github.com/hairyhenderson/gomplate/v3@v3.11.7/internal/iohelpers/readers.go (about)

     1  package iohelpers
     2  
     3  import (
     4  	"io"
     5  	"sync"
     6  )
     7  
     8  // LazyReadCloser provides an interface to a ReadCloser that will open on the
     9  // first access. The wrapped io.ReadCloser must be provided by 'open'.
    10  func LazyReadCloser(open func() (io.ReadCloser, error)) io.ReadCloser {
    11  	return &lazyReadCloser{
    12  		opened: sync.Once{},
    13  		open:   open,
    14  	}
    15  }
    16  
    17  type lazyReadCloser struct {
    18  	r io.ReadCloser
    19  	// caches the error that came from open(), if any
    20  	openErr error
    21  	open    func() (io.ReadCloser, error)
    22  	opened  sync.Once
    23  }
    24  
    25  var _ io.ReadCloser = (*lazyReadCloser)(nil)
    26  
    27  func (l *lazyReadCloser) openReader() (r io.ReadCloser, err error) {
    28  	l.opened.Do(func() {
    29  		l.r, l.openErr = l.open()
    30  	})
    31  	return l.r, l.openErr
    32  }
    33  
    34  func (l *lazyReadCloser) Close() error {
    35  	r, err := l.openReader()
    36  	if err != nil {
    37  		return err
    38  	}
    39  	return r.Close()
    40  }
    41  
    42  func (l *lazyReadCloser) Read(p []byte) (n int, err error) {
    43  	r, err := l.openReader()
    44  	if err != nil {
    45  		return 0, err
    46  	}
    47  	return r.Read(p)
    48  }