ContainerWait on remove: don't stuck on rm fail

Currently, if a container removal has failed for some reason,
any client waiting for removal (e.g. `docker run --rm`) is
stuck, waiting for removal to succeed while it has failed already.
For more details and the reproducer, please check
https://github.com/moby/moby/issues/34945

This commit addresses that by allowing `ContainerWait()` with
`container.WaitCondition == "removed"` argument to return an
error in case of removal failure. The `ContainerWaitOKBody`
stucture returned to a client is amended with a pointer to `struct Error`,
containing an error message string, and the `Client.ContainerWait()`
is modified to return the error, if any, to the client.

Note that this feature is only available for API version >= 1.34.
In order for the old clients to be unstuck, we just close the connection
without writing anything -- this causes client's error.

Now, docker-cli would need a separate commit to bump the API to 1.34
and to show an error returned, if any.

[v2: recreate the waitRemove channel after closing]
[v3: document; keep legacy behavior for older clients]
[v4: convert Error from string to pointer to a struct]
[v5: don't emulate old behavior, send empty response in error case]
[v6: rename legacy* vars to include version suffix]

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

api/server/router/container/container_routes.go

@@ -280,11 +280,12 @@ func (s *containerRouter) postContainersWait(ctx context.Context, w http.Respons
 	// Behavior changed in version 1.30 to handle wait condition and to
 	// return headers immediately.
 	version := httputils.VersionFromContext(ctx)
-	legacyBehavior := versions.LessThan(version, "1.30")
+	legacyBehaviorPre130 := versions.LessThan(version, "1.30")
+	legacyRemovalWaitPre134 := false
 
 	// The wait condition defaults to "not-running".
 	waitCondition := containerpkg.WaitConditionNotRunning
-	if !legacyBehavior {
+	if !legacyBehaviorPre130 {
 		if err := httputils.ParseForm(r); err != nil {
 			return err
 		}
@@ -293,6 +294,7 @@ func (s *containerRouter) postContainersWait(ctx context.Context, w http.Respons
 			waitCondition = containerpkg.WaitConditionNextExit
 		case container.WaitConditionRemoved:
 			waitCondition = containerpkg.WaitConditionRemoved
+			legacyRemovalWaitPre134 = versions.LessThan(version, "1.34")
 		}
 	}
 
@@ -306,7 +308,7 @@ func (s *containerRouter) postContainersWait(ctx context.Context, w http.Respons
 
 	w.Header().Set("Content-Type", "application/json")
 
-	if !legacyBehavior {
+	if !legacyBehaviorPre130 {
 		// Write response header immediately.
 		w.WriteHeader(http.StatusOK)
 		if flusher, ok := w.(http.Flusher); ok {
@@ -317,8 +319,22 @@ func (s *containerRouter) postContainersWait(ctx context.Context, w http.Respons
 	// Block on the result of the wait operation.
 	status := <-waitC
 
+	// With API < 1.34, wait on WaitConditionRemoved did not return
+	// in case container removal failed. The only way to report an
+	// error back to the client is to not write anything (i.e. send
+	// an empty response which will be treated as an error).
+	if legacyRemovalWaitPre134 && status.Err() != nil {
+		return nil
+	}
+
+	var waitError *container.ContainerWaitOKBodyError
+	if status.Err() != nil {
+		waitError = &container.ContainerWaitOKBodyError{Message: status.Err().Error()}
+	}
+
 	return json.NewEncoder(w).Encode(&container.ContainerWaitOKBody{
 		StatusCode: int64(status.ExitCode()),
+		Error:      waitError,
 	})
 }
 

api/swagger.yaml

@@ -5723,6 +5723,13 @@ paths:
                 description: "Exit code of the container"
                 type: "integer"
                 x-nullable: false
+              Error:
+                description: "container waiting error, if any"
+                type: "object"
+                properties:
+                  Message:
+                    description: "Details of an error"
+                    type: "string"
         404:
           description: "no such container"
           schema:

api/types/container/container_wait.go

@@ -7,10 +7,22 @@ package container
 // See hack/generate-swagger-api.sh
 // ----------------------------------------------------------------------------
 
