Added exponential backoff for copying npm installation

src/nvm.go

@@ -8,6 +8,7 @@ import (
   "io/ioutil"
   "regexp"
   "bytes"
+  "time"
   "./nvm/web"
   "./nvm/arch"
   "./nvm/file"
@@ -280,13 +281,26 @@ func install(version string, cpuarch string) {
         os.Rename(filepath.Join(tempNpmBin, "npx.cmd"), filepath.Join(env.root, "v"+version, "npx.cmd"))
       }
 
-      os.Rename(filepath.Join(tempDir, "nvm-npm", "npm-"+npmv), filepath.Join(env.root, "v"+version, "node_modules", "npm"))
+      time.Sleep(10000*time.Millisecond)
+      err := os.Rename(filepath.Join(tempDir, "nvm-npm", "npm-"+npmv), filepath.Join(env.root, "v"+version, "node_modules", "npm"))
+      if err != nil {
+        // sometimes Windows can take some time to enable access to large amounts of files after unzip, use exponential backoff to wait until it is ready
+        for _, i := range [5]int{1, 2, 4, 8, 16} {
+          time.Sleep(time.Duration(i)*time.Second)
+          err = os.Rename(filepath.Join(tempDir, "nvm-npm", "npm-"+npmv), filepath.Join(env.root, "v"+version, "node_modules", "npm"))
+          if err == nil { break }
+        }
+      }
 
-      // Remove the temp directory
-      // may consider keep the temp files here
-      os.RemoveAll(tempDir)
+      if err == nil {
+        // Remove the temp directory
+        // may consider keep the temp files here
+        os.RemoveAll(tempDir)
 
-      fmt.Println("\n\nInstallation complete. If you want to use this version, type\n\nnvm use "+version)
+        fmt.Println("\n\nInstallation complete. If you want to use this version, type\n\nnvm use "+version)
+      } else {
+        fmt.Println("Error: Unable to install NPM: "+err.Error());
+      }
     } else {
       fmt.Println("Could not download npm for node v"+version+".")
       fmt.Println("Please visit https://github.com/npm/npm/releases/tag/v"+npmv+" to download npm.")