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16 <p class="apache">Apache HTTP Server Version 2.3</p>
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21 <div id="page-content">
22 <div id="preamble"><h1>Apache Module mod_proxy_ajp</h1>
24 <p><span>Available Languages: </span><a href="../en/mod/mod_proxy_ajp.html" title="English"> en </a> |
25 <a href="../ja/mod/mod_proxy_ajp.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a></p>
27 <table class="module"><tr><th><a href="module-dict.html#Description">Description:</a></th><td>AJP support module for
28 <code class="module"><a href="../mod/mod_proxy.html">mod_proxy</a></code></td></tr>
29 <tr><th><a href="module-dict.html#Status">Status:</a></th><td>Extension</td></tr>
30 <tr><th><a href="module-dict.html#ModuleIdentifier">Module Identifier:</a></th><td>proxy_ajp_module</td></tr>
31 <tr><th><a href="module-dict.html#SourceFile">Source File:</a></th><td>proxy_ajp.c</td></tr>
32 <tr><th><a href="module-dict.html#Compatibility">Compatibility:</a></th><td>Available in version 2.1 and later</td></tr></table>
35 <p>This module <em>requires</em> the service of <code class="module"><a href="../mod/mod_proxy.html">mod_proxy</a></code>. It provides support for the
36 <code>Apache JServ Protocol version 1.3</code> (hereafter
39 <p>Thus, in order to get the ability of handling <code>AJP13</code>
40 protocol, <code class="module"><a href="../mod/mod_proxy.html">mod_proxy</a></code> and
41 <code class="module"><a href="../mod/mod_proxy_ajp.html">mod_proxy_ajp</a></code> have to be present in the server.</p>
43 <div class="warning"><h3>Warning</h3>
44 <p>Do not enable proxying until you have <a href="mod_proxy.html#access">secured your server</a>. Open proxy
45 servers are dangerous both to your network and to the Internet at
49 <div id="quickview"><h3 class="directives">Directives</h3>
50 <p>This module provides no
54 <li><img alt="" src="../images/down.gif" /> <a href="#overviewprotocol">Overview of the protocol</a></li>
55 <li><img alt="" src="../images/down.gif" /> <a href="#basppacketstruct">Basic Packet Structure</a></li>
56 <li><img alt="" src="../images/down.gif" /> <a href="#rpacetstruct">Request Packet Structure</a></li>
57 <li><img alt="" src="../images/down.gif" /> <a href="#resppacketstruct">Response Packet Structure</a></li>
58 </ul><h3>See also</h3>
60 <li><code class="module"><a href="../mod/mod_proxy.html">mod_proxy</a></code></li>
62 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
64 <h2><a name="overviewprotocol" id="overviewprotocol">Overview of the protocol</a></h2>
65 <p>The <code>AJP13</code> protocol is packet-oriented. A binary format
66 was presumably chosen over the more readable plain text for reasons of
67 performance. The web server communicates with the servlet container over
68 TCP connections. To cut down on the expensive process of socket creation,
69 the web server will attempt to maintain persistent TCP connections to the
70 servlet container, and to reuse a connection for multiple request/response
72 <p>Once a connection is assigned to a particular request, it will not be
73 used for any others until the request-handling cycle has terminated. In
74 other words, requests are not multiplexed over connections. This makes
75 for much simpler code at either end of the connection, although it does
76 cause more connections to be open at once.</p>
77 <p>Once the web server has opened a connection to the servlet container,
78 the connection can be in one of the following states:</p>
80 <li> Idle <br /> No request is being handled over this connection. </li>
81 <li> Assigned <br /> The connecton is handling a specific request.</li>
83 <p>Once a connection is assigned to handle a particular request, the basic
84 request informaton (e.g. HTTP headers, etc) is sent over the connection in
85 a highly condensed form (e.g. common strings are encoded as integers).
86 Details of that format are below in Request Packet Structure. If there is a
87 body to the request <code>(content-length > 0)</code>, that is sent in a
88 separate packet immediately after.</p>
89 <p>At this point, the servlet container is presumably ready to start
90 processing the request. As it does so, it can send the
91 following messages back to the web server:</p>
93 <li>SEND_HEADERS <br />Send a set of headers back to the browser.</li>
94 <li>SEND_BODY_CHUNK <br />Send a chunk of body data back to the browser.
