"CONNECTION: ''" Error on CentOS while the omnisharp server is successfully running

[AlseinX]

neofetch:

OS: CentOS Linux 7 (Core) x86_64
Host: Bochs
Kernel: 3.10.0-514.26.2.el7.x86_64
Uptime: 81 days, 1 hour, 28 mins
Packages: 670 (rpm)
Shell: zsh 5.0.2
Terminal: /dev/pts/1
CPU: Intel Xeon E5-26xx v4 (1) @ 2.399GH
GPU: Cirrus Logic GD 5446
Memory: 223MiB / 1839MiB

vim version:

root@VM_0_2_centos ~/CoreProjects/CoreTest1/src/CoreTest1$ vim --version                                                                                                                                         
VIM - Vi IMproved 8.1 (2018 May 18, compiled Sep 17 2018 01:06:46)
Included patches: 1-398
Compiled by root@VM_0_2_centos
Huge version without GUI.  Features included (+) or not (-):
+acl               +extra_search      +mouse_netterm     +tag_old_static
+arabic            +farsi             +mouse_sgr         -tag_any_white
+autocmd           +file_in_path      -mouse_sysmouse    -tcl
+autochdir         +find_in_path      +mouse_urxvt       +termguicolors
-autoservername    +float             +mouse_xterm       +terminal
-balloon_eval      +folding           +multi_byte        +terminfo
+balloon_eval_term -footer            +multi_lang        +termresponse
-browse            +fork()            -mzscheme          +textobjects
++builtin_terms    +gettext           +netbeans_intg     +timers
+byte_offset       -hangul_input      +num64             +title
+channel           +iconv             +packages          -toolbar
+cindent           +insert_expand     +path_extra        +user_commands
-clientserver      +job               -perl              +vartabs
-clipboard         +jumplist          +persistent_undo   +vertsplit
+cmdline_compl     +keymap            +postscript        +virtualedit
+cmdline_hist      +lambda            +printer           +visual
+cmdline_info      +langmap           +profile           +visualextra
+comments          +libcall           +python            +viminfo
+conceal           +linebreak         -python3           +vreplace
+cryptv            +lispindent        +quickfix          +wildignore
+cscope            +listcmds          +reltime           +wildmenu
+cursorbind        +localmap          +rightleft         +windows
+cursorshape       -lua               -ruby              +writebackup
+dialog_con        +menu              +scrollbind        -X11
+diff              +mksession         +signs             -xfontset
+digraphs          +modify_fname      +smartindent       -xim
-dnd               +mouse             +startuptime       -xpm
-ebcdic            -mouseshape        +statusline        -xsmp
+emacs_tags        +mouse_dec         -sun_workshop      -xterm_clipboard
+eval              -mouse_gpm         +syntax            -xterm_save
+ex_extra          -mouse_jsbterm     +tag_binary        
   system vimrc file: "$VIM/vimrc"
     user vimrc file: "$HOME/.vimrc"
 2nd user vimrc file: "~/.vim/vimrc"
      user exrc file: "$HOME/.exrc"
       defaults file: "$VIMRUNTIME/defaults.vim"
  fall-back for $VIM: "/usr/local/share/vim"
Compilation: gcc -std=gnu99 -c -I. -Iproto -DHAVE_CONFIG_H     -g -O2 -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=1       
Linking: gcc -std=gnu99   -L/usr/local/lib -Wl,--as-needed -o vim        -lm -ltinfo -lnsl   -ldl    -L/usr/lib64/python2.7/config -lpython2.7 -lpthread -ldl -lutil -lm -Xlinker -export-dynamic

.vimrc:

let g:OmniSharp_server_use_mono = 1

" OmniSharp won't work without this setting
filetype plugin on

" Set the type lookup function to use the preview window instead of echoing it
"let g:OmniSharp_typeLookupInPreview = 1

" Timeout in seconds to wait for a response from the server
let g:OmniSharp_timeout = 5

" Don't autoselect first omnicomplete option, show options even if there is only
" one (so the preview documentation is accessible). Remove 'preview' if you
" don't want to see any documentation whatsoever.
set completeopt=longest,menuone,preview

" Fetch full documentation during omnicomplete requests.
" There is a performance penalty with this (especially on Mono).
" By default, only Type/Method signatures are fetched. Full documentation can
" still be fetched when you need it with the :OmniSharpDocumentation command.
"let g:omnicomplete_fetch_full_documentation = 1

" Set desired preview window height for viewing documentation.
" You might also want to look at the echodoc plugin.
set previewheight=5

" Tell ALE to use OmniSharp for linting C# files, and no other linters.
let g:ale_linters = { 'cs': ['OmniSharp'] }

augroup omnisharp_commands
    autocmd!

