skipping amp transport on large requests

[WendelHime]

AMP requests with payloads larger than 6kb doesn't even reach the broker side

Resolve getlantern/engineering#2871

[Copilot]

Pull request overview

This PR adds logic to skip the AMP transport when handling HTTP requests with payloads larger than 6KB, addressing an issue where such large requests were failing to reach the broker.

Key Changes:

• Introduces a 6KB content length limit constant (ampMaxContentLength = 6000)
• Adds Content-Length header checking logic before launching transport goroutines
• Skips the AMP transport when request size exceeds the limit

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[myleshorton]

I really think this should be part of a new interface for all transports.

I.e. something like a KindlingTransport interface that would have something like:

MaxLength() int
ConnectedRoundTripper(...) http.RoundTripper

[WendelHime]

you mean adding as part of namedRoundTripper function? I'll add a commit that I can revert later if this isn't what you meant.

[WendelHime]

Added cb4f44b

[myleshorton]

No I think we should generalize it all like this in kindling.go, with likely just keeping around a slice of transports vs roundTripGenerators.

type Transport interface {
	// NewRoundTripper creates a new http.RoundTripper that is already connected
	NewRoundTripper(ctx context.Context, addr string) (http.RoundTripper, error)
	MaxLength() int
	Name() string
}

func WithTransport(transport Transport) Option {
	return newOption(func(k *kindling) {
		log.Info("Setting custom transport")
		if transport == nil {
			log.Error("Transport instance is nil")
			return
		}
		k.transports = append(k.transports, transport)
	})
}

[myleshorton]

I just started coding this for the example -- should have a PR soon!

[myleshorton]

OK yeah here's that refactor: #26