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authorxsipewe <[email protected]>2016-06-21 15:50:34 +0200
committerLukas Larsson <[email protected]>2016-07-13 11:30:48 +0200
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tree3f1550c75327118ad0255220344ee43313f52a67 /erts/doc/src/erl_dist_protocol.xml
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erts: Editorial changes
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<file>erl_dist_protocol.xml</file>
</header>
-<p>
-The description here is far from complete and will therefore be further
-refined in upcoming releases.
-
-The protocols both from Erlang nodes towards
-EPMD (Erlang Port Mapper Daemon) and between Erlang nodes, however, are
-stable since many years.
-</p>
-
-<p>The distribution protocol can be divided into four (4) parts:</p>
-<list>
- <item>
- <p>
- 1. Low level socket connection.
- </p>
- </item>
- <item>
- 2. Handshake, interchange node name and authenticate.
- </item>
- <item>
- 3. Authentication (done by net_kernel).
- </item>
- <item>
- 4. Connected.
- </item>
-</list>
-<p>
- A node fetches the Port number of another node through the EPMD (at the
- other host) in order to initiate a connection request.
-</p>
-<p>
-For each host where a distributed Erlang node is running there should also
-be an EPMD running. The EPMD can be started explicitly or automatically
-as a result of the Erlang node startup.
-</p>
-<p>
-By default EPMD listens on port 4369.
-</p>
-<p>
- 3 and 4 are performed at the same level but the net_kernel disconnects the
- other node if it communicates using an invalid cookie (after one (1) second).
-</p>
-
-<p>The integers in all multi-byte fields are in big-endian order.</p>
+ <p>This description is far from complete. It will be updated if the
+ protocol is updated. However, the protocols, both from Erlang
+ nodes to the Erlang Port Mapper Daemon (EPMD) and between Erlang nodes
+ are stable since many years.</p>
+
+ <p>The distribution protocol can be divided into four parts:</p>
+
+ <list type="bulleted">
+ <item>
+ <p>Low-level socket connection (1)</p>
+ </item>
+ <item>
+ <p>Handshake, interchange node name, and authenticate (2)</p>
+ </item>
+ <item>
+ <p>Authentication (done by <seealso marker="kernel:net_kernel">
+ <c>kernel:net_kernel</c></seealso>) (3)</p>
+ </item>
+ <item>
+ <p>Connected (4)</p>
+ </item>
+ </list>
+
+ <p>A node fetches the port number of another node through the EPMD (at the
+ other host) to initiate a connection request.</p>
+
+ <p>For each host, where a distributed Erlang node is running, also an EPMD
+ is to be running. The EPMD can be started explicitly or automatically
+ as a result of the Erlang node startup.</p>
+
+ <p>By default the EPMD listens on port 4369.</p>
+
+ <p>(3) and (4) above are performed at the same level but the <c>net_kernel</c>
+ disconnects the other node if it communicates using an invalid cookie (after
+ 1 second).</p>
+
+ <p>The integers in all multibyte fields are in big-endian order.</p>
<section>
<title>EPMD Protocol</title>
- <p>
- The requests served by the EPMD (Erlang Port Mapper Daemon) are
- summarized in the figure below.
- </p>
-
- <image file="erl_ext_fig.gif">
- <icaption>
- Summary of EPMD requests.
- </icaption>
- </image>
- <p>
- Each request <c>*_REQ</c> is preceded by a two-byte length field.
- Thus, the overall request format is:
- </p>
+ <p>The requests served by the EPMD are summarized in the following
+ figure.</p>
+
+ <image file="erl_ext_fig.gif">
+ <icaption>Summary of EPMD Requests</icaption>
+ </image>
+
+ <p>Each request <c>*_REQ</c> is preceded by a 2 byte length field.
+ Thus, the overall request format is as follows:</p>
+
+ <table align="left">
+ <row>
+ <cell align="center">2</cell>
+ <cell align="center">n</cell>
+ </row>
+ <row>
+ <cell align="center"><c>Length</c></cell>
+ <cell align="center"><c>Request</c></cell>
+ </row>
+ <tcaption>Request Format</tcaption>
+ </table>
+
+ <section>
+ <title>Register a Node in EPMD</title>
+ <p>When a distributed node is started it registers itself in the EPMD.
+ The message <c>ALIVE2_REQ</c> described below is sent from the node to
+ the EPMD. The response from the EPMD is <c>ALIVE2_RESP</c>.</p>
+
+ <table align="left">
+ <row>
+ <cell align="center">1</cell>
+ <cell align="center">2</cell>
+ <cell align="center">1</cell>
+ <cell align="center">1</cell>
+ <cell align="center">2</cell>
+ <cell align="center">2</cell>
+ <cell align="center">2</cell>
+ <cell align="center">Nlen</cell>
+ <cell align="center">2</cell>
+ <cell align="center">Elen</cell>
+ </row>
+ <row>
+ <cell align="center"><c>120</c></cell>
+ <cell align="center"><c>PortNo</c></cell>
+ <cell align="center"><c>NodeType</c></cell>
+ <cell align="center"><c>Protocol</c></cell>
+ <cell align="center"><c>HighestVersion</c></cell>
+ <cell align="center"><c>LowestVersion</c></cell>
+ <cell align="center"><c>Nlen</c></cell>
+ <cell align="center"><c>NodeName</c></cell>
+ <cell align="center"><c>Elen</c></cell>
+ <cell align="center"><c>Extra</c></cell>
+ </row>
+ <tcaption>ALIVE2_REQ (120)</tcaption>
+ </table>
+
+ <taglist>
+ <tag><c>PortNo</c></tag>
+ <item>
+ <p>The port number on which the node accept connection requests.</p>
+ </item>
+ <tag><c>NodeType</c></tag>
+ <item>
+ <p>77 = normal Erlang node, 72 = hidden node (C-node), ...</p>
+ </item>
+ <tag><c>Protocol</c></tag>
+ <item>
+ <p>0 = TCP/IPv4, ...</p>
+ </item>
+ <tag><c>HighestVersion</c></tag>
+ <item>
+ <p>The highest distribution version that this node can handle.
+ The value in Erlang/OTP R6B and later is 5.</p>
+ </item>
+ <tag><c>LowestVersion</c></tag>
+ <item>
+ <p>The lowest distribution version that this node can handle.
