Scaffold PGP mail modules with WKD key discovery and demo app

- Maven multi-module build on JDK 27 and Spring Boot 4.1.1 (BOM import)
- core: WKD discovery (advanced -> direct fallback), HTTP fetcher with
  timeouts, no redirects and a size limit, Caffeine cache with per-outcome
  TTLs capped at key expiry, pinned keys, composite chain
- autoconfigure: mail.pgp.* properties and discovery beans
- demo: sends test mails (plaintext for now) and reports the WKD result
- docs/PLAN.md: design, decisions and milestones

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01G71TQ5jDETVwdUJxGAwaiT

mailsender-demo/src/main/java/io/github/sneakybugmaster/mailsender/demo/DemoApplication.java

@@ -0,0 +1,14 @@
+package io.github.sneakybugmaster.mailsender.demo;
+
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+import org.springframework.boot.context.properties.ConfigurationPropertiesScan;
+
+@SpringBootApplication
+@ConfigurationPropertiesScan
+public class DemoApplication {
+
+    public static void main(String[] args) {
+        SpringApplication.run(DemoApplication.class, args);
+    }
+}

mailsender-demo/src/main/java/io/github/sneakybugmaster/mailsender/demo/DemoProperties.java

@@ -0,0 +1,16 @@
+package io.github.sneakybugmaster.mailsender.demo;
+
+import org.springframework.boot.context.properties.ConfigurationProperties;
+import org.springframework.boot.context.properties.bind.DefaultValue;
+
+/**
+ * @param to    recipient of the test mails
+ * @param from  sender address; most SMTP providers require it to match the authenticated account
+ * @param count number of test mails to send
+ */
+@ConfigurationProperties("demo")
+public record DemoProperties(
+        @DefaultValue("test@thinhha.pro") String to,
+        String from,
+        @DefaultValue("1") int count) {
+}

mailsender-demo/src/main/java/io/github/sneakybugmaster/mailsender/demo/TestMailRunner.java

@@ -0,0 +1,76 @@
+package io.github.sneakybugmaster.mailsender.demo;
+
+import java.time.OffsetDateTime;
+import java.util.HexFormat;
+import java.util.stream.Collectors;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import org.springframework.boot.ApplicationArguments;
+import org.springframework.boot.ApplicationRunner;
+import org.springframework.mail.javamail.JavaMailSender;
+import org.springframework.mail.javamail.MimeMessageHelper;
+import org.springframework.stereotype.Component;
+
+import io.github.sneakybugmaster.mailsender.pgp.discovery.DiscoveryResult;
+import io.github.sneakybugmaster.mailsender.pgp.discovery.KeyDiscovery;
+import jakarta.mail.MessagingException;
+import jakarta.mail.internet.MimeMessage;
+
+/**
+ * Looks up the recipient's key via WKD, then sends {@code demo.count} test mails describing what was found.
+ * <p>
+ * Encryption is not wired in yet (milestones 3–6), so the mails go out in plaintext.
+ */
+@Component
+class TestMailRunner implements ApplicationRunner {
+
+    private static final Logger log = LoggerFactory.getLogger(TestMailRunner.class);
+
+    private final DemoProperties properties;
+    private final KeyDiscovery keyDiscovery;
+    private final JavaMailSender mailSender;
+
+    TestMailRunner(DemoProperties properties, KeyDiscovery keyDiscovery, JavaMailSender mailSender) {
+        this.properties = properties;
+        this.keyDiscovery = keyDiscovery;
+        this.mailSender = mailSender;
+    }
+
+    @Override
+    public void run(ApplicationArguments args) throws MessagingException {
+        DiscoveryResult discovery = keyDiscovery.discover(properties.to());
+        String summary = describe(discovery);
+        log.info("Key discovery for {}: {}", properties.to(), summary);
+
+        for (int i = 1; i <= properties.count(); i++) {
+            MimeMessage message = mailSender.createMimeMessage();
+            MimeMessageHelper helper = new MimeMessageHelper(message, "UTF-8");
+            if (properties.from() != null) {
+                helper.setFrom(properties.from());
+            }
+            helper.setTo(properties.to());
+            helper.setSubject("mailsender test %d/%d".formatted(i, properties.count()));
+            helper.setText("""
+                    Test mail %d of %d from the mailsender demo, sent %s.
+
+                    Key discovery for %s: %s
+
+                    This message was sent in plaintext: PGP/MIME encryption is not implemented yet.
+                    """.formatted(i, properties.count(), OffsetDateTime.now(), properties.to(), summary));
+            mailSender.send(message);
+            log.info("Sent test mail {}/{} to {}", i, properties.count(), properties.to());
+        }
+    }
+
+    private static String describe(DiscoveryResult result) {
+        return switch (result) {
+            case DiscoveryResult.Found found -> "found via " + found.source() + ", fingerprint(s) "
+                    + found.certificates().stream()
+                            .map(c -> HexFormat.of().withUpperCase().formatHex(c.getFingerprint()))
+                            .collect(Collectors.joining(", "));
+            case DiscoveryResult.NotFound ignored -> "no key published";
+            case DiscoveryResult.Unreachable u -> "lookup failed (" + u.reason() + ")";
+        };
+    }
+}

