libgo/go/cmd/go/internal/cache/default.go

   1 // Copyright 2017 The Go Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style
   3 // license that can be found in the LICENSE file.
   4
   5 package cache
   6
   7 import (
   8         "cmd/go/internal/base"
   9         "io/ioutil"
  10         "os"
  11         "path/filepath"
  12         "runtime"
  13         "sync"
  14 )
  15
  16 // Default returns the default cache to use, or nil if no cache should be used.
  17 func Default() *Cache {
  18         defaultOnce.Do(initDefaultCache)
  19         return defaultCache
  20 }
  21
  22 var (
  23         defaultOnce  sync.Once
  24         defaultCache *Cache
  25 )
  26
  27 // cacheREADME is a message stored in a README in the cache directory.
  28 // Because the cache lives outside the normal Go trees, we leave the
  29 // README as a courtesy to explain where it came from.
  30 const cacheREADME = `This directory holds cached build artifacts from the Go build system.
  31 Run "go clean -cache" if the directory is getting too large.
  32 See golang.org to learn more about Go.
  33 `
  34
  35 // initDefaultCache does the work of finding the default cache
  36 // the first time Default is called.
  37 func initDefaultCache() {
  38         dir := DefaultDir()
  39         if dir == "off" {
  40                 return
  41         }
  42         if err := os.MkdirAll(dir, 0777); err != nil {
  43                 base.Fatalf("initializing cache in $GOCACHE: %s", err)
  44         }
  45         if _, err := os.Stat(filepath.Join(dir, "README")); err != nil {
  46                 // Best effort.
  47                 ioutil.WriteFile(filepath.Join(dir, "README"), []byte(cacheREADME), 0666)
  48         }
  49
  50         c, err := Open(dir)
  51         if err != nil {
  52                 base.Fatalf("initializing cache in $GOCACHE: %s", err)
  53         }
  54         defaultCache = c
  55 }
  56
  57 // DefaultDir returns the effective GOCACHE setting.
  58 // It returns "off" if the cache is disabled.
  59 func DefaultDir() string {
  60         dir := os.Getenv("GOCACHE")
  61         if dir != "" {
  62                 return dir
  63         }
  64
  65         // Compute default location.
  66         // TODO(rsc): This code belongs somewhere else,
  67         // like maybe ioutil.CacheDir or os.CacheDir.
  68         switch runtime.GOOS {
  69         case "windows":
  70                 dir = os.Getenv("LocalAppData")
  71                 if dir == "" {
  72                         // Fall back to %AppData%, the old name of
  73                         // %LocalAppData% on Windows XP.
  74                         dir = os.Getenv("AppData")
  75                 }
  76                 if dir == "" {
  77                         return "off"
  78                 }
  79
  80         case "darwin":
  81                 dir = os.Getenv("HOME")
  82                 if dir == "" {
  83                         return "off"
  84                 }
  85                 dir += "/Library/Caches"
  86
  87         case "plan9":
  88                 dir = os.Getenv("home")
  89                 if dir == "" {
  90                         return "off"
  91                 }
  92                 // Plan 9 has no established per-user cache directory,
  93                 // but $home/lib/xyz is the usual equivalent of $HOME/.xyz on Unix.
  94                 dir += "/lib/cache"
  95
  96         default: // Unix
  97                 // https://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html
  98                 dir = os.Getenv("XDG_CACHE_HOME")
  99                 if dir == "" {
 100                         dir = os.Getenv("HOME")
 101                         if dir == "" {
 102                                 return "off"
 103                         }
 104                         dir += "/.cache"
 105                 }
 106         }
 107         return filepath.Join(dir, "go-build")
 108 }