Why Does My `json.RawMessage` Marshal as Base64?

Marshalling json.RawMessage: Unveiling the Reason Behind Base64 Encoding

In this intriguing scenario, you've encountered an anomalous behavior while attempting to marshal a json.RawMessage instance. Surprisingly, instead of obtaining the anticipated unencoded JSON string, you've encountered a meticulously base64 encoded version. To resolve this enigma, let's del delve into the depths of the underlying mechanics.

It's essential to recognize that when employing the Marshal function on a json.RawMessage, the crucial factor lies in ensuring that the input value is in fact a pointer. This seemingly subtle distinction plays a pivotal role in the behavior of json.RawMessage.

As you rightfully pointed out, json.RawMessage's implementation of MarshalJSON is designed to simply return the underlying byte slice. However, if the input value is not a pointer, the Marshal function will automatically apply base64 encoding to the byte slice before outputting it.

To rectify this situation and obtain the desired result, the solution is as simple as passing a pointer to your json.RawMessage. By doing so, you effectively instruct the Marshal function to operate upon the underlying byte slice directly, thus bypassing the undesirable base64 encoding process.

Consider the following modified code snippet:

package main

import (
    "encoding/json"
    "fmt"
)

func main() {
    raw := json.RawMessage(`{"foo":"bar"}`)
    j, err := json.Marshal(&raw) // Pass a pointer to json.RawMessage
    if err != nil {
        panic(err)
    }
    fmt.Println(string(j))
}

By implementing this subtle yet essential change, you can now confidently anticipate the expected outcome:

{"foo":"bar"}

This modified code aligns with the Marshal function's requirement for pointer-based input values, effectively eliminating the unwanted base64 encoding. Armed with this newfound knowledge, you can now confidently tackle similar challenges and ensure the desired JSON marshalling behavior in your Go applications.

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