How to Efficiently Convert a UTF-8 String to []byte for JSON Unmarshalling in Go?

Converting UTF-8 Strings to []byte for JSON Unmarshalling

To unmarshal a JSON string in Go, we need to provide a []byte slice as input. If we only have a UTF-8 string, how can we convert it to []byte?

Simple Conversion and String to []byte Copy

The Go type system allows us to convert directly from a string to []byte using:

s := "some text"
b := []byte(s) // b is type []byte

However, this operation creates a copy of the string, which can be inefficient for large strings.

Efficient Conversion Using io.Reader

An alternative solution involves creating an io.Reader using strings.NewReader():

s := `{"somekey":"somevalue"}`
r := strings.NewReader(s)

This io.Reader can then be passed to json.NewDecoder() for unmarshalling without creating a string copy:

var result interface{}
err := json.NewDecoder(r).Decode(&result)

Overhead Considerations

Using strings.NewReader() and json.NewDecoder() has some overhead, so for small JSON strings, converting to []byte directly may be more efficient:

s := `{"somekey":"somevalue"}`
var result interface{}
err := json.Unmarshal([]byte(s), &result)

Direct io.Reader Input

If the JSON string input is available as an io.Reader (e.g., a file or network connection), it can be passed directly to json.NewDecoder():

var result interface{}
err := json.NewDecoder(myReader).Decode(&result)

This eliminates the need for intermediate conversions or copies.

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