Add comments clarifying copyWithBuffer implementation

amrmahdi · amrmahdi · commit 5618423a0e3b · 2020-11-19T00:58:55.000Z
Signed-off-by: Amr Mahdi <amramahdi@gmail.com> (cherry picked from commit b81917e) Signed-off-by: Amr Mahdi <amramahdi@gmail.com>
diff --git a/content/helpers.go b/content/helpers.go
@@ -229,6 +229,10 @@ func seekReader(r io.Reader, offset, size int64) (io.Reader, error) {
 	return r, nil
 }
 
+// copyWithBuffer is very similar to  io.CopyBuffer https://golang.org/pkg/io/#CopyBuffer
+// but instead of using Read to read from the src, we use ReadAtLeast to make sure we have
+// a full buffer before we do a write operation to dst to reduce overheads associated
+// with the write operations of small buffers.
 func copyWithBuffer(dst io.Writer, src io.Reader) (written int64, err error) {
 	// If the reader has a WriteTo method, use it to do the copy.
 	// Avoids an allocation and a copy.
@@ -259,6 +263,8 @@ func copyWithBuffer(dst io.Writer, src io.Reader) (written int64, err error) {
 			}
 		}
 		if er != nil {
+			// If an EOF happens after reading fewer than the requested bytes,
+			// ReadAtLeast returns ErrUnexpectedEOF.
 			if er != io.EOF && er != io.ErrUnexpectedEOF {
 				err = er
 			}

Original file line number	Diff line number	Diff line change
`@@ -229,6 +229,10 @@ func seekReader(r io.Reader, offset, size int64) (io.Reader, error) {`
`229`	`229`	`return r, nil`
`230`	`230`	`}`
`231`	`231`
	`232`	`+// copyWithBuffer is very similar to io.CopyBuffer https://golang.org/pkg/io/#CopyBuffer`
	`233`	`+// but instead of using Read to read from the src, we use ReadAtLeast to make sure we have`
	`234`	`+// a full buffer before we do a write operation to dst to reduce overheads associated`
	`235`	`+// with the write operations of small buffers.`
`232`	`236`	`func copyWithBuffer(dst io.Writer, src io.Reader) (written int64, err error) {`
`233`	`237`	`// If the reader has a WriteTo method, use it to do the copy.`
`234`	`238`	`// Avoids an allocation and a copy.`
`@@ -259,6 +263,8 @@ func copyWithBuffer(dst io.Writer, src io.Reader) (written int64, err error) {`
`259`	`263`	`}`
`260`	`264`	`}`
`261`	`265`	`if er != nil {`
	`266`	`+ // If an EOF happens after reading fewer than the requested bytes,`
	`267`	`+ // ReadAtLeast returns ErrUnexpectedEOF.`
`262`	`268`	`if er != io.EOF && er != io.ErrUnexpectedEOF {`
`263`	`269`	`err = er`
`264`	`270`	`}`