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bug: float values like 1.0 output as integers (1) — type fidelity loss breaks downstream schema #444
Description
Summary
JSON float values that happen to be whole numbers (e.g., 1.0, 2.0, 100.0) are output as integers (1, 2, 100). This changes the JSON type from number-with-decimal to integer, which can break downstream schema inference and type mappings.
Root Cause
The scanner correctly identifies 1.0 as a float (the . triggers is_float = true in scanner.rs line ~194). The value is stored as f64 via append_float_by_idx. However, write_row_json uses Rust's format!("{}", v) to render float values, and Rust's f64::Display drops trailing zeros:
// crates/logfwd-output/src/lib.rs line ~188
"float" => {
let v = arr.value(row);
let _ = Write::write_fmt(out, format_args!("{}", v));
// 1.0f64 displays as "1", not "1.0"
}Reproduction
printf '{"temp":1.0,"pressure":2.0,"ratio":1.5}\n' > /tmp/float.loginput:
type: file
path: /tmp/float.log
format: json
output:
type: stdoutActual output:
{"temp":1,"pressure":2,"ratio":1.5}Expected output:
{"temp":1.0,"pressure":2.0,"ratio":1.5}Impact
- Elasticsearch: infers
tempaslonginstead ofdouble, then rejects1.5in a later batch with a mapping conflict - ClickHouse: creates
Int64column instead ofFloat64 - JSON schema validation: downstream validators may reject changed types
- Round-trip fidelity:
input → logfwd → outputchanges the data representation
Fix
Use a float-specific formatter that preserves at least one decimal place:
"float" => {
let v = arr.value(row);
if v.fract() == 0.0 && v.is_finite() {
let _ = write!(out, "{}.0", v); // Preserve float type
} else {
let _ = write!(out, "{}", v);
}
}Or use ryu crate for fast, correct float-to-string conversion that preserves the decimal.
Activity
github-actions commentedon Mar 31, 2026
No clear duplicate found for this issue.
3 related issues
write_row_json; the resolution there is useful context for where this issue likely needs a fix._int/_floathandling in output and documents how numeric type handling can cause loss or omission in emitted JSON.Note
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fix: output sinks dispatch on Arrow DataType, not column name suffix
fix: output sinks dispatch on Arrow DataType, not column name suffix
strawgate commentedon Apr 2, 2026
Closed — write_json_value dispatches on DataType::Float64 (PR #568).