bugfixes, new features

CHANGELOG

@@ -1,3 +1,11 @@
+1.4.4:
+
+ - Security: Error responses now return safe HTTP status text instead of detailed database error messages to prevent information leakage
+ - Security: Added MAX_CONNECTIONS environment variable to limit concurrent database connections and prevent resource exhaustion (DoS protection)
+ - Fix: Fixed race condition in GetById() when upgrading from read lock to write lock
+ - Fix: Fixed memory leak in RunMaintenance() where prepared statement deletions were not persisted to the connection pool
+ - Feature: Error responses now use consistent JSON format with api_version, error, and status fields
+
 1.4.3:
 
  - Fix: minor bugfixes

Makefile

@@ -1,5 +1,5 @@
 PROJECT_NAME := sql-proxy
-BUILD_VERSION := 1.4.3
+BUILD_VERSION := 1.4.4
 BUILD_TIME := $(shell date -u '+%Y-%m-%d_%H:%M:%S')
 BUILD_DIR := build
 GO_FILES := src/main.go
@@ -18,6 +18,8 @@ GOAMD64 := v2
 BIND_PORT := 8080
 BIND_ADDR := localhost
 MAX_ROWS := 10000
+MAX_CONNECTIONS := 100
+
 DEBUG_LOG := true
 #TLS_CERT := $(BUILD_DIR)/server.crt
 #TLS_KEY := $(BUILD_DIR)/server.key
@@ -50,7 +52,7 @@ debug: clean
 # Run
 run: debug
 	@echo "Running $(PROJECT_NAME) in debug mode..."
-	BIND_ADDR=$(BIND_ADDR) BIND_PORT=$(BIND_PORT) MAX_ROWS=$(MAX_ROWS) TLS_CERT=$(TLS_CERT) TLS_KEY=$(TLS_KEY) DEBUG_LOG=$(DEBUG_LOG) $(BUILD_DIR)/$(PROJECT_NAME)-debug
+	BIND_ADDR=$(BIND_ADDR) BIND_PORT=$(BIND_PORT) MAX_ROWS=$(MAX_ROWS) MAX_CONNECTIONS=$(MAX_CONNECTIONS) TLS_CERT=$(TLS_CERT) TLS_KEY=$(TLS_KEY) DEBUG_LOG=$(DEBUG_LOG) $(BUILD_DIR)/$(PROJECT_NAME)-debug
 
 # Run test
 test:

README.md

@@ -31,6 +31,7 @@ Note that this service is not limited to 1C and can be utilized in other context
 * Secure Credential Management : Does not store SQL credentials, ensuring sensitive information remains protected;
 * Secure Communication : Supports HTTPS for secure data transmission;
 * Efficient Connection Pooling : Utilizes a shared, reusable SQL connection pool with automated maintenance tasks to remove stale or dead connections;
+* Connection Limiting : Configurable maximum number of concurrent database connections to prevent resource exhaustion;
 * Command Support : Currently supports all SQL commands with no limitation. The SELECT command returns query results as a flexible JSON-formatted recordset;
 * Result Limitation : Allows configuration to limit the number of rows returned by SELECT statements;
 * Prepared Statements : supported;
@@ -48,7 +49,7 @@ Current API version is 1.2. See Swagger OpenAPI 3.0 specification in /docs/api
 
 ## How to compile
 
-Current version is 1.4.3. Execute in the command line:
+Current version is 1.4.4. Execute in the command line:
 
 ```
 make prod
@@ -59,7 +60,7 @@ make prod
 Just run the binary. Settings may be passed with environment variables, see Makefile for details and default values:
 
 ```
-BIND_ADDR=localhost BIND_PORT=8081 MAX_ROWS=10000 sql-proxy
+BIND_ADDR=localhost BIND_PORT=8081 MAX_ROWS=10000 MAX_CONNECTIONS=100 sql-proxy
 ```
 
 or install it as a systemd service with install.sh script. Parameters may be changed later in sql-proxy.service file.

README.ru.md

@@ -36,6 +36,7 @@
 + Безопасное управление учетными данными: не хранит данные учетных записей, гарантируя защиту конфиденциальной информации;
 + Защищённое соединение: при необходимости, поддерживает HTTPS для безопасной передачи данных;
 + Пул соединений: использует общий переиспользуемый пул SQL-соединений с регламентными задачами обслуживания для удаления устаревших или зависших соединений;
++ Ограничение соединений: настраиваемый лимит одновременных подключений к базе данных для предотвращения исчерпания ресурсов;
 + Поддержка языка SQL: поддерживает любые SQL-команды без ограничений. Команда SELECT возвращает результаты запроса в виде гибкого JSON-формата набора записей;
 + Ограничение результатов: позволяет настраивать ограничения на количество строк, возвращаемых командами SELECT;
 + Поддержка подготовленных выражений: реализована;
@@ -53,7 +54,7 @@
 
 ## Как скомпилировать
 
-Номер текущей версии: 1.4.3. Выполнить в командной строке:
+Номер текущей версии: 1.4.4. Выполнить в командной строке:
 
