Add exists command

src/connection_manager/command_handler.rs

@@ -1,7 +1,7 @@
 use std::borrow::Cow;
 
 use super::{
-    commands::{handle_echo, handle_get, handle_ping, handle_set, ignore_command},
+    commands::{handle_echo, handle_exists, handle_get, handle_ping, handle_set, ignore_command},
     utils::serialize_error,
 };
 use crate::{deserialize, resp::deserialize::RespResponse, store::db::Cache};
@@ -21,6 +21,7 @@ pub fn handle_command(human_readable: Cow<'_, str>, cache: &Cache) -> String {
                         "echo" => handle_echo(args),
                         "set" => handle_set(args, cache),
                         "get" => handle_get(args, cache),
+                        "exists" => handle_exists(args, cache),
                         unknown_command => {
                             let message = "-unknown command '".to_owned() + unknown_command + "'";
                             serialize_error(message.as_str())
@@ -152,4 +153,21 @@ mod tests {
             handle_command(set_input, &cache)
         );
     }
+
+    #[test]
+    fn should_return_existing_values() {
+        let cache = Cache::new();
+        cache.set("name".to_string(), "name_val".to_string());
+        cache.set("name1".to_string(), "name_val_1".to_string());
+        cache.set("name2".to_string(), "name_val_2".to_string());
+        let input = Cow::Borrowed("*4\r\n$6\r\nexists\r\n$4\r\nname\r\n$5\r\nname1\r\n$5\r\nname2\r\n");
+        assert_eq!(serialize(InputVariants::NumberVariant(3)), handle_command(input, &cache))
+    }
+
+    #[test]
+    fn should_return_zero_if_not_exists() {
+        let cache = Cache::new();
+        let input = Cow::Borrowed("*2\r\n$6\r\nexists\r\n$4\r\nname\r\n");
+        assert_eq!(serialize(InputVariants::NumberVariant(0)), handle_command(input, &cache))
+    }
 }

src/connection_manager/commands.rs

@@ -88,3 +88,11 @@ fn handle_set_with_expiration(args: &[String], cache: &Cache, time: Duration) ->
         serialize_error("-invalid SET arguments")
     }
 }
+
+pub fn handle_exists(args: &[String], cache: &Cache) -> String {
+    let count = args.iter().filter(|key| cache.exists(key)).count();
+    match i32::try_from(count) {
+        Ok(count_i32) => serialize(InputVariants::NumberVariant(count_i32)),
+        Err(_) => serialize_error("-something went wrong during exists"),
+    }
+}

src/store/db.rs

@@ -48,6 +48,11 @@ impl Cache {
         let data = self.data.read().unwrap();
         data.get(key).cloned()
     }
+
+    pub fn exists(&self, key: &str) -> bool {
+        let data = self.data.read().unwrap();
+        data.contains_key(key)
+    }
 }
 
 #[cfg(test)]