feat: auto-format JSON display everywhere

- Shared prettyJson/truncate/isJson utility in src/utils/format.ts
- MessageStream: collapsed preview + expanded view both auto-format JSON
- LogPanel: log details with JSON content auto-formatted
- PresetList: payload preview auto-formatted
- Deduplicated isJson/formatPayload logic

src/components/dashboard/LogPanel.vue

@@ -2,6 +2,7 @@
 import { ref, computed, watch, nextTick } from 'vue'
 import { useLogs } from '../../stores/useLogs'
 import { mqttGetLogDir } from '../../stores/useMqttBridge'
+import { prettyJson } from '../../utils/format'
 import { ElMessage } from 'element-plus'
 
 const { logs, clear } = useLogs()
@@ -121,7 +122,7 @@ function eventIcon(event: string): string {
           <span v-if="log.details" class="log-dtl-btn" @click="toggleDetails(log.id)">{{ expandedDetails.has(log.id) ? '收起' : '详情' }}</span>
         </div>
         <div v-if="log.details && expandedDetails.has(log.id)" class="log-dtl-content">
-          {{ log.details }}
+          {{ prettyJson(log.details) }}
         </div>
       </div>
     </div>

src/components/dashboard/MessageStream.vue

@@ -1,6 +1,7 @@
 <script setup lang="ts">
 import { ref, watch, nextTick } from 'vue'
 import type { MqttMessage } from '../../types/mqtt'
+import { prettyJson, isJson, truncate } from '../../utils/format'
 
 const props = defineProps<{
   messages: MqttMessage[]
@@ -50,11 +51,6 @@ function onScroll() {
 
 // ─── Payload Format Helpers ────────────────────────────────────
 
-function isJson(str: string): boolean {
-  try { JSON.parse(str); return true }
-  catch { return false }
-}
-
 function getEffectiveFormat(msg: MqttMessage): string {
   const fmt = messageFormats.value[msg.id] || 'auto'
   if (fmt === 'auto') return isJson(msg.payload) ? 'json' : 'plain'
@@ -64,18 +60,11 @@ function getEffectiveFormat(msg: MqttMessage): string {
 function formatPayload(msg: MqttMessage): string {
   const fmt = getEffectiveFormat(msg)
   switch (fmt) {
-    case 'json':
-      try {
-        const parsed = JSON.parse(msg.payload)
-        return JSON.stringify(parsed, null, 2)
-      } catch { return msg.payload }
-    case 'hex':
-      return bytesToHex(new TextEncoder().encode(msg.payload))
-    case 'base64':
-      return btoa(msg.payload)
+    case 'json': return prettyJson(msg.payload)
+    case 'hex': return bytesToHex(new TextEncoder().encode(msg.payload))
+    case 'base64': return btoa(msg.payload)
     case 'plain':
-    default:
-      return msg.payload
+    default: return msg.payload
   }
 }
 
@@ -180,7 +169,7 @@ function formatTime(ts: number): string {
           v-if="expandedPayloads.has(msg.id)"
           :class="['payload-full', { 'is-json': getEffectiveFormat(msg) === 'json' }]"
         >{{ formatPayload(msg) }}</pre>
-        <pre v-else class="payload-truncated">{{ msg.payload.substring(0, 200) }}{{ msg.payload.length > 200 ? '...' : '' }}</pre>
+        <pre v-else class="payload-truncated">{{ truncate(prettyJson(msg.payload), 200) }}</pre>
       </div>
     </div>
   </div>

src/components/presets/PresetList.vue

@@ -3,6 +3,7 @@ import { ref } from 'vue'
 import { ElMessage, ElMessageBox } from 'element-plus'
 import type { Preset } from '../../types/mqtt'
 import { usePresets } from '../../stores/usePresets'
+import { prettyJson, truncate } from '../../utils/format'
 import PresetForm from './PresetForm.vue'
 
 // eslint-disable-next-line @typescript-eslint/no-unused-vars
@@ -76,7 +77,7 @@ const qosLabel = (qos: number) => `QoS ${qos}`
       </el-table-column>
       <el-table-column label="Payload 预览" min-width="200">
         <template #default="{ row }">
-          <span class="payload-preview">{{ row.payloadTemplate.substring(0, 50) }}{{ row.payloadTemplate.length > 50 ? '...' : '' }}</span>
+          <span class="payload-preview">{{ truncate(prettyJson(row.payloadTemplate), 50) }}</span>
         </template>
       </el-table-column>
       <el-table-column label="操作" width="160" fixed="right">

src/utils/format.ts

@@ -0,0 +1,33 @@
+/**
+ * Pretty-print a JSON string if it's valid JSON.
+ * Returns the original string if it's not valid JSON.
+ */
+export function prettyJson(str: string): string {
+  if (!str || str.trim() === '') return str
+  try {
+    const parsed = JSON.parse(str)
+    return JSON.stringify(parsed, null, 2)
+  } catch {
+    return str
+  }
+}
+
+/**
+ * Check if a string is valid JSON.
+ */
+export function isJson(str: string): boolean {
+  try {
+    JSON.parse(str)
+    return true
+  } catch {
+    return false
+  }
+}
+
+/**
+ * Truncate a string to a maximum length, adding an ellipsis if truncated.
+ */
+export function truncate(str: string, maxLen: number): string {
+  if (str.length <= maxLen) return str
+  return str.substring(0, maxLen) + '...'
+}