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fix: Use buffered reader in peer to fix ShortBuffer #303

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Merged
merged 3 commits into from
Feb 17, 2022
Merged

fix: Use buffered reader in peer to fix ShortBuffer #303

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60cb674
fix: Use buffered reader in peer to fix ShortBuffer
kylecarbs Feb 16, 2022
ea40bed
Merge branch 'main' into buffered
kylecarbs Feb 16, 2022
2b411ae
Merge branch 'main' into buffered
kylecarbs Feb 17, 2022
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1 change: 1 addition & 0 deletions .vscode/settings.json
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Original file line number Diff line number Diff line change
Expand Up @@ -57,6 +57,7 @@
"tfexec",
"tfstate",
"unconvert",
"webrtc",
"xerrors",
"yamux"
]
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21 changes: 19 additions & 2 deletions peer/channel.go
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Original file line number Diff line number Diff line change
@@ -1,6 +1,7 @@
package peer

import (
"bufio"
"context"
"io"
"net"
Expand Down Expand Up @@ -78,7 +79,8 @@ type Channel struct {
dc *webrtc.DataChannel
// This field can be nil. It becomes set after the DataChannel
// has been opened and is detached.
rwc datachannel.ReadWriteCloser
rwc datachannel.ReadWriteCloser
reader io.Reader

closed chan struct{}
closeMutex sync.Mutex
Expand Down Expand Up @@ -130,6 +132,21 @@ func (c *Channel) init() {
_ = c.closeWithError(xerrors.Errorf("detach: %w", err))
return
}
// pion/webrtc will return an io.ErrShortBuffer when a read
// is triggerred with a buffer size less than the chunks written.
//
// This makes sense when considering UDP connections, because
// bufferring of data that has no transmit guarantees is likely
// to cause unexpected behavior.
//
// When ordered, this adds a bufio.Reader. This ensures additional
// data on TCP-like connections can be read in parts, while still
// being bufferred.
Comment on lines +142 to +144
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Thanks for documenting this, very helpful. Wouldn't have been clear to me why we need this otherwise 👍

if c.opts.Unordered {
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ooo, wonder if we have the same issue with wsnet 🤔

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I was really confused why wsnet doesn't have this problem, but I think it's because we pipe using net.Dial for everything. So the problem exists, but it's hidden behind the TCP buffering there maybe?

ssh is a specific protocol in the agent, so we're exchanging much smaller payloads here, which made me notice this bug.

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for context, I was getting weird short buffer errors (that I had no idea how to reproduce easily or diagnose) when I tried to remove the envagent proxying, so I wonder whether this would've fixed it

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Oh, this almost certainly would have!

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Curious if we use unordered connections via WebRTC in the product today?

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Nah, we don't!

c.reader = c.rwc
} else {
c.reader = bufio.NewReader(c.rwc)
}
close(c.opened)
})

Expand Down Expand Up @@ -181,7 +198,7 @@ func (c *Channel) Read(bytes []byte) (int, error) {
}
}

bytesRead, err := c.rwc.Read(bytes)
bytesRead, err := c.reader.Read(bytes)
if err != nil {
if c.isClosed() {
return 0, c.closeError
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21 changes: 21 additions & 0 deletions peer/conn_test.go
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Expand Up @@ -267,6 +267,27 @@ func TestConn(t *testing.T) {
_, err := client.Ping()
require.NoError(t, err)
})

t.Run("ShortBuffer", func(t *testing.T) {
t.Parallel()
client, server, _ := createPair(t)
exchange(client, server)
go func() {
channel, err := client.Dial(context.Background(), "test", nil)
require.NoError(t, err)
_, err = channel.Write([]byte{1, 2})
require.NoError(t, err)
}()
channel, err := server.Accept(context.Background())
require.NoError(t, err)
data := make([]byte, 1)
_, err = channel.Read(data)
require.NoError(t, err)
require.Equal(t, uint8(0x1), data[0])
_, err = channel.Read(data)
require.NoError(t, err)
require.Equal(t, uint8(0x2), data[0])
})
}

func createPair(t *testing.T) (client *peer.Conn, server *peer.Conn, wan *vnet.Router) {
Expand Down