rtk-ai/rtk · error · anyhow::Error

legacy dictionary format is unsupported

Error message

legacy dictionary format is unsupported

What it means

skip_string_dictionary rejects binlog fileFormatVersion < 10, the legacy string-dictionary layout introduced before the modern format. This reader only understands the post-v10 dictionary encoding, so old binlogs fail explicitly.

Source

Thrown at src/cmds/dotnet/binlog.rs:512

    if (file_format_version < 13 && read_importance) || (flags & FLAG_IMPORTANCE != 0) {
        let _ = reader.read_7bit_i32()?;
    }

    Ok(result)
}

fn skip_build_event_context(reader: &mut BinReader<'_>, file_format_version: i32) -> Result<()> {
    let count = if file_format_version > 1 { 7 } else { 6 };
    for _ in 0..count {
        let _ = reader.read_7bit_i32()?;
    }
    Ok(())
}

fn skip_string_dictionary(reader: &mut BinReader<'_>, file_format_version: i32) -> Result<()> {
    if file_format_version < 10 {
        anyhow::bail!("legacy dictionary format is unsupported");
    }

    let _ = reader.read_7bit_i32()?;
    Ok(())
}

fn read_optional_string(
    reader: &mut BinReader<'_>,
    parsed: &ParsedBinlog,
) -> Result<Option<String>> {
    read_deduplicated_string(reader, parsed)
}

fn read_deduplicated_string(
    reader: &mut BinReader<'_>,
    parsed: &ParsedBinlog,
) -> Result<Option<String>> {
    let index = reader.read_7bit_i32()?;

View on GitHub (pinned to 36788f6bd4)

Solutions

1. Regenerate the log with a modern .NET SDK / MSBuild 17 (emits format 18)
2. Do not attempt to parse binlogs older than format 10 with this tool
3. Find a newer artifact, or convert the log via MSBuild Structured Log Viewer then re-export

fn binlog_supports_dictionary(bytes: &[u8]) -> bool {
    if bytes.len() < 12 { return false; }
    i32::from_le_bytes([bytes[8], bytes[9], bytes[10], bytes[11]]) >= 10
}

match parse_events_from_binlog(&path) {
    Ok(b) => use_events(&b),
    Err(e) if e.to_string().contains("legacy dictionary") => {
        eprintln!("pre-v10 binlog not supported; regenerate with a modern SDK");
    }
    Err(e) => return Err(e),
}

When it happens

Trigger: read_event_fields encounters an event referencing the string dictionary while the binlog header's fileFormatVersion is below 10 — i.e., a binlog from a very old MSBuild (pre-2018 era, MSBuild 15.3 and earlier).

Common situations: Replaying ancient archived .binlog artifacts; legacy CI servers with very old .NET Framework MSBuild; vendored sample binlogs from old repos.

Related errors

• Failed to parse binlog at {}: unsupported binlog format {}
• Failed to parse binlog at {}: empty file
• negative record length: {}
• negative event length: {}
• unexpected end of stream

AI-assisted analysis of rtk-ai/rtk@36788f6bd4 (2026-09-03). Data as JSON: /api/errors/3913759cd370122b. Report an issue: GitHub.