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// Copyright 2020 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package fs
import "io"
// ReadFileFS is the interface implemented by a file system
// that provides an optimized implementation of [ReadFile].
type ReadFileFS interface {
FS
// ReadFile reads the named file and returns its contents.
// A successful call returns a nil error, not io.EOF.
// (Because ReadFile reads the whole file, the expected EOF
// from the final Read is not treated as an error to be reported.)
//
// The caller is permitted to modify the returned byte slice.
// This method should return a copy of the underlying data.
ReadFile(name string) ([]byte, error)
}
// ReadFile reads the named file from the file system fs and returns its contents.
// A successful call returns a nil error, not [io.EOF].
// (Because ReadFile reads the whole file, the expected EOF
// from the final Read is not treated as an error to be reported.)
//
// If fs implements [ReadFileFS], ReadFile calls fs.ReadFile.
// Otherwise ReadFile calls fs.Open and uses Read and Close
// on the returned [File].
func ReadFile(fsys FS, name string) ([]byte, error) {
if fsys, ok := fsys.(ReadFileFS); ok {
return fsys.ReadFile(name)
}
file, err := fsys.Open(name)
if err != nil {
return nil, err
}
defer file.Close()
var size int
if info, err := file.Stat(); err == nil {
size64 := info.Size()
if int64(int(size64)) == size64 {
size = int(size64)
}
}
data := make([]byte, 0, size+1)
for {
if len(data) >= cap(data) {
d := append(data[:cap(data)], 0)
data = d[:len(data)]
}
n, err := file.Read(data[len(data):cap(data)])
data = data[:len(data)+n]
if err != nil {
if err == io.EOF {
err = nil
}
return data, err
}
}
}
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