    " When Syntastic is available but not ALE, automatic syntax check on events
    " (TextChanged requires Vim 7.4)
    " autocmd BufEnter,TextChanged,InsertLeave *.cs SyntasticCheck

    " Show type information automatically when the cursor stops moving
    autocmd CursorHold *.cs call OmniSharp#TypeLookupWithoutDocumentation()

    " The following commands are contextual, based on the cursor position.
    autocmd FileType cs nnoremap <buffer> gd :OmniSharpGotoDefinition<CR>
    autocmd FileType cs nnoremap <buffer> <Leader>fi :OmniSharpFindImplementations<CR>
    autocmd FileType cs nnoremap <buffer> <Leader>fs :OmniSharpFindSymbol<CR>
    autocmd FileType cs nnoremap <buffer> <Leader>fu :OmniSharpFindUsages<CR>

    " Finds members in the current buffer
    autocmd FileType cs nnoremap <buffer> <Leader>fm :OmniSharpFindMembers<CR>

    autocmd FileType cs nnoremap <buffer> <Leader>fx :OmniSharpFixUsings<CR>
    autocmd FileType cs nnoremap <buffer> <Leader>tt :OmniSharpTypeLookup<CR>
    autocmd FileType cs nnoremap <buffer> <Leader>dc :OmniSharpDocumentation<CR>
    autocmd FileType cs nnoremap <buffer> <C-\> :OmniSharpSignatureHelp<CR>
    autocmd FileType cs inoremap <buffer> <C-\> <C-o>:OmniSharpSignatureHelp<CR>


    " Navigate up and down by method/property/field
    autocmd FileType cs nnoremap <buffer> <C-k> :OmniSharpNavigateUp<CR>
    autocmd FileType cs nnoremap <buffer> <C-j> :OmniSharpNavigateDown<CR>
augroup END

" Contextual code actions (uses fzf, CtrlP or unite.vim when available)
nnoremap <Leader><Space> :OmniSharpGetCodeActions<CR>
" Run code actions with text selected in visual mode to extract method
xnoremap <Leader><Space> :call OmniSharp#GetCodeActions('visual')<CR>

" Rename with dialog
nnoremap <Leader>nm :OmniSharpRename<CR>
nnoremap <F2> :OmniSharpRename<CR>
" Rename without dialog - with cursor on the symbol to rename: `:Rename newname`
command! -nargs=1 Rename :call OmniSharp#RenameTo("<args>")

nnoremap <Leader>cf :OmniSharpCodeFormat<CR>

" Start the omnisharp server for the current solution
nnoremap <Leader>ss :OmniSharpStartServer<CR>
nnoremap <Leader>sp :OmniSharpStopServer<CR>

" Add syntax highlighting for types and interfaces
nnoremap <Leader>th :OmniSharpHighlightTypes<CR>

" Enable snippet completion
let g:OmniSharp_want_snippet=1

call plug#begin('~/.vim/plugged')

Plug 'OmniSharp/omnisharp-vim'
Plug 'SirVer/ultisnips'
Plug 'w0rp/ale'

call plug#end()

the folder structure which was briefly made by dotnet commands:

├── CoreTest1.sln
└── src
    └── CoreTest1
        ├── CoreTest1.csproj
        └── Program.cs

building succesfully:

root@VM_0_2_centos ~/CoreProjects/CoreTest1$ dotnet build                                                                                                      
Microsoft (R) Build Engine version 15.8.166+gd4e8d81a88 for .NET Core
Copyright (C) Microsoft Corporation. All rights reserved.

