axiom//s3.core An Amazon AWS-S3-based Hasher

Author: Temporarily Removed  (
Date: 25 April 2018
Version: 0.4.1

1    Introduction

This library provides a hasher that stores its content in Amazon's S3.

The library requires configuration providing credentials for accessing S3, as well as a bucket name, that is assumed to pre-exist. It provides the resources storage and hasher in return.

2    storage

As its definition in permacode, storage is a pair of functions (see file-store as an example), which store content under a key, and fetch stored content given a key, respectively.

It depends on s3-config, a map of properties containing the :bucket-name in which values are to be stored, as well as credentials for accessing S3. See clj-aws-s3 documentation for more details.

(let [config {:bucket-name "foo"
             :access-key "bar"
             :secret-key "baz"}
     $ (di/injector {:s3-config config})]
 (module $)
 (di/startup $)
 (di/do-with! $ [storage]
              (let [[store retr] storage
                    content (.getBytes "foo bar" "UTF-8")]
                (store "abcd" content) => true
                 ( content) => ..inp..
                 (s3/put-object config "foo" "abcd" ..inp..) => irrelevant)
                (retr "abcd") => content
                 (s3/get-object config "foo" "abcd") => {:content ..inp2..}
                 (hasher/slurp-bytes ..inp2..) => content))))

2.1    Local Storage with S3 Fallback

Developers working in their own environments often want their solution local, without the need to provide credentials. An alternative storage resource provides just that.

If the resources storage-local-path and storage-fetch-url exist, a storage resource is provided.

(def path (str "/tmp/store" (rand-int 1000000)))
 (let [$ (di/injector {:storage-local-path path
                     :storage-fetch-url "http://some.url"})]
 (module $)
 (di/startup $)
 (di/do-with! $ [storage]
              (def storage storage)))

This storage will read and write content from and to a local file, located directly under the path specified by storage-local-path.

(let [[store retr] storage]
 (store "abcd" (.getBytes "Foo Bar"))
 (slurp (str path "/abcd")) => "Foo Bar"

 (let [bytes (retr "abcd")]
   (-> bytes class str) => "class [B"
   (String. bytes) => "Foo Bar"))

If we retreive a key and it does not exist in the local directory, an HTTP GET request is made to a URL made of the storage-fetch-url and the key.

(let [[store retr] storage]
 (retr "hash-that-does-not-exist") => ..content..
  (http-get "http://some.url/hash-that-does-not-exist") => ..input-stream..
  (hasher/slurp-bytes ..input-stream..) => ..content..))

3    hasher

The hasher resource is a nippy-multi-hasher based on the storage resource as its storage.

(let [calls (transient [])
     $ (di/injector {:storage [(fn [k v]
                                 (conj! calls [:store k v]))
                               (fn [k])]})]
 (module $)
 (di/startup $)
 (di/do-with! $ [hasher]
              (let [[hash unhash] hasher]
                (hash ..expr..) => ..hashcode..
                 (nippy/freeze ..expr.. nil) => ..bin..
                 (digest/sha2-256 ..bin..) => ..mhash..
                 (multihash/base58 ..mhash..) => ..hashcode..)
                (persistent! calls) => [[:store ..hashcode.. ..bin..]])))

4    Usage Example

To actually work against S3 we need to provide real credentials. We provide them using environment variables:

 (def config {:bucket-name "brosenan-test"
            :access-key (System/getenv "AWS_ACCESS_KEY")
            :secret-key (System/getenv "AWS_SECRET_KEY")})

We provide this to the injector, and start it.

 (def $ (di/injector {:s3-config config}))
 (module $)
 (di/startup $)

We will randomize a value to be sure we actually store and retrieve a new value.

 (def value (rand-int 100000))

Now we can store a value.

 (di/do-with! $ [hasher]
            (let [[hash unhash] hasher]
              (def hash-code (hash {:value value}))))

...and retrieve it...

 (di/do-with! $ [hasher]
            (let [[hash unhash] hasher]
              (unhash hash-code) => {:value value}))