MarshalJSON without having all objects in memory at once

Question

I want to use json.Encoder to encode a large stream of data without loading all of it into memory at once.

// I want to marshal this
t := struct         


        

Answer 1

You can unpack the channel in the MarshalJSON method in your struct like this:

type S struct {
    Foo string
    Bar chan string 
}

func (s *S) MarshalJSON() (b []byte, err error) {
    b, err := json.Marshal(s.Foo)

    if err != nil { return nil, err }

    for x := range s.Bar {
        tmp, err := json.Marshal(x)

        if err != nil { return nil, err }

        b = append(b, tmp...)
    }

    return
}