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From Oliver Boermans <>
Subject Re: Creating attachments from HTML's INPUT type="file"
Date Sun, 19 Apr 2009 09:16:42 GMT
2009/4/19 Curt Arnold <>:
> The only mechanism that seems to provide access to the local filesystem is
> HTML's file-select control and does not appear to provide a mechanism to
> control the request sent to the action URL so that it could conform to the
> CouchDB API.

Hey Curt,
Have been tackling this problem myself recently. Here are some notes
of what I discovered. If I am wrong or others have better techniques
hopefully they will share them here. Regardless, I hope this helps you
get to the bottom of it more quickly than I did!

To upload a file from a HTML form to CouchDB (without middleware and
while preserving it’s mime type ) use a regular form POST to an
_existing_ document.

Set the name of the file input as _attachments. CouchDB also expects
to receive a matching revision value for modifications to existing
documents. A hidden field named _rev in the same form will do that
providing it has the correct value.

If the uploaded file name matches an existing attachment of the same
document, the existing file will be replaced. Otherwise the new file
will be appended to that document’s array of attachments.

To do this with the guise of an ajax operation (file data cannot be
uploaded with ajax as far as I can tell) I made a small modification
to the jquery.form plugin <>:

                    var ta = doc.getElementsByTagName('textarea')[0];
                    xhr.responseText = ta ? ta.value : xhr.responseText;
                    var ta = doc.getElementsByTagName('pre')[0];
                    xhr.responseText = $(ta).text();

The plugin loads the server response into a generated iframe while
providing access to the server response. Trouble is it expects the
server to send the json response wrapped in a <textarea> rather than a
<pre> as CouchDB does.

With the above modification the server response can be handled to grab
the new rev and to check success. The form plugin will always report
success when sending file data - calling the success function,
fortunately it is simple to check the server response for error or ok
within that function as respond accordingly.

If there is no existing document to attach the file to, one can be
created using a AJAX PUT first. Grabbing the response for this will
provide the _rev necessary to further modify it by attachiing your

The one gotcha I am yet to satisfy is modifying other values of these
documents with attachments (with a HTML form submission) trashes the
file data. I guess because POSTing new data without the attachment
stub means a new document without attachments! My workaround has been
to make attachment specific documents and save related data in a
separate documents. Clunky but functional.


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