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From "Sorin Manolache" <sor...@gmail.com>
Subject Re: apr_open_file and apr_write_file in post_read_request and log_transaction
Date Tue, 09 Sep 2008 14:56:01 GMT
On Tue, Sep 9, 2008 at 16:10, Andrej van der Zee
<andrejvanderzee@gmail.com> wrote:
> Hi,
>
> I am new to Apache modules and I am trying to open a file in the hook
> post_read_request and write to the file in log_transaction. The file
> is supposed to be only valid for the duration of the request and is
> named with a unique identifier (created by mod_unique_id). The
> apr_file_t is carried, with other data, in the configuration vector
> (request_config) between the different hooks. In post_read_reqeust I
> open it like this (req_cfg is the configuration vector
> request_config):
>
>    req_cfg->log_file = NULL;
>    req_cfg->filepath = (char*) apr_pstrcat(r->pool, path_name,
> unique_id, NULL);
>    apr_int32_t flags = APR_WRITE | APR_CREATE | APR_EXCL | APR_APPEND;
>    rv = apr_file_open(&req_cfg->log_file, req_cfg->filepath, flags,
> APR_OS_DEFAULT, r->pool);
>    if (rv != APR_SUCCESS || req_cfg->log_file == NULL) {
>       ap_log_error(APLOG_MARK, APLOG_ERR, 0, NULL, "Failed to create
> resource log file: %s",
>                                   req_cfg->filepath);
>       return DECLINED;
>  }
>
> After this I am able to write to the file in this hook function. But,
> when I try to write to the file in the hook log_transaction like this:
>
>    char *msg = (char*) apr_psprintf(r->pool, "%s", "some msg");
>    len = strlen(msg);
>    apr_file_write(req_cfg->log_file, msg, &len);
>
> Then I get a segfault because req_cfg->log_file is NULL. Here the
> output from gdb:
>
> Core was generated by `/usr/local/apache2/bin/httpd -k start'.
> Program terminated with signal 11, Segmentation fault.
> [New process 16759]
> #0  apr_file_write (thefile=0x0, buf=0x81841d0, nbytes=0xbf8e5d94) at
> file_io/unix/readwrite.c:151
> 151         if (thefile->buffered) {
> (gdb) print thefile
> $1 = (apr_file_t *) 0x0
> (gdb) Quit
>
> Because the file is opened with r->pool (with r request_rec) in
> post_read_request I expect it to be open in the hook log_transaction.
> So I guess I am wrong? Is it closed by the cleanup handlers? And if
> so, what is the way to make sure it is still open?
>
> Cheers,
> Andrej
>

I've more or less replicated your code and everything goes fine. The
difference is that I don't use unique_id but I hard-code the path in
the call to apr_file_open and I do not use APR_EXCL.

Maybe you fail to open the file and the error is not logged correctly. Write

ap_log_error(APLOG_MARK, APLOG_ERR, 0, r->server, "Failed to create
resource log file: %s", req_cfg->filepath);

instead of

ap_log_error(APLOG_MARK, APLOG_ERR, 0, NULL, "Failed to create
resource log file: %s", req_cfg->filepath);


Slightly off-topic, I think creating a file, writing to it, and
closing it for each request is not an efficient solution. Can't you
open just one single log file once for the whole server (in
post_config for example), generate the unique id in post_read, put the
ID in the request notes (the "notes" field of the request_rec
structure) and then use it in log_transaction?

S

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