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+=================
+Electrum Protocol
+=================
+
+Until now there was no written specification of the Electrum protocol
+that I am aware of; this document is an attempt to fill that gap.  It
+is intended to be a reference for client and server authors alike.
+
+I have attempted to ensure what is written is correct for the three
+known server implementations: electrum-server, jelectrum and
+ElectrumX, and also for Electrum clients of the 2.x series.  We know
+other clients exist but I am not aware of the source of any being
+publicly available.
+
+
+Message Stream
+--------------
+
+Clients and servers communicate using JSON RPC over an unspecified
+underlying stream transport protocol, typically TCP or SSL.
+
+`JSON RPC 1.0`_ and `JSON RPC 2.0`_ are specified; use of version 2.0
+is encouraged but not required.  Server support of batch requests is
+encouraged for version 1.0 but not required.  Clients making batch
+requests should limit their size depending on the nature of their
+query, because servers will limit response size as an anti-DoS
+mechanism.
+
+RPC calls and responses are separated by newlines in the stream.  The
+JSON specification does not permit control characters within strings,
+so no confusion is possible there.  However it does permit newlines as
+extraneous whitespace between elements; client and server MUST NOT use
+newlines in such a way.
+
+If using JSON RPC 2.0's feature of parameter passing by name, the
+names shown in the protocol versions's description MUST be used.
+
+A server advertising support for a particular protocol version MUST
+support each method documented for that protocol version, unless the
+method is explicitly marked optional.  It may support other methods or
+additional parameters with unspecified behaviour.  Use of additional
+parameters is discouraged as it may conflict with future versions of
+the protocol.
+
+Notifications
+-------------
+
+Some methods are subscriptions, which will respond with notifications
+when the thing subscribed to changes.  The `method` of the
+notification is the same as the method of the subscription, and the
+`params` of the notification (and their names) are given in the
+documentation of the method.
+
+
+Protocol Negotiation
+--------------------
+
+It is desirable to have a way to enhance and improve the protocol
+without forcing servers and clients to upgrade at the same time.
+Protocol negotiation is not implemented in any client or server at
+present to the best of my knowledge, so care is needed to ensure
+current clients and servers continue to operate as expected.
+
+Protocol versions are denoted by [major_number, minor_number] pairs,
+for example protocol version 1.15 is [1, 15] as a pair.
+
+A party to a connection speak all protocol versions in a range, say
+from `protocol_min` to `protocol_max`.  This min and max may be the
+same.  When a connection is made, both client and server must
+initially assume the protocol to use is their own `protocol_min`.
+
+The client should send a `server.version` RPC call as early as
+possible in order to negotiate the precise protocol version; see its
+description for more detail.  All responses received in the stream
+from and including the server's response to this call will use the
+negotiated protocol version.
+
+
+Protocol Version 1.0
+--------------------
+
+server.version
+==============
+
+Identifies the client to the server.
+
+  server.version(**client_name**, **protocol_version**)
+
+  **client_name**
+
+    An optional string identifying the connecting client software.
+
+  **protocol_verion**
+
+    Optional.  The value passed is ignored.
+
+**Response**
+
+  A string identifying the server software.
+
+**Example**::
+
+  server.version("2.7.11", "1.0")
+
+
+blockchain.address.get_balance
+==============================
+
+Return the confirmed and unconfirmed balances of a bitcoin address.
+
+  blockchain.address.get_balance(**address**)
+
+  **address**
+
+    The address as a Base58 string.
+
+**Response**
+
+  A dictionary with keys *confirmed* and *unconfirmed*.  The value of
+  each is the appropriate balance in coin units as a string.
+
+**Response Example**::
+
+  {
+    "confirmed": "1.03873966",
+    "unconfirmed": "0.236844"
+  }
+
+
+blockchain.address.get_history
+==============================
+
+Return the confirmed and unconfirmed history of a bitcoin address.
+
+  blockchain.address.get_history(**address**)
+
+  **address**
+
+    The address as a Base58 string.
+
+**Response**
+
+    A list of confirmed transactions in blockchain order, with the
+    output of *blockchain.address.get_mempool* appended to the list.
