ssh completion is slow if /etc/hosts is long

[nthapaliya]

> cat /etc/hosts| wc -l
   47737

If /etc/hosts is a large file (for example, using https://github.com/StevenBlack/hosts to block adware), then ssh completion is really slow. I've isolated the offending line that causes most of the hangup:
https://github.com/fish-shell/fish-shell/blob/master/share/functions/__fish_print_hostnames.fish#L12

If that line is replaced with a grep/awk pipeline, ssh completion feels instantaneous again.

For example:

diff --git a/share/functions/__fish_print_hostnames.fish b/share/functions/__fish_print_hostnames.fish
index aabbf0f6..748eda2c 100644
--- a/share/functions/__fish_print_hostnames.fish
+++ b/share/functions/__fish_print_hostnames.fish
@@ -9,7 +9,7 @@ function __fish_print_hostnames -d "Print a list of known hostnames"
         getent hosts | string match -r -v '^0.0.0.0' | string replace -r '^\s*\S+\s+' '' | string split ' '
     else if test -r /etc/hosts
         # Ignore commented lines and functionally empty lines.
-        string match -r -v '^\s*0.0.0.0|^\s*#|^\s*$' </etc/hosts | string replace -r -a '#.*$' '' | string replace -r '^\s*\S+\s+' '' | string trim | string replace -r -a '\s+' ' ' | string split ' '
+        grep -Ev '^\s*0.0.0.0|^\s*#|^\s*$' /etc/hosts | awk '{print $NF}' | sort | uniq
     end
 
     # Print nfs servers from /etc/fstab

Two solutions come to mind:

1. Long term: profile and optimize the string match builtin.
   • Pros: all scripts benefit from this.
   • Cons: probably more work, as someone needs to dig into the c/c++ code (out of my skillset)
2. Short term: Replace those offending lines with some grep/awk.
   • Pros: Easier to implement. Similar work on this done here: Improve ssh completions/__fish_print_hostnames #4378 and 3b3bcc9
   • Cons: need to be careful about cross compatibility

MacOS High Sierra
fish, version 2.7.0

[faho]

@nthapaliya: Please try #4610. I have a hosts file of about 30k entries, and for me that speeds up __fish_print_hostnames from 240ms to 70ms.

[nthapaliya]

@faho its much better, much more usable now. ssh <tab> completes much faster.

However __complete_user_at_hosts doesn't seem to be working as intended: ssh root@<tab> doesn't complete, just rings the visual bell. If it is an unrelated problem, I'm glad to open another issue.

[faho]

However __complete_user_at_hosts doesn't seem to be working as intended: ssh root@ doesn't complete, just rings the visual bell. If it is an unrelated problem, I'm glad to open another issue.

Are you sure that worked before? That function is defined as

# Defined in /usr/share/fish/functions/__fish_complete_user_at_hosts.fish @ line 1
function __fish_complete_user_at_hosts --description 'Print list host-names with user@'
	for user_at in (commandline -ct | string match -r '.*@'; or echo "")(__fish_print_hostnames)
        echo $user_at
    end
end

So there's some string stuff involved. With the current token being "root@", that commandline -ct stuff should echo it, so it should be crossed with __fish_print_hostnames - which you have already confirmed works. It's possible that some bytes get skipped (an off-by-one-error or similar), but this is the first I'm seeing of that.

[nthapaliya]

Are you sure that worked before?

Now that you mention it, that 'broken' behavior existed before your patch, and is unrelated to your changes. I am convinced I was able to complete ssh root@<tab> at some point in the past, but I don't remember when.