podman create/run need to load information from the image

We should be pulling information out of the image to set the
defaults to use when setting up the container.

Signed-off-by: Daniel J Walsh <dwalsh@redhat.com>

Closes: #110
Approved by: mheon

pkg/chrootuser/user.go

@@ -0,0 +1,71 @@
+package chrootuser
+
+import (
+	"os/user"
+	"strconv"
+	"strings"
+
+	"github.com/pkg/errors"
+)
+
+// GetUser will return the uid, gid of the user specified in the userspec
+// it will use the /etc/password and /etc/shadow files inside of the rootdir
+// to return this information.
+// userspace format [user | user:group | uid | uid:gid | user:gid | uid:group ]
+func GetUser(rootdir, userspec string) (uint32, uint32, error) {
+	var gid64 uint64
+	var gerr error = user.UnknownGroupError("error looking up group")
+
+	spec := strings.SplitN(userspec, ":", 2)
+	userspec = spec[0]
+	groupspec := ""
+	if userspec == "" {
+		return 0, 0, nil
+	}
+	if len(spec) > 1 {
+		groupspec = spec[1]
+	}
+
+	uid64, uerr := strconv.ParseUint(userspec, 10, 32)
+	if uerr == nil && groupspec == "" {
+		// We parsed the user name as a number, and there's no group
+		// component, so try to look up the primary GID of the user who
+		// has this UID.
+		var name string
+		name, gid64, gerr = lookupGroupForUIDInContainer(rootdir, uid64)
+		if gerr == nil {
+			userspec = name
+		} else {
+			// Leave userspec alone, but swallow the error and just
+			// use GID 0.
+			gid64 = 0
+			gerr = nil
+		}
+	}
+	if uerr != nil {
+		// The user ID couldn't be parsed as a number, so try to look
+		// up the user's UID and primary GID.
+		uid64, gid64, uerr = lookupUserInContainer(rootdir, userspec)
+		gerr = uerr
+	}
+
+	if groupspec != "" {
+		// We have a group name or number, so parse it.
+		gid64, gerr = strconv.ParseUint(groupspec, 10, 32)
+		if gerr != nil {
+			// The group couldn't be parsed as a number, so look up
+			// the group's GID.
+			gid64, gerr = lookupGroupInContainer(rootdir, groupspec)
+		}
+	}
+
+	if uerr == nil && gerr == nil {
+		return uint32(uid64), uint32(gid64), nil
+	}
+
+	err := errors.Wrapf(uerr, "error determining run uid")
+	if uerr == nil {
+		err = errors.Wrapf(gerr, "error determining run gid")
+	}
+	return 0, 0, err
+}