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+.. cmake-manual-description: CMake Server
+
+cmake-server(7)
+***************
+
+.. only:: html
+
+   .. contents::
+
+Introduction
+============
+
+:manual:`cmake(1)` is capable of providing semantic information about
+CMake code it executes to generate a buildsystem.  If executed with
+the ``-E server`` command line options, it starts in a long running mode
+and allows a client to request the available information via a JSON protocol.
+
+The protocol is designed to be useful to IDEs, refactoring tools, and
+other tools which have a need to understand the buildsystem in entirety.
+
+A single :manual:`cmake-buildsystem(7)` may describe buildsystem contents
+and build properties which differ based on
+:manual:`generation-time context <cmake-generator-expressions(7)>`
+including:
+
+* The Platform (eg, Windows, APPLE, Linux).
+* The build configuration (eg, Debug, Release, Coverage).
+* The Compiler (eg, MSVC, GCC, Clang) and compiler version.
+* The language of the source files compiled.
+* Available compile features (eg CXX variadic templates).
+* CMake policies.
+
+The protocol aims to provide information to tooling to satisfy several
+needs:
+
+#. Provide a complete and easily parsed source of all information relevant
+   to the tooling as it relates to the source code.  There should be no need
+   for tooling to parse generated buildsystems to access include directories
+   or compile definitions for example.
+#. Semantic information about the CMake buildsystem itself.
+#. Provide a stable interface for reading the information in the CMake cache.
+#. Information for determining when cmake needs to be re-run as a result of
+   file changes.
+
+
+Operation
+=========
+
+Start :manual:`cmake(1)` in the server command mode, supplying the path to
+the build directory to process::
+
+  cmake -E server
+
+The server will start up and reply with an hello message on stdout::
+
+  [== CMake Server ==[
+  {"supportedProtocolVersions":[{"major":0,"minor":1}],"type":"hello"}
+  ]== CMake Server ==]
+
+Messages sent to and from the process are wrapped in magic strings::
+
+  [== CMake Server ==[
+  {
+    ... some JSON message ...
+  }
+  ]== CMake Server ==]
+
+The server is now ready to accept further requests via stdin.
+
+
+Protocol API
+============
+
+
+General Message Layout
+----------------------
+
+All messages need to have a "type" value, which identifies the type of
+message that is passed back or forth. E.g. the initial message sent by the
+server is of type "hello". Messages without a type will generate an response
+of type "error".
+
+All requests sent to the server may contain a "cookie" value. This value
+will he handed back unchanged in all responses triggered by the request.
+
+All responses will contain a value "inReplyTo", which may be empty in
+case of parse errors, but will contain the type of the request message
+in all other cases.
+
+
+Type "reply"
+^^^^^^^^^^^^
+
+This type is used by the server to reply to requests.
+
+The message may -- depending on the type of the original request --
+contain values.
+
+Example::
+
+  [== CMake Server ==[
+  {"cookie":"zimtstern","inReplyTo":"handshake","type":"reply"}
+  ]== CMake Server ==]
+
+
+Type "error"
+^^^^^^^^^^^^
+
+This type is used to return an error condition to the client. It will
+contain an "errorMessage".
+
+Example::
+
+  [== CMake Server ==[
+  {"cookie":"","errorMessage":"Protocol version not supported.","inReplyTo":"handshake","type":"error"}
+  ]== CMake Server ==]
+
+
+Type "progress"
+^^^^^^^^^^^^^^^
+
+When the server is busy for a long time, it is polite to send back replies of
+type "progress" to the client. These will contain a "progressMessage" with a
+string describing the action currently taking place as well as
+"progressMinimum", "progressMaximum" and "progressCurrent" with integer values
+describing the range of progess.
+
+Messages of type "progress" will be followed by more "progress" messages or with
+a message of type "reply" or "error" that complete the request.
+
+"progress" messages may not be emitted after the "reply" or "error" message for
+the request that triggered the responses was delivered.
+
+
+Specific Message Types
+----------------------
+
+
+Type "hello"
+^^^^^^^^^^^^
+
+The initial message send by the cmake server on startup is of type "hello".
+This is the only message ever sent by the server that is not of type "reply",
+"progress" or "error".
+
+It will contain "supportedProtocolVersions" with an array of server protocol
+versions supported by the cmake server. These are JSON objects with "major" and
+"minor" keys containing non-negative integer values.
+
+Example::
+
+  [== CMake Server ==[
+  {"supportedProtocolVersions":[{"major":0,"minor":1}],"type":"hello"}
+  ]== CMake Server ==]
+
+
+Type "handshake"
+^^^^^^^^^^^^^^^^
+
+The first request that the client may send to the server is of type "handshake".
+
+This request needs to pass one of the "supportedProtocolVersions" of the "hello"
+type response received earlier back to the server in the "protocolVersion" field.
+
+Each protocol version may request additional attributes to be present.
+
+Protocol version 1.0 requires the following attributes to be set:
+
+  * "sourceDirectory" with a path to the sources
+  * "buildDirectory" with a path to the build directory
+  * "generator" with the generator name
+  * "extraGenerator" (optional!) with the extra generator to be used.
+
+Example::
+
+  [== CMake Server ==[
+  {"cookie":"zimtstern","type":"handshake","protocolVersion":{"major":0},
+   "sourceDirectory":"/home/code/cmake", "buildDirectory":"/tmp/testbuild",
+   "generator":"Ninja"}
+  ]== CMake Server ==]
+
+which will result in a response type "reply"::
+
+  [== CMake Server ==[
+  {"cookie":"zimtstern","inReplyTo":"handshake","type":"reply"}
+  ]== CMake Server ==]
+
+indicating that the server is ready for action.