athttpd-cgi.html
来自「ecos3.0 beta 的官方文档,html格式」· HTML 代码 · 共 457 行
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>eCos Reference Manual</TH
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>Chapter 65. The ATHTTP Server</TD
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CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="ATHTTPD-CGI"
>CGI</A
></H1
><P
>The web server allows writing of pseudo-CGI programs. This is helpful in order
to modify the functionality of the server without having to recompile it and
reflash it.</P
><P
>One way to implement CGI is, of course, the C language callback mechanism
described above: This assumes, of course, that all the callbacks are written
by compile time and cannot be modified later on. Another way to perform the
same functionality is the use of a library in the form of an object file.
These object files reside in the file system and are loaded, executed and
unloaded on demand.</P
><P
>Yet a third way is the use of a scripting language. Since full fledged
implementation of the most popular scripting languages such as Python or Perl
are too large for most embedded systems, a slim down implementation of tcl
was chosen for this server. Most of the tcl functionality is still there,
and makes writing cgi a lot easier.</P
><P
>In order to limit the footprint of the operating system support for both
the objloader and the tcl script for dealing with cgi files can be
independently selected out. Tcl support in particular increases the memory
requirements considerably.</P
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="ATHTTPD-CGI-OBJLOADER"
>CGI via objloader</A
></H2
><P
>In order to use the cgi mechanism the CYGPKG_OBJLOADER must be included
when building the operating system. This will enable the proper option in the
configuration tool and if selected, the necessary code will be compiled
in the eCos kernel. The user will then have to compile the necessary libraries
and place them in the file system under a directory defined by
CYGDAT_NET_ATHTTPD_SERVEROPT_CGIDIR.
When a request is made, the web server checks if the root directory of the
requested URL is inside the CYGDAT_NET_ATHTTPD_SERVEROPT_CGIDIR directory.
If so, the server assumes that the user requested a cgi file and looks into the
directory to see if a library by the same name is present, and if so load it
and tries to execute a function inside the library with the following prototype:</P
><TABLE
BORDER="5"
BGCOLOR="#E0E0F0"
WIDTH="70%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>void exec_cgi(CYG_HTTPD_STATE *)</PRE
></TD
></TR
></TABLE
><P
>The pointer <B
CLASS="COMMAND"
>CYG_HTTPD_STATE*</B
> gives access to the socket
data: The user will use this pointer to access the 'outbuffer' and use it to
copy data to send data out.</P
><P
>When using the OBJLOADER package within the HTTP server a number of functions
are automatically added to the externals table of the OBJLOADER package. These
functions are likely to be used inside the library and the relocator need to
have a pointer to them. In order to add more functions, see the OBJLOADER
documentation. The complete list of the functions automatically added is:</P
><P
></P
><UL
><LI
><P
>cyg_httpd_start_chunked()</P
></LI
><LI
><P
>cyg_httpd_write_chunked()</P
></LI
><LI
><P
>cyg_httpd_end_chunked()</P
></LI
><LI
><P
>cyg_httpd_write()</P
></LI
><LI
><P
>cyg_httpd_find_form_variable()</P
></LI
><LI
><P
>cyg_httpd_find_ires()</P
></LI
><LI
><P
>cyg_httpd_send_ires()</P
></LI
><LI
><P
>diag_printf()</P
></LI
><LI
><P
>cyg_httpd_format_header()</P
></LI
><LI
><P
>cyg_httpd_find_mime_string()</P
></LI
></UL
><P
>Every time the web client issues a GET or POST request for a file with an
extension of '.o'in the /cgi-bin directory (or whatever path the user chooses
to hold the libraries) then the library by that name is loaded, run and
when the execution is over, it is dumped from memory.