96 <li>GET_BODY_CHUNK <br />Get further data from the request if it hasn't all
97 been transferred yet. This is necessary because the packets have a fixed
98 maximum size and arbitrary amounts of data can be included the body of a
99 request (for uploaded files, for example). (Note: this is unrelated to
100 HTTP chunked tranfer).</li>
101 <li>END_RESPONSE <br /> Finish the request-handling cycle.</li>
103 <p>Each message is accompanied by a differently formatted packet of data.
104 See Response Packet Structures below for details.</p>
105 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
106 <div class="section">
107 <h2><a name="basppacketstruct" id="basppacketstruct">Basic Packet Structure</a></h2>
108 <p>There is a bit of an XDR heritage to this protocol, but it differs
109 in lots of ways (no 4 byte alignment, for example).</p>
110 <p>Byte order: I am not clear about the endian-ness of the individual
111 bytes. I'm guessing the bytes are little-endian, because that's what
112 XDR specifies, and I'm guessing that sys/socket library is magically
113 making that so (on the C side). If anyone with a better knowledge of
114 socket calls can step in, that would be great.</p>
115 <p>There are four data types in the protocol: bytes, booleans,
116 integers and strings.</p>
118 <dt><strong>Byte</strong></dt><dd>A single byte.</dd>
119 <dt><strong>Boolean</strong></dt>
120 <dd>A single byte, <code>1 = true</code>, <code>0 = false</code>.
121 Using other non-zero values as true (i.e. C-style) may work in some places,
122 but it won't in others.</dd>
123 <dt><strong>Integer</strong></dt>
124 <dd>A number in the range of <code>0 to 2^16 (32768)</code>. Stored in
125 2 bytes with the high-order byte first.</dd>
126 <dt><strong>String</strong></dt>
127 <dd>A variable-sized string (length bounded by 2^16). Encoded with
128 the length packed into two bytes first, followed by the string
129 (including the terminating '\0'). Note that the encoded length does
130 <strong>not</strong> include the trailing '\0' -- it is like
131 <code>strlen</code>. This is a touch confusing on the Java side, which
132 is littered with odd autoincrement statements to skip over these
133 terminators. I believe the reason this was done was to allow the C
134 code to be extra efficient when reading strings which the servlet
135 container is sending back -- with the terminating \0 character, the
136 C code can pass around references into a single buffer, without copying.
137 if the \0 was missing, the C code would have to copy things out in order
138 to get its notion of a string.</dd>
142 <p>According to much of the code, the max packet size is <code>
143 8 * 1024 bytes (8K)</code>. The actual length of the packet is encoded in
146 <h3>Packet Headers</h3>
147 <p>Packets sent from the server to the container begin with
148 <code>0x1234</code>. Packets sent from the container to the server
149 begin with <code>AB</code> (that's the ASCII code for A followed by the
150 ASCII code for B). After those first two bytes, there is an integer
151 (encoded as above) with the length of the payload. Although this might
152 suggest that the maximum payload could be as large as 2^16, in fact, the
153 code sets the maximum to be 8K.</p>
156 <td colspan="6"><em>Packet Format (Server->Container)</em></td>
170 <td colspan="2">Data Length (n)</td>
176 <td colspan="6"><em>Packet Format (Container->Server)</em></td>
190 <td colspan="2">Data Length (n)</td>
194 <p>For most packets, the first byte of the payload encodes the type of
195 message. The exception is for request body packets sent from the server to
196 the container -- they are sent with a standard packet header (<code>
197 0x1234</code> and then length of the packet), but without any prefix code
199 <p>The web server can send the following messages to the servlet
204 <td>Type of Packet</td>
209 <td>Forward Request</td>
210 <td>Begin the request-processing cycle with the following data</td>
215 <td>The web server asks the container to shut itself down.</td>
220 <td>The web server asks the container to take control
221 (secure login phase).</td>
226 <td>The web server asks the container to respond quickly with a CPong.
232 <td>Size (2 bytes) and corresponding body data.</td>
235 <p>To ensure some basic security, the container will only actually do the
236 <code>Shutdown</code> if the request comes from the same machine on which
238 <p>The first <code>Data</code> packet is send immediatly after the
239 <code>Forward Request</code> by the web server.</p>
240 <p>The servlet container can send the following types of messages to the
245 <td>Type of Packet</td>
250 <td>Send Body Chunk</td>
251 <td>Send a chunk of the body from the servlet container to the web
252 server (and presumably, onto the browser). </td>
256 <td>Send Headers</td>
257 <td>Send the response headers from the servlet container to the web
258 server (and presumably, onto the browser).</td>
262 <td>End Response</td>
263 <td>Marks the end of the response (and thus the request-handling cycle).