+    Each transaction is a dictionary with keys *height* and *tx_hash*.
+    *height* is the integer height of the block the transaction was
+    confirmed in, and *tx_hash* the transaction hash in hexadecimal.
+
+**Response Examples**
+
+::
+
+    [
+      {
+        "height": 200004,
+        "tx_hash": "acc3758bd2a26f869fcc67d48ff30b96464d476bca82c1cd6656e7d506816412"
+      },
+      {
+        "height": 215008,
+        "tx_hash": "f3e1bf48975b8d6060a9de8884296abb80be618dc00ae3cb2f6cee3085e09403"
+      }
+    ]
+
+::
+
+    [
+      {
+        "fee": 20000,
+        "height": 0,
+        "tx_hash": "9fbed79a1e970343fcd39f4a2d830a6bde6de0754ed2da70f489d0303ed558ec"
+      }
+    ]
+
+
+blockchain.address.get_mempool
+==============================
+
+Return the unconfirmed transactions of a bitcoin address.
+
+  blockchain.address.get_mempool(**address**)
+
+  **address**
+
+    The address as a Base58 string.
+
+**Response**
+
+    A list of mempool transactions in arbitrary order.  Each
+    transaction is a dictionary with keys *height* , *tx_hash* and
+    *fee*.  *tx_hash* the transaction hash in hexadecimal, *height* is
+    `0` if all inputs are confirmed, and `-1` otherwise, and *fee* is
+    the transaction fee in coin units.
+
+**Response Examples**
+
+::
+
+  [
+    {
+      "tx_hash": "45381031132c57b2ff1cbe8d8d3920cf9ed25efd9a0beb764bdb2f24c7d1c7e3",
+      "height": 0,
+      "fee": 24310
+    }
+  ]
+
+
+blockchain.address.get_proof
+============================
+
+This method is optional and deprecated, and hence its response will
+not be described here.
+
+  blockchain.address.get_proof(**address**)
+
+  **address**
+
+    The address as a Base58 string.
+
+
+blockchain.address.listunspent
+==============================
+
+Return an ordered list of UTXOs sent to a bitcoin address.
+
+  blockchain.address.listunspent(**address**)
+
+  **address**
+
+    The address as a Base58 string.
+
+**Response**
+
+    A list of unspent outputs in blockchain order.  Each transaction
+    is a dictionary with keys *height* , *tx_pos*, *tx_height* and
+    *value* keys.  *height* is the integer height of the block the
+    transaction was confirmed in, *tx_hash* the transaction hash in
+    hexadecimal, *tx_pos* the zero-based index of the output in the
+    transaction's list of outputs, and *value* its integer value in
+    minimum coin units (satoshis in the case of Bitcoin).
+
+**Response Example**
+
+::
+
+  [
+    {
+      "tx_pos": 0,
+      "value": 45318048,
+      "tx_hash": "9f2c45a12db0144909b5db269415f7319179105982ac70ed80d76ea79d923ebf",
+      "height": 437146
+    },
+    {
+      "tx_pos": 0,
+      "value": 919195,
+      "tx_hash": "3d2290c93436a3e964cfc2f0950174d8847b1fbe3946432c4784e168da0f019f",
+      "height": 441696
+    }
+  ]
+
+
+blockchain.address.subscribe
+============================
+
+Subscribe to a bitcoin address.
+
+  blockchain.address.subscribe(**address**)
+
+  **address**
+
+    The address as a Base58 string.
+
+**Response**
+
+  The *status* [1]_ of the address.
+
+**Notifications**
+
+  As this is a subcription, the client will receive a notification
+  when the status of the address changes.  The parameters are:
+
+    [**address**, **status**]
+
+.. [1] To calculate the *status* of an address, order confirmed
+       transactions touching the address by height (and position in
+       the block if there are more than one in a block).  Form a
+       string that is the concatenation of strings 'tx_hash:height:'
+       for each transaction in order.  *tx_hash* is the transaction
+       hash in hexadecimal, *height* the height of the block it is in.
