How Can I Handle Non-Panic Errors When Using json.Marshal in Go?

Getting a Non-Panic Error from json.Marshal in Go

The Go standard json.Marshal function is designed to convert Go data structures into JSON strings. However, it's important to be aware that there are certain limitations to the types of data structures it can handle.

Cyclic Data Structures

One such limitation is that json.Marshal cannot represent cyclic data structures. Attempting to do so will result in an infinite recursion that will ultimately lead to a runtime panic.

Invalid Types and Values

To avoid this unintended behavior, json.Marshal implements mechanisms to identify and report potentially problematic inputs. When presented with an invalid type, such as a channel, it will return an instance of json.UnsupportedTypeError.

For instance:

<code class="go">_, err := json.Marshal(make(chan int))
_, ok := err.(*json.UnsupportedTypeError) // ok == true</code>

Additionally, json.Marshal can detect and report invalid values, such as positive or negative infinity. In these cases, it will return an instance of json.UnsupportedValueError.

Here's an example:

<code class="go">_, err := json.Marshal(math.Inf(1))
_, ok := err.(*json.UnsupportedValueError) // ok == true</code>

Conclusion

By being aware of the input types and values that can cause json.Marshal to return an error, you can avoid potential runtime panics and ensure that your code remains robust and reliable.

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