Support sending email message via Notifications passthrough API

src/main/java/org/opensearch/commons/destination/message/LegacyCustomWebhookMessage.java

@@ -236,8 +236,9 @@ public String getMessage() {
     @Override
     public void writeTo(StreamOutput streamOutput) throws IOException {
         super.writeTo(streamOutput);
-        // Making LegacyCustomWebhookMessage streamable is purely to support the new pass through API from ISM -> Notification plugin
-        // and it only supports LegacyCustomWebhookMessage when the url is already constructed by ISM.
+        // Making LegacyCustomWebhookMessage streamable is purely to support the new pass through API from Alerting/ISM -> Notification
+        // plugin
+        // and it only supports LegacyCustomWebhookMessage when the url is already constructed by Alerting/ISM.
         if (Strings.isNullOrEmpty(getUrl())) {
             throw new IllegalStateException("Cannot use LegacyCustomWebhookMessage across transport wire without defining full url.");
         }

src/main/java/org/opensearch/commons/destination/message/LegacyDestinationType.java

@@ -11,5 +11,6 @@
 public enum LegacyDestinationType {
     LEGACY_CHIME,
     LEGACY_SLACK,
-    LEGACY_CUSTOM_WEBHOOK
+    LEGACY_CUSTOM_WEBHOOK,
+    LEGACY_EMAIL
 }

src/main/java/org/opensearch/commons/destination/message/LegacyEmailMessage.java

@@ -0,0 +1,234 @@
+/*
+ * Copyright OpenSearch Contributors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package org.opensearch.commons.destination.message;
+
+import java.io.IOException;
+import java.net.URI;
+import java.util.List;
+
+import org.opensearch.common.Strings;
+import org.opensearch.common.io.stream.StreamInput;
+import org.opensearch.common.io.stream.StreamOutput;
+import org.opensearch.commons.notifications.model.MethodType;
+
+/**
+ * This class holds the content of an CustomWebhook message
+ */
+public class LegacyEmailMessage extends LegacyBaseMessage {
+
+    private final String accountName;
+    private final String host;
+    private final int port;
+    private final String method;
+    private final String from;
+    private final List<String> recipients;
+    private final String subject;
+    private final String message;
+
+    private LegacyEmailMessage(
+        final String destinationName,
+        final String accountName,
+        final String host,
+        final Integer port,
+        final String method,
+        final String from,
+        final List<String> recipients,
+        final String subject,
+        final String message
+    ) {
+        super(LegacyDestinationType.LEGACY_EMAIL, destinationName, message);
+
+        if (Strings.isNullOrEmpty(message)) {
+            throw new IllegalArgumentException("Message content is missing");
+        }
+
+        if (Strings.isNullOrEmpty(accountName)) {
+            throw new IllegalArgumentException("Account name should be provided");
+        }
+
+        if (Strings.isNullOrEmpty(host)) {
+            throw new IllegalArgumentException("Host name should be provided");
+        }
+
+        if (Strings.isNullOrEmpty(from)) {
+            throw new IllegalArgumentException("From address should be provided");
+        }
+
+        if (recipients == null || recipients.isEmpty()) {
+            throw new IllegalArgumentException("List of recipients should be provided");
+        }
+
+        this.message = message;
+        this.accountName = accountName;
+        this.host = host;
+        this.port = port == null ? 25 : port;
+
+        if (Strings.isNullOrEmpty(method)) {
+            // Default to "none"
+            this.method = "none";
+        } else if (!MethodType.NONE.toString().equals(method)
+            && !MethodType.SSL.toString().equals(method)
+            && !MethodType.START_TLS.toString().equals(method)) {
+            throw new IllegalArgumentException("Invalid method supplied. Only none, ssl and start_tls are allowed");
+        } else {
+            this.method = method;
+        }
+
+        this.from = from;
+        this.recipients = recipients;
+        this.subject = Strings.isNullOrEmpty(subject) ? destinationName : subject;
+    }
+
+    public LegacyEmailMessage(StreamInput streamInput) throws IOException {
+        super(streamInput);
+        this.message = super.getMessageContent();
+        this.accountName = streamInput.readString();
+        this.host = streamInput.readString();
+        this.port = streamInput.readInt();
+        this.method = streamInput.readString();
+        this.from = streamInput.readString();
+        this.recipients = streamInput.readStringList();
+        this.subject = streamInput.readString();
+    }
+
+    @Override
+    public String toString() {
+        return "DestinationType: "
+            + getChannelType()
+            + ", DestinationName:"
+            + destinationName
+            + ", AccountName:"
+            + accountName
+            + ", From: "
+            + from
+            + ", Host: "
+            + host
+            + ", Port: "
+            + port
+            + ", Method: "
+            + method
+            + ", Subject: <...>"
+            + ", Message: <...>";
+    }
+
+    public static class Builder {
+        private final String destinationName;
+        private String accountName;
+        private String host;
+        private Integer port;
+        private String method;
+        private String from;
+        private List<String> recipients;
+        private String subject;
+        private String message;
+
+        public Builder(String destinationName) {
+            this.destinationName = destinationName;
+        }
+
+        public LegacyEmailMessage.Builder withAccountName(String accountName) {
+            this.accountName = accountName;
+            return this;
+        }
+
+        public LegacyEmailMessage.Builder withHost(String host) {
+            this.host = host;
+            return this;
+        }
+
+        public LegacyEmailMessage.Builder withPort(Integer port) {
+            this.port = port;
+            return this;
+        }
+
+        public LegacyEmailMessage.Builder withMethod(String method) {
+            this.method = method;
+            return this;
+        }
+
+        public LegacyEmailMessage.Builder withFrom(String from) {
+            this.from = from;
+            return this;
+        }
+
+        public LegacyEmailMessage.Builder withRecipients(List<String> recipients) {
+            this.recipients = recipients;
+            return this;
+        }
+
+        public LegacyEmailMessage.Builder withSubject(String subject) {
+            this.subject = subject;
+            return this;
+        }
+
+        public LegacyEmailMessage.Builder withMessage(String message) {
+            this.message = message;
+            return this;
+        }
+
+        public LegacyEmailMessage build() {
+            return new LegacyEmailMessage(
+                this.destinationName,
+                this.accountName,
+                this.host,
+                this.port,
+                this.method,
+                this.from,
+                this.recipients,
+                this.subject,
+                this.message
+            );
+        }
+    }
+
+    public String getAccountName() {
+        return accountName;
+    }
+
+    public String getHost() {
+        return host;
+    }
+
+    public int getPort() {
+        return port;
+    }
+
+    public String getMethod() {
+        return method;
+    }
+
+    public String getFrom() {
+        return from;
+    }
+
+    public List<String> getRecipients() {
+        return recipients;
+    }
+
+    public String getSubject() {
+        return subject;
+    }
+
+    public String getMessage() {
+        return message;
+    }
+
+    public URI getUri() {
+        return buildUri(null, null, host, port, null, null);
+    }
+
+    @Override
+    public void writeTo(StreamOutput streamOutput) throws IOException {
+        super.writeTo(streamOutput);
+        streamOutput.writeString(accountName);
+        streamOutput.writeString(host);
+        streamOutput.writeInt(port);
+        streamOutput.writeString(method);
+        streamOutput.writeString(from);
+        streamOutput.writeStringCollection(recipients);
+        streamOutput.writeString(subject);
+    }
+}

