深入理解Hugo: OverlayFs Afero
 
package main |
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import ( "bytes" "fmt" "github.com/spf13/afero" "golang.org/x/tools/txtar" "os" ) |
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func main() { ofs := New([]afero.Fs{ projectModuleFs(), mythemeModuleFs()}) a, _ := ofs.Open("a.md") defer a.Close() b, _ := ofs.Open("b.md") defer b.Close() c, _ := ofs.Open("c.md") defer c.Close() |
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fmt.Println(readFile(a)) fmt.Println(readFile(b)) fmt.Println(readFile(c)) } |
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func projectModuleFs() afero.Fs { ps := "-- a.md --\n" + "project: a\n" + "-- c.md --\n" + "project: c" return fsFromTxtTar(ps) } |
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func mythemeModuleFs() afero.Fs { ms := "-- a.md --\n" + "mytheme: a\n" + "-- b.md --\n" + "mytheme: b" return fsFromTxtTar(ms) } |
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func fsFromTxtTar(s string) afero.Fs { data := txtar.Parse([]byte(s)) fs := afero.NewMemMapFs() for _, f := range data.Files { if err := afero.WriteFile( fs, f.Name, bytes.TrimSuffix(f.Data, []byte("\n")), 0o666); err != nil { panic(err) } } return fs } |
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OverlayFs is a filesystem that overlays multiple filesystems. It’s by default a read-only filesystem. For all operations, the filesystems are checked in order until found. |
type OverlayFs struct { fss []afero.Fs } |
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New creates a new OverlayFs with the given options. |
func New(fss []afero.Fs) *OverlayFs { return &OverlayFs{ fss: fss, } } |
func (ofs *OverlayFs) stat(name string) ( afero.Fs, os.FileInfo, bool, error) { for _, fs := range ofs.fss { if fi, err := fs.Stat(name); err == nil || !os.IsNotExist(err) { return fs, fi, false, err } } return nil, nil, false, os.ErrNotExist } |
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Open opens a file, returning it or an error, if any happens. If name is a directory, a *Dir is returned representing all directories matching name. Note that a *Dir must not be used after it’s closed. |
func (ofs *OverlayFs) Open(name string) ( afero.File, error) { fs, fi, _, err := ofs.stat(name) if err != nil { return nil, err } |
if fi.IsDir() { panic("dir not supported yet.") } |
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return fs.Open(name) } |
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func readFile(f afero.File) string { b, _ := afero.ReadAll(f) return string(b) } |
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OverlayFs based on afero.Fs Result of merge layer |
project: a mytheme: b project: c |
Program exited.
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Next example: Radix Tree.