BasicSocket#recv* return `nil` rather than an empty packet

[Bug #19012]

man recvmsg(2) states:

> Return Value
> These calls return the number of bytes received, or -1 if an error occurred.
> The return value will be 0 when the peer has performed an orderly shutdown.

Not too sure how one is supposed to make the difference between a packet of
size 0 and a closed connection.

3 files changed, 26 insertions, 0 deletions

diff --git a/ext/socket/ancdata.c b/ext/socket/ancdata.c
index 7406177de2..6ef040b692 100644
--- a/ext/socket/ancdata.c
+++ b/ext/socket/ancdata.c
@@ -1555,6 +1555,10 @@ bsock_recvmsg_internal(VALUE sock,
 
     ss = rb_recvmsg(fptr->fd, &mh, flags);
 
+    if (ss == 0 && !rsock_is_dgram(fptr)) {
+        return Qnil;
+    }
+
     if (ss == -1) {
         int e;
         if (!nonblock && rb_io_maybe_wait_readable(errno, fptr->self, RUBY_IO_TIMEOUT_DEFAULT)) {
diff --git a/ext/socket/init.c b/ext/socket/init.c
index 557d4374a5..e9dc6f8483 100644
--- a/ext/socket/init.c
+++ b/ext/socket/init.c
@@ -116,6 +116,7 @@ recvfrom_blocking(void *data)
     ssize_t ret;
     ret = recvfrom(arg->fd, RSTRING_PTR(arg->str), arg->length,
                    arg->flags, &arg->buf.addr, &arg->alen);
+
     if (ret != -1 && len0 < arg->alen)
         arg->alen = len0;
 
@@ -147,6 +148,18 @@ recvfrom_locktmp(VALUE v)
     return rb_thread_io_blocking_region(recvfrom_blocking, arg, arg->fd);
 }
 
+int
+rsock_is_dgram(rb_io_t *fptr)
+{
+    int socktype;
+    socklen_t optlen = (socklen_t)sizeof(socktype);
+    int ret = getsockopt(fptr->fd, SOL_SOCKET, SO_TYPE, (void*)&socktype, &optlen);
+    if (ret == -1) {
+        rb_sys_fail("getsockopt(SO_TYPE)");
+    }
+    return socktype == SOCK_DGRAM;
+}
+
 VALUE
 rsock_s_recvfrom(VALUE socket, int argc, VALUE *argv, enum sock_recv_type from)
 {
@@ -187,6 +200,9 @@ rsock_s_recvfrom(VALUE socket, int argc, VALUE *argv, enum sock_recv_type from)
 
         slen = (long)rb_str_locktmp_ensure(str, recvfrom_locktmp, (VALUE)&arg);
 
+        if (slen == 0 && !rsock_is_dgram(fptr)) {
+            return Qnil;
+        }
         if (slen >= 0) break;
 
         if (!rb_io_maybe_wait_readable(errno, socket, RUBY_IO_TIMEOUT_DEFAULT))
@@ -259,6 +275,10 @@ rsock_s_recvfrom_nonblock(VALUE sock, VALUE len, VALUE flg, VALUE str,
     if (slen != -1 && len0 < alen)
         alen = len0;
 
+    if (slen == 0 && !rsock_is_dgram(fptr)) {
+        return Qnil;
+    }
+
     if (slen < 0) {
         int e = errno;
         switch (e) {
diff --git a/ext/socket/rubysocket.h b/ext/socket/rubysocket.h
index 5f803ba0da..7c5739808d 100644
--- a/ext/socket/rubysocket.h
+++ b/ext/socket/rubysocket.h
@@ -459,6 +459,8 @@ VALUE rsock_write_nonblock(VALUE sock, VALUE buf, VALUE ex);
 
 void rsock_make_fd_nonblock(int fd);
 
+int rsock_is_dgram(rb_io_t *fptr);
+
 #if !defined HAVE_INET_NTOP && ! defined _WIN32
 const char *inet_ntop(int, const void *, char *, size_t);
 #elif defined __MINGW32__