+       Next, with mempool transactions in any order, append a string
+       that is the same, but where *height* is `-1` if the transaction
+       has at least one unconfirmed input, and `0` if all inputs are
+       confirmed.  The *status* is the **sha256** hash of this string
+       expressed in hexadecimal.
+
+
+blockchain.block.get_header
+===========================
+
+Return the *deserialized header* [2]_ of the block at the given height.
+
+  blockchain.block.get_chunk(**height**)
+
+  **height**
+
+    The height of the block, an integer.
+
+**Response**
+
+.. [2] The *deserialized header* of a block is a dictionary like
+       so::
+
+        {
+            "block_height": <integer>,
+            'version': <integer>,
+            'prev_block_hash': <hexadecimal string>,
+            'merkle_root':  <hexadecimal string>,
+            'timestamp': <integer>,
+            'bits': <integer>,
+            'nonce': <integer>,
+        }
+
+
+blockchain.block.get_chunk
+==========================
+
+Return a concatenated chunk of block headers.  A chunk consists of a
+fixed number of block headers over at the end of which difficulty is
+retargeted.
+
+So in the case of Bitcoin a chunk is 2,016 headers, each of 80 bytes,
+and chunk 5 is the block headers from height 10,080 to 12,095
+inclusive.  When encoded as hexadecimal, the response string is twice
+as long, so for Bitcoin it is 322,560 bytes long, making this a
+bandwidth-intensive request.
+
+  blockchain.block.get_chunk(**index**)
+
+  **index**
+
+    The zero-based index of the chunk, an integer.
+
+**Response**
+
+    The binary block headers, as hexadecimal strings, in order
+    concatenated together.
+
+
+blockchain.estimatefee
+======================
+
+Return the estimated transaction fee per kilobyte for a transaction to
+be confirmed within a certain number of blocks.
+
+  blockchain.block.get_chunk(**number**)
+
+  **number**
+
+    The number of blocks to target for confirmation.
+
+**Response**
+
+  The estimated transaction fee in coin units per kilobyte, as a
+  floating point number.  If the daemon does not have enough
+  information to make an estimate, the integer `-1` is returned.
+
+**Example Response**
+
+::
+  0.00101079
+
+
+blockchain.headers.subscribe
+============================
+
+Subscribe to receive block headers when a new block is found.
+
+  blockchain.headers.subscribe()
+
+**Response**
+
+  The *deserialized header* [2]_ of the current block.
+
+**Notification Parameters**
+
+  As this is a subcription, the client will receive a notification
+  when a new block is found.  The parameters are:
+
+    [**header**]
+
+
+blockchain.numblocks.subscribe
+==============================
+
+Subscribe to receive the block height when a new block is found.  This
+subscription is deprecated in favour of *blockchain.headers.subscribe*
+which provides more detailed information.
+
+  blockchain.numblocks.subscribe()
+
+**Response**
+
+  The height of the current block, an integer
+
+**Notification Parameters**
+
+  As this is a subcription, the client will receive a notification
+  when a new block is found.  The parameters are:
+
+    [**height**]
+
+
+blockchain.relayfee
+===================
+
+Return the minimum fee a low-priority tx must pay in order to be accepted
+to the daemon's memory pool.
+
+  blockchain.relayfee()
+
+**Response**
+
+  The fee in coin units as a floating point number.
+
+**Example Responses**
+
+::
+   1e-05
+
+::
+   0.0
+
+blockchain.transaction.broadcast
+================================
+
+Broadcast a transaction to the network.
+
+  blockchain.transaction.broadcast(**raw_tx**)
+
+  **raw_tx**
+
+    The raw transaction as a hexadecimal string.
+
+**Response**
+
+  Unfortunately the protocol version 1.0 API does not obey the JSON
+  specification for the response; this will be fixed in a future
+  version of the protocol.
+
+  If the daemon accepts the transaction, return the transaction hash
+  as a hexadecimal string.  If the daemon rejects the transaction, the
+  server must not return an error, but instead return the error
+  message string as the result.  The client needs to determine if an
+  error occurred by comparing the result to the expected transaction
+  hash.
