tauri-apps/tauri · error · Error

unexpected channel value $channelDef

Error message

unexpected channel value $channelDef

What it means

The Android ChannelDeserializer strips the channel prefix from the incoming channel definition string and parses the remainder as a Long callback ID. If the remainder is not a valid Long, it throws this Error with the offending string embedded. This means the webview sent a channel value in an unexpected format.

Solutions

1. Verify the channel definition string logged in the error and ensure it contains a numeric ID after the channel prefix.
2. Keep the Tauri Android runtime and Rust core versions in sync so the channel wire format matches.
3. Replace any hand-built channel identifiers in plugin code with channels created via the official Channel/IPC APIs.
4. Clear app state and reload the webview to rule out a stale cached message after an app update.

Example fix

// before: hand-rolled channel string
window.__TAURI_INTERNALS__.invoke('cmd', { ch: '__CHANNEL__:' + arbitraryText })
// after: use a real channel object
const ch = new Channel((data) => console.log(data))
invoke('cmd', { ch })

fun isValidChannelDef(def: String) = def.removePrefix(CHANNEL_PREFIX).toLongOrNull() != null

try {
  channelManager.deserialize(json)
} catch (e: Error) {
  if (e.message?.startsWith("unexpected channel value") == true) {
    // resync versions / re-register channel
  }
}

When it happens

Trigger: deserialize() receives a JSON string whose content after the CHANNEL_PREFIX is null/blank/non-numeric, or exceeds Long range, so toLongOrNull() returns null.

Common situations: Rust/JS and Android plugin versions disagree on the channel serialization format, hand-constructed channel strings from custom plugin code, or corrupted IPC messages after a hot reload of the webview.

Understand the failure class

Background: "Invalid ... format", "must be in format X", "does not look like a ..." — invalid argument format errors across CLI tools and libraries — this error's family across 17 libraries.

Related errors

• Invalid channel ID from \(channelDef)
• No command found for plugin
• Not all items are instances of the given type
• Invalid channel definition from \(channelDef)
• the plugin manager has no activity to launch from

AI-assisted analysis of tauri-apps/tauri@460ec35447 (2026-09-18). Data as JSON: /api/errors/bb95e4889190a406. Report an issue: GitHub.

Appendix: source

Thrown at crates/tauri/mobile/android/src/main/java/app/tauri/plugin/Channel.kt:20

// SPDX-License-Identifier: Apache-2.0
// SPDX-License-Identifier: MIT

package app.tauri.plugin

import com.fasterxml.jackson.core.JsonParser
import com.fasterxml.jackson.databind.DeserializationContext
import com.fasterxml.jackson.databind.JsonDeserializer
import com.fasterxml.jackson.databind.ObjectMapper

const val CHANNEL_PREFIX = "__CHANNEL__:"

internal class ChannelDeserializer(val sendChannelData: (channelId: Long, data: String) -> Unit, private val objectMapper: ObjectMapper): JsonDeserializer<Channel>() {
  override fun deserialize(
    jsonParser: JsonParser?,
    deserializationContext: DeserializationContext
  ): Channel {
    val channelDef = deserializationContext.readValue(jsonParser, String::class.java)
    val callback = channelDef.substring(CHANNEL_PREFIX.length).toLongOrNull() ?: throw Error("unexpected channel value $channelDef")
    return Channel(callback, { res -> sendChannelData(callback, res) }, objectMapper)
  }
}

class Channel(val id: Long, private val handler: (data: String) -> Unit, private val objectMapper: ObjectMapper) {
  fun send(data: JSObject) {
    handler(PluginResult(data).toString())
  }

  fun sendObject(data: Any) {
    handler(objectMapper.writeValueAsString(data))
  }
}

View on GitHub (pinned to 460ec35447)