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The history api allows to retrieve any number of messages stored in a channel. As the number of messages that can be returned in a single response is limited by the size of a response (as per #413), a system of pagination is required. This system is implemented with the introduction of the StartFromID query parameter. An client that already received a response with a certain number of messages can send a new request to the API with the StartFromID set to the ID of the oldest message it received (first in the array). The storage query will then begin to retrieve messages starting at the ID preceding the ID provided in the query, to generate the next page of messages.
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,95 @@ | ||
| /********************************************************************************** | ||
| * Copyright (c) 2009-2020 Misakai Ltd. | ||
| * This program is free software: you can redistribute it and/or modify it under the | ||
| * terms of the GNU Affero General Public License as published by the Free Software | ||
| * Foundation, either version 3 of the License, or(at your option) any later version. | ||
| * | ||
| * This program is distributed in the hope that it will be useful, but WITHOUT ANY | ||
| * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A | ||
| * PARTICULAR PURPOSE. See the GNU Affero General Public License for more details. | ||
| * | ||
| * You should have received a copy of the GNU Affero General Public License along | ||
| * with this program. If not, see<http://www.gnu.org/licenses/>. | ||
| ************************************************************************************/ | ||
|
|
||
| package history | ||
|
|
||
| import ( | ||
| "encoding/json" | ||
|
|
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| "github.com/emitter-io/emitter/internal/errors" | ||
| "github.com/emitter-io/emitter/internal/message" | ||
| "github.com/emitter-io/emitter/internal/provider/logging" | ||
| "github.com/emitter-io/emitter/internal/security" | ||
| "github.com/emitter-io/emitter/internal/service" | ||
| ) | ||
|
|
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| // Request represents a historical messages request. | ||
| type Request struct { | ||
| Key string `json:"key"` // The channel key for this request. | ||
| Channel string `json:"channel"` // The target channel for this request. | ||
| StartFromID message.ID `json:"startFromID,omitempty"` | ||
| } | ||
|
|
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| type Message struct { | ||
| ID message.ID `json:"id"` | ||
| Topic string `json:"topic"` // The channel of the message | ||
| Payload string `json:"payload"` // The payload of the message | ||
| } | ||
| type Response struct { | ||
| Request uint16 `json:"req,omitempty"` // The corresponding request ID. | ||
| Messages []Message `json:"messages"` // The history of messages. | ||
| } | ||
|
|
||
| // ForRequest sets the request ID in the response for matching | ||
| func (r *Response) ForRequest(id uint16) { | ||
| r.Request = id | ||
| } | ||
|
|
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| // OnRequest handles a request of historical messages. | ||
| func (s *Service) OnRequest(c service.Conn, payload []byte) (service.Response, bool) { | ||
| var request Request | ||
| if err := json.Unmarshal(payload, &request); err != nil { | ||
| return errors.ErrBadRequest, false | ||
| } | ||
|
|
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| channel := security.ParseChannel([]byte(request.Channel)) | ||
| if channel.ChannelType == security.ChannelInvalid { | ||
| return errors.ErrBadRequest, false | ||
| } | ||
|
|
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| // Check the authorization and permissions | ||
| _, key, allowed := s.auth.Authorize(channel, security.AllowLoad) | ||
| if !allowed { | ||
| return errors.ErrUnauthorized, false | ||
| } | ||
|
|
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| // Use limit = 1 if not specified, otherwise use the limit option. The limit now | ||
| // defaults to one as per MQTT spec we always need to send retained messages. | ||
| limit := int64(1) | ||
| if v, ok := channel.Last(); ok { | ||
| limit = v | ||
| } | ||
|
|
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| ssid := message.NewSsid(key.Contract(), channel.Query) | ||
| t0, t1 := channel.Window() // Get the window | ||
|
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| msgs, err := s.store.Query(ssid, t0, t1, request.StartFromID, int(limit)) | ||
| if err != nil { | ||
| logging.LogError("conn", "query last messages", err) | ||
| return errors.ErrServerError, false | ||
| } | ||
|
|
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| resp := &Response{ | ||
| Messages: make([]Message, 0, len(msgs)), | ||
| } | ||
| for _, m := range msgs { | ||
| msg := m | ||
| resp.Messages = append(resp.Messages, Message{ | ||
| ID: msg.ID, | ||
| Topic: string(msg.Channel), // The channel for this message. | ||
| Payload: string(msg.Payload), // The payload for this message. | ||
| }) | ||
| } | ||
| return resp, true | ||
| } |
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