*channel.txt* Nvim NVIM REFERENCE MANUAL by Thiago de Arruda Nvim asynchronous IO *channel* Type |gO| to see the table of contents. ============================================================================== 1. Introduction *channel-intro* Channels are nvim's way of communicating with external processes. There are several ways to open a channel: 1. Through stdin/stdout when `nvim` is started with `--headless`, and a startup script or --cmd command opens the stdio channel using |stdioopen()|. 2. Through stdin, stdout and stderr of a process spawned by |jobstart()|. 3. Through the PTY master end of a PTY opened with `jobstart(..., {'pty': v:true})` or |termopen()|. 4. By connecting to a TCP/IP socket or named pipe with |sockconnect()|. 5. By another process connecting to a socket listened to by nvim. This only supports RPC channels, see |rpc-connecting|. Channels support multiple modes or protocols. In the most basic mode of operation, raw bytes are read and written to the channel. The |RPC| protocol, based on the msgpack-rpc standard, enables nvim and the process at the other end to send remote calls and events to each other. The builtin |terminal-emulator| is also implemented on top of PTY channels. Channel Id *channel-id* Each channel is identified by an integer id, unique for the life of the current Nvim session. Functions like |stdioopen()| return channel ids; functions like |chansend()| consume channel ids. ============================================================================== 2. Reading and writing raw bytes *channel-bytes* Channels opened by Vimscript functions operate with raw bytes by default. For a job channel using RPC, bytes can still be read over its stderr. Similarly, only bytes can be written to Nvim's own stderr. *channel-callback* on_stdout({chan-id}, {data}, {name}) *on_stdout* on_stderr({chan-id}, {data}, {name}) *on_stderr* on_stdin({chan-id}, {data}, {name}) *on_stdin* on_data({chan-id}, {data}, {name}) *on_data* Scripts can react to channel activity (received data) via callback functions assigned to the `on_stdout`, `on_stderr`, `on_stdin`, or `on_data` option keys. Callbacks should be fast: avoid potentially slow/expensive work. Parameters: ~ {chan-id} Channel handle. |channel-id| {data} Raw data (|readfile()|-style list of strings) read from the channel. EOF is a single-item list: `['']`. First and last items may be partial lines! |channel-lines| {name} Stream name (string) like "stdout", so the same function can handle multiple streams. Event names depend on how the channel was opened and in what mode/protocol. *channel-buffered* The callback is invoked immediately as data is available, where a single-item list `['']` indicates EOF (stream closed). Alternatively set the `stdout_buffered`, `stderr_buffered`, `stdin_buffered`, or `data_buffered` option keys to invoke the callback only after all output was gathered and the stream was closed. *E5210* If a buffering mode is used without a callback, the data is saved in the stream {name} key of the options dict. It is an error if the key exists. *channel-lines* Stream event handlers receive data as it becomes available from the OS, thus the first and last items in the {data} list may be partial lines. Empty string completes the previous partial line. Examples (not including the final `['']` emitted at EOF): - `foobar` may arrive as `['fo'], ['obar']` - `foo\nbar` may arrive as `['foo','bar']` or `['foo',''], ['bar']` or `['foo'], ['','bar']` or `['fo'], ['o','bar']` There are two ways to deal with this: 1. To wait for the entire output, use |channel-buffered| mode. 2. To read line-by-line, use the following code: > let s:lines = [''] func! s:on_event(job_id, data, event) dict let eof = (a:data == ['']) " Complete the previous line. let s:lines[-1] .= a:data[0] " Append (last item may be a partial line, until EOF). call extend(s:lines, a:data[1:]) endf < If the callback functions are |Dictionary-function|s, |self| refers to the options dictionary containing the callbacks. |Partial|s can also be used as callbacks. Data can be sent to the channel using the |chansend()| function. Here is a simple example, echoing some data through a cat-process: > function! s:OnEvent(id, data, event) dict let str = join(a:data, "\n") echomsg str endfunction let id = jobstart(['cat'], {'on_stdout': function('s:OnEvent') } ) call chansend(id, "hello!") < Here is a example of setting a buffer to the result of grep, but only after all data has been processed: > function! s:OnEvent(id, data, event) dict call nvim_buf_set_lines(2, 0, -1, v:true, a:data) endfunction let id = jobstart(['grep', '^[0-9]'], { 'on_stdout': function('s:OnEvent'), \ 'stdout_buffered':v:true } ) call chansend(id, "stuff\n10 PRINT \"NVIM\"\nxx") " no output is received, buffer is empty call chansend(id, "xx\n20 GOTO 10\nzz\n") call chanclose(id, 'stdin') " now buffer has result < For additional examples with jobs, see |job-control|. *channel-pty* Special case: PTY channels opened with `jobstart(..., {'pty': v:true})` do not preprocess ANSI escape sequences, these will be sent raw to the callback. However, change of PTY size can be signaled to the slave using |jobresize()|. See also |terminal-emulator|. Terminal characteristics (termios) for |:terminal| and PTY channels are copied from the host TTY, or if Nvim is |--headless| it uses default values: > :echo system('nvim --headless +"te stty -a" +"sleep 1" +"1,/^$/print" +q') ============================================================================== 3. Communicating using msgpack-rpc *channel-rpc* When channels are opened with the `rpc` option set to true, the channel can be used for remote method calls in both directions, see |msgpack-rpc|. Note that rpc channels are implicitly trusted and the process at the other end can invoke any |api| function! ============================================================================== 4. Standard IO channel *channel-stdio* Nvim uses stdin/stdout to interact with the user over the terminal interface (TUI). If Nvim is |--headless| the TUI is not started and stdin/stdout can be used as a channel. See also |--embed|. Call |stdioopen()| during |startup| to open the stdio channel as |channel-id| 1. Nvim's stderr is always available as |v:stderr|, a write-only bytes channel. Example: > func! OnEvent(id, data, event) if a:data == [""] quit end call chansend(a:id, map(a:data, {i,v -> toupper(v)})) endfunc call stdioopen({'on_stdin': 'OnEvent'}) < Put this in `uppercase.vim` and run: > nvim --headless --cmd "source uppercase.vim" ============================================================================== 5. Using a prompt buffer *prompt-buffer* If you want to type input for the job in a Vim window you have a few options: - Use a normal buffer and handle all possible commands yourself. This will be complicated, since there are so many possible commands. - Use a terminal window. This works well if what you type goes directly to the job and the job output is directly displayed in the window. See |terminal|. - Use a window with a prompt buffer. This works well when entering a line for the job in Vim while displaying (possibly filtered) output from the job. A prompt buffer is created by setting 'buftype' to "prompt". You would normally only do that in a newly created buffer. The user can edit and enter one line of text at the very last line of the buffer. When pressing Enter in the prompt line the callback set with |prompt_setcallback()| is invoked. It would normally send the line to a job. Another callback would receive the output from the job and display it in the buffer, below the prompt (and above the next prompt). Only the text in the last line, after the prompt, is editable. The rest of the buffer is not modifiable with Normal mode commands. It can be modified by calling functions, such as |append()|. Using other commands may mess up the buffer. After setting 'buftype' to "prompt" Vim does not automatically start Insert mode, use `:startinsert` if you want to enter Insert mode, so that the user can start typing a line. The text of the prompt can be set with the |prompt_setprompt()| function. If no prompt is set with |prompt_setprompt()|, "% " is used. You can get the effective prompt text for a buffer, with |prompt_getprompt()|. The user can go to Normal mode and navigate through the buffer. This can be useful to see older output or copy text. The CTRL-W key can be used to start a window command, such as CTRL-W w to switch to the next window. This also works in Insert mode (use Shift-CTRL-W to delete a word). When leaving the window Insert mode will be stopped. When coming back to the prompt window Insert mode will be restored. Any command that starts Insert mode, such as "a", "i", "A" and "I", will move the cursor to the last line. "A" will move to the end of the line, "I" to the start of the line. Here is an example for Unix. It starts a shell in the background and prompts for the next shell command. Output from the shell is displayed above the prompt. > " Function handling a line of text that has been typed. func TextEntered(text) " Send the text to a shell with Enter appended. call chansend(g:shell_job, [a:text, '']) endfunc " Function handling output from the shell: Added above the prompt. func GotOutput(channel, msg, name) call append(line("$") - 1, a:msg) endfunc " Function handling the shell exit: close the window. func JobExit(job, status, event) quit! endfunc " Start a shell in the background. let shell_job = jobstart(["/bin/sh"], #{ \ on_stdout: function('GotOutput'), \ on_stderr: function('GotOutput'), \ on_exit: function('JobExit'), \ }) new set buftype=prompt let buf = bufnr('') call prompt_setcallback(buf, function("TextEntered")) call prompt_setprompt(buf, "shell command: ") " start accepting shell commands startinsert < vim:tw=78:ts=8:noet:ft=help:norl: