Fix reasoning_content for chat_template include <think> tag as input

vllm/entrypoints/openai/reasoning_parsers/deepseek_r1_reasoning_parser.py

 # SPDX-License-Identifier: Apache-2.0
 
 import re
-from typing import Optional, Sequence, Tuple, Union
+from collections.abc import Sequence
+from typing import Optional, Union
 
 from transformers import PreTrainedTokenizerBase
 
@@ -44,6 +45,19 @@ class DeepSeekR1ReasoningParser(ReasoningParser):
                 "DeepSeek R1 reasoning parser could not locate think start/end "
                 "tokens in the tokenizer!")
 
+    # TODO: need to rebase by PR #14428
+    def is_reasoning_end(self, input_ids: list[int]) -> bool:
+        return self.think_end_token_id in input_ids
+
+    def extract_content_ids(self, input_ids: list[int]) -> list[int]:
+        """
+        Extract the content after the end tokens
+        """
+        if self.think_end_token_id not in input_ids[:-1]:
+            return []
+        else:
+            return input_ids[input_ids.index(self.think_end_token_id) + 1:]
+
     def extract_reasoning_content_streaming(
         self,
         previous_text: str,
@@ -67,6 +81,8 @@ class DeepSeekR1ReasoningParser(ReasoningParser):
         ]):
             return None
 
+        # Check if <think> is present in previous or delta.
+        # Keep compatibility with models that don't generate <think> tokens.
         if self.think_start_token_id in previous_token_ids:
             if self.think_end_token_id in delta_token_ids:
                 # <think> in previous, </think> in delta,
@@ -85,7 +101,6 @@ class DeepSeekR1ReasoningParser(ReasoningParser):
                 # reasoning content continues
                 return DeltaMessage(reasoning_content=delta_text)
         elif self.think_start_token_id in delta_token_ids:
-            logger.info(delta_text)
             if self.think_end_token_id in delta_token_ids:
                 # <think> in delta, </think> in delta, extract reasoning content
                 start_index = delta_text.find(self.think_start_token)
@@ -101,35 +116,46 @@ class DeepSeekR1ReasoningParser(ReasoningParser):
                 # reasoning content continues
                 return DeltaMessage(reasoning_content=delta_text)
         else:
-            # No <think> in previous or delta, reasoning content continues.
+            # No <think> in previous or delta, also need to check for </think>.
+            # Because the model may have generated </think> without <think>
+            # Ref https://huggingface.co/deepseek-ai/DeepSeek-R1/commit/8a58a132790c9935686eb97f042afa8013451c9f
+            if self.think_end_token_id in delta_token_ids:
+                # </think> in delta with more tokens,
+                # extract reasoning content and content
+                end_index = delta_text.find(self.think_end_token)
+                reasoning_content = delta_text[:end_index]
+                content = delta_text[end_index + len(self.think_end_token):]
+                return DeltaMessage(reasoning_content=reasoning_content,
+                                    content=content if content else None)
+            elif self.think_end_token_id in previous_token_ids:
+                # </think> in previous, thinking content ends
                 return DeltaMessage(content=delta_text)
+            else:
+                # no </think> in previous or delta, reasoning content continues
+                return DeltaMessage(reasoning_content=delta_text)
 
     def extract_reasoning_content(
             self, model_output: str, request: ChatCompletionRequest
-    ) -> Tuple[Optional[str], Optional[str]]:
+    ) -> tuple[Optional[str], Optional[str]]:
 
-        # Check if the model output contains the <think> tokens.
-        if (self.think_start_token not in model_output
-                or self.think_end_token not in model_output):
-            return None, model_output
+        # DeepSeek R1 doesn't generate <think> now.
+        # Thus we assume the reasoning content is always at the start.
+        # Ref https://huggingface.co/deepseek-ai/DeepSeek-R1/commit/8a58a132790c9935686eb97f042afa8013451c9f
+        if self.think_end_token not in model_output:
+            return model_output, None
         else:
+            # Add a start token if it's missing to keep compatibility.
+            if self.think_start_token not in model_output:
+                model_output = f"{self.think_start_token}{model_output}"
             # Use a regex to find the reasoning content
             reasoning_content = self.reasoning_regex.findall(model_output)[0]
 
-            # Remove the reasoning content from the model output
-            # Although deepseek's <think> token is always at the
-            # beginning of the line, we cannot guarantee that the
-            # other models will follow this convention.
-            # Therefore, we need to add :start_index.
-            start_index = model_output.find(self.think_start_token)
-            if start_index != -1:
-                end_index = start_index + len(
+            end_index = len(
                 f"{self.think_start_token}{reasoning_content}{self.think_end_token}"
             )
-                model_output = model_output[:start_index] + \
-                                model_output[end_index:]
+            final_output = model_output[end_index:]
 
-                if len(model_output) == 0:
+            if len(final_output) == 0:
                 return reasoning_content, None
 
-            return reasoning_content, model_output
+            return reasoning_content, final_output
\ No newline at end of file