55 lines
1.6 KiB
Go
55 lines
1.6 KiB
Go
package xbee
|
|
import (
|
|
"sync"
|
|
"errors"
|
|
)
|
|
|
|
// A connTrack is a simple frame mark utility for xbee packets. The xbee api frame
|
|
// takes a mark that is used when sending the response - this allows to coordinate
|
|
// the sent packet and the response, since there may be other packets emitted
|
|
// between them.
|
|
type connTrack struct {
|
|
mu sync.RWMutex // use RW mutex to allow for multiple readers
|
|
internal map[uint8]bool // map frame tag to if it's been used.
|
|
// the map is set when writing a frame, and deleted when recieving a matching frame.
|
|
}
|
|
|
|
// GetMark finds the next available marker and takes it, returning the value of
|
|
// the mark. If no mark can be acquired, it returns an error.
|
|
func (ct *connTrack) GetMark() (uint8, error) {
|
|
// get a read lock.
|
|
ct.mu.RLock()
|
|
|
|
// NOTE: we start at one. This is because 0 will not return a frame ever - it's
|
|
// the "silent mode" mark
|
|
for i := 1; i < 256; i++ {
|
|
if !ct.internal[uint8(i)] {
|
|
// it's free.
|
|
// discard our read lock and lock for write.
|
|
ct.mu.RUnlock()
|
|
|
|
ct.mu.Lock()
|
|
// update the value to true.
|
|
ct.internal[uint8(i)] = true
|
|
ct.mu.Unlock()
|
|
return uint8(i), nil
|
|
}
|
|
}
|
|
ct.mu.RUnlock()
|
|
return 0, errors.New("no available marks")
|
|
}
|
|
// ClearMark removes a given mark from the set if it exists, or returns an error.
|
|
func (ct *connTrack) ClearMark(mark uint8) error {
|
|
ct.mu.RLock()
|
|
// FIXME: should this be the other way around (swap if and normal execution
|
|
if ct.internal[mark] {
|
|
ct.mu.RUnlock()
|
|
ct.mu.Lock()
|
|
delete(ct.internal, mark)
|
|
ct.mu.Unlock()
|
|
return nil
|
|
}
|
|
ct.mu.RUnlock()
|
|
return errors.New("mark was not set")
|
|
}
|