You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: transport.go
    path of file: ./repos/podman/vendor/github.com/hugelgupf/p9/p9
    
    the code of the file until where you have to start completion: // Copyright 2018 The gVisor Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package p9

import (
	"errors"
	"fmt"
	"io"
	"io/ioutil"
	"net"
	"sync"

	"github.com/hugelgupf/p9/vecnet"
	"github.com/u-root/uio/ulog"
)

// ConnError is returned in cases of a connection issue.
//
// This may be treated differently than other errors.
type ConnError struct {
	// error is the socket error.
	error
}

func (e ConnError) Error() string {
	return fmt.Sprintf("socket error: %v", e.error)
}


    
func recv(l ulog.Logger, r io.Reader, msize uint32, lookup lookupTagAndType) (tag, message, error) {
	// Read a header.
	var hdr [headerLength]byte

	if _, err := io.ReadAtLeast(r, hdr[:], int(headerLength)); err != nil {
		return noTag, nil, ConnError{err}
	}

	// Decode the header.
	headerBuf := buffer{data: hdr[:]}
	size := headerBuf.Read32()
	t := headerBuf.ReadMsgType()
	tag := headerBuf.ReadTag()
	if size < headerLength {
		// The message is too small.
		//
		// See above: it's probably screwed.
		return noTag, nil, ConnError{ErrNoValidMessage}
	}
	if size > maximumLength || size > msize {
		// The message is too big.
		return noTag, nil, ConnError{&ErrMessageTooLarge{size, msize}}
	}
	remaining := size - headerLength

	// Find our message to decode.
	m, err := lookup(tag, t)
	if err != nil {
		// Throw away the contents of this message.
		if remaining > 0 {
			_, _ = io.Copy(ioutil.Discard, io.LimitReader(r, int64(remaining)))
		}
		return tag, nil, err
	}

	// Not yet initialized.
	var dataBuf buffer
	var vecs vecnet.Buffers

	appendBuffer := func(size int) *[]byte {
		// Pull a data buffer from the pool.
		datap := dataPool.Get().(*[]byte)
		data := *datap
		if size > len(data) {
			// Create a larger data buffer.
			data = make([]byte, size)
			datap = &data
		} else {
			// Limit the data buffer.
			data = data[:size]
		}
		dataBuf = buffer{data: data}
		vecs = append(vecs, data)
		return datap
	}

	// Read the rest of the payload.
	//
	// This requires some special care to ensure that the vectors all line
	// up the way they should. We do this to minimize copying data around.
	if payloader, ok := m.(payloader); ok {
		fixedSize := payloader.FixedSize()

		// Do we need more than there is?
		if fixedSize > remaining {
			// This is not a valid message.
			if remaining > 0 {
				_, _ = io.Copy(ioutil.Discard, io.LimitReader(r, int64(remaining)))
			}
			return noTag, nil, ErrNoValidMessage
		}

		if fixedSize != 0 {
			datap := appendBuffer(int(fixedSize))
			defer dataPool.Put(datap)
		}

		// Include the payload.
		p := payloader.Payload()
		if p == nil || len(p) != int(remaining-fixedSize) {
			p = make([]byte, remaining-fixedSize)
			payloader.SetPayload(p)
		}
		if len(p) > 0 {
			vecs = append(vecs, p)
		}
	} else if remaining != 0 {
		datap := appendBuffer(int(remaining))
		defer dataPool.Put(datap)
	}

	if len(vecs) > 0 {
		if _, err := vecs.ReadFrom(r); err != nil {
			return noTag, nil, ConnError{err}
		}
	}

	// Decode the message data.
	m.decode(&dataBuf)
	if dataBuf.isOverrun() {
		// No need to drain the socket.
		return noTag, nil, ErrNoValidMessage
	}

	l.Printf("recv [r %p] [Tag %06d] %s", r, tag, m)

	// All set.
	return tag, m, nil
}