support setting warnings from frontends

api/services/control/control.proto

@@ -104,6 +104,7 @@ message StatusResponse {
 	repeated Vertex vertexes = 1;
 	repeated VertexStatus statuses = 2;
 	repeated VertexLog logs = 3;
+	repeated VertexWarning warnings = 4;
 }
 
 message Vertex {
@@ -134,6 +135,12 @@ message VertexLog {
 	bytes msg = 4;
 }
 
+message VertexWarning {
+	string vertex = 1 [(gogoproto.customtype) = "github.com/opencontainers/go-digest.Digest", (gogoproto.nullable) = false];
+	int64 level = 2;
+	bytes msg = 3;
+}
+
 message BytesMessage {
 	bytes data = 1;
 }

client/build.go

@@ -148,3 +148,8 @@ func (g *gatewayClientForBuild) ExecProcess(ctx context.Context, opts ...grpc.Ca
 	ctx = buildid.AppendToOutgoingContext(ctx, g.buildID)
 	return g.gateway.ExecProcess(ctx, opts...)
 }
+
+func (g *gatewayClientForBuild) Warn(ctx context.Context, in *gatewayapi.WarnRequest, opts ...grpc.CallOption) (*gatewayapi.WarnResponse, error) {
+	ctx = buildid.AppendToOutgoingContext(ctx, g.buildID)
+	return g.gateway.Warn(ctx, in)
+}

client/build_test.go

@@ -26,6 +26,7 @@ import (
 	utilsystem "github.com/moby/buildkit/util/system"
 	"github.com/moby/buildkit/util/testutil/echoserver"
 	"github.com/moby/buildkit/util/testutil/integration"
+	digest "github.com/opencontainers/go-digest"
 	"github.com/pkg/errors"
 	"github.com/stretchr/testify/require"
 	"golang.org/x/crypto/ssh/agent"
@@ -51,6 +52,7 @@ func TestClientGatewayIntegration(t *testing.T) {
 		testClientGatewaySlowCacheExecError,
 		testClientGatewayExecFileActionError,
 		testClientGatewayContainerExtraHosts,
+		testWarnings,
 	}, integration.WithMirroredImages(integration.OfficialImages("busybox:latest")))
 
 	integration.Run(t, []integration.Test{
@@ -151,6 +153,90 @@ func testClientGatewaySolve(t *testing.T, sb integration.Sandbox) {
 	checkAllReleasable(t, c, sb, true)
 }
 
+func testWarnings(t *testing.T, sb integration.Sandbox) {
+	requiresLinux(t)
+
+	ctx := sb.Context()
+
+	c, err := New(ctx, sb.Address())
+	require.NoError(t, err)
+	defer c.Close()
+
+	product := "buildkit_test"
+
+	b := func(ctx context.Context, c client.Client) (*client.Result, error) {
+		st := llb.Scratch().File(llb.Mkfile("/dummy", 0600, []byte("foo")))
+
+		def, err := st.Marshal(ctx)
+		if err != nil {
+			return nil, errors.Wrap(err, "failed to marshal state")
+		}
+
+		dgst, _, _, _, err := st.Output().Vertex(ctx, def.Constraints).Marshal(ctx, def.Constraints)
+		if err != nil {
+			return nil, err
+		}
+
+		r, err := c.Solve(ctx, client.SolveRequest{
+			Definition: def.ToPB(),
+		})
+		if err != nil {
+			return nil, errors.Wrap(err, "failed to solve")
+		}
+
+		require.NoError(t, c.Warn(ctx, dgst, "this is warning"))
+		return r, nil
+	}
+
+	status := make(chan *SolveStatus)
+	statusDone := make(chan struct{})
+	done := make(chan struct{})
+
+	var warnings []*VertexWarning
+	vertexes := map[digest.Digest]struct{}{}
+
+	go func() {
+		defer close(statusDone)
+		for {
+			select {
+			case st, ok := <-status:
+				if !ok {
+					return
+				}
+				for _, s := range st.Vertexes {
+					vertexes[s.Digest] = struct{}{}
+				}
+				warnings = append(warnings, st.Warnings...)
+			case <-done:
+				return
+			}
+		}
+	}()
+
+	_, err = c.Build(ctx, SolveOpt{}, product, b, status)
+	require.NoError(t, err)
+
+	select {
+	case <-statusDone:
+	case <-time.After(10 * time.Second):
+		close(done)
+	}
+
+	<-statusDone
+
+	require.Equal(t, 1, len(vertexes))
+	require.Equal(t, 1, len(warnings))
+
+	w := warnings[0]
+
+	require.Equal(t, "this is warning", string(w.Message))
+	require.Equal(t, 1, w.Level)
+	_, ok := vertexes[w.Vertex]
+	require.True(t, ok)
+
+	checkAllReleasable(t, c, sb, true)
+}
+
 func testClientGatewayFailedSolve(t *testing.T, sb integration.Sandbox) {
 	requiresLinux(t)
 