+ The value in Erlang/OTP R6B and later is 5.</p>
+ </item>
+ <tag><c>Nlen</c></tag>
+ <item>
+ <p>The length (in bytes) of field <c>NodeName</c>.</p>
+ </item>
+ <tag><c>NodeName</c></tag>
+ <item>
+ <p>The node name as an UTF-8 encoded string of <c>Nlen</c> bytes.</p>
+ </item>
+ <tag><c>Elen</c></tag>
+ <item>
+ <p>The length of field <c>Extra</c>.</p>
+ </item>
+ <tag><c>Extra</c></tag>
+ <item>
+ <p>Extra field of <c>Elen</c> bytes.</p>
+ </item>
+ </taglist>
+
+ <p>The connection created to the EPMD must be kept as long as the
+ node is a distributed node. When the connection is closed,
+ the node is automatically unregistered from the EPMD.</p>
+
+ <p>The response message <c>ALIVE2_RESP</c> is as follows:</p>
+
+ <table align="left">
+ <row>
+ <cell align="center">1</cell>
+ <cell align="center">1</cell>
+ <cell align="center">2</cell>
+ </row>
+ <row>
+ <cell align="center"><c>121</c></cell>
+ <cell align="center"><c>Result</c></cell>
+ <cell align="center"><c>Creation</c></cell>
+ </row>
+ <tcaption>ALIVE2_RESP (121)</tcaption>
+ </table>
+
+ <p>Result = 0 -> ok, result &gt; 0 -> error.</p>
+ </section>
+
+ <section>
+ <title>Unregister a Node from EPMD</title>
+ <p>A node unregisters itself from the EPMD by closing the TCP
+ connection to EPMD established when the node was registered.</p>
+ </section>
+
+ <section>
+ <title>Get the Distribution Port of Another Node</title>
+ <p>When one node wants to connect to another node it starts with
+ a <c>PORT_PLEASE2_REQ</c> request to the EPMD on the host where the
+ node resides to get the distribution port that the node listens to.</p>
+
+ <table align="left">
+ <row>
+ <cell align="center">1</cell>
+ <cell align="center">N</cell>
+ </row>
+ <row>
+ <cell align="center"><c>122</c></cell>
+ <cell align="center"><c>NodeName</c></cell>
+ </row>
+ <tcaption>PORT_PLEASE2_REQ (122)</tcaption>
+ </table>
+
+ <p>where N = <c>Length</c> - 1.</p>
+
+ <table align="left">
+ <row>
+ <cell align="center">1</cell>
+ <cell align="center">1</cell>
+ </row>
+ <row>
+ <cell align="center"><c>119</c></cell>
+ <cell align="center"><c>Result</c></cell>
+ </row>
+ <tcaption>PORT2_RESP (119) Response Indicating Error, Result &gt; 0
+ </tcaption>
+ </table>
+
+ <p>or</p>
+
+ <table align="left">
+ <row>
+ <cell align="center">1</cell>
+ <cell align="center">1</cell>
+ <cell align="center">2</cell>
+ <cell align="center">1</cell>
+ <cell align="center">1</cell>
+ <cell align="center">2</cell>
+ <cell align="center">2</cell>
+ <cell align="center">2</cell>
+ <cell align="center">Nlen</cell>
+ <cell align="center">2</cell>
+ <cell align="center">Elen</cell>
+ </row>
+ <row>
+ <cell align="center"><c>119</c></cell>
+ <cell align="center"><c>Result</c></cell>
+ <cell align="center"><c>PortNo</c></cell>
+ <cell align="center"><c>NodeType</c></cell>
+ <cell align="center"><c>Protocol</c></cell>
+ <cell align="center"><c>HighestVersion</c></cell>
+ <cell align="center"><c>LowestVersion</c></cell>
+ <cell align="center"><c>Nlen</c></cell>
+ <cell align="center"><c>NodeName</c></cell>
+ <cell align="center"><c>Elen</c></cell>
+ <cell align="center">><c>Extra</c></cell>
+ </row>
+ <tcaption>PORT2_RESP, Result = 0</tcaption>
+ </table>
+
+ <p>If <c>Result</c> &gt; 0, the packet only consists of
+ <c>[119, Result]</c>.</p>
+
+ <p>The EPMD closes the socket when it has sent the information.</p>
+ </section>
+
+ <section>
+ <title>Get All Registered Names from EPMD</title>
+ <p>This request is used through the Erlang function
+ <seealso marker="kernel:net_adm#names/1,2">
+ <c>net_adm:names/1,2</c></seealso>. A TCP connection is opened
+ to the EPMD and this request is sent.</p>
+
+ <table align="left">
+ <row>
+ <cell align="center">1</cell>
+ </row>
+ <row>
+ <cell align="center"><c>110</c></cell>
+ </row>
+ <tcaption>NAMES_REQ (110)</tcaption>
+ </table>
+
+ <p>The response for a <c>NAMES_REQ</c> is as follows:</p>
+
+ <table align="left">
+ <row>
+ <cell align="center">4</cell>
+ <cell align="center">&nbsp;</cell>
+ </row>
+ <row>
+ <cell align="center"><c>EPMDPortNo</c></cell>
+ <cell align="center"><c>NodeInfo*</c></cell>
+ </row>
+ <tcaption>NAMES_RESP</tcaption>
+ </table>
+
+ <p><c>NodeInfo</c> is a string written for each active node.
+ When all <c>NodeInfo</c> has been written the connection is
+ closed by the EPMD.</p>
+
+ <p><c>NodeInfo</c> is, as expressed in Erlang:</p>
+
+ <code>
+io:format("name ~ts at port ~p~n", [NodeName, Port]).</code>
+ </section>
+
+ <section>
+ <title>Dump All Data from EPMD</title>
+ <p>This request is not really used, it is to be regarded as a debug
+ feature.</p>
+
+ <table align="left">
+ <row>
+ <cell align="center">1</cell>
+ </row>
+ <row>
+ <cell align="center"><c>100</c></cell>
+ </row>
+ <tcaption>DUMP_REQ</tcaption>
+ </table>
+
+ <p>The response for a <c>DUMP_REQ</c> is as follows:</p>
+
+ <table align="left">
+ <row>
+ <cell align="center">4</cell>
+ <cell align="center">&nbsp;</cell>
+ </row>
+ <row>
+ <cell align="center"><c>EPMDPortNo</c></cell>
+ <cell align="center"><c>NodeInfo*</c></cell>
+ </row>
+ <tcaption>DUMP_RESP</tcaption>
+ </table>
+
+ <p><c>NodeInfo</c> is a string written for each node kept in the EPMD.
+ When all <c>NodeInfo</c> has been written the connection is
+ closed by the EPMD.</p>
+
+ <p><c>NodeInfo</c> is, as expressed in Erlang:</p>
+
+ <code>
+io:format("active name ~ts at port ~p, fd = ~p~n",
+ [NodeName, Port, Fd]).</code>
+
+ <p>or</p>
+
+ <code>
+io:format("old/unused name ~ts at port ~p, fd = ~p ~n",
+ [NodeName, Port, Fd]).</code>
+ </section>
+
+ <section>
+ <title>Kill EPMD</title>
+ <p>This request kills the running EPMD. It is almost never used.</p>
+
+ <table align="left">
+ <row>
+ <cell align="center">1</cell>
+ </row>
+ <row>
+ <cell align="center"><c>107</c></cell>
+ </row>
+ <tcaption>KILL_REQ</tcaption>
+ </table>
+
+ <p>The response for a <c>KILL_REQ</c> is as follows:</p>
<table align="left">
- <row>
- <cell align="center">2</cell>
- <cell align="center">n</cell>
- </row>
- <row>
- <cell align="center">Length</cell>
- <cell align="center">Request</cell>
- </row>
- <tcaption></tcaption></table>
-
- <section>
- <title>Register a node in the EPMD</title>
- <p>
- When a distributed node is started it registers itself in EPMD.
- The message ALIVE2_REQ described below is sent from the node towards
- EPMD. The response from EPMD is ALIVE2_RESP.
- </p>
- <table align="left">
- <row>
- <cell align="center">1</cell>
- <cell align="center">2</cell>
- <cell align="center">1</cell>
- <cell align="center">1</cell>
- <cell align="center">2</cell>
- <cell align="center">2</cell>
- <cell align="center">2</cell>
- <cell align="center">Nlen</cell>
- <cell align="center">2</cell>
- <cell align="center">Elen</cell>
- </row>
- <row>
- <cell align="center">120</cell>
- <cell align="center">PortNo</cell>
- <cell align="center">NodeType</cell>
- <cell align="center">Protocol</cell>
- <cell align="center">HighestVersion</cell>
- <cell align="center">LowestVersion</cell>
- <cell align="center">Nlen</cell>
- <cell align="center">NodeName</cell>
- <cell align="center">Elen</cell>
- <cell align="center">Extra</cell>
- </row>
- <tcaption>ALIVE2_REQ (120)</tcaption></table>
- <taglist>
- <tag><c>PortNo</c></tag>
- <item>
- The port number on which the node accept connection requests.
- </item>
- <tag><c>NodeType</c></tag>
- <item>
- 77 = normal Erlang node, 72 = hidden node (C-node),...
- </item>
- <tag><c>Protocol</c></tag>
- <item>
- 0 = tcp/ip-v4, ...
- </item>
- <tag><c>HighestVersion</c></tag>
- <item>
- The highest distribution version that this node can handle.
- The value in R6B and later is 5.
- </item>
- <tag><c>LowestVersion</c></tag>
- <item>
- The lowest distribution version that this node can handle.
- The value in R6B and later is 5.
- </item>
- <tag><c>Nlen</c></tag>
- <item>
- The length (in bytes) of the <c>NodeName</c> field.
- </item>
- <tag><c>NodeName</c></tag>
- <item>
- The NodeName as an UTF-8 encoded string of
- <c>Nlen</c> bytes.
- </item>
- <tag><c>Elen</c></tag>
- <item>
- The length of the <c>Extra</c> field.
- </item>
- <tag><c>Extra</c></tag>
- <item>
- Extra field of <c>Elen</c> bytes.
- </item>
- </taglist>
- <p>
- The connection created to the EPMD must be kept as long as the
- node is a distributed node. When the connection is closed
- the node is automatically unregistered from the EPMD.
- </p>
- <p>
- The response message ALIVE2_RESP is described below.
- </p>
-
- <table align="left">
- <row>
- <cell align="center">1</cell>
- <cell align="center">1</cell>
- <cell align="center">2</cell>
- </row>
- <row>
- <cell align="center">121</cell>
- <cell align="center">Result</cell>
- <cell align="center">Creation</cell>
- </row>
- <tcaption>ALIVE2_RESP (121)</tcaption></table>
- <p>
- Result = 0 -> ok, Result > 0 -> error
- </p>
- </section>
-
- <section>
- <title>Unregister a node from the EPMD</title>
- <p>
- A node unregisters itself from the EPMD by simply closing the
- TCP connection towards EPMD established when the node was registered.
