[ruby-core:109961] [Ruby master Bug#19012] BasicSocket#recv* methods return an empty packet instead of nil on closed connections

[ruby-core:109961] [Ruby master Bug#19012] BasicSocket#recv* methods return an empty packet instead of nil on closed connections

[byroot (Jean Boussier)]

Issue #19012 has been reported by byroot (Jean Boussier).

----------------------------------------
Bug #19012: BasicSocket#recv* methods return an empty packet instead of nil on closed connections
https://bugs.ruby-lang.org/issues/19012

* Author: byroot (Jean Boussier)
* Status: Open
* Priority: Normal
* Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN
----------------------------------------
`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.

But somehow the entire `receiv` family of methods in Ruby seem to interpret `0` as empty string instead of "EOF".

```ruby
require 'socket'

puts "=== pipes ==="
r, w = IO.pipe
r.read_nonblock(1, exception: false) # => :wait_readable
w.close
r.read_nonblock(1, exception: false) # => nil (EOF)

puts "=== sockets ===="
r, w = UNIXSocket.socketpair
r.read_nonblock(1, exception: false) # => :wait_readable
r.recvmsg_nonblock(1, exception: false) # => :wait_readable
r.recv_nonblock(1, exception: false) # => :wait_readable

w.close

r.read_nonblock(1, exception: false) # => nil (EOF)
r.recvmsg_nonblock(1, exception: false) # => ["", #<Addrinfo: empty-sockaddr SOCK_STREAM>, 128]]
r.recvmsg # => ["", #<Addrinfo: empty-sockaddr SOCK_STREAM>, 0]]
r.recv_nonblock(1, exception: false) # => ""
```

### Expected behavior

I would expect `recvmsg_nonblock`, `recvmsg`, `recv_nonblock` and `recv` to return `nil` when the connection is closed.





-- 
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[ruby-core:109962] [Ruby master Bug#19012] BasicSocket#recv* methods return an empty packet instead of nil on closed connections

[byroot (Jean Boussier)]

Issue #19012 has been updated by byroot (Jean Boussier).


I opened a PoC patch for it: https://github.com/ruby/ruby/pull/6407

----------------------------------------
Bug #19012: BasicSocket#recv* methods return an empty packet instead of nil on closed connections
https://bugs.ruby-lang.org/issues/19012#change-99212

* Author: byroot (Jean Boussier)
* Status: Open
* Priority: Normal
* Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN
----------------------------------------
`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.

But somehow the entire `receiv` family of methods in Ruby seem to interpret `0` as empty string instead of "EOF".

```ruby
require 'socket'

puts "=== pipes ==="
r, w = IO.pipe
r.read_nonblock(1, exception: false) # => :wait_readable
w.close
r.read_nonblock(1, exception: false) # => nil (EOF)

puts "=== sockets ===="
r, w = UNIXSocket.socketpair
r.read_nonblock(1, exception: false) # => :wait_readable
r.recvmsg_nonblock(1, exception: false) # => :wait_readable
r.recv_nonblock(1, exception: false) # => :wait_readable

w.close

r.read_nonblock(1, exception: false) # => nil (EOF)
r.recvmsg_nonblock(1, exception: false) # => ["", #<Addrinfo: empty-sockaddr SOCK_STREAM>, 128]]
r.recvmsg # => ["", #<Addrinfo: empty-sockaddr SOCK_STREAM>, 0]]
r.recv_nonblock(1, exception: false) # => ""
```

### Expected behavior

I would expect `recvmsg_nonblock`, `recvmsg`, `recv_nonblock` and `recv` to return `nil` when the connection is closed.





-- 
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[ruby-core:109972] [Ruby master Bug#19012] BasicSocket#recv* methods return an empty packet instead of nil on closed connections

[byroot (Jean Boussier)]

Issue #19012 has been updated by byroot (Jean Boussier).


@akr pointed on the PR that this behavior might be desirable for "connection-less" sockets such as `DGRAM`.

That said I think we should try to distinguish between "nothing was received" and "we received an empty packet".

I'm not quite familiar enough with `recv` (yet) to know whether it's possible to make the difference though. I'll try to research this more when I have a bit of time.

----------------------------------------
Bug #19012: BasicSocket#recv* methods return an empty packet instead of nil on closed connections
https://bugs.ruby-lang.org/issues/19012#change-99222

* Author: byroot (Jean Boussier)
* Status: Open
* Priority: Normal
* Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN
----------------------------------------
`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.

But somehow the entire `receiv` family of methods in Ruby seem to interpret `0` as empty string instead of "EOF".

```ruby
require 'socket'

puts "=== pipes ==="
r, w = IO.pipe
r.read_nonblock(1, exception: false) # => :wait_readable
w.close
r.read_nonblock(1, exception: false) # => nil (EOF)

puts "=== sockets ===="
r, w = UNIXSocket.socketpair
r.read_nonblock(1, exception: false) # => :wait_readable
r.recvmsg_nonblock(1, exception: false) # => :wait_readable
r.recv_nonblock(1, exception: false) # => :wait_readable

w.close

r.read_nonblock(1, exception: false) # => nil (EOF)
r.recvmsg_nonblock(1, exception: false) # => ["", #<Addrinfo: empty-sockaddr SOCK_STREAM>, 128]]
r.recvmsg # => ["", #<Addrinfo: empty-sockaddr SOCK_STREAM>, 0]]
r.recv_nonblock(1, exception: false) # => ""
```

### Expected behavior

I would expect `recvmsg_nonblock`, `recvmsg`, `recv_nonblock` and `recv` to return `nil` when the connection is closed.