client/graph.go

@@ -34,10 +34,17 @@ type VertexLog struct {
 	Timestamp time.Time
 }
 
+type VertexWarning struct {
+	Vertex  digest.Digest
+	Level   int
+	Message []byte
+}
+
 type SolveStatus struct {
 	Vertexes []*Vertex
 	Statuses []*VertexStatus
 	Logs     []*VertexLog
+	Warnings []*VertexWarning
 }
 
 type SolveResponse struct {

client/llb/marshal.go

@@ -12,9 +12,10 @@ import (
 // Definition is the LLB definition structure with per-vertex metadata entries
 // Corresponds to the Definition structure defined in solver/pb.Definition.
 type Definition struct {
-	Def      [][]byte
-	Metadata map[digest.Digest]pb.OpMetadata
-	Source   *pb.Source
+	Def         [][]byte
+	Metadata    map[digest.Digest]pb.OpMetadata
+	Source      *pb.Source
+	Constraints *Constraints
 }
 
 func (def *Definition) ToPB() *pb.Definition {

client/llb/state.go

@@ -29,6 +29,18 @@ type Vertex interface {
 	Inputs() []Output
 }
 
+func NewConstraints(co ...ConstraintsOpt) *Constraints {
+	defaultPlatform := platforms.Normalize(platforms.DefaultSpec())
+	c := &Constraints{
+		Platform:      &defaultPlatform,
+		LocalUniqueID: identity.NewID(),
+	}
+	for _, o := range co {
+		o.SetConstraintsOption(c)
+	}
+	return c
+}
+
 func NewState(o Output) State {
 	s := State{
 		out: o,
@@ -112,18 +124,12 @@ func (s State) SetMarshalDefaults(co ...ConstraintsOpt) State {
 }
 
 func (s State) Marshal(ctx context.Context, co ...ConstraintsOpt) (*Definition, error) {
+	c := NewConstraints(append(s.opts, co...)...)
 	def := &Definition{
-		Metadata: make(map[digest.Digest]pb.OpMetadata, 0),
+		Metadata:    make(map[digest.Digest]pb.OpMetadata, 0),
+		Constraints: c,
 	}
 
-	defaultPlatform := platforms.Normalize(platforms.DefaultSpec())
-	c := &Constraints{
-		Platform:      &defaultPlatform,
-		LocalUniqueID: identity.NewID(),
-	}
-	for _, o := range append(s.opts, co...) {
-		o.SetConstraintsOption(c)
-	}
 	if s.Output() == nil || s.Output().Vertex(ctx, c) == nil {
 		return def, nil
 	}

client/solve.go

@@ -292,6 +292,13 @@ func (c *Client) solve(ctx context.Context, def *llb.Definition, runGateway runG
 					Timestamp: v.Timestamp,
 				})
 			}
+			for _, v := range resp.Warnings {
+				s.Warnings = append(s.Warnings, &VertexWarning{
+					Vertex:  v.Vertex,
+					Level:   int(v.Level),
+					Message: v.Msg,
+				})
+			}
 			if statusChan != nil {
 				statusChan <- &s
 			}

control/control.go

@@ -376,6 +376,13 @@ func (c *Controller) Status(req *controlapi.StatusRequest, stream controlapi.Con
 						break
 					}
 				}
+				for _, v := range ss.Warnings {
+					sr.Warnings = append(sr.Warnings, &controlapi.VertexWarning{
+						Vertex: v.Vertex,
+						Level:  int64(v.Level),
+						Msg:    v.Message,
+					})
+				}
 				if err := stream.SendMsg(&sr); err != nil {
 					return err
 				}

control/gateway/gateway.go

@@ -176,3 +176,11 @@ func (gwf *GatewayForwarder) ExecProcess(srv gwapi.LLBBridge_ExecProcessServer)
 	}
 	return fwd.ExecProcess(srv)
 }
+
+func (gwf *GatewayForwarder) Warn(ctx context.Context, req *gwapi.WarnRequest) (*gwapi.WarnResponse, error) {
+	fwd, err := gwf.lookupForwarder(ctx)
+	if err != nil {
+		return nil, errors.Wrap(err, "forwarding Warn")
+	}
+	return fwd.Warn(ctx, req)
+}