- </p>
- </section>
-
- <section>
- <title>Get the distribution port of another node</title>
- <p>
- When one node wants to connect to another node it starts with
- a PORT_PLEASE2_REQ request towards EPMD on the host where the
- node resides in order to get the distribution port that the node
- listens to.
- </p>
-
- <table align="left">
- <row>
- <cell align="center">1</cell>
- <cell align="center">N</cell>
- </row>
- <row>
- <cell align="center">122</cell>
- <cell align="center">NodeName</cell>
- </row>
- <tcaption>PORT_PLEASE2_REQ (122)</tcaption></table>
- <p>
- where N = Length - 1
- </p>
-
- <p>
- </p>
+ <row>
+ <cell align="center">2</cell>
+ </row>
+ <row>
+ <cell align="center"><c>OKString</c></cell>
+ </row>
+ <tcaption>KILL_RESP</tcaption>
+ </table>
+
+ <p>where <c>OKString</c> is "OK".</p>
+ </section>
+
+ <section>
+ <title>STOP_REQ (Not Used)</title>
+ <table align="left">
+ <row>
+ <cell align="center">1</cell>
+ <cell align="center">n</cell>
+ </row>
+ <row>
+ <cell align="center"><c>115</c></cell>
+ <cell align="center"><c>NodeName</c></cell>
+ </row>
+ <tcaption>STOP_REQ</tcaption>
+ </table>
+
+ <p>where n = <c>Length</c> - 1.</p>
+
+ <p>The current implementation of Erlang does not care if the connection
+ to the EPMD is broken.</p>
+
+ <p>The response for a <c>STOP_REQ</c> is as follows:</p>
+
<table align="left">
- <row>
- <cell align="center">1</cell>
- <cell align="center">1</cell>
- </row>
- <row>
- <cell align="center">119</cell>
- <cell align="center">Result</cell>
- </row>
- <tcaption>
- PORT2_RESP (119) response indicating error, Result > 0.
- </tcaption>
+ <row>
+ <cell align="center">7</cell>
+ </row>
+ <row>
+ <cell align="center"><c>OKString</c></cell>
+ </row>
+ <tcaption>STOP_RESP</tcaption>
</table>
- <p>Or</p>
+
+ <p>where <c>OKString</c> is "STOPPED".</p>
+
+ <p>A negative response can look as follows:</p>
+
<table align="left">
- <row>
- <cell align="center">1</cell>
- <cell align="center">1</cell>
- <cell align="center">2</cell>
- <cell align="center">1</cell>
- <cell align="center">1</cell>
- <cell align="center">2</cell>
- <cell align="center">2</cell>
- <cell align="center">2</cell>
- <cell align="center">Nlen</cell>
- <cell align="center">2</cell>
- <cell align="center">Elen</cell>
- </row>
- <row>
- <cell align="center">119</cell>
- <cell align="center">Result</cell>
- <cell align="center">PortNo</cell>
- <cell align="center">NodeType</cell>
- <cell align="center">Protocol</cell>
- <cell align="center">HighestVersion</cell>
- <cell align="center">LowestVersion</cell>
- <cell align="center">Nlen</cell>
- <cell align="center">NodeName</cell>
- <cell align="center">Elen</cell>
- <cell align="center">Extra</cell>
- </row>
- <tcaption>PORT2_RESP when Result = 0.</tcaption></table>
-<p>
-If Result > 0, the packet only consists of [119, Result].
-</p>
-
- <p>EPMD will close the socket as soon as it has sent the information.</p>
- </section>
-
- <section>
- <title>Get all registered names from EPMD</title>
- <p>
- This request is used via the Erlang function
- <c>net_adm:names/1,2</c>. A TCP connection is opened
- towards EPMD and this request is sent.
- </p>
- <table align="left">
- <row>
- <cell align="center">1</cell>
- </row>
- <row>
- <cell align="center">110</cell>
- </row>
- <tcaption>NAMES_REQ (110)</tcaption></table>
-
-
- <p>The response for a <c>NAMES_REQ</c> looks like this:</p>
- <table align="left">
- <row>
- <cell align="center">4</cell>
- <cell align="center">&nbsp;</cell>
- </row>
- <row>
- <cell align="center">EPMDPortNo</cell>
- <cell align="center">NodeInfo*</cell>
- </row>
- <tcaption>NAMES_RESP</tcaption></table>
- <p>
- NodeInfo is a string written for each active node.
- When all NodeInfo has been written the connection is
- closed by EPMD.
- </p>
- <p>
- NodeInfo is, as expressed in Erlang:
- </p>
- <code>
- io:format("name ~ts at port ~p~n", [NodeName, Port]).
- </code>
- </section>
-
-
- <section>
- <title>Dump all data from EPMD</title>
- <p>
- This request is not really used, it should be regarded as a debug
- feature.
- </p>
- <table align="left">
- <row>
- <cell align="center">1</cell>
- </row>
- <row>
- <cell align="center">100</cell>
- </row>
- <tcaption>DUMP_REQ</tcaption></table>
-
- <p>The response for a <c>DUMP_REQ</c> looks like this:</p>
- <table align="left">
- <row>
- <cell align="center">4</cell>
- <cell align="center">&nbsp;</cell>
- </row>
- <row>
- <cell align="center">EPMDPortNo</cell>
- <cell align="center">NodeInfo*</cell>
- </row>
- <tcaption>DUMP_RESP</tcaption></table>
- <p>
- NodeInfo is a string written for each node kept in EPMD.
- When all NodeInfo has been written the connection is
- closed by EPMD.
- </p>
- <p>
- NodeInfo is, as expressed in Erlang:
- </p>
- <code>
- io:format("active name ~ts at port ~p, fd = ~p~n",
- [NodeName, Port, Fd]).
- </code>
- <p>
- or
- </p>
- <code>
- io:format("old/unused name ~ts at port ~p, fd = ~p ~n",
- [NodeName, Port, Fd]).
- </code>
-
- </section>
-
- <section>
- <title>Kill the EPMD</title>
- <p>
- This request will kill the running EPMD. It is almost never used.
- </p>
- <table align="left">
- <row>
- <cell align="center">1</cell>
- </row>
- <row>
- <cell align="center">107</cell>
- </row>
- <tcaption>KILL_REQ</tcaption></table>
-
- <p>The response fo a <c>KILL_REQ</c> looks like this:</p>
- <table align="left">
- <row>
- <cell align="center">2</cell>
- </row>
- <row>
- <cell align="center">OKString</cell>
- </row>
- <tcaption>KILL_RESP</tcaption></table>
- <p>
- where <c>OKString</c> is "OK".
- </p>
- </section>
-
- <section>
- <title>STOP_REQ (Not Used)</title>
- <p></p>
- <table align="left">
- <row>
- <cell align="center">1</cell>
- <cell align="center">n</cell>
- </row>
- <row>
- <cell align="center">115</cell>
- <cell align="center">NodeName</cell>
- </row>
- <tcaption>STOP_REQ</tcaption></table>
- <p>
- where n = Length - 1
- </p>
- <p>
- The current implementation of Erlang does not care if the connection
- to the EPMD is broken.
- </p>
- <p>The response for a <c>STOP_REQ</c> looks like this.</p>
- <table align="left">
- <row>
- <cell align="center">7</cell>
- </row>
- <row>
- <cell align="center">OKString</cell>
- </row>
- <tcaption>STOP_RESP</tcaption></table>
- <p>
- where OKString is "STOPPED".
- </p>
- <p>A negative response can look like this.</p>
- <table align="left">
- <row>
- <cell align="center">7</cell>
- </row>
- <row>
- <cell align="center">NOKString</cell>
- </row>
- <tcaption>STOP_NOTOK_RESP</tcaption></table>
- <p>
- where NOKString is "NOEXIST".
- </p>
- </section>
+ <row>
+ <cell align="center">7</cell>
+ </row>
+ <row>
+ <cell align="center"><c>NOKString</c></cell>
+ </row>
+ <tcaption>STOP_NOTOK_RESP</tcaption>
+ </table>
+
+ <p>where <c>NOKString</c> is "NOEXIST".</p>
+ </section>
<!--
- <section>
- <title>ALIVE_REQ (97)</title>
- <p></p>
-
- <table align="left">
- <row>
- <cell align="center">1</cell>
- <cell align="center">2</cell>
- <cell align="center">n</cell>
- </row>
- <row>
- <cell align="center">97</cell>
- <cell align="center">PortNo</cell>
- <cell align="center">NodeName</cell>
- </row>
- <tcaption></tcaption></table>
-
- <p>
- where n = Length - 3
- </p>
- <p>
- The connection created to the EPMD must be kept until the node is
- not a distributed node any longer.
