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The Aleph's diameter was probably little more than an inch, but all space was there, actual and undiminished. Each thing (a mirror's face, let us say) was infinite things, since I distinctly saw it from every angle of the universe¹

Aleph is part of the mediachain project and is an integral component of the Phase II architecture.

Aleph provides two main components. First is a client for the HTTP API exposed by concat, the reference go peer implementation. Second is a lightweight peer in its own right.

For system-wide Mediachain documentation see https://mediachain.github.io/mediachain-docs.

Installation

Aleph requires node 6 or greater, and has primarily been tested with 6.5 and above.

To globally install a release from npm: npm install --global aleph. This will install the aleph command, which provides a remote query command and an interactive REPL for exploring the mediachain network. It also installs the mcclient command, which you can use to control and interact with a concat node.

If you'd prefer to install from the source repository, clone this repo and run npm install, followed by npm link, which will create a mcclient and aleph symlinks that run the latest compiled version of the code. This is very useful during development.

If you don't want mcclient or aleph on your path at all, you can just run npm install and execute ./bin/mcclient.js and ./bin/aleph.js directly instead.

Usage

Installing the aleph package will install two command line tools: mcclient and aleph.

mcclient

mcclient is a wrapper around the HTTP API exposed by concat, aleph's heavy-lifting counterpart.

mcclient contains several sub-commands, so the general invocation is mcclient [global-options] <command> [command-options].

At the moment, the only global option is --apiUrl or -p, which sets the location of the remote node's HTTP API. By default, mcclient will attempt to connect to a concat node running on localhost at port 9002, which is concat's default listen address for the HTTP API. If you've configured concat to run on a different port or on a remote machine, use the -p flag to pass in a new URL, e.g. mcclient -p http://localhost:5678 id

Some useful commands include:

• id: print the node's peer id and publisher id
• status:
  • with no arguments, prints the current status (online, offline, or public)
  • set the status with e.g. mcclient status online
• publish: publish JSON metadata to the node's local store. see mcclient publish --help for more info.
• statement: retrieve a statement by its id
• query: run a mediachain query against the node's local store.

To see a full list of supported commands, run mcclient --help

aleph

While mcclient is a front-end for the golang peer implementation concat, the aleph command provides access to the javascript peer implementation. The two are interoperable, but they do not have feature parity. Most notably, the javascript peer has no local storage for mediachain statements or data objects, so it can't be used to provide mediachain data. However, aleph is useful for interacting with local and remote concat nodes, and for exploring the mediachain network and peer-to-peer architecture.

There are currently two aleph subcommands, aleph repl and aleph query

aleph repl

The aleph repl command provides an interactive Read-Eval-Print-Loop for controlling a javascript mediachain node. When you start the repl, a new peer identity is created and stored in the ~/.mediachain/aleph directory. You can override that default with the --identityPath flag.

The repl provides a javascript prompt, and a global node object. This is an instance of the MediachainNode class, which implements the peer-to-peer protocols.

The repl can be used to remotely interact with another node using the mediachain protocol. For example:

א > node.ping('/ip4/54.205.184.122/tcp/9001/p2p/QmeiY2eHMwK92Zt6X4kUUC3MsjMmVb2VnGZ17DhnhRPCEQ')
true

The long string above is a multiaddr, which is a format for representing and combining addresses for multiple network protocols. The string above is for the peer-to-peer node with id QmeiY2eHMwK92Zt6X4kUUC3MsjMmVb2VnGZ17DhnhRPCEQ, located at the IP4 address 54.205.184.122, on tcp port 9001. The /p2p/ protocol identifier is not yet part of the multiaddr standard, but it is in the works as a replacement for the /ipfs/ identifier, and we've adopted it in anticipation of it being integrated into the standard soon.

Let's make our addresses a bit simpler by connecting to the Mediachain Labs directory server:

א > node.setDirectory('/ip4/52.7.126.237/tcp/9000/p2p/QmSdJVceFki4rDbcSrW7JTJZgU9so25Ko7oKHE97mGmkU6')

Now we can just use the peer identifier portion of the address, and the directory will provide us with the full address behind the scenes:

א > node.ping('QmeiY2eHMwK92Zt6X4kUUC3MsjMmVb2VnGZ17DhnhRPCEQ')
true

You can also provide the directory server address at the command line when launching the repl:

$ aleph repl --dir /ip4/52.7.126.237/tcp/9000/p2p/QmSdJVceFki4rDbcSrW7JTJZgU9so25Ko7oKHE97mGmkU6

This will set the directory address on startup, and avoid the need for the node.setDirectory call.

Pairing a remote node

Since the aleph repl is at its most useful when interacting with a remote node, there's built-in support for "pairing" the javascript aleph node to a remote node (most likely a concat node).

To do so, just provide the --remotePeer flag when launching the repl, and give it a multiaddr where the peer is located:

$ aleph repl --remotePeer /ip4/54.205.184.122/tcp/9001/p2p/QmeiY2eHMwK92Zt6X4kUUC3MsjMmVb2VnGZ17DhnhRPCEQ

Now, in addition to the global node object, you also have a remote object that represents the remote peer.

