*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


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