feat: multi tenant support

backend/internal/web/middleware/TenantSchemaMiddleware.go

@@ -0,0 +1,73 @@
+package middleware
+
+import (
+	"context"
+	"fmt"
+	"net/http"
+	"regexp"
+
+	"gorm.io/gorm"
+)
+
+type contextKey string
+
+const TxKey contextKey = "tenant_db_tx"
+
+// Alphanumeric or underscores only to prevent SQL Injection in schema names
+var safeSchemaRegex = regexp.MustCompile(`^[a-zA-Z0-9_:-]+$`)
+
+// TenantSchemaMiddleware isolates database connections per request using PostgreSQL schemas
+func TenantSchemaMiddleware(db *gorm.DB) func(http.Handler) http.Handler {
+	return func(next http.Handler) http.Handler {
+		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			tenantID := r.Header.Get("X-Tenant-Id")
+			if tenantID == "" {
+				w.Header().Set("Content-Type", "application/json")
+				w.WriteHeader(http.StatusBadRequest)
+				_, _ = w.Write([]byte(`{"error": "Missing X-Tenant-Id header"}`))
+				return
+			}
+
+			// Validate schema name to guarantee safety against SQL injection
+			if !safeSchemaRegex.MatchString(tenantID) {
+				w.Header().Set("Content-Type", "application/json")
+				w.WriteHeader(http.StatusBadRequest)
+				_, _ = w.Write([]byte(`{"error": "Invalid characters in tenant ID"}`))
+				return
+			}
+
+			// Start a fresh transaction scoped exclusively to this HTTP request
+			tx := db.Begin()
+
+			// Set the local search_path for the duration of this transaction block
+			if err := tx.Exec(fmt.Sprintf("SET LOCAL search_path TO %s", tenantID)).Error; err != nil {
+				tx.Rollback()
+				w.Header().Set("Content-Type", "application/json")
+				w.WriteHeader(http.StatusInternalServerError)
+				_, _ = w.Write([]byte(`{"error": "Failed to resolve tenant storage isolation"}`))
+				return
+			}
+
+			// Embed the transaction database instance into the request context
+			ctx := context.WithValue(r.Context(), TxKey, tx)
+
+			// Execute the subsequent request handlers
+			next.ServeHTTP(w, r.WithContext(ctx))
+
+			// Commit or Rollback based on the transaction error status
+			if tx.Error != nil {
+				tx.Rollback()
+			} else {
+				tx.Commit()
+			}
+		})
+	}
+}
+
+// GetDB retrieves the transaction-bound tenant GORM DB instance from context
+func GetDB(ctx context.Context) *gorm.DB {
+	if tx, ok := ctx.Value(TxKey).(*gorm.DB); ok {
+		return tx.WithContext(ctx)
+	}
+	panic("GetDB was invoked outside of TenantSchemaMiddleware")
+}