Add more extensive logging.

This patch 1) makes obfs4proxy log its output to file and 2) adds a log
message that prints the error message (if any) after sending a "SIGNAL
ACTIVE" tor tor.

tor.go

@@ -63,7 +63,7 @@ func writeConfigToTorrc(tmpFh io.Writer, dataDir string) error {
 		"SafeLogging 0\n"+
 		"Log notice file %s/tor.log\n"+
 		"DataDirectory %s\n"+
-		"ClientTransportPlugin obfs2,obfs3,obfs4,scramblesuit exec /usr/bin/obfs4proxy\n"+
+		"ClientTransportPlugin obfs2,obfs3,obfs4,scramblesuit exec /usr/bin/obfs4proxy -enableLogging -logLevel DEBUG\n"+
 		"Bridge %s\n"+
 		"Bridge %s\n"+
 		"Bridge %s\n", getDomainSocketPath(dataDir), dataDir, dataDir,
@@ -206,6 +206,7 @@ func (c *TorContext) TestBridgeLines(bridgeLines []string) *TestResult {
 	// SETCONF.  See the following issue for more details:
 	// https://gitlab.torproject.org/tpo/anti-censorship/bridgestrap/-/issues/12
 	if _, err := c.Ctrl.Request("SIGNAL ACTIVE"); err != nil {
+		log.Printf("Bug: error after sending SIGNAL ACTIVE: %s", err)
 		result.Error = err.Error()
 		return result
 	}

tor_test.go

@@ -16,7 +16,7 @@ SocksPort auto
 SafeLogging 0
 Log notice file /foo/tor.log
 DataDirectory /foo
-ClientTransportPlugin obfs2,obfs3,obfs4,scramblesuit exec /usr/bin/obfs4proxy
+ClientTransportPlugin obfs2,obfs3,obfs4,scramblesuit exec /usr/bin/obfs4proxy -enableLogging -logLevel DEBUG
 Bridge obfs4 192.95.36.142:443 CDF2E852BF539B82BD10E27E9115A31734E378C2 cert=qUVQ0srL1JI/vO6V6m/24anYXiJD3QP2HgzUKQtQ7GRqqUvs7P+tG43RtAqdhLOALP7DJQ iat-mode=1
 Bridge obfs4 193.11.166.194:27015 2D82C2E354D531A68469ADF7F878FA6060C6BACA cert=4TLQPJrTSaDffMK7Nbao6LC7G9OW/NHkUwIdjLSS3KYf0Nv4/nQiiI8dY2TcsQx01NniOg iat-mode=0
 Bridge obfs4 37.218.245.14:38224 D9A82D2F9C2F65A18407B1D2B764F130847F8B5D cert=bjRaMrr1BRiAW8IE9U5z27fQaYgOhX1UCmOpg2pFpoMvo6ZgQMzLsaTzzQNTlm7hNcb+Sg iat-mode=0