athttpd-callback.html

来自「ecos3.0 beta 的官方文档,html格式」· HTML 代码 · 共 338 行

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>C language callback functions</TITLE
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><A
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>C language callback functions</A
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><P
>The server allows the association of particular URLs to C language callback 
functions. eCos tables are used to define the association between a URL and its
corresponding callback. The syntax of the macro to add callback entries to 
the table is:</P
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>CYG_HTTPD_HANDLER_TABLE_ENTRY(entry_label, url_string, callback);

entry table      : an identifier unique to this entry.
url_string       : a string with the extension url that will be appended to the
                   default directory.
callback         : a function with a prototype:
                   cyg_int32 callback_function(CYG_HTTPD_STATE*); 
                   Return value is ignored - just return 0.</PRE
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><P
><B
CLASS="COMMAND"
>CYG_HTTPD_STATE*</B
> is a pointer to a structure that
contains, among others, a buffer (outbuffer) that can be used to send data
out. The definitions of the structure is in http.h.</P
><P
>The following is an example of how to add a callback to a function myForm()
whenever the URL /myform.cgi is requested:</P
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>CYG_HTTPD_HANDLER_TABLE_ENTRY(hal_cb_entry, "/myform.cgi", myForm);</PRE
></TD
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><P
>and somewhere in the source tree there is a function:</P
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CLASS="PROGRAMLISTING"
>cyg_int32 myForm(CYG_HTTPD_STATE* p)
{
   cyg_httpd_start_chunked("html");
   strcpy(p-&#62;outbuffer, "eCos Web Server");
   cyg_httpd_write_chunked(p-&#62;outbuffer, strlen(p-&#62;outbuffer))
   cyg_httpd_end_chunked();
}  </PRE
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><P
>This function also shows the correct method of using the chunked frames
API inside a c language callback and also shows the use of outbuffer to
collect data to send out.</P
><P
>Chunked frames are useful when the size of the frame is not known upfront. 
In this case it possible to send a response in chunks of various sizes, and
terminate it with a null chunk (See RFC 2616 for details). To use chunked 
frames, the <B
CLASS="COMMAND"
>cyg_httpd_start_chunked()</B
> function is used. 
The prototype is the following:</P
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><PRE
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>ssize_t cyg_httpd_start_chunked(char *);</PRE
></TD
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></TABLE
><P
>The only parameter is the <B
CLASS="COMMAND"
>extension</B
> to use in the 
search for the MIME type. For most files this will be "html" or "htm" and
it will be searched in the MIME table for an approriate MIME type that will
be sent along in the header. The function returns the number of bytes sent
out.</P
><P
>The chunked frame must be terminated by a call to 
<B
CLASS="COMMAND"
>cyg_httpd_end_chunked()</B
>:</P
><TABLE
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><PRE
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>void cyg_httpd_end_chunked()(void);</PRE
></TD
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><P
>In between these two calls, the user can call the function
<B
CLASS="COMMAND"
>cyg_httpd_write_chunked()</B
> to send out data any number of
times. It is important that <B
CLASS="COMMAND"
>cyg_httpd_write_chunked()</B
> be
the only function used to send data out for chunked frames. This
guarantees that proper formatting of the response is respected.
The prototype for the function is:</P
><TABLE
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><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>ssize_t cyg_httpd_write_chunked(char* p, int len);</PRE
></TD
></TR
></TABLE
><P
>The 'char*' points to the data to send out, the 'int' is the length of the
data to send.</P
><P
>In the case in which the size of the data is known upfront, the
callback can instead create the header with a call to
<B
CLASS="COMMAND"
>cyg_httpd_create_std_header()</B
> with the following
prototype:</P
><TABLE
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><PRE
CLASS="PROGRAMLISTING"
>void cyg_httpd_create_std_header(char *ext, int len);

extension   : the extension used in the search of the MIME type
len         : length of the data to send out</PRE
></TD
></TR
></TABLE
><P
>and use
<B
CLASS="COMMAND"
>cyg_httpd_write()</B
> to send data out to the client. The
 prototype of <B
CLASS="COMMAND"
>cyg_httpd_write()</B
> is the same as 
<B
CLASS="COMMAND"
>cyg_httpd_write_chunked()</B
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