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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
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<TITLE>Reading Client Input in Apache 1.2</TITLE>
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<H1 ALIGN="CENTER">Reading Client Input in Apache 1.2</H1>
<HR>
<P>Apache 1.1 and earlier let modules handle POST and PUT requests by
themselves. The module would, on its own, determine whether the
request had an entity, how many bytes it was, and then called a
function (<CODE>read_client_block</CODE>) to get the data.
<P>However, HTTP/1.1 requires several things of POST and PUT request
handlers that did not fit into this module, and all existing modules
have to be rewritten. The API calls for handling this have been
further abstracted, so that future HTTP protocol changes can be
accomplished while remaining backwards-compatible.</P>
<HR>
<H3>The New API Functions</H3>
<PRE>
int ap_setup_client_block (request_rec *, int read_policy);
int ap_should_client_block (request_rec *);
long ap_get_client_block (request_rec *, char *buffer, int buffer_size);
</PRE>
<OL>
<LI>Call <CODE>ap_setup_client_block()</CODE> near the beginning of the request
handler. This will set up all the necessary properties, and
will return either OK, or an error code. If the latter,
the module should return that error code. The second parameter
selects the policy to apply if the request message indicates a
body, and how a chunked
transfer-coding should be interpreted. Choose one of
<PRE>
REQUEST_NO_BODY Send 413 error if message has any body
REQUEST_CHUNKED_ERROR Send 411 error if body without Content-Length
REQUEST_CHUNKED_DECHUNK If chunked, remove the chunks for me.
REQUEST_CHUNKED_PASS Pass the chunks to me without removal.
</PRE>
In order to use the last two options, the caller MUST provide a buffer
large enough to hold a chunk-size line, including any extensions.
<LI>When you are ready to possibly accept input, call
<CODE>ap_should_client_block()</CODE>.
This will tell the module whether or not to read input. If it is 0,
the module should assume that the input is of a non-entity type
(<EM>e.g.</EM>, a GET request). A nonzero response indicates that the module
should proceed (to step 3).
This step also sends a 100 Continue response
to HTTP/1.1 clients, so should not be called until the module
is <STRONG>*definitely*</STRONG> ready to read content. (otherwise, the
point of the
100 response is defeated). Never call this function more than once.
<LI>Finally, call <CODE>ap_get_client_block</CODE> in a loop. Pass it a
buffer and its
size. It will put data into the buffer (not necessarily the full
buffer, in the case of chunked inputs), and return the length of
the input block. When it is done reading, it will
return 0 if EOF, or -1 if there was an error.
</OL>
<P>As an example, please look at the code in
<CODE>mod_cgi.c</CODE>. This is properly written to the new API
guidelines.</P>
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