Make unix Readdir and windows Readdirnames return partially successful results on error.

Make plan 9 Readdir & Readdirnames return os.EOF at end.
Also fix typos in the unix and windows comments.

R=golang-dev, fshahriar, bradfitz, rsc, r
CC=golang-dev
https://golang.org/cl/4557053

4 files changed, 49 insertions, 45 deletions

diff --git a/src/pkg/os/dir_plan9.go b/src/pkg/os/dir_plan9.go
index 14decfce10..bbc2cb6472 100644
--- a/src/pkg/os/dir_plan9.go
+++ b/src/pkg/os/dir_plan9.go
@@ -9,35 +9,46 @@ import (
 )
 
 // Readdir reads the contents of the directory associated with file and
-// returns an array of up to count FileInfo structures, in directory order. 
-// Subsequent calls on the same file will yield further FileInfos.
-// A negative count means to read until EOF.
-// Readdir returns the array and an Error, if any.
-func (file *File) Readdir(count int) (fi []FileInfo, err Error) {
+// returns an array of up to n FileInfo structures, as would be returned
+// by Lstat, in directory order. Subsequent calls on the same file will yield
+// further FileInfos.
+//
+// If n > 0, Readdir returns at most n FileInfo structures. In this case, if
+// Readdirnames returns an empty slice, it will return a non-nil error
+// explaining why. At the end of a directory, the error is os.EOF.
+//
+// If n <= 0, Readdir returns all the FileInfo from the directory in
+// a single slice. In this case, if Readdir succeeds (reads all
+// the way to the end of the directory), it returns the slice and a
+// nil os.Error. If it encounters an error before the end of the
+// directory, Readdir returns the FileInfo read until that point
+// and a non-nil error.
+func (file *File) Readdir(n int) (fi []FileInfo, err Error) {
 	// If this file has no dirinfo, create one.
 	if file.dirinfo == nil {
 		file.dirinfo = new(dirInfo)
 	}
 	d := file.dirinfo
-	size := count
-	if size < 0 {
+	size := n
+	if size <= 0 {
 		size = 100
+		n = -1
 	}
 	result := make([]FileInfo, 0, size) // Empty with room to grow.
-	for count != 0 {
+	for n != 0 {
 		// Refill the buffer if necessary
 		if d.bufp >= d.nbuf {
 			d.bufp = 0
 			var e Error
 			d.nbuf, e = file.Read(d.buf[:])
 			if e != nil && e != EOF {
-				return nil, &PathError{"readdir", file.name, e}
+				return result, &PathError{"readdir", file.name, e}
 			}
 			if e == EOF {
 				break
 			}
 			if d.nbuf < syscall.STATFIXLEN {
-				return nil, &PathError{"readdir", file.name, Eshortstat}
+				return result, &PathError{"readdir", file.name, Eshortstat}
 			}
 		}
 
@@ -45,39 +56,44 @@ func (file *File) Readdir(count int) (fi []FileInfo, err Error) {
 		m, _ := gbit16(d.buf[d.bufp:])
 		m += 2
 		if m < syscall.STATFIXLEN {
-			return nil, &PathError{"readdir", file.name, Eshortstat}
+			return result, &PathError{"readdir", file.name, Eshortstat}
 		}
 		dir, e := UnmarshalDir(d.buf[d.bufp : d.bufp+int(m)])
 		if e != nil {
-			return nil, &PathError{"readdir", file.name, e}
+			return result, &PathError{"readdir", file.name, e}
 		}
 		var f FileInfo
 		fileInfoFromStat(&f, dir)
 		result = append(result, f)
 
 		d.bufp += int(m)
-		count--
+		n--
 	}
-	return result, nil
-}
 
-// Readdirnames returns an array of up to count file names residing in the 
-// directory associated with file. A negative count will return all of them.
-// Readdir returns the array and an Error, if any.
-func (file *File) Readdirnames(count int) (names []string, err Error) {
-	fi, e := file.Readdir(count)
-
-	if e != nil {
-		return []string{}, e
+	if n >= 0 && len(result) == 0 {
+		return result, EOF
 	}
+	return result, nil
+}
 