+
+**Response Examples**
+
+::
+
+   'a76242fce5753b4212f903ff33ac6fe66f2780f34bdb4b33b175a7815a11a98e'
+
+::
+
+  '258: txn-mempool-conflict'
+
+
+blockchain.transaction.get
+==========================
+
+Return a raw transaction.
+
+  blockchain.transaction.get(**tx_hash**, **height**)
+
+  **tx_hash**
+
+    The transaction hash as a hexadecimal string.
+
+  **height**
+
+    The height at which it was confirmed, an integer.  This parameter
+    is optional and ignored; it is recommended that clients do not
+    send it as it will be removed in a future protocol version.
+
+**Response**
+
+    The raw transaction as a hexadecimal string.
+
+
+blockchain.transaction.get_merkle
+=================================
+
+Return the markle branch to a confirmed transaction given its hash
+and height.
+
+  blockchain.transaction.get(**tx_hash**, **height**)
+
+  **tx_hash**
+
+    The transaction hash as a hexadecimal string.
+
+  **height**
+
+    The height at which it was confirmed, an integer.
+
+**Response**
+
+  A dictionary with keys *block_height*, *merkle* and *pos*.
+  *block_height* is the height of the block the transaction was
+  confirmed in.  *merkle* is a list of transaction hashes the current
+  hash is paired with, recursively, in order to trace up to obtain
+  merkle root of the block, deepest pairing first.  *pos* is the
+  0-based index of the position of the transaction in the ordered list
+  of transactions in the block.
+
+**Response Examples**
+
+::
+
+  {
+    "merkle":
+    [
+      "713d6c7e6ce7bbea708d61162231eaa8ecb31c4c5dd84f81c20409a90069cb24",
+      "03dbaec78d4a52fbaf3c7aa5d3fccd9d8654f323940716ddf5ee2e4bda458fde",
+      "e670224b23f156c27993ac3071940c0ff865b812e21e0a162fe7a005d6e57851",
+      "369a1619a67c3108a8850118602e3669455c70cdcdb89248b64cc6325575b885",
+      "4756688678644dcb27d62931f04013254a62aeee5dec139d1aac9f7b1f318112",
+      "7b97e73abc043836fd890555bfce54757d387943a6860e5450525e8e9ab46be5",
+      "61505055e8b639b7c64fd58bce6fc5c2378b92e025a02583303f69930091b1c3",
+      "27a654ff1895385ac14a574a0415d3bbba9ec23a8774f22ec20d53dd0b5386ff",
+      "5312ed87933075e60a9511857d23d460a085f3b6e9e5e565ad2443d223cfccdc",
+      "94f60b14a9f106440a197054936e6fb92abbd69d6059b38fdf79b33fc864fca0",
+      "2d64851151550e8c4d337f335ee28874401d55b358a66f1bafab2c3e9f48773d"
+    ],
+    "block_height": 450538,
+    "pos": 710
+  }
+
+
+blockchain.utxo.get_address
+===========================
+
+Return the address paid to by a UTXO.  This method is optional and
+deprecated.
+
+  blockchain.utxo.get_address(**tx_hash**, **index**)
+
+  **tx_hash**
+
+    The transaction hash as a hexadecimal string.
+
+  **index**
+
+    The zero-based index of the UTXO in the transaction.
+
+**Response**
+
+  A Base58 address string, or *null*.  If the transaction doesn't
+  exist, the index is out of range, or the output is not paid to and
+  address, *null* must be returned.  If the output is spent *null* may
+  be returned.
+
+
+server.banner
+=============
+
+Return a banner to be shown in the Electrum console.
+
+  server.banner()
+
+The return value is a string.
+
+
+server.donation_address
+=======================
+
+Return a server donation address.
+
+  server.donation_address()
+
+The return value is a string.
+
+
+server.peers.subscribe
+======================
+
+Return a list of peer servers.  Despite the name this is not a
+subscription and the server must send no notifications.
