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moby--moby/volume/volume_windows.go
David Calavera a793564b25 Remove static errors from errors package.
Moving all strings to the errors package wasn't a good idea after all.

Our custom implementation of Go errors predates everything that's nice
and good about working with errors in Go. Take as an example what we
have to do to get an error message:

```go
func GetErrorMessage(err error) string {
	switch err.(type) {
	case errcode.Error:
		e, _ := err.(errcode.Error)
		return e.Message

	case errcode.ErrorCode:
		ec, _ := err.(errcode.ErrorCode)
		return ec.Message()

	default:
		return err.Error()
	}
}
```

This goes against every good practice for Go development. The language already provides a simple, intuitive and standard way to get error messages, that is calling the `Error()` method from an error. Reinventing the error interface is a mistake.

Our custom implementation also makes very hard to reason about errors, another nice thing about Go. I found several (>10) error declarations that we don't use anywhere. This is a clear sign about how little we know about the errors we return. I also found several error usages where the number of arguments was different than the parameters declared in the error, another clear example of how difficult is to reason about errors.

Moreover, our custom implementation didn't really make easier for people to return custom HTTP status code depending on the errors. Again, it's hard to reason about when to set custom codes and how. Take an example what we have to do to extract the message and status code from an error before returning a response from the API:

```go
	switch err.(type) {
	case errcode.ErrorCode:
		daError, _ := err.(errcode.ErrorCode)
		statusCode = daError.Descriptor().HTTPStatusCode
		errMsg = daError.Message()

	case errcode.Error:
		// For reference, if you're looking for a particular error
		// then you can do something like :
		//   import ( derr "github.com/docker/docker/errors" )
		//   if daError.ErrorCode() == derr.ErrorCodeNoSuchContainer { ... }

		daError, _ := err.(errcode.Error)
		statusCode = daError.ErrorCode().Descriptor().HTTPStatusCode
		errMsg = daError.Message

	default:
		// This part of will be removed once we've
		// converted everything over to use the errcode package

		// FIXME: this is brittle and should not be necessary.
		// If we need to differentiate between different possible error types,
		// we should create appropriate error types with clearly defined meaning
		errStr := strings.ToLower(err.Error())
		for keyword, status := range map[string]int{
			"not found":             http.StatusNotFound,
			"no such":               http.StatusNotFound,
			"bad parameter":         http.StatusBadRequest,
			"conflict":              http.StatusConflict,
			"impossible":            http.StatusNotAcceptable,
			"wrong login/password":  http.StatusUnauthorized,
			"hasn't been activated": http.StatusForbidden,
		} {
			if strings.Contains(errStr, keyword) {
				statusCode = status
				break
			}
		}
	}
```

You can notice two things in that code:

1. We have to explain how errors work, because our implementation goes against how easy to use Go errors are.
2. At no moment we arrived to remove that `switch` statement that was the original reason to use our custom implementation.

This change removes all our status errors from the errors package and puts them back in their specific contexts.
IT puts the messages back with their contexts. That way, we know right away when errors used and how to generate their messages.
It uses custom interfaces to reason about errors. Errors that need to response with a custom status code MUST implementent this simple interface:

```go
type errorWithStatus interface {
	HTTPErrorStatusCode() int
}
```

This interface is very straightforward to implement. It also preserves Go errors real behavior, getting the message is as simple as using the `Error()` method.

I included helper functions to generate errors that use custom status code in `errors/errors.go`.

By doing this, we remove the hard dependency we have eeverywhere to our custom errors package. Yes, you can use it as a helper to generate error, but it's still very easy to generate errors without it.

Please, read this fantastic blog post about errors in Go: http://dave.cheney.net/2014/12/24/inspecting-errors

Signed-off-by: David Calavera <david.calavera@gmail.com>
2016-02-26 15:49:09 -05:00

