patch 7.4.1191
Problem: The channel feature isn't working yet.
Solution: Add the connect(), disconnect(), sendexpr() and sendraw()
functions. Add initial documentation. Add a demo server.
diff --git a/runtime/doc/channel.txt b/runtime/doc/channel.txt
new file mode 100644
index 0000000..21ce4eb
--- /dev/null
+++ b/runtime/doc/channel.txt
@@ -0,0 +1,218 @@
+*channel.txt* For Vim version 7.4. Last change: 2016 Jan 28
+
+
+ VIM REFERENCE MANUAL by Bram Moolenaar
+
+
+ Inter-process communication *channel*
+
+DRAFT DRAFT DRAFT DRAFT DRAFT DRAFT DRAFT DRAFT DRAFT DRAFT
+
+Vim uses channels to communicate with other processes.
+A channel uses a socket. *socket-interface*
+
+Vim current supports up to 10 simultanious channels.
+The Netbeans interface also uses a channel. |netbeans|
+
+1. Demo |channel-demo|
+2. Opening a channel |channel-open|
+3. Using a JSON channel |channel-use|
+4. Vim commands |channel-commands|
+5. Using a raw channel |channel-use|
+6. Job control |job-control|
+
+{Vi does not have any of these features}
+{only available when compiled with the |+channel| feature}
+
+==============================================================================
+1. Demo *channel-demo*
+
+This requires Python. The demo program can be found in
+$VIMRUNTIME/tools/demoserver.py
+Run it in one terminal. We will call this T1.
+
+Run Vim in another terminal. Connect to the demo server with: >
+ let handle = connect('localhost:8765', 'json')
+
+In T1 you should see:
+ === socket opened === ~
+
+You can now send a message to the server: >
+ echo sendexpr(handle, 'hello!')
+
+The message is received in T1 and a response is sent back to Vim.
+You can see the raw messages in T1. What Vim sends is:
+ [1,"hello!"] ~
+And the response is:
+ [1,"got it"] ~
+The number will increase every time you send a message.
+
+The server can send a command to Vim. Type this on T1 (literally, including
+the quotes): >
+ NOT IMPLEMENTED YET
+ ["ex","echo 'hi there'"]
+And you should see the message in Vim.
+
+To handle asynchronous communication a callback needs to be used: >
+ func MyHandler(handle, msg)
+ echo "from the handler: " . a:msg
+ endfunc
+ call sendexpr(handle, 'hello!', "MyHandler")
+
+Instead of giving a callback with every send call, it can also be specified
+when opening the channel: >
+ call disconnect(handle)
+ let handle = connect('localhost:8765', 'json', "MyHandler")
+ call sendexpr(handle, 'hello!', 0)
+
+==============================================================================
+2. Opening a channel *channel-open*
+
+To open a channel:
+ let handle = connect({address}, {mode}, {callback})
+
+{address} has the form "hostname:port". E.g., "localhost:8765".
+
+{mode} can be: *channel-mode*
+ "json" - Use JSON, see below; most convenient way
+ "raw" - Use raw messages
+
+ *channel-callback*
+{callback} is a function that is called when a message is received that is not
+handled otherwise. It gets two arguments: the channel handle and the received
+message. Example: >
+ func Handle(handle, msg)
+ echo 'Received: ' . a:msg
+ endfunc
+ let handle = connect("localhost:8765", 'json', "Handle")
+
+When {mode} is "json" the "msg" argument is the body of the received message,
+converted to Vim types.
+When {mode} is "raw" the "msg" argument is the whole message as a string.
+
+When {mode} is "json" the {callback} is optional. When omitted it is only
+possible to receive a message after sending one.
+
+The handler can be added or changed later: >
+ call sethandler(handle, {callback})
+When {callback} is empty (zero or an empty string) the handler is removed.
+
+Once done with the channel, disconnect it like this: >
+ call disconnect(handle)
+
+==============================================================================
+3. Using a JSON channel *channel-use*
+
+If {mode} is "json" then a message can be sent synchronously like this: >
+ let response = sendexpr(handle, {expr})
+This awaits a response from the other side.
+
+To send a message, without handling a response: >
+ call sendexpr(handle, {expr}, 0)
+
+To send a message and letting the response handled by a specific function,
+asynchronously: >
+ call sendexpr(handle, {expr}, {callback})
+
+The {expr} is converted to JSON and wrapped in an array. An example of the
+message that the receiver will get when {expr} is the string "hello":
+ [12,"hello"] ~
+
+The format of the JSON sent is:
+ [{number},{expr}]
+
+In which {number} is different every time. It must be used in the response
+(if any):
+
+ [{number},{response}]
+
+This way Vim knows which sent message matches with which received message and
+can call the right handler. Also when the messages arrive out of order.
+
+The sender must always send valid JSON to Vim. Vim can check for the end of
+the message by parsing the JSON. It will only accept the message if the end
+was received.
+
+When the process wants to send a message to Vim without first receiving a
+message, it must use the number zero:
+ [0,{response}]
+
+Then channel handler will then get {response} converted to Vim types. If the
+channel does not have a handler the message is dropped.
+
+On read error or disconnect() the string "DETACH" is sent, if still possible.
+The channel will then be inactive.
+
+==============================================================================
+4. Vim commands *channel-commands*
+
+NOT IMPLEMENTED YET
+
+With a "json" channel the process can send commands to Vim that will be
+handled by Vim internally, it does not require a handler for the channel.
+
+Possible commands are:
+ ["ex", {Ex command}]
+ ["normal", {Normal mode command}]
+ ["eval", {number}, {expression}]
+ ["expr", {expression}]
+
+With all of these: Be careful what these commands do! You can easily
+interfere with what the user is doing. To avoid trouble use |mode()| to check
+that the editor is in the expected state. E.g., to send keys that must be
+inserted as text, not executed as a command: >
+ ["ex","if mode() == 'i' | call feedkeys('ClassName') | endif"]
+
+The "ex" command is executed as any Ex command. There is no response for
+completion or error. You could use functions in an |autoload| script.
+You can also invoke |feedkeys()| to insert anything.
+
+The "normal" command is executed like with |:normal|.
+
+The "eval" command will result in sending back the result of the expression:
+ [{number}, {result}]
+Here {number} is the same as what was in the request.
+
+The "expr" command is similar, but does not send back any response.
+Example:
+ ["expr","setline('$', ['one', 'two', 'three'])"]
+
+==============================================================================
+5. Using a raw channel *channel-raw*
+
+If {mode} is "raw" then a message can be send like this: >
+ let response = sendraw(handle, {string})
+The {string} is sent as-is. The response will be what can be read from the
+channel right away. Since Vim doesn't know how to recognize the end of the
+message you need to take care of it yourself.
+
+To send a message, without expecting a response: >
+ call sendraw(handle, {string}, 0)
+The process can send back a response, the channel handler will be called with
+it.
+
+To send a message and letting the response handled by a specific function,
+asynchronously: >
+ call sendraw(handle, {string}, {callback})
+
+This {string} can also be JSON, use |jsonencode()| to create it and
+|jsondecode()| to handle a received JSON message.
+
+==============================================================================
+6. Job control *job-control*
+
+NOT IMPLEMENTED YET
+
+To start another process: >
+ call startjob({command})
+
+This does not wait for {command} to exit.
+
+TODO:
+
+ let handle = startjob({command}, 's') # uses stdin/stdout
+ let handle = startjob({command}, '', {address}) # uses socket
+ let handle = startjob({command}, 'd', {address}) # start if connect fails
+
+
+ vim:tw=78:ts=8:ft=help:norl: