Add dry-run option to the CLI

This commit adds a new mode of operation to the CLI, the dry-run mode.
In this mode, the CLI will not execute any changes, but will instead
print them to the console.

Closes #28

src/main.rs

@@ -19,6 +19,9 @@ struct Args {
     /// path to the config file
     #[arg(long)]
     config: String,
+    /// Dry run mode
+    #[arg(long)]
+    dry_run: bool,
 }
 
 fn main() {
@@ -61,7 +64,7 @@ fn main() {
         }
     };
 
-    let mut proxysql = ProxySQL::new(&config);
+    let mut proxysql = ProxySQL::new(&config, args.dry_run);
 
     let running_mode = match config.operation_mode {
         Some(mode) => mode,

src/proxysql.rs

@@ -15,6 +15,7 @@ pub struct ProxySQL {
     warmup_time_s: u16,
     conn: mysql::Conn,
     hosts: Vec<Host>,
+    dry_run: bool,
 }
 
 impl ProxySQL {
@@ -27,7 +28,7 @@ impl ProxySQL {
     /// # Returns
     ///
     /// A new ProxySQL struct.
-    pub fn new(config: &config::Config) -> Self {
+    pub fn new(config: &config::Config, dry_run: bool) -> Self {
         let mut conn = Conn::new(
             OptsBuilder::new()
                 .ip_or_hostname(Some(config.proxysql_host.as_str()))
@@ -59,9 +60,20 @@ impl ProxySQL {
             readyset_hostgroup: config.readyset_hostgroup,
             warmup_time_s: config.warmup_time_s.unwrap_or(0),
             hosts,
+            dry_run,
         }
     }
 
+    /// This function is used to get the dry_run field.
+    /// This field is used to indicate if the ProxySQL operations should be executed or not.
+    ///
+    /// # Returns
+    ///
+    /// A boolean indicating if the ProxySQL operations should be executed or not.
+    pub fn dry_run(&self) -> bool {
+        self.dry_run
+    }
+
     /// This function is used to add a query rule to ProxySQL.
     ///
     /// # Arguments
@@ -199,6 +211,10 @@ impl ProxySQL {
                     .as_str(),
                 );
                 host.change_status(status);
+                if self.dry_run {
+                    messages::print_info("Dry run, skipping changes to ProxySQL");
+                    continue;
+                }
                 let _ = self.conn.query_drop(format!(
                     "UPDATE mysql_servers SET status = '{}' {}",
                     host.get_status(),

src/queries.rs

@@ -193,13 +193,17 @@ impl QueryDiscovery {
                                 .as_str(),
                         );
                         queries_added_or_change = true;
-                        proxysql.get_online_hosts().iter_mut().for_each(|host| {
-                            host.cache_query(query)
-                                .expect("Failed to create readyset cache");
-                        });
-                        proxysql
-                            .add_as_query_rule(query)
-                            .expect("Failed to add query rule");
+                        if !proxysql.dry_run() {
+                            proxysql.get_online_hosts().iter_mut().for_each(|host| {
+                                host.cache_query(query)
+                                    .expect("Failed to create readyset cache");
+                            });
+                            proxysql
+                                .add_as_query_rule(query)
+                                .expect("Failed to add query rule");
+                        } else {
+                            messages::print_info("Dry run, not adding query");
+                        }
                         current_queries_digest.push(query.get_digest().to_string());
                     }
                     Ok(false) => {