# PostgreSQL Wire Protocol Package

This package implements PostgreSQL wire protocol support for SeaweedFS, enabling universal compatibility with PostgreSQL clients, tools, and applications.

## Package Structure

```
weed/server/postgres/
├── README.md           # This documentation
├── server.go          # Main PostgreSQL server implementation  
├── protocol.go        # Wire protocol message handlers with MQ integration
├── DESIGN.md          # Architecture and design documentation
└── IMPLEMENTATION.md  # Complete implementation guide
```

## Core Components

### `server.go`
- **PostgreSQLServer**: Main server structure with connection management
- **PostgreSQLSession**: Individual client session handling  
- **PostgreSQLServerConfig**: Server configuration options
- **Authentication System**: Trust, password, and MD5 authentication
- **TLS Support**: Encrypted connections with custom certificates
- **Connection Pooling**: Resource management and cleanup

### `protocol.go` 
- **Wire Protocol Implementation**: Full PostgreSQL 3.0 protocol support
- **Message Handlers**: Startup, query, parse/bind/execute sequences
- **Response Generation**: Row descriptions, data rows, command completion
- **Data Type Mapping**: SeaweedFS to PostgreSQL type conversion
- **SQL Parser**: Uses PostgreSQL-native parser for full dialect compatibility
- **Error Handling**: PostgreSQL-compliant error responses
- **MQ Integration**: Direct integration with SeaweedFS SQL engine for real topic data
- **System Query Support**: Essential PostgreSQL system queries (version, current_user, etc.)
- **Database Context**: Session-based database switching with USE commands

## Key Features

### Real MQ Topic Integration
The PostgreSQL server now directly integrates with SeaweedFS Message Queue topics, providing:

- **Live Topic Discovery**: Automatically discovers MQ namespaces and topics from the filer
- **Real Schema Information**: Reads actual topic schemas from broker configuration
- **Actual Data Access**: Queries real MQ data stored in Parquet and log files
- **Dynamic Updates**: Reflects topic additions and schema changes automatically
- **Consistent SQL Engine**: Uses the same SQL engine as `weed sql` command

### Database Context Management
- **Session Isolation**: Each PostgreSQL connection has its own database context
- **USE Command Support**: Switch between namespaces using standard `USE database` syntax
- **Auto-Discovery**: Topics are discovered and registered on first access
- **Schema Caching**: Efficient caching of topic schemas and metadata

## Usage

### Import the Package
```go
import "github.com/seaweedfs/seaweedfs/weed/server/postgres"
```

### Create and Start Server
```go
config := &postgres.PostgreSQLServerConfig{
    Host:        "localhost",
    Port:        5432,
    AuthMethod:  postgres.AuthMD5,
    Users:       map[string]string{"admin": "secret"},
    Database:    "default",
    MaxConns:    100,
    IdleTimeout: time.Hour,
}

server, err := postgres.NewPostgreSQLServer(config, "localhost:9333")
if err != nil {
    return err
}

err = server.Start()
if err != nil {
    return err
}

// Server is now accepting PostgreSQL connections
```

## Authentication Methods

The package supports three authentication methods:

### Trust Authentication
```go
AuthMethod: postgres.AuthTrust
```
- No password required
- Suitable for development/testing
- Not recommended for production

### Password Authentication  
```go
AuthMethod: postgres.AuthPassword,
Users: map[string]string{"user": "password"}
```
- Clear text password transmission
- Simple but less secure
- Requires TLS for production use

### MD5 Authentication
```go  
AuthMethod: postgres.AuthMD5,
Users: map[string]string{"user": "password"}
```
- Secure hashed authentication with salt
- **Recommended for production**
- Compatible with all PostgreSQL clients

## TLS Configuration

Enable TLS encryption for secure connections:

```go
cert, err := tls.LoadX509KeyPair("server.crt", "server.key")
if err != nil {
    return err
}

config.TLSConfig = &tls.Config{
    Certificates: []tls.Certificate{cert},
}
```

## Client Compatibility

This implementation is compatible with:

### Command Line Tools
- `psql` - PostgreSQL command line client
- `pgcli` - Enhanced command line with auto-completion
- Database IDEs (DataGrip, DBeaver)

### Programming Languages
- **Python**: psycopg2, asyncpg
- **Java**: PostgreSQL JDBC driver
- **JavaScript**: pg (node-postgres)
- **Go**: lib/pq, pgx
- **.NET**: Npgsql
- **PHP**: pdo_pgsql
- **Ruby**: pg gem

