Large post body are causing the bySimilarity to hang, and posts to crash

It appears that similarity search is causing the editor to hang. When I have a large post body that goes over the size of a http header I get this in the js console :

OPTIONS https://api.utopian.io/api/posts/?limit=5&skip=0&section=all&sortBy=created…678901234567890123456789012345678901234567890%60%60%60%0A%0A%0A&reset=true net::ERR_EMPTY_RESPONSE
c._end @ client.js:770
c.end @ client.js:674
(anonymous) @ request-base.js:238
r.then @ request-base.js:237
p @ api.js:20
(anonymous) @ api.js:87
(anonymous) @ index.js:37
(anonymous) @ errorMiddleware.js:18
dispatch @ applyMiddleware.js:35
(anonymous) @ contributions.js:19
(anonymous) @ index.js:11
(anonymous) @ api.js:46
(anonymous) @ index.js:37
(anonymous) @ errorMiddleware.js:18
(anonymous) @ bindActionCreators.js:3
(anonymous) @ SimilarPosts.js:35
r @ debounce.js:95
d @ debounce.js:142
h @ debounce.js:130
SimilarPosts.js:46 Uncaught (in promise) TypeError: Cannot read property 'results' of undefined
    at SimilarPosts.js:46

Looking at the network trace, I see the problem

curl 'https://api.utopian.io/api/posts/?limit=5&skip=0&section=all&sortBy=created&type=bug-hunting&bySimilarity=Large%20words%20are%20causing%20the%20editor%20to%20hang%0AIt%20appears%20that%20something%20is%20causing%20the%20editor%20to%20hang.%0A%0A1234567... .hug body truncated.. 6789012345678901234567890&reset=true' -X OPTIONS -H 'Access-Control-Request-Method: GET' -H 'Origin: https://utopian.io' -H 'Referer: https://utopian.io/write?draft=1603aee6dc2' -H 'User-Agent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/57.0.2987.98 Safari/537.36' -H 'Access-Control-Request-Headers: session' --compressed

Then saving also crashes the server

POST https://api.utopian.io/api/sc2/broadcast 500 (Internal Server Error)
editorActions.js:146 Error: Internal Server Error
    at c.<anonymous> (client.js:423)
    at c.r.emit (index.js:133)
    at XMLHttpRequest.t.onreadystatechange (client.js:703)