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tcpconn.go
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tcpconn.go
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package buffstreams
import (
"errors"
"io"
"net"
"sync"
)
var (
// ErrZeroBytesReadHeader is thrown when the value parsed from the header is not valid
ErrZeroBytesReadHeader = errors.New("0 Bytes parsed from header. Connection Closed")
// ErrLessThanZeroBytesReadHeader is thrown when the value parsed from the header caused some kind of underrun
ErrLessThanZeroBytesReadHeader = errors.New("Less than zero bytes parsed from header. Connection Closed")
)
// TCPConn is an abstraction over the normal net.TCPConn, but optimized for wtiting
// data encoded in a length+data format, like you would treat networked protocol
// buffer messages
type TCPConn struct {
// General
socket *net.TCPConn
address string
headerByteSize int
maxMessageSize int
// For processing incoming data
incomingHeaderBuffer []byte
// For processing outgoing data
writeLock sync.Mutex
outgoingDataBuffer []byte
}
// TCPConnConfig representss the information needed to begin listening for
// writing messages.
type TCPConnConfig struct {
// Controls how large the largest Message may be. The server will reject any messages whose clients
// header size does not match this configuration.
MaxMessageSize int
// Address is the address to connect to for writing streaming messages.
Address string
}
func newTCPConn(cfg *TCPConnConfig) (*TCPConn, error) {
maxMessageSize := DefaultMaxMessageSize
// 0 is the default, and the message must be atleast 1 byte large
if cfg.MaxMessageSize != 0 {
maxMessageSize = cfg.MaxMessageSize
}
headerByteSize := messageSizeToBitLength(maxMessageSize)
return &TCPConn{
maxMessageSize: maxMessageSize,
headerByteSize: headerByteSize,
address: cfg.Address,
incomingHeaderBuffer: make([]byte, headerByteSize),
writeLock: sync.Mutex{},
outgoingDataBuffer: make([]byte, maxMessageSize),
}, nil
}
// DialTCP creates a TCPWriter, and dials a connection to the remote
// endpoint. It does not begin writing anything until you begin to do so.
func DialTCP(cfg *TCPConnConfig) (*TCPConn, error) {
c, err := newTCPConn(cfg)
if err != nil {
return nil, err
}
if err := c.open(); err != nil {
return nil, err
}
return c, nil
}
// open will dial a connection to the remote endpoint.
func (c *TCPConn) open() error {
tcpAddr, err := net.ResolveTCPAddr("tcp", c.address)
if err != nil {
return err
}
conn, err := net.DialTCP("tcp", nil, tcpAddr)
if err != nil {
return err
}
c.socket = conn
return err
}
// Reopen allows you to close and re-establish a connection to the existing Address
// without needing to create a whole new TCPWriter object.
func (c *TCPConn) Reopen() error {
if err := c.Close(); err != nil {
return err
}
if err := c.open(); err != nil {
return err
}
return nil
}
// Close will immediately call close on the connection to the remote endpoint. Per
// the golang source code for the netFD object, this call uses a special mutex to
// control access to the underlying pool of readers/writers. This call should be
// threadsafe, so that any other threads writing will finish, or be blocked, when
// this is invoked.
func (c *TCPConn) Close() error {
return c.socket.Close()
}
// Write allows you to send a stream of bytes as messages. Each array of bytes
// you pass in will be pre-pended with it's size. If the connection isn't open
// you will receive an error. If not all bytes can be written, Write will keep
// trying until the full message is delivered, or the connection is broken.
func (c *TCPConn) Write(data []byte) (int, error) {
// Calculate how big the message is, using a consistent header size.
// Append the size to the message, so now it has a header
c.outgoingDataBuffer = append(intToByteArray(int64(len(data)), c.headerByteSize), data...)
toWriteLen := len(c.outgoingDataBuffer)
// Three conditions could have occured:
// 1. There was an error
// 2. Not all bytes were written
// 3. Both 1 and 2
// If there was an error, that should take handling precedence. If the connection
// was closed, or is otherwise in a bad state, we have to abort and re-open the connection
// to try again, as we can't realistically finish the write. We have to retry it, or return
// and error to the user?
// TODO configurable message retries
// If there was not an error, and we simply didn't finish the write, we should enter
// a write-until-complete loop, where we continue to write the data until the server accepts
// all of it.
// If both issues occurred, we'll need to find a way to determine if the error
// is recoverable (is the connection in a bad state) or not.
var writeError error
var totalBytesWritten = 0
var bytesWritten = 0
// First, read the number of bytes required to determine the message length
for totalBytesWritten < toWriteLen && writeError == nil {
// While we haven't read enough yet
// If there are remainder bytes, adjust the contents of toWrite
// totalBytesWritten will be the index of the nextByte waiting to be read
bytesWritten, writeError = c.socket.Write(c.outgoingDataBuffer[totalBytesWritten:])
totalBytesWritten += bytesWritten
}
if writeError != nil {
c.Close()
}
// Return the bytes written, any error
return totalBytesWritten, writeError
}
func (c *TCPConn) lowLevelRead(buffer []byte) (int, error) {
var totalBytesRead = 0
var err error
var bytesRead = 0
var toRead = len(buffer)
// This fills the buffer
bytesRead, err = c.socket.Read(buffer)
totalBytesRead += bytesRead
for totalBytesRead < toRead && err == nil {
bytesRead, err = c.socket.Read(buffer[totalBytesRead:])
totalBytesRead += bytesRead
}
// Output the content of the bytes to the queue
if totalBytesRead == 0 && err != nil && err == io.EOF {
// "End of individual transmission"
// We're just done reading from that conn
return totalBytesRead, err
} else if err != nil {
//"Underlying network failure?"
// Not sure what this error would be, but it could exist and i've seen it handled
// as a general case in other networking code. Following in the footsteps of (greatness|madness)
return totalBytesRead, err
}
// Read some bytes, return the length
return totalBytesRead, nil
}
func (c *TCPConn) Read(b []byte) (int, error) {
// Read the header
hLength, err := c.lowLevelRead(c.incomingHeaderBuffer)
if err != nil {
return hLength, err
}
// Decode it
msgLength, bytesParsed := byteArrayToUInt32(c.incomingHeaderBuffer)
if bytesParsed == 0 {
// "Buffer too small"
c.Close()
return hLength, ErrZeroBytesReadHeader
} else if bytesParsed < 0 {
// "Buffer overflow"
c.Close()
return hLength, ErrLessThanZeroBytesReadHeader
}
// Using the header, read the remaining body
bLength, err := c.lowLevelRead(b[:msgLength])
if err != nil {
c.Close()
}
return bLength, err
}