Windows: Security warning based on server OS

Signed-off-by: John Howard <jhoward@microsoft.com>

httputils/httputils.go

@@ -1,8 +1,11 @@
 package httputils
 
 import (
+	"errors"
 	"fmt"
 	"net/http"
+	"regexp"
+	"strings"
 
 	"github.com/docker/docker/pkg/jsonmessage"
 )
@@ -25,3 +28,31 @@ func NewHTTPRequestError(msg string, res *http.Response) error {
 		Code:    res.StatusCode,
 	}
 }
+
+type ServerHeader struct {
+	App string // docker
+	Ver string // 1.8.0-dev
+	OS  string // windows or linux
+}
+
+// parseServerHeader extracts pieces from am HTTP server header
+// which is in the format "docker/version (os)" eg docker/1.8.0-dev (windows)
+func ParseServerHeader(hdr string) (*ServerHeader, error) {
+	re := regexp.MustCompile(`.*\((.+)\).*$`)
+	r := &ServerHeader{}
+	if matches := re.FindStringSubmatch(hdr); matches != nil {
+		r.OS = matches[1]
+		parts := strings.Split(hdr, "/")
+		if len(parts) != 2 {
+			return nil, errors.New("Bad header: '/' missing")
+		}
+		r.App = parts[0]
+		v := strings.Split(parts[1], " ")
+		if len(v) != 2 {
+			return nil, errors.New("Bad header: Expected single space")
+		}
+		r.Ver = v[0]
+		return r, nil
+	}
+	return nil, errors.New("Bad header: Failed regex match")
+}