detect.go

package main

import (
	"errors"
	"fmt"
	"log"
	"net"
	"net/url"
	"time"
)

type DetectParams struct {
	Target        string
	RequestMethod string

	DetectMethod     DetectMethod
	SmugglingMethod  SmugglingMethod
	SmugglingVariant SmugglingVariant
	PaddingMethod    PaddingMethod
}

func (p *DetectParams) String() string {
	return fmt.Sprintf(
		"target=%s, http_method=%s, detect_method=%s, "+
			"smuggling_method=%s, smuggling_variant=%s, padding_method=%s",
		p.Target,
		p.RequestMethod,
		p.DetectMethod,
		p.SmugglingMethod,
		p.SmugglingVariant,
		p.PaddingMethod,
	)
}

type DetectResult int

const (
	Indistinguishable DetectResult = iota
	DistinguishableByTiming
	DistinguishableNotByTiming
)

func (r DetectResult) String() string {
	switch r {
	case Indistinguishable:
		return "indistinguishable"
	case DistinguishableByTiming:
		return "distinguishable by timing"
	case DistinguishableNotByTiming:
		return "distinguishable not by timing"
	default:
		return fmt.Sprintf("unknown result value: %#v", r)
	}
}

func Detect(params *DetectParams,
	connectTo string,
	timeout time.Duration,
	verbose bool) (DetectResult, error) {

	u, err := url.Parse(params.Target)
	if err != nil {
		return Indistinguishable, err
	}
	prefixHeaders := params.PaddingMethod.Headers()
	valid, invalid := params.DetectMethod.GetRequests(params.SmugglingMethod, u, params.SmugglingVariant)
	valid.AdditionalHeaders = prefixHeaders.Combine(valid.AdditionalHeaders)
	invalid.AdditionalHeaders = prefixHeaders.Combine(invalid.AdditionalHeaders)

	validResponses := &ResponseSet{}
	invalidResponses := &ResponseSet{}

	for i := 0; i < 14 && validResponses.DistinguishableFrom(invalidResponses); i++ {
		// The order is: V I ( V V V I I I ) x 4
		doValid := i == 0 || (i >= 2 && ((i-2)/3)%2 == 0)
		request := valid
		if !doValid {
			request = invalid
		}
		var (
			response  *HTTPMessage
			err       = errNotStarted
			triesLeft = 3
		)

		for err != nil && mayResolveInFuture(err) && triesLeft > 0 {
			triesLeft--
			response, err = DoRequest(&RequestParams{
				Target:          u,
				Method:          params.RequestMethod,
				ConnectAddr:     connectTo,
				Headers:         request.AdditionalHeaders,
				Body:            request.Body,
				Timeout:         timeout,
				BodyPartsDelay:  request.BodyPartsDelay,
				SkipBodyEndFlag: request.SkipBodyEndFlag,
			})
		}

		if err != nil && (verbose || (!isRSTError(err) && !isTimeoutError(err))) {
			log.Printf("request: %v, error: %v", params, err)
		}

		if doValid {
			validResponses.AccountResponse(response, isTimeoutError(err))
		} else {
			invalidResponses.AccountResponse(response, isTimeoutError(err))
		}
	}

	result := Indistinguishable
	if validResponses.DistinguishableFrom(invalidResponses) {
		if validResponses.AllResponsesAreTimeouts() || invalidResponses.AllResponsesAreTimeouts() {
			result = DistinguishableByTiming
		} else {
			result = DistinguishableNotByTiming
		}
	}

	if verbose {
		log.Printf("%s: valid=%s, invalid=%s, result=%v",
			params, validResponses, invalidResponses, result)
	}
	return result, nil
}

func isRSTError(err error) bool {
	_, ok := err.(ConnDropError)
	return ok
}

func isTimeoutError(err error) bool {
	n, ok := err.(net.Error)
	if !ok {
		return false
	}
	return n.Timeout()
}

var errNotStarted = errors.New("not started")

func mayResolveInFuture(err error) bool {
	if err == errNotStarted {
		return true
	}
	n, ok := err.(net.Error)
	if !ok {
		return false
	}
	return n.Timeout() || n.Temporary()
}