README.md

@@ -227,7 +227,7 @@ operation and a mock filesystem during testing or as needed.
 
 ```go
 appfs := afero.NewOsFs()
-appfs.MkdirAll("src/a", 0755))
+appfs.MkdirAll("src/a", 0755)
 ```
 
 ## Memory Backed Storage
@@ -241,7 +241,7 @@ safely.
 
 ```go
 mm := afero.NewMemMapFs()
-mm.MkdirAll("src/a", 0755))
+mm.MkdirAll("src/a", 0755)
 ```
 
 #### InMemoryFile
@@ -306,7 +306,7 @@ Any Afero FileSystem can be used as an httpFs.
 
 ```go
 httpFs := afero.NewHttpFs(<ExistingFS>)
-fileserver := http.FileServer(httpFs.Dir(<PATH>)))
+fileserver := http.FileServer(httpFs.Dir(<PATH>))
 http.Handle("/", fileserver)
 ```
 

composite_test.go

@@ -477,7 +477,8 @@ func TestUnionFileReaddirAskForTooMany(t *testing.T) {
 	base := &MemMapFs{}
 	overlay := &MemMapFs{}
 
-	for i := 0; i < 5; i++ {
+	const testFiles = 5
+	for i := 0; i < testFiles; i++ {
 		WriteFile(base, fmt.Sprintf("file%d.txt", i), []byte("afero"), 0777)
 	}
 
@@ -490,13 +491,24 @@ func TestUnionFileReaddirAskForTooMany(t *testing.T) {
 
 	defer f.Close()
 
-	names, err := f.Readdirnames(6)
+	// Read part of all files
+	wantNames := 3
+	names, err := f.Readdirnames(wantNames)
 	if err != nil {
 		t.Fatal(err)
 	}
+	if len(names) != wantNames {
+		t.Fatalf("got %d names %v, want %d", len(names), names, wantNames)
+	}
 
-	if len(names) != 5 {
-		t.Fatal(names)
+	// Try to read more files than remaining
+	wantNames = testFiles - len(names)
+	names, err = f.Readdirnames(wantNames + 1)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(names) != wantNames {
+		t.Fatalf("got %d names %v, want %d", len(names), names, wantNames)
 	}
 
 	// End of directory

mem/file.go

@@ -225,11 +225,11 @@ func (f *File) Seek(offset int64, whence int) (int64, error) {
 		return 0, ErrFileClosed
 	}
 	switch whence {
-	case 0:
+	case io.SeekStart:
 		atomic.StoreInt64(&f.at, offset)
-	case 1:
-		atomic.AddInt64(&f.at, int64(offset))
-	case 2:
+	case io.SeekCurrent:
+		atomic.AddInt64(&f.at, offset)
+	case io.SeekEnd:
 		atomic.StoreInt64(&f.at, int64(len(f.fileData.data))+offset)
 	}
 	return f.at, nil
@@ -260,7 +260,7 @@ func (f *File) Write(b []byte) (n int, err error) {
 	}
 	setModTime(f.fileData, time.Now())
 
-	atomic.StoreInt64(&f.at, int64(len(f.fileData.data)))
+	atomic.AddInt64(&f.at, int64(n))
 	return
 }
 

mem/file_test.go

@@ -1,6 +1,7 @@
 package mem
 
 import (
+	"bytes"
 	"io"
 	"testing"
 	"time"
@@ -205,3 +206,42 @@ func TestFileReadAtSeekOffset(t *testing.T) {
 		t.Fatal(err)
 	}
 }
+
+func TestFileWriteAndSeek(t *testing.T) {
+	fd := CreateFile("foo")
+	f := NewFileHandle(fd)
+
+	assert := func(expected bool, v ...interface{}) {
+		if !expected {
+			t.Helper()
+			t.Fatal(v...)
+		}
+	}
+
+	data4 := []byte{0, 1, 2, 3}
+	data20 := bytes.Repeat(data4, 5)
+	var off int64
+
+	for i := 0; i < 100; i++ {
+		// write 20 bytes
+		n, err := f.Write(data20)
+		assert(err == nil, err)
+		off += int64(n)
+		assert(n == len(data20), n)
+		assert(off == int64((i+1)*len(data20)), off)
+
+		// rewind to start and write 4 bytes there
+		cur, err := f.Seek(-off, io.SeekCurrent)
+		assert(err == nil, err)
+		assert(cur == 0, cur)
+
+		n, err = f.Write(data4)
+		assert(err == nil, err)
+		assert(n == len(data4), n)
+
+		// back at the end
+		cur, err = f.Seek(off-int64(n), io.SeekCurrent)
+		assert(err == nil, err)
+		assert(cur == off, cur, off)
+	}
+}

unionFile.go

@@ -186,25 +186,22 @@ func (f *UnionFile) Readdir(c int) (ofi []os.FileInfo, err error) {
 		}
 		f.files = append(f.files, merged...)
 	}
+	files := f.files[f.off:]
 
-	if c <= 0 && len(f.files) == 0 {
-		return f.files, nil
+	if c <= 0 {
+		return files, nil
 	}
 
-	if f.off >= len(f.files) {
+	if len(files) == 0 {
 		return nil, io.EOF
 	}
 
-	if c <= 0 {
-		return f.files[f.off:], nil
-	}
-
-	if c > len(f.files) {
-		c = len(f.files)
+	if c > len(files) {
+		c = len(files)
 	}
 
 	defer func() { f.off += c }()
-	return f.files[f.off:c], nil
+	return files[:c], nil
 }
 
 func (f *UnionFile) Readdirnames(c int) ([]string, error) {