 ```
 make prod
@@ -64,7 +65,7 @@ make prod
 Просто запустите бинарник. Все параметры передаются через переменные окружения, см. Makefile для детальной информации и значений настроек по умолчанию:
 
 ```
-BIND_ADDR=localhost BIND_PORT=8081 MAX_ROWS=10000 sql-proxy
+BIND_ADDR=localhost BIND_PORT=8081 MAX_ROWS=10000 MAX_CONNECTIONS=100 sql-proxy
 ```
 
 или установите как службу systemd с помощью скрипта install.sh. Параметры можно изменить прямо в этом скрипте перед установкой, или отредактировать потом файл sql-proxy.service.

src/db/dblist.go

@@ -9,11 +9,11 @@ import (
 
 	"time"
 
-	"slices"
-
 	"github.com/google/uuid"
 )
 
+var ErrConnectionLimit = fmt.Errorf("connection pool limit reached")
+
 // Init map
 func (o *DbList) Init() {
 
@@ -22,23 +22,33 @@ func (o *DbList) Init() {
 
 }
 
+// Returns current pool size
+func (o *DbList) Size() int {
+	o.mu.RLock()
+	defer o.mu.RUnlock()
+	return len(o.items)
+}
+
 // Gets SQL server connection by GUID
 func (o *DbList) GetById(id string, updateTimestamp bool) (*sql.DB, bool) {
 
-	o.mu.RLock()
+	if updateTimestamp {
+		o.mu.Lock()
+		defer o.mu.Unlock()
 
-	if dbConn, ok := o.items[id]; ok {
-		if updateTimestamp {
-			o.mu.RUnlock()
-			o.mu.Lock()
+		if dbConn, ok := o.items[id]; ok {
 			dbConn.Timestamp = time.Now()
 			o.items[id] = dbConn
-			o.mu.Unlock()
+			return dbConn.DB, true
 		}
-		return dbConn.DB, true
-	}
+	} else {
+		o.mu.RLock()
+		defer o.mu.RUnlock()
 
-	o.mu.RUnlock()
+		if dbConn, ok := o.items[id]; ok {
+			return dbConn.DB, true
+		}
+	}
 
 	app.Logger.Errorf("SQL connection with guid='%s' not found", id)
 	return nil, false
@@ -47,12 +57,11 @@ func (o *DbList) GetById(id string, updateTimestamp bool) (*sql.DB, bool) {
 
 // Gets the new SQL server connection with parameters given.
 // First lookups in pool, if fails opens new one and returns GUID value
-func (o *DbList) GetByParams(connInfo *DbConnInfo) (string, bool) {
+func (o *DbList) GetByParams(connInfo *DbConnInfo) (string, error) {
 	hash, err := connInfo.GetHash()
 	if err != nil {
-		errMsg := "Hash calculation failed"
-		app.Logger.Error(errMsg)
-		return errMsg, false
+		app.Logger.Error("Hash calculation failed")
+		return "", fmt.Errorf("hash calculation failed")
 	}
 
 	guid := ""
@@ -70,7 +79,7 @@ func (o *DbList) GetByParams(connInfo *DbConnInfo) (string, bool) {
 			if err = dbConn.DB.Ping(); err == nil {
 				o.mu.RUnlock()
 				// Everything is ok, return guid
-				return guid, true
+				return guid, nil
 			} else {
 				// Bad connection, need to clean
 				o.mu.RUnlock()
@@ -90,11 +99,17 @@ func (o *DbList) GetByParams(connInfo *DbConnInfo) (string, bool) {
 }
 
 // Creates the new SQL connection regarding concurrency
-func (o *DbList) getNewConnection(connInfo *DbConnInfo, hash [32]byte) (string, bool) {
+func (o *DbList) getNewConnection(connInfo *DbConnInfo, hash [32]byte) (string, error) {
 
 	o.mu.Lock()
 	defer o.mu.Unlock()
 
