Adding SocketChannel toString to connection exception messages

[Steven Schlansker]

> On Dec 21, 2017, at 11:11 AM, Steven Schlansker <stevenschlansker at gmail.com> wrote:
> 
> What if ConnectException included the attempted hostname / IP / port SocketAddress?
> java.net.ConnectException: Connection to 'foo.mycorp.com[10.x.x.x]:12345' refused
> Much more useful!  This could also be extended to various other socket exceptions.

I started hacking around with this, first with PlainSocketImpl only.
I apologize in advance for what is likely to be terrible JNI style, as I don't have much experience
with it and I omitted any error handling for the POC - but I think it proves that this isn't too big of a project, as
I would want to cover SocketChannelImpl and maybe UnixAsynchronousSocketChannelImpl and call it good enough for my uses.

Behold!

[me at myhost]% java pkg.SocketFail
java.net.ConnectException: Connection refused (Connection refused)

[me at myhost]% ~/code/jdk10/build/macosx-x86_64-normal-server-release/jdk/bin/java pkg.SocketFail
java.net.ConnectException: Connection refused (Connection refused: localhost/127.0.0.1:12345)


Am I correct that the best path towards acceptance for this kind of change is to target jdk10 and then beg for a backport to jdk9u?
Thanks again for considering this improvement! WIP patch below inline.


diff --git a/src/java.base/unix/native/libnet/PlainSocketImpl.c b/src/java.base/unix/native/libnet/PlainSocketImpl.c
--- a/src/java.base/unix/native/libnet/PlainSocketImpl.c
+++ b/src/java.base/unix/native/libnet/PlainSocketImpl.c
@@ -217,6 +217,9 @@
     (*env)->SetIntField(env, fdObj, IO_fd_fdID, fd);
 }

+// private helper for socketConnect to describe errors
+static void sockErrDescribe(JNIEnv *env, char* errbuf, char* msg, jobject ia, jint port);
+
 /*
  * inetAddress is the address object passed to the socket connect
  * call.
@@ -230,6 +233,7 @@
                                             jobject iaObj, jint port,
                                             jint timeout)
 {
+    char errmsg[256];
     jint localport = (*env)->GetIntField(env, this, psi_localportID);
     int len = 0;
     /* fdObj is the FileDescriptor field on this */
@@ -249,7 +253,8 @@
     int connect_rv = -1;

     if (IS_NULL(fdObj)) {
-        JNU_ThrowByName(env, JNU_JAVANETPKG "SocketException", "Socket closed");
+        sockErrDescribe(env, errmsg, "Socket closed", iaObj, port);
+        JNU_ThrowByName(env, JNU_JAVANETPKG "SocketException", errmsg);
         return;
     } else {
         fd = (*env)->GetIntField(env, fdObj, IO_fd_fdID);
@@ -329,8 +334,8 @@
             jlong prevNanoTime = JVM_NanoTime(env, 0);

             if (errno != EINPROGRESS) {
-                NET_ThrowByNameWithLastError(env, JNU_JAVANETPKG "ConnectException",
-                             "connect failed");
+                sockErrDescribe(env, errmsg, "connect failed", iaObj, port);
+                NET_ThrowByNameWithLastError(env, JNU_JAVANETPKG "ConnectException", errmsg);
                 SET_BLOCKING(fd);
                 return;
             }
@@ -372,8 +377,8 @@
             } /* while */

             if (connect_rv == 0) {
-                JNU_ThrowByName(env, JNU_JAVANETPKG "SocketTimeoutException",
-                            "connect timed out");
+                sockErrDescribe(env, errmsg, "connect timed out", iaObj, port);
+                JNU_ThrowByName(env, JNU_JAVANETPKG "SocketTimeoutException", errmsg);

