feat: Add BindJSONStrict() for strict JSON decoding

[Utkarsh0uchiha]

Problem

BindJSON() currently uses Go's default JSON decoder behavior.

This means unknown JSON fields are silently ignored.

Example:

{
    "name": "John",
    "age": 20,
    "unexpected": true
}

The extra field is discarded without notifying the developer.

For APIs requiring strict validation, this may hide client-side mistakes.

---

Proposed Solution

Introduce a separate helper:

err := c.BindJSONStrict(&req)

Internally:

decoder := json.NewDecoder(c.Request.Body)
decoder.DisallowUnknownFields()

This preserves the existing BindJSON() behavior while offering an opt-in strict alternative.

---

Why This Matters

Many production APIs prefer rejecting unexpected fields because they often indicate:

• Client typos
• Version mismatches
• Invalid requests

Providing both APIs gives developers flexibility without introducing breaking changes.

---

Tests

Add coverage for:

• Valid JSON
• Unknown fields returning an error
• Validation still working correctly

---

Backward Compatibility

No breaking changes.

Existing BindJSON() remains unchanged.

Hey @DevanshuTripathi, I'd be happy to work on this implementation, #GSSOC'26.

[prasiddhi-105]

Hiii, @DevanshuTripathi are there any open issues, I would love to contribute!!!

[DevanshuTripathi]

Hi @Utkarsh0uchiha this feature will cause complexity for a small change dont you think?

[DevanshuTripathi]

@prasiddhi-105 You can go through the project and open an issue regarding bugs or feature requests

[Utkarsh0uchiha]

Hey @DevanshuTripathi , That's a fair point.

I was thinking of keeping the existing BindJSON() behavior unchanged while providing an opt-in strict variant, mainly for APIs that prefer rejecting unknown fields.

That said, I understand adding another public API increases the maintenance surface for a relatively small feature. If you feel it doesn't fit Vodka's design philosophy, I'm happy to close this and work on something with a better cost-to-value ratio instead.

[aaniya22]

pls assign this to me under gssoc