Add common LDAP connection pooling code

ldap/pool.go

+package ldaputil
+
+import (
+	"context"
+	"errors"
+	"net/url"
+
+	"gopkg.in/ldap.v2"
+)
+
+// ConnectionPool provides a goroutine-safe pool of long-lived LDAP
+// connections that will reconnect on errors.
+type ConnectionPool struct {
+	network string
+	addr    string
+	bindDN  string
+	bindPw  string
+
+	c chan *ldap.Conn
+}
+
+func (p *ConnectionPool) connect() (*ldap.Conn, error) {
+	conn, err := ldap.Dial(p.network, p.addr)
+	if err != nil {
+		return nil, err
+	}
+
+	if err = conn.Bind(p.bindDN, p.bindPw); err != nil {
+		conn.Close()
+		return nil, err
+	}
+
+	return conn, err
+}
+
+// Get a fresh connection from the pool.
+func (p *ConnectionPool) Get(ctx context.Context) (*ldap.Conn, error) {
+	select {
+	case conn := <-p.c:
+		return conn, nil
+	case <-ctx.Done():
+		return nil, ctx.Err()
+	}
+}
+
+// Release a used connection onto the pool.
+func (p *ConnectionPool) Release(conn *ldap.Conn, err error) {
+	// We assume that if we get an ErrorNetwork, then we need to reconnect.
+	for err != nil && ldap.IsErrorWithCode(err, ldap.ErrorNetwork) {
+		if conn != nil {
+			conn.Close()
+		}
+		conn, err = p.connect()
+	}
+	p.c <- conn
+}
+
+// Close all connections. Not implemented yet.
+func (p *ConnectionPool) Close() {}
+
+// Parse a LDAP URI into network and address strings suitable for
+// ldap.Dial.
+func parseLDAPURI(uri string) (string, string, error) {
+	u, err := url.Parse(uri)
+	if err != nil {
+		return "", "", err
+	}
+
+	network := "tcp"
+	addr := "localhost:389"
+	switch u.Scheme {
+	case "ldap":
+		if u.Host != "" {
+			addr = u.Host
+		}
+	case "ldapi":
+		network = "unix"
+		addr = u.Path
+	default:
+		return "", "", errors.New("unsupported scheme")
+	}
+
+	return network, addr, nil
+}
+
+// NewConnectionPool creates a new pool of LDAP connections to the
+// specified server, using the provided bind credentials. The pool
+// will contain numConns connections.
+func NewConnectionPool(uri, bindDN, bindPw string, numConns int) (*ConnectionPool, error) {
+	network, addr, err := parseLDAPURI(uri)
+	if err != nil {
+		return nil, err
+	}
+
+	p := &ConnectionPool{
+		c:       make(chan *ldap.Conn, numConns),
+		network: network,
+		addr:    addr,
+		bindDN:  bindDN,
+		bindPw:  bindPw,
+	}
+
+	for i := 0; i < numConns; i++ {
+		conn, err := p.connect()
+		if err != nil {
+			p.Close()
+			return nil, err
+		}
+		p.c <- conn
+	}
+
+	return p, nil
+}