[PATCH pve-network 09/10] api: add dry-run endpoint for sdn apply to preview changes

[Gabriel Goller <g.goller@proxmox.com>]

Allows users to see the diff of frr configuration before applying
SDN changes. Previously this was not possible and the user had to apply
and then see what changed. Ideally this would also include the ifupdown2
config, but that's a bit tricky since we add config lines in perl-rs as
well.

Signed-off-by: Gabriel Goller <g.goller@proxmox.com>
---
 src/PVE/API2/Network/SDN.pm | 67 +++++++++++++++++++++++++++++++++++++
 src/PVE/Network/SDN.pm      |  9 +++--
 2 files changed, 74 insertions(+), 2 deletions(-)

diff --git a/src/PVE/API2/Network/SDN.pm b/src/PVE/API2/Network/SDN.pm
index b35a588d391d..9208d6f4e8b3 100644
--- a/src/PVE/API2/Network/SDN.pm
+++ b/src/PVE/API2/Network/SDN.pm
@@ -3,6 +3,9 @@ package PVE::API2::Network::SDN;
 use strict;
 use warnings;
 
+use File::Temp qw(tempfile);
+use Encode qw(decode);
+
 use PVE::Cluster qw(cfs_lock_file cfs_read_file cfs_write_file);
 use PVE::Exception qw(raise_param_exc);
 use PVE::JSONSchema qw(get_standard_option);
@@ -325,4 +328,68 @@ __PACKAGE__->register_method({
     },
 });
 
+sub get_diff {
+    my ($filename_one, $filename_two) = @_;
+
+    my $diff = '';
+
+    my $cmd = ['/usr/bin/diff', '-b', '-N', '-u', $filename_one, $filename_two];
+    PVE::Tools::run_command(
+        $cmd,
+        noerr => 1,
+        outfunc => sub {
+            my ($line) = @_;
+            $diff .= decode('UTF-8', $line) . "\n";
+        },
+    );
+
+    $diff = undef if !$diff;
+
+    return $diff;
+}
+
+__PACKAGE__->register_method({
+    name => 'dry-apply',
+    path => 'dry-apply',
+    method => 'PUT',
+    permissions => {
+        check => ['perm', '/nodes/{node}', ['Sys.Modify']],
+    },
+    description => "Dry-Run the SDN apply",
+    protected => 1,
+    proxyto => 'node',
+    parameters => {
+        additionalProperties => 0,
+        properties => {
+            node => get_standard_option('pve-node'),
+        },
+    },
+
+    returns => {
+        type => 'object',
+        properties => {
+            "frr-diff" =>
+                { type => 'string', description => 'The frr config generated by SDN.' },
+        },
+    },
+    code => sub {
+        my ($param) = @_;
+
+        my $config = PVE::Network::SDN::compile_running_cfg();
+
+        my $fabric_config = PVE::Network::SDN::Fabrics::config(0);
+        my $frr_config = PVE::Network::SDN::generate_frr_raw_config($config, $fabric_config);
+        my $new_config_frr = PVE::Network::SDN::Frr::raw_config_to_string($frr_config);
+
+        my ($frr_tmp_fh, $frr_tmp_filename) = tempfile();
+        print $frr_tmp_fh $new_config_frr;
+
+        my $return_value = {};
+        $return_value->{"frr-diff"} = get_diff('/etc/frr/frr.conf', $frr_tmp_filename);
+
+        close($frr_tmp_fh);
+        return $return_value;
+    },
+});
+
 1;
diff --git a/src/PVE/Network/SDN.pm b/src/PVE/Network/SDN.pm
index c000bed498ec..18938d73ba70 100644
--- a/src/PVE/Network/SDN.pm
+++ b/src/PVE/Network/SDN.pm
@@ -187,8 +187,7 @@ sub pending_config {
 
 }
 
-sub commit_config {
-
+sub compile_running_cfg {
     my $cfg = cfs_read_file($running_cfg);
     my $version = $cfg->{version};
 
@@ -219,6 +218,12 @@ sub commit_config {
         fabrics => $fabrics,
     };
 
+    return $cfg;
+}
+
+sub commit_config {
+    my $cfg = compile_running_cfg();
+
     cfs_write_file($running_cfg, $cfg);
 }
 
-- 
2.47.3