#427: Added support for maximum email size validation with a possible EmailTooBig exception as result (as cause)

Author: bbottema

modules/core-module/src/main/java/org/simplejavamail/api/mailer/EmailTooBigException.java

@@ -0,0 +1,14 @@
+package org.simplejavamail.api.mailer;
+
+import static java.lang.String.format;
+
+/**
+ * Thrown when an email (as MimeMessage) is bigger than the maximum allowed size.
+ *
+ * @see MailerGenericBuilder#withMaximumEmailSize(int)
+ */
+public class EmailTooBigException extends RuntimeException {
+    public EmailTooBigException(final long emailSize, final long maximumEmailSize) {
+        super(format("Email size of %s bytes exceeds maximum allowed size of %s bytes", emailSize, maximumEmailSize));
+    }
+}

modules/core-module/src/main/java/org/simplejavamail/api/mailer/MailerGenericBuilder.java

@@ -260,6 +260,14 @@ public interface MailerGenericBuilder<T extends MailerGenericBuilder<?>> {
 	 */
 	T withEmailOverrides(@NotNull Email emailoverrides);
 
+	/**
+	 * Sets a maximum size for emails (as MimeMessage) in bytes. If an email exceeds this size, exception @{@link EmailTooBigException} will be thrown (as the cause).
+	 *
+	 * @param maximumEmailSize Maximum size of an email (as MimeMessage) in bytes.
+	 * @see #clearMaximumEmailSize()
+	 */
+	T withMaximumEmailSize(int maximumEmailSize);
+
 	/**
 	 * Signs this <em>all emails by default</em> with an <a href="https://tools.ietf.org/html/rfc5751">S/MIME</a> signature, so the receiving client
 	 * can verify whether the email content was tampered with.
@@ -685,6 +693,13 @@ public interface MailerGenericBuilder<T extends MailerGenericBuilder<?>> {
 	 */
 	T clearEmailOverrides();
 
+	/**
+	 * Makes the maximum email size <code>null</code>, meaning no size check will be performed.
+	 *
+	 * @see #withMaximumEmailSize(int)
+	 */
+	T clearMaximumEmailSize();
+
 	/**
 	 * Removes S/MIME signing, so emails won't be signed by default.
 	 *
@@ -780,6 +795,12 @@ public interface MailerGenericBuilder<T extends MailerGenericBuilder<?>> {
 	@Nullable
 	Email getEmailOverrides();
 
+	/**
+	 * @see #withMaximumEmailSize(int)
+	 */
+	@Nullable
+	Integer getMaximumEmailSize();
+
 	/**
 	 * @see #signByDefaultWithSmime(Pkcs12Config)
 	 * @see #signByDefaultWithSmime(InputStream, String, String, String)

modules/core-module/src/main/java/org/simplejavamail/api/mailer/config/EmailGovernance.java

@@ -26,7 +26,7 @@
 @Getter()
 public class EmailGovernance {
 
-	public static final EmailGovernance NO_GOVERNANCE = new EmailGovernance(null, null, null, null);
+	public static final EmailGovernance NO_GOVERNANCE = new EmailGovernance(null, null, null, null, null);
 
 	/**
 	 * The effective email validator used for email validation. Can be <code>null</code> if no validation should be done.
@@ -56,4 +56,10 @@ public class EmailGovernance {
 	 * @see MailerGenericBuilder#withEmailOverrides(Email)
 	 */
 	@Nullable private final Email emailOverrides;
+
+	/**
+	 * Determines at what size Simple Java Mail should reject a MimeMessage. Useful if you know your SMTP server has a limit.
+	 * @see MailerGenericBuilder#withMaximumEmailSize(int)
+	 */
+	@Nullable private final Integer maximumEmailSize;
 }

modules/simple-java-mail/src/main/java/org/simplejavamail/converter/EmailConverter.java

@@ -447,7 +447,7 @@ public static MimeMessage emailToMimeMessage(@NotNull final Email email, @NotNul
 		try {
 			return MimeMessageProducerHelper.produceMimeMessage(
 					checkNonEmptyArgument(email, "email"),
-					new EmailGovernance(null, checkNonEmptyArgument(defaultSmimeSigningStore, "defaultSmimeSigningStore"), null, null),
+					new EmailGovernance(null, checkNonEmptyArgument(defaultSmimeSigningStore, "defaultSmimeSigningStore"), null, null, null),
 					checkNonEmptyArgument(session, "session"));
 		} catch (UnsupportedEncodingException | MessagingException e) {
 			// this should never happen, so we don't acknowledge this exception (and simply bubble up)

modules/simple-java-mail/src/main/java/org/simplejavamail/internal/moduleloader/ModuleLoader.java

