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a793564b25
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>
122 lines
2.7 KiB
Go
122 lines
2.7 KiB
Go
package exec
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import (
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"fmt"
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"sync"
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"time"
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"github.com/docker/docker/daemon/execdriver"
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"github.com/docker/docker/pkg/stringid"
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"github.com/docker/docker/runconfig"
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)
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// Config holds the configurations for execs. The Daemon keeps
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// track of both running and finished execs so that they can be
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// examined both during and after completion.
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type Config struct {
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sync.Mutex
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*runconfig.StreamConfig
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ID string
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Running bool
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ExitCode *int
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ProcessConfig *execdriver.ProcessConfig
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OpenStdin bool
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OpenStderr bool
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OpenStdout bool
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CanRemove bool
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ContainerID string
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DetachKeys []byte
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// waitStart will be closed immediately after the exec is really started.
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waitStart chan struct{}
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}
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// NewConfig initializes the a new exec configuration
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func NewConfig() *Config {
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return &Config{
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ID: stringid.GenerateNonCryptoID(),
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StreamConfig: runconfig.NewStreamConfig(),
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waitStart: make(chan struct{}),
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}
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}
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// Store keeps track of the exec configurations.
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type Store struct {
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commands map[string]*Config
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sync.RWMutex
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}
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// NewStore initializes a new exec store.
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func NewStore() *Store {
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return &Store{commands: make(map[string]*Config, 0)}
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}
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// Commands returns the exec configurations in the store.
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func (e *Store) Commands() map[string]*Config {
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e.RLock()
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commands := make(map[string]*Config, len(e.commands))
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for id, config := range e.commands {
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commands[id] = config
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}
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e.RUnlock()
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return commands
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}
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// Add adds a new exec configuration to the store.
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func (e *Store) Add(id string, Config *Config) {
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e.Lock()
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e.commands[id] = Config
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e.Unlock()
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}
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// Get returns an exec configuration by its id.
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func (e *Store) Get(id string) *Config {
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e.RLock()
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res := e.commands[id]
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e.RUnlock()
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return res
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}
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// Delete removes an exec configuration from the store.
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func (e *Store) Delete(id string) {
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e.Lock()
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delete(e.commands, id)
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e.Unlock()
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}
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// List returns the list of exec ids in the store.
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func (e *Store) List() []string {
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var IDs []string
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e.RLock()
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for id := range e.commands {
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IDs = append(IDs, id)
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}
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e.RUnlock()
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return IDs
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}
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// Wait waits until the exec process finishes or there is an error in the error channel.
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func (c *Config) Wait(cErr chan error) error {
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// Exec should not return until the process is actually running
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select {
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case <-c.waitStart:
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case err := <-cErr:
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return err
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}
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return nil
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}
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// Close closes the wait channel for the progress.
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func (c *Config) Close() {
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close(c.waitStart)
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}
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// Resize changes the size of the terminal for the exec process.
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func (c *Config) Resize(h, w int) error {
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select {
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case <-c.waitStart:
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case <-time.After(time.Second):
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return fmt.Errorf("Exec %s is not running, so it can not be resized.", c.ID)
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}
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return c.ProcessConfig.Terminal.Resize(h, w)
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}
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