Forgot to add the cache file, which supports 1 writer and multiple readers.

commit/cache.go

+/*
+ * Copyright 2015 Manish R Jain <manishrjain@gmail.com>
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * 		http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package commit
+
+import (
+	"errors"
+	"io"
+	"io/ioutil"
+	"sync"
+)
+
+var E_WRITE = errors.New("Unable to write")
+
+type Cache struct {
+	sync.RWMutex
+	buf []byte
+}
+
+func (c *Cache) Write(p []byte) (n int, err error) {
+	c.Lock()
+	defer c.Unlock()
+	c.buf = append(c.buf, p...)
+	return len(p), nil
+}
+
+func (c *Cache) ReadAt(pos int, p []byte) (n int, err error) {
+	c.RLock()
+	defer c.RUnlock()
+
+	if len(c.buf[pos:]) == 0 {
+		return 0, io.EOF
+	}
+
+	n = copy(p, c.buf[pos:])
+	return n, nil
+}
+
+// Reader isn't thread-safe. But multiple readers can be used to read the
+// same cache.
+type Reader struct {
+	c   *Cache
+	pos int
+}
+
+func NewReader(c *Cache) *Reader {
+	r := new(Reader)
+	r.c = c
+	return r
+}
+
+func (r *Reader) Read(p []byte) (n int, err error) {
+	n, err = r.c.ReadAt(r.pos, p)
+	r.pos += n
+	return
+}
+
+func (r *Reader) Discard(n int) {
+	r.pos += n
+}
+
+func FillCache(c *Cache, path string) error {
+	buf, err := ioutil.ReadFile(path)
+	if err != nil {
+		return err
+	}
+	n, err := c.Write(buf)
+	if err != nil {
+		return err
+	}
+	if n < len(buf) {
+		return E_WRITE
+	}
+	return nil
+}