145 lines
4 KiB
Go
145 lines
4 KiB
Go
package conn
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import (
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"errors"
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"net"
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"time"
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"github.com/go-kit/kit/log"
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)
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// Dialer imitates net.Dial. Dialer is assumed to yield connections that are
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// safe for use by multiple concurrent goroutines.
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type Dialer func(network, address string) (net.Conn, error)
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// AfterFunc imitates time.After.
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type AfterFunc func(time.Duration) <-chan time.Time
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// Manager manages a net.Conn.
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//
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// Clients provide a way to create the connection with a Dialer, network, and
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// address. Clients should Take the connection when they want to use it, and Put
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// back whatever error they receive from its use. When a non-nil error is Put,
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// the connection is invalidated, and a new connection is established.
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// Connection failures are retried after an exponential backoff.
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type Manager struct {
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dialer Dialer
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network string
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address string
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after AfterFunc
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logger log.Logger
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takec chan net.Conn
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putc chan error
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}
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// NewManager returns a connection manager using the passed Dialer, network, and
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// address. The AfterFunc is used to control exponential backoff and retries.
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// The logger is used to log errors; pass a log.NopLogger if you don't care to
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// receive them. For normal use, prefer NewDefaultManager.
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func NewManager(d Dialer, network, address string, after AfterFunc, logger log.Logger) *Manager {
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m := &Manager{
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dialer: d,
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network: network,
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address: address,
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after: after,
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logger: logger,
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takec: make(chan net.Conn),
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putc: make(chan error),
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}
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go m.loop()
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return m
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}
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// NewDefaultManager is a helper constructor, suitable for most normal use in
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// real (non-test) code. It uses the real net.Dial and time.After functions.
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func NewDefaultManager(network, address string, logger log.Logger) *Manager {
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return NewManager(net.Dial, network, address, time.After, logger)
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}
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// Take yields the current connection. It may be nil.
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func (m *Manager) Take() net.Conn {
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return <-m.takec
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}
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// Put accepts an error that came from a previously yielded connection. If the
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// error is non-nil, the manager will invalidate the current connection and try
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// to reconnect, with exponential backoff. Putting a nil error is a no-op.
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func (m *Manager) Put(err error) {
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m.putc <- err
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}
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// Write writes the passed data to the connection in a single Take/Put cycle.
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func (m *Manager) Write(b []byte) (int, error) {
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conn := m.Take()
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if conn == nil {
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return 0, ErrConnectionUnavailable
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}
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n, err := conn.Write(b)
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defer m.Put(err)
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return n, err
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}
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func (m *Manager) loop() {
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var (
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conn = dial(m.dialer, m.network, m.address, m.logger) // may block slightly
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connc = make(chan net.Conn, 1)
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reconnectc <-chan time.Time // initially nil
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backoff = time.Second
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)
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// If the initial dial fails, we need to trigger a reconnect via the loop
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// body, below. If we did this in a goroutine, we would race on the conn
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// variable. So we use a buffered chan instead.
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connc <- conn
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for {
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select {
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case <-reconnectc:
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reconnectc = nil // one-shot
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go func() { connc <- dial(m.dialer, m.network, m.address, m.logger) }()
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case conn = <-connc:
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if conn == nil {
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// didn't work
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backoff = exponential(backoff) // wait longer
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reconnectc = m.after(backoff) // try again
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} else {
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// worked!
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backoff = time.Second // reset wait time
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reconnectc = nil // no retry necessary
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}
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case m.takec <- conn:
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case err := <-m.putc:
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if err != nil && conn != nil {
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m.logger.Log("err", err)
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conn = nil // connection is bad
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reconnectc = m.after(time.Nanosecond) // trigger immediately
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}
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}
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}
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}
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func dial(d Dialer, network, address string, logger log.Logger) net.Conn {
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conn, err := d(network, address)
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if err != nil {
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logger.Log("err", err)
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conn = nil // just to be sure
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}
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return conn
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}
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func exponential(d time.Duration) time.Duration {
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d *= 2
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if d > time.Minute {
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d = time.Minute
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}
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return d
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}
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// ErrConnectionUnavailable is returned by the Manager's Write method when the
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// manager cannot yield a good connection.
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var ErrConnectionUnavailable = errors.New("connection unavailable")
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