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concat1: concatenating cat, by contrast to copycat, used in a previous prototype

concat is a set of daemons that provide the backbone of the Mediachain peer-to-peer network. Please see RFC 4, and the Mediachain 1.0 developer update for a high level overview of this design.

The two main programs in concat are mcnode, which is the implementation of a fully featured Mediachain node, and mcdir, which implements a directory server for facilitating node discovery and connectivity.

For system-wide Mediachain documentation see


Precompiled Binaries

You can download the latest release mcnode binary for your platform (Linux or Mac) from releases.

Installing from Source

Concat requires Go 1.7 or later.

First clone the repo in your $GOPATH:

$ mkdir -p $GOPATH/src/
$ git clone $GOPATH/src/

You can then run the setup and install scripts which will build dependencies and install the programs in $GOPATH/bin:

$ cd $GOPATH/src/
$ ./ && ./ 

Warning: is quite slow; among the dependencies is gorocksdb, which takes several minutes to compile.

Running on Windows

We haven't succeeded building on Windows yet, as rocksdb dependencies do not build correctly under mingw-w64; see Issue 65.

You can however use the Linux binaries with the Linux Subsystem for Windows on Windows 10:

$ sudo add-apt-repository ppa:ubuntu-toolchain-r/test
$ sudo apt-get update
$ sudo apt-get install libstdc++6

You can then download the and unpack the mcnode Linux binary from Precompiled Binaries.


Getting Started

You can run your local mediachain node by invoking mcnode without arguments:

$ mcnode
2016/10/20 19:29:24 Generating new node identity
2016/10/20 19:29:25 Saving key to /home/vyzo/.mediachain/mcnode/identity.node
2016/10/20 19:29:25 Node ID: QmeBkfxcaBfA9pvzivRwhF2PM7sXpp4HHQbp7jfTkRCWEa
2016/10/20 19:29:25 Generating new publisher identity
2016/10/20 19:29:25 Saving key to /home/vyzo/.mediachain/mcnode/identity.publisher
2016/10/20 19:29:25 Publisher ID: 4XTTMADSKQUN3jkeZngbtuE35w9y5YnDTicVTeeji7N2Npkey
2016/10/20 19:29:25 Node is offline
2016/10/20 19:29:25 Serving client interface at

The first time you run mcnode, it will generate a pair of persistent identities and initialize the local store. By default, mcnode uses ~/.mediachain/mcnode as its root directory, but you can change this using the -d path/to/mcnode/home command line option.

mcnode is intended to be run as a daemon, so you can run it in a docker container, use daemon to daemonize, or simply run it inside a screen.

By default, the node starts disconnected from the p2p network and provides a client control api in localhost. You can control and use your node through the api using curl, but it is recommended to install Aleph. Aleph provides a fully featured client for mcnode named mcclient and we use it in the examples below.

Once your node is up and running you can check its status:

$ mcclient id
Peer ID: QmeBkfxcaBfA9pvzivRwhF2PM7sXpp4HHQbp7jfTkRCWEa
Publisher ID: 4XTTMADSKQUN3jkeZngbtuE35w9y5YnDTicVTeeji7N2Npkey
$ mcclient status

At this point you should designate some directories for looking up peers:

$ mcclient config dir /ip4/ /ip4/
Set 2 directory servers:

And your node is ready to go online:

$ mcclient status online
status set to online
$ mcclient listPeers
$ mcclient id QmeiY2eHMwK92Zt6X4kUUC3MsjMmVb2VnGZ17DhnhRPCEQ
Peer ID: QmeiY2eHMwK92Zt6X4kUUC3MsjMmVb2VnGZ17DhnhRPCEQ
Publisher ID: 4XTTM4K8sqTb7xYviJJcRDJ5W6TpQxMoJ7GtBstTALgh5wzGm
Info: Metadata for CC images from DPLA, 500px, and pexels; operated by Mediachain Labs.

Basic Operations

The basic mediachain operations are queries, local or remote, and merges of remote datasets.

