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# cepis
Rust client for the [public CEP API at cep.is](https://cep.is). Official
Correios data (DNE), refreshed every two weeks.
```rust
let address = cepis::lookup("01001-000")?;
println!("{} {} {}", address.logradouro, address.localidade, address.uf);
// Praça da Sé São Paulo SP
```
## Installation
```toml
[dependencies]
cepis = { git = "https://git.cep.is/rust.git" }
```
Requires Rust 1.85 or newer. Two dependencies: `ureq` — the standard library
has no HTTP client, and `ureq` is the smallest established blocking one, with
TLS through `rustls` and no async runtime — and `serde_json`.
## Usage
### A single lookup
`lookup` accepts the CEP masked or unmasked and returns an `Address`:
```rust
let a = cepis::lookup("01310-100")?;
a.logradouro; // "Avenida Paulista"
a.localidade; // "São Paulo"
a.uf; // "SP"
a.ibge; // "3550308"
a.cep; // "01310100" (always unmasked)
a.formatted_cep(); // "01310-100"
```
Fields the database does not have for that CEP come back as empty strings.
`a.raw` holds the response exactly as it arrived, so a field the API grows
before this crate is updated is not lost.
### Coordinates
About 57% of CEPs have a coordinate. When they do not, `geo` is `None`:
```rust
if let Some(geo) = &a.geo {
println!("{} {}", geo.lat, geo.lon); // -23.567202 -46.649659
println!("{}", geo.raio_m); // 1084
println!("{}", geo.precisao); // "logradouro"
}
```
**Check `precisao` before computing distance.** There are two kinds of point,
and the difference between them is tens of kilometres:
| `precisao` | typical radius | what the point is |
| --- | --- | --- |
| `logradouro` | 110–140 m | the stretch of street — good for maps and distance |
| `localidade` | 7–40 km | the municipality centroid: the CEP *is* the whole city |
`geo.is_precise()` is the shorthand for `precisao == "logradouro"`:
```rust
let cost = match &a.geo {
Some(geo) if geo.is_precise() => shipping_from(geo.lat, geo.lon),
_ => shipping_from_municipality(&a.ibge),
};
```
### Many CEPs at once
Do not loop over `lookup`. Use `lookup_many`, which resolves up to 500 CEPs per
request:
```rust
let ceps = ["01001000", "99999999", "20040020"];
for (requested, address) in ceps.iter().zip(cepis::lookup_many(&ceps)?) {
match address {
Some(a) => println!("{requested}: {}", a.localidade),
None => println!("{requested}: not found"),
}
}
```
The returned `Vec` has **the same length and the same order** as the input. A
CEP that does not exist, or is malformed, becomes `None` at its position — it
does not vanish, and it is not an error.
Slices longer than 500 are chunked automatically.
> **Batches carry no coordinate.** The endpoint behind them is CSV, and the CSV
> has no `geo` column. Every `Address` from `lookup_many` has `geo: None`,
> including for CEPs that do have one. Need `geo`? Use `lookup`, one at a time.
### API health
Useful for two things: checking the API answers, and knowing **which version of
the database** is live:
```rust
let h = cepis::health()?;
h.ok(); // true
h.dne; // "26071" identifier of the fortnightly database
h.ceps; // 1596168
h.base_gerada_em; // "2026-07-24T03:48:28Z"
```
An API reporting itself degraded is not an error — that arrives in `h.status`.
## Configuration
For anything beyond the defaults, build a `Client` and reuse it. It keeps no
state between calls, is safe to share across threads, and pools connections:
```rust
use std::time::Duration;
let client = cepis::Client::builder()
.base_url("https://cep.is") // point at another instance
.timeout(Duration::from_secs(10)) // per socket operation
.max_attempts(3) // counting the first; 1 disables retrying
.backoff_base(Duration::from_millis(500)) // base of the exponential wait
.backoff_max(Duration::from_secs(8)) // cap on each wait
.total_timeout(Some(Duration::from_secs(30))) // cap on the whole call
.user_agent("my-app/1.0")
.build();
let address = client.lookup("01001000")?;
```
Retries cover 429, 5xx and network failures, with exponential backoff and
jitter; 400 and 404 are never retried.
The free functions (`cepis::lookup`, and so on) share one default client, built
on first use. Need a different configuration? Build your own.
### Pointing at a local instance
`base_url` is the only setting that usually changes between environments. The
API repo brings a local instance up with `just up`:
```rust
let client = cepis::Client::builder()
.base_url("http://localhost:8080")
.build();
```
From the command line, to confirm quickly that it answers:
```sh
cargo run --bin cepis -- --base-url http://localhost:8080 01001000
```
## Errors
Everything is one `Error`. Its variants split by **the decision you have to
make**, not by the HTTP status that caused it:
| variant | when | does retrying help? |
| --- | --- | --- |
| `InvalidCep` | not 8 digits | no |
| `NotFound` | well-formed, not in the database | no |
| `RateLimited` | 429; carries `retry_after` | yes, later |
| `Server` | 5xx; carries `status` | yes, later |
| `Network` | DNS, connection, timeout, TLS | yes, later |
| `InvalidResponse` | unintelligible response | probably not |
```rust
match cepis::lookup(&cep_from_form) {
Ok(address) => render(address),
Err(cepis::Error::NotFound { .. }) => ask_for_another_cep(),
Err(err) if err.is_retriable() => reschedule(),
Err(err) => eprintln!("{err}"),
}
```
`InvalidResponse` almost always means something between you and the API is
answering instead of it — a captive Wi-Fi portal, a corporate proxy, an HTML
error page. Useful as a diagnosis: the problem is not in your code.
## Development
Everything runs through `make`, which shells out to `cargo`:
```sh
make # list the targets
make test # cargo test
make lint # clippy + rustfmt check, touches nothing
make format # apply rustfmt (writes)
make build # release build
make check # lint, then test, then build
```
## Licence
ISC. See [LICENSE](LICENSE).
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