Repository: gofiber/fiber
File: ctx.go (Go)

Code before:
			return s
		}

		return c.fasthttp.RemoteIP().String()
	}

	// default behavior if IP validation is not enabled is just to return whatever value is
	// in the proxy header. Even if it is empty or invalid
	return c.Get(c.app.config.ProxyHeader)
}

// IPs returns a string slice of IP addresses specified in the X-Forwarded-For request header.
// When IP validation is enabled, only valid IPs are returned.
func (c *DefaultCtx) IPs() []string {
	return c.extractIPsFromHeader(HeaderXForwardedFor)
}

// Is returns the matching content type,
// if the incoming request's Content-Type HTTP header field matches the MIME type specified by the type parameter
func (c *DefaultCtx) Is(extension string) bool {
	extensionHeader := utils.GetMIME(extension)
	if extensionHeader == "" {
		return false
	}

	ct := c.app.getString(c.fasthttp.Request.Header.ContentType())
	if i := strings.IndexByte(ct, ';'); i != -1 {
		ct = ct[:i]
	}
	ct = strings.TrimSpace(ct)
	return utils.EqualFold(ct, extensionHeader)
}

// JSON converts any interface or string to JSON.
// Array and slice values encode as JSON arrays,
// except that []byte encodes as a base64-encoded string,
// and a nil slice encodes as the null JSON value.
// If the ctype parameter is given, this method will set the
// Content-Type header equal to ctype. If ctype is not given,
// The Content-Type header will be set to application/json.
func (c *DefaultCtx) JSON(data any, ctype ...string) error {
	raw, err := c.app.config.JSONEncoder(data)
	if err != nil {
		return err
	}
	c.fasthttp.Response.SetBodyRaw(raw)
	if len(ctype) > 0 {
		c.fasthttp.Response.Header.SetContentType(ctype[0])
	} else {
		c.fasthttp.Response.Header.SetContentType(MIMEApplicationJSON)
	}

Review comment (suggestion):
I think we can still use `utils.UnsafeString` here, we don't need the immutability here because we're not returning this string

Code after:
			return s
		}

		return c.fasthttp.RemoteIP().String()
	}

	// default behavior if IP validation is not enabled is just to return whatever value is
	// in the proxy header. Even if it is empty or invalid
	return c.Get(c.app.config.ProxyHeader)
}

// IPs returns a string slice of IP addresses specified in the X-Forwarded-For request header.
// When IP validation is enabled, only valid IPs are returned.
func (c *DefaultCtx) IPs() []string {
	return c.extractIPsFromHeader(HeaderXForwardedFor)
}

// Is returns the matching content type,
// if the incoming request's Content-Type HTTP header field matches the MIME type specified by the type parameter
func (c *DefaultCtx) Is(extension string) bool {
	extensionHeader := utils.GetMIME(extension)
	if extensionHeader == "" {
		return false
	}

	ct := c.app.getString(c.fasthttp.Request.Header.ContentType())
	if i := strings.IndexByte(ct, ';'); i != -1 {
		ct = ct[:i]
	}
	ct = utils.Trim(ct, ' ')
	return utils.EqualFold(ct, extensionHeader)
}

// JSON converts any interface or string to JSON.
// Array and slice values encode as JSON arrays,
// except that []byte encodes as a base64-encoded string,
// and a nil slice encodes as the null JSON value.
// If the ctype parameter is given, this method will set the
// Content-Type header equal to ctype. If ctype is not given,
// The Content-Type header will be set to application/json.
func (c *DefaultCtx) JSON(data any, ctype ...string) error {
	raw, err := c.app.config.JSONEncoder(data)
	if err != nil {
		return err
	}
	c.fasthttp.Response.SetBodyRaw(raw)
	if len(ctype) > 0 {
		c.fasthttp.Response.Header.SetContentType(ctype[0])
	} else {
		c.fasthttp.Response.Header.SetContentType(MIMEApplicationJSON)
	}