fup: add extractstatic command

This extracts the hash-named static assets into a directory.  This is primarily
useful if you have multiple instances of fup running and you therefore need to
serve /static from a shared filesystem of some sort.

web/fup/cmd/extractstatic.go

@@ -0,0 +1,83 @@
+package cmd
+
+import (
+	"fmt"
+	"io"
+	"io/fs"
+	"log"
+	"os"
+	"path/filepath"
+
+	"github.com/spf13/cobra"
+	"hg.lukegb.com/lukegb/depot/web/fup/fupstatic"
+)
+
+func init() {
+	rootCmd.AddCommand(extractstaticCmd)
+
+	extractstaticCmd.Flags().BoolVarP(&extractstaticForceOverwrite, "force", "f", false, "If set, will overwrite existing files.")
+}
+
+var (
+	extractstaticForceOverwrite bool
+
+	extractstaticCmd = &cobra.Command{
+		Use:     "extractstatic dir",
+		Example: "extractstatic /srv/http/static",
+		Short:   "Extracts static assets into a target directory.",
+		Args:    cobra.ExactArgs(1),
+		RunE: func(cmd *cobra.Command, args []string) error {
+			targetDir := args[0]
+			log.Printf("extracting assets to %v", targetDir)
+			return fs.WalkDir(fupstatic.Static, ".", func(fpath string, d fs.DirEntry, err error) error {
+				if err != nil {
+					return err
+				}
+				targetPath := filepath.Join(targetDir, fpath)
+				fi, err := os.Stat(targetPath)
+				if err != nil && !os.IsNotExist(err) {
+					return fmt.Errorf("checking for existence of %q: %w", targetPath, err)
+				}
+				if d.IsDir() {
+					switch {
+					case fi != nil && !fi.IsDir():
+						return fmt.Errorf("%q already exists and is not a directory", targetPath)
+					case fi != nil:
+						return nil
+					default:
+						// Ensure directory exists.
+						return os.Mkdir(filepath.Join(targetDir, fpath), 0755)
+					}
+				}
+
+				switch {
+				case fi != nil && fi.IsDir():
+					return fmt.Errorf("%q already exists and is a directory", targetPath)
+				case fi != nil && !extractstaticForceOverwrite:
+					return nil
+				}
+
+				src, err := fupstatic.Static.Open(fpath)
+				if err != nil {
+					return fmt.Errorf("open source %q: %w", fpath, err)
+				}
+				defer src.Close() // Don't care about errors for closing read-only file.
+
+				dst, err := os.Create(targetPath)
+				if err != nil {
+					return fmt.Errorf("create target %q: %w", targetPath, err)
+				}
+
+				if _, err := io.Copy(dst, src); err != nil {
+					return fmt.Errorf("copying from source %q to target %q: %w", fpath, targetPath, err)
+				}
+
+				if err := dst.Close(); err != nil {
+					return fmt.Errorf("close target %q: %w", targetPath, err)
+				}
+
+				return nil
+			})
+		},
+	}
+)