Crate fits_header 

fits-header

A pure-Rust, MSVC-safe library for reading and writing the header of a FITS file.

It reads a header unit into an ordered Header of records, retaining every card so untouched cards serialize byte-for-byte and only created or modified cards are re-rendered. Access is strict and keyword-oriented: Header::get and friends take a Key that is either a bare name (unique-or-FitsError::AmbiguousKeyword) or (name, occurrence). Values read through a generic FromCard and write through IntoValue; batch edits are atomic; long strings use the CONTINUE convention.

use fits_header::{Header, StructuralHints};

let mut h = Header::new();
h.set("OBJECT", "M31").unwrap();
h.set("EXPTIME", 120.0).unwrap();
assert_eq!(h.get::<f64>("EXPTIME").unwrap(), Some(120.0));

let bytes = h.to_bytes(&StructuralHints::default()).unwrap();
assert_eq!(bytes.len() % fits_header::BLOCK_LEN, 0);

Design

• Pure Rust, no C or system libraries; builds with the MSVC toolchain.
• An untouched card (and untouched long-string run) re-emits identical bytes.
• Ambiguous keyword access errors instead of guessing.

Features

• serde (off) — derive Serialize/Deserialize on the public types.
• coords (off) — sexagesimal RA/Dec and MJD↔calendar helpers.

Structs

Fixed

Write a float with a fixed number of decimal places.

Header

An ordered FITS header unit: records in appearance order, with strict keyword access and CRUD.

Literal

Write a literal token verbatim (numeric text a vendor supplied, or a value you don’t want reformatted).

Record

One header card. Carries its parsed content plus, when parsed and unmodified, the original bytes of its physical card(s) so it can be serialized verbatim.

Sci

Write a float in scientific notation with N significant digits (uppercase E).

StructuralHints

Image geometry used only when Header::to_bytes must synthesize missing structural cards.

Enums

FitsError

Errors from validated header mutations, ambiguous lookups, and oversized standalone serialization.

Key

Selects a record by keyword.

RecordKind

The semantic content of a record.

Value

A value card’s payload.

Constants

BLOCK_LEN

Bytes per FITS block (36 cards).

CARD_LEN

Bytes per header card.

MAX_ZERO_FILL

Largest data segment Header::to_bytes will zero-fill, in bytes (1 GiB).

Traits

FromCard

Convert a record’s value into a Rust type. The extension point behind Header::get.

IntoValue

Convert a Rust value into a Value. The extension point behind Header::set / append.

Functions

datetime_to_mjd

Convert a calendar date/time to a Modified Julian Date.

deg_to_sexagesimal_dec

Format degrees as a sexagesimal declination ±DD MM SS.ss (sign preserved).

deg_to_sexagesimal_ra

Format degrees as a sexagesimal right ascension HH MM SS.sss (re-parses to the input within millisecond-of-arc precision).

format_datetime

Format a date/time back to the FITS civil form (YYYY-MM-DDThh:mm:ss[.fff]), dropping a zero sub-second part.

mjd_to_datetime

Convert a Modified Julian Date to a calendar date/time.

parse

Parse one FITS header unit from raw bytes.

parse_datetime

Parse a FITS civil date/time (YYYY-MM-DD[Thh:mm:ss[.fff]]), timezone-naive.

parse_f64

Parse a float, accepting the Fortran D exponent (1.5D3).

parse_i64

Parse an integer, accepting decimal-form integers ("20.0" → 20).

sexagesimal_dec_to_deg

Parse a sexagesimal declination (±D M S) to degrees. The sign is taken from the leading token, so it is preserved even when the degrees field is 0 (-00 30 00 → -0.5). Requires the coords feature.

sexagesimal_ra_to_deg

Parse a sexagesimal right ascension (H M S, space- or colon-separated, optional fractional seconds) to degrees (hours × 15). Requires the coords feature.