268 <td>Get Body Chunk</td>
269 <td>Get further data from the request if it hasn't all been
270 transferred yet.</td>
275 <td>The reply to a CPing request</td>
278 <p>Each of the above messages has a different internal structure, detailed
281 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
282 <div class="section">
283 <h2><a name="rpacetstruct" id="rpacetstruct">Request Packet Structure</a></h2>
284 <p>For messages from the server to the container of type
285 <em>Forward Request</em>:</p>
286 <div class="example"><pre>
287 AJP13_FORWARD_REQUEST :=
288 prefix_code (byte) 0x02 = JK_AJP13_FORWARD_REQUEST
295 server_port (integer)
297 num_headers (integer)
298 request_headers *(req_header_name req_header_value)
299 attributes *(attribut_name attribute_value)
300 request_terminator (byte) OxFF
302 <p>The <code>request_headers</code> have the following structure:
303 </p><div class="example"><pre>
305 sc_req_header_name | (string) [see below for how this is parsed]
307 sc_req_header_name := 0xA0xx (integer)
309 req_header_value := (string)
311 <p>The <code>attributes</code> are optional and have the following
313 <div class="example"><pre>
314 attribute_name := sc_a_name | (sc_a_req_attribute string)
316 attribute_value := (string)
319 <p>Not that the all-important header is <code>content-length</code>,
320 because it determines whether or not the container looks for another
321 packet immediately.</p>
322 <h3>Detailed description of the elements of Forward Request
324 <h3>Request prefix</h3>
325 <p>For all requests, this will be 2. See above for details on other Prefix
329 <p>The HTTP method, encoded as a single byte:</p>
331 <tr><td>Command Name</td><td>Code</td></tr>
332 <tr><td>OPTIONS</td><td>1</td></tr>
333 <tr><td>GET</td><td>2</td></tr>
334 <tr><td>HEAD</td><td>3</td></tr>
335 <tr><td>POST</td><td>4</td></tr>
336 <tr><td>PUT</td><td>5</td></tr>
337 <tr><td>DELETE</td><td>6</td></tr>
338 <tr><td>TRACE</td><td>7</td></tr>
339 <tr><td>PROPFIND</td><td>8</td></tr>
340 <tr><td>PROPPATCH</td><td>9</td></tr>
341 <tr><td>MKCOL</td><td>10</td></tr>
342 <tr><td>COPY</td><td>11</td></tr>
343 <tr><td>MOVE</td><td>12</td></tr>
344 <tr><td>LOCK</td><td>13</td></tr>
345 <tr><td>UNLOCK</td><td>14</td></tr>
346 <tr><td>ACL</td><td>15</td></tr>
347 <tr><td>REPORT</td><td>16</td></tr>
348 <tr><td>VERSION-CONTROL</td><td>17</td></tr>
349 <tr><td>CHECKIN</td><td>18</td></tr>
350 <tr><td>CHECKOUT</td><td>19</td></tr>
351 <tr><td>UNCHECKOUT</td><td>20</td></tr>
352 <tr><td>SEARCH</td><td>21</td></tr>
353 <tr><td>MKWORKSPACE</td><td>22</td></tr>
354 <tr><td>UPDATE</td><td>23</td></tr>
355 <tr><td>LABEL</td><td>24</td></tr>
356 <tr><td>MERGE</td><td>25</td></tr>
357 <tr><td>BASELINE_CONTROL</td><td>26</td></tr>
358 <tr><td>MKACTIVITY</td><td>27</td></tr>
360 <p>Later version of ajp13, will transport
361 additional methods, even if they are not in this list.</p>
363 <h3>protocol, req_uri, remote_addr, remote_host, server_name,
364 server_port, is_ssl</h3>
365 <p>These are all fairly self-explanatory. Each of these is required, and
366 will be sent for every request.</p>
369 <p>The structure of <code>request_headers</code> is the following:
370 First, the number of headers <code>num_headers</code> is encoded.
371 Then, a series of header name <code>req_header_name</code> / value
372 <code>req_header_value</code> pairs follows.