@@ -7,8 +7,8 @@
 import org.simplejavamail.internal.modules.SMIMEModule;
 import org.simplejavamail.internal.util.MiscUtil;
 
-import java.util.ArrayList;
-import java.util.Collection;
+import java.util.HashSet;
+import java.util.Set;
 import java.util.HashMap;
 import java.util.Map;
 
@@ -22,8 +22,8 @@ public class ModuleLoader {
 	private static final Map<Class, Object> LOADED_MODULES = new HashMap<>();
 
 	// used from junit tests
-	private static final Collection<Class> FORCED_DISABLED_MODULES = new ArrayList<>();
-	private static final Collection<Class> FORCED_RECHECK_MODULES = new ArrayList<>();
+	private static final Set<Class> FORCED_DISABLED_MODULES = new HashSet<>();
+	private static final Set<Class> FORCED_RECHECK_MODULES = new HashSet<>();
 
 	public static AuthenticatedSocksModule loadAuthenticatedSocksModule() {
 		if (!LOADED_MODULES.containsKey(AuthenticatedSocksModule.class)) {

modules/simple-java-mail/src/main/java/org/simplejavamail/mailer/internal/MailerException.java

@@ -5,14 +5,14 @@
 /**
  * This exception is used to communicate errors during the sending of email.
  */
-@SuppressWarnings("serial")
 class MailerException extends MailException {
 
 	static final String ERROR_READING_SMIME_FROM_INPUTSTREAM = "Was unable to read S/MIME data from input stream";
 	static final String ERROR_READING_FROM_FILE = "Error reading from file: %s";
 	static final String MISSING_OAUTH2_TOKEN = "TransportStrategy is OAUTH2 but no OAUTH2 token provided as password";
 	static final String INVALID_PROXY_SLL_COMBINATION = "Proxy is not supported for SSL connections (this is a limitation by the underlying JavaMail framework)";
 	static final String ERROR_CONNECTING_SMTP_SERVER = "Was unable to connect to SMTP server";
+	static final String MAILER_ERROR = "Failed to send email [%s]";
 	static final String GENERIC_ERROR = "Failed to send email [%s], reason: Third party error";
 	static final String INVALID_ENCODING = "Failed to send email [%s], reason: Encoding not accepted";
 	static final String UNKNOWN_ERROR = "Failed to send email [%s], reason: Unknown error";

modules/simple-java-mail/src/main/java/org/simplejavamail/mailer/internal/MailerGenericBuilderImpl.java

@@ -123,6 +123,12 @@ abstract class MailerGenericBuilderImpl<T extends MailerGenericBuilderImpl<?>> i
 	@Nullable
 	private Email emailOverrides;
 
+	/**
+	 * @see MailerGenericBuilder#withMaximumEmailSize(int)
+	 */
+	@Nullable
+	private Integer maximumEmailSize;
+
 	/**
 	 * @see MailerGenericBuilder#signByDefaultWithSmime(Pkcs12Config)
 	 */
@@ -296,7 +302,12 @@ private void validateProxy() {
 	 * For internal use.
 	 */
 	EmailGovernance buildEmailGovernance() {
-		return new EmailGovernance(getEmailValidator(), getPkcs12ConfigForSmimeSigning(), getEmailDefaults(), getEmailOverrides());
+		return new EmailGovernance(
+				getEmailValidator(),
+				getPkcs12ConfigForSmimeSigning(),
+				getEmailDefaults(),
+				getEmailOverrides(),
+				getMaximumEmailSize());
 	}
 
 	/**
@@ -454,6 +465,15 @@ public T withEmailOverrides(@NotNull Email emailOverrides) {
 		return (T) this;
 	}
 
+	/**
+	 * @see MailerGenericBuilder#withMaximumEmailSize(int)
+	 */
+	@Override
+	public T withMaximumEmailSize(int maximumEmailSize) {
+		this.maximumEmailSize = maximumEmailSize;
+		return (T) this;
+	}
+
 	/**
 	 * @param pkcs12StoreFile The file containing the keystore
 	 * @param storePassword  The password to get keys from the store
@@ -843,6 +863,15 @@ public T clearEmailOverrides() {
 		return (T) this;
 	}
 
