*channel.txt*      For Vim version 7.4.  Last change: 2016 Feb 16


		  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 or pipes			*socket-interface*
Jobs can be used to start processes and communicate with them.

Vim current supports up to 10 simultaneous channels.
The Netbeans interface also uses a channel. |netbeans|

1. Overview				|job-channel-overview|
2. Channel demo				|channel-demo|
3. Opening a channel			|channel-open|
4. Using a JSON or JS channel		|channel-use|
5. Channel commands			|channel-commands|
6. Using a RAW or NL channel		|channel-raw|
7. More channel functions		|channel-more|
8. Starting a job with a channel	|job-start|
9. Starting a job without a channel	|job-start-nochannel|
10. Job options				|job-options|
11. Controlling a job			|job-control|

{Vi does not have any of these features}
{only when compiled with the |+channel| feature for channel stuff}
{only when compiled with the |+job| feature for job stuff}

==============================================================================
1. Overview						*job-channel-overview*

There are four main types of jobs:
1. A deamon, serving several Vim instances.
   Vim connects to it with a socket.
2. One job working with one Vim instance, asynchronously.
   Uses a socket or pipes.
3. A job performing some work for a short time, asynchronously.
   Uses a socket or pipes.
4. Running a filter, synchronously.
   Uses pipes.

For when using sockets See |job-start|, |job-may-start| and |channel-open|.
For 2 and 3, one or more jobs using pipes, see |job-start|.
For 4 use the ":{range}!cmd" command, see |filter|.

Over the socket and pipes these protocols are available:
RAW	nothing known, Vim cannot tell where a message ends
NL	every message ends in a NL (newline) character
JSON	JSON encoding |json_encode()|
JS	JavaScript style JSON-like encoding |js_encode()|

Common combination are:
- Using a job connected through pipes in NL mode.  E.g., to run a style
  checker and receive errors and warnings.
- Using a deamon, connecting over a socket in JSON mode.  E.g. to lookup
  crosss-refrences in a database.

==============================================================================
2. Channel 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 channel = ch_open('localhost:8765')

In T1 you should see:
	=== socket opened === ~

You can now send a message to the server: >
	echo ch_sendexpr(channel, '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):
	["ex","echo 'hi there'"] ~
And you should see the message in Vim. You can move the cursor a word forward:
	["normal","w"] ~

To handle asynchronous communication a callback needs to be used: >
	func MyHandler(channel, msg)
	  echo "from the handler: " . a:msg
	endfunc
	call ch_sendexpr(channel, 'hello!', "MyHandler")
Vim will not wait for a response.  Now the server can send the response later
and MyHandler will be invoked.

Instead of giving a callback with every send call, it can also be specified
when opening the channel: >
	call ch_close(channel)
	let channel = ch_open('localhost:8765', {'callback': "MyHandler"})
	call ch_sendexpr(channel, 'hello!', 0)

==============================================================================
3. Opening a channel					*channel-open*

To open a channel: >
    let channel = ch_open({address} [, {options}])

Use |ch_status()| to see if the channel could be opened.

{address} has the form "hostname:port".  E.g., "localhost:8765".

{options} is a dictionary with optional entries:

"mode" can be:						*channel-mode*
	"json" - Use JSON, see below; most convenient way. Default.
	"js"   - Use JS (JavaScript) encoding, more efficient than JSON.
	"nl"   - Use messages that end in a NL character
	"raw"  - Use raw messages

							*channel-callback*
"callback"	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(channel, msg)
	  echo 'Received: ' . a:msg
	endfunc
	let channel = ch_open("localhost:8765", {"callback": "Handle"})
<
		TODO:
"err-cb"	A function like "callback" but used for stderr.  Only for when
		the channel uses pipes.

		TODO:
"close-cb"	A function that is called when the channel gets closed, other
		than by calling ch_close().  It should be defined like this: >
	func MyCloseHandler(channel)

"waittime"	The time to wait for the connection to be made in
		milliseconds.  The default is zero, don't wait, which is
		useful if the server is supposed to be running already.  A
		negative number waits forever.

"timeout"	The time to wait for a request when blocking, using
		ch_sendexpr().  Again in milliseconds.  The default is 2000 (2
		seconds).

When "mode" is "json" or "js" 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" or "js" the "callback" is optional.  When omitted it is
only possible to receive a message after sending one.

TODO:
To change the channel options after opening it use ch_setoptions().  The
arguments are similar to what is passed to ch_open(), but "waittime" cannot be
given, since that only applies to opening the channel.

The handler can be added or changed: >
    call ch_setoptions(channel, {'callback': callback})
When "callback" is empty (zero or an empty string) the handler is removed.

