Types: Add a new cookie type

Used as a specialized context in state callbacks and for cancellation

1 files changed, 81 insertions, 0 deletions

diff --git a/types/cookie/cookie.go b/types/cookie/cookie.go
new file mode 100644
index 0000000..e1cffca
--- /dev/null
+++ b/types/cookie/cookie.go
@@ -0,0 +1,81 @@
+// package cookie implements a specialized version of a context
+// - It is cancellable
+// - It has a channel associated with it to reply to state callbacks
+// - It can be marshalled by having a cgo Handle attached to it
+package cookie
+
+import (
+	"context"
+	"encoding/json"
+	"runtime/cgo"
+
+	"github.com/go-errors/errors"
+)
+
+type Cookie struct {
+	c         chan string
+	ctx       context.Context
+	ctxCancel context.CancelFunc
+	H         cgo.Handle
+}
+
+// NewWithContext creates a new cookie with a context
+// It stores the cancel and channel inside of the struct
+func NewWithContext(ctx context.Context) Cookie {
+	ctx, cancel := context.WithCancel(ctx)
+	return Cookie{
+		c:         make(chan string),
+		ctx:       ctx,
+		ctxCancel: cancel,
+	}
+}
+
+// MarshalJSON marshals the cookie to JSON
+func (c *Cookie) MarshalJSON() ([]byte, error) {
+	if c.H == 0 {
+		return nil, errors.New("no associated handle found")
+	}
+	return json.Marshal(c.H)
+}
+
+// Receive receives a value from the cookie up until the context is done or errchan gets an error
+// This error chan is used for goroutines to signal errors that we have to exit early
+func (c *Cookie) Receive(errchan chan error) (string, error) {
+	select {
+	case r := <-c.c:
+		return r, nil
+	case e := <-errchan:
+		return "", e
+	case <-c.ctx.Done():
+		return "", errors.WrapPrefix(context.Canceled, "receive cookie", 0)
+	}
+}
+
+// Cancel cancels the cookie by calling the context cancel function
+// It returns an error if no such function exists
+func (c *Cookie) Cancel() error {
+	if c.ctxCancel == nil {
+		return errors.New("no cancel function found")
+	}
+	c.ctxCancel()
+	return nil
+}
+
+// Send sends data to the cookie channel if the context is not canceled
+func (c *Cookie) Send(data string) error {
+	select {
+	case <-c.ctx.Done():
+		return errors.WrapPrefix(context.Canceled, "send cookie", 0)
+	default:
+		if c.c == nil {
+			return errors.New("channel is nil")
+		}
+		c.c <- data
+		return nil
+	}
+}
+
+// Context gets the underlying context of the cookie
+func (c *Cookie) Context() context.Context {
+	return c.ctx
+}