Implement EXISTS command (#160)

Implemented EXISTS command - @NicoleStrel

Author: NicoleStrel

README.md

@@ -210,6 +210,7 @@ Benchmark script options:
 * [DECR](https://sugardb.io/docs/commands/generic/decr)
 * [DECRBY](https://sugardb.io/docs/commands/generic/decrby)
 * [DEL](https://sugardb.io/docs/commands/generic/del)
+* [EXISTS](https://sugardb.io/docs/commands/generic/exists)
 * [EXPIRE](https://sugardb.io/docs/commands/generic/expire)
 * [EXPIRETIME](https://sugardb.io/docs/commands/generic/expiretime)
 * [FLUSHALL](https://sugardb.io/docs/commands/generic/flushall)

coverage/coverage.out

@@ -0,0 +1,47 @@
+import Tabs from '@theme/Tabs';
+import TabItem from '@theme/TabItem';
+
+# EXISTS
+
+### Syntax
+```
+EXISTS
+```
+
+### Module
+<span className="acl-category">generic</span>
+
+### Categories 
+<span className="acl-category">fast</span>
+<span className="acl-category">read</span>
+<span className="acl-category">keyspace</span>
+
+### Description
+Returns the number of keys that exists from the provided list of keys. Note: If duplicate keys are provided, each one is counted separately.
+
+### Examples
+
+<Tabs
+  defaultValue="go"
+  values={[
+    { label: 'Go (Embedded)', value: 'go', },
+    { label: 'CLI', value: 'cli', },
+  ]}
+>
+  <TabItem value="go">
+  Return the number of keys that exists:
+  ```go
+  db, err := sugardb.NewSugarDB()
+  if err != nil {
+    log.Fatal(err)
+  }
+  key, err := db.Exists("key1")
+  ```
+  </TabItem>
+  <TabItem value="cli">
+  Return the number of keys that exists:
+  ```
+  > EXISTS key1 key2
+  ```
+  </TabItem>
+</Tabs> 

docs/docs/commands/generic/exists.mdx

@@ -692,6 +692,24 @@ func handleRenamenx(params internal.HandlerFuncParams) ([]byte, error) {
 	return handleRename(params)
 }
 
+func handleExists(params internal.HandlerFuncParams) ([]byte, error) {
+	keys, err := existsKeyFunc(params.Command)
+	if err != nil {
+		return nil, err
+	}
+
+	// check if key exists and count
+	existingKeys := params.KeysExist(params.Context, keys.ReadKeys)
+	keyCount := 0
+	for _, key := range keys.ReadKeys {
+		if existingKeys[key] {
+			keyCount++
+		}
+	}
+
+	return []byte(fmt.Sprintf(":%d\r\n", keyCount)), nil
+}
+
 func handleFlush(params internal.HandlerFuncParams) ([]byte, error) {
 	if len(params.Command) != 1 {
 		return nil, errors.New(constants.WrongArgsResponse)
@@ -1393,5 +1411,15 @@ The REPLACE option removes the destination key before copying the value to it.`,
 			KeyExtractionFunc: renamenxKeyFunc,
 			HandlerFunc:       handleRenamenx,
 		},
+		{
+			Command:           "exists",
+			Module:            constants.GenericModule,
+			Categories:        []string{constants.KeyspaceCategory, constants.ReadCategory, constants.FastCategory},
+			Description:       "(EXISTS key [key ...]) Returns the number of keys that exist from the provided list of keys.",
+			Sync:              false,
+			Type:              "BUILT_IN",
+			KeyExtractionFunc: existsKeyFunc,
+			HandlerFunc:       handleExists,
+		},
 	}
 }

internal/modules/generic/commands.go

@@ -2391,6 +2391,118 @@ func Test_Generic(t *testing.T) {
 		}
 	})
 
