Streams (#47)

* Streams Service (WIP)

* Complete Streams Service

streams/handler/list_messages.go

@@ -0,0 +1,45 @@
+package handler
+
+import (
+	"context"
+
+	"github.com/micro/micro/v3/service/errors"
+	"github.com/micro/micro/v3/service/logger"
+	pb "github.com/micro/services/streams/proto"
+)
+
+const DefaultLimit = 25
+
+// List the messages within a conversation in reverse chronological order, using sent_before to
+// offset as older messages need to be loaded
+func (s *Streams) ListMessages(ctx context.Context, req *pb.ListMessagesRequest, rsp *pb.ListMessagesResponse) error {
+	// validate the request
+	if len(req.ConversationId) == 0 {
+		return ErrMissingConversationID
+	}
+
+	// construct the query
+	q := s.DB.Where(&Message{ConversationID: req.ConversationId}).Order("sent_at DESC")
+	if req.SentBefore != nil {
+		q = q.Where("sent_at < ?", req.SentBefore.AsTime())
+	}
+	if req.Limit != nil {
+		q.Limit(int(req.Limit.Value))
+	} else {
+		q.Limit(DefaultLimit)
+	}
+
+	// execute the query
+	var msgs []Message
+	if err := q.Find(&msgs).Error; err != nil {
+		logger.Errorf("Error reading messages: %v", err)
+		return errors.InternalServerError("DATABASE_ERROR", "Error connecting to database")
+	}
+
+	// serialize the response
+	rsp.Messages = make([]*pb.Message, len(msgs))
+	for i, m := range msgs {
+		rsp.Messages[i] = m.Serialize()
+	}
+	return nil
+}