The timeout can be changed: >
    call ch_setoptions(channel, {'timeout': msec})
<
							  *E906*
Once done with the channel, disconnect it like this: >
    call ch_close(channel)
When a socket is used this will close the socket for both directions.  When
pipes are used (stdin/stdout/stderr) they are all closed.  This might not be
what you want!  Stopping the job with job_stop() might be better.

TODO:
Currently up to 10 channels can be in use at the same time. *E897*

When the channel can't be opened you will get an error message.  There is a
difference between MS-Windows and Unix: On Unix when the port doesn't exist
ch_open() fails quickly.  On MS-Windows "waittime" applies.
*E898* *E899* *E900* *E901* *E902*

If there is an error reading or writing a channel it will be closed.
*E896* *E630* *E631* 

==============================================================================
4. Using a JSON or JS channel					*channel-use*

If mode is JSON then a message can be sent synchronously like this: >
    let response = ch_sendexpr(channel, {expr})
This awaits a response from the other side.

When mode is JS this works the same, except that the messages use
JavaScript encoding.  See |js_encode()| for the difference.

To send a message, without handling a response: >
    call ch_sendexpr(channel, {expr}, 0)

To send a message and letting the response handled by a specific function,
asynchronously: >
    call ch_sendexpr(channel, {expr}, {callback})

Vim will match the response with the request using the message ID.  Once the
response is received the callback will be invoked.  Further responses with the
same ID will be ignored.  If your server sends back multiple responses you
need to send them with ID zero, they will be passed to the channel 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 ch_close() the string "DETACH" is sent, if still possible.
The channel will then be inactive.

It is also possible to use ch_sendraw() on a JSON or JS channel.  The caller
is then completely responsible for correct encoding and decoding.

==============================================================================
5. Channel commands					*channel-commands*

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:				*E903* *E904* *E905*
    ["redraw"  {forced}]
    ["ex",     {Ex command}]
    ["normal", {Normal mode command}]
    ["eval",   {expression}, {number}]
    ["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"] ~

Errors in these commands are normally not reported to avoid them messing up
the display.  If you do want to see them, set the 'verbose' option to 3 or
higher.


Command "redraw" ~

The other commands do not update the screen, so that you can send a sequence
of commands without the cursor moving around.  You must end with the "redraw"
command to show any changed text and show the cursor where it belongs.

The argument is normally an empty string:
	["redraw", ""] ~
To first clear the screen pass "force":
	["redraw", "force"] ~


Command "ex" ~

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:
	["ex","call myscript#MyFunc(arg)"]

You can also use "call |feedkeys()|" to insert any key sequence.


Command "normal" ~

The "normal" command is executed like with ":normal!", commands are not
mapped.  Example to open the folds under the cursor:
	["normal" "zO"]


Command "eval" ~

The "eval" command an be used to get the result of an expression.  For
example, to get the number of lines in the current buffer:
	["eval","line('$')"] ~

it will send back the result of the expression:
	[{number}, {result}]
Here {number} is the same as what was in the request.  Use a negative number
to avoid confusion with message that Vim sends.

{result} is the result of the evaluation and is JSON encoded.  If the
evaluation fails or the result can't be encoded in JSON it is the string
"ERROR".


Command "expr" ~

The "expr" command is similar to "eval", but does not send back any response.
Example:
	["expr","setline('$', ['one', 'two', 'three'])"] ~

==============================================================================
6. Using a RAW or NL channel				*channel-raw*

If mode is RAW or NL then a message can be send like this: >
    let response = ch_sendraw(channel, {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.  The timeout applies for reading
the first byte, after that it will not wait for anything more.

If mode is "nl" you can send a message in a similar way.  You are expected
to put in the NL after each message.  Thus you can also send several messages
ending in a NL at once.  The response will be the text up to and including the
first NL.  This can also be just the NL for an empty response.
If no NL was read before the channel timeout an empty string is returned.

To send a message, without expecting a response: >
    call ch_sendraw(channel, {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 ch_sendraw(channel, {string}, {callback})

This {string} can also be JSON, use |json_encode()| to create it and
|json_decode()| to handle a received JSON message.

It is not possible to use |ch_sendexpr()| on a raw channel.

==============================================================================
7. More channel functions				*channel-more*

To obtain the status of a channel: ch_status(channel).  The possible results
are:
	"fail"		Failed to open the channel.
	"open"		The channel can be used.
	"closed"	The channel was closed.

TODO:
To objain the job associated with a channel: ch_getjob(channel)

TODO:
To read one message from a channel: >
	let output = ch_read(channel)
This uses the channel timeout.  To read without a timeout, just get any
message that is available: >
	let output = ch_read(channel, 0)
When no message was available then the result is v:none for a JSON or JS mode
channels, an empty string for a RAW or NL channel.

