Added jni_socket_keep_alive logging

app/src/main/java/eu/faircode/email/EmailService.java

@@ -1057,10 +1057,10 @@ public class EmailService implements AutoCloseable {
 
                 int fd = ParcelFileDescriptor.fromSocket(socket).getFd();
                 int errno = jni_socket_keep_alive(fd, TCP_KEEP_ALIVE_INTERVAL);
-                if (errno != 0)
-                    throw new ErrnoException("TCP_KEEPIDLE", errno);
-
-                socket.setKeepAlive(true);
+                if (errno == 0)
+                    Log.i("Enabled TCP keep alive");
+                else
+                    throw new ErrnoException("jni_socket_keep_alive", errno);
             }
         } catch (Throwable ex) {
             Log.e(ex);

app/src/main/jni/fairemail.cc

@@ -62,14 +62,54 @@ JNIEXPORT jint JNICALL
 Java_eu_faircode_email_EmailService_jni_1socket_1keep_1alive(
         JNIEnv *env, jclass clazz,
         jint fd, jint seconds) {
-    // https://linux.die.net/man/2/setsockopt
-    // https://linux.die.net/man/3/setsockopt
     // https://tldp.org/HOWTO/html_single/TCP-Keepalive-HOWTO/#setsockopt
-    int value = seconds;
 
-    int res = setsockopt(fd, SOL_TCP, TCP_KEEPIDLE, (void *) &value, sizeof(value));
+    int optval;
+    socklen_t optlen = sizeof(optval);
+
+    if (getsockopt(fd, SOL_TCP, TCP_KEEPCNT, &optval, &optlen) == 0)
+        log_android(ANDROID_LOG_INFO, "Default TCP_KEEPCNT=%d", optval);
+    if (getsockopt(fd, SOL_TCP, TCP_KEEPINTVL, &optval, &optlen) == 0)
+        log_android(ANDROID_LOG_INFO, "Default TCP_KEEPINTVL=%d", optval);
+    if (getsockopt(fd, SOL_TCP, TCP_KEEPIDLE, &optval, &optlen) == 0)
+        log_android(ANDROID_LOG_INFO, "Default TCP_KEEPIDLE=%d", optval);
+    if (getsockopt(fd, SOL_SOCKET, SO_KEEPALIVE, &optval, &optlen) == 0)
+        log_android(ANDROID_LOG_INFO, "Default SO_KEEPALIVE=%d", optval);
+
+    int res;
+    int on = 1;
+    int tcp_keepalive_probes = 9;
+    int tcp_keepalive_intvl = 75;
+    int tcp_keepalive_time = seconds; // default 7200
+
+    log_android(ANDROID_LOG_INFO, "Set TCP_KEEPCNT=%d", tcp_keepalive_probes);
+    res = setsockopt(fd, SOL_TCP, TCP_KEEPCNT, &tcp_keepalive_probes, sizeof(tcp_keepalive_probes));
+    if (res < 0)
+        return errno;
+
+    log_android(ANDROID_LOG_INFO, "Set TCP_KEEPINTVL=%d", tcp_keepalive_intvl);
+    res = setsockopt(fd, SOL_TCP, TCP_KEEPINTVL, &tcp_keepalive_intvl, sizeof(tcp_keepalive_intvl));
     if (res < 0)
-        res = errno;
+        return errno;
+
+    log_android(ANDROID_LOG_INFO, "Set TCP_KEEPIDLE=%d", tcp_keepalive_time);
+    res = setsockopt(fd, SOL_TCP, TCP_KEEPIDLE, &tcp_keepalive_time, sizeof(tcp_keepalive_time));
+    if (res < 0)
+        return errno;
+
+    log_android(ANDROID_LOG_INFO, "Set SO_KEEPALIVE=%d", on);
+    res = setsockopt(fd, SOL_SOCKET, SO_KEEPALIVE, &on, sizeof(on));
+    if (res < 0)
+        return errno;
+
+    if (getsockopt(fd, SOL_TCP, TCP_KEEPCNT, &optval, &optlen) == 0)
+        log_android(ANDROID_LOG_INFO, "Check TCP_KEEPCNT=%d", optval);
+    if (getsockopt(fd, SOL_TCP, TCP_KEEPINTVL, &optval, &optlen) == 0)
+        log_android(ANDROID_LOG_INFO, "Check TCP_KEEPINTVL=%d", optval);
+    if (getsockopt(fd, SOL_TCP, TCP_KEEPIDLE, &optval, &optlen) == 0)
+        log_android(ANDROID_LOG_INFO, "Check TCP_KEEPIDLE=%d", optval);
+    if (getsockopt(fd, SOL_SOCKET, SO_KEEPALIVE, &optval, &optlen) == 0)
+        log_android(ANDROID_LOG_INFO, "Check SO_KEEPALIVE=%d", optval);
 
     return res;
 }