src/main/kotlin/org/opensearch/commons/notifications/action/LegacyPublishNotificationRequest.kt

@@ -14,6 +14,7 @@ import org.opensearch.commons.destination.message.LegacyBaseMessage
 import org.opensearch.commons.destination.message.LegacyChimeMessage
 import org.opensearch.commons.destination.message.LegacyCustomWebhookMessage
 import org.opensearch.commons.destination.message.LegacyDestinationType
+import org.opensearch.commons.destination.message.LegacyEmailMessage
 import org.opensearch.commons.destination.message.LegacySlackMessage
 import java.io.IOException
 
@@ -50,6 +51,7 @@ class LegacyPublishNotificationRequest : ActionRequest {
             LegacyDestinationType.LEGACY_CHIME -> LegacyChimeMessage(input)
             LegacyDestinationType.LEGACY_CUSTOM_WEBHOOK -> LegacyCustomWebhookMessage(input)
             LegacyDestinationType.LEGACY_SLACK -> LegacySlackMessage(input)
+            LegacyDestinationType.LEGACY_EMAIL -> LegacyEmailMessage(input)
         }
     }
 

src/main/kotlin/org/opensearch/commons/notifications/model/NotificationEvent.kt

@@ -8,9 +8,12 @@ import org.opensearch.common.io.stream.StreamInput
 import org.opensearch.common.io.stream.StreamOutput
 import org.opensearch.common.io.stream.Writeable
 import org.opensearch.common.xcontent.ToXContent
+import org.opensearch.common.xcontent.ToXContent.EMPTY_PARAMS
 import org.opensearch.common.xcontent.XContentBuilder
+import org.opensearch.common.xcontent.XContentHelper
 import org.opensearch.common.xcontent.XContentParser
 import org.opensearch.common.xcontent.XContentParserUtils
+import org.opensearch.common.xcontent.XContentType
 import org.opensearch.commons.notifications.NotificationConstants.EVENT_SOURCE_TAG
 import org.opensearch.commons.notifications.NotificationConstants.STATUS_LIST_TAG
 import org.opensearch.commons.utils.logger
@@ -102,4 +105,13 @@ data class NotificationEvent(
             .field(STATUS_LIST_TAG, statusList)
             .endObject()
     }
+
+    // Overriding toString so consuming plugins can log/output this from the  sendNotification response if needed
+    override fun toString(): String {
+        return try {
+            XContentHelper.toXContent(this, XContentType.JSON, EMPTY_PARAMS, true).utf8ToString()
+        } catch (e: IOException) {
+            super.toString() + " threw " + e.toString()
+        }
+    }
 }