+	// Check connection pool limit
+	if len(o.items) >= MaxConnections {
+		app.Logger.Errorf("Connection pool limit reached: %d", MaxConnections)
+		return "", ErrConnectionLimit
+	}
+
 	// Prepare DSN string
 	var dsn string
 
@@ -115,9 +130,9 @@ func (o *DbList) getNewConnection(connInfo *DbConnInfo, hash [32]byte) (string,
 		dsn = fmt.Sprintf("%s:%s@tcp(%s:%d)/%s",
 			connInfo.User, encodedPassword, connInfo.Host, connInfo.Port, connInfo.DbName)
 	default:
-		errMsg := fmt.Sprintf("No suitable driver implemented for server type '%s'", connInfo.DbType)
+		errMsg := fmt.Sprintf("unsupported database type '%s'", connInfo.DbType)
 		app.Logger.Error(errMsg)
-		return errMsg, false
+		return "", fmt.Errorf("%s", errMsg)
 	}
 
 	// Open new SQL server connection
@@ -128,16 +143,14 @@ func (o *DbList) getNewConnection(connInfo *DbConnInfo, hash [32]byte) (string,
 
 	// Check for failure
 	if err != nil {
-		errMsg := "Error establishing SQL server connection"
-		app.Logger.Error(errMsg)
-		return errMsg, false
+		app.Logger.Errorf("Error establishing SQL server connection: %v", err)
+		return "", fmt.Errorf("error establishing SQL server connection")
 	}
 
 	// Check if alive
 	if err = newDb.Ping(); err != nil {
-		errMsg := "Just created SQL connection is dead"
-		app.Logger.Error(errMsg)
-		return errMsg, false
+		app.Logger.Errorf("Just created SQL connection is dead: %v", err)
+		return "", fmt.Errorf("error establishing SQL server connection")
 	}
 
 	// Insert into pool
@@ -161,7 +174,7 @@ func (o *DbList) getNewConnection(connInfo *DbConnInfo, hash [32]byte) (string,
 		newId,
 	)
 
-	return newId, true
+	return newId, nil
 }
 
 // Deletes SQL server connection
@@ -230,15 +243,17 @@ func (o *DbList) ClosePreparedStatement(connId, stmtId string) bool {
 	if !ok {
 		return false
 	}
-	for i := range dbConn.Stmt {
-		if dbConn.Stmt[i].Id == stmtId {
-			dbConn.Stmt[i].Stmt.Close()
-			dbConn.Stmt = slices.Delete(dbConn.Stmt, i, i+1)
-			break
+
+	for i, stmt := range dbConn.Stmt {
+		if stmt.Id == stmtId {
+			stmt.Stmt.Close()
+			dbConn.Stmt = append(dbConn.Stmt[:i], dbConn.Stmt[i+1:]...)
+			o.items[connId] = dbConn
+			return true
 		}
 	}
 
-	return true
+	return false
 
 }
 
@@ -258,40 +273,37 @@ func (o *DbList) RunMaintenance() {
 		o.mu.Lock()
 
 		for key, dbConn := range o.items {
-
-			var lostStmts []string
 			countConn++
 
+			isDead := false
 			if err := dbConn.DB.Ping(); err != nil {
 				// dead connection
 				deadItems = append(deadItems, key)
 				countDeadConn++
+				isDead = true
 			} else if time.Since(dbConn.Timestamp).Abs().Minutes() > 20 {
 				// connection not used for last 20 minutes
 				deadItems = append(deadItems, key)
 				countDeadConn++
+				isDead = true
 			}
 
-			// check prepared statements
+			// Close and remove expired prepared statements
+			activeStmts := make([]DbStmt, 0, len(dbConn.Stmt))
 			for _, stmt := range dbConn.Stmt {
-				// prepared statements not used last 20 minutes
 				if time.Since(stmt.Timestamp).Abs().Minutes() > 20 {
-					lostStmts = append(lostStmts, stmt.Id)
+					stmt.Stmt.Close()
 					countStmt++
+				} else {
+					activeStmts = append(activeStmts, stmt)
 				}
 			}
+			dbConn.Stmt = activeStmts
 
-			// delete lost prepared statements
-			for _, lost := range lostStmts {
-				for i := range dbConn.Stmt {
-					if dbConn.Stmt[i].Id == lost {
-						dbConn.Stmt[i].Stmt.Close()
-						dbConn.Stmt = slices.Delete(dbConn.Stmt, i, i+1)
-						break
-					}
-				}
+			// Update connection in pool (without timestamp change)
+			if !isDead {
+				o.items[key] = dbConn
 			}
-
 		}
 