+// ContainerWaitOKBodyError container waiting error, if any
+// swagger:model ContainerWaitOKBodyError
+type ContainerWaitOKBodyError struct {
+
+	// Details of an error
+	Message string `json:"Message,omitempty"`
+}
+
 // ContainerWaitOKBody container wait o k body
 // swagger:model ContainerWaitOKBody
 type ContainerWaitOKBody struct {
 
+	// error
+	// Required: true
+	Error *ContainerWaitOKBodyError `json:"Error"`
+
 	// Exit code of the container
 	// Required: true
 	StatusCode int64 `json:"StatusCode"`

container/state.go

@@ -29,7 +29,7 @@ type State struct {
 	Dead              bool
 	Pid               int
 	ExitCodeValue     int    `json:"ExitCode"`
-	ErrorMsg          string `json:"Error"` // contains last known error when starting the container
+	ErrorMsg          string `json:"Error"` // contains last known error during container start or remove
 	StartedAt         time.Time
 	FinishedAt        time.Time
 	Health            *Health
@@ -319,7 +319,10 @@ func (s *State) SetRestarting(exitStatus *ExitStatus) {
 // know the error that occurred when container transits to another state
 // when inspecting it
 func (s *State) SetError(err error) {
-	s.ErrorMsg = err.Error()
+	s.ErrorMsg = ""
+	if err != nil {
+		s.ErrorMsg = err.Error()
+	}
 }
 
 // IsPaused returns whether the container is paused or not.
@@ -385,8 +388,18 @@ func (s *State) IsDead() bool {
 // closes the internal waitRemove channel to unblock callers waiting for a
 // container to be removed.
 func (s *State) SetRemoved() {
+	s.SetRemovalError(nil)
+}
+
+// SetRemovalError is to be called in case a container remove failed.
+// It sets an error and closes the internal waitRemove channel to unblock
+// callers waiting for the container to be removed.
+func (s *State) SetRemovalError(err error) {
+	s.SetError(err)
 	s.Lock()
 	close(s.waitRemove) // Unblock those waiting on remove.
+	// Recreate the channel so next ContainerWait will work
+	s.waitRemove = make(chan struct{})
 	s.Unlock()
 }
 

daemon/delete.go

@@ -120,12 +120,16 @@ func (daemon *Daemon) cleanupContainer(container *container.Container, forceRemo
 		metadata, err := daemon.stores[container.OS].layerStore.ReleaseRWLayer(container.RWLayer)
 		layer.LogReleaseMetadata(metadata)
 		if err != nil && err != layer.ErrMountDoesNotExist && !os.IsNotExist(errors.Cause(err)) {
-			return errors.Wrapf(err, "driver %q failed to remove root filesystem for %s", daemon.GraphDriverName(container.OS), container.ID)
+			e := errors.Wrapf(err, "driver %q failed to remove root filesystem for %s", daemon.GraphDriverName(container.OS), container.ID)
+			container.SetRemovalError(e)
+			return e
 		}
 	}
 
 	if err := system.EnsureRemoveAll(container.Root); err != nil {
-		return errors.Wrapf(err, "unable to remove filesystem for %s", container.ID)
+		e := errors.Wrapf(err, "unable to remove filesystem for %s", container.ID)
+		container.SetRemovalError(e)
+		return e
 	}
 
 	linkNames := daemon.linkIndex.delete(container)

docs/api/version-history.md

@@ -17,6 +17,13 @@ keywords: "API, Docker, rcli, REST, documentation"
 
 [Docker Engine API v1.34](https://docs.docker.com/engine/api/v1.34/) documentation
 
+* `POST /containers/(name)/wait?condition=removed` now also also returns
+  in case of container removal failure. A pointer to a structure named
+  `Error` added to the response JSON in order to indicate a failure.
+  If `Error` is `null`, container removal has succeeded, otherwise
+  the test of an error message indicating why container removal has failed
+  is available from `Error.Message` field.
+
 ## v1.33 API changes
 
 [Docker Engine API v1.33](https://docs.docker.com/engine/api/v1.33/) documentation