Pumpkin-MC/Pumpkin · error · WritingError

Serde failure

Error message

Serde failure: {0}

What it means

WritingError::Serde(String) is the serde::ser::Error::custom implementation for the protocol's writer. It is raised when serializing a packet's fields fails semantically — the serializer refuses to encode a value (e.g. a string too long to be length-prefixed, a value violating the format's invariants) rather than failing on IO.

Solutions

1. Read the embedded message to find which field failed to serialize.
2. Validate packet field contents (string byte lengths, value ranges) before constructing the packet.
3. Truncate or split payloads exceeding protocol limits (e.g. long chat/component JSON).
4. Check custom Serialize impls for bugs introduced by your own packet types.

Example fix

// before: sending an arbitrarily long custom payload
let p = Packet::new(CustomChannel, plugin_data);

// after: enforce the protocol's length cap first
let data = if plugin_data.len() > MAX_PAYLOAD { &plugin_data[..MAX_PAYLOAD] } else { plugin_data };
let p = Packet::new(CustomChannel, data);

// check string sizes against the protocol's VarInt length cap before building the packet
fn fits_length_prefix(s: &str, max: usize) -> bool { s.len() <= max }
assert!(fits_length_prefix(&payload, 32767), "payload too long for packet");

match packet.write(&mut stream).await {
    Err(WritingError::Serde(msg)) => {
        error!("packet field failed to serialize: {msg}");
        // fix or drop the offending packet, keep the connection alive
    }
    other => /* ... */,
}

When it happens

Trigger: Serializing any packet via the serde writer when a field cannot be encoded: calls to WritingError::custom from Serialize impls or the length-checked encoders (strings whose byte length exceeds what a VarInt prefix allows, invalid identifiers, etc.).

Common situations: Plugins/custom code putting oversized or malformed data into a packet body; building a TextComponent that serializes to JSON too large; constructing packets manually with values the wire format cannot represent.

Understand the failure class

Background: "JSON serialization failed", "not JSON serializable", "Failed to serialize": why JSON marshaling errors happen and how to fix them — this error's family across 46 libraries.

Related errors

• Failed to serialize packet
• {0}
• JSON parse error
• Invalid slot
• Player ' ' tried to interact with a closed container

AI-assisted analysis of Pumpkin-MC/Pumpkin@8d4639e25a (2026-09-09). Data as JSON: /api/errors/f8cb49ca56debe44. Report an issue: GitHub.

Appendix: source

Thrown at crates/pumpkin-protocol/src/ser/mod.rs:41

    #[error("incomplete: {0}")]
    Incomplete(String),
    #[error("too large: {0}")]
    TooLarge(String),
    #[error("{0}")]
    Message(String),
}

impl serde::de::Error for ReadingError {
    fn custom<T: std::fmt::Display>(msg: T) -> Self {
        Self::Message(msg.to_string())
    }
}

#[derive(Debug, Error)]
pub enum WritingError {
    #[error("IO error: {0}")]
    IoError(#[from] std::io::Error),
    #[error("Serde failure: {0}")]
    Serde(String),
    #[error("Packet is not supported in Minecraft version {0:?}")]
    UnsupportedVersion(JavaMinecraftVersion),
    #[error("Failed to serialize packet: {0}")]
    Message(String),
}

impl serde::ser::Error for WritingError {
    fn custom<T: std::fmt::Display>(msg: T) -> Self {
        Self::Serde(msg.to_string())
    }
}

struct NetworkReadDataSource<'a, R: NetworkReadExt + ?Sized>(&'a mut R);

impl<'a, R: NetworkReadExt + ?Sized> pumpkin_nbt::deserializer::NbtDataSource<'a>
    for NetworkReadDataSource<'a, R>
{

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