### BI Tools
- Tableau (native PostgreSQL connector)
- Power BI (PostgreSQL data source)
- Grafana (PostgreSQL plugin)
- Apache Superset

## Supported SQL Operations

### Data Queries
```sql
SELECT * FROM topic_name;
SELECT id, message FROM topic_name WHERE condition;
SELECT COUNT(*) FROM topic_name;
SELECT MIN(id), MAX(id), AVG(amount) FROM topic_name;
```

### Schema Information
```sql
SHOW DATABASES;
SHOW TABLES; 
DESCRIBE topic_name;
DESC topic_name;
```

### System Information
```sql
SELECT version();
SELECT current_database();
SELECT current_user;
```

### System Columns
```sql
SELECT id, message, _timestamp_ns, _key, _source FROM topic_name;
```

## Configuration Options

### Server Configuration
- **Host/Port**: Server binding address and port
- **Authentication**: Method and user credentials  
- **Database**: Default database/namespace name
- **Connections**: Maximum concurrent connections
- **Timeouts**: Idle connection timeout
- **TLS**: Certificate and encryption settings

### Performance Tuning
- **Connection Limits**: Prevent resource exhaustion
- **Idle Timeout**: Automatic cleanup of unused connections
- **Memory Management**: Efficient session handling
- **Query Streaming**: Large result set support

## Error Handling

The package provides PostgreSQL-compliant error responses:

- **Connection Errors**: Authentication failures, network issues
- **SQL Errors**: Invalid syntax, missing tables
- **Resource Errors**: Connection limits, timeouts
- **Security Errors**: Permission denied, invalid credentials

## Development and Testing

### Unit Tests
Run PostgreSQL package tests:
```bash
go test ./weed/server/postgres
```

### Integration Testing  
Use the provided Python test client:
```bash
python postgres-examples/test_client.py --host localhost --port 5432
```

### Manual Testing
Connect with psql:
```bash
psql -h localhost -p 5432 -U seaweedfs -d default
```

## Documentation

- **DESIGN.md**: Complete architecture and design overview
- **IMPLEMENTATION.md**: Detailed implementation guide
- **postgres-examples/**: Client examples and test scripts
- **Command Documentation**: `weed db -help`

## Security Considerations

### Production Deployment
- Use MD5 or stronger authentication
- Enable TLS encryption
- Configure appropriate connection limits
- Monitor for suspicious activity
- Use strong passwords
- Implement proper firewall rules

### Access Control
- Create dedicated read-only users
- Use principle of least privilege
- Monitor connection patterns
- Log authentication attempts

## Architecture Notes

### SQL Parser Dialect Considerations

**✅ POSTGRESQL ONLY**: SeaweedFS SQL engine exclusively supports PostgreSQL syntax:

- **✅ Core Engine**: `engine.go` uses custom PostgreSQL parser for proper dialect support
- **PostgreSQL Server**: Uses PostgreSQL parser for optimal wire protocol compatibility  
- **Parser**: Custom lightweight PostgreSQL parser for full PostgreSQL compatibility
- **Support Status**: Only PostgreSQL syntax is supported - MySQL parsing has been removed

**Key Benefits of PostgreSQL Parser**:
- **Native Dialect Support**: Correctly handles PostgreSQL-specific syntax and semantics
- **System Catalog Compatibility**: Supports `pg_catalog`, `information_schema` queries
- **Operator Compatibility**: Handles `||` string concatenation, PostgreSQL-specific operators  
- **Type System Alignment**: Better PostgreSQL type inference and coercion
- **Reduced Translation Overhead**: Eliminates need for dialect translation layer

**PostgreSQL Syntax Support**:
- **Identifier Quoting**: Uses PostgreSQL double quotes (`"`) for identifiers
- **String Concatenation**: Supports PostgreSQL `||` operator
- **System Functions**: Full support for PostgreSQL system catalogs (`pg_catalog`) and functions
- **Standard Compliance**: Follows PostgreSQL SQL standard and dialect

**Implementation Features**:
- Native PostgreSQL query processing in `protocol.go`
- System query support (`SELECT version()`, `BEGIN`, etc.)
- Type mapping between PostgreSQL and SeaweedFS schema types
- Error code mapping to PostgreSQL standards
- Comprehensive PostgreSQL wire protocol support

This package provides enterprise-grade PostgreSQL compatibility, enabling seamless integration of SeaweedFS with the entire PostgreSQL ecosystem.