- </p>
- </section>
-
- <section>
- <title>ALIVE_OK_RESP (89)</title>
- <p></p>
- <table align="left">
- <row>
- <cell align="center">1</cell>
- <cell align="center">2</cell>
- </row>
- <row>
- <cell align="center">89</cell>
- <cell align="center">Creation</cell>
- </row>
- <tcaption></tcaption></table>
- </section>
-
-
- <section>
- <title>ALIVE_NOTOK_RESP ()</title>
- <p>
- EPMD closed the connection.
- </p>
- </section>
-
- <section>
- <title>PORT_PLEASE_REQ (112)</title>
- <p></p>
+ <section>
+ <title>ALIVE_REQ (97)</title>
+ <table align="left">
+ <row>
+ <cell align="center">1</cell>
+ <cell align="center">2</cell>
+ <cell align="center">n</cell>
+ </row>
+ <row>
+ <cell align="center"><c>97</c></cell>
+ <cell align="center"><c>PortNo</c></cell>
+ <cell align="center"><c>NodeName</c></cell>
+ </row>
+ <tcaption></tcaption>
+ </table>
+
+ <p>where n = <c>Length</c> - 3.</p>
+
+ <p>The connection created to the EPMD must be kept until the node is
+ not a distributed node any longer.</p>
+ </section>
+
+ <section>
+ <title>ALIVE_OK_RESP (89)</title>
+ <table align="left">
+ <row>
+ <cell align="center">1</cell>
+ <cell align="center">2</cell>
+ </row>
+ <row>
+ <cell align="center"><c>89</c></cell>
+ <cell align="center"><c>Creation</c></cell>
+ </row>
+ <tcaption></tcaption>
+ </table>
+ </section>
+
+ <section>
+ <title>ALIVE_NOTOK_RESP ()</title>
+ <p>The EPMD closed the connection.</p>
+ </section>
+
+ <section>
+ <title>PORT_PLEASE_REQ (112)</title>
<table align="left">
- <row>
- <cell align="center">1</cell>
- <cell align="center">n</cell>
- </row>
- <row>
- <cell align="center">112</cell>
- <cell align="center">NodeName</cell>
- </row>
- <tcaption></tcaption></table>
- <p>
- where n = Length - 1
- </p>
- </section>
-
- <section>
- <title>PORT_OK_RESP ()</title>
- <p></p>
- <table align="left">
- <row>
- <cell align="center">2</cell>
- </row>
- <row>
- <cell align="center">PortNo</cell>
- </row>
- <tcaption></tcaption></table>
-
- </section>
-
- <section>
- <title>PORT_NOTOK_RESP ()</title>
- <p>
- EPMD closed the connection.
- </p>
- </section>
-
-
- <section>
- <title>PORT_NOTOK_RESP ()</title>
- <p>
- EPMD closed the connection.
- </p>
- </section>
+ <row>
+ <cell align="center">1</cell>
+ <cell align="center">n</cell>
+ </row>
+ <row>
+ <cell align="center"><c>112</c></cell>
+ <cell align="center"><c>NodeName</c></cell>
+ </row>
+ <tcaption></tcaption>
+ </table>
+
+ <p>where n = <c>Length</c> - 1.</p>
+ </section>
+
+ <section>
+ <title>PORT_OK_RESP ()</title>
+ <table align="left">
+ <row>
+ <cell align="center">2</cell>
+ </row>
+ <row>
+ <cell align="center"><c>PortNo</c></cell>
+ </row>
+ <tcaption></tcaption>
+ </table>
+ </section>
+
+ <section>
+ <title>PORT_NOTOK_RESP ()</title>
+ <p>The EPMD closed the connection.</p>
+ </section>
+
+ <section>
+ <title>PORT_NOTOK_RESP ()</title>
+ <p>The EPMD closed the connection.</p>
+ </section>
-->
+ </section>
+ <section>
+ <marker id="distribution_handshake"/>
+ <title>Distribution Handshake</title>
+ <p>This section describes the distribution handshake protocol introduced
+ in Erlang/OTP R6. This description was previously located in
+ <c>$ERL_TOP/lib/kernel/internal_doc/distribution_handshake.txt</c> and
+ has more or less been copied and "formatted" here. It has been almost
+ unchanged since 1999, but the handshake has not changed much since then
+ either.</p>
+
+ <section>
+ <title>General</title>
+ <p>The TCP/IP distribution uses a handshake that expects a
+ connection-based protocol, that is, the protocol does not include any
+ authentication after the handshake procedure.</p>
+
+ <p>This is not entirely safe, as it is vulnerable against takeover
+ attacks, but it is a tradeoff between fair safety and performance.</p>
+
+ <p>The cookies are never sent in cleartext and the handshake procedure
+ expects the client (called <c>A</c>) to be the first one to prove that
+ it can generate a sufficient digest. The digest is generated with the
+ MD5 message digest algorithm and the challenges are expected to be
+ random numbers.</p>
+ </section>
+
+ <section>
+ <title>Definitions</title>
+ <p>A challenge is a 32-bit integer in big-endian order. Below the function
+ <c>gen_challenge()</c> returns a random 32-bit integer used as a
+ challenge.</p>
+
+ <p>A digest is a (16 bytes) MD5 hash of the challenge (as text)
+ concatenated with the cookie (as text). Below, the function
+ <c>gen_digest(Challenge, Cookie)</c> generates a digest as described
+ above.</p>
+
+ <p>An <c>out_cookie</c> is the cookie used in outgoing communication to a
+ certain node, so that <c>A</c>'s <c>out_cookie</c> for <c>B</c> is to
+ correspond with <c>B</c>'s <c>in_cookie</c> for <c>A</c> and conversely.
+ <c>A</c>'s <c>out_cookie</c> for <c>B</c> and <c>A</c>'s
+ <c>in_cookie</c> for <c>B</c> need <em>not</em> be the same. Below the
+ function <c>out_cookie(Node)</c> returns the current node's
+ <c>out_cookie</c> for <c>Node</c>.</p>
+
+ <p>An <c>in_cookie</c> is the cookie expected to be used by another node
+ when communicating with us, so that <c>A</c>'s <c>in_cookie</c> for
+ <c>B</c> corresponds with <c>B</c>'s <c>out_cookie</c> for <c>A</c>.
+ Below the function <c>in_cookie(Node)</c> returns the current node's
+ <c>in_cookie</c> for <c>Node</c>.</p>
+
+ <p>The cookies are text strings that can be viewed as passwords.</p>
+
+ <p>Every message in the handshake starts with a 16-bit big-endian integer,
+ which contains the message length (not counting the two initial bytes).
+ In Erlang this corresponds to option <c>{packet, 2}</c> in
+ <seealso marker="kernel:gen_tcp"><c>kernel:gen_tcp</c></seealso>.
+ Notice that after the handshake, the distribution switches to 4 byte
+ packet headers.</p>
</section>
- <section>
- <title>Distribution Handshake</title>
- <p>
- <marker id="distribution_handshake"/>
- This section describes the distribution handshake protocol
- introduced in the OTP-R6 release of Erlang/OTP. This
- description was previously located in
- <c>$ERL_TOP/lib/kernel/internal_doc/distribution_handshake.txt</c>,
- and has more or less been copied and "formatted" here. It has been
- more or less unchanged since the year 1999, but the handshake
- should not have changed much since then either.
- </p>
- <section>
- <title>General</title>
- <p>
- The TCP/IP distribution uses a handshake which expects a
- connection based protocol, i.e. the protocol does not include
- any authentication after the handshake procedure.
- </p>
- <p>
- This is not entirely safe, as it is vulnerable against takeover
- attacks, but it is a tradeoff between fair safety and performance.
- </p>
- <p>
- The cookies are never sent in cleartext and the handshake procedure
- expects the client (called A) to be the first one to prove that it can
- generate a sufficient digest. The digest is generated with the
- MD5 message digest algorithm and the challenges are expected to be very
- random numbers.
- </p>
- </section>
- <section>
- <title>Definitions</title>
- <p>
- A challenge is a 32 bit integer number in big endian order. Below the function
- <c>gen_challenge()</c> returns a random 32 bit integer used as a challenge.
