for common headers are:</p>
|
|
<table>
|
|
<tr><td>Name</td><td>Code value</td></tr>
|
|
<tr><td>Content-Type</td><td>0xA001</td></tr>
|
|
<tr><td>Content-Language</td><td>0xA002</td></tr>
|
|
<tr><td>Content-Length</td><td>0xA003</td></tr>
|
|
<tr><td>Date</td><td>0xA004</td></tr>
|
|
<tr><td>Last-Modified</td><td>0xA005</td></tr>
|
|
<tr><td>Location</td><td>0xA006</td></tr>
|
|
<tr><td>Set-Cookie</td><td>0xA007</td></tr>
|
|
<tr><td>Set-Cookie2</td><td>0xA008</td></tr>
|
|
<tr><td>Servlet-Engine</td><td>0xA009</td></tr>
|
|
<tr><td>Status</td><td>0xA00A</td></tr>
|
|
<tr><td>WWW-Authenticate</td><td>0xA00B</td></tr>
|
|
</table>
|
|
<p> After the code or the string header name, the header value is
|
|
immediately encoded.</p>
|
|
</section>
|
|
<section><title>End Response</title>
|
|
<p>Signals the end of this request-handling cycle. If the
|
|
<code>reuse</code> flag is true <code>(==1)</code>, this TCP connection can
|
|
now be used to handle new incoming requests. If <code>reuse</code> is false
|
|
(anything other than 1 in the actual C code), the connection should
|
|
be closed.</p>
|
|
</section>
|
|
<section><title>Get Body Chunk</title>
|
|
<p>The container asks for more data from the request (If the body was
|
|
too large to fit in the first packet sent over or when the request is
|
|
chuncked). The server will send a body packet back with an amount of data
|
|
which is the minimum of the <code>request_length</code>, the maximum send
|
|
body size <code>(8186 (8 Kbytes - 6))</code>, and the number of bytes
|
|
actually left to send from the request body.<br/>
|
|
If there is no more data in the body (i.e. the servlet container is
|
|
trying to read past the end of the body), the server will send back an
|
|
<em>empty</em> packet, which is a body packet with a payload length of 0.
|
|
<code>(0x12,0x34,0x00,0x00)</code></p>
|
|
</section>
|
|
</section>
|
|
|
|
|
|
</modulesynopsis>
|