+	/**
+	 * @see MailerGenericBuilder#clearMaximumEmailSize()
+	 */
+	@Override
+	public T clearMaximumEmailSize() {
+		this.maximumEmailSize = null;
+		return (T) this;
+	}
+
 	/**
 	 * @see MailerGenericBuilder#clearSignByDefaultWithSmime()
 	 */
@@ -974,6 +1003,15 @@ public Email getEmailOverrides() {
 		return emailOverrides;
 	}
 
+	/**
+	 * @see MailerGenericBuilder#getMaximumEmailSize()
+	 */
+	@Override
+	@Nullable
+	public Integer getMaximumEmailSize() {
+		return maximumEmailSize;
+	}
+
 	/**
 	 * @see MailerGenericBuilder#getPkcs12ConfigForSmimeSigning()
 	 */

modules/simple-java-mail/src/main/java/org/simplejavamail/mailer/internal/SendMailClosure.java

@@ -7,13 +7,16 @@
 import org.jetbrains.annotations.Nullable;
 import org.simplejavamail.api.email.Email;
 import org.simplejavamail.api.internal.authenticatedsockssupport.socks5server.AnonymousSocks5Server;
+import org.simplejavamail.api.mailer.EmailTooBigException;
 import org.simplejavamail.api.mailer.config.OperationalConfig;
 import org.simplejavamail.mailer.internal.util.TransportRunner;
 
 import java.util.concurrent.atomic.AtomicInteger;
 
 import static java.lang.String.format;
+import static java.util.Optional.ofNullable;
 import static org.simplejavamail.mailer.internal.MailerException.GENERIC_ERROR;
+import static org.simplejavamail.mailer.internal.MailerException.MAILER_ERROR;
 import static org.simplejavamail.mailer.internal.MailerException.UNKNOWN_ERROR;
 
 /**
@@ -53,13 +56,18 @@ public void executeClosure() {
 			}
 		} catch (final MessagingException e) {
 			handleException(e, GENERIC_ERROR);
+		} catch (final MailerException | EmailTooBigException e) {
+			handleException(e, MAILER_ERROR);
 		} catch (final Exception e) {
 			handleException(e, UNKNOWN_ERROR);
 		}
 	}
 
 	private void handleException(final Exception e, String errorMsg) {
-		LOGGER.trace("Failed to send email {}\n{}", email.getId(), email);
-		throw new MailerException(format(errorMsg, email.getId()), e);
+		LOGGER.trace("Failed to send email {}\n{}\n\t{}", email.getId(), email, errorMsg);
+		val emailId = ofNullable(email.getId())
+				.map(id -> format("ID: '%s'", id))
+				.orElse(format("Subject: '%s'", email.getSubject()));
+		throw new MailerException(format(errorMsg, emailId), e);
 	}
 }

modules/simple-java-mail/src/main/java/org/simplejavamail/mailer/internal/SessionBasedEmailToMimeMessageConverter.java

@@ -9,13 +9,16 @@
 import lombok.val;
 import org.jetbrains.annotations.NotNull;
 import org.simplejavamail.api.email.Email;
+import org.simplejavamail.api.mailer.EmailTooBigException;
 import org.simplejavamail.api.mailer.config.EmailGovernance;
 import org.simplejavamail.api.mailer.config.OperationalConfig;
 import org.simplejavamail.converter.internal.mimemessage.MimeMessageProducerHelper;
 import org.simplejavamail.mailer.internal.util.SessionLogger;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
 import java.io.UnsupportedEncodingException;
 
 import static java.lang.String.format;
@@ -54,12 +57,29 @@ public static void unprimeSession(@NotNull Session session) {
     @NotNull
     public static MimeMessage convertAndLogMimeMessage(Session session, final Email email) throws MessagingException {
         val mimeMessageConverter = (SessionBasedEmailToMimeMessageConverter) session.getProperties().get(MIMEMESSAGE_CONVERTER_KEY);
-        return mimeMessageConverter.convertAndLogMimeMessage(email);
+        val mimeMessage = mimeMessageConverter.convertAndLogMimeMessage(email);
+        val governance = mimeMessageConverter.emailGovernance;
+
+        if (governance.getMaximumEmailSize() != null) {
+            val emailSize = calculateEmailSize(mimeMessage);
+            if (emailSize > governance.getMaximumEmailSize()) {
+                throw new EmailTooBigException(emailSize, governance.getMaximumEmailSize());
+            }
+        }
+        return mimeMessage;
+    }
+
+    private static int calculateEmailSize(MimeMessage mimeMessage) throws MessagingException {
+        try (ByteArrayOutputStream os = new ByteArrayOutputStream()) {
+            mimeMessage.writeTo(os);
+            return os.size();
+        } catch (IOException e) {
+            throw new RuntimeException("error trying to calculate email size", e);
+        }
     }
 
