[8.19] Add Mistral AI Chat Completion support to Inference Plugin (elastic#128538) (elastic#128947)

* Change versions for Mistral Chat Completion version

* Refactor model handling in MistralService to use instanceof for cleaner code

* Update Mistral Chat Completion 8.19 Version

Author: Jan-Kazlouski-elastic

docs/changelog/128538.yaml

@@ -0,0 +1,5 @@
+pr: 128538
+summary: "Added Mistral Chat Completion support to the Inference Plugin"
+area: Machine Learning
+type: enhancement
+issues: []

server/src/main/java/org/elasticsearch/TransportVersions.java

@@ -237,7 +237,7 @@ static TransportVersion def(int id) {
     public static final TransportVersion ESQL_REGEX_MATCH_WITH_CASE_INSENSITIVITY_8_19 = def(8_841_0_44);
     public static final TransportVersion ESQL_QUERY_PLANNING_DURATION_8_19 = def(8_841_0_45);
     public static final TransportVersion SEARCH_SOURCE_EXCLUDE_VECTORS_PARAM_8_19 = def(8_841_0_46);
-
+    public static final TransportVersion ML_INFERENCE_MISTRAL_CHAT_COMPLETION_ADDED_8_19 = def(8_841_0_47);
     /*
      * STOP! READ THIS FIRST! No, really,
      *        ____ _____ ___  ____  _        ____  _____    _    ____    _____ _   _ ___ ____    _____ ___ ____  ____ _____ _

server/src/main/java/org/elasticsearch/inference/UnifiedCompletionRequest.java

@@ -78,6 +78,14 @@ public record UnifiedCompletionRequest(
      * {@link #MAX_COMPLETION_TOKENS_FIELD}. Providers are expected to pass in their supported field name.
      */
     private static final String MAX_TOKENS_PARAM = "max_tokens_field";
+    /**
+     * Indicates whether to include the `stream_options` field in the JSON output.
+     * Some providers do not support this field. In such cases, this parameter should be set to "false",
+     * and the `stream_options` field will be excluded from the output.
+     * For providers that do support stream options, this parameter is left unset (default behavior),
+     * which implicitly includes the `stream_options` field in the output.
+     */
+    public static final String INCLUDE_STREAM_OPTIONS_PARAM = "include_stream_options";
 
     /**
      * Creates a {@link org.elasticsearch.xcontent.ToXContent.Params} that causes ToXContent to include the key values:
@@ -91,6 +99,23 @@ public static Params withMaxTokens(String modelId, Params params) {
         );
     }
 
+    /**
+     * Creates a {@link org.elasticsearch.xcontent.ToXContent.Params} that causes ToXContent to include the key values:
+     * - Key: {@link #MODEL_FIELD}, Value: modelId
+     * - Key: {@link #MAX_TOKENS_FIELD}, Value: {@link #MAX_TOKENS_FIELD}
+     * - Key: {@link #INCLUDE_STREAM_OPTIONS_PARAM}, Value: "false"
+     */
+    public static Params withMaxTokensAndSkipStreamOptionsField(String modelId, Params params) {
+        return new DelegatingMapParams(
+            Map.ofEntries(
+                Map.entry(MODEL_ID_PARAM, modelId),
+                Map.entry(MAX_TOKENS_PARAM, MAX_TOKENS_FIELD),
+                Map.entry(INCLUDE_STREAM_OPTIONS_PARAM, Boolean.FALSE.toString())
+            ),
+            params
+        );
+    }
+
     /**
      * Creates a {@link org.elasticsearch.xcontent.ToXContent.Params} that causes ToXContent to include the key values:
      * - Key: {@link #MODEL_FIELD}, Value: modelId

x-pack/plugin/inference/qa/inference-service-tests/src/javaRestTest/java/org/elasticsearch/xpack/inference/InferenceGetServicesIT.java