- </p>
- <p>
- A digest is a (16 bytes) MD5 hash of the Challenge (as text) concatenated
- with the cookie (as text). Below, the function <c>gen_digest(Challenge, Cookie)</c>
- generates a digest as described above.
- </p>
- <p>
- An out_cookie is the cookie used in outgoing communication to a certain node,
- so that A's out_cookie for B should correspond with B's in_cookie for A and
- the other way around. A's out_cookie for B and A's in_cookie for B need <em>NOT</em>
- be the same. Below the function <c>out_cookie(Node)</c> returns the current
- node's out_cookie for <c>Node</c>.
- </p>
- <p>
- An in_cookie is the cookie expected to be used by another node when
- communicating with us, so that A's in_cookie for B corresponds with B's
- out_cookie for A. Below the function <c>in_cookie(Node)</c> returns the current
- node's <c>in_cookie</c> for <c>Node</c>.
- </p>
- <p>
- The cookies are text strings that can be viewed as passwords.
- </p>
- <p>
- Every message in the handshake starts with a 16 bit big endian integer
- which contains the length of the message (not counting the two initial bytes).
- In erlang this corresponds to the <c>gen_tcp</c> option <c>{packet, 2}</c>. Note that after
- the handshake, the distribution switches to 4 byte packet headers.
- </p>
-
- </section>
- <section>
- <title>The Handshake in Detail</title>
- <p>
- Imagine two nodes, node A, which initiates the handshake and node B, which
- accepts the connection.
- </p>
- <taglist>
- <tag>1) connect/accept</tag>
- <item><p>A connects to B via TCP/IP and B accepts the connection.</p></item>
- <tag>2) send_name/receive_name</tag>
- <item><p>A sends an initial identification to B. B receives the message.
- The message looks like this (every "square" being one byte and the packet
- header removed):
- </p>
-<pre>
+
+ <section>
+ <title>The Handshake in Detail</title>
+ <p>Imagine two nodes, <c>A</c> that initiates the handshake and <c>B</c>
+ that accepts the connection.</p>
+
+ <taglist>
+ <tag>1) connect/accept</tag>
+ <item>
+ <p><c>A</c> connects to <c>B</c> through TCP/IP and <c>B</c> accepts
+ the connection.</p>
+ </item>
+ <tag>2) <c>send_name</c>/<c>receive_name</c></tag>
+ <item>
+ <p><c>A</c> sends an initial identification to <c>B</c>, which
+ receives the message. The message looks as follows (every "square"
+ is one byte and the packet header is removed):</p>
+ <pre>
+---+--------+--------+-----+-----+-----+-----+-----+-----+-...-+-----+
|'n'|Version0|Version1|Flag0|Flag1|Flag2|Flag3|Name0|Name1| ... |NameN|
-+---+--------+--------+-----+-----+-----+-----+-----+-----+-... +-----+
-</pre>
- <p>
- The 'n' is just a message tag.
- Version0 and Version1 is the distribution version selected by node A,
- based on information from EPMD. (16 bit big endian)
- Flag0 ... Flag3 are capability flags, the capabilities defined in
- <c>$ERL_TOP/lib/kernel/include/dist.hrl</c>.
- (32 bit big endian)
- Name0 ... NameN is the full nodename of A, as a string of bytes (the
- packet length denotes how long it is).
- </p></item>
- <tag>3) recv_status/send_status</tag>
- <item><p>B sends a status message to A, which indicates
- if the connection is allowed. The following status codes are defined:</p>
- <taglist>
- <tag><c>ok</c></tag>
- <item>The handshake will continue.</item>
- <tag><c>ok_simultaneous</c></tag>
- <item>The handshake will continue, but A is informed that B
- has another ongoing connection attempt that will be
- shut down (simultaneous connect where A's name is
- greater than B's name, compared literally).</item>
- <tag><c>nok</c></tag>
- <item>The handshake will not continue, as B already has an ongoing handshake
- which it itself has initiated. (simultaneous connect where B's name is
- greater than A's).</item>
- <tag><c>not_allowed</c></tag>
- <item>The connection is disallowed for some (unspecified) security
- reason.</item>
- <tag><c>alive</c></tag>
- <item>A connection to the node is already active, which either means
- that node A is confused or that the TCP connection breakdown
- of a previous node with this name has not yet reached node B.
- See 3B below.</item>
- </taglist>
- <p>This is the format of the status message:</p>
-<pre>
++---+--------+--------+-----+-----+-----+-----+-----+-----+-... +-----+</pre>
+ <p>'n' is the message tag. 'Version0' and 'Version1' is the
+ distribution version selected by <c>A</c>, based on information
+ from the EPMD. (16-bit big-endian) 'Flag0' ... 'Flag3' are
+ capability flags, the capabilities are defined in
+ <c>$ERL_TOP/lib/kernel/include/dist.hrl</c>. (32-bit big-endian)
+ 'Name0' ... 'NameN' is the full node name of <c>A</c>, as a string
+ of bytes (the packet length denotes how long it is).</p>
+ </item>
+ <tag>3) <c>recv_status</c>/<c>send_status</c></tag>
+ <item>
+ <p><c>B</c> sends a status message to <c>A</c>, which indicates if the
+ connection is allowed. The following status codes are defined:</p>
+ <taglist>
+ <tag><c>ok</c></tag>
+ <item>
+ <p>The handshake will continue.</p>
+ </item>
+ <tag><c>ok_simultaneous</c></tag>
+ <item>
+ <p>The handshake will continue, but <c>A</c> is informed that
+ <c>B</c> has another ongoing connection attempt that will be
+ shut down (simultaneous connect where <c>A</c>'s name is
+ greater than <c>B</c>'s name, compared literally).</p>
+ </item>
+ <tag><c>nok</c></tag>
+ <item>
+ <p>The handshake will not continue, as <c>B</c> already has an
+ ongoing handshake, which it itself has initiated (simultaneous
+ connect where <c>B</c>'s name is greater than <c>A</c>'s).</p>
+ </item>
+ <tag><c>not_allowed</c></tag>
+ <item>
+ <p>The connection is disallowed for some (unspecified) security
+ reason.</p>
+ </item>
+ <tag><c>alive</c></tag>
+ <item>
+ <p>A connection to the node is already active, which either means
+ that node <c>A</c> is confused or that the TCP connection
+ breakdown of a previous node with this name has not yet reached
+ node <c>B</c>. See step 3B below.</p>
+ </item>
+ </taglist>
+ <p>The format of the status message is as follows:</p>
+ <pre>
+---+-------+-------+-...-+-------+
|'s'|Status0|Status1| ... |StatusN|
-+---+-------+-------+-...-+-------+
-</pre>
- <p>
- 's' is the message tag Status0 ... StatusN is the status as a string (not terminated)
- </p>
- </item>
- <tag>3B) send_status/recv_status</tag>
- <item><p>If status was 'alive', node A will answer with
- another status message containing either 'true' which means that the
- connection should continue (The old connection from this node is broken), or
- <c>'false'</c>, which simply means that the connection should be closed, the
- connection attempt was a mistake.</p></item>
- <tag>4) recv_challenge/send_challenge</tag>
- <item><p>If the status was <c>ok</c> or <c>ok_simultaneous</c>,
- The handshake continues with B sending A another message, the challenge.
- The challenge contains the same type of information as the "name" message
- initially sent from A to B, with the addition of a 32 bit challenge:</p>
-<pre>
++---+-------+-------+-...-+-------+</pre>
+ <p>'s' is the message tag. 'Status0' ... 'StatusN' is the status as a
+ string (not terminated).</p>
+ </item>
+ <tag>3B) <c>send_status</c>/<c>recv_status</c></tag>
+ <item>
+ <p>If status was <c>alive</c>, node <c>A</c> answers with another
+ status message containing either <c>true</c>, which means that the
+ connection is to continue (the old connection from this node is
+ broken), or <c>false</c>, which means that the connection is to be
+ closed (the connection attempt was a mistake.</p>
+ </item>
+ <tag>4) <c>recv_challenge</c>/<c>send_challenge</c></tag>
+ <item>
+ <p>If the status was <c>ok</c> or <c>ok_simultaneous</c>, the
+ handshake continues with <c>B</c> sending <c>A</c> another message,
+ the challenge. The challenge contains the same type of information
+ as the "name" message initially sent from <c>A</c> to <c>B</c>, plus
+ a 32-bit challenge:</p>
+ <pre>
+---+--------+--------+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-...-+-----+
|'n'|Version0|Version1|Flag0|Flag1|Flag2|Flag3|Chal0|Chal1|Chal2|Chal3|Name0|Name1| ... |NameN|
-+---+--------+--------+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-... +-----+
-</pre>
- <p>
- Where Chal0 ... Chal3 is the challenge as a 32 bit big endian integer
- and the other fields are B's version, flags and full nodename.
