Buscar CEP diretamente no Correios

search_cep.php

<?php
function getAddressDetails($cep)
{
    $data = [
        'cepEntrada' => $cep,
        'tipoCep' => '',
        'cepTemp' => '',
        'metodo' => 'buscarCep'
    ];
    $requestOptions = [
        CURLOPT_URL => 'http://m.correios.com.br/movel/buscaCepConfirma.do',
        CURLOPT_HEADER => false,
        CURLOPT_POST => true,
        CURLOPT_POSTFIELDS => http_build_query($data),
        CURLOPT_RETURNTRANSFER => true
    ];

    $handler = curl_init();

    curl_setopt_array($handler, $requestOptions);

    $response = curl_exec($handler);

    curl_close($handler);

    return $response;
}

function searchDomByText($xpath, $text)
{
    $result = $xpath->query(
        '//span[@class="resposta"][contains(., "' . $text . '")]/following-sibling::span'
    )->item(0);

    if ($result) {
        return $result->nodeValue;
    }

    return null;
}

function fetchAddressDetails($html)
{
    libxml_use_internal_errors(true);

    $dom = new DOMDocument();
    $dom->preserveWhiteSpace = false;
    $dom->loadHTML($html);
    $xpath = new DOMXPath($dom);

    $results = [
        'cep' => searchDomByText($xpath, 'CEP'),
        'address' => searchDomByText($xpath, 'Logradouro'),
        'district' => searchDomByText($xpath, 'Bairro'),
        'city' => null,
        'state' => null
    ];

    $cityWithState = searchDomByText($xpath, 'Localidade / UF');

    if ($cityWithState != null) {
        list($city, $state) = explode('/', $cityWithState);

        $results['city'] = $city;
        $results['state'] = $state;

        unset($cityWithState, $city, $state);
    }

    return array_map('trim', $results);
}

$cep = '13537-000';
$html = getAddressDetails($cep);
$results = fetchAddressDetails($html);

var_dump($results);