Initial commit

.gitignore

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+.idea/
+*.iml

LICENSE

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+                                 Apache License
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+
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+      "Contribution" shall mean any work of authorship, including
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+      on behalf of whom a Contribution has been received by Licensor and
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+      Contribution(s) alone or by combination of their Contribution(s)
+      with the Work to which such Contribution(s) was submitted. If You
+      institute patent litigation against any entity (including a
+      cross-claim or counterclaim in a lawsuit) alleging that the Work
+      or a Contribution incorporated within the Work constitutes direct
+      or contributory patent infringement, then any patent licenses
+      granted to You under this License for that Work shall terminate
+      as of the date such litigation is filed.
+
+   4. Redistribution. You may reproduce and distribute copies of the
+      Work or Derivative Works thereof in any medium, with or without
+      modifications, and in Source or Object form, provided that You
+      meet the following conditions:
+
+      (a) You must give any other recipients of the Work or
+          Derivative Works a copy of this License; and
+
+      (b) You must cause any modified files to carry prominent notices
+          stating that You changed the files; and
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+          notices within Derivative Works that You distribute, alongside
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+      reproduction, and distribution of the Work otherwise complies with
+      the conditions stated in this License.
+
+   5. Submission of Contributions. Unless You explicitly state otherwise,
+      any Contribution intentionally submitted for inclusion in the Work
+      by You to the Licensor shall be under the terms and conditions of
+      this License, without any additional terms or conditions.
+      Notwithstanding the above, nothing herein shall supersede or modify
+      the terms of any separate license agreement you may have executed
+      with Licensor regarding such Contributions.
+
+   6. Trademarks. This License does not grant permission to use the trade
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+   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.

go.mod

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+module heckel.io/notifyme
+
+go 1.16

main.go

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+package main
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"io"
+	"log"
+	"math/rand"
+	"net/http"
+	"sync"
+	"time"
+)
+
+type Message struct {
+	Time int64 `json:"time"`
+	Message string `json:"message"`
+}
+
+type Channel struct {
+	id string
+	listeners map[int]listener
+	last time.Time
+	ctx context.Context
+	mu sync.Mutex
+}
+
+type Server struct {
+	channels map[string]*Channel
+	mu sync.Mutex
+}
+
+type listener func(msg *Message)
+
+func main() {
+	s := &Server{
+		channels: make(map[string]*Channel),
+	}
+	go func() {
+		for {
+			time.Sleep(5 * time.Second)
+			s.mu.Lock()
+			log.Printf("channels: %d", len(s.channels))
+			s.mu.Unlock()
+		}
+	}()
+	http.HandleFunc("/", s.handle)
+	if err := http.ListenAndServe(":9997", nil); err != nil {
+		log.Fatalln(err)
+	}
+}
+
+func (s *Server) handle(w http.ResponseWriter, r *http.Request) {
+	if err := s.handleInternal(w, r); err != nil {
+		w.WriteHeader(http.StatusInternalServerError)
+		_, _ = io.WriteString(w, err.Error())
+	}
+}
+
+func (s *Server) handleInternal(w http.ResponseWriter, r *http.Request) error {
+	if len(r.URL.Path) == 0 {
+		return errors.New("invalid path")
+	}
+	channel := s.channel(r.URL.Path[1:])
+	switch r.Method {
+	case http.MethodGet:
+		return s.handleGET(w, r, channel)
+	case http.MethodPut:
+		return s.handlePUT(w, r, channel)
+	default:
+		return errors.New("invalid method")
+	}
+}
+
+func (s *Server) handleGET(w http.ResponseWriter, r *http.Request, ch *Channel) error {
+	fl, ok := w.(http.Flusher)
+	if !ok {
+		return errors.New("not a flusher")
+	}
+	listenerID := rand.Int()
+	l := func (msg *Message) {
+		json.NewEncoder(w).Encode(&msg)
+		fl.Flush()
+	}
+	ch.mu.Lock()
+	ch.listeners[listenerID] = l
+	ch.last = time.Now()
+	ch.mu.Unlock()
+	select {
+	case <-ch.ctx.Done():
+	case <-r.Context().Done():
+	}
+	ch.mu.Lock()
+	delete(ch.listeners, listenerID)
+	if len(ch.listeners) == 0 {
+		s.mu.Lock()
+		delete(s.channels, ch.id)
+		s.mu.Unlock()
+	}
+	ch.mu.Unlock()
+	return nil
+}
+
+func (s *Server) handlePUT(w http.ResponseWriter, r *http.Request, ch *Channel) error {
+	ch.mu.Lock()
+	defer ch.mu.Unlock()
+	if len(ch.listeners) == 0 {
+		return errors.New("no listeners")
+	}
+	defer r.Body.Close()
+	ch.last = time.Now()
+	msg, _ := io.ReadAll(r.Body)
+	for _, l := range ch.listeners {
+		l(&Message{
+			Time:    time.Now().UnixMilli(),
+			Message: string(msg),
+		})
+	}
+	return nil
+}
+
+func (s *Server) channel(channelID string) *Channel {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	c, ok := s.channels[channelID]
+	if !ok {
+		ctx, _ := context.WithCancel(context.Background()) // FIXME
+		c = &Channel{
+			id:        channelID,
+			listeners: make(map[int]listener),
+			last:      time.Now(),
+			ctx:       ctx,
+			mu:        sync.Mutex{},
+		}
+		s.channels[channelID] = c
+	}
+	return c
+}