hasura/graphql-engine · error · BuildRequestError

Serialization error: {0}

Error message

Serialization error: {0}

What it means

A generic serde_json serialization failure while producing the request payload for the pre-NDC-response plugin (#[from] serde_json::Error). The response object could not be turned into JSON at all — non-string map keys, a broken Serialize impl, or non-representable values. Distinct from PluginRequestParseError which covers parsing the plugin's reply.

Source

Thrown at v3/crates/plugins/pre-ndc-response-plugin/src/execute.rs:59

    InvalidHeaderName {
        header_name: String,
        #[source]
        error: InvalidHeaderName,
    },
    #[error("Invalid header value for header {header_name}: {error}")]
    InvalidHeaderValue {
        header_name: HeaderName,
        #[source]
        error: InvalidHeaderValue,
    },
    #[error("Failed to convert session: {0}")]
    SessionConversionError(String),
    #[error("Failed to convert session variable '{variable_name}': {error}")]
    SessionVariableConversionError {
        variable_name: SessionVariableName,
        error: serde_json::Error,
    },
    #[error("Serialization error: {0}")]
    SerializationError(#[from] serde_json::Error),
}

impl TraceableError for Error {
    fn visibility(&self) -> ErrorVisibility {
        match self {
            Error::BuildRequestError(_, _) => ErrorVisibility::Internal,
            Error::PluginUserError { .. }
            | Error::ReqwestError(_)
            | Error::PluginRequestParseError(_)
            | Error::ErrorWhileMakingHTTPRequestToTheHook(_, _)
            | Error::UnexpectedStatusCode(_)
            | Error::PluginInternalError { .. } => ErrorVisibility::User,
        }
    }
}

/// Operation type determines the request and response types that are expected in the payload and optionally the response

View on GitHub (pinned to 724551b9ae)

Solutions

1. Log the payload being serialized to find the offending field
2. Ensure map keys are strings and all values are JSON-representable
3. Fix or simplify custom Serialize implementations
4. Rebuild engine and plugins from the same release so schemas match

serde_json::to_value(&sample_payload)?; // catch serialization issues in tests

match serde_json::to_value(&payload) {
    Ok(v) => v,
    Err(e) => return Err(Error::SerializationError(e)),
}

When it happens

Trigger: serde_json serialization of the outgoing hook request fails, e.g. a BTreeMap with non-string keys or a custom Serialize implementation returning an error.

Common situations: Custom plugin/connector code extending the response with non-JSON types; version skew between engine and plugin crates changing the payload schema.

Related errors

• Serialization error: {0}
• Error parsing the request: {0}
• Error parsing the request: {0}
• Error parsing the engine response: {0}
• Error serializing the modified response: {0}

AI-assisted analysis of hasura/graphql-engine@724551b9ae (2026-08-28). Data as JSON: /api/errors/3e39568f80b3ddd2. Report an issue: GitHub.