How to Marshal JSON Streams Without Loading the Entire Object in Memory?

Marshaling JSON Streams Without Loading Entire Objects

Your goal is to encode a large data stream without holding the entire stream in memory. While JSON is a common data format, the standard library's json.Marshaler interface doesn't offer a straightforward way to achieve this.

Custom String Building

Currently, you're manually constructing the JSON string using WriteString, which is a reasonable approach given the lack of built-in functionality. This method ensures you only handle small chunks of data at a time.

Modifying encoding/json

If you're willing to modify the encoding/json package, you could patch the reflectValueQuoted function to handle channels as arrays. This would allow you to traverse channels and encode their values as they become available without buffering the entire stream.

Code Patch Example

Here's a modified version of the encoding/json code you could use:

<code class="go">// Inside switch:
case reflect.Chan:
    e.WriteByte('[')
    i := 0
    for {
        x, ok := v.Recv()
        if !ok {
            break
        }
        if i > 0 {
            e.WriteByte(',')
        }
        e.reflectValue(x)
        i++
    }
    e.WriteByte(']')</code>

Conclusion

The only current option to marshal JSON streams without loading the entire data is to manually construct the string as you're currently doing or modify the encoding/json package. Modifying the package requires some knowledge of the internal implementation and should be considered carefully.

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