  Restore completed in 58.08 ms for /root/CoreProjects/CoreTest1/src/CoreTest1/CoreTest1.csproj.
  CoreTest1 -> /root/CoreProjects/CoreTest1/src/CoreTest1/bin/Debug/netcoreapp2.1/CoreTest1.dll

Build succeeded.
    0 Warning(s)
    0 Error(s)

Time Elapsed 00:00:01.71

result of manually running the omnisharp server:

root@VM_0_2_centos ~/CoreProjects/CoreTest1/src/CoreTest1$ mono /root/.omnisharp/omnisharp-roslyn/OmniSharp.exe -p 60410 -s /root/CoreProjects/CoreTest1/CoreTest1.sln                                           
info: OmniSharp.Http.Startup[0]
      Starting OmniSharp on centos 7.0 (x64)
info: OmniSharp.Cake.CakeProjectSystem[0]
      Detecting Cake files in '/root/CoreProjects/CoreTest1'.
info: OmniSharp.Cake.CakeProjectSystem[0]
      Could not find any Cake files
info: OmniSharp.WorkspaceInitializer[0]
      Project system 'OmniSharp.DotNet.DotNetProjectSystem' is disabled in the configuration.
info: OmniSharp.MSBuild.ProjectSystem[0]
      Detecting projects in '/root/CoreProjects/CoreTest1/CoreTest1.sln'.
info: OmniSharp.MSBuild.ProjectManager[0]
      Queue project update for '/root/CoreProjects/CoreTest1/src/CoreTest1/CoreTest1.csproj'
info: OmniSharp.Script.ScriptProjectSystem[0]
      Detecting CSX files in '/root/CoreProjects/CoreTest1'.
info: OmniSharp.Script.ScriptProjectSystem[0]
      Could not find any CSX files
info: OmniSharp.WorkspaceInitializer[0]
      Invoking Workspace Options Provider: OmniSharp.Roslyn.CSharp.Services.CSharpWorkspaceOptionsProvider
info: OmniSharp.WorkspaceInitializer[0]
      Configuration finished.
info: OmniSharp.Http.Startup[0]
      Omnisharp server running on port '60410' at location '/root/CoreProjects/CoreTest1' on host -1.
info: OmniSharp.MSBuild.ProjectManager[0]
      Loading project: /root/CoreProjects/CoreTest1/src/CoreTest1/CoreTest1.csproj
info: OmniSharp.MSBuild.ProjectManager[0]
      Successfully loaded project file '/root/CoreProjects/CoreTest1/src/CoreTest1/CoreTest1.csproj'.
info: OmniSharp.MSBuild.ProjectManager[0]
      Adding project '/root/CoreProjects/CoreTest1/src/CoreTest1/CoreTest1.csproj'
info: OmniSharp.MSBuild.ProjectManager[0]
      Update project: CoreTest1

there seems not to be a problem. C-c exited.

vim Program.cs entering vim, and nothing was changed, like omnisharp-vim was never installed.

making sure server was automatically started by the plugin:
:!ps -ef | grep omnisharp

root     24387 24384  3 04:20 ?        00:00:04 mono /root/.omnisharp/omnisharp-roslyn/OmniSharp.exe -p 36234 -s /root/CoreProjects/CoreTest1/CoreTest1.sln
root     24521 24384  0 04:23 pts/0    00:00:00 /bin/zsh -c ps -ef | grep omnisharp

running :OmniSharpCodeFormat and got this screen with red error texts "CONNECTION: ''":

using System;

namespace CoreTest1
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("Hello World!");
        }
    }
}
~
~
~
~
~
~
~
~
~
~
~
CONNECTION: ''

[nickspoons]

Hi there,

There's an issue with the latest releases of omnisharp-roslyn not accepting Http connections. Please try the latest working version, by running this from the vim command line:

:OmniSharpInstall 'v1.32.1'

If you still have problems (hopefully not), try removing your set g:OmniSharp_server_use_mono = 1 line and then running the above OmniSharpInstall again. You generally don't need it on Linux (although I haven't tried CentOS to be sure) but it controls which omnisharp-roslyn to download as well as how it's executed, so if you change the setting you need to install the new server too.