mailsender-demo/src/main/resources/application.yml

@@ -0,0 +1,23 @@
+spring:
+  main:
+    web-application-type: none
+  mail:
+    host: ${SMTP_HOST:localhost}
+    port: ${SMTP_PORT:587}
+    username: ${SMTP_USERNAME:}
+    password: ${SMTP_PASSWORD:}
+    properties:
+      mail.smtp.auth: ${SMTP_AUTH:true}
+      mail.smtp.starttls.enable: ${SMTP_STARTTLS:true}
+      mail.smtp.starttls.required: ${SMTP_STARTTLS:true}
+      mail.smtp.connectiontimeout: 10000
+      mail.smtp.timeout: 10000
+
+demo:
+  to: ${DEMO_TO:test@thinhha.pro}
+  from: ${DEMO_FROM:${SMTP_USERNAME:}}
+  count: ${DEMO_COUNT:1}
+
+logging:
+  level:
+    io.github.sneakybugmaster.mailsender: DEBUG

mailsender-demo/src/test/java/io/github/sneakybugmaster/mailsender/demo/TestMailRunnerTest.java

@@ -0,0 +1,59 @@
+package io.github.sneakybugmaster.mailsender.demo;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import org.junit.jupiter.api.AfterAll;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.test.context.DynamicPropertyRegistry;
+import org.springframework.test.context.DynamicPropertySource;
+
+import com.icegreen.greenmail.util.GreenMail;
+import com.icegreen.greenmail.util.GreenMailUtil;
+import com.icegreen.greenmail.util.ServerSetupTest;
+
+import jakarta.mail.internet.MimeMessage;
+
+@SpringBootTest(properties = {
+        "spring.mail.properties.mail.smtp.auth=false",
+        "spring.mail.properties.mail.smtp.starttls.enable=false",
+        "spring.mail.properties.mail.smtp.starttls.required=false",
+        "spring.mail.username=",
+        "demo.from=demo@mailsender.test",
+        "demo.count=2",
+        // keep the test offline: no real WKD lookup
+        "mail.pgp.wkd.enabled=false"
+})
+class TestMailRunnerTest {
+
+    // Started before the Spring context, because the runner sends while the context starts.
+    static GreenMail greenMail;
+
+    @BeforeAll
+    static void startSmtp() {
+        greenMail = new GreenMail(ServerSetupTest.SMTP.dynamicPort());
+        greenMail.start();
+    }
+
+    @AfterAll
+    static void stopSmtp() {
+        greenMail.stop();
+    }
+
+    @DynamicPropertySource
+    static void smtp(DynamicPropertyRegistry registry) {
+        registry.add("spring.mail.host", () -> "127.0.0.1");
+        registry.add("spring.mail.port", () -> greenMail.getSmtp().getPort());
+    }
+
+    @Test
+    void sendsTestMailsToConfiguredRecipient() throws Exception {
+        MimeMessage[] received = greenMail.getReceivedMessages();
+
+        assertThat(received).hasSize(2);
+        assertThat(received[0].getAllRecipients()).extracting(Object::toString).containsExactly("test@thinhha.pro");
+        assertThat(received[0].getSubject()).isEqualTo("mailsender test 1/2");
+        assertThat(GreenMailUtil.getBody(received[0])).contains("no key published");
+    }
+}