How to Achieve Case-Sensitive JSON Unmarshaling in Go?

Handling Case-Sensitive JSON Unmarshaling

When utilizing JSON, there may arise situations where case-sensitive handling is desired during the unmarshaling process. However, the standard JSON library in Go prioritizes case-insensitive matches, potentially leading to unexpected behavior.

Case-Insensitive Match Behavior

As per the official documentation, during unmarshaling, incoming JSON keys are compared against struct field names or tags. The library prefers exact matches but also tolerates case-insensitive ones. This can lead to conflicts if, for instance, you receive JSON containing keys like "e" and "E" and wish to unmarshal only the "e" variant.

Lack of Case-Sensitive Unmarshalling

Regrettably, the standard JSON library doesn't currently offer a straightforward mechanism to disable case-insensitive unmarshalling. The documentation at https://golang.org/pkg/encoding/json/#Unmarshal explicitly states:

"Unmarshal matches incoming object keys to the keys used by Marshal (either the struct field name or its tag), preferring an exact match but also accepting a case-insensitive match."

Alternate Solutions

Since the standard library doesn't provide an out-of-the-box solution, one possible workaround is to create a custom JSON decoder by extending the encoding/json package. This decoder could implement a field-level case-sensitive unmarshalling mechanism that ignores tags with differing casing.

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