[nickspoons]

@AlseinX I've just made a change so the default :OmniSharpInstall installs OmniSharp-Roslyn v1.32.1, so you can still run the above command, or just

:OmniSharpInstall

If this doesn't solve your problem, please re-open this issue.

[AlseinX]

running :OmniSharpInstall 'v1.32.1' there are even more problems, the omnisharp server stops working.

root@VM_0_2_centos ~/CoreProjects/CoreTest1/src/CoreTest1$ mono /root/.omnisharp/omnisharp-roslyn/OmniSharp.exe -p 60410 -s /root/CoreProjects/CoreTest1/CoreTest1.sln
info: OmniSharp.Http.Startup[0]
      Starting OmniSharp on centos 7.0 (x64)
info: OmniSharp.Cake.CakeProjectSystem[0]
      Detecting Cake files in '/root/CoreProjects/CoreTest1'.
info: OmniSharp.Cake.CakeProjectSystem[0]
      Could not find any Cake files
info: OmniSharp.Http.Startup[0]
      Project system 'OmniSharp.DotNet.DotNetProjectSystem' is disabled in the configuration.
info: OmniSharp.MSBuild.ProjectSystem[0]
      Detecting projects in '/root/CoreProjects/CoreTest1/CoreTest1.sln'.
info: OmniSharp.MSBuild.ProjectManager[0]
      Queue project update for '/root/CoreProjects/CoreTest1/src/CoreTest1/CoreTest1.csproj'
info: OmniSharp.Script.ScriptProjectSystem[0]
      Detecting CSX files in '/root/CoreProjects/CoreTest1'.
info: OmniSharp.Script.ScriptProjectSystem[0]
      Could not find any CSX files
info: OmniSharp.Http.Startup[0]
      Invoking Workspace Options Provider: OmniSharp.Roslyn.CSharp.Services.CSharpWorkspaceOptionsProvider
info: OmniSharp.Http.Startup[0]
      Configuration finished.
info: OmniSharp.Http.Startup[0]
      Omnisharp server running on port '60410' at location '/root/CoreProjects/CoreTest1' on host -1.
info: OmniSharp.MSBuild.ProjectManager[0]
      Loading project: /root/CoreProjects/CoreTest1/src/CoreTest1/CoreTest1.csproj
System.AggregateException: One or more errors occurred. (libuv) ---> System.DllNotFoundException: libuv
  at (wrapper managed-to-native) Microsoft.AspNetCore.Server.Kestrel.Internal.Networking.Libuv+NativeMethods.uv_loop_size()
  at Microsoft.AspNetCore.Server.Kestrel.Internal.Networking.Libuv.loop_size () [0x00000] in <43555eec0dc34d2abb4f01227fa5a2e9>:0 
  at Microsoft.AspNetCore.Server.Kestrel.Internal.Networking.UvLoopHandle.Init (Microsoft.AspNetCore.Server.Kestrel.Internal.Networking.Libuv uv) [0x0000c] in <43555eec0dc34d2abb4f01227fa5a2e9>:0 
  at Microsoft.AspNetCore.Server.Kestrel.Internal.KestrelThread.ThreadStart (System.Object parameter) [0x00029] in <43555eec0dc34d2abb4f01227fa5a2e9>:0 
   --- End of inner exception stack trace ---
  at System.Threading.Tasks.Task.ThrowIfExceptional (System.Boolean includeTaskCanceledExceptions) [0x00011] in <dac57913d8d54bde9ace4c332c44c2f5>:0 
  at System.Threading.Tasks.Task.Wait (System.Int32 millisecondsTimeout, System.Threading.CancellationToken cancellationToken) [0x00043] in <dac57913d8d54bde9ace4c332c44c2f5>:0 
  at System.Threading.Tasks.Task.Wait () [0x00000] in <dac57913d8d54bde9ace4c332c44c2f5>:0 
  at Microsoft.AspNetCore.Server.Kestrel.Internal.KestrelEngine.Start (System.Int32 count) [0x00037] in <43555eec0dc34d2abb4f01227fa5a2e9>:0 
  at Microsoft.AspNetCore.Server.Kestrel.KestrelServer.Start[TContext] (Microsoft.AspNetCore.Hosting.Server.IHttpApplication`1[TContext] application) [0x0044b] in <43555eec0dc34d2abb4f01227fa5a2e9>:0 
  at Microsoft.AspNetCore.Hosting.Internal.WebHost.Start () [0x00053] in <24af31b64ae843689736582353a19b3a>:0 
  at OmniSharp.Http.Host.Start () [0x000ab] in <8959a21458834a128afcd6caf0ea47d5>:0 
  at OmniSharp.Http.Driver.Program+<>c__DisplayClass0_1.<Main>b__1 () [0x0004f] in <689cc1cd84ed4fa1ba7232b3270b50a7>:0 
  at OmniSharp.CommandLineApplication+<>c__DisplayClass11_0.<OnExecute>b__0 () [0x0000b] in <3239e8b00e0a4ebd9dc65c215d41bd64>:0 
  at Microsoft.Extensions.CommandLineUtils.CommandLineApplication.Execute (System.String[] args) [0x0035b] in <e56ebbc3ed87488b8e26736bbadaa5d3>:0 
  at OmniSharp.CommandLineApplication.Execute (System.Collections.Generic.IEnumerable`1[T] args) [0x00042] in <3239e8b00e0a4ebd9dc65c215d41bd64>:0 
  at OmniSharp.Http.Driver.Program+<>c__DisplayClass0_0.<Main>b__0 () [0x00028] in <689cc1cd84ed4fa1ba7232b3270b50a7>:0 
  at OmniSharp.HostHelpers.Start (System.Func`1[TResult] action) [0x0001c] in <3239e8b00e0a4ebd9dc65c215d41bd64>:0 
---> (Inner Exception #0) System.DllNotFoundException: libuv
  at (wrapper managed-to-native) Microsoft.AspNetCore.Server.Kestrel.Internal.Networking.Libuv+NativeMethods.uv_loop_size()
  at Microsoft.AspNetCore.Server.Kestrel.Internal.Networking.Libuv.loop_size () [0x00000] in <43555eec0dc34d2abb4f01227fa5a2e9>:0 
  at Microsoft.AspNetCore.Server.Kestrel.Internal.Networking.UvLoopHandle.Init (Microsoft.AspNetCore.Server.Kestrel.Internal.Networking.Libuv uv) [0x0000c] in <43555eec0dc34d2abb4f01227fa5a2e9>:0 
  at Microsoft.AspNetCore.Server.Kestrel.Internal.KestrelThread.ThreadStart (System.Object parameter) [0x00029] in <43555eec0dc34d2abb4f01227fa5a2e9>:0 <---

