add formatting support to print function

Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>

build/build.go

@@ -87,7 +87,12 @@ type Options struct {
 
 	// Linked marks this target as exclusively linked (not requested by the user).
 	Linked    bool
-	PrintFunc string
+	PrintFunc *PrintFunc
+}
+
+type PrintFunc struct {
+	Name   string
+	Format string
 }
 
 type Inputs struct {
@@ -1050,13 +1055,13 @@ func BuildWithResultHandler(ctx context.Context, drivers []DriverInfo, opt map[s
 							var isFallback bool
 							var origErr error
 							for {
-								if opt.PrintFunc != "" {
+								if opt.PrintFunc != nil {
 									if _, ok := req.FrontendOpt["frontend.caps"]; !ok {
 										req.FrontendOpt["frontend.caps"] = "moby.buildkit.frontend.subrequests+forward"
 									} else {
 										req.FrontendOpt["frontend.caps"] += ",moby.buildkit.frontend.subrequests+forward"
 									}
-									req.FrontendOpt["requestid"] = "frontend." + opt.PrintFunc
+									req.FrontendOpt["requestid"] = "frontend." + opt.PrintFunc.Name
 									if isFallback {
 										req.FrontendOpt["build-arg:BUILDKIT_SYNTAX"] = printFallbackImage
 									}
@@ -1086,7 +1091,7 @@ func BuildWithResultHandler(ctx context.Context, drivers []DriverInfo, opt map[s
 									}
 									return nil, err
 								}
-								if opt.PrintFunc != "" {
+								if opt.PrintFunc != nil {
 									printRes = res.Metadata
 								}
 								results.Set(resultKey(dp.driverIndex, k), res)
@@ -1686,7 +1691,7 @@ func tryNodeIdentifier(configDir string) (out string) {
 
 func noPrintFunc(opt map[string]Options) bool {
 	for _, v := range opt {
-		if v.PrintFunc != "" {
+		if v.PrintFunc != nil {
 			return false
 		}
 	}

commands/build.go

@@ -123,6 +123,11 @@ func runBuild(dockerCli command.Cli, in buildOptions) (err error) {
 		return err
 	}
 
+	printFunc, err := parsePrintFunc(in.printFunc)
+	if err != nil {
+		return err
+	}
+
 	opts := build.Options{
 		Inputs: build.Inputs{
 			ContextPath:    in.contextPath,
@@ -142,7 +147,7 @@ func runBuild(dockerCli command.Cli, in buildOptions) (err error) {
 		Tags:          in.tags,
 		Target:        in.target,
 		Ulimits:       in.ulimits,
-		PrintFunc:     in.printFunc,
+		PrintFunc:     printFunc,
 	}
 
 	platforms, err := platformutil.Parse(in.platforms)
@@ -310,7 +315,7 @@ func buildTargets(ctx context.Context, dockerCli command.Cli, opts map[string]bu
 	printWarnings(os.Stderr, printer.Warnings(), progressMode)
 
 	for k := range resp {
-		if opts[k].PrintFunc != "" {
+		if opts[k].PrintFunc != nil {
 			if err := printResult(opts[k].PrintFunc, resp[k].ExporterResponse); err != nil {
 				return "", nil, err
 			}
@@ -610,6 +615,34 @@ func parseContextNames(values []string) (map[string]build.NamedContext, error) {
 	return result, nil
 }
 
+func parsePrintFunc(str string) (*build.PrintFunc, error) {
+	if str == "" {
+		return nil, nil
+	}
+	csvReader := csv.NewReader(strings.NewReader(str))
+	fields, err := csvReader.Read()
+	if err != nil {
+		return nil, err
+	}
+	f := &build.PrintFunc{}
+	for _, field := range fields {
+		parts := strings.SplitN(field, "=", 2)
+		if len(parts) == 2 {
+			if parts[0] == "format" {
+				f.Format = parts[1]
+			} else {
+				return nil, errors.Errorf("invalid print field: %s", field)
+			}
+		} else {
+			if f.Name != "" {
+				return nil, errors.Errorf("invalid print value: %s", str)
+			}
+			f.Name = field
+		}
+	}
+	return f, nil
+}
+
 func writeMetadataFile(filename string, dt interface{}) error {
 	b, err := json.MarshalIndent(dt, "", "  ")
 	if err != nil {

commands/print.go

@@ -2,28 +2,25 @@ package commands
 
 import (
 	"fmt"
+	"io"
 	"log"
 	"os"
 
+	"github.com/docker/buildx/build"
+	"github.com/docker/docker/api/types/versions"
 	"github.com/moby/buildkit/frontend/subrequests"
 	"github.com/moby/buildkit/frontend/subrequests/outline"
 	"github.com/moby/buildkit/frontend/subrequests/targets"
 )
 
-func printResult(f string, res map[string]string) error {
+func printResult(f *build.PrintFunc, res map[string]string) error {
-	switch f {
+	switch f.Name {
 	case "outline":
-		if err := outline.PrintOutline([]byte(res["result.json"]), os.Stdout); err != nil {
+		return printValue(outline.PrintOutline, outline.SubrequestsOutlineDefinition.Version, f.Format, res)
-			return err
-		}
 	case "targets":
-		if err := targets.PrintTargets([]byte(res["result.json"]), os.Stdout); err != nil {
+		return printValue(targets.PrintTargets, targets.SubrequestsTargetsDefinition.Version, f.Format, res)
-			return err
-		}
 	case "subrequests.describe":
-		if err := subrequests.PrintDescribe([]byte(res["result.json"]), os.Stdout); err != nil {
+		return printValue(subrequests.PrintDescribe, subrequests.SubrequestsDescribeDefinition.Version, f.Format, res)
-			return err
-		}
 	default:
 		if dt, ok := res["result.txt"]; ok {
 			fmt.Print(dt)
@@ -33,3 +30,19 @@ func printResult(f string, res map[string]string) error {
 	}
 	return nil
 }
+
+type printFunc func([]byte, io.Writer) error
+
+func printValue(printer printFunc, version string, format string, res map[string]string) error {
+	if format == "json" {
+		fmt.Fprintln(os.Stdout, res["result.json"])
+		return nil
+	}
+
+	if res["version"] != "" && versions.LessThan(version, res["version"]) && res["result.txt"] != "" {
+		// structure is too new and we don't know how to print it
+		fmt.Fprint(os.Stdout, res["result.txt"])
+		return nil
+	}
+	return printer([]byte(res["result.json"]), os.Stdout)
+}