*: add a 1 minute HTTP inactivity timeout

As described in issue github-release#26, sometimes the Github server seems to disappear
and Go's net/http doesn't seem to notice. This makes github-release(1) hang
indefinitely (or at least a very long time, until the OS decides to close
the TCP conn).

Attempt to work around this by setting a read/write timeout.

Updates github-release#26.

github/github.go

@@ -29,7 +29,7 @@ func DoAuthRequest(method, url, mime, token string, headers map[string]string, b
 		return nil, err
 	}
 
-	resp, err := http.DefaultClient.Do(req)
+	resp, err := client.Do(req)
 	if err != nil {
 		return nil, err
 	}
@@ -149,7 +149,7 @@ func (c Client) getPaginated(uri string) (io.ReadCloser, error) {
 		v.Set("access_token", c.Token)
 	}
 	u.RawQuery = v.Encode()
-	resp, err := http.Get(u.String())
+	resp, err := client.Get(u.String())
 	if err != nil {
 		return nil, err
 	}

github/http.go

@@ -0,0 +1,76 @@
+package github
+
+import (
+	"context"
+	"net"
+	"net/http"
+	"time"
+)
+
+// Github's HTTP endpoint for asset uploads is flaky. Often it will drop a
+// TCP connection *. The HTTP POST will just hang indefinitely. To solve
+// this without using absolute deadlines (which would be hard to predict as
+// it depends on the size of the asset and the speed of the users'
+// connection), we use a modified http.Client which resets a timeout every
+// time the kernel accepts a read/write on the socket. Doing so basically
+// creates a sort of "inactivity watcher".
+//
+// We can't use the http.Client.Timeout field, as that's an absolute timeout
+// which doesn't get reset whenever there's some activity.
+//
+// * At least that's what I think is happening, I have never observed this
+//   myself since I never upload big assets, see issue
+//   http://github.com/aktau/github-release/issues/26.
+
+// HTTPReadWriteTimeout is the read/write timeout after which connections
+// will be closed.
+const HTTPReadWriteTimeout = 1 * time.Minute
+
+// dialer for use by the transport below, initialized like the net/http
+// dialer.
+var dialer = &net.Dialer{
+	Timeout:   30 * time.Second,
+	KeepAlive: 30 * time.Second,
+	DualStack: true,
+}
+
+// transport for use by the http.Client below.
+//
+// TODO: enable HTTP/2 transport as documented in net/http.
+var transport = &http.Transport{
+	Proxy: http.ProxyFromEnvironment,
+	DialContext: func(ctx context.Context, netw, addr string) (net.Conn, error) {
+		return newWatchdogConn(dialer.DialContext(ctx, netw, addr))
+	},
+	MaxIdleConns:          100,
+	IdleConnTimeout:       90 * time.Second,
+	TLSHandshakeTimeout:   10 * time.Second,
+	ExpectContinueTimeout: 1 * time.Second,
+	ResponseHeaderTimeout: 1 * time.Minute,
+}
+
+// client is an HTTP client suited for use with GitHub. It includes watchdog
+// functionality that will break of an upload/download attempt after
+// HTTPReadWriteTimeout.
+var client = &http.Client{Transport: transport}
+
+// watchdogConn wraps a net.Conn, on every read and write it sets a timeout.
+// If no bytes are read or written in that time, the connection is closed.
+type watchdogConn struct {
+	net.Conn
+	timeout time.Duration // The amount of time to wait between reads/writes on the connection before cancelling it.
+}
+
+func newWatchdogConn(conn net.Conn, err error) (net.Conn, error) {
+	return &watchdogConn{Conn: conn, timeout: HTTPReadWriteTimeout}, err
+}
+
+func (c *watchdogConn) Read(b []byte) (n int, err error) {
+	c.SetReadDeadline(time.Now().Add(c.timeout))
+	return c.Conn.Read(b)
+}
+
+func (c *watchdogConn) Write(b []byte) (n int, err error) {
+	c.SetWriteDeadline(time.Now().Add(c.timeout))
+	return c.Conn.Write(b)
+}