wip: cdx lookup

1 files changed, 92 insertions, 0 deletions

diff --git a/skate/cache.go b/skate/cache.go
new file mode 100644
index 0000000..e5b0171
--- /dev/null
+++ b/skate/cache.go
@@ -0,0 +1,92 @@
+package skate
+
+import (
+	"crypto/sha1"
+	"errors"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"os"
+	"path"
+
+	"git.archive.org/martin/cgraph/skate/atomic"
+)
+
+var ErrCacheMiss = errors.New("cache miss")
+
+type Cache struct {
+	Dir         string
+	initialized bool
+}
+
+// Init creates all directories.
+func (c *Cache) init() error {
+	for i := 0; i < 256; i++ {
+		s := fmt.Sprintf("%02x", i)
+		d := path.Join(c.Dir, s)
+		if _, err := os.Stat(d); os.IsNotExist(err) {
+			if err := os.MkdirAll(d, 0755); err != nil {
+				return err
+			}
+		}
+	}
+	c.initialized = true
+	return nil
+}
+
+func (c *Cache) Has(k string) bool {
+	var (
+		shard, name = shardedHash(k)
+		spath       = path.Join(c.Dir, shard, name)
+	)
+	if _, err := os.Stat(spath); os.IsNotExist(err) {
+		return false
+	}
+	return true
+}
+
+func (c *Cache) Get(k string) ([]byte, error) {
+	var (
+		shard, name = shardedHash(k)
+		spath       = path.Join(c.Dir, shard, name)
+	)
+	if !c.initialized {
+		if err := c.init(); err != nil {
+			return nil, err
+		}
+	}
+	if _, err := os.Stat(spath); os.IsNotExist(err) {
+		return nil, ErrCacheMiss
+	}
+	f, err := os.Open(spath)
+	if err != nil {
+		return nil, err
+	}
+	defer f.Close()
+	return ioutil.ReadAll(f)
+}
+
+func (c *Cache) Set(k string, v []byte) error {
+	var (
+		shard, name = shardedHash(k)
+		spath       = path.Join(c.Dir, shard, name)
+	)
+	if !c.initialized {
+		if err := c.init(); err != nil {
+			return err
+		}
+	}
+	if err := atomic.WriteFile(spath, v, 0755); err != nil {
+		return err
+	}
+	return nil
+}
+
+// shardedHash returns a sha1 shard (2) and name (38) for a given string value
+// (e.g. a URL).
+func shardedHash(v string) (shard, name string) {
+	h := sha1.New()
+	_, _ = io.WriteString(h, v)
+	name = fmt.Sprintf("%x", h.Sum(nil))
+	return name[:2], name[2:]
+}