Carry the municipality of a CEP that does not existHEADv0.2.0main

A 404 that only says "not found" is correct and useless. The CEP that
fails is almost never random: it is someone who knows the city and
guessed the number, and the classic guess is the -000 that 957
municipalities never received.

The API now names the municipality on the 404, so surface it as
Error.Faixa instead of throwing the body away.

1 files changed, 11 insertions, 1 deletions

diff --git a/client.go b/client.go
index 53ada45..f1e3d90 100644
--- a/client.go
+++ b/client.go
@@ -225,11 +225,21 @@ func (c *Client) Lookup(ctx context.Context, cep string) (*Address, error) {
 
 	switch resp.status {
 	case http.StatusNotFound:
+		// The body may name the municipality the CEP would fall in; when it
+		// does, say so in the message too, because most callers only ever
+		// print the error.
+		faixa := decodeFaixa(resp.body)
+		message := "CEP " + number + " does not exist in the DNE database"
+		if faixa != nil {
+			message += " (range of " + faixa.Localidade + "/" + faixa.UF +
+				", which goes from " + faixa.CEPIni + " to " + faixa.CEPFim + ")"
+		}
 		return nil, &Error{
 			Kind:    ErrCEPNotFound,
 			CEP:     number,
 			Status:  resp.status,
-			Message: "CEP " + number + " does not exist in the DNE database",
+			Faixa:   faixa,
+			Message: message,
 		}
 	case http.StatusBadRequest:
 		return nil, &Error{