To read all output from a RAW or NL channel that is available: >
	let output = ch_readall(channel)
To read the error output: >
	let output = ch_readall(channel, "err")
TODO: use channel timeout, no timeout or specify timeout?

==============================================================================
8. Starting a job with a channel			*job-start* *job*

To start a job and open a channel for stdin/stdout/stderr: >
    let job = job_start(command, {options})

You can get the channel with: >
    let channel = job_getchannel(job)

The channel will use NL mode.  If you want another mode it's best to specify
this in {options}.  When changing the mode later some text may have already
been received and not parsed correctly.

If the command produces a line of output that you want to deal with, specify
a handler for stdout: >
    let job = job_start(command, {"out-cb": "MyHandler"})
The function will be called with the channel and a message. You would define
it like this: >
    func MyHandler(channel, msg)

Without the handler you need to read the output with ch_read().

The handler defined for "out-cb" will also receive stderr.  If you want to
handle that separately, add an "err-cb" handler: >
    let job = job_start(command, {"out-cb": "MyHandler",
	    \			  "err-cb": "ErrHandler"})

You can send a message to the command with ch_sendraw().  If the channel is in
JSON or JS mode you can use ch_sendexpr().

There are several options you can use, see |job-options|.

TODO:
To run a job and read its output once it is done: >

	let job = job_start({command}, {'exit-cb': 'MyHandler'})
	func MyHandler(job, status)
	  let channel = job_getchannel()
	  let output = ch_readall(channel)
	  " parse output
	endfunc

==============================================================================
9. Starting a job without a channel			*job-start-nochannel*

To start another process without creating a channel: >
    let job = job_start(command, {"in-io": "null", "out-io": "null"})

This starts {command} in the background, Vim does not wait for it to finish.

TODO:
When Vim sees that neither stdin, stdout or stderr are connected, no channel
will be created.  Often you will want to include redirection in the command to
avoid it getting stuck.

There are several options you can use, see |job-options|.

TODO:							*job-may-start*
To start a job only when connecting to an address does not work use
job_maystart('command', {address}, {options}), For Example: >
	let job = job_maystart(command, address, {"waittime": 1000})
	let channel = job_gethandle(job)

This comes down to: >
	let channel = ch_open(address, {"waittime": 0})
	if ch_status(channel) == "fail"
	  let job = job_start(command)
	  let channel = ch_open(address, {"waittime": 1000})
	  call job_sethandle(channel)
	endif
Note that the specified waittime applies to when the job has been started.
This gives the job some time to make the port available.

==============================================================================
10. Job options						*job-options*

The {options} argument in job_start() is a dictionary.  All entries are
optional.  The same options can be used with job_setoptions(job, {options}).

TODO:						*job-out-cb*
"callback": handler
"out-cb": handler	Callback for when there is something to read on
			stdout.
TODO:						*job-err-cb*
"err-cb": handler	Callback for when there is something to read on
			stderr.  Defaults to the same callback as "out-cb".
TODO:						*job-close-cb*
"close-cb": handler	Callback for when the channel is closed.  Same as
			"close-cb" on ch_open().
TODO:						*job-exit-cb*
"exit-cb": handler	Callback for when the job ends.  The arguments are the
			job and the exit status.
TODO:						*job-killonexit*
"killonexit": 1		Stop the job when Vim exits.
"killonexit": 0		Do not stop the job when Vim exits.
			The default is 1.
TODO:						*job-term*
"term": "open"		Start a terminal and connect the job
			stdin/stdout/stderr to it.

TODO:						*job-in-io*
"in-io": "null"		disconnect stdin
"in-io": "pipe"		stdin is connected to the channel (default)
"in-io": "file"		stdin reads from a file
"in-file": "/path/file"	the file to read from

TODO:						*job-out-io*
"out-io": "null"	disconnect stdout
"out-io": "pipe"	stdout is connected to the channel (default)
"out-io": "file"	stdout writes to a file
"out-file": "/path/file" the file to write to
"out-io": "buffer" 	stdout appends to a buffer
"out-buffer": "name" 	buffer to append to

TODO:						*job-err-io*
"err-io": "out"		same type as stdout (default)
"err-io": "null"	disconnect stderr
"err-io": "pipe"	stderr is connected to the channel
"err-io": "file"	stderr writes to a file
"err-file": "/path/file" the file to write to
"err-io": "buffer" 	stderr appends to a buffer
"err-buffer": "name" 	buffer to append to

TODO: more options


==============================================================================
11. Controlling a job					*job-control*

To get the status of a job: >
	echo job_status(job)

To make a job stop running: >
	job_stop(job)

This is the normal way to end a job. On Unix it sends a SIGTERM to the job.
It is possible to use other ways to stop the job, or even send arbitrary
signals.  E.g. to force a job to stop, "kill it": >
	job_stop(job, "kill")

For more options see |job_stop()|.


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