Initial version of Blimp BlobCache.

blimp/common/blob_cache/blob_cache.h

Index: blimp/common/blob_cache/blob_cache.h
diff --git a/blimp/common/blob_cache/blob_cache.h b/blimp/common/blob_cache/blob_cache.h
new file mode 100644
index 0000000000000000000000000000000000000000..033b8c045ff54c03f2e43fdfe7061fe03a18d165
--- /dev/null
+++ b/blimp/common/blob_cache/blob_cache.h
@@ -0,0 +1,38 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef BLIMP_COMMON_BLOB_CACHE_BLOB_CACHE_H_
+#define BLIMP_COMMON_BLOB_CACHE_BLOB_CACHE_H_
+
+#include <string>
+#include <vector>
+
+#include "base/memory/ref_counted.h"
+#include "blimp/common/blimp_common_export.h"
+
+namespace blimp {
+
+using BlobId = const std::string;
+using BlobData = scoped_refptr<base::RefCountedData<const std::string>>;
+
+// An interface for a cache of blobs.
+class BLIMP_COMMON_EXPORT BlobCache {
+ public:
+  virtual ~BlobCache() {}
+
+  // Returns true if there is a cache item |id|.
+  virtual bool Contains(BlobId& id) const = 0;

[nyquist, 2016/04/16 00:25:30]

This makes cpplint angry (here and in the sha1util):

//blimp/common/blob_cache/blob_cache.h:25:  Is this a non-const reference? If
so, make const or use a pointer: BlobId& id  [runtime/references] [2]


But BlobId is already const, so I'm not sure why it's complaining. We can't
typedef in const?

Please advise.

[vmpstr, 2016/04/16 00:52:47]

I don't think linter is smart enough to do this. Also, I think we should keep
const outside of the using clause.. That is, you can have BlodId = std::string,
and then const BlodId& wherever you use this.

[vmpstr, 2016/04/16 00:55:08]

Can you just make this a string in general and not use BlobId? I'm not sure what
it buys you.

[nyquist, 2016/04/16 01:10:50]

As a pure std::string I'm not sure either. Since we've used some time internally
to decide on what we wanted for BlobData I'm kind of inclined to keep it very
well defined here for now.

kmarshall: What do you think?

+
+  // Stores |data| with the identifier |id| in the cache.
+  // Command is ignored if there is already a cache item stored under |id|.
+  virtual void Put(BlobId& id, BlobData data) = 0;
+
+  // Returns a pointer to the cache item |id|, or nullptr if no cache item
+  // exists under that identifier.
+  virtual BlobData Get(BlobId& id) const = 0;
+};
+
+}  // namespace blimp
+
+#endif  // BLIMP_COMMON_BLOB_CACHE_BLOB_CACHE_H_