warning: Division by zero in /modules/img_assist/img_assist.module on line 794.

I see suggestions on the php site to use getimagesize() or exif_imagetype() to check if a file is an image. exif_imagetype() is supposed to be faster but not sure if it works on all types of images.

I fixed the first problem by adding this to php.ini:

upload_tmp_dir = "/tmp"

To find this, I wrote a test.php script to upload an image and print out $_FILES:

<? var_dump($_FILES); ?>
<form enctype="multipart/form-data" name="test" method="post" action="test.php">
  <input type="hidden" name="MAX_FILE_SIZE" value="3000000" />
  <input enctype="multipart/form-data" type="file" name="edit[image]"
         class="form-file" id="edit-image" size="60" /><br>
  <input type="submit" name="op" value="Submit"  class="form-submit" />
</form>

when I uploaded my file, I saw:

...
["error"]=>
array(1) {
["image"]=>
int(6)
}
...

error 6 (from this page http://fr.php.net/manual/en/features.file-upload.errors.php) is "Missing a temporary folder."

This solved my original problem. The outcome of this is that I see 2 bugs to fix:

1) the error from the post is not properly reported
2) image_exact should check if the file is indeed an image (see above)

This patch to image_exact.module let's the user know that the file being resize failed because it was run on a non-image file. I used getimagesize() to determine if it was an image.

This patch to file.inc tells the user why the upload failed. The bug was that the error checking was occuring only if the file was uploaded. I moved the error check before this if statement. I also added 2 new error conditions from php5.

I wanted to stop things before they got to the division by zero. The obvious thing is that the return value from file_check_upload() is false. However, nothing seems to listen to this return value. Here's what I see:

file_check_upload() is called in node.module at line 1574 like this:

function node_object_prepare(&$node) {
...
node_invoke($node, 'prepare'); <-- file_check_upload() is called here
node_invoke_nodeapi($node, 'prepare');
}

There's no way for node_object_prepare to return the fact that node_invoke() returned. I'll let someone more knowledgeble in the archetecture deal with this.

I noticed an annoyance with the file.inc patch I just posted. If you edit the image later and change the title, you get an error 'The file image could not be saved, because the upload did not complete.' but the title is indeed changed.

I fixed the annoyance, here is a better version of the file.inc patch.