add library support for tuning TCP_KEEPALIVE

This adds three new options to control the behavior of TCP keepalives:

- CURLOPT_TCP_KEEPALIVE: enable/disable probes
- CURLOPT_TCP_KEEPIDLE: idle time before sending first probe
- CURLOPT_TCP_KEEPINTVL: delay between successive probes

While not all operating systems support the TCP_KEEPIDLE and
TCP_KEEPINTVL knobs, the library will still allow these options to be
set by clients, silently ignoring the values.

3 files changed, 54 insertions, 0 deletions

diff --git a/lib/connect.c b/lib/connect.c
index b5082d896..5747b0431 100644
--- a/lib/connect.c
+++ b/lib/connect.c
@@ -91,6 +91,35 @@
 
 static bool verifyconnect(curl_socket_t sockfd, int *error);
 
+static void
+tcpkeepalive(struct SessionHandle *data,
+             int sockfd)
+{
+  int optval = data->set.tcp_keepalive;
+
+  /* only set IDLE and INTVL if setting KEEPALIVE is successful */
+  if(setsockopt(sockfd, SOL_SOCKET, SO_KEEPALIVE,
+        (void *)&optval, sizeof(optval)) < 0) {
+    infof(data, "Failed to set SO_KEEPALIVE on fd %d\n", sockfd);
+  }
+  else {
+#ifdef TCP_KEEPIDLE
+    optval = data->set.tcp_keepidle;
+    if(setsockopt(sockfd, IPPROTO_TCP, TCP_KEEPIDLE,
+          (void *)&optval, sizeof(optval)) < 0) {
+      infof(data, "Failed to set TCP_KEEPIDLE on fd %d\n", sockfd);
+    }
+#endif
+#ifdef TCP_KEEPINTVL
+    optval = data->set.tcp_keepintvl;
+    if(setsockopt(sockfd, IPPROTO_TCP, TCP_KEEPINTVL,
+          (void *)&optval, sizeof(optval)) < 0) {
+      infof(data, "Failed to set TCP_KEEPINTVL on fd %d\n", sockfd);
+    }
+#endif
+  }
+}
+
 static CURLcode
 singleipconnect(struct connectdata *conn,
                 const Curl_addrinfo *ai, /* start connecting to this */
@@ -876,6 +905,9 @@ singleipconnect(struct connectdata *conn,
 
   Curl_sndbufset(sockfd);
 
+  if(data->set.tcp_keepalive)
+    tcpkeepalive(data, sockfd);
+
   if(data->set.fsockopt) {
     /* activate callback for setting socket options */
     error = data->set.fsockopt(data->set.sockopt_client,
diff --git a/lib/url.c b/lib/url.c
index 395055f4e..c89234d74 100644
--- a/lib/url.c
+++ b/lib/url.c
@@ -748,6 +748,13 @@ CURLcode Curl_init_userdefined(struct UserDefined *set)
   set->chunk_bgn      = ZERO_NULL;
   set->chunk_end      = ZERO_NULL;
 
+  /* tcp keepalives are disabled by default, but provide reasonable values for
+   * the interval and idle times.
+   */
+  set->tcp_keepalive = 0;
+  set->tcp_keepintvl = 60;
+  set->tcp_keepidle = 60;
+
   return res;
 }
 
@@ -811,6 +818,7 @@ CURLcode Curl_open(struct SessionHandle **curl)
        multi stack. */
   }
 
+
   if(res) {
     Curl_resolver_cleanup(data->state.resolver);
     if(data->state.headerbuff)
@@ -2545,6 +2553,16 @@ CURLcode Curl_setopt(struct SessionHandle *data, CURLoption option,
     result = Curl_set_dns_servers(data, va_arg(param, char *));
     break;
 
+  case CURLOPT_TCP_KEEPALIVE:
+    data->set.tcp_keepalive = (0 != va_arg(param, long))?TRUE:FALSE;
+    break;
+  case CURLOPT_TCP_KEEPIDLE:
+    data->set.tcp_keepidle = va_arg(param, long);
+    break;
+  case CURLOPT_TCP_KEEPINTVL:
+    data->set.tcp_keepintvl = va_arg(param, long);
+    break;
+
   default:
     /* unknown tag and its companion, just ignore: */
     result = CURLE_UNKNOWN_OPTION;
diff --git a/lib/urldata.h b/lib/urldata.h
index adabf5b73..a959bc716 100644
--- a/lib/urldata.h
+++ b/lib/urldata.h
@@ -1539,6 +1539,10 @@ struct UserDefined {
 
   long gssapi_delegation; /* GSSAPI credential delegation, see the
                              documentation of CURLOPT_GSSAPI_DELEGATION */
+
+  bool tcp_keepalive;    /* use TCP keepalives */
+  long tcp_keepidle;     /* seconds in idle before sending keepalive probe */
+  long tcp_keepintvl;    /* seconds between TCP keepalive probes */
 };
 
 struct Names {