[vim/vim] revenge: Add ch_listen() function for socket server support (PR #19231)
mattn
Summary
This patch adds ch_listen() function to Vim, allowing scripts to create listening sockets and accept incoming network connections. This enables Vim to act as a simple network server for various use cases.
Changes
New Functions
-
ch_listen(address [, options])- Listen on a socket and accept connections- Returns a channel representing the listening socket
- Calls a callback function when a new client connects
- Supports both IPv4 and Unix domain sockets
-
channel_listen_unix(path, callback)- Unix domain socket support -
channel_listen_func(argvars)- Vim script interface
Implementation Details
- Added
ch_listenfield tostruct channel_Sto mark listening sockets - Modified
channel_read()to handle accept() on listening sockets - When a connection is accepted, a new channel is created and passed to the callback
- The callback receives the accepted channel and client address
API Usage
function! OnConnect(channel, address) echomsg 'Client connected from: ' . a:address call ch_setoptions(a:channel, { \ 'callback': function('OnData'), \ }) endfunction function! OnData(channel, data) echomsg 'Received: ' . a:data endfunction let server = ch_listen('127.0.0.1:8080', { \ 'callback': function('OnConnect'), \ })
Use Cases
- Simple HTTP server for serving static files
- Network protocol implementation for testing
- Local IPC between Vim and other processes
- Learning network programming concepts
Testing
- Implemented test case
Test_listen()intest_channel.vim - Tested with multiple concurrent connections
- Verified callback invocation and data transmission
Related Features
This complements the existing ch_open() function:
ch_open()- connect to a serverch_listen()- accept connections as a server
Limitations
- No SSL/TLS support
- Single-threaded (blocks Vim event loop during processing)
- No built-in HTTP parsing (simple callbacks only)
This is demonstration of HTTP server written in Vim script.
image.png (view on web)You can view, comment on, or merge this pull request online at:
https://github.com/vim/vim/pull/19231
Commit Summary
- 61d4cda support ch_listen
File Changes
(7 files)
- M runtime/doc/channel.txt (17)
- M src/channel.c (360)
- M src/errors.h (4)
- M src/evalfunc.c (6)
- M src/proto/channel.pro (4)
- M src/structs.h (9)
- M src/testdir/test_channel.vim (34)
Patch Links:
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mattn
mattn left a comment (vim/vim#19231)I'll fix test fail in later.
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mattn
@mattn pushed 1 commit.
- 2d56f55 fix build
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Christian Brabandt
chrisbra left a comment (vim/vim#19231)Thanks that is nice. But I'll move this after the Vim 9.2 release.
Can a few people try it out? I'd also think that we should have a very simple practical example for this in the help.
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bfrg
bfrg left a comment (vim/vim#19231)It is not clear from the docs how ch_listen() differs from ch_open({address} [, {options}])? See :h channel-address for possible values of address.
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mattn
mattn left a comment (vim/vim#19231)@chrisbra This is simple practice example working as HTTP file server.
https://gist.github.com/mattn/3e691419c37fe7ce501dc37e2a1bb545
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Christian Brabandt
chrisbra left a comment (vim/vim#19231)Thanks.
ch_listen(address [, options]) - Listen on a socket and accept connections
Returns a channel representing the listening socket
Calls a callback function when a new client connects
Supports both IPv4 and Unix domain sockets
channel_listen_unix(path, callback) - Unix domain socket support
Why do we need channel_list_unix()? It looks like this is already supported via ch_listen() anyhow, no?
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Maxim Kim
habamax left a comment (vim/vim#19231)I wonder if this would help @yegappan lsp to support lsp servers without stdio, e.g. godot lsp server that works only over http?
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mattn
mattn left a comment (vim/vim#19231)Call tree is below. Should we rename channel_listen to channel_listen_tcp ?
f_ch_listen
channel_listen_func
channel_listen (TCP)
channel_listen_unix (Unix Domain Socket)
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Christian Brabandt
chrisbra left a comment (vim/vim#19231)I think we should have one single ch_listen() function, that accepts either a TCP address or a Unix domain socket, similar to ch_open(). I don't think we need separate vim script functions for tcp and unix domain sockets.
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bfrg
bfrg left a comment (vim/vim#19231)I wonder if this would help @yegappan lsp to support lsp servers without
stdio, e.g. godot lsp server that works only over http?
This is already possible, see :h channel-address. You need to open a channel with ch_open() and then pass that channel to job_start() using its channel option (explained under :h job-options [below :h job-term] ). There's also an example in the docs under :h channel-demo using a Python server.
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mattn
mattn left a comment (vim/vim#19231)@chrisbra
The current implementation already follows this approach. ch_listen() accepts both TCP addresses and Unix domain sockets using the same pattern as ch_open():
- TCP:
ch_listen('127.0.0.1:12345', ...) - Unix socket:
ch_listen('unix:/path/to/socket', ...)
The channel_listen_func() detects the unix: prefix and internally calls either channel_listen_unix() or channel_listen() accordingly. There is no separate ch_listen_tcp() or ch_listen_unix() function exposed to Vim script.
