nikivdev/code · error

failed to decode json bytes: {err}

Error message

failed to decode json bytes: {err}

What it means

parse_json_bytes_in_place's fallback path uses serde_json::from_slice when simd-json is unavailable for the target/features. Decode failures are wrapped as "failed to decode json bytes: {err}" with the serde_json error detail.

Source

Thrown at src/json_parse.rs:45

#[inline]
pub fn parse_json_bytes_in_place<T: DeserializeOwned>(bytes: &mut [u8]) -> Result<T> {
    #[cfg(all(
        feature = "linux-host-simd-json",
        target_os = "linux",
        any(target_arch = "x86_64", target_arch = "aarch64")
    ))]
    {
        return simd_json::serde::from_slice(bytes)
            .map_err(|err| anyhow!("failed to decode json bytes with simd-json: {err}"));
    }

    #[cfg(not(all(
        feature = "linux-host-simd-json",
        target_os = "linux",
        any(target_arch = "x86_64", target_arch = "aarch64")
    )))]
    {
        serde_json::from_slice(bytes).map_err(|err| anyhow!("failed to decode json bytes: {err}"))
    }
}

View on GitHub (pinned to a747e741ae)

Solutions

1. Read the wrapped serde_json error for the exact position and cause
2. Verify the buffer holds one complete JSON value with no trailing garbage
3. Update the target struct to match the current producer schema
4. If input may have a BOM, strip it before parsing

Example fix

// before
let v: Event = parse_json_bytes_in_place(bytes)?;
// after
let bytes = bytes.strip_prefix(b"\xef\xbb\xbf").unwrap_or(bytes);
let v: Event = parse_json_bytes_in_place(bytes)?;

fn is_complete_json_bytes(bytes: &[u8]) -> bool {
    serde_json::from_slice::<serde_json::Value>(bytes).is_ok()
}

match parse_json_bytes_in_place::<Event>(bytes) {
    Ok(v) => handle(v),
    Err(e) => {
        eprintln!("bad json bytes: {e:#}");
        // quarantine bytes for inspection
    }
}

When it happens

Trigger: Malformed or schema-incompatible JSON bytes passed to parse_json_bytes_in_place on non-simd builds (non-Linux, non-x86_64/aarch64, or feature disabled).

Common situations: Truncated file reads; extra whitespace/BOM at the start; producer schema changed (renamed fields, different types) while consumer struct is stale.

Understand the failure class

• Parsing and encoding errors: unexpected token, malformed input — why parsers reject input and how to find the real culprit.

Related errors

• failed to decode json line: {err}
• failed to decode json bytes with simd-json: {err}
• failed to decode json line with simd-json: {err}
• 'codanna mcp get_index_info' failed: {}

AI-assisted analysis of nikivdev/code@a747e741ae (2026-09-01). Data as JSON: /api/errors/765a4016d37354ba. Report an issue: GitHub.