                 /*
                  * Timeout out but connection may still be established.
@@ -419,36 +424,37 @@
          * a more descriptive exception text is used.
          */
         if (connect_rv == -1 && errno == EINVAL) {
-            JNU_ThrowByName(env, JNU_JAVANETPKG "SocketException",
-                "Invalid argument or cannot assign requested address");
+            sockErrDescribe(errmsg, "Invalid argument or cannot assign requested address", iaObj, port)
+            JNU_ThrowByName(env, JNU_JAVANETPKG "SocketException", errmsg);
             return;
         }
 #endif
 #if defined(EPROTO)
         if (errno == EPROTO) {
-            NET_ThrowByNameWithLastError(env, JNU_JAVANETPKG "ProtocolException",
-                           "Protocol error");
+            sockErrDescribe(env, errmsg, "Protocol error", iaObj, port);
+            NET_ThrowByNameWithLastError(env, JNU_JAVANETPKG "ProtocolException", errmsg);
             return;
         }
 #endif
         if (errno == ECONNREFUSED) {
-            NET_ThrowByNameWithLastError(env, JNU_JAVANETPKG "ConnectException",
-                           "Connection refused");
+            sockErrDescribe(env, errmsg, "Connection refused", iaObj, port);
+            NET_ThrowByNameWithLastError(env, JNU_JAVANETPKG "ConnectException", errmsg);
         } else if (errno == ETIMEDOUT) {
-            NET_ThrowByNameWithLastError(env, JNU_JAVANETPKG "ConnectException",
-                           "Connection timed out");
+            sockErrDescribe(env, errmsg, "Connection timed out", iaObj, port);
+            NET_ThrowByNameWithLastError(env, JNU_JAVANETPKG "ConnectException", errmsg);
         } else if (errno == EHOSTUNREACH) {
-            NET_ThrowByNameWithLastError(env, JNU_JAVANETPKG "NoRouteToHostException",
-                           "Host unreachable");
+            sockErrDescribe(env, errmsg, "Host unreachable", iaObj, port);
+            NET_ThrowByNameWithLastError(env, JNU_JAVANETPKG "NoRouteToHostException", errmsg);
         } else if (errno == EADDRNOTAVAIL) {
-            NET_ThrowByNameWithLastError(env, JNU_JAVANETPKG "NoRouteToHostException",
-                             "Address not available");
+            sockErrDescribe(env, errmsg, "Address not available", iaObj, port);
+            NET_ThrowByNameWithLastError(env, JNU_JAVANETPKG "NoRouteToHostException", errmsg);
         } else if ((errno == EISCONN) || (errno == EBADF)) {
-            JNU_ThrowByName(env, JNU_JAVANETPKG "SocketException",
-                            "Socket closed");
+            sockErrDescribe(env, errmsg, "Socket closed", iaObj, port);
+            JNU_ThrowByName(env, JNU_JAVANETPKG "SocketException", errmsg);
         } else {
+            sockErrDescribe(env, errmsg, "connect failed", iaObj, port);
             JNU_ThrowByNameWithMessageAndLastError
-                (env, JNU_JAVANETPKG "SocketException", "connect failed");
+                (env, JNU_JAVANETPKG "SocketException", errmsg);
         }
         return;
     }
@@ -479,6 +485,15 @@
     }
 }

+static void sockErrDescribe(JNIEnv *env, char* errbuf, char* msg, jobject ia, jint port) {
+    jclass obj = (*env)->FindClass(env, "java/lang/Object");
+    jmethodID toStr = (*env)->GetMethodID(env, obj, "toString", "()Ljava/lang/String;");
+    jstring iaJstr = (*env)->CallObjectMethod(env, ia, toStr);
+    const char *iaStr = (*env)->GetStringUTFChars(env, iaJstr, 0);
+    jio_snprintf(errbuf, 128, "%s: %s:%d", msg, iaStr, port);
+    (*env)->ReleaseStringUTFChars(env, iaJstr, iaStr);
+}
+
 /*
  * Class:     java_net_PlainSocketImpl
  * Method:    socketBind