     @NotNull
     private MimeMessage convertAndLogMimeMessage(final Email email) throws MessagingException {
-        // fill and send wrapped mime message parts
         val message = convertMimeMessage(email, session, emailGovernance);
 
         SessionLogger.logSession(session, operationalConfig.isAsync(), "mail");

modules/simple-java-mail/src/test/java/org/simplejavamail/mailer/MailerLiveTest.java

@@ -1,6 +1,7 @@
 package org.simplejavamail.mailer;
 
 import jakarta.mail.MessagingException;
+import jakarta.mail.Session;
 import jakarta.mail.internet.MimeMessage;
 import lombok.val;
 import org.jetbrains.annotations.NotNull;
@@ -14,7 +15,10 @@
 import org.simplejavamail.api.email.OriginalSmimeDetails.SmimeMode;
 import org.simplejavamail.api.email.Recipient;
 import org.simplejavamail.api.internal.smimesupport.model.PlainSmimeDetails;
+import org.simplejavamail.api.mailer.CustomMailer;
+import org.simplejavamail.api.mailer.EmailTooBigException;
 import org.simplejavamail.api.mailer.Mailer;
+import org.simplejavamail.api.mailer.config.OperationalConfig;
 import org.simplejavamail.converter.EmailConverter;
 import org.simplejavamail.email.EmailBuilder;
 import org.simplejavamail.email.internal.InternalEmailPopulatingBuilder;
@@ -41,6 +45,7 @@
 import static java.util.Optional.ofNullable;
 import static java.util.stream.Collectors.toList;
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
 import static org.assertj.core.data.MapEntry.entry;
 import static org.simplejavamail.api.email.ContentTransferEncoding.BIT7;
 import static org.simplejavamail.converter.EmailConverter.mimeMessageToEmail;
@@ -541,4 +546,59 @@ private void assertAttachmentMetadata(AttachmentResource embeddedImg, String mim
 		assertThat(embeddedImg.getDataSource().getContentType()).isEqualTo(mimeType);
 		assertThat(embeddedImg.getName()).isEqualTo(filename);
 	}
+
+	@Test
+	public void testMaximumEmailSize() {
+		val mailer = MailerBuilder
+				.withSMTPServer("localhost", SERVER_PORT, USERNAME, PASSWORD)
+				.withMaximumEmailSize(4)
+				.buildMailer();
+
+		sendAndVerifyEmailTooBigException(mailer);
+	}
+
+	@Test
+	public void testMaximumEmailSize_CustomMailer() {
+		val mailer = MailerBuilder
+				.withCustomMailer(new CustomMailer() {
+					@Override
+					public void testConnection(@NotNull OperationalConfig operationalConfig, @NotNull Session session) {
+						throw new RuntimeException("should reach here");
+					}
+
+					@Override
+					public void sendMessage(@NotNull OperationalConfig operationalConfig, @NotNull Session session, @NotNull Email email, @NotNull MimeMessage message) {
+						throw new RuntimeException("should reach here");
+					}
+				})
+				.withMaximumEmailSize(4)
+				.buildMailer();
+
+		sendAndVerifyEmailTooBigException(mailer);
+	}
+
+	@Test
+	public void testMaximumEmailSize_DontSendOnlyLog() {
+		val mailer = MailerBuilder
+				.withTransportModeLoggingOnly()
+				.withMaximumEmailSize(4)
+				.buildMailer();
+
+		sendAndVerifyEmailTooBigException(mailer);
+	}
+
+	private static void sendAndVerifyEmailTooBigException(Mailer mailer) {
+		val email = EmailBuilder.startingBlank()
+				.withPlainText("non empty text")
+				.withSubject("email size test")
+				.from("[email protected]")
+				.to("[email protected]")
+				.buildEmail();
+
+		assertThatThrownBy(() -> mailer.sendMail(email))
+				.hasMessageStartingWith("Failed to send email [ID:")
+				.getCause()
+				.isInstanceOf(EmailTooBigException.class)
+				.hasMessageContaining("bytes exceeds maximum allowed size of 4 bytes");
+	}
 }