199 lines
6.5 KiB
Go

package volume
import (
"fmt"
"os"
"path/filepath"
"regexp"
"strings"
"github.com/Sirupsen/logrus"
)
// read-write modes
var rwModes = map[string]bool{
"rw": true,
}
// read-only modes
var roModes = map[string]bool{
"ro": true,
}
const (
// Spec should be in the format [source:]destination[:mode]
//
// Examples: c:\foo bar:d:rw
// c:\foo:d:\bar
// myname:d:
// d:\
//
// Explanation of this regex! Thanks @thaJeztah on IRC and gist for help. See
// https://gist.github.com/thaJeztah/6185659e4978789fb2b2. A good place to
// test is https://regex-golang.appspot.com/assets/html/index.html
//
// Useful link for referencing named capturing groups:
// http://stackoverflow.com/questions/20750843/using-named-matches-from-go-regex
//
// There are three match groups: source, destination and mode.
//
// RXHostDir is the first option of a source
RXHostDir = `[a-z]:\\(?:[^\\/:*?"<>|\r\n]+\\?)*`
// RXName is the second option of a source
RXName = `[^\\/:*?"<>|\r\n]+`
// RXReservedNames are reserved names not possible on Windows
RXReservedNames = `(con)|(prn)|(nul)|(aux)|(com[1-9])|(lpt[1-9])`
// RXSource is the combined possibilities for a source
RXSource = `((?P<source>((` + RXHostDir + `)|(` + RXName + `))):)?`
// Source. Can be either a host directory, a name, or omitted:
// HostDir:
// - Essentially using the folder solution from
// https://www.safaribooksonline.com/library/view/regular-expressions-cookbook/9781449327453/ch08s18.html
// but adding case insensitivity.
// - Must be an absolute path such as c:\path
// - Can include spaces such as `c:\program files`
// - And then followed by a colon which is not in the capture group
// - And can be optional
// Name:
// - Must not contain invalid NTFS filename characters (https://msdn.microsoft.com/en-us/library/windows/desktop/aa365247(v=vs.85).aspx)
// - And then followed by a colon which is not in the capture group
// - And can be optional
// RXDestination is the regex expression for the mount destination
RXDestination = `(?P<destination>([a-z]):((?:\\[^\\/:*?"<>\r\n]+)*\\?))`
// Destination (aka container path):
// - Variation on hostdir but can be a drive followed by colon as well
// - If a path, must be absolute. Can include spaces
// - Drive cannot be c: (explicitly checked in code, not RegEx)
//
// RXMode is the regex expression for the mode of the mount
RXMode = `(:(?P<mode>(?i)rw))?`
// Temporarily for TP4, disabling the use of ro as it's not supported yet
// in the platform. TODO Windows: `(:(?P<mode>(?i)ro|rw))?`
// mode (optional)
// - Hopefully self explanatory in comparison to above.
// - Colon is not in the capture group
//
)
// BackwardsCompatible decides whether this mount point can be
// used in old versions of Docker or not.
// Windows volumes are never backwards compatible.
func (m *MountPoint) BackwardsCompatible() bool {
return false
}
// ParseMountSpec validates the configuration of mount information is valid.
func ParseMountSpec(spec string, volumeDriver string) (*MountPoint, error) {
var specExp = regexp.MustCompile(`^` + RXSource + RXDestination + RXMode + `$`)
// Ensure in platform semantics for matching. The CLI will send in Unix semantics.
match := specExp.FindStringSubmatch(filepath.FromSlash(strings.ToLower(spec)))
// Must have something back
if len(match) == 0 {
return nil, errInvalidSpec(spec)
}
// Pull out the sub expressions from the named capture groups
matchgroups := make(map[string]string)
for i, name := range specExp.SubexpNames() {
matchgroups[name] = strings.ToLower(match[i])
}
mp := &MountPoint{
Source: matchgroups["source"],
Destination: matchgroups["destination"],
RW: true,
}
if strings.ToLower(matchgroups["mode"]) == "ro" {
mp.RW = false
}
// Volumes cannot include an explicitly supplied mode eg c:\path:rw
if mp.Source == "" && mp.Destination != "" && matchgroups["mode"] != "" {
return nil, errInvalidSpec(spec)
}
// Note: No need to check if destination is absolute as it must be by
// definition of matching the regex.
if filepath.VolumeName(mp.Destination) == mp.Destination {
// Ensure the destination path, if a drive letter, is not the c drive
if strings.ToLower(mp.Destination) == "c:" {
return nil, fmt.Errorf("Destination drive letter in '%s' cannot be c:", spec)
}
} else {
// So we know the destination is a path, not drive letter. Clean it up.
mp.Destination = filepath.Clean(mp.Destination)
// Ensure the destination path, if a path, is not the c root directory
if strings.ToLower(mp.Destination) == `c:\` {
return nil, fmt.Errorf(`Destination path in '%s' cannot be c:\`, spec)
}
}
// See if the source is a name instead of a host directory
if len(mp.Source) > 0 {
validName, err := IsVolumeNameValid(mp.Source)
if err != nil {
return nil, err
}
if validName {
// OK, so the source is a name.
mp.Name = mp.Source
mp.Source = ""
// Set the driver accordingly
mp.Driver = volumeDriver
if len(mp.Driver) == 0 {
mp.Driver = DefaultDriverName
}
} else {
// OK, so the source must be a host directory. Make sure it's clean.
mp.Source = filepath.Clean(mp.Source)
}
}
// Ensure the host path source, if supplied, exists and is a directory
if len(mp.Source) > 0 {
var fi os.FileInfo
var err error
if fi, err = os.Stat(mp.Source); err != nil {
return nil, fmt.Errorf("Source directory '%s' could not be found: %s", mp.Source, err)
}
if !fi.IsDir() {
return nil, fmt.Errorf("Source '%s' is not a directory", mp.Source)
}
}
logrus.Debugf("MP: Source '%s', Dest '%s', RW %t, Name '%s', Driver '%s'", mp.Source, mp.Destination, mp.RW, mp.Name, mp.Driver)
return mp, nil
}
// IsVolumeNameValid checks a volume name in a platform specific manner.
func IsVolumeNameValid(name string) (bool, error) {
nameExp := regexp.MustCompile(`^` + RXName + `$`)
if !nameExp.MatchString(name) {
return false, nil
}
nameExp = regexp.MustCompile(`^` + RXReservedNames + `$`)
if nameExp.MatchString(name) {
return false, fmt.Errorf("Volume name %q cannot be a reserved word for Windows filenames", name)
}
return true, nil
}
// ValidMountMode will make sure the mount mode is valid.
// returns if it's a valid mount mode or not.
func ValidMountMode(mode string) bool {
return roModes[strings.ToLower(mode)] || rwModes[strings.ToLower(mode)]
}
// ReadWrite tells you if a mode string is a valid read-write mode or not.
func ReadWrite(mode string) bool {
return rwModes[strings.ToLower(mode)]
}