373 Common header names are encoded as integers,
374 to save space. If the header name is not in the list of basic headers,
375 it is encoded normally (as a string, with prefixed length). The list of
376 common headers <code>sc_req_header_name</code>and their codes
377 is as follows (all are case-sensitive):</p>
379 <tr><td>Name</td><td>Code value</td><td>Code name</td></tr>
380 <tr><td>accept</td><td>0xA001</td><td>SC_REQ_ACCEPT</td></tr>
381 <tr><td>accept-charset</td><td>0xA002</td><td>SC_REQ_ACCEPT_CHARSET
383 <tr><td>accept-encoding</td><td>0xA003</td><td>SC_REQ_ACCEPT_ENCODING
385 <tr><td>accept-language</td><td>0xA004</td><td>SC_REQ_ACCEPT_LANGUAGE
387 <tr><td>authorization</td><td>0xA005</td><td>SC_REQ_AUTHORIZATION</td>
389 <tr><td>connection</td><td>0xA006</td><td>SC_REQ_CONNECTION</td></tr>
390 <tr><td>content-type</td><td>0xA007</td><td>SC_REQ_CONTENT_TYPE</td>
392 <tr><td>content-length</td><td>0xA008</td><td>SC_REQ_CONTENT_LENGTH</td>
394 <tr><td>cookie</td><td>0xA009</td><td>SC_REQ_COOKIE</td></tr>
395 <tr><td>cookie2</td><td>0xA00A</td><td>SC_REQ_COOKIE2</td></tr>
396 <tr><td>host</td><td>0xA00B</td><td>SC_REQ_HOST</td></tr>
397 <tr><td>pragma</td><td>0xA00C</td><td>SC_REQ_PRAGMA</td></tr>
398 <tr><td>referer</td><td>0xA00D</td><td>SC_REQ_REFERER</td></tr>
399 <tr><td>user-agent</td><td>0xA00E</td><td>SC_REQ_USER_AGENT</td></tr>
401 <p>The Java code that reads this grabs the first two-byte integer and if
402 it sees an <code>'0xA0'</code> in the most significant
403 byte, it uses the integer in the second byte as an index into an array of
404 header names. If the first byte is not <code>0xA0</code>, it assumes that
405 the two-byte integer is the length of a string, which is then read in.</p>
406 <p>This works on the assumption that no header names will have length
407 greater than <code>0x9999 (==0xA000 - 1)</code>, which is perfectly
408 reasonable, though somewhat arbitrary.</p>
409 <div class="note"><h3>Note:</h3>
410 The <code>content-length</code> header is extremely
411 important. If it is present and non-zero, the container assumes that
412 the request has a body (a POST request, for example), and immediately
413 reads a separate packet off the input stream to get that body.
417 <p>The attributes prefixed with a <code>?</code>
418 (e.g. <code>?context</code>) are all optional. For each, there is a
419 single byte code to indicate the type of attribute, and then a string to
420 give its value. They can be sent in any order (thogh the C code always
421 sends them in the order listed below). A special terminating code is
422 sent to signal the end of the list of optional attributes. The list of
425 <tr><td>Information</td><td>Code Value</td><td>Note</td></tr>
426 <tr><td>?context</td><td>0x01</td><td>Not currently implemented
428 <tr><td>?servlet_path</td><td>0x02</td><td>Not currently implemented
430 <tr><td>?remote_user</td><td>0x03</td><td /></tr>
431 <tr><td>?auth_type</td><td>0x04</td><td /></tr>
432 <tr><td>?query_string</td><td>0x05</td><td /></tr>
433 <tr><td>?jvm_route</td><td>0x06</td><td /></tr>
434 <tr><td>?ssl_cert</td><td>0x07</td><td /></tr>
435 <tr><td>?ssl_cipher</td><td>0x08</td><td /></tr>
436 <tr><td>?ssl_session</td><td>0x09</td><td /></tr>
437 <tr><td>?req_attribute</td><td>0x0A</td><td>Name (the name of the
438 attribute follows)</td></tr>
439 <tr><td>?ssl_key_size</td><td>0x0B</td><td /></tr>
440 <tr><td>are_done</td><td>0xFF</td><td>request_terminator</td></tr>
442 <p>The <code>context</code> and <code>servlet_path</code> are not
443 currently set by the C code, and most of the Java code completely ignores
444 whatever is sent over for those fields (and some of it will actually break
445 if a string is sent along after one of those codes). I don't know if this
446 is a bug or an unimplemented feature or just vestigial code, but it's
447 missing from both sides of the connection.</p>
448 <p>The <code>remote_user</code> and <code>auth_type</code> presumably
449 refer to HTTP-level authentication, and communicate the remote user's
450 username and the type of authentication used to establish their identity
451 (e.g. Basic, Digest).</p>
452 <p>The <code>query_string</code>, <code>ssl_cert</code>,
453 <code>ssl_cipher</code>, and <code>ssl_session</code> refer to the
454 corresponding pieces of HTTP and HTTPS.</p>
455 <p>The <code>jvm_route</code>, is used to support sticky
456 sessions -- associating a user's sesson with a particular Tomcat instance
457 in the presence of multiple, load-balancing servers.</p>
458 <p>Beyond this list of basic attributes, any number of other attributes
459 can be sent via the <code>req_attribute</code> code <code>0x0A</code>.
