Add support for ssl dial string (#184)

* Add support for ssl dial string

* Ensure we dont override user settings

* update examples

* update ssl value parsing

* PingSsl test

* skip test requiring system certificates

example_test.go

@@ -137,7 +137,21 @@ func ExampleSession_concurrency() {
 
 func ExampleDial_usingSSL() {
 	// To connect via TLS/SSL (enforced for MongoDB Atlas for example) requires
-	// configuring the dialer to use a TLS connection:
+	// to set the ssl query param to true.
+	url := "mongodb://localhost:40003?ssl=true"
+
+	session, err := Dial(url)
+	if err != nil {
+		panic(err)
+	}
+
+	// Use session as normal
+	session.Close()
+}
+
+func ExampleDial_tlsConfig() {
+	// You can define a custom tlsConfig, this one enables TLS, like if you have
+	// ssl=true in the connection string.
 	url := "mongodb://localhost:40003"
 
 	tlsConfig := &tls.Config{

session.go

@@ -28,6 +28,7 @@ package mgo
 
 import (
 	"crypto/md5"
+	"crypto/tls"
 	"crypto/x509"
 	"crypto/x509/pkix"
 	"encoding/asn1"
@@ -294,6 +295,12 @@ const (
 //        The identifier of this client application. This parameter is used to
 //        annotate logs / profiler output and cannot exceed 128 bytes.
 //
+//     ssl=<true|false>
+//
+//        true: Initiate the connection with TLS/SSL.
+//        false: Initiate the connection without TLS/SSL.
+//        The default value is false.
+//
 // Relevant documentation:
 //
 //     http://docs.mongodb.org/manual/reference/connection-string/
@@ -331,6 +338,7 @@ func ParseURL(url string) (*DialInfo, error) {
 	if err != nil {
 		return nil, err
 	}
+	ssl := false
 	direct := false
 	mechanism := ""
 	service := ""
@@ -345,6 +353,10 @@ func ParseURL(url string) (*DialInfo, error) {
 	safe := Safe{}
 	for _, opt := range uinfo.options {
 		switch opt.key {
+		case "ssl":
+			if v, err := strconv.ParseBool(opt.value); err == nil && v {
+				ssl = true
+			}
 		case "authSource":
 			source = opt.value
 		case "authMechanism":
@@ -460,6 +472,13 @@ func ParseURL(url string) (*DialInfo, error) {
 		MinPoolSize:    minPoolSize,
 		MaxIdleTimeMS:  maxIdleTimeMS,
 	}
+	if ssl && info.DialServer == nil {
+		// Set DialServer only if nil, we don't want to override user's settings.
+		info.DialServer = func(addr *ServerAddr) (net.Conn, error) {
+			conn, err := tls.Dial("tcp", addr.String(), &tls.Config{})
+			return conn, err
+		}
+	}
 	return &info, nil
 }
 

session_test.go

@@ -87,6 +87,15 @@ func (s *S) TestPing(c *C) {
 	c.Assert(stats.ReceivedOps, Equals, 1)
 }
 
+func (s *S) TestPingSsl(c *C) {
+	c.Skip("this test requires the usage of the system provided certificates")
+	session, err := mgo.Dial("localhost:40001?ssl=true")
+	c.Assert(err, IsNil)
+	defer session.Close()
+
+	c.Assert(session.Ping(), IsNil)
+}
+
 func (s *S) TestDialIPAddress(c *C) {
 	session, err := mgo.Dial("127.0.0.1:40001")
 	c.Assert(err, IsNil)
@@ -135,6 +144,25 @@ func (s *S) TestURLParsing(c *C) {
 	}
 }
 
+func (s *S) TestURLSsl(c *C) {
+	type test struct {
+		url           string
+		nilDialServer bool
+	}
+
+	tests := []test{
+		{"localhost:40001", true},
+		{"localhost:40001?ssl=false", true},
+		{"localhost:40001?ssl=true", false},
+	}
+
+	for _, test := range tests {
+		info, err := mgo.ParseURL(test.url)
+		c.Assert(err, IsNil)
+		c.Assert(info.DialServer == nil, Equals, test.nilDialServer)
+	}
+}
+
 func (s *S) TestURLReadPreference(c *C) {
 	type test struct {
 		url  string