+// Readdirnames reads and returns a slice of names from the directory f.
+//
+// If n > 0, Readdirnames returns at most n names. In this case, if
+// Readdirnames returns an empty slice, it will return a non-nil error
+// explaining why. At the end of a directory, the error is os.EOF.
+//
+// If n <= 0, Readdirnames returns all the names from the directory in
+// a single slice. In this case, if Readdirnames succeeds (reads all
+// the way to the end of the directory), it returns the slice and a
+// nil os.Error. If it encounters an error before the end of the
+// directory, Readdirnames returns the names read until that point and
+// a non-nil error.
+func (file *File) Readdirnames(n int) (names []string, err Error) {
+	fi, err := file.Readdir(n)
 	names = make([]string, len(fi))
-	err = nil
-
 	for i := range fi {
 		names[i] = fi[i].Name
 	}
-
 	return
 }
 
diff --git a/src/pkg/os/dir_windows.go b/src/pkg/os/dir_windows.go
index a4df9d3eab..d76e88fdb7 100644
--- a/src/pkg/os/dir_windows.go
+++ b/src/pkg/os/dir_windows.go
@@ -6,11 +6,6 @@ package os
 
 func (file *File) Readdirnames(n int) (names []string, err Error) {
 	fis, err := file.Readdir(n)
-	// If n > 0 and we get an error, we return now.
-	// If n < 0, we return whatever we got + any error.
-	if n > 0 && err != nil {
-		return nil, err
-	}
 	names = make([]string, len(fis))
 	for i, fi := range fis {
 		names[i] = fi.Name
diff --git a/src/pkg/os/file_unix.go b/src/pkg/os/file_unix.go
index c65c5b3ffd..def9b3bf07 100644
--- a/src/pkg/os/file_unix.go
+++ b/src/pkg/os/file_unix.go
@@ -69,12 +69,12 @@ func (file *File) Stat() (fi *FileInfo, err Error) {
 }
 
 // Readdir reads the contents of the directory associated with file and
-// returns an array of up to count FileInfo structures, as would be returned
+// returns an array of up to n FileInfo structures, as would be returned
 // by Lstat, in directory order. Subsequent calls on the same file will yield
 // further FileInfos.
 //
-// If n > 0, Readdir returns at most n names. In this case, if
-// Readdirnames returns an empty slice, it will return a non-nil error
+// If n > 0, Readdir returns at most n FileInfo structures. In this case, if
+// Readdir returns an empty slice, it will return a non-nil error
 // explaining why. At the end of a directory, the error is os.EOF.
 //
 // If n <= 0, Readdir returns all the FileInfo from the directory in
@@ -89,11 +89,7 @@ func (file *File) Readdir(n int) (fi []FileInfo, err Error) {
 		dirname = "."
 	}
 	dirname += "/"
-	wantAll := n < 0
-	names, namesErr := file.Readdirnames(n)
-	if namesErr != nil && !wantAll {
-		return nil, namesErr
-	}
+	names, err := file.Readdirnames(n)
 	fi = make([]FileInfo, len(names))
 	for i, filename := range names {
 		fip, err := Lstat(dirname + filename)
@@ -103,9 +99,6 @@ func (file *File) Readdir(n int) (fi []FileInfo, err Error) {
 			fi[i] = *fip
 		}
 	}
-	if !wantAll && namesErr != EOF {
-		err = namesErr
-	}
 	return
 }
 
diff --git a/src/pkg/os/file_windows.go b/src/pkg/os/file_windows.go
index ac37b8e2d3..80886f6f52 100644
--- a/src/pkg/os/file_windows.go
+++ b/src/pkg/os/file_windows.go
@@ -123,12 +123,12 @@ func (file *File) Stat() (fi *FileInfo, err Error) {
 }
 
 // Readdir reads the contents of the directory associated with file and
-// returns an array of up to count FileInfo structures, as would be returned
+// returns an array of up to n FileInfo structures, as would be returned
 // by Lstat, in directory order. Subsequent calls on the same file will yield
 // further FileInfos.
 //
-// If n > 0, Readdir returns at most n names. In this case, if
-// Readdirnames returns an empty slice, it will return a non-nil error
+// If n > 0, Readdir returns at most n FileInfo structures. In this case, if
+// Readdir returns an empty slice, it will return a non-nil error
 // explaining why. At the end of a directory, the error is os.EOF.
 //
 // If n <= 0, Readdir returns all the FileInfo from the directory in