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handler.go
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handler.go
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package cocaine12
import (
"context"
"errors"
"io"
"syscall"
)
type request struct {
messageTypeDetector
fromWorker chan *Message
toHandler chan *Message
closed chan struct{}
}
const (
cworkererrorcategory = 42
cdefaulterrrorcode = 100
)
var (
// ErrStreamIsClosed means that a response stream is closed
ErrStreamIsClosed = errors.New("Stream is closed")
// ErrBadPayload means that a message payload is malformed
ErrBadPayload = errors.New("payload is not []byte")
// ErrMalformedErrorMessage means that we receive a corrupted or
// unproper message
ErrMalformedErrorMessage = &ErrRequest{
Message: "malformed error message",
Category: cworkererrorcategory,
Code: cdefaulterrrorcode,
}
)
func newRequest(mtd messageTypeDetector) *request {
request := &request{
messageTypeDetector: mtd,
fromWorker: make(chan *Message),
toHandler: make(chan *Message),
closed: make(chan struct{}),
}
go loop(
// input
request.fromWorker,
// output
request.toHandler,
// onclose
request.closed,
)
return request
}
func (request *request) Read(ctx context.Context) ([]byte, error) {
select {
// Choke never reaches this select,
// as it is simulated by closing toHandler channel.
// So msg can be either Chunk or Error.
case msg, ok := <-request.toHandler:
if !ok {
return nil, ErrStreamIsClosed
}
if request.isChunk(msg) {
if result, isByte := msg.Payload[0].([]byte); isByte {
return result, nil
}
return nil, ErrBadPayload
}
// Error message
if len(msg.Payload) == 0 {
return nil, ErrMalformedErrorMessage
}
var perr struct {
CodeInfo [2]int
Message string
}
if err := convertPayload(msg.Payload, &perr); err != nil {
return nil, err
}
return nil, &ErrRequest{
Message: perr.Message,
Category: perr.CodeInfo[0],
Code: perr.CodeInfo[1],
}
case <-ctx.Done():
return nil, ctx.Err()
}
}
func (request *request) push(msg *Message) {
request.fromWorker <- msg
}
func (request *request) Close() {
close(request.closed)
}
type response struct {
handlerProtocolGenerator
session uint64
toWorker asyncSender
closed bool
}
func newResponse(h handlerProtocolGenerator, session uint64, toWorker asyncSender) *response {
response := &response{
handlerProtocolGenerator: h,
session: session,
toWorker: toWorker,
closed: false,
}
return response
}
// Write sends chunk of data to a client.
// It copies data to follow io.Writer rule about not retaining a buffer
func (r *response) Write(data []byte) (n int, err error) {
// According to io.Writer spec
// I must not retain provided []byte
var cpy = append([]byte(nil), data...)
if err := r.ZeroCopyWrite(cpy); err != nil {
return 0, err
}
return len(data), nil
}
// ZeroCopyWrite sends data to a client.
// Response takes the ownership of the buffer, so provided buffer must not be edited.
func (r *response) ZeroCopyWrite(data []byte) error {
if r.isClosed() {
return io.ErrClosedPipe
}
r.toWorker.Send(r.newChunk(r.session, data))
return nil
}
// Notify a client about finishing the datastream.
func (r *response) Close() error {
if r.isClosed() {
// we treat it as a network connection
return syscall.EINVAL
}
r.close()
r.toWorker.Send(r.newChoke(r.session))
return nil
}
// Send error to a client. Specify code and message, which describes this error.
func (r *response) ErrorMsg(code int, message string) error {
if r.isClosed() {
return io.ErrClosedPipe
}
r.close()
r.toWorker.Send(r.newError(
// current session number
r.session,
// category
cworkererrorcategory,
// error code
code,
// error message
message,
))
return nil
}
func (r *response) close() {
r.closed = true
}
func (r *response) isClosed() bool {
return r.closed
}
func loop(input <-chan *Message, output chan *Message, onclose <-chan struct{}) {
defer close(output)
var (
pending []*Message
closed = onclose
)
for {
var (
out chan *Message
first *Message
)
if len(pending) > 0 {
// if we have data to send,
// pick the first element from the queue
// and unlock `out case` in select
// Othrewise `out` is nil
first = pending[0]
out = output
} else if closed == nil {
// Pending queue is empty
// and there will be no incoming data
// as request is closed
return
}
select {
case incoming := <-input:
pending = append(pending, incoming)
case out <- first:
// help GC a bit
pending[0] = nil
// it should be done
// without memory copy/allocate
pending = pending[1:]
case <-closed:
// It will be triggered on
// the next iteration as closed is closed
closed = nil
}
}
}