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dkearns
dkearns left a comment (vim/vim#19231)I think we should have one single
ch_listen()function, that accepts either a TCP address or a Unix domain socket, similar toch_open(). I don't think we need separate vim script functions for tcp and unix domain sockets.
ch_open() is the only builtin Vim script function added, the others are implementation functions.
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Copilot
@Copilot commented on this pull request.
Pull request overview
This PR adds server socket functionality to Vim by implementing the ch_listen() function, enabling Vim scripts to accept incoming network connections. This complements the existing ch_open() function, which allows Vim to act as a client.
Changes:
- Added
ch_listen()function with support for IPv4, IPv6, and Unix domain sockets - Implemented callback mechanism to handle incoming connections
- Added test coverage in
test_channel.vim
Reviewed changes
Copilot reviewed 9 out of 9 changed files in this pull request and generated 5 comments.
Show a summary per file| File | Description |
|---|---|
| src/channel.c | Core implementation of listen functionality and accept handling |
| src/structs.h | Added ch_listen field to mark listening sockets |
| src/proto/channel.pro | Function prototypes for new channel listening functions |
| src/evalfunc.c | Registered ch_listen as a Vim script function |
| src/errors.h | Added error messages for listen failures |
| src/testdir/test_channel.vim | Added test case and fixed indentation throughout file |
| runtime/doc/usr_41.txt | Updated function list and alphabetical ordering |
| runtime/doc/channel.txt | Added documentation for ch_listen() |
| runtime/doc/builtin.txt | Added ch_listen() to built-in function list |
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In src/channel.c:
> + else + sprintf((char *)namebuf, "unix:%s", + ((struct sockaddr_un*)&client)->sun_path);
For Unix domain sockets, the client address structure populated by accept() does not contain a meaningful path in sun_path. Unix domain sockets only provide the path for the listening socket, not for accepted connections. This will likely result in garbage or empty data being passed to the callback. Consider passing an empty string or a generic identifier like 'unix:anonymous' for Unix domain socket clients.
- else - sprintf((char *)namebuf, "unix:%s", - ((struct sockaddr_un*)&client)->sun_path); + else if (client.ss_family == AF_UNIX) + sprintf((char *)namebuf, "unix:anonymous"); + else + sprintf((char *)namebuf, "unknown");
In src/channel.c:
> + if (client.ss_family == AF_INET) + sprintf((char *)namebuf, "%s:%d", + inet_ntoa(((struct sockaddr_in*)&client)->sin_addr), + ntohs(((struct sockaddr_in*)&client)->sin_port)); + else + sprintf((char *)namebuf, "unix:%s", + ((struct sockaddr_un*)&client)->sun_path);
The else branch assumes all non-IPv4 connections are Unix domain sockets, but the code supports IPv6 addresses (as shown in channel_listen_func). When an IPv6 client connects, this will incorrectly try to interpret the address as a Unix socket path. Add explicit handling for AF_INET6 using inet_ntop() to format IPv6 addresses.
In src/channel.c:
> + sprintf((char *)namebuf, "%s:%d", + inet_ntoa(((struct sockaddr_in*)&client)->sin_addr), + ntohs(((struct sockaddr_in*)&client)->sin_port)); + else + sprintf((char *)namebuf, "unix:%s",
Using sprintf without bounds checking creates a buffer overflow risk. The namebuf is declared as 256 bytes, but sprintf doesn't verify this limit. Use snprintf instead to ensure the formatted string doesn't exceed the buffer size.
⬇️ Suggested change- sprintf((char *)namebuf, "%s:%d", - inet_ntoa(((struct sockaddr_in*)&client)->sin_addr), - ntohs(((struct sockaddr_in*)&client)->sin_port)); - else - sprintf((char *)namebuf, "unix:%s", + snprintf((char *)namebuf, sizeof(namebuf), "%s:%d", + inet_ntoa(((struct sockaddr_in*)&client)->sin_addr), + ntohs(((struct sockaddr_in*)&client)->sin_port)); + else + snprintf((char *)namebuf, sizeof(namebuf), "unix:%s",
In src/testdir/test_channel.vim:
> + func s:test_listen_accept(ch, addr) + let g:server_received_addr = a:addr + let g:server_received_msg = ch_readraw(a:ch) + endfunction
The test doesn't verify that g:server_received_addr contains the expected client address. Add an assertion like call assert_match('127.0.0.1:', g:server_received_addr) to ensure the callback receives correct address information.
In src/testdir/test_channel.vim:
> + func Test_listen()
+ call ch_log('Test_listen()')
+ let server = ch_listen('127.0.0.1:12345', {'callback': function('s:test_listen_accept')})
+ if ch_status(server) == 'fail'
+ call assert_report("Can't listen channel")
+ return
+ endif
The test doesn't verify error handling for invalid addresses or port conflicts. Consider adding test cases for scenarios like invalid port numbers, ports already in use, or malformed addresses to ensure proper error reporting.
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