Here, we query the namespaces for statements in the discovered peer's datastore and take a small sample from the images.dpla namespace:

$ mcclient query -r QmeiY2eHMwK92Zt6X4kUUC3MsjMmVb2VnGZ17DhnhRPCEQ "SELECT namespace FROM *"

$ mcclient query -r QmeiY2eHMwK92Zt6X4kUUC3MsjMmVb2VnGZ17DhnhRPCEQ "SELECT COUNT(*) FROM images.dpla"

$ mcclient query -r QmeiY2eHMwK92Zt6X4kUUC3MsjMmVb2VnGZ17DhnhRPCEQ "SELECT * FROM images.dpla LIMIT 5"
{ id: '4XTTM4K8sqTb7xYviJJcRDJ5W6TpQxMoJ7GtBstTALgh5wzGm:1476970964:0',
  publisher: '4XTTM4K8sqTb7xYviJJcRDJ5W6TpQxMoJ7GtBstTALgh5wzGm',
  namespace: 'images.dpla',
   { Body: 
      { Simple: 
         { object: 'Qma1LUdw5PAjfuZLXCbT5Qm5xnQFLkEejyXbLuvcKinF8K',
           refs: [ 'dpla_1349ede833fa9417b6f55be6bb402f6d' ] } } },
  timestamp: 1476970964,
  signature: 'mZMSMdMrahd40uyJChHAFLMvB5diR8qh9QI2kw0XUR7HxTo6sh2jtCzHZVBaKnOa7w9QkSrPdEU8qqfAsBEiDA==' }

We can merge remote datasets using a query; the node will merge in the statements selected by the query and associated metadata:

$ mcclient merge QmeiY2eHMwK92Zt6X4kUUC3MsjMmVb2VnGZ17DhnhRPCEQ "SELECT * FROM images.dpla LIMIT 5"
merged 5 statements and 5 objects

The statements and the associated metadata our now stored in the local node:

$ mcclient query "SELECT * FROM images.dpla"
{ id: '4XTTM4K8sqTb7xYviJJcRDJ5W6TpQxMoJ7GtBstTALgh5wzGm:1476970964:0',
  publisher: '4XTTM4K8sqTb7xYviJJcRDJ5W6TpQxMoJ7GtBstTALgh5wzGm',
  namespace: 'images.dpla',
   { Body: 
      { Simple: 
         { object: 'Qma1LUdw5PAjfuZLXCbT5Qm5xnQFLkEejyXbLuvcKinF8K',
           refs: [ 'dpla_1349ede833fa9417b6f55be6bb402f6d' ] } } },
  timestamp: 1476970964,
  signature: 'mZMSMdMrahd40uyJChHAFLMvB5diR8qh9QI2kw0XUR7HxTo6sh2jtCzHZVBaKnOa7w9QkSrPdEU8qqfAsBEiDA==' }

$ mcclient getData Qma1LUdw5PAjfuZLXCbT5Qm5xnQFLkEejyXbLuvcKinF8K
{ orientation: null,
  dedupe_hsh: '4e0783f1e8f41bac',
  licenses: [ { details: null } ],
  native_id: 'dpla_',
  keywords: [],
  date_created_original: null,
  title: [ 'Page 91' ],
  camera_exif: {},
  source: { url: '', name: 'dpla' },
  transient_info: { score_hotnessviews: null, likes: null },
  date_captured: null,
  location: { lat_lon: null, place_name: [] },
  attribution: null,
  description: 'kada',
  source_tags: [ '' ],
  date_created_at_source: null,
   [ { name: 'dpla' },
     { name: 'University of Southern California. Libraries' } ],
  date_source_version: null,
   [ { bytes: null,
       height: 120,
       uri_external: '',
       width: 66,
       content_type: 'image/jpeg',
       dpi: null } ],
  source_dataset: 'dpla',
  artist_names: [],
  url_direct: { url: '' },
   { medium: null,
     predicted_tags: null,
     has_people: null,
     colors: null,
     general_type: null,
     time_period: null },
  url_shown_at: { url: '' },
  aspect_ratio: 0.55 }

If you decide you no longer want to keep the statements you merged in your local store, you can delete them:

$ mcclient delete "DELETE FROM images.dpla"
Deleted 5 statements

Publishing Statements

You can publish statements to your local node by creating json objects with the metadata you want to publish.

