Add handling to reasoning models for Generic OpenAI connector (#3183)

* Add handling to resoning models for Generic OpenAI connector
resolves #3177

* linting

server/utils/AiProviders/genericOpenAi/index.js

@@ -3,8 +3,9 @@ const {
   LLMPerformanceMonitor,
 } = require("../../helpers/chat/LLMPerformanceMonitor");
 const {
-  handleDefaultStreamResponseV2,
   formatChatHistory,
+  writeResponseChunk,
+  clientAbortedHandler,
 } = require("../../helpers/chat/responses");
 const { toValidNumber } = require("../../http");
 
@@ -142,6 +143,21 @@ class GenericOpenAiLLM {
     ];
   }
 
+  /**
+   * Parses and prepends reasoning from the response and returns the full text response.
+   * @param {Object} response
+   * @returns {string}
+   */
+  #parseReasoningFromResponse({ message }) {
+    let textResponse = message?.content;
+    if (
+      !!message?.reasoning_content &&
+      message.reasoning_content.trim().length > 0
+    )
+      textResponse = `<think>${message.reasoning_content}</think>${textResponse}`;
+    return textResponse;
+  }
+
   async getChatCompletion(messages = null, { temperature = 0.7 }) {
     const result = await LLMPerformanceMonitor.measureAsyncFunction(
       this.openai.chat.completions
@@ -163,7 +179,7 @@ class GenericOpenAiLLM {
       return null;
 
     return {
-      textResponse: result.output.choices[0].message.content,
+      textResponse: this.#parseReasoningFromResponse(result.output.choices[0]),
       metrics: {
         prompt_tokens: result.output?.usage?.prompt_tokens || 0,
         completion_tokens: result.output?.usage?.completion_tokens || 0,
@@ -191,8 +207,141 @@ class GenericOpenAiLLM {
     return measuredStreamRequest;
   }
 
+  // TODO: This is a copy of the generic handleStream function in responses.js
+  // to specifically handle the DeepSeek reasoning model `reasoning_content` field.
+  // When or if ever possible, we should refactor this to be in the generic function.
   handleStream(response, stream, responseProps) {
-    return handleDefaultStreamResponseV2(response, stream, responseProps);
+    const { uuid = uuidv4(), sources = [] } = responseProps;
+    let hasUsageMetrics = false;
+    let usage = {
+      completion_tokens: 0,
+    };
+
+    return new Promise(async (resolve) => {
+      let fullText = "";
+      let reasoningText = "";
+
+      // Establish listener to early-abort a streaming response
+      // in case things go sideways or the user does not like the response.
+      // We preserve the generated text but continue as if chat was completed
+      // to preserve previously generated content.
+      const handleAbort = () => {
+        stream?.endMeasurement(usage);
+        clientAbortedHandler(resolve, fullText);
+      };
+      response.on("close", handleAbort);
+
+      try {
+        for await (const chunk of stream) {
+          const message = chunk?.choices?.[0];
+          const token = message?.delta?.content;
+          const reasoningToken = message?.delta?.reasoning_content;
+
+          if (
+            chunk.hasOwnProperty("usage") && // exists
+            !!chunk.usage && // is not null
+            Object.values(chunk.usage).length > 0 // has values
+          ) {
+            if (chunk.usage.hasOwnProperty("prompt_tokens")) {
+              usage.prompt_tokens = Number(chunk.usage.prompt_tokens);
+            }
+
+            if (chunk.usage.hasOwnProperty("completion_tokens")) {
+              hasUsageMetrics = true; // to stop estimating counter
+              usage.completion_tokens = Number(chunk.usage.completion_tokens);
+            }
+          }
+
+          // Reasoning models will always return the reasoning text before the token text.
+          if (reasoningToken) {
+            // If the reasoning text is empty (''), we need to initialize it
+            // and send the first chunk of reasoning text.
+            if (reasoningText.length === 0) {
+              writeResponseChunk(response, {
+                uuid,
+                sources: [],
+                type: "textResponseChunk",
+                textResponse: `<think>${reasoningToken}`,
+                close: false,
+                error: false,
+              });
+              reasoningText += `<think>${reasoningToken}`;
+              continue;
+            } else {
+              writeResponseChunk(response, {
+                uuid,
+                sources: [],
+                type: "textResponseChunk",
+                textResponse: reasoningToken,
+                close: false,
+                error: false,
+              });
+              reasoningText += reasoningToken;
+            }
+          }
+
+          // If the reasoning text is not empty, but the reasoning token is empty
+          // and the token text is not empty we need to close the reasoning text and begin sending the token text.
+          if (!!reasoningText && !reasoningToken && token) {
+            writeResponseChunk(response, {
+              uuid,
+              sources: [],
+              type: "textResponseChunk",
+              textResponse: `</think>`,
+              close: false,
+              error: false,
+            });
+            fullText += `${reasoningText}</think>`;
+            reasoningText = "";
+          }
+
+          if (token) {
+            fullText += token;
+            // If we never saw a usage metric, we can estimate them by number of completion chunks
+            if (!hasUsageMetrics) usage.completion_tokens++;
+            writeResponseChunk(response, {
+              uuid,
+              sources: [],
+              type: "textResponseChunk",
+              textResponse: token,
+              close: false,
+              error: false,
+            });
+          }
+
+          if (
+            message?.hasOwnProperty("finish_reason") && // Got valid message and it is an object with finish_reason
+            message.finish_reason !== "" &&
+            message.finish_reason !== null
+          ) {
+            writeResponseChunk(response, {
+              uuid,
+              sources,
+              type: "textResponseChunk",
+              textResponse: "",
+              close: true,
+              error: false,
+            });
+            response.removeListener("close", handleAbort);
+            stream?.endMeasurement(usage);
+            resolve(fullText);
+            break; // Break streaming when a valid finish_reason is first encountered
+          }
+        }
+      } catch (e) {
+        console.log(`\x1b[43m\x1b[34m[STREAMING ERROR]\x1b[0m ${e.message}`);
+        writeResponseChunk(response, {
+          uuid,
+          type: "abort",
+          textResponse: null,
+          sources: [],
+          close: true,
+          error: e.message,
+        });
+        stream?.endMeasurement(usage);
+        resolve(fullText);
+      }
+    });
   }
 
   // Simple wrapper for dynamic embedder & normalize interface for all LLM implementations