@@ -134,7 +134,7 @@ public void testGetServicesWithRerankTaskType() throws IOException {
 
     public void testGetServicesWithCompletionTaskType() throws IOException {
         List<Object> services = getServices(TaskType.COMPLETION);
-        assertThat(services.size(), equalTo(13));
+        assertThat(services.size(), equalTo(14));
 
         var providers = providers(services);
 
@@ -154,15 +154,16 @@ public void testGetServicesWithCompletionTaskType() throws IOException {
                     "openai",
                     "streaming_completion_test_service",
                     "hugging_face",
-                    "amazon_sagemaker"
+                    "amazon_sagemaker",
+                    "mistral"
                 ).toArray()
             )
         );
     }
 
     public void testGetServicesWithChatCompletionTaskType() throws IOException {
         List<Object> services = getServices(TaskType.CHAT_COMPLETION);
-        assertThat(services.size(), equalTo(7));
+        assertThat(services.size(), equalTo(8));
 
         var providers = providers(services);
 
@@ -176,7 +177,8 @@ public void testGetServicesWithChatCompletionTaskType() throws IOException {
                     "streaming_completion_test_service",
                     "hugging_face",
                     "amazon_sagemaker",
-                    "googlevertexai"
+                    "googlevertexai",
+                    "mistral"
                 ).toArray()
             )
         );

x-pack/plugin/inference/src/main/java/org/elasticsearch/xpack/inference/InferenceNamedWriteablesProvider.java

@@ -100,6 +100,7 @@
 import org.elasticsearch.xpack.inference.services.jinaai.embeddings.JinaAIEmbeddingsTaskSettings;
 import org.elasticsearch.xpack.inference.services.jinaai.rerank.JinaAIRerankServiceSettings;
 import org.elasticsearch.xpack.inference.services.jinaai.rerank.JinaAIRerankTaskSettings;
+import org.elasticsearch.xpack.inference.services.mistral.completion.MistralChatCompletionServiceSettings;
 import org.elasticsearch.xpack.inference.services.mistral.embeddings.MistralEmbeddingsServiceSettings;
 import org.elasticsearch.xpack.inference.services.openai.completion.OpenAiChatCompletionServiceSettings;
 import org.elasticsearch.xpack.inference.services.openai.completion.OpenAiChatCompletionTaskSettings;
@@ -266,6 +267,13 @@ private static void addMistralNamedWriteables(List<NamedWriteableRegistry.Entry>
                 MistralEmbeddingsServiceSettings::new
             )
         );
+        namedWriteables.add(
+            new NamedWriteableRegistry.Entry(
+                ServiceSettings.class,
+                MistralChatCompletionServiceSettings.NAME,
+                MistralChatCompletionServiceSettings::new
+            )
+        );
 
         // note - no task settings for Mistral embeddings...
     }

x-pack/plugin/inference/src/main/java/org/elasticsearch/xpack/inference/external/response/ErrorMessageResponseEntity.java

@@ -21,12 +21,13 @@
  * A pattern is emerging in how external providers provide error responses.
  *
  * At a minimum, these return:
+ * <pre><code>
  * {
  *     "error: {
  *         "message": "(error message)"
  *     }
  * }
- *
+ * </code></pre>
  * Others may return additional information such as error codes specific to the service.
  *
  * This currently covers error handling for Azure AI Studio, however this pattern

x-pack/plugin/inference/src/main/java/org/elasticsearch/xpack/inference/external/response/streaming/StreamingErrorResponse.java

