Streams (#47)

* Streams Service (WIP)

* Complete Streams Service

streams/handler/recent_messages.go

@@ -0,0 +1,49 @@
+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"
+	"gorm.io/gorm"
+)
+
+// RecentMessages returns the most recent messages in a group of conversations. By default the
+// most messages retrieved per conversation is 25, however this can be overriden using the
+// limit_per_conversation option
+func (s *Streams) RecentMessages(ctx context.Context, req *pb.RecentMessagesRequest, rsp *pb.RecentMessagesResponse) error {
+	// validate the request
+	if len(req.ConversationIds) == 0 {
+		return ErrMissingConversationIDs
+	}
+
+	limit := DefaultLimit
+	if req.LimitPerConversation != nil {
+		limit = int(req.LimitPerConversation.Value)
+	}
+
+	// query the database
+	var msgs []Message
+	err := s.DB.Transaction(func(tx *gorm.DB) error {
+		for _, id := range req.ConversationIds {
+			var cms []Message
+			if err := tx.Where(&Message{ConversationID: id}).Order("sent_at DESC").Limit(limit).Find(&cms).Error; err != nil {
+				return err
+			}
+			msgs = append(msgs, cms...)
+		}
+		return nil
+	})
+	if 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
+}