-- 
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[ruby-core:111139] [Ruby master Bug#19012] BasicSocket#recv* methods return an empty packet instead of nil on closed connections

[mame (Yusuke Endoh)]

Issue #19012 has been updated by mame (Yusuke Endoh).


This is what @akr said at the dev meeting. (My understanding)

> The proposed behavior might be possible for stream. On the other hand, for datagram, the current behavior is better. I am not sure if there is a portable way to determine if the file descriptor behind an IO object is stream or datagram.

----------------------------------------
Bug #19012: BasicSocket#recv* methods return an empty packet instead of nil on closed connections
https://bugs.ruby-lang.org/issues/19012#change-100419

* Author: byroot (Jean Boussier)
* Status: Open
* Priority: Normal
* Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN
----------------------------------------
`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.

But somehow the entire `receiv` family of methods in Ruby seem to interpret `0` as empty string instead of "EOF".

```ruby
require 'socket'

puts "=== pipes ==="
r, w = IO.pipe
r.read_nonblock(1, exception: false) # => :wait_readable
w.close
r.read_nonblock(1, exception: false) # => nil (EOF)

puts "=== sockets ===="
r, w = UNIXSocket.socketpair
r.read_nonblock(1, exception: false) # => :wait_readable
r.recvmsg_nonblock(1, exception: false) # => :wait_readable
r.recv_nonblock(1, exception: false) # => :wait_readable

w.close

r.read_nonblock(1, exception: false) # => nil (EOF)
r.recvmsg_nonblock(1, exception: false) # => ["", #<Addrinfo: empty-sockaddr SOCK_STREAM>, 128]]
r.recvmsg # => ["", #<Addrinfo: empty-sockaddr SOCK_STREAM>, 0]]
r.recv_nonblock(1, exception: false) # => ""
```

### Expected behavior

I would expect `recvmsg_nonblock`, `recvmsg`, `recv_nonblock` and `recv` to return `nil` when the connection is closed.





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[ruby-core:111152] [Ruby master Bug#19012] BasicSocket#recv* methods return an empty packet instead of nil on closed connections

[byroot (Jean Boussier)]

Issue #19012 has been updated by byroot (Jean Boussier).


>  I am not sure if there is a portable way to determine if the file descriptor behind an IO object is stream or datagram.

Yeah, me neither. I'll try to dig more.

----------------------------------------
Bug #19012: BasicSocket#recv* methods return an empty packet instead of nil on closed connections
https://bugs.ruby-lang.org/issues/19012#change-100436

* Author: byroot (Jean Boussier)
* Status: Open
* Priority: Normal
* Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN
----------------------------------------
`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.

But somehow the entire `receiv` family of methods in Ruby seem to interpret `0` as empty string instead of "EOF".

```ruby
require 'socket'

puts "=== pipes ==="
r, w = IO.pipe
r.read_nonblock(1, exception: false) # => :wait_readable
w.close
r.read_nonblock(1, exception: false) # => nil (EOF)

puts "=== sockets ===="
r, w = UNIXSocket.socketpair
r.read_nonblock(1, exception: false) # => :wait_readable
r.recvmsg_nonblock(1, exception: false) # => :wait_readable
r.recv_nonblock(1, exception: false) # => :wait_readable

w.close

r.read_nonblock(1, exception: false) # => nil (EOF)
r.recvmsg_nonblock(1, exception: false) # => ["", #<Addrinfo: empty-sockaddr SOCK_STREAM>, 128]]
r.recvmsg # => ["", #<Addrinfo: empty-sockaddr SOCK_STREAM>, 0]]
r.recv_nonblock(1, exception: false) # => ""
```

### Expected behavior

I would expect `recvmsg_nonblock`, `recvmsg`, `recv_nonblock` and `recv` to return `nil` when the connection is closed.





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[ruby-core:111153] [Ruby master Bug#19012] BasicSocket#recv* methods return an empty packet instead of nil on closed connections

[byroot (Jean Boussier)]

Issue #19012 has been updated by byroot (Jean Boussier).


Apparently we can get this via `getsockopt(fd, SOL_SOCKET, SO_TYPE, &type, &length);`, the question being how portable it is.

----------------------------------------
Bug #19012: BasicSocket#recv* methods return an empty packet instead of nil on closed connections
https://bugs.ruby-lang.org/issues/19012#change-100437

* Author: byroot (Jean Boussier)
* Status: Open
* Priority: Normal
* Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN
----------------------------------------
`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.

