How to Convert UTF-8 Strings to Byte Arrays for JSON Unmarshaling in Go?

Converting UTF-8 Strings to Byte Arrays for JSON Unmarshaling

To unmarshal a JSON string, one must provide an array of bytes ([]byte) as input to the designated function. This article explores methods to convert UTF-8 strings to []byte for this purpose.

Method 1: Direct Type Conversion

The Go language allows direct conversion of strings to []byte using a simple type cast:

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

This method is sanctioned by the language specification, where it states that converting a string to a []byte results in a slice containing individual bytes of the string.

Method 2: Using an io.Reader with json.NewDecoder()

Alternatively, an io.Reader can be utilized with json.NewDecoder(). The provided io.Reader will read from a string without creating a copy, optimizing the process:

s := `{"somekey":"somevalue"}`

var result interface{}
err := json.NewDecoder(strings.NewReader(s)).Decode(&result)

This method avoids the overhead of copying the string content to a []byte, making it preferable for larger JSON texts.

Note: For small JSON strings, direct type conversion using []byte(s) is still a viable option with negligible performance impact.

Conclusion

This article demonstrates two methods to convert UTF-8 strings to []byte for JSON unmarshaling: a direct type cast and using an io.Reader with json.NewDecoder(). The appropriate method to employ depends on the specific use case and data size.

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