460 A pair of strings to represent the attribute name and value are sent
461 immediately after each instance of that code. Environment values are passed
462 in via this method.</p>
463 <p>Finally, after all the attributes have been sent, the attribute
464 terminator, <code>0xFF</code>, is sent. This signals both the end of the
465 list of attributes and also then end of the Request Packet.</p>
467 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
468 <div class="section">
469 <h2><a name="resppacketstruct" id="resppacketstruct">Response Packet Structure</a></h2>
470 <p>for messages which the container can send back to the server.</p>
471 <div class="example"><pre>
472 AJP13_SEND_BODY_CHUNK :=
474 chunk_length (integer)
478 AJP13_SEND_HEADERS :=
480 http_status_code (integer)
481 http_status_msg (string)
482 num_headers (integer)
483 response_headers *(res_header_name header_value)
486 sc_res_header_name | (string) [see below for how this is parsed]
488 sc_res_header_name := 0xA0 (byte)
490 header_value := (string)
492 AJP13_END_RESPONSE :=
497 AJP13_GET_BODY_CHUNK :=
499 requested_length (integer)
502 <h3>Send Body Chunk</h3>
503 <p>The chunk is basically binary data, and is sent directly back to the
506 <h3>Send Headers</h3>
507 <p>The status code and message are the usual HTTP things
508 (e.g. <code>200</code> and <code>OK</code>). The response header names are
509 encoded the same way the request header names are. See header_encoding above
510 for details about how the the codes are distinguished from the strings.<br />
511 The codes for common headers are:</p>
513 <tr><td>Name</td><td>Code value</td></tr>
514 <tr><td>Content-Type</td><td>0xA001</td></tr>
515 <tr><td>Content-Language</td><td>0xA002</td></tr>
516 <tr><td>Content-Length</td><td>0xA003</td></tr>
517 <tr><td>Date</td><td>0xA004</td></tr>
518 <tr><td>Last-Modified</td><td>0xA005</td></tr>
519 <tr><td>Location</td><td>0xA006</td></tr>
520 <tr><td>Set-Cookie</td><td>0xA007</td></tr>
521 <tr><td>Set-Cookie2</td><td>0xA008</td></tr>
522 <tr><td>Servlet-Engine</td><td>0xA009</td></tr>
523 <tr><td>Status</td><td>0xA00A</td></tr>
524 <tr><td>WWW-Authenticate</td><td>0xA00B</td></tr>
526 <p> After the code or the string header name, the header value is
527 immediately encoded.</p>
529 <h3>End Response</h3>
530 <p>Signals the end of this request-handling cycle. If the
531 <code>reuse</code> flag is true <code>(==1)</code>, this TCP connection can
532 now be used to handle new incoming requests. If <code>reuse</code> is false
533 (anything other than 1 in the actual C code), the connection should
536 <h3>Get Body Chunk</h3>
537 <p>The container asks for more data from the request (If the body was
538 too large to fit in the first packet sent over or when the request is
539 chuncked). The server will send a body packet back with an amount of data
540 which is the minimum of the <code>request_length</code>, the maximum send
541 body size <code>(8186 (8 Kbytes - 6))</code>, and the number of bytes
542 actually left to send from the request body.<br />
543 If there is no more data in the body (i.e. the servlet container is
544 trying to read past the end of the body), the server will send back an
545 <em>empty</em> packet, which is a body packet with a payload length of 0.
546 <code>(0x12,0x34,0x00,0x00)</code></p>
550 <div class="bottomlang">
551 <p><span>Available Languages: </span><a href="../en/mod/mod_proxy_ajp.html" title="English"> en </a> |
552 <a href="../ja/mod/mod_proxy_ajp.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a></p>
553 </div><div id="footer">
554 <p class="apache">Copyright 1995-2006 The Apache Software Foundation or its licensors, as applicable.<br />Licensed under the <a href="http://www.apache.org/licenses/LICENSE-2.0">Apache License, Version 2.0</a>.</p>
555 <p class="menu"><a href="../mod/">Modules</a> | <a href="../mod/directives.html">Directives</a> | <a href="../faq/">FAQ</a> | <a href="../glossary.html">Glossary</a> | <a href="../sitemap.html">Sitemap</a></p></div>