+
+  server.peers.subscribe()
+
+**Response**
+
+  An array of peer servers.  Each entry is a triple like
+
+  ["107.150.45.210", "e.anonyhost.org", ["v1.0", "p10000", "t", "s995"]]
+
+  The first element is the IP address, the second is the host name
+  (which might also be an IP address), and the third is a list of
+  server features.  Each feature and starts with a letter.  'v'
+  indicates the server minimum protocol version, 'p' its pruning limit
+  and is omitted if it does not prune, 't' is the TCP port number, and
+  's' is the SSL port number.  If a port is not given for 's' or 't'
+  the default port for the coin network is implied.  If 's' or 't' is
+  missing then the server does not support that transport.
+
+
+Version 1.1 (provisional)
+-------------------------
+
+This protocol version is the same as version `1.0` except for the
+following changes:
+
+* improved semantics of `server.version` to aid protocol negotiation
+* deprecated methods `blockchain.address.get_proof`,
+  'blockchain.utxo.get_address' and `blockchain.numblocks.subscribe`
+  have been removed.
+* method `blockchain.transaction.get` no longer takes a *height*
+  argument
+* method `blockchain.transaction.broadcast` returns errors like any
+  other JSON RPC call.  A *tx_hash* result is only returned on
+  success.
+* new methods `server.features` and `server.add_peer`
+
+
+server.version
+==============
+
+Identify the client and inform the server the range of understood
+protocol versions.
+
+  server.version(**client_name**, **protocol_version** = ((1, 1), (1, 1)))
+
+**client_name**
+
+  An optional string identifying the connecting client software.
+
+**protocol_verion**
+
+  Optional with default value ((1, 1), (1, 1)).
+
+  It must be a pair [`protocol_min`, `protocol_max`], each of which is
+  itself a [major_version, minor_version] pair.
+
+  If a string was passed it should be interpreted as `protocol_min` and
+  `protocol_max` both being [1, 0].
+
+The server should use the highest protocol version both support:
+
+  protocol_version_to_use = min(client.protocol_max, server.protocol_max)
+
+If this is below
+
+  min(client.protocol_min, server.protocol_min)
+
+there is no protocol version in common and the server must close the
+connection.  Otherwise it should send a response appropriate for that
+protocol version.
+
+**Response**
+
+  A pair
+
+     [identifying_string, protocol_version]
+
+  identifying the server and the protocol version that will be used
+  for future communication.
+
+**Example**
+
+::
+
+  server.version('2.7.11', ((1, 0), (2, 0)))
+
+
+server.add_peer
+===============
+
+This call is intended for a new server to get itself into the server's
+peers list.
+
+  server.add_peer(**features**)
+
+  * **features**
+
+    The same information as a call to the client server's
+    **server.features** RPC call would return.
+
+
+server.features
+===============
+
+Get a list of features and services supported by the server.
+
+  server.features()
+
+**Response**
+
+  A dictionary of keys and values.  Each key represents a feature or
+  service of the server, and the value gives additional information.
+
+  The following features MUST be reported by the server.  Additional
+  key-value pairs may be returned.
+
+  * **hosts**
+
+    A dictionary of host names the server can be reached at.  Each
+    value is a dictionary with keys "ssl_port" and "tcp_port" at which
+    the given host can be reached.  If there is no open port for a
+    transport, its value should be *null*.
+
+  * **server_version**
+
+    The same identifying string as returned in response to *server.version*.
+
+  * **protocol_version**
+
+    A pair [`protocol_min`, `protocol_max`] of the protocols supported
+    by the server, each of which is itself a [major_version,
+    minor_version] pair.
+
+  * **pruning**
+
+    The history pruning limit of the server.  If the server does not
+    prune return *null*.
+
+**Example Response**
+
+::
+
+  {
+     "server_version": "ElectrumX 0.10.14",
+     "protocol_version": [[1, 0], [1, 1]],
+     "hosts": {"14.3.140.101": {"ssl_port": 50002, "tcp_port": 50001}},
+     "pruning": null
+  }
+
+.. _JSON RPC 1.0: http://json-rpc.org/wiki/specification
+.. _JSON RPC 2.0: http://json-rpc.org/specification