SSH.pm: Print a friendlier message if connecting fails

"got EOF while expecting 8 bytes from remote side" is not very
helpful.

2 files changed, 12 insertions, 4 deletions

diff --git a/perl/lib/Nix/CopyClosure.pm b/perl/lib/Nix/CopyClosure.pm
index 1520f1012c7d..800feb3b413a 100644
--- a/perl/lib/Nix/CopyClosure.pm
+++ b/perl/lib/Nix/CopyClosure.pm
@@ -57,6 +57,7 @@ sub copyTo {
     if ($@) {
         chomp $@;
         warn "$@; falling back to old closure copying method\n";
+        $@ = "";
         return oldCopyTo(@_);
     }
 
diff --git a/perl/lib/Nix/SSH.pm b/perl/lib/Nix/SSH.pm
index 9e0c10beb0e0..95393d881450 100644
--- a/perl/lib/Nix/SSH.pm
+++ b/perl/lib/Nix/SSH.pm
@@ -1,5 +1,6 @@
 package Nix::SSH;
 
+use utf8;
 use strict;
 use File::Temp qw(tempdir);
 use IPC::Open2;
@@ -89,10 +90,16 @@ sub connectToRemoteNix {
     my $pid = open2($from, $to, "exec ssh -x -a $sshHost @globalSshOpts @{$sshOpts} nix-store --serve --write $extraFlags");
 
     # Do the handshake.
-    my $SERVE_MAGIC_1 = 0x390c9deb; # FIXME
-    my $clientVersion = 0x200;
-    syswrite($to, pack("L<x4L<x4", $SERVE_MAGIC_1, $clientVersion)) or die;
-    die "did not get valid handshake from remote host\n" if readInt($from) != 0x5452eecb;
+    my $magic;
+    eval {
+        my $SERVE_MAGIC_1 = 0x390c9deb; # FIXME
+        my $clientVersion = 0x200;
+        syswrite($to, pack("L<x4L<x4", $SERVE_MAGIC_1, $clientVersion)) or die;
+        $magic = readInt($from);
+    };
+    die "unable to connect to ‘$sshHost’\n" if $@;
+    die "did not get valid handshake from remote host\n" if $magic  != 0x5452eecb;
+
     my $serverVersion = readInt($from);
     die "unsupported server version\n" if $serverVersion < 0x200 || $serverVersion >= 0x300;