For example, let's publish hello world in a couple different variations:

$ cat /tmp/hello.json 
{"id": "hello_1", "hello": "world"}
{"id": "hello_2", "hola": "mundo"}
$ mcclient publish --idSelector 'id' scratch.hello /tmp/hello.json
statement id: 4XTTMADSKQUN3jkeZngbtuE35w9y5YnDTicVTeeji7N2Npkey:1477063161:0 -- body: QmZDxgNgUT1J3rgjvnGjoxoA5efGNSN9Qvhq4FpvefmwnA -- refs: ["hello_1"]
statement id: 4XTTMADSKQUN3jkeZngbtuE35w9y5YnDTicVTeeji7N2Npkey:1477063161:1 -- body: QmcdACgobENfs7vuD2CpQGi8RdEkNyAmbmyqVvrA7Z57xu -- refs: ["hello_2"]
All statements published successfully

The statements and the metadata are now stored by the local node:

$ mcclient query 'SELECT * FROM scratch.hello'
{ id: '4XTTMADSKQUN3jkeZngbtuE35w9y5YnDTicVTeeji7N2Npkey:1477063161:0',
  publisher: '4XTTMADSKQUN3jkeZngbtuE35w9y5YnDTicVTeeji7N2Npkey',
  namespace: 'scratch.hello',
   { Body: 
      { Simple: 
         { object: 'QmZDxgNgUT1J3rgjvnGjoxoA5efGNSN9Qvhq4FpvefmwnA',
           refs: [ 'hello_1' ] } } },
  timestamp: 1477063161,
  signature: 'Q79Vgp7bl4J7rJo3DOmtueLGqHQpG3lpSyiXbTqX60oOdbPdju06m4epiQNrGLarfCsj2Opa0psX6EWm6BJkDw==' }
{ id: '4XTTMADSKQUN3jkeZngbtuE35w9y5YnDTicVTeeji7N2Npkey:1477063161:1',
  publisher: '4XTTMADSKQUN3jkeZngbtuE35w9y5YnDTicVTeeji7N2Npkey',
  namespace: 'scratch.hello',
   { Body: 
      { Simple: 
         { object: 'QmcdACgobENfs7vuD2CpQGi8RdEkNyAmbmyqVvrA7Z57xu',
           refs: [ 'hello_2' ] } } },
  timestamp: 1477063161,
  signature: 'bN7mAW3JKJAHtInSGM08IXoUx//qFJpySaCWPEe8P6Pm46XxoOrepG2Q2KrIQ5bs5oLKJkU7qHqFI2dQaHETCQ==' }

$ mcclient getData QmZDxgNgUT1J3rgjvnGjoxoA5efGNSN9Qvhq4FpvefmwnA
{ id: 'hello_1', hello: 'world' }

Going Public

In order to distribute statements stored in your node, it needs to become discoverable and accessible to other nodes. This happens by taking the node public, which registers with the directory.

Before you can take your node public however, you need to ensure that it is reachable in the network. By default, mcnode binds its p2p interface in port 9001 for all interfaces, so if your node is directly connected to the Internet (eg in a vps host), you don't have to do anything.

However, chances are your node is behind a NAT and you will need to configure it for traversal through the nat option.

Configuring NAT traversal

First, take the node offline because NAT config changes only take effect when the node goes online:

$ mcclient status offline

If you are behind a home router which supports upnp port mapping, you can set your NAT configuration to "auto":

$ mcclient config nat auto

If you are behind multiple NATs or behind a firewall that doesn't support port mapping (eg an AWS instance), then you need to manually configure your network to route traffic to the p2p port in your host. If you mapped the port transparently, you can set your NAT configuration to "*", which will automatically detect the IP address and advertise the locally bound port:

$ mcclient config nat "*"

If you have mapped a different port to your host interface, then you need to specify it explicitly:

$ mcclient config nat "*:port"

Registering with the Directory

As a final preperation for goind public, you should add a short description about your node and its contents:

$ mcclient config info "Metadata from ...; Operated by ..."

Then your node should be ready to take it public:

$ mcclient status public

This will register the node with the configured directory, which will make it visible to other nodes through mcclient listPeers.

If you want to take your node back offline, you can simply do so with status offline:

$ mcclient status offline



The node contains the statement db and the datastore.

The datastore contains the metadata per se, as CBOR objects (IPLD compatible to the best of our ability) of unspecified schema, stored in RocksDB in point lookup mode.

The statement db contains statements about one (currently) or more metadata objects: their publisher, namespace, timestamp and signature. Statements are protobuf objects sent over the wire between peers to signal publication or sharing of metadata; when stored, they act as an index to the datastore. This db is currently stored in SQLite.


