feat(miniooni): implement torsf tunnel (#921)

This diff adds to miniooni support for using the torsf tunnel. Such a
tunnel consists of a snowflake pluggable transport in front of a custom
instance of tor and requires tor to be installed.

The usage is like:

```
./miniooni --tunnel=torsf [...]
```

The default snowflake rendezvous method is "domain_fronting". You can
select the AMP cache instead using "amp":

```
./miniooni --snowflake-rendezvous=amp --tunnel=torsf [...]
```

Part of https://github.com/ooni/probe/issues/1955

internal/cmd/miniooni/main.go

@@ -25,25 +25,26 @@ import (
 
 // Options contains the options you can set from the CLI.
 type Options struct {
-	Annotations      []string
-	Emoji            bool
-	ExtraOptions     []string
-	HomeDir          string
-	Inputs           []string
-	InputFilePaths   []string
-	MaxRuntime       int64
-	NoJSON           bool
-	NoCollector      bool
-	ProbeServicesURL string
-	Proxy            string
-	Random           bool
-	RepeatEvery      int64
-	ReportFile       string
-	TorArgs          []string
-	TorBinary        string
-	Tunnel           string
-	Verbose          bool
-	Yes              bool
+	Annotations         []string
+	Emoji               bool
+	ExtraOptions        []string
+	HomeDir             string
+	Inputs              []string
+	InputFilePaths      []string
+	MaxRuntime          int64
+	NoJSON              bool
+	NoCollector         bool
+	ProbeServicesURL    string
+	Proxy               string
+	Random              bool
+	RepeatEvery         int64
+	ReportFile          string
+	SnowflakeRendezvous string
+	TorArgs             []string
+	TorBinary           string
+	Tunnel              string
+	Verbose             bool
+	Yes                 bool
 }
 
 // main is the main function of miniooni.
@@ -125,6 +126,13 @@ func main() {
 		"set the output report file path (default: \"report.jsonl\")",
 	)
 
+	flags.StringVar(
+		&globalOptions.SnowflakeRendezvous,
+		"snowflake-rendezvous",
+		"domain_fronting",
+		"rendezvous method for --tunnel=torsf (one of: \"domain_fronting\" and \"amp\")",
+	)
+
 	flags.StringSliceVar(
 		&globalOptions.TorArgs,
 		"tor-args",
@@ -143,7 +151,7 @@ func main() {
 		&globalOptions.Tunnel,
 		"tunnel",
 		"",
-		"tunnel to use to communicate with the OONI backend (one of: tor, psiphon)",
+		"tunnel to use to communicate with the OONI backend (one of: psiphon, tor, torsf)",
 	)
 
 	flags.BoolVarP(

internal/cmd/miniooni/session.go

@@ -36,14 +36,15 @@ func newSessionOrPanic(ctx context.Context, currentOptions *Options,
 	runtimex.PanicOnError(err, "cannot create tunnelDir")
 
 	config := engine.SessionConfig{
-		KVStore:         kvstore,
-		Logger:          logger,
-		ProxyURL:        proxyURL,
-		SoftwareName:    softwareName,
-		SoftwareVersion: softwareVersion,
-		TorArgs:         currentOptions.TorArgs,
-		TorBinary:       currentOptions.TorBinary,
-		TunnelDir:       tunnelDir,
+		KVStore:             kvstore,
+		Logger:              logger,
+		ProxyURL:            proxyURL,
+		SnowflakeRendezvous: currentOptions.SnowflakeRendezvous,
+		SoftwareName:        softwareName,
+		SoftwareVersion:     softwareVersion,
+		TorArgs:             currentOptions.TorArgs,
+		TorBinary:           currentOptions.TorBinary,
+		TunnelDir:           tunnelDir,
 	}
 	if currentOptions.ProbeServicesURL != "" {
 		config.AvailableProbeServices = []model.OOAPIService{{