א > remote.query('SELECT * FROM images.dpla LIMIT 1')
[ { value: { simple: [Object] } } ]

The query result is printed at the repl in condensed form. To examine it further, we can use the "magic" _ variable, which holds the result of the last repl command. Assign it to a new variable, and we can interact with it more easily:

var result = _
console.dir(result[0].value.simple)
{ stmt: 
   { id: '4XTTM4K8sqTb7xYviJJcRDJ5W6TpQxMoJ7GtBstTALgh5wzGm:1478267497:1',
     publisher: '4XTTM4K8sqTb7xYviJJcRDJ5W6TpQxMoJ7GtBstTALgh5wzGm',
     namespace: 'images.dpla',
     body: 
      { simple: 
         { object: 'QmeFJSTPKSEiNqebxZvYcduWH8UBmxqNq724gHEQnxV5D1',
           refs: [ 'dpla_1ff6b36174426026847c8f8ca216ffa9' ],
           tags: [],
           deps: [ 'QmYGRQYmWC3BAtTAi88mFb7GVeFsUKGM4nm25SBUB9vfc9' ] } },
     timestamp: 1478267497,
     signature: 
      Buffer [...] } }

To also fetch the data objects associated with each result, use remote.queryWithData instead of remote.query.

aleph query

aleph query --remotePeer <peerAddress> <queryString> will execute a query on a remote peer using the peer-to-peer query protocol. This is very similar to the mcclient query command, with the exception that the --remotePeer argument is not optional, since the local aleph node does not have a local datastore.

Mediachain records are composed of two main components: statements and objects. Objects are the core metadata objects that represent a given artwork, person, or other resource. A statement is a mediachain-specific record that contextualizes an object within the mediachain network. For example, the statement includes the namespace in which the record was published, the ids of the publisher, the well-known identifiers attached to the record, etc.

By default, the aleph query command will only show the statements that match the query results. However, it's common that you'll want to see the content of the objects themselves.

Use the --includeData or -i flag to dereference the objects for each statement in the query results. For example:

$ aleph query --remotePeer /ip4/54.205.184.122/tcp/9001/ipfs/QmeiY2eHMwK92Zt6X4kUUC3MsjMmVb2VnGZ17DhnhRPCEQ --includeData 'SELECT * FROM images.dpla LIMIT 1' 

{
  "simple": {
    "stmt": {
      "id": "4XTTM4K8sqTb7xYviJJcRDJ5W6TpQxMoJ7GtBstTALgh5wzGm:1478267497:1",
      "publisher": "4XTTM4K8sqTb7xYviJJcRDJ5W6TpQxMoJ7GtBstTALgh5wzGm",
      "namespace": "images.dpla",
      "body": {
        "simple": {
          "object": {
            "key": "QmeFJSTPKSEiNqebxZvYcduWH8UBmxqNq724gHEQnxV5D1",
            "data": {
              "schema": {
                "/": "QmYGRQYmWC3BAtTAi88mFb7GVeFsUKGM4nm25SBUB9vfc9"
              },
              "data": {
                "artist_names": [
                  [
                    "Meredith L. Clausen"
                  ]
                ],
                "aspect_ratio": 0.7166666666666667,
                "attribution": [
                  {
                    "name": "Meredith L. Clausen"
                  }
                ],
                "omitted_for_bevity": "..."
              }
            }
          },
          "refs": [
            "dpla_1ff6b36174426026847c8f8ca216ffa9"
          ],
          "tags": [],
          "deps": [
            "QmYGRQYmWC3BAtTAi88mFb7GVeFsUKGM4nm25SBUB9vfc9"
          ]
        }
      },
      "timestamp": 1478267497,
      "signature": "yDhPpc/RIkW3+sHjl/cB00j3jurqMsDdb/tUyVMUfa6I4EnNiYdSqasxWTiRGtsaT2M/xX++RgRNQQ/97x8IDA=="
    }
  }
}

Development and contribution

Thanks! We welcome all contributions of ideas, bug reports, code, and whatever else you'd like to send our way. Please take a look at our contributing guidelines -- they are very friendly.

Code structure

The code lives in src, and is organized into a few main subdirectories:

• client/api contains the RestClient class, which provides a Promise-based wrapper around concat's HTTP API
• client/cli contains the code for the mcclient command line app, which uses RestClient for all of its functionality. The cli is powered by the yargs argument parser, and each subcommand is contained in its own module in client/cli/commands
• peer contains the javascript implementation of mediachain peer-to-peer nodes. There are two main node types, a DirectoryNode that corresponds to concat's mcdir command, and a MediachainNode that corresponds to concat's mcnode. Both use the LibP2PNode class (defined in src/peer/libp2p_node.js) for low-level peer-to-peer networking.
• protobuf contains protocol-buffer definitions for messages exchanged between nodes, and is kept in sync with concat.