@@ -0,0 +1,128 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0; you may not use this file except in compliance with the Elastic License
+ * 2.0.
+ */
+
+package org.elasticsearch.xpack.inference.external.response.streaming;
+
+import org.elasticsearch.core.Nullable;
+import org.elasticsearch.xcontent.ConstructingObjectParser;
+import org.elasticsearch.xcontent.ParseField;
+import org.elasticsearch.xcontent.XContentFactory;
+import org.elasticsearch.xcontent.XContentParser;
+import org.elasticsearch.xcontent.XContentParserConfiguration;
+import org.elasticsearch.xcontent.XContentType;
+import org.elasticsearch.xpack.inference.external.http.HttpResult;
+import org.elasticsearch.xpack.inference.external.http.retry.ErrorResponse;
+import org.elasticsearch.xpack.inference.external.response.ErrorMessageResponseEntity;
+
+import java.util.Objects;
+import java.util.Optional;
+
+/**
+ * Represents an error response from a streaming inference service.
+ * This class extends {@link ErrorResponse} and provides additional fields
+ * specific to streaming errors, such as code, param, and type.
+ * An example error response for a streaming service might look like:
+ * <pre><code>
+ *     {
+ *         "error": {
+ *             "message": "Invalid input",
+ *             "code": "400",
+ *             "param": "input",
+ *             "type": "invalid_request_error"
+ *         }
+ *     }
+ * </code></pre>
+ * TODO: {@link ErrorMessageResponseEntity} is nearly identical to this, but doesn't parse as many fields. We must remove the duplication.
+ */
+public class StreamingErrorResponse extends ErrorResponse {
+    private static final ConstructingObjectParser<Optional<ErrorResponse>, Void> ERROR_PARSER = new ConstructingObjectParser<>(
+        "streaming_error",
+        true,
+        args -> Optional.ofNullable((StreamingErrorResponse) args[0])
+    );
+    private static final ConstructingObjectParser<StreamingErrorResponse, Void> ERROR_BODY_PARSER = new ConstructingObjectParser<>(
+        "streaming_error",
+        true,
+        args -> new StreamingErrorResponse((String) args[0], (String) args[1], (String) args[2], (String) args[3])
+    );
+
+    static {
+        ERROR_BODY_PARSER.declareString(ConstructingObjectParser.constructorArg(), new ParseField("message"));
+        ERROR_BODY_PARSER.declareStringOrNull(ConstructingObjectParser.optionalConstructorArg(), new ParseField("code"));
+        ERROR_BODY_PARSER.declareStringOrNull(ConstructingObjectParser.optionalConstructorArg(), new ParseField("param"));
+        ERROR_BODY_PARSER.declareString(ConstructingObjectParser.constructorArg(), new ParseField("type"));
+
+        ERROR_PARSER.declareObjectOrNull(
+            ConstructingObjectParser.optionalConstructorArg(),
+            ERROR_BODY_PARSER,
+            null,
+            new ParseField("error")
+        );
+    }
+
+    /**
+     * Standard error response parser. This can be overridden for those subclasses that
+     * have a different error response structure.
+     * @param response The error response as an HttpResult
+     */
+    public static ErrorResponse fromResponse(HttpResult response) {
+        try (
+            XContentParser parser = XContentFactory.xContent(XContentType.JSON)
+                .createParser(XContentParserConfiguration.EMPTY, response.body())
+        ) {
+            return ERROR_PARSER.apply(parser, null).orElse(ErrorResponse.UNDEFINED_ERROR);
+        } catch (Exception e) {
+            // swallow the error
+        }
+
+        return ErrorResponse.UNDEFINED_ERROR;
+    }
+
+    /**
+     * Standard error response parser. This can be overridden for those subclasses that
+     * have a different error response structure.
+     * @param response The error response as a string
+     */
+    public static ErrorResponse fromString(String response) {
+        try (
+            XContentParser parser = XContentFactory.xContent(XContentType.JSON).createParser(XContentParserConfiguration.EMPTY, response)
+        ) {
+            return ERROR_PARSER.apply(parser, null).orElse(ErrorResponse.UNDEFINED_ERROR);
+        } catch (Exception e) {
+            // swallow the error
+        }
+
+        return ErrorResponse.UNDEFINED_ERROR;
+    }
+
+    @Nullable
+    private final String code;
+    @Nullable
+    private final String param;
+    private final String type;
+
+    StreamingErrorResponse(String errorMessage, @Nullable String code, @Nullable String param, String type) {
+        super(errorMessage);
+        this.code = code;
+        this.param = param;
+        this.type = Objects.requireNonNull(type);
+    }
+
+    @Nullable
+    public String code() {
+        return code;
+    }
+
+    @Nullable
+    public String param() {
+        return param;
+    }
+
+    public String type() {
+        return type;
+    }
+}

x-pack/plugin/inference/src/main/java/org/elasticsearch/xpack/inference/external/unified/UnifiedChatCompletionRequestEntity.java

