Search for file in Go using filepath

I am trying to find a file in a directory using Go. I am using Walk function from filepath package. In the findFile function, I am getting the file and assigning it the pointer to the file being passed. But this does not seem to work, the value of file after calling findFile is still nil. Please advice if I am doing something wrong or if this approach is not correct.

func example() { 
   var file *os.File
   err = filepath.Walk("uploads", findFile(fileId, file))
   if err != nil {
	   http.Error(w, err.Error(), http.StatusBadRequest)
	   return
   }
}

func findFile(fileId string, file *os.File) func(path string, info os.FileInfo, err error) error {
    return func(path string, info os.FileInfo, err error) error {
	    if err != nil {
		     return err
	    }

	    if !info.IsDir() && isFileMatching(info.Name(), fileId) {
		     file, err = os.Open(path)
		     if err != nil {
			     return err
		     }
	    }
	    return nil
    }

}

You are change the value of the pointer variable, not the value the pointer pointed to.

It should be:

f, err := os.Open(path)
if err != nil {
    return err
}
*file = *f

Note:

*file = *f is actually a copy of a os.File.

This is not a good practice. You might want to consider using a channel (and a goroutine) for this kind of work.

And you might also want to check if there is only one path that can pass isFileMatching, or it is a file descriptor leak (not closing opened file).

Regarding the previous answer you can use slice to collect the files, they will not get copied and you can close them all at the end.

func example() {
	var files []*os.File
	err := filepath.Walk("uploads", findFile(fileId, &files))
	if err != nil {
		http.Error(w, err.Error(), http.StatusBadRequest)
		return
	}
}

func findFile(fileId string, files *[]*os.File) func(path string, info os.FileInfo, err error) error {
	return func(path string, info os.FileInfo, err error) error {
		if err != nil {
			return err
		}

		if !info.IsDir() && isFileMatching(info.Name(), fileId) {
			file, err := os.Open(path)
			if err != nil {
				return err
			}
			*files = append(*files, file)
		}
		return nil
	}

}

Another option is filepath.WalkDir:

package main

import (
   "errors"
   "io/fs"
   "os"
   "path/filepath"
)

func open(root, name string) (*os.File, error) {
   var f *os.File
   filepath.WalkDir(root, func(s string, d fs.DirEntry, e error) error {
      if e != nil { return e }
      if d.Name() != name { return nil }
      f, e = os.Open(s)
      if e != nil { return e }
      return errors.New("found")
   })
   if f == nil {
      return nil, errors.New("not found")
   }
   return f, nil
}

func main() {
   f, e := open(`C:\go`, "path.go")
   if e != nil {
      panic(e)
   }
   defer f.Close()
   println(f.Name())
}

https://golang.org/pkg/path/filepath#WalkDir