feat: add util function to split long message (#184)

* feat: add util function to split long message

* fix: move util to message/message.go to avoid import cycle

* fix: review opinions and add test

client/group_msg.go

@@ -49,7 +49,7 @@ func (c *QQClient) SendGroupMessage(groupCode int64, m *message.SendingMessage,
 		}
 	}
 	msgLen := message.EstimateLength(m.Elements)
-	if msgLen > 5000 || imgCount > 50 {
+	if msgLen > message.MaxMessageSize || imgCount > 50 {
 		return nil
 	}
 	if !useFram && (msgLen > 100 || imgCount > 2) {

client/private_msg.go

@@ -26,7 +26,7 @@ func (c *QQClient) SendPrivateMessage(target int64, m *message.SendingMessage) *
 		}
 	}
 	msgLen := message.EstimateLength(m.Elements)
-	if msgLen > 5000 || imgCount > 50 {
+	if msgLen > message.MaxMessageSize || imgCount > 50 {
 		return nil
 	}
 	if frag && (msgLen > 300 || imgCount > 2) {

message/message.go

@@ -203,6 +203,9 @@ func (msg *SendingMessage) ToFragmented() [][]IMessageElement {
 	return fragmented
 }
 
+// 单条消息发送的大小限制（预估）
+const MaxMessageSize = 5000
+
 func EstimateLength(elems []IMessageElement) int {
 	sum := 0
 	for _, elem := range elems {
@@ -624,3 +627,161 @@ func FaceNameById(id int) string {
 	}
 	return "未知表情"
 }
+
+// SplitLongMessage 将过长的消息分割为若干个适合发送的消息
+func SplitLongMessage(sendingMessage *SendingMessage) []*SendingMessage {
+	// 合并连续文本消息
+	sendingMessage = mergeContinuousTextMessages(sendingMessage)
+
+	// 分割过长元素
+	sendingMessage = splitElements(sendingMessage)
+
+	// 将元素分为多组，确保各组不超过单条消息的上限
+	splitMessages := splitMessages(sendingMessage)
+
+	return splitMessages
+}
+
+// mergeContinuousTextMessages 预先将所有连续的文本消息合并为到一起，方便后续统一切割
+func mergeContinuousTextMessages(sendingMessage *SendingMessage) *SendingMessage {
+	// 检查下是否有连续的文本消息，若没有，则可以直接返回
+	lastIsText := false
+	hasContinuousText := false
+	for _, message := range sendingMessage.Elements {
+		if message.Type() == Text {
+			if lastIsText {
+				// 有连续的文本消息，需要进行处理
+				hasContinuousText = true
+				break
+			}
+
+			// 遇到文本元素先存放起来，方便将连续的文本元素合并
+			lastIsText = true
+			continue
+		} else {
+			lastIsText = false
+		}
+	}
+	if !hasContinuousText {
+		return sendingMessage
+	}
+
+	// 存在连续的文本消息，需要进行合并处理
+	textBuffer := strings.Builder{}
+	lastIsText = false
+	totalMessageCount := 0
+	for _, message := range sendingMessage.Elements {
+		if msgVal, ok := message.(*TextElement); ok {
+			// 遇到文本元素先存放起来，方便将连续的文本元素合并
+			textBuffer.WriteString(msgVal.Content)
+			lastIsText = true
+			continue
+		}
+
+		// 如果之前的是文本元素（可能是多个合并起来的），则在这里将其实际放入消息中
+		if lastIsText {
+			sendingMessage.Elements[totalMessageCount] = NewText(textBuffer.String())
+			totalMessageCount += 1
+			textBuffer.Reset()
+		}
+		lastIsText = false
+
+		// 非文本元素则直接处理
+		sendingMessage.Elements[totalMessageCount] = message
+		totalMessageCount += 1
+	}
+	// 处理最后几个元素是文本的情况
+	if textBuffer.Len() != 0 {
+		sendingMessage.Elements[totalMessageCount] = NewText(textBuffer.String())
+		totalMessageCount += 1
+		textBuffer.Reset()
+	}
+	sendingMessage.Elements = sendingMessage.Elements[:totalMessageCount]
+
+	return sendingMessage
+}
+
+// splitElements 将原有消息的各个元素先尝试处理，如过长的文本消息按需分割为多个元素
+func splitElements(sendingMessage *SendingMessage) *SendingMessage {
+	// 检查下是否存在需要文本消息，若不存在，则直接返回
+	needSplit := false
+	for _, message := range sendingMessage.Elements {
+		if msgVal, ok := message.(*TextElement); ok {
+			if textNeedSplit(msgVal.Content) {
+				needSplit = true
+				break
+			}
+		}
+	}
+	if !needSplit {
+		return sendingMessage
+	}
+
+	// 开始尝试切割
+	messageParts := NewSendingMessage()
+
+	for _, message := range sendingMessage.Elements {
+		switch msgVal := message.(type) {
+		case *TextElement:
+			messageParts.Elements = append(messageParts.Elements, splitPlainMessage(msgVal.Content)...)
+		default:
+			messageParts.Append(message)
+		}
+	}
+
+	return messageParts
+}
+
+// splitMessages 根据大小分为多个消息进行发送
+func splitMessages(sendingMessage *SendingMessage) []*SendingMessage {
+	var splitMessages []*SendingMessage
+
+	messagePart := NewSendingMessage()
+	msgSize := 0
+	for _, part := range sendingMessage.Elements {
+		estimateSize := EstimateLength([]IMessageElement{part})
+		// 若当前分消息加上新的元素后大小会超限，且已经有元素（确保不会无限循环），则开始切分为新的一个元素
+		if msgSize+estimateSize > MaxMessageSize && len(messagePart.Elements) > 0 {
+			splitMessages = append(splitMessages, messagePart)
+
+			messagePart = NewSendingMessage()
+			msgSize = 0
+		}
+
+		// 加上新的元素
+		messagePart.Append(part)
+		msgSize += estimateSize
+	}
+	// 将最后一个分片加上
+	if len(messagePart.Elements) != 0 {
+		splitMessages = append(splitMessages, messagePart)
+	}
+
+	return splitMessages
+}
+
+func splitPlainMessage(content string) []IMessageElement {
+	if !textNeedSplit(content) {
+		return []IMessageElement{NewText(content)}
+	}
+
+	splittedMessage := make([]IMessageElement, 0, (len(content)+MaxMessageSize-1)/MaxMessageSize)
+
+	last := 0
+	for runeIndex, runeValue := range content {
+		// 如果加上新的这个字符后，会超出大小，则从这个字符前分一次片
+		if runeIndex+len(string(runeValue))-last > MaxMessageSize {
+			splittedMessage = append(splittedMessage, NewText(content[last:runeIndex]))
+			last = runeIndex
+		}
+	}
+	if last != len(content) {
+		splittedMessage = append(splittedMessage, NewText(content[last:len(content)]))
+	}
+
+	return splittedMessage
+}
+
+func textNeedSplit(content string) bool {
+	return len(content) > MaxMessageSize
+}

message/message_test.go

@@ -0,0 +1,36 @@
+package message
+
+import (
+	"strings"
+	"testing"
+)
+
+func Test_mergeContinuousTextMessages(t *testing.T) {
+	msg := NewSendingMessage()
+	msg.Append(NewText("短片段一"))
+	msg.Append(NewText(strings.Repeat("长一", 800))) // 6*800
+	msg.Append(NewText("短片段二"))
+	msg.Append(NewText(strings.Repeat("长二", 1200))) // 6*1200
+	msg.Append(NewText("短片段三"))
+
+	// 总长度为 12036
+	totalSize := EstimateLength(msg.Elements)
+	expectedPart := (totalSize + MaxMessageSize - 1) / MaxMessageSize
+
+	messages := SplitLongMessage(msg)
+	// 应分为 3段
+	if len(messages) != expectedPart {
+		t.Errorf("should split into %v part", expectedPart)
+	}
+	partsSize := 0
+	for idx, message := range messages {
+		partSize := EstimateLength(message.Elements)
+		if partSize > MaxMessageSize {
+			t.Errorf("part %v size=%v is more than %v", idx, partSize, MaxMessageSize)
+		}
+		partsSize += partSize
+	}
+	if partsSize != totalSize {
+		t.Errorf("parts size sum=%v is not equal to total size=%v", partsSize, totalSize)
+	}
+}