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https://issues.apache.org/jira/browse/COUCHDB-1521?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14165692#comment-14165692
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Robert Newson commented on COUCHDB-1521:
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Jan enhanced multipart so that each part can have headers (including
filenames), which I think was the fix for mixups?
> multipart parser gets multiple attachments mixed up
> ---------------------------------------------------
>
> Key: COUCHDB-1521
> URL: https://issues.apache.org/jira/browse/COUCHDB-1521
> Project: CouchDB
> Issue Type: Bug
> Components: HTTP Interface
> Affects Versions: 1.2
> Reporter: Jens Alfke
> Assignee: Randall Leeds
>
> When receiving a document PUT in multipart format, CouchDB gets the
> attachments and MIME parts mixed up. Instead of looking at the headers of a
> MIME part to identify which attachment it is (most likely by using the
> 'filename' property of the 'Content-Disposition:' header), it processes the
> attachments according to the order in which their metadata objects appear in
> the JSON body's '_attachments:' object.
> The problem with this is that JSON objects (dictionaries) are _not_ ordered
> collections. I know that Erlang's implementation of them (as linked lists of
> key/value pairs) happens to be ordered, and I think some JavaScript
> implementations have the side effect of preserving order; but in many
> languages these are implemented as hash tables and genuinely unordered.
> This means that when a program written in such a language converts a native
> object to JSON, it has no control over (and probably no knowledge of) the
> order in which the keys of the JSON object are written out. This makes it
> impossible to then write the attachments in the same order.
> The only workaround seems to be for the program to implement its own custom
> JSON encoder just so that it can write object keys in a known order (probably
> sorted), which then enables it to write the attachment bodies in the same
> order.
> NOTE: This is the flip side of COUCHDB-1368 which I filed last year; that bug
> has to do with the same ordering issue when CouchDB _generates_ multipart
> responses (and presents similar problems for clients not written in Erlang.)
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