在Go中流式传输BSON-> JSON HTTP回复？

Question

Currently I am running this in a http handler:

err := mongoCollection.Find(bson.M{"name": vars["name"]}).One(&result)
data, err := json.Marshal(result)
w.Write(data)

How can I begin serving the result before the full BSON data is in?

Edit: the answer needs to go beyond the mgo extension and go into bson. mgo as far as I can see will only serve full documents if I not mistaken. I have one - possibly large - document as my code example clearly shows.

Answer 1

In order for this to be possible, you would need these things:

1. Access to a Reader for the incoming bson stream
2. A datatype for generic document parts
3. A streaming decoder for bson which reads from the Reader and produces document parts
4. A streaming encoder for json that consumes document parts and writes to a Writer

mgo does not provide number 1. encoding/json does not provide number 2 or 4. mgo/bson does not provide number 3. A bit of googling doesn't turn up any help for any of those points in Go, though there are streaming json parsers in other languages (see answers for Is there a streaming API for JSON?).

Your desire to do this is reasonable, but the support just doesn't exist yet. Fortunately, json and bson are simple enough and all the components you're using are open source, so in theory you could write the tools you need.