Error Handling in Golang JSON Marshalling

JSON data structures cannot represent cyclic references, and Go's json.Marshal function cannot handle them. As a result, passing cyclic structures to Marshal leads to an infinite recursion and a runtime panic.

Beyond cyclic structures, json.Marshal can also return non-nil errors in situations where it encounters unsupported types or invalid values.

Unsupported Types

Marshal returns an UnsupportedTypeError when attempting to marshal an unsupported data type. For example:

import "encoding/json"

func main() {
    ch := make(chan int)
    _, err := json.Marshal(ch)
    if _, ok := err.(*json.UnsupportedTypeError); ok {
        // Error: Unmarshal: unsupported type: chan int
    }
}

Unsupported Values

Marshal can also return an UnsupportedValueError when attempting to marshal an invalid value. For instance:

import (
    "encoding/json"
    "math"
)

func main() {
    positiveInfinity := math.Inf(1)
    _, err := json.Marshal(positiveInfinity)
    if _, ok := err.(*json.UnsupportedValueError); ok {
        // Error: json: unsupported value:  Inf
    }
}

By understanding these conditions, developers can handle errors gracefully and ensure that json.Marshal returns the expected results or handle the appropriate errors.