build: change build handler to evaluate instead of onresult

This changes the build handler to customize the behavior of evaluate
rather than onresult and also simplifies the `ResultHandle`. The
`ResultHandle` is now only valid within the gateway callback and can be
used to start containers from the handler.

`Evaluate` now executes inside of the gateway callback rather than
having a separate implementation that executes or re-invokes the build.
This keeps the gateway callback session open until the debugger has
returned.

The `ErrReload` for monitor has now been moved into the `build` package
and been renamed to `ErrRestart`. This is because it restarts the build
so the name makes a bit more sense. The actual use of this functionality
is still tied to the monitor reload.

Signed-off-by: Jonathan A. Sternberg <[email protected]>

Author: jsternberg

build/build.go

@@ -59,6 +59,8 @@ const (
 	printLintFallbackImage = "docker/dockerfile:1.8.1@sha256:e87caa74dcb7d46cd820352bfea12591f3dba3ddc4285e19c7dcd13359f7cefd"
 )
 
+var ErrRestart = errors.New("build: restart")
+
 type Options struct {
 	Inputs Inputs
 
@@ -312,7 +314,7 @@ func toRepoOnly(in string) (string, error) {
 }
 
 type Handler struct {
-	OnResult func(driverIdx int, rCtx *ResultHandle)
+	Evaluate func(ctx context.Context, c gateway.Client, res *gateway.Result) error
 }
 
 func Build(ctx context.Context, nodes []builder.Node, opts map[string]Options, docker *dockerutil.Client, cfg *confutil.Config, w progress.Writer) (resp map[string]*client.SolveResponse, err error) {
@@ -479,9 +481,14 @@ func BuildWithResultHandler(ctx context.Context, nodes []builder.Node, opts map[
 					ch, done := progress.NewChannel(pw)
 					defer func() { <-done }()
 
-					cc := c
-					var callRes map[string][]byte
-					buildFunc := func(ctx context.Context, c gateway.Client) (*gateway.Result, error) {
+					var (
+						callRes     map[string][]byte
+						frontendErr error
+					)
+					buildFunc := func(ctx context.Context, c gateway.Client) (_ *gateway.Result, retErr error) {
+						// Capture the error from this build function.
+						defer catchFrontendError(&retErr, &frontendErr)
+
 						if opt.CallFunc != nil {
 							if _, ok := req.FrontendOpt["frontend.caps"]; !ok {
 								req.FrontendOpt["frontend.caps"] = "moby.buildkit.frontend.subrequests+forward"
@@ -504,24 +511,25 @@ func BuildWithResultHandler(ctx context.Context, nodes []builder.Node, opts map[
 						results.Set(rKey, res)
 
 						if children := childTargets[rKey]; len(children) > 0 {
-							if err := waitForChildren(ctx, res, results, children); err != nil {
+							if err := waitForChildren(ctx, bh, c, res, results, children); err != nil {
+								return nil, err
+							}
+						} else if bh != nil && bh.Evaluate != nil {
+							if err := bh.Evaluate(ctx, c, res); err != nil {
 								return nil, err
 							}
 						}
 						return res, nil
 					}
+
 					buildRef := fmt.Sprintf("%s/%s/%s", node.Builder, node.Name, so.Ref)
 
-					var rr *client.SolveResponse
-					if bh != nil && bh.OnResult != nil {
-						var resultHandle *ResultHandle
-						resultHandle, rr, err = NewResultHandle(ctx, cc, *so, "buildx", buildFunc, ch)
-						bh.OnResult(dp.driverIndex, resultHandle)
-					} else {
-						span, ctx := tracing.StartSpan(ctx, "build")
-						rr, err = c.Build(ctx, *so, "buildx", buildFunc, ch)
-						tracing.FinishWithError(span, err)
+					span, ctx := tracing.StartSpan(ctx, "build")
+					rr, err := c.Build(ctx, *so, "buildx", buildFunc, ch)
+					if errors.Is(frontendErr, ErrRestart) {
+						err = ErrRestart
 					}
+					tracing.FinishWithError(span, err)
 
 					if !so.Internal && desktop.BuildBackendEnabled() && node.Driver.HistoryAPISupported(ctx) {
 						if err != nil {
@@ -1191,7 +1199,7 @@ func solve(ctx context.Context, c gateway.Client, req gateway.SolveRequest) (*ga
 	return res, nil
 }
 
-func waitForChildren(ctx context.Context, res *gateway.Result, results *waitmap.Map, children []string) error {
+func waitForChildren(ctx context.Context, bh *Handler, c gateway.Client, res *gateway.Result, results *waitmap.Map, children []string) error {
 	// wait for the child targets to register their LLB before evaluating
 	_, err := results.Get(ctx, children...)
 	if err != nil {
@@ -1200,6 +1208,9 @@ func waitForChildren(ctx context.Context, res *gateway.Result, results *waitmap.
 	// we need to wait until the child targets have completed before we can release
 	eg, ctx := errgroup.WithContext(ctx)
 	eg.Go(func() error {
+		if bh != nil && bh.Evaluate != nil {
+			return bh.Evaluate(ctx, c, res)
+		}
 		return res.EachRef(func(ref gateway.Reference) error {
 			return ref.Evaluate(ctx)
 		})
@@ -1210,3 +1221,12 @@ func waitForChildren(ctx context.Context, res *gateway.Result, results *waitmap.
 	})
 	return eg.Wait()
 }
+
+func catchFrontendError(retErr, frontendErr *error) {
+	*frontendErr = *retErr
+	if errors.Is(*retErr, ErrRestart) {
+		// Overwrite the sentinel error with a more user friendly message.
+		// This gets stored only in the return error.
+		*retErr = errors.New("build restarted by client")
+	}
+}

build/invoke.go

@@ -56,26 +56,18 @@ type Container struct {
 func NewContainer(ctx context.Context, resultCtx *ResultHandle, cfg *InvokeConfig) (*Container, error) {
 	mainCtx := ctx
 
-	ctrCh := make(chan *Container)
-	errCh := make(chan error)
+	ctrCh := make(chan *Container, 1)
+	errCh := make(chan error, 1)
 	go func() {
-		err := resultCtx.build(func(ctx context.Context, c gateway.Client) (*gateway.Result, error) {
-			ctx, cancel := context.WithCancelCause(ctx)
-			go func() {
-				<-mainCtx.Done()
-				cancel(errors.WithStack(context.Canceled))
-			}()
-
-			containerCfg, err := resultCtx.getContainerConfig(cfg)
-			if err != nil {
-				return nil, err
-			}
+		err := func() error {
 			containerCtx, containerCancel := context.WithCancelCause(ctx)
 			defer containerCancel(errors.WithStack(context.Canceled))
-			bkContainer, err := c.NewContainer(containerCtx, containerCfg)
+
+			bkContainer, err := resultCtx.NewContainer(containerCtx, cfg)
 			if err != nil {
-				return nil, err
+				return err
 			}
+
 			releaseCh := make(chan struct{})
 			container := &Container{
 				containerCancel: containerCancel,
@@ -92,8 +84,8 @@ func NewContainer(ctx context.Context, resultCtx *ResultHandle, cfg *InvokeConfi
 			ctrCh <- container
 			<-container.releaseCh
 
-			return nil, bkContainer.Release(ctx)
-		})
+			return bkContainer.Release(ctx)
+		}()
 		if err != nil {
 			errCh <- err
 		}