frontend/frontend.go

@@ -17,6 +17,7 @@ type Frontend interface {
 type FrontendLLBBridge interface {
 	Solve(ctx context.Context, req SolveRequest, sid string) (*Result, error)
 	ResolveImageConfig(ctx context.Context, ref string, opt llb.ResolveImageConfigOpt) (digest.Digest, []byte, error)
+	Warn(ctx context.Context, dgst digest.Digest, level int, msg string) error
 }
 
 type SolveRequest = gw.SolveRequest

frontend/gateway/client/client.go

@@ -18,6 +18,7 @@ type Client interface {
 	BuildOpts() BuildOpts
 	Inputs(ctx context.Context) (map[string]llb.State, error)
 	NewContainer(ctx context.Context, req NewContainerRequest) (Container, error)
+	Warn(ctx context.Context, dgst digest.Digest, msg string) error
 }
 
 // NewContainerRequest encapsulates the requirements for a client to define a

frontend/gateway/forwarder/forward.go

@@ -19,6 +19,7 @@ import (
 	opspb "github.com/moby/buildkit/solver/pb"
 	"github.com/moby/buildkit/util/apicaps"
 	"github.com/moby/buildkit/worker"
+	digest "github.com/opencontainers/go-digest"
 	"github.com/pkg/errors"
 	fstypes "github.com/tonistiigi/fsutil/types"
 	"golang.org/x/sync/errgroup"
@@ -216,6 +217,10 @@ func (c *bridgeClient) discard(err error) {
 	}
 }
 
+func (c *bridgeClient) Warn(ctx context.Context, dgst digest.Digest, msg string) error {
+	return c.FrontendLLBBridge.Warn(ctx, dgst, 1, msg)
+}
+
 func (c *bridgeClient) NewContainer(ctx context.Context, req client.NewContainerRequest) (client.Container, error) {
 	ctrReq := gateway.NewContainerRequest{
 		ContainerID: identity.NewID(),

frontend/gateway/gateway.go

@@ -993,6 +993,14 @@ func (lbf *llbBridgeForwarder) ReleaseContainer(ctx context.Context, in *pb.Rele
 	return &pb.ReleaseContainerResponse{}, stack.Enable(err)
 }
 
+func (lbf *llbBridgeForwarder) Warn(ctx context.Context, in *pb.WarnRequest) (*pb.WarnResponse, error) {
+	err := lbf.llbBridge.Warn(ctx, in.Digest, int(in.Level), string(in.Message))
+	if err != nil {
+		return nil, err
+	}
+	return &pb.WarnResponse{}, nil
+}
+
 type processIO struct {
 	id       string
 	mu       sync.Mutex

frontend/gateway/grpcclient/client.go

@@ -298,6 +298,15 @@ func (c *grpcClient) requestForRef(ref client.Reference) (*pb.SolveRequest, erro
 	return req, nil
 }
 
+func (c *grpcClient) Warn(ctx context.Context, dgst digest.Digest, msg string) error {
+	_, err := c.client.Warn(ctx, &pb.WarnRequest{
+		Digest:  dgst,
+		Level:   1,
+		Message: []byte(msg),
+	})
+	return err
+}
+
 func (c *grpcClient) Solve(ctx context.Context, creq client.SolveRequest) (res *client.Result, err error) {
 	if creq.Definition != nil {
 		for _, md := range creq.Definition.Metadata {

frontend/gateway/pb/caps.go

@@ -51,6 +51,9 @@ const (
 	// results. This is generally used by the client to return and handle solve
 	// errors.
 	CapGatewayEvaluateSolve apicaps.CapID = "gateway.solve.evaluate"
+
+	// CapGatewayWarnings is the capability to log warnings from frontend
+	CapGatewayWarnings apicaps.CapID = "gateway.warnings"
 )
 
 func init() {
@@ -180,4 +183,11 @@ func init() {
 		Enabled: true,
 		Status:  apicaps.CapStatusExperimental,
 	})
+
+	Caps.Init(apicaps.Cap{
+		ID:      CapGatewayWarnings,
+		Name:    "logging warnings",
+		Enabled: true,
+		Status:  apicaps.CapStatusExperimental,
+	})
 }