Re-add tests for write failures

Commit d2173f5f0e removed the complete
os & syscall mocking layer as overly complex. This commit adds back
the simplest possible thing: hooks to control the database file
writes.

Missing tests: TestDBOpenMetaFileError, TestDBMmapStatError.
These are harder to test without more extensive mocking.

Conflicts:
	db_test.go

db.go

@@ -34,6 +34,11 @@ type DB struct {
 	rwlock   sync.Mutex   // Allows only one writer at a time.
 	metalock sync.Mutex   // Protects meta page access.
 	mmaplock sync.RWMutex // Protects mmap access during remapping.
+
+	ops struct {
+		writeAt     func(b []byte, off int64) (n int, err error)
+		metaWriteAt func(b []byte, off int64) (n int, err error)
+	}
 }
 
 // Path returns the path to currently open database file.
@@ -74,6 +79,14 @@ func (db *DB) Open(path string, mode os.FileMode) error {
 		return err
 	}
 
+	// default values for test hooks
+	if db.ops.writeAt == nil {
+		db.ops.writeAt = db.file.WriteAt
+	}
+	if db.ops.metaWriteAt == nil {
+		db.ops.metaWriteAt = db.metafile.WriteAt
+	}
+
 	// Initialize the database if it doesn't exist.
 	if info, err := db.file.Stat(); err != nil {
 		return &Error{"stat error", err}
@@ -226,7 +239,7 @@ func (db *DB) init() error {
 	p.count = 0
 
 	// Write the buffer to our data file.
-	if _, err := db.metafile.WriteAt(buf, 0); err != nil {
+	if _, err := db.ops.metaWriteAt(buf, 0); err != nil {
 		return err
 	}
 

db_test.go

@@ -1,6 +1,7 @@
 package bolt
 
 import (
+	"io"
 	"io/ioutil"
 	"math/rand"
 	"os"
@@ -50,6 +51,67 @@ func TestDBReopen(t *testing.T) {
 	})
 }
 
+// Ensure that the database returns an error if the file handle cannot be open.
+func TestDBOpenFileError(t *testing.T) {
+	withDBFile(func(db *DB, path string) {
+		exp := &os.PathError{
+			Op:   "open",
+			Path: path + "/youre-not-my-real-parent",
+			Err:  syscall.ENOTDIR,
+		}
+		err := db.Open(path+"/youre-not-my-real-parent", 0666)
+		assert.Equal(t, err, exp)
+	})
+}
+
+// Ensure that write errors to the meta file handler during initialization are returned.
+func TestDBMetaInitWriteError(t *testing.T) {
+	withDB(func(db *DB, path string) {
+		// Mock the file system.
+		db.ops.metaWriteAt = func(p []byte, offset int64) (n int, err error) { return 0, io.ErrShortWrite }
+
+		// Open the database.
+		err := db.Open(path, 0666)
+		assert.Equal(t, err, io.ErrShortWrite)
+	})
+}
+
+// Ensure that a database that is too small returns an error.
+func TestDBFileTooSmall(t *testing.T) {
+	withDBFile(func(db *DB, path string) {
+		// corrupt the database
+		err := os.Truncate(path, int64(os.Getpagesize()))
+		assert.NoError(t, err)
+
+		err = db.Open(path, 0666)
+		assert.Equal(t, err, &Error{"file size too small", nil})
+	})
+}
+
+// Ensure that corrupt meta0 page errors get returned.
+func TestDBCorruptMeta0(t *testing.T) {
+	withDB(func(db *DB, path string) {
+		var m meta
+		m.magic = magic
+		m.version = version
+		m.pageSize = 0x8000
+
+		// Create a file with bad magic.
+		b := make([]byte, 0x10000)
+		p0, p1 := (*page)(unsafe.Pointer(&b[0x0000])), (*page)(unsafe.Pointer(&b[0x8000]))
+		p0.meta().magic = 0
+		p0.meta().version = version
+		p1.meta().magic = magic
+		p1.meta().version = version
+		err := ioutil.WriteFile(path, b, 0666)
+		assert.NoError(t, err)
+
+		// Open the database.
+		err = db.Open(path, 0666)
+		assert.Equal(t, err, &Error{"meta error", ErrInvalid})
+	})
+}
+
 // Ensure that a database cannot open a transaction when it's not open.
 func TestDBTxErrDatabaseNotOpen(t *testing.T) {
 	withDB(func(db *DB, path string) {

tx.go

@@ -337,7 +337,7 @@ func (t *Tx) write() error {
 		size := (int(p.overflow) + 1) * t.db.pageSize
 		buf := (*[maxAllocSize]byte)(unsafe.Pointer(p))[:size]
 		offset := int64(p.id) * int64(t.db.pageSize)
-		if _, err := t.db.file.WriteAt(buf, offset); err != nil {
+		if _, err := t.db.ops.writeAt(buf, offset); err != nil {
 			return err
 		}
 	}
@@ -359,7 +359,7 @@ func (t *Tx) writeMeta() error {
 	t.meta.write(p)
 
 	// Write the meta page to file.
-	if _, err := t.db.metafile.WriteAt(buf, int64(p.id)*int64(t.db.pageSize)); err != nil {
+	if _, err := t.db.ops.metaWriteAt(buf, int64(p.id)*int64(t.db.pageSize)); err != nil {
 		return err
 	}