Add support for reasoning_content field in chat completion messages for DeepSeek R1

[goodenough227]

feat: Add support for reasoning_content field in chat completion messages

This PR adds support for the reasoning_content field in the ChatCompletionMessage struct to accommodate models that return their reasoning process separately from the main content. This feature is particularly useful for:

• DeepSeek R1 model

Both models return their step-by-step reasoning process through this field.

Changes:

• Added reasoning_content field to ChatCompletionMessage struct
• Updated JSON marshaling/unmarshaling to handle the new field
• Field is optional (omitempty) to maintain backwards compatibility

Example response structure:

{
    "role": "assistant",
    "reasoning_content": "1. First, I analyze the question...\n2. Based on the given information...",
    "content": "The final answer is..."
}

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.87%. Comparing base (774fc9d) to head (5273861).
Report is 85 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #925      +/-   ##
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+ Coverage   98.46%   98.87%   +0.41%     
==========================================
  Files          24       27       +3     
  Lines        1364     1783     +419     
==========================================
+ Hits         1343     1763     +420     
+ Misses         15       14       -1     
  Partials        6        6              

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[sashabaranov]

@goodenough227 could you please point to the OpenAI API reference for this one? Or is this field only supported by DeepSeek currently?

[yayanet]

@goodenough227 could you please point to the OpenAI API reference for this one? Or is this field only supported by DeepSeek currently?

I also have a need for this feature.
The reasoning_content field is currently specific to deepseek-reasoner model (docs)

[goodenough227]

@goodenough227 could you please point to the OpenAI API reference for this one? Or is this field only supported by DeepSeek currently?

sorry for this wrong description generated by AI code hepler. "reasoning_content" field is only supported by deepseek R1 currently.

[sashabaranov]

Originally, this repository was targeted on the official OpenAI API. But, in the context of the official client popping up — I'm willing to merge this reasoning_content field that OpenAI API might not support.

My only ask here is: can we please clearly indicate that this field is not supported by OpenAI? Ideally, it should be obvious from the variable name and from reading the docs. Thank you!

[goodenough227]

Originally, this repository was targeted on the official OpenAI API. But, in the context of the official client popping up — I'm willing to merge this reasoning_content field that OpenAI API might not support.

My only ask here is: can we please clearly indicate that this field is not supported by OpenAI? Ideally, it should be obvious from the variable name and from reading the docs. Thank you!

Get it. I have written a comment on this field.

[goodenough227]

@sashabaranov I have added comments in a similar way as in the previous code, please review

[He-hongjun]

Hope to merge and support this as soon as possible. Thank you for your contribution! @sashabaranov @goodenough227

[wangriyu]

please review&approved, thank you @sashabaranov @goodenough227

[xiaozhi747]

mark