Awesome

github.com/ooni/oohttp

This repository contains a fork of Go's standard library net/http package including patches to allow using this HTTP code with github.com/refraction-networking/utls.

Motivation and maintenance

We created this package because it simplifies testing URLs using specific TLS Client Hello messages. We will continue to keep it up to date as long as it serves our goals.

Limitations

This fork does not include a fork of pprof because such package depends on the stdlib's internal/profile package. If your code uses http/pprof, then you cannot switch to this fork.
This fork's httptrace package is partly broken because there is no support for network events tracing, which requires the stdlib's internal/nettrace package. If your code depends on network events tracing, then you cannot switch to this fork.
This fork tracks the latest stable version of Go by merging upstream changes into the main branch. This means that it may not be working with earlier versions of Go. For example, when writing this note we are at Go 1.16 and this package accordingly uses io.ReadAll. If you are compiling using Go 1.15, you should get build errors because io.ReadAll did not exist before Go 1.16.

Usage

The follow diagram shows your typical app architecture when you're using this library as an alternative HTTP library.

architecture

From the diagram, it stems that we need to discuss two interfaces:

the interface between your code and this library;
the interface between this library and a TLS library.

Interface between your code and this library

The simplest approach is to just replace

import "net/http"

with

import "github.com/ooni/oohttp"

everywhere in your codebase.

This approach is not practical when your code or a dependency of yours already assumes net/http. In such a case, use stdlibwrapper.go, which provides you with an adapter implementing net/http.Transport. It takes the stdlib's net/http.Request as input and returns the stdlib's net/http.Response as output. But, internally, it uses the Transport defined by this library:

// StdlibTransport is an adapter for integrating net/http dependend code.
// It looks like an http.RoundTripper but uses this fork internally.
type StdlibTransport struct {
	*Transport
}

// RoundTrip implements the http.RoundTripper interface.
func (txp *StdlibTransport) RoundTrip(stdReq *http.Request) (*http.Response, error) {
	// ...
}

See example/internal/utlsx/utlsx.go for a real world example where we use StdlibTransport to be net/http compatible.

Interface between this library and any TLS library

You need to write a wrapper for your definition of the TLS connection that implements the TLSConn interface:

// TLSConn is the interface representing a *tls.Conn compatible
// connection, which could possibly be different from a *tls.Conn
// as long as it implements the interface. You can use, for
// example, refraction-networking/utls instead of the stdlib.
type TLSConn interface {
	// net.Conn is the underlying interface
	net.Conn

	// ConnectionState returns the ConnectionState according
	// to the standard library.
	ConnectionState() tls.ConnectionState

	// HandshakeContext performs an TLS handshake bounded
	// in time by the given context.
	HandshakeContext(ctx context.Context) error

	// NetConn returns the underlying net.Conn
	NetConn() net.Conn
}

If you are using crypto/tls, then your tls.Conn is already a valid TLSConn and you don't need to do anything in particular. (However, if you are using crypto/tls, you shouldn't probably be using oohttp at all!)

If you are using refraction-networking/utls (or Yawning/utls), you need to write an adapter. Your TLS connection is already a net.Conn. But you need to implement ConnectionState. And you also need to implement HandshakeContext.

The following code shows, for reference, how we initially implemented this functionality in ooni/probe-cli:

// uconn is an adapter from utls.UConn to TLSConn.
type uconn struct {
	*utls.UConn
}

// ConnectionState implements TLSConn's ConnectionState.
func (c *uconn) ConnectionState() tls.ConnectionState {
	ustate := c.UConn.ConnectionState()
	return tls.ConnectionState{
		Version:                     ustate.Version,
		HandshakeComplete:           ustate.HandshakeComplete,
		//
		// [...]
		//
		// You get the idea. You need to copy all fields. We
		// intentionally snip early here so we are not forced
		// to ensure this code is always up-to-date.
	}
}

// HandshakeContext implements TLSConn's HandshakeContext.
func (c *uconn) HandshakeContext(ctx context.Context) error {
	errch := make(chan error, 1)
	go func() {
		errch <- c.UConn.Handshake()
	}()
	select {
	case err := <-errch:
		return err
	case <-ctx.Done():
		return ctx.Err()
	}
}

See example/internal/utlsx/utlsx.go for a real-world example of writing a TLSConn compatible adapter.

Once you have the adapter in place, you should write a factory for creating the specific uTLS connection you'd like to use; for example:

// utlsFactory creates a new uTLS connection.
func utlsFactory(conn net.Conn, config *tls.Config) oohttp.TLSConn {
	uConfig := &utls.Config{
		RootCAs:                     config.RootCAs,
		NextProtos:                  config.NextProtos,
		ServerName:                  config.ServerName,
		InsecureSkipVerify:          config.InsecureSkipVerify,
		DynamicRecordSizingDisabled: config.DynamicRecordSizingDisabled,
	}
	return &uconn{utls.UClient(conn, uConfig, utls.HelloFirefox_55)}
}

Finally, you should configure utlsFactory as being your TLSClientFactory by setting the corresponding field of the oohttp.Transport:

txp := &oohttp.Transport{
	// ...
	TLSClientFactory: utlsFactory,
}

This TLSClientFactory will also work when using a proxy.

See example/example-utls for a complete example that does not use a proxy. Likewise, see example/example-proxy for an example that uses a proxy. A more complex example, where we override Transport.DialTLSContext is example/example-utls-with-dial.

Issue tracker

Please, report issues in the ooni/probe repository. Make sure you mention oohttp in the issue title.

Patches

We started from the src/net/http subtree at go1.16 and we applied patches to fork the codebase (#1, #2 and #3). Then, we introduced the http.TLSConn abstraction that allows using different TLS libraries (#4). We added the StdlibTransport wrapped in #8. and #9. We added support for TLSClientFactory in #16, #19, and #22.

Every major change is documented by a pull request. We may push minor changes (e.g., updating docs) directly on the main branch.

Update procedure

(Adapted from refraction-networking/utls instructions.)