build: split buildflags package

Planned to be imported by nerdctl in future.

Signed-off-by: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>

util/buildflags/output.go

@@ -0,0 +1,115 @@
+package buildflags
+
+import (
+	"encoding/csv"
+	"io"
+	"os"
+	"strings"
+
+	"github.com/containerd/console"
+	"github.com/moby/buildkit/client"
+	"github.com/pkg/errors"
+)
+
+func ParseOutputs(inp []string) ([]client.ExportEntry, error) {
+	var outs []client.ExportEntry
+	if len(inp) == 0 {
+		return nil, nil
+	}
+	for _, s := range inp {
+		csvReader := csv.NewReader(strings.NewReader(s))
+		fields, err := csvReader.Read()
+		if err != nil {
+			return nil, err
+		}
+
+		out := client.ExportEntry{
+			Attrs: map[string]string{},
+		}
+		if len(fields) == 1 && fields[0] == s && !strings.HasPrefix(s, "type=") {
+			if s != "-" {
+				outs = append(outs, client.ExportEntry{
+					Type:      client.ExporterLocal,
+					OutputDir: s,
+				})
+				continue
+			}
+			out = client.ExportEntry{
+				Type: client.ExporterTar,
+				Attrs: map[string]string{
+					"dest": s,
+				},
+			}
+		}
+
+		if out.Type == "" {
+			for _, field := range fields {
+				parts := strings.SplitN(field, "=", 2)
+				if len(parts) != 2 {
+					return nil, errors.Errorf("invalid value %s", field)
+				}
+				key := strings.TrimSpace(strings.ToLower(parts[0]))
+				value := parts[1]
+				switch key {
+				case "type":
+					out.Type = value
+				default:
+					out.Attrs[key] = value
+				}
+			}
+		}
+		if out.Type == "" {
+			return nil, errors.Errorf("type is required for output")
+		}
+
+		// handle client side
+		switch out.Type {
+		case client.ExporterLocal:
+			dest, ok := out.Attrs["dest"]
+			if !ok {
+				return nil, errors.Errorf("dest is required for local output")
+			}
+			out.OutputDir = dest
+			delete(out.Attrs, "dest")
+		case client.ExporterOCI, client.ExporterDocker, client.ExporterTar:
+			dest, ok := out.Attrs["dest"]
+			if !ok {
+				if out.Type != client.ExporterDocker {
+					dest = "-"
+				}
+			}
+			if dest == "-" {
+				if _, err := console.ConsoleFromFile(os.Stdout); err == nil {
+					return nil, errors.Errorf("output file is required for %s exporter. refusing to write to console", out.Type)
+				}
+				out.Output = wrapWriteCloser(os.Stdout)
+			} else if dest != "" {
+				fi, err := os.Stat(dest)
+				if err != nil && !os.IsNotExist(err) {
+					return nil, errors.Wrapf(err, "invalid destination file: %s", dest)
+				}
+				if err == nil && fi.IsDir() {
+					return nil, errors.Errorf("destination file %s is a directory", dest)
+				}
+				f, err := os.Create(dest)
+				if err != nil {
+					return nil, errors.Errorf("failed to open %s", err)
+				}
+				out.Output = wrapWriteCloser(f)
+			}
+			delete(out.Attrs, "dest")
+		case "registry":
+			out.Type = client.ExporterImage
+			out.Attrs["push"] = "true"
+		}
+
+		outs = append(outs, out)
+	}
+	return outs, nil
+}
+
+func wrapWriteCloser(wc io.WriteCloser) func(map[string]string) (io.WriteCloser, error) {
+	return func(map[string]string) (io.WriteCloser, error) {
+		return wc, nil
+	}
+}