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<!-- Copyright (C) 2003 Red Hat, Inc. -->
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<HTML
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><HEAD
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><TITLE
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>Server Organization</TITLE
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"><LINK
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REL="HOME"
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TITLE="eCos Reference Manual"
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HREF="ecos-ref.html"><LINK
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REL="UP"
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TITLE="Embedded HTTP Server"
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HREF="net-httpd-chapter.html"><LINK
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REL="PREVIOUS"
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TITLE="Embedded HTTP Server"
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HREF="net-httpd-chapter.html"><LINK
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REL="NEXT"
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TITLE="Server Configuration"
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HREF="net-httpd-configuration.html"></HEAD
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><BODY
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CLASS="SECT1"
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SUMMARY="Header navigation table"
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ALIGN="center"
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>eCos Reference Manual</TH
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></TR
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><TR
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><TD
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WIDTH="10%"
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ALIGN="left"
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VALIGN="bottom"
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><A
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HREF="net-httpd-chapter.html"
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ACCESSKEY="P"
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>Prev</A
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></TD
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><TD
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WIDTH="80%"
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ALIGN="center"
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VALIGN="bottom"
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>Chapter 48. Embedded HTTP Server</TD
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><TD
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WIDTH="10%"
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ALIGN="right"
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VALIGN="bottom"
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><A
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HREF="net-httpd-configuration.html"
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ACCESSKEY="N"
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>Next</A
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></TD
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></TR
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></TABLE
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><HR
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WIDTH="100%"></DIV
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><DIV
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CLASS="SECT1"
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><H1
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CLASS="SECT1"
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><A
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NAME="NET-HTTPD-ORGANIZATION">Server Organization</H1
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><P
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>The server consists of one or more threads running in parallel to any
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application threads and which serve web pages to clients. Apart from
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defining content, the application does not need to do anything to
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start the HTTP server.</P
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><P
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>The HTTP server is started by a static constructor. This simply
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creates an initial thread and sets it running. Since this is called
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before the scheduler is started, nothing will happen until the
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application calls <TT
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CLASS="FUNCTION"
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>cyg_scheduler_start()</TT
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>.</P
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><P
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>When the thread gets to run it first optionally delays for some period
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of time. This is to allow the application to perform any
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initialization free of any interference from the HTTP server. When the
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thread does finally run it creates a socket, binds it to the HTTP
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server port, and puts it into listen mode. It will then create any
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additional HTTPD server threads that have been configured before
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becoming a server thread itself.</P
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><P
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>Each HTTPD server thread simply waits for a connection to be made to
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the server port. When the connection is made it reads the HTTP request
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and extracts the filename being accessed. If the request also contains
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form data, this is also preserved. The filename is then looked up in a
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table.</P
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><P
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>Each table entry contains a filename pattern string, a
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pointer to a handler function, and a user defined argument for the
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function. Table entries are defined using the same link-time table
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building mechanism used to generate device tables. This is all handled
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by the <TT
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CLASS="LITERAL"
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>CYG_HTTPD_TABLE_ENTRY()</TT
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> macro which has the
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following format:</P
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><TABLE
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><TR
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><TD
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><PRE
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CLASS="PROGRAMLISTING"
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> #include <cyg/httpd/httpd.h>
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CYG_HTTPD_TABLE_ENTRY( __name, __pattern, __handler, __arg ) </PRE
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></TD
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></TR
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></TABLE
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><P
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>The <TT
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CLASS="PARAMETER"
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><I
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>__name</I
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></TT
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> argument is a variable name for the
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table entry since C does not allow us to define anonymous data
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structures. This name should be chosen so that it is unique and does
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not pollute the name space. The <TT
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CLASS="PARAMETER"
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><I
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>__pattern</I
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></TT
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>
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argument is the match pattern. The <TT
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CLASS="PARAMETER"
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><I
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>__handler</I
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></TT
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>
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argument is a pointer to the handler function and
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<TT
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CLASS="PARAMETER"
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><I
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>__arg</I
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></TT
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> the user defined value.</P
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><P
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>The link-time table building means that several different pieces of
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code can define server table entries, and so long as the patterns do
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not clash they can be totally oblivious of each other. However, note
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also that this mechanism does not guarantee the order in which entries
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appear, this depends on the order of object files in the link, which
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could vary from one build to the next. So any tricky pattern matching
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that relies on this may not always work.</P
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><P
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>A request filename matches an entry in the table if either it exactly
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matches the pattern string, or if the pattern ends in an asterisk, and
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it matches everything up to that point. So for example the pattern
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"/monitor/threads.html" will only match that exact filename,
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but the pattern "/monitor/thread-*" will match
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"/monitor/thread-0040.html",
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"/monitor/thread-0100.html" and any other filename starting
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with "/monitor/thread-".</P
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><P
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>When a pattern is matched, the hander function is called. It has the
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following prototype:</P
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><TABLE
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BORDER="5"
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BGCOLOR="#E0E0F0"
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WIDTH="70%"
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><TR
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><TD
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><PRE
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CLASS="PROGRAMLISTING"
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>cyg_bool cyg_httpd_handler(FILE *client,
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char *filename,
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char *formdata,
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void *arg);</PRE
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></TD
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></TR
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></TABLE
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><P
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>The <TT
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CLASS="PARAMETER"
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><I
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>client</I
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></TT
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> argument is the TCP connection to
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the client: anything output through this stream will be returned to
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the browser. The <TT
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CLASS="PARAMETER"
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><I
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>filename</I
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></TT
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> argument is the
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filename from the HTTP request and the <TT
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CLASS="PARAMETER"
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><I
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>formdata</I
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></TT
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>
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argument is any form response data, or NULL if none was sent. The
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<TT
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CLASS="PARAMETER"
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><I
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>arg</I
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></TT
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> argument is the user defined value from the
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table entry.</P
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><P
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>The handler is entirely responsible for generating the response to the
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client, both HTTP header and content. If the handler decides that it
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does not want to generate a response it can return
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<TT
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CLASS="LITERAL"
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>false</TT
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>, in which case the table scan is resumed for
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another match. If no match is found, or no handler returns true, then
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a default response page is generated indicating that the requested
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page cannot be found.</P
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><P
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>Finally, the server thread closes the connection to the client and
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loops back to accept a new connection.</P
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></DIV
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CLASS="NAVFOOTER"
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WIDTH="33%"
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ALIGN="left"
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VALIGN="top"
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><A
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HREF="net-httpd-chapter.html"
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ACCESSKEY="P"
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>Prev</A
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><TD
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WIDTH="34%"
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ALIGN="center"
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VALIGN="top"
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><A
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HREF="ecos-ref.html"
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ACCESSKEY="H"
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>Home</A
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WIDTH="33%"
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ALIGN="right"
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VALIGN="top"
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HREF="net-httpd-configuration.html"
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ACCESSKEY="N"
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>Next</A
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WIDTH="33%"
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ALIGN="left"
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VALIGN="top"
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>Embedded HTTP Server</TD
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><TD
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WIDTH="34%"
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ALIGN="center"
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VALIGN="top"
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><A
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HREF="net-httpd-chapter.html"
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ACCESSKEY="U"
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>Up</A
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><TD
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WIDTH="33%"
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ALIGN="right"
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VALIGN="top"
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>Server Configuration</TD
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></TR
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></DIV
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></BODY
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>
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