The library must be compiled separately, using the same toolchain used to
compile the server and then added to the file system.</P
><P
>In order to reduce the footprint of the server, CGI through OBJLOADER
can be compiled out by unchecking CYGOPT_NET_ATHTTPD_USE_CGIBIN_OBJLOADER
in the configuration tool.</P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="ATHTTPD-CGI-TCL"
>CGI via the simple tcl interpreter</A
></H2
><P
>A small tcl interpreter has been added to the web server, and it can
be used to write simple cgi scripts. The interpreter is admittedly very
minimal, and it is only useful for very simple applications, but it is an
excellent starting point for further development.</P
><P
>In order for the scripting language to be useful, it has to access
the form variables passed on during the GET or POST request. Because of
this, all form variables registered with the CYG_HTTPD_FVAR_TABLE_ENTRY()
macro are accessible via tcl. For example, if we have registered a
form variable called foo, and during the GET request we are defining foo
as being "1":</P
><TABLE
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BGCOLOR="#E0E0F0"
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><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>GET /myForm.cgi?foo=1</PRE
></TD
></TR
></TABLE
><P
>then tcl will be able to access the variable foo as $foo. The data
in the body of a POST request is also accessible through the use of the variable
$post_data. This is useful if the data is not in "multipart/form-data"
and tcl has to perform any type of processing on the data itself.</P
><P
>In order to send back a response to the client a few functions have been
added to the interpreter. These functions are:</P
><DIV
CLASS="SECT3"
><H3
CLASS="SECT3"
><A
NAME="ATHTTPD-START-CHUNKED"
>start_chunked</A
></H3
><TABLE
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BGCOLOR="#E0E0F0"
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><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>start_chunked "extension";</PRE
></TD
></TR
></TABLE
><P
>"extension" is a string used to search the
table of the mime types. For example, to send back to the client an HTML file,
we can use: start_chunked "html";</P
></DIV
><DIV
CLASS="SECT3"
><H3
CLASS="SECT3"
><A
NAME="ATHTTPD-WRITE-CHUNKED"
>write_chunked</A
></H3
><TABLE
BORDER="5"
BGCOLOR="#E0E0F0"
WIDTH="70%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>write_chunked content;</PRE
></TD
></TR
></TABLE
><P
>content is a string to send back to the client. </P
></DIV
><DIV
CLASS="SECT3"
><H3
CLASS="SECT3"
><A
NAME="ATHTTPD-END-CHUNKED"
>end_chunked</A
></H3
><TABLE
BORDER="5"
BGCOLOR="#E0E0F0"
WIDTH="70%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>end_chunked;</PRE
></TD
></TR
></TABLE
><P
>No parameters. Send back an end of frame to the client.</P
></DIV
><DIV
CLASS="SECT3"
><H3
CLASS="SECT3"
><A
NAME="ATHTTPD-TCL-HELLO-WORLD"
>tcl hello world example</A
></H3
><P
>The following example demonstrates how to send a log file in the file
<TT
CLASS="FILENAME"
>/ram/log</TT
> to a web client. It replaces
newline characters with <TT
CLASS="LITERAL"
><br></TT
> so that it is formatted on the
browser correctly.
<TABLE
BORDER="5"
BGCOLOR="#E0E0F0"
WIDTH="70%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>start_chunked "html";
set fp [aio.open "/ram/log" r];
$fp seek 0 end;
set fsize [$fp tell];
$fp seek 0 start;
set data "abcxxx";
set data [$fp read $fsize];
$fp close;
set data [string map {\n <br>} $data];
set datax "";
append datax "<html><body>" $data "</body></html>";
write_chunked $datax;
end_chunked;</PRE
></TD
></TR
></TABLE
></P
><P
>The above file should exist on a filesystem
on the embedded target within its <TT
CLASS="FILENAME"
>cgi-bin</TT
>
directory, for example as <TT
CLASS="FILENAME"
>/cgi-bin/hello.tcl</TT
>. Thereafter
it may be accessed at the URL
<TT
CLASS="LITERAL"
>http://<TT
CLASS="REPLACEABLE"
><I
>TARGET_NAME</I
></TT
>/cgi-bin/hello.tcl</TT
>.</P
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>C language callback functions</TD
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