2 releases
0.1.1 | Dec 1, 2023 |
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0.1.0 | Dec 1, 2023 |
#32 in #fixed-length
Used in nr-cif
13KB
175 lines
Fixed-length Format Parser
Write parsers for fixed-length formatted flat files quickly.
Goal
This project provides a macro to quickly build a parser for formats where there exists records which begin with an identifier, then continue with a format of fixed length.
Example
Consider the following file:
AA20231201
PNDarth Vader 123 Death Star Way AB12 3CD
ZZ001
Schema
This could be seen as a file with the format specified below:
Record types:
- Header ("AA")
- Person ("PN")
- Trailer ("ZZ")
Note: Record types can be represented by any number of characters, but must always be present at the start of the record, and must always be the same length as each other.
Header:
Field | Value | Length | Description |
---|---|---|---|
Type | "AA" | 2 | The header type |
Date | YYYYMMDD | 8 | The date the file was produced. |
Person:
Field | Value | Length | Description |
---|---|---|---|
Type | "PN" | 2 | The person type |
Forename | String | 10 | The forename of the person |
Surname | String | 20 | The surname of the person |
Address line | String | 30 | The address line |
Postcode | String | 8 | The postcode in UK format |
Trailer:
Field | Value | Length | Description |
---|---|---|---|
Type | "ZZ" | 2 | The trailer type |
Number of records | Number | 3 | The number of records in the file. |
Example Parser
use fixedlength_format_parser::FixedLengthFormatParser;
#[derive(FixedLengthFormatParser)]
pub enum PersonRecord {
#[record_type = "AA"]
Header {
#[field_starts = 2]
#[field_length = 8]
// You could also specify the end instead of the length. End is exclusive.
// #[field_ends = 10]
date: String,
},
#[record_type = "PN"]
Person {
#[field_starts = 2]
#[field_length = 10]
forename: String,
// `field_starts` is optional. If unspecified, it starts at 0 then increments by the length for each field.
#[field_length = 20]
surname: String,
#[field_length = 30]
address_line: String,
#[field_length = 8]
postcode: String,
},
#[record_type = "ZZ"]
Trailer {
// Any type is allowed, as long as it implements [`std::str::FromStr`].
#[field_starts = 2]
#[field_length = 3]
num_records: usize,
},
}
// You can now invoke the parser for each record:
fn parse_record(record: &str) -> PersonRecord {
record.parse::<PersonRecord>().expect("the record should be valid")
}
Dependencies
~240–690KB
~16K SLoC