- </p></item>
- <tag>5) send_challenge_reply/recv_challenge_reply</tag>
- <item><p>Now A has generated a digest and its own challenge. Those are
- sent together in a package to B:</p>
-<pre>
++---+--------+--------+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-... +-----+</pre>
+ <p>'Chal0' ... 'Chal3' is the challenge as a 32-bit big-endian integer
+ and the other fields are <c>B</c>'s version, flags, and full node
+ name.</p>
+ </item>
+ <tag>5) <c>send_challenge_reply</c>/<c>recv_challenge_reply</c></tag>
+ <item>
+ <p>Now <c>A</c> has generated a digest and its own challenge. Those
+ are sent together in a package to <c>B</c>:</p>
+ <pre>
+---+-----+-----+-----+-----+-----+-----+-----+-----+-...-+------+
|'r'|Chal0|Chal1|Chal2|Chal3|Dige0|Dige1|Dige2|Dige3| ... |Dige15|
-+---+-----+-----+-----+-----+-----+-----+-----+-----+-...-+------+
-</pre>
- <p>
- Where 'r' is the tag, Chal0 ... Chal3 is A's challenge for B to handle and
- Dige0 ... Dige15 is the digest that A constructed from the challenge B sent
- in the previous step.
- </p></item>
- <tag>6) recv_challenge_ack/send_challenge_ack</tag>
- <item><p>B checks that the digest received from A is correct and generates a
- digest from the challenge received from A. The digest is then sent to A. The
- message looks like this:</p>
-<pre>
++---+-----+-----+-----+-----+-----+-----+-----+-----+-...-+------+</pre>
+ <p>'r' is the tag. 'Chal0' ... 'Chal3' is <c>A</c>'s challenge for
+ <c>B</c> to handle. 'Dige0' ... 'Dige15' is the digest that <c>A</c>
+ constructed from the challenge <c>B</c> sent in the previous
+ step.</p>
+ </item>
+ <tag>6) <c>recv_challenge_ack</c>/<c>send_challenge_ack</c></tag>
+ <item>
+ <p><c>B</c> checks that the digest received from <c>A</c> is correct
+ and generates a digest from the challenge received from <c>A</c>.
+ The digest is then sent to <c>A</c>. The message is as follows:</p>
+ <pre>
+---+-----+-----+-----+-----+-...-+------+
|'a'|Dige0|Dige1|Dige2|Dige3| ... |Dige15|
-+---+-----+-----+-----+-----+-...-+------+
-</pre>
- <p>
- Where 'a' is the tag and Dige0 ... Dige15 is the digest calculated by B
- for A's challenge.</p></item>
- <tag>7)</tag>
- <item><p>A checks the digest from B and the connection is up.</p></item>
- </taglist>
- </section>
- <section>
- <title>Semigraphic View</title>
-<pre>
-A (initiator) B (acceptor)
-
-TCP connect -----------------------------------------&gt;
- TCP accept
-
-send_name -----------------------------------------&gt;
- recv_name
-
- &lt;---------------------------------------- send_status
++---+-----+-----+-----+-----+-...-+------+</pre>
+ <p>'a' is the tag. 'Dige0' ... 'Dige15' is the digest calculated by
+ <c>B</c> for <c>A</c>'s challenge.</p>
+ </item>
+ <tag>7) check</tag>
+ <item>
+ <p><c>A</c> checks the digest from <c>B</c> and the connection is
+ up.</p>
+ </item>
+ </taglist>
+ </section>
+
+ <section>
+ <title>Semigraphic View</title>
+ <pre>
+A (initiator) B (acceptor)
+
+TCP connect ------------------------------------&gt;
+ TCP accept
+
+send_name --------------------------------------&gt;
+ recv_name
+
+&lt;---------------------------------------------- send_status
recv_status
(if status was 'alive'
- send_status - - - - - - - - - - - - - - - - - - - -&gt;
- recv_status)
- ChB = gen_challenge()
- (ChB)
- &lt;---------------------------------------- send_challenge
+ send_status - - - - - - - - - - - - - - - - - -&gt;
+ recv_status)
+ ChB = gen_challenge()
+ (ChB)
+&lt;---------------------------------------------- send_challenge
recv_challenge
-
ChA = gen_challenge(),
OCA = out_cookie(B),
DiA = gen_digest(ChB,OCA)
- (ChA, DiA)
-send_challenge_reply --------------------------------&gt;
- recv_challenge_reply
- ICB = in_cookie(A),
- check:
- DiA == gen_digest
- (ChB, ICB) ?
- - if OK:
- OCB = out_cookie(A),
- DiB = gen_digest
- (DiB) (ChA, OCB)
- &lt;----------------------------------------- send_challenge_ack
-recv_challenge_ack DONE
-ICA = in_cookie(B), - else
-check: CLOSE
-DiB == gen_digest(ChA,ICA) ?
-- if OK
+ (ChA, DiA)
+send_challenge_reply ---------------------------&gt;
+ recv_challenge_reply
+ ICB = in_cookie(A),
+ check:
+ DiA == gen_digest (ChB, ICB)?
+ - if OK:
+ OCB = out_cookie(A),
+ DiB = gen_digest (ChA, OCB)
+ (DiB)
+&lt;----------------------------------------------- send_challenge_ack
+recv_challenge_ack DONE
+ICA = in_cookie(B), - else:
+check: CLOSE
+DiB == gen_digest(ChA,ICA)?
+- if OK:
DONE
-- else
- CLOSE
-</pre>
- </section>
- <marker id="dflags"/>
- <section>
- <title>The Currently Defined Distribution Flags</title>
- <p>
- Currently (OTP-R16) the following capability flags are defined:
- </p>
-<pre>
-%% The node should be published and part of the global namespace
--define(DFLAG_PUBLISHED,1).
-
-%% The node implements an atom cache (obsolete)
--define(DFLAG_ATOM_CACHE,2).
-
-%% The node implements extended (3 * 32 bits) references. This is
-%% required today. If not present connection will be refused.
--define(DFLAG_EXTENDED_REFERENCES,4).
-
-%% The node implements distributed process monitoring.
--define(DFLAG_DIST_MONITOR,8).
-
-%% The node uses separate tag for fun's (lambdas) in the distribution protocol.
--define(DFLAG_FUN_TAGS,16#10).
-
-%% The node implements distributed named process monitoring.
--define(DFLAG_DIST_MONITOR_NAME,16#20).
-
-%% The (hidden) node implements atom cache (obsolete)
--define(DFLAG_HIDDEN_ATOM_CACHE,16#40).
-
-%% The node understand new fun-tags
--define(DFLAG_NEW_FUN_TAGS,16#80).
-
-%% The node is capable of handling extended pids and ports. This is
-%% required today. If not present connection will be refused.
--define(DFLAG_EXTENDED_PIDS_PORTS,16#100).
-
-%%
--define(DFLAG_EXPORT_PTR_TAG,16#200).
-
-%%
--define(DFLAG_BIT_BINARIES,16#400).
-
-%% The node understands new float format
--define(DFLAG_NEW_FLOATS,16#800).
-
-%%
--define(DFLAG_UNICODE_IO,16#1000).
-
-%% The node implements atom cache in distribution header.
--define(DFLAG_DIST_HDR_ATOM_CACHE,16#2000).
-
-%% The node understand the SMALL_ATOM_EXT tag
--define(DFLAG_SMALL_ATOM_TAGS, 16#4000).
-
-%% The node understand UTF-8 encoded atoms
--define(DFLAG_UTF8_ATOMS, 16#10000).
-
-</pre>
- </section>
- </section>
-
- <section>
- <marker id="connected_nodes"/>
- <title>Protocol between connected nodes</title>
- <p>
- As of erts version 5.7.2 the runtime system passes a distribution
- flag in the handshake stage that enables the use of a
- <seealso marker="erl_ext_dist#distribution_header">distribution
- header</seealso> on all messages passed. Messages passed between
- nodes are in this case on the following format:
- </p>
- <table align="left">
- <row>
- <cell align="center">4</cell>
- <cell align="center">d</cell>
- <cell align="center">n</cell>
- <cell align="center">m</cell>
- </row>
- <row>
- <cell align="center"><c>Length</c></cell>
- <cell align="center"><c>DistributionHeader</c></cell>
- <cell align="center"><c>ControlMessage</c></cell>
- <cell align="center"><c>Message</c></cell>
- </row>
- <tcaption></tcaption></table>
- <p>
- where:
- </p>
- <p>
- <c>Length</c> is equal to d + n + m
- </p>
- <p>
- <c>ControlMessage</c> is a tuple passed using the external format of
- Erlang.