But somehow the entire `receiv` family of methods in Ruby seem to interpret `0` as empty string instead of "EOF".

```ruby
require 'socket'

puts "=== pipes ==="
r, w = IO.pipe
r.read_nonblock(1, exception: false) # => :wait_readable
w.close
r.read_nonblock(1, exception: false) # => nil (EOF)

puts "=== sockets ===="
r, w = UNIXSocket.socketpair
r.read_nonblock(1, exception: false) # => :wait_readable
r.recvmsg_nonblock(1, exception: false) # => :wait_readable
r.recv_nonblock(1, exception: false) # => :wait_readable

w.close

r.read_nonblock(1, exception: false) # => nil (EOF)
r.recvmsg_nonblock(1, exception: false) # => ["", #<Addrinfo: empty-sockaddr SOCK_STREAM>, 128]]
r.recvmsg # => ["", #<Addrinfo: empty-sockaddr SOCK_STREAM>, 0]]
r.recv_nonblock(1, exception: false) # => ""
```

### Expected behavior

I would expect `recvmsg_nonblock`, `recvmsg`, `recv_nonblock` and `recv` to return `nil` when the connection is closed.





-- 
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[ruby-core:111227] [Ruby master Bug#19012] BasicSocket#recv* methods return an empty packet instead of nil on closed connections

[byroot (Jean Boussier)]

Issue #19012 has been updated by byroot (Jean Boussier).


I was able to implement the desired behavior in https://github.com/ruby/ruby/pull/6407

----------------------------------------
Bug #19012: BasicSocket#recv* methods return an empty packet instead of nil on closed connections
https://bugs.ruby-lang.org/issues/19012#change-100516

* Author: byroot (Jean Boussier)
* Status: Open
* Priority: Normal
* Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN
----------------------------------------
`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.

But somehow the entire `receiv` family of methods in Ruby seem to interpret `0` as empty string instead of "EOF".

```ruby
require 'socket'

puts "=== pipes ==="
r, w = IO.pipe
r.read_nonblock(1, exception: false) # => :wait_readable
w.close
r.read_nonblock(1, exception: false) # => nil (EOF)

puts "=== sockets ===="
r, w = UNIXSocket.socketpair
r.read_nonblock(1, exception: false) # => :wait_readable
r.recvmsg_nonblock(1, exception: false) # => :wait_readable
r.recv_nonblock(1, exception: false) # => :wait_readable

w.close

r.read_nonblock(1, exception: false) # => nil (EOF)
r.recvmsg_nonblock(1, exception: false) # => ["", #<Addrinfo: empty-sockaddr SOCK_STREAM>, 128]]
r.recvmsg # => ["", #<Addrinfo: empty-sockaddr SOCK_STREAM>, 0]]
r.recv_nonblock(1, exception: false) # => ""
```

### Expected behavior

I would expect `recvmsg_nonblock`, `recvmsg`, `recv_nonblock` and `recv` to return `nil` when the connection is closed.





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[ruby-core:115768] [Ruby master Bug#19012] BasicSocket#recv* methods return an empty packet instead of nil on closed connections

[zverok (Victor Shepelev) via ruby-core]

Issue #19012 has been updated by zverok (Victor Shepelev).


Should the docs for [BasicSocket#recv_nonblock](https://docs.ruby-lang.org/en/master/BasicSocket.html#method-i-recv_nonblock) be updated? Now they state

> When recvfrom(2) returns 0, Socket#recv_nonblock returns an empty string as data. The meaning depends on the socket: EOF on TCP, empty packet on UDP, etc.

I am not sure whether the change affects all the cases (this thing about datagrams got me confused).

Other affected methods don't have a similar clause, but this one seems to directly contradict the implemented behavior now.

----------------------------------------
Bug #19012: BasicSocket#recv* methods return an empty packet instead of nil on closed connections
https://bugs.ruby-lang.org/issues/19012#change-105705

* Author: byroot (Jean Boussier)
* Status: Closed
* Priority: Normal
* Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN
----------------------------------------
`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.

But somehow the entire `receiv` family of methods in Ruby seem to interpret `0` as empty string instead of "EOF".

```ruby
require 'socket'

puts "=== pipes ==="
r, w = IO.pipe
r.read_nonblock(1, exception: false) # => :wait_readable
w.close
r.read_nonblock(1, exception: false) # => nil (EOF)

puts "=== sockets ===="
r, w = UNIXSocket.socketpair
r.read_nonblock(1, exception: false) # => :wait_readable
r.recvmsg_nonblock(1, exception: false) # => :wait_readable
r.recv_nonblock(1, exception: false) # => :wait_readable

w.close

r.read_nonblock(1, exception: false) # => nil (EOF)
r.recvmsg_nonblock(1, exception: false) # => ["", #<Addrinfo: empty-sockaddr SOCK_STREAM>, 128]]
r.recvmsg # => ["", #<Addrinfo: empty-sockaddr SOCK_STREAM>, 0]]
r.recv_nonblock(1, exception: false) # => ""
```

### Expected behavior

I would expect `recvmsg_nonblock`, `recvmsg`, `recv_nonblock` and `recv` to return `nil` when the connection is closed.





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