Add context management and error handling to connection pool

Introduced context support and enhanced error handling in connpool.go. Added detailed comments for better maintainability and introduced a wrapper for net.Conn to manage connection close behavior. The changes improve the robustness and clarity of the connection pool's operation.

connpool.go

@@ -5,7 +5,9 @@
 package mail
 
 import (
+	"context"
 	"errors"
+	"fmt"
 	"net"
 	"sync"
 )
@@ -15,7 +17,11 @@ import (
 // concurrency template.
 
 var (
+	// ErrPoolInvalidCap is returned when the connection pool's capacity settings are
+	// invalid (e.g., initial capacity is negative).
 	ErrPoolInvalidCap = errors.New("invalid connection pool capacity settings")
+	// ErrClosed is returned when an operation is attempted on a closed connection pool.
+	ErrClosed = errors.New("connection pool is closed")
 )
 
 // Pool interface describes a connection pool implementation. A Pool is
@@ -36,12 +42,28 @@ type Pool interface {
 
 // connPool implements the Pool interface
 type connPool struct {
-	// mutex is used to synchronize access to the connection pool to ensure thread-safe operations
+	// mutex is used to synchronize access to the connection pool to ensure thread-safe operations.
 	mutex sync.RWMutex
-	// conns is a channel used to manage and distribute net.Conn objects within the connection pool
+	// conns is a channel used to manage and distribute net.Conn objects within the connection pool.
 	conns chan net.Conn
-	// dialCtx represents the actual net.Conn returned by the DialContextFunc
-	dialCtx DialContextFunc
+
+	// dialCtxFunc represents the actual net.Conn returned by the DialContextFunc.
+	dialCtxFunc DialContextFunc
+	// dialContext is the context used for dialing new network connections within the connection pool.
+	dialContext context.Context
+	// dialNetwork specifies the network type (e.g., "tcp", "udp") used to establish connections in
+	// the connection pool.
+	dialNetwork string
+	// dialAddress specifies the address used to establish network connections within the connection pool.
+	dialAddress string
+}
+
+// PoolConn is a wrapper around net.Conn to modify the the behavior of net.Conn's Close() method.
+type PoolConn struct {
+	net.Conn
+	mutex    sync.RWMutex
+	pool     *connPool
+	unusable bool
 }
 
 // NewConnPool returns a new pool based on buffered channels with an initial
@@ -50,40 +72,104 @@ type connPool struct {
 // fill the Pool until a new Get() is called. During a Get(), if there is no
 // new connection available in the pool, a new connection will be created via
 // the corresponding DialContextFunc() method.
-func NewConnPool(initialCap, maxCap int, dialCtxFunc DialContextFunc) (Pool, error) {
+func NewConnPool(ctx context.Context, initialCap, maxCap int, dialCtxFunc DialContextFunc,
+	network, address string) (Pool, error) {
 	if initialCap < 0 || maxCap <= 0 || initialCap > maxCap {
 		return nil, ErrPoolInvalidCap
 	}
 
 	pool := &connPool{
-		conns:   make(chan net.Conn, maxCap),
-		dialCtx: dialCtxFunc,
+		conns:       make(chan net.Conn, maxCap),
+		dialCtxFunc: dialCtxFunc,
+		dialContext: ctx,
+		dialAddress: address,
+		dialNetwork: network,
 	}
 
-	// create initial connections, if something goes wrong,
-	// just close the pool error out.
+	// Initial connections for the pool. Pool will be closed on connection error
 	for i := 0; i < initialCap; i++ {
-		/*
-			conn, err := dialCtxFunc()
-			if err != nil {
-				pool.Close()
-				return nil, fmt.Errorf("factory is not able to fill the pool: %s", err)
-			}
-			c.conns <- conn
+		conn, err := dialCtxFunc(ctx, network, address)
+		if err != nil {
+			pool.Close()
+			return nil, fmt.Errorf("dialContextFunc is not able to fill the connection pool: %s", err)
+		}
+		pool.conns <- conn
 
-		*/
 	}
 
 	return pool, nil
 }
 
-func (c *connPool) Get() (net.Conn, error) {
-	return nil, nil
-}
-func (c *connPool) Close() {
-	return
+// Get satisfies the Get() method of the Pool inteface. If there is no new
+// connection available in the Pool, a new connection will be created via the
+// DialContextFunc() method.
+func (p *connPool) Get() (net.Conn, error) {
+	ctx, conns, dialCtxFunc := p.getConnsAndDialContext()
+	if conns == nil {
+		return nil, ErrClosed
+	}
+
+	// wrap the connections into the custom net.Conn implementation that puts
+	// connections back to the pool
+	select {
+	case <-ctx.Done():
+		return nil, ctx.Err()
+	case conn := <-conns:
+		if conn == nil {
+			return nil, ErrClosed
+		}
+		return p.wrapConn(conn), nil
+	default:
+		conn, err := dialCtxFunc(ctx, p.dialNetwork, p.dialAddress)
+		if err != nil {
+			return nil, err
+		}
+		return p.wrapConn(conn), nil
+	}
 }
 
-func (c *connPool) Len() int {
-	return 0
+// Close terminates all connections in the pool and frees associated resources. Once closed,
+// the pool is no longer usable.
+func (p *connPool) Close() {
+	p.mutex.Lock()
+	conns := p.conns
+	p.conns = nil
+	p.dialCtxFunc = nil
+	p.dialContext = nil
+	p.dialAddress = ""
+	p.dialNetwork = ""
+	p.mutex.Unlock()
+
+	if conns == nil {
+		return
+	}
+
+	close(conns)
+	for conn := range conns {
+		_ = conn.Close()
+	}
+}
+
+// Len returns the current number of connections in the connection pool.
+func (p *connPool) Len() int {
+	_, conns, _ := p.getConnsAndDialContext()
+	return len(conns)
+}
+
+// getConnsAndDialContext returns the connection channel and the DialContext function for the
+// connection pool.
+func (p *connPool) getConnsAndDialContext() (context.Context, chan net.Conn, DialContextFunc) {
+	p.mutex.RLock()
+	conns := p.conns
+	dialCtxFunc := p.dialCtxFunc
+	ctx := p.dialContext
+	p.mutex.RUnlock()
+	return ctx, conns, dialCtxFunc
+}
+
+// wrapConn wraps a given net.Conn with a PoolConn, modifying the net.Conn's Close() method.
+func (p *connPool) wrapConn(conn net.Conn) net.Conn {
+	poolconn := &PoolConn{pool: p}
+	poolconn.Conn = conn
+	return poolconn
 }