[COUCHDB-1521] multipart parser gets multiple attachments mixed up

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Won't Fix
• Affects Version/s: 1.2
• Component/s: HTTP Interface
• Assignee: Randall Leeds
• Reporter: Jens Alfke
• Created: 08/Aug/12 17:05
• Updated: 02/Sep/18 06:39
• Resolved: 02/Sep/18 06:39

Description

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.)

Issue Links

• is related to: COUCHDB-1368 multipart/related document body doesn't identify which part is which attachment