MCQL is a query language for retrieving statements from the node's statement db. It supports SELECT (and DELETE) statements with a syntax very similar to SQL, where namespaces play the role of tables.

Some basic MCQL statements:

-- count statements in the database

-- see all namespaces in the database
SELECT namespace FROM *

-- count statements in the namespace images.dpla
SELECT COUNT(*) FROM images.dpla

-- lookup statements by media WKI
SELECT * FROM images.dpla WHERE wki = dpla_871570744a860166dba198ca95e13590

-- retrieve a sample of 5 statements from namespace
SELECT * FROM images.dpla LIMIT 5

-- retrieve the last 5 statements merged in the db
SELECT * FROM images.dpla ORDER BY counter DESC LIMIT 5

-- retrieve statement id, insertion counter tuples
SELECT (id, counter) FROM images.dpla

-- see all publishers in the namespace
SELECT publisher FROM images.dpla

-- retrieve all statements by a publisher
SELECT * FROM images.dpla WHERE publisher = 4XTTM4K8sqTb7xYviJJcRDJ5W6TpQxMoJ7GtBstTALgh5wzGm

The full grammar for MCQL is defined as a PEG in query.peg


A REST API is provided for controlling the node. This is an administrative interface and should NOT be accessible to the wider network.

  • GET /id -- node info for the local node
  • GET /id/{peerId} -- node info for peer given by peerId
  • GET /ping/{peerId} -- ping! [DEPRECATED]
  • POST /publish/{namespace} -- publish a batch of statements to the specified namespace
  • POST /publish/{namespace}/{combine} -- publish a batch of statements with CompoundStatement grouping
  • POST /import -- ingest a stream of json-encoded signed statements (e.g. from an archive)
  • GET /stmt/{statementId} -- retrieve statement by statementId
  • POST /query -- issue MCQL SELECT query on the local node
  • POST /query/{peerId} -- issue MCQL SELECT query on a remote peer
  • POST /merge/{peerId} -- query a peer and merge the resulting statements and metadata
  • POST /push/{peerId} -- issue a local query and push the resulting statements to a remote peer.
  • POST /delete -- delete statements matching this MCQL DELETE query
  • POST vacuum/incremental -- perform an incremental statement db vacuum
  • POST vacuum/full -- perform a full statement db vacuum
  • POST /data/put -- add a batch of data objects to datastore
  • POST /data/get -- get a batch of objects from the datastore
  • GET /data/get/{objectId} -- get a single object from the datastore; 404 semantics
  • POST /data/merge/{peerId} -- merge raw data objects from peer
  • POST /data/gc -- garbage collect the datastore; deletes objects unreferenced by any statement
  • POST /data/compact -- compact the datastore
  • POST /data/sync -- sync the datastore and flush the WAL
  • GET /data/keys -- dump all object keys in the datastore
  • GET /status -- get node network state
  • POST /status/{state} -- control network state (online/offline/public)
  • GET /auth -- retrieve all push authorization rules
  • GET/POST /auth/{peerId} -- retrieve/grant/revoke push authorization to a peer
  • GET/POST /config/dir -- retrieve/set configured directories
  • GET/POST /config/nat -- retrieve/set NAT setting
  • GET/POST /config/info -- retrieve/set info string
  • GET/POST /manifest -- get/set the node manifest list
  • GET /manifest/self -- make a manifest body for this node
  • GET /manifest/{peerId} -- retrieve the manifest list of a remote peer
  • GET /dir/list -- list all peers registered with the directory
  • GET /dir/list/{namespace} -- list peers providing namespace in the directory
  • GET /dir/listns -- list namespaces in the directory
  • GET /dir/listmf/{entity} -- list manifests in the directory for entity
  • GET /net/addr -- list self addresses
  • GET /net/addr/{peerId} -- list known addresses for peer
  • GET /net/conns -- list active peer connections
  • GET /net/lookup/{peerId} -- lookup a peer address in the network
  • GET /net/identify/{peerId} -- identify a peer using the ipfs/identify protocol
  • GET /net/ping/{peerId} -- ping a peer using the ipfs/ping protocol
  • POST /shutdown -- shutdown the node




See also roles.



  1. alternately funes, cf. aleph