 		// remove dead connections

src/db/vars.go

@@ -1,6 +1,7 @@
 package db
 
 var (
-	Handler DbList
-	MaxRows uint32 = 10000
+	Handler        DbList
+	MaxRows        uint32 = 10000
+	MaxConnections int    = 100
 )

src/handlers/common.go

@@ -17,13 +17,25 @@ type ResponseEnvelope struct {
 	Rows           []map[string]any `json:"rows"`
 }
 
+type ErrorEnvelope struct {
+	ApiVersion string `json:"api_version"`
+	Error      string `json:"error"`
+	Status     int    `json:"status"`
+}
+
 func checkApiVersion(w http.ResponseWriter, r *http.Request) bool {
 
 	apiVersion := r.Header.Get("API-Version")
 	if apiVersion != app.ApiVersion {
 		message := "Unsupported API version"
 		app.Logger.Error(message)
-		http.Error(w, message, http.StatusNotImplemented)
+		w.Header().Set("Content-Type", "application/json")
+		w.WriteHeader(http.StatusNotImplemented)
+		json.NewEncoder(w).Encode(ErrorEnvelope{
+			ApiVersion: app.ApiVersion,
+			Error:      message,
+			Status:     http.StatusNotImplemented,
+		})
 		return false
 	} else {
 		return true
@@ -34,7 +46,14 @@ func checkApiVersion(w http.ResponseWriter, r *http.Request) bool {
 func errorResponce(w http.ResponseWriter, message string, httpStatus int) {
 
 	app.Logger.Error(message)
-	http.Error(w, message, httpStatus)
+	w.Header().Set("Content-Type", "application/json")
+	w.WriteHeader(httpStatus)
+	errResp := ErrorEnvelope{
+		ApiVersion: app.ApiVersion,
+		Error:      http.StatusText(httpStatus),
+		Status:     httpStatus,
+	}
+	json.NewEncoder(w).Encode(errResp)
 
 }
 

src/handlers/connection.go

@@ -2,6 +2,7 @@ package handlers
 
 import (
 	"encoding/json"
+	"errors"
 	"net/http"
 	"sql-proxy/src/db"
 )
@@ -19,9 +20,17 @@ func CreateConnection(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	if connGuid, ok := db.Handler.GetByParams(&dbConnInfo); !ok {
-		errorResponce(w, "Failed to get SQL connection", http.StatusInternalServerError)
-	} else if _, err := w.Write([]byte(connGuid)); err != nil {
+	connGuid, err := db.Handler.GetByParams(&dbConnInfo)
+	if err != nil {
+		if errors.Is(err, db.ErrConnectionLimit) {
+			errorResponce(w, err.Error(), http.StatusTooManyRequests)
+		} else {
+			errorResponce(w, err.Error(), http.StatusInternalServerError)
+		}
+		return
+	}
+
+	if _, err = w.Write([]byte(connGuid)); err != nil {
 		errorResponce(w, err.Error(), http.StatusInternalServerError)
 	}
 

src/main.go

@@ -42,6 +42,8 @@ func (p *program) run() {
 	}
 	bindPort := app.GetEnvInt("BIND_PORT", 8080)
 	db.MaxRows = uint32(app.GetEnvInt("MAX_ROWS", 10000))
+	db.MaxConnections = app.GetEnvInt("MAX_CONNECTIONS", 100)
+
 	tlsCert := app.GetEnvString("TLS_CERT", "")
 	tlsKey := app.GetEnvString("TLS_KEY", "")
 
@@ -67,10 +69,11 @@ func (p *program) run() {
 	router.HandleFunc("/livez", handlers.Livez).Methods("GET")
 	router.Handle("/metrics", promhttp.Handler())
 
-	app.Logger.Info("(c) 2025 Almaz Sharipov, MIT license, https://github.com/alm494/sql_proxy  ")
+	app.Logger.Info("(c) 2025-2026 Almaz Sharipov, MIT license, https://github.com/alm494/sql_proxy  ")
 	app.Logger.Infof("build_version=%s, build_time=%s", app.BuildVersion, app.BuildTime)
 	app.Logger.Infof("Server started with the following parameters: "+
-		"bind_port=%d, bind_address=%s, tls_cert=%s, tls_key=%s", bindPort, bindAddress, tlsCert, tlsKey)
+		"bind_port=%d, bind_address=%s, max_connections=%d, max_rows=%d, tls_cert=%s, tls_key=%s",
+		bindPort, bindAddress, db.MaxConnections, db.MaxRows, tlsCert, tlsKey)
 
 	addr := fmt.Sprintf("%s:%d", bindAddress, bindPort)