- </p>
- <p>
- <c>Message</c> is the message sent to another node using the '!'
- (in external format). Note that <c>Message</c> is only passed in
- combination with a <c>ControlMessage</c> encoding a send ('!').
- </p>
- <p>
- Also note that <seealso marker="erl_ext_dist#overall_format">the
- version number is omitted from the terms that follow a
- distribution header</seealso>.
- </p>
- <p>
- Nodes with an erts version less than 5.7.2 does not pass the
- distribution flag that enables the distribution header. Messages
- passed between nodes are in this case on the following format:
- </p>
- <table align="left">
- <row>
- <cell align="center">4</cell>
- <cell align="center">1</cell>
- <cell align="center">n</cell>
- <cell align="center">m</cell>
- </row>
- <row>
- <cell align="center"><c>Length</c></cell>
- <cell align="center"><c>Type</c></cell>
- <cell align="center"><c>ControlMessage</c></cell>
- <cell align="center"><c>Message</c></cell>
- </row>
- <tcaption></tcaption></table>
- <p>
- where:
- </p>
- <p>
- <c>Length</c> is equal to 1 + n + m
- </p>
- <p>
- Type is: 112 (pass through)
- </p>
- <p>
- <c>ControlMessage</c> is a tuple passed using the external format of
- Erlang.
- </p>
- <p>
- <c>Message</c> is the message sent to another node using the '!'
- (in external format). Note that <c>Message</c> is only passed in
- combination with a <c>ControlMessage</c> encoding a send ('!').
- </p>
- <p>
- The <c>ControlMessage</c> is a tuple, where the first element
- indicates which distributed operation it encodes.
- </p>
- <taglist>
- <tag><c>LINK</c></tag>
- <item>
- <p>
- <c>{1, FromPid, ToPid}</c>
- </p>
- </item>
-
- <tag><c>SEND</c></tag>
- <item>
- <p>
- <c>{2, Unused, ToPid}</c>
- </p>
- <p>
- <em>Note</em> followed by <c>Message</c>
- </p>
- <p>
- <c>Unused</c> is kept for backward compatibility
- </p>
- </item>
-
- <tag><c>EXIT</c></tag>
- <item>
- <p>
- <c>{3, FromPid, ToPid, Reason}</c>
- </p>
- </item>
-
- <tag><c>UNLINK</c></tag>
- <item>
- <p>
- <c>{4, FromPid, ToPid}</c>
- </p>
- </item>
-
- <tag><c>NODE_LINK</c></tag>
- <item>
- <p>
- <c>{5}</c>
- </p>
- </item>
-
- <tag><c>REG_SEND</c></tag>
- <item>
- <p>
- <c>{6, FromPid, Unused, ToName}</c>
- </p>
- <p>
- <em>Note</em> followed by <c>Message</c>
- </p>
- <p>
- <c>Unused</c> is kept for backward compatibility
- </p>
- </item>
-
- <tag><c>GROUP_LEADER</c></tag>
- <item>
- <p>
- <c>{7, FromPid, ToPid}</c>
- </p>
- </item>
-
- <tag><c>EXIT2</c></tag>
- <item>
- <p>
- <c>{8, FromPid, ToPid, Reason}</c>
- </p>
- </item>
- </taglist>
- </section>
-
-
- <section>
- <title>New Ctrlmessages for distrvsn = 1 (OTP R4)</title>
- <taglist>
- <tag><c>SEND_TT</c></tag>
- <item>
- <p>
- <c>{12, Unused, ToPid, TraceToken}</c>
- </p>
- <p>
- <em>Note</em> followed by <c>Message</c>
- </p>
- <p>
- <c>Unused</c> is kept for backward compatibility
- </p>
- </item>
-
- <tag><c>EXIT_TT</c></tag>
- <item>
- <p>
- <c>{13, FromPid, ToPid, TraceToken, Reason}</c>
- </p>
- </item>
-
- <tag><c>REG_SEND_TT</c></tag>
- <item>
- <p>
- <c>{16, FromPid, Unused, ToName, TraceToken}</c>
- </p>
- <p>
- <em>Note</em> followed by <c>Message</c>
- </p>
- <p>
- <c>Unused</c> is kept for backward compatibility
- </p>
- </item>
-
- <tag><c>EXIT2_TT</c></tag>
- <item>
- <p>
- <c>{18, FromPid, ToPid, TraceToken, Reason}</c>
- </p>
- </item>
- </taglist>
- </section>
-
- <section>
- <title>New Ctrlmessages for distrvsn = 2</title>
- <p>
- distrvsn 2 was never used.
- </p>
- </section>
-
- <section>
- <title>New Ctrlmessages for distrvsn = 3 (OTP R5C)</title>
- <p>
- None, but the version number was increased anyway.
- </p>
+- else:
+ CLOSE</pre>
</section>
<section>
- <title>New Ctrlmessages for distrvsn = 4 (OTP R6)</title>
- <p>
- These are only recognized by Erlang nodes, not by hidden nodes.
- </p>
+ <marker id="dflags"/>
+ <title>Distribution Flags</title>
+ <p>The following capability flags are defined:</p>
<taglist>
- <tag><c>MONITOR_P</c></tag>
- <item>
- <p>
- <c>{19, FromPid, ToProc, Ref}</c>
-
- <c>FromPid</c> = monitoring process
- <c>ToProc</c> = monitored process pid or name (atom)
- </p>
- </item>
-
- <tag><c>DEMONITOR_P</c></tag>
- <item>
- <p>
- <c>{20, FromPid, ToProc, Ref}</c>
- We include the FromPid just in case we want to trace this.
-
- <c>FromPid</c> = monitoring process
- <c>ToProc</c> = monitored process pid or name (atom)
- </p>
- </item>
-
- <tag><c>MONITOR_P_EXIT</c></tag>
- <item>
- <p>
- <c>{21, FromProc, ToPid, Ref, Reason}</c>
-
- <c>FromProc</c> = monitored process pid or name (atom)
- <c>ToPid</c> = monitoring process
- <c>Reason</c> = exit reason for the monitored process
- </p>
- </item>
+ <tag><c>-define(DFLAG_PUBLISHED,1).</c></tag>
+ <item>
+ <p>The node is to be published and part of the global namespace.</p>
+ </item>
+ <tag><c>-define(DFLAG_ATOM_CACHE,2).</c></tag>
+ <item>
+ <p>The node implements an atom cache (obsolete).</p>
+ </item>
+ <tag><c>-define(DFLAG_EXTENDED_REFERENCES,4).</c></tag>
+ <item>
+ <p>The node implements extended (3 &times; 32 bits) references. This
+ is required today. If not present, the connection is refused.</p>
+ </item>
+ <tag><c>-define(DFLAG_DIST_MONITOR,8).</c></tag>
+ <item>
+ <p>The node implements distributed process monitoring.</p>
+ </item>
+ <tag><c>-define(DFLAG_FUN_TAGS,16#10).</c></tag>
+ <item>
+ <p>The node uses separate tag for funs (lambdas) in the distribution
+ protocol.</p>
+ </item>
+ <tag><c>-define(DFLAG_DIST_MONITOR_NAME,16#20).</c></tag>
+ <item>
+ <p>The node implements distributed named process monitoring.</p>
+ </item>
+ <tag><c>-define(DFLAG_HIDDEN_ATOM_CACHE,16#40).</c></tag>
+ <item>
+ <p>The (hidden) node implements atom cache (obsolete).</p>
+ </item>
+ <tag><c>-define(DFLAG_NEW_FUN_TAGS,16#80).</c></tag>
+ <item>
+ <p>The node understand new fun tags.</p>
+ </item>
+ <tag><c>-define(DFLAG_EXTENDED_PIDS_PORTS,16#100).</c></tag>
+ <item>
+ <p>The node can handle extended pids and ports. This is required
+ today. If not present, the connection is refused.</p>
+ </item>
+ <tag><c>-define(DFLAG_EXPORT_PTR_TAG,16#200).</c></tag>
+ <item>
+ </item>
+ <tag><c>-define(DFLAG_BIT_BINARIES,16#400).</c></tag>
+ <item>
+ </item>
+ <tag><c>-define(DFLAG_NEW_FLOATS,16#800).</c></tag>
+ <item>
+ <p>The node understands new float format.</p>
+ </item>
+ <tag><c>-define(DFLAG_UNICODE_IO,16#1000).</c></tag>
+ <item>
+ </item>
+ <tag><c>-define(DFLAG_DIST_HDR_ATOM_CACHE,16#2000).</c></tag>
+ <item>
+ <p>The node implements atom cache in distribution header.</p>
+ </item>
+ <tag><c>-define(DFLAG_SMALL_ATOM_TAGS, 16#4000).</c></tag>
+ <item>
+ <p>The node understand the <c>SMALL_ATOM_EXT</c> tag.</p>
+ </item>
+ <tag><c>-define(DFLAG_UTF8_ATOMS, 16#10000).</c></tag>
+ <item>
+ <p>The node understand UTF-8 encoded atoms.</p>
+ </item>
</taglist>
</section>
- </chapter>
+ </section>
+
+ <section>
+ <marker id="connected_nodes"/>
+ <title>Protocol between Connected Nodes</title>
+ <p>As from <c>ERTS</c> 5.7.2 the runtime system passes a distribution flag
+ in the handshake stage that enables the use of a
+ <seealso marker="erl_ext_dist#distribution_header">distribution header
+ </seealso> on all messages passed. Messages passed between nodes have in
+ this case the following format:</p>
+
+ <table align="left">
+ <row>
+ <cell align="center">4</cell>
+ <cell align="center">d</cell>
+ <cell align="center">n</cell>
+ <cell align="center">m</cell>
+ </row>
+ <row>
+ <cell align="center"><c>Length</c></cell>
+ <cell align="center"><c>DistributionHeader</c></cell>
+ <cell align="center"><c>ControlMessage</c></cell>
+ <cell align="center"><c>Message</c></cell>
+ </row>
+ <tcaption>Format of Messages Passed between Nodes (as from ERTS 5.7.2)
+ </tcaption>
+ </table>
+
+ <taglist>
+ <tag><c>Length</c></tag>
+ <item>
+ <p>Equal to d + n + m.</p>
+ </item>
+ <tag><c>ControlMessage</c></tag>
+ <item>
+ <p>A tuple passed using the external format of Erlang.</p>
+ </item>
+ <tag><c>Message</c></tag>
+ <item>
+ <p>The message sent to another node using the '!' (in external format).