warn: OmniSharp.MSBuild.ProjectManager[0]
      Failed to load project file '/root/CoreProjects/CoreTest1/src/CoreTest1/CoreTest1.csproj'.

I triple checked I do have libuv installed.
BTW I can't remove let g:OmniSharp_server_use_mono = 1 because the runtime included in omnisharp server itself seems too old to support a .NET Core 2.1 projects. Having this line and upgrading the mono version to Nightly channel was the only way that I could make the omnisharp server work with no warns or errors.

[nickspoons]

OmniSharp-roslyn has no problems for with the latest .NET core.

Did you try removing the g:OmniSharp_server_use_mono line and running :OmniSharpInstall ?

[nickspoons]

When testing the server from the commandline, try using the run script instead of explicitly calling OmniSharp.exe

[AlseinX]

If I remove this line, the omnisharp-vim calls run script to start the omnisharp server.
And run scripts always output

warn: OmniSharp.MSBuild.ProjectManager[0]
      Failed to load project file '/root/CoreProjects/CoreTest1/src/CoreTest1/CoreTest1.csproj'.
fail: OmniSharp.MSBuild.ProjectManager[0]
      Attemped to update project that is not loaded: /root/CoreProjects/CoreTest1/src/CoreTest1/CoreTest1.csproj

[AlseinX]

Luckily I tried installing libuv-devel as well and v1.32.1 eventually works.