@@ -15,6 +15,12 @@
 import java.io.IOException;
 import java.util.Objects;
 
+import static org.elasticsearch.inference.UnifiedCompletionRequest.INCLUDE_STREAM_OPTIONS_PARAM;
+
+/**
+ * Represents a unified chat completion request entity.
+ * This class is used to convert the unified chat input into a format that can be serialized to XContent.
+ */
 public class UnifiedChatCompletionRequestEntity implements ToXContentFragment {
 
     public static final String STREAM_FIELD = "stream";
@@ -42,7 +48,8 @@ public XContentBuilder toXContent(XContentBuilder builder, Params params) throws
         builder.field(NUMBER_OF_RETURNED_CHOICES_FIELD, 1);
 
         builder.field(STREAM_FIELD, stream);
-        if (stream) {
+        // If request is streamed and skip stream options parameter is not true, include stream options in the request.
+        if (stream && params.paramAsBoolean(INCLUDE_STREAM_OPTIONS_PARAM, true)) {
             builder.startObject(STREAM_OPTIONS_FIELD);
             builder.field(INCLUDE_USAGE_FIELD, true);
             builder.endObject();

x-pack/plugin/inference/src/main/java/org/elasticsearch/xpack/inference/services/mistral/MistralCompletionResponseHandler.java

@@ -0,0 +1,29 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0; you may not use this file except in compliance with the Elastic License
+ * 2.0.
+ */
+
+package org.elasticsearch.xpack.inference.services.mistral;
+
+import org.elasticsearch.xpack.inference.external.http.retry.ResponseParser;
+import org.elasticsearch.xpack.inference.services.mistral.response.MistralErrorResponse;
+import org.elasticsearch.xpack.inference.services.openai.OpenAiChatCompletionResponseHandler;
+
+/**
+ * Handles non-streaming completion responses for Mistral models, extending the OpenAI completion response handler.
+ * This class is specifically designed to handle Mistral's error response format.
+ */
+public class MistralCompletionResponseHandler extends OpenAiChatCompletionResponseHandler {
+
+    /**
+     * Constructs a MistralCompletionResponseHandler with the specified request type and response parser.
+     *
+     * @param requestType The type of request being handled (e.g., "mistral completions").
+     * @param parseFunction The function to parse the response.
+     */
+    public MistralCompletionResponseHandler(String requestType, ResponseParser parseFunction) {
+        super(requestType, parseFunction, MistralErrorResponse::fromResponse);
+    }
+}

x-pack/plugin/inference/src/main/java/org/elasticsearch/xpack/inference/services/mistral/MistralConstants.java

@@ -9,6 +9,7 @@
 
 public class MistralConstants {
     public static final String API_EMBEDDINGS_PATH = "https://api.mistral.ai/v1/embeddings";
+    public static final String API_COMPLETIONS_PATH = "https://api.mistral.ai/v1/chat/completions";
 
     // note - there is no bounds information available from Mistral,
     // so we'll use a sane default here which is the same as Cohere's
@@ -18,4 +19,8 @@ public class MistralConstants {
     public static final String MODEL_FIELD = "model";
     public static final String INPUT_FIELD = "input";
     public static final String ENCODING_FORMAT_FIELD = "encoding_format";
+    public static final String MAX_TOKENS_FIELD = "max_tokens";
+    public static final String DETAIL_FIELD = "detail";
+    public static final String MSG_FIELD = "msg";
+    public static final String MESSAGE_FIELD = "message";
 }