+	t.Run("Test_HandleEXISTS", func(t *testing.T) {
+		t.Parallel()
+
+		conn, err := internal.GetConnection("localhost", port)
+		if err != nil {
+			t.Error(err)
+			return
+		}
+		defer func() {
+			_ = conn.Close()
+		}()
+		client := resp.NewConn(conn)
+
+		tests := []struct {
+			name             string
+			presetKeys       map[string]string
+			checkKeys        []string
+			expectedResponse int
+		}{
+			{
+				name:             "1. Key doesn't exist",
+				presetKeys:       map[string]string{},
+				checkKeys:        []string{"nonExistentKey"},
+				expectedResponse: 0,
+			},
+			{
+				name:             "2. Key exists",
+				presetKeys:       map[string]string{"existentKey": "value"},
+				checkKeys:        []string{"existentKey"},
+				expectedResponse: 1,
+			},
+			{
+				name: "3. All keys exist",
+				presetKeys: map[string]string{
+					"key1": "value1",
+					"key2": "value2",
+					"key3": "value3",
+				},
+				checkKeys:        []string{"key1", "key2", "key3"},
+				expectedResponse: 3,
+			},
+			{
+				name: "4. Only some keys exist",
+				presetKeys: map[string]string{
+					"key1": "value1",
+					"key2": "value2",
+				},
+				checkKeys:        []string{"key1", "key2", "nonExistentKey"},
+				expectedResponse: 2,
+			},
+			{
+				name: "5. All keys exist with duplicates",
+				presetKeys: map[string]string{
+					"key1": "value1",
+					"key2": "value2",
+					"key3": "value3",
+				},
+				checkKeys:        []string{"key1", "key2", "key3", "key1", "key2"},
+				expectedResponse: 5,
+			},
+		}
+
+		for _, test := range tests {
+			t.Run(test.name, func(t *testing.T) {
+				// Preset keys
+				for key, value := range test.presetKeys {
+					command := []resp.Value{resp.StringValue("SET"), resp.StringValue(key), resp.StringValue(value)}
+					if err = client.WriteArray(command); err != nil {
+						t.Error(err)
+						return
+					}
+					res, _, err := client.ReadValue()
+					if err != nil {
+						t.Error(err)
+						return
+					}
+					if !strings.EqualFold(res.String(), "OK") {
+						t.Errorf("expected preset response to be OK, got %s", res.String())
+						return
+					}
+				}
+
+				// Check EXISTS command
+				existsCommand := []resp.Value{resp.StringValue("EXISTS")}
+				for _, key := range test.checkKeys {
+					existsCommand = append(existsCommand, resp.StringValue(key))
+				}
+
+				if err = client.WriteArray(existsCommand); err != nil {
+					t.Error(err)
+					return
+				}
+
+				res, _, err := client.ReadValue()
+				if err != nil {
+					t.Error(err)
+					return
+				}
+
+				actualCount, err := strconv.Atoi(res.String())
+				if err != nil {
+					t.Errorf("error parsing response to int: %s", err)
+					return
+				}
+
+				if actualCount != test.expectedResponse {
+					t.Errorf("expected %d existing keys, got %d", test.expectedResponse, actualCount)
+				}
+			})
+		}
+	})
+
 	t.Run("Test_HandlerDECRBY", func(t *testing.T) {
 		t.Parallel()
 		conn, err := internal.GetConnection("localhost", port)

internal/modules/generic/commands_test.go

@@ -310,3 +310,14 @@ func moveKeyFunc(cmd []string) (internal.KeyExtractionFuncResult, error) {
 		WriteKeys: []string{cmd[1]},
 	}, nil
 }
+
+func existsKeyFunc(cmd []string) (internal.KeyExtractionFuncResult, error) {
+	if len(cmd) < 2 {
+		return internal.KeyExtractionFuncResult{}, errors.New(constants.WrongArgsResponse)
+	}
+	return internal.KeyExtractionFuncResult{
+		Channels:  make([]string, 0),
+		ReadKeys:  cmd[1:],
+		WriteKeys: make([]string, 0),
+	}, nil
+}

internal/modules/generic/key_funcs.go

@@ -806,3 +806,19 @@ func (server *SugarDB) Move(key string, destinationDB int) (int, error) {
 	}
 	return internal.ParseIntegerResponse(b)
 }
+
+// Exists returns the number of keys that exist from the provided list of keys.
+// Note: Duplicate keys in the argument list are each counted separately.
+//
+// Parameters:
+//
+// `keys` - ...string - the keys whose existence should be checked.
+//
+// Returns: An integer representing the number of keys that exist.
+func (server *SugarDB) Exists(keys ...string) (int, error) {
+	b, err := server.handleCommand(server.context, internal.EncodeCommand(append([]string{"EXISTS"}, keys...)), nil, false, true)
+	if err != nil {
+		return 0, err
+	}
+	return internal.ParseIntegerResponse(b)
+}

sugardb/api_generic.go

@@ -1410,6 +1410,39 @@ func TestSugarDB_RANDOMKEY(t *testing.T) {
 
 }
 
+func TestSugarDB_Exists(t *testing.T) {
+	server := createSugarDB()
+
+	// Test with no keys
+	keys := []string{"key1", "key2", "key3"}
+	existsCount, err := server.Exists(keys...)
+	if err != nil {
+		t.Error(err)
+		return
+	}
+	if existsCount != 0 {
+		t.Errorf("EXISTS error, expected 0, got %d", existsCount)
+	}
+
+	// Test with some keys
+	for _, k := range keys {
+		err := presetValue(server, context.Background(), k, "")
+		if err != nil {
+			t.Error(err)
+			return
+		}
+	}
+
+	existsCount, err = server.Exists(keys...)
+	if err != nil {
+		t.Error(err)
+		return
+	}
+	if existsCount != len(keys) {
+		t.Errorf("EXISTS error, expected %d, got %d", len(keys), existsCount)
+	}
+}
+
 func TestSugarDB_DBSize(t *testing.T) {
 	server := createSugarDB()
 	got, err := server.DBSize()