+ Notice that <c>Message</c> is only passed in combination with a
+ <c>ControlMessage</c> encoding a send ('!').</p>
+ </item>
+ </taglist>
+
+ <p>Notice that <seealso marker="erl_ext_dist#overall_format">the version
+ number is omitted from the terms that follow a distribution header
+ </seealso>.</p>
+
+ <p>Nodes with an <c>ERTS</c> version earlier than 5.7.2 does not pass the
+ distribution flag that enables the distribution header. Messages passed
+ between nodes have in this case the following format:</p>
+
+ <table align="left">
+ <row>
+ <cell align="center">4</cell>
+ <cell align="center">1</cell>
+ <cell align="center">n</cell>
+ <cell align="center">m</cell>
+ </row>
+ <row>
+ <cell align="center"><c>Length</c></cell>
+ <cell align="center"><c>Type</c></cell>
+ <cell align="center"><c>ControlMessage</c></cell>
+ <cell align="center"><c>Message</c></cell>
+ </row>
+ <tcaption>Format of Messages Passed between Nodes (before ERTS 5.7.2)
+ </tcaption>
+ </table>
+
+ <taglist>
+ <tag><c>Length</c></tag>
+ <item>
+ <p>Equal to 1 + n + m.</p>
+ </item>
+ <tag><c>Type</c></tag>
+ <item>
+ <p>Equal to <c>112</c> (pass through).</p>
+ </item>
+ <tag><c>ControlMessage</c></tag>
+ <item>
+ <p>A tuple passed using the external format of Erlang.</p>
+ </item>
+ <tag><c>Message</c></tag>
+ <item>
+ <p>The message sent to another node using the '!' (in external format).
+ Notice that <c>Message</c> is only passed in combination with a
+ <c>ControlMessage</c> encoding a send ('!').</p>
+ </item>
+ </taglist>
+
+ <p>The <c>ControlMessage</c> is a tuple, where the first element indicates
+ which distributed operation it encodes:</p>
+
+ <taglist>
+ <tag><c>LINK</c></tag>
+ <item>
+ <p><c>{1, FromPid, ToPid}</c></p>
+ </item>
+ <tag><c>SEND</c></tag>
+ <item>
+ <p><c>{2, Unused, ToPid}</c></p>
+ <p>Followed by <c>Message</c>.</p>
+ <p><c>Unused</c> is kept for backward compatibility.</p>
+ </item>
+ <tag><c>EXIT</c></tag>
+ <item>
+ <p><c>{3, FromPid, ToPid, Reason}</c></p>
+ </item>
+ <tag><c>UNLINK</c></tag>
+ <item>
+ <p><c>{4, FromPid, ToPid}</c></p>
+ </item>
+ <tag><c>NODE_LINK</c></tag>
+ <item>
+ <p><c>{5}</c></p>
+ </item>
+ <tag><c>REG_SEND</c></tag>
+ <item>
+ <p><c>{6, FromPid, Unused, ToName}</c></p>
+ <p>Followed by <c>Message</c>.</p>
+ <p><c>Unused</c> is kept for backward compatibility.</p>
+ </item>
+ <tag><c>GROUP_LEADER</c></tag>
+ <item>
+ <p><c>{7, FromPid, ToPid}</c></p>
+ </item>
+ <tag><c>EXIT2</c></tag>
+ <item>
+ <p><c>{8, FromPid, ToPid, Reason}</c></p>
+ </item>
+ </taglist>
+ </section>
+
+ <section>
+ <title>New Ctrlmessages for distrvsn = 1 (Erlang/OTP R4)</title>
+ <taglist>
+ <tag><c>SEND_TT</c></tag>
+ <item>
+ <p><c>{12, Unused, ToPid, TraceToken}</c></p>
+ <p>Followed by <c>Message</c>.</p>
+ <p><c>Unused</c> is kept for backward compatibility.</p>
+ </item>
+ <tag><c>EXIT_TT</c></tag>
+ <item>
+ <p><c>{13, FromPid, ToPid, TraceToken, Reason}</c></p>
+ </item>
+ <tag><c>REG_SEND_TT</c></tag>
+ <item>
+ <p><c>{16, FromPid, Unused, ToName, TraceToken}</c></p>
+ <p>Followed by <c>Message</c>.</p>
+ <p><c>Unused</c> is kept for backward compatibility.</p>
+ </item>
+ <tag><c>EXIT2_TT</c></tag>
+ <item>
+ <p><c>{18, FromPid, ToPid, TraceToken, Reason}</c></p>
+ </item>
+ </taglist>
+ </section>
+
+ <section>
+ <title>New Ctrlmessages for distrvsn = 2</title>
+ <p><c>distrvsn</c> 2 was never used.</p>
+ </section>
+
+ <section>
+ <title>New Ctrlmessages for distrvsn = 3 (Erlang/OTP R5C)</title>
+ <p>None, but the version number was increased anyway.</p>
+ </section>
+
+ <section>
+ <title>New Ctrlmessages for distrvsn = 4 (Erlang/OTP R6)</title>
+ <p>These are only recognized by Erlang nodes, not by hidden nodes.</p>
+
+ <taglist>
+ <tag><c>MONITOR_P</c></tag>
+ <item>
+ <p><c>{19, FromPid, ToProc, Ref}</c>, where
+ <c>FromPid</c> = monitoring process and
+ <c>ToProc</c> = monitored process pid or name (atom)</p>
+ </item>
+ <tag><c>DEMONITOR_P</c></tag>
+ <item>
+ <p><c>{20, FromPid, ToProc, Ref}</c>, where
+ <c>FromPid</c> = monitoring process and
+ <c>ToProc</c> = monitored process pid or name (atom)</p>
+ <p>We include <c>FromPid</c> just in case we want to trace this.</p>
+ </item>
+ <tag><c>MONITOR_P_EXIT</c></tag>
+ <item>
+ <p><c>{21, FromProc, ToPid, Ref, Reason}</c>, where
+ <c>FromProc</c> = monitored process pid or name (atom),
+ <c>ToPid</c> = monitoring process, and
+ <c>Reason</c> = exit reason for the monitored process</p>
+ </item>
+ </taglist>
+ </section>
+</chapter>