fix: Gemini & Vertex empty content error

[tbphp]

PR 报告：修复 Gemini/Vertex 因消息内容为空导致的请求失败问题

一、问题描述

问题现象：
当 API 请求中 messages 数组包含 content 字段为空的条目时，向 Gemini 及 Vertex 渠道发送的请求会失败，上游服务返回 400 Bad Request 错误。

复现步骤:

curl -X POST http://127.0.0.1:3000/v1/chat/completions \
-H "Content-Type: application/json" \
-H "Authorization: Bearer sk-123456" \
-d '{
    "model": "gemini-pro",
    "messages": [
        {
            "role": "user",
            "content": "hello"
        },
        {
            "role": "user",
            "content": "" 
        }
    ]
}'

上游错误响应 (Error Response):

{
    "error": {
        "message": "Unable to submit request because it must include at least one parts field...",
        "code": 400
    }
}

背景：
此问题在多个客户端（如 SillyTavern, Cherry Studio 等）中都有出现，推测可能与上游服务（Google）近期对 API 请求参数校验规则的调整有关（因为最近才收到比较多的反馈）。

---

二、根本原因分析

在请求转换过程中，项目将 OpenAI 格式的 messages 转换为 Gemini 格式。当遇到 content 为空的 message 时，会生成一个 parts 字段为 null 的 content 对象。

转换后错误的请求体片段：

{
  "contents": [
    {
      "role": "user",
      "parts": [{ "text": "hello" }]
    },
    {
      "role": "user",
      "parts": null  // 此处为问题根源
    }
  ]
}

根据 Gemini API 的规范，parts 字段必须是一个包含至少一个有效元素的数组，null 值或空数组均不被接受，从而导致请求校验失败。

---

三、解决方案

在将消息转换为 Gemini 格式的 contents 数组时，增加一道过滤逻辑：如果一个 message 对象转换后的 parts 数组为空，则直接跳过该消息，不将其添加到最终的 contents 数组中。

代码实现：
在 relay/channel/gemini/relay-gemini.go 文件约 377 行处，增加对 parts 数组长度的判断。

// 代码示例
if len(content.Parts) > 0 {
    // 只有当 parts 不为空时，才将此 content 添加到请求体中
    geminiRequest.Contents = append(geminiRequest.Contents, content)
}

此修改可以从根本上避免生成不符合上游规范的请求体。

---

四、测试与验证

已在本地环境完成以下场景的回归测试，确保修复方案的正确性，且未引入新的问题：

• ✅ 核心功能：成功处理包含空消息的请求，不再报错。
• ✅ 多模态：图片和文本混合输入功能正常。
• ❌ 纯图片：只有图片没有文字的场景，上游报错400。经验证不是此pr影响，目前正式版本仍然有此问题。
• ✅ 多渠道兼容性：
  • ✅ Google AI Studio
  • ✅ Vertex AI
  • ✅ Vertex Express Mode(快速模式)
• ✅ 功能完整性：
  • ✅ 流式与非流式输出
  • ✅ 长上下文（>200k）处理
  • ✅ 长时间（>5m）请求
• ✅ MCP：支持正常。

除了本地自测之外，也正在邀请我站内的用户进行更大范围的用户场景测试，也许1，2天后会更新多场景测试结果。此修复对于提升 Gemini 渠道的稳定性至关重要，建议合并。

Summary by CodeRabbit

• Bug Fixes
  • Improved message handling to prevent empty messages from appearing in requests.

[coderabbitai]

Walkthrough

The update changes the logic in the CovertGemini2OpenAI function to only append GeminiChatContent objects to the request if their Parts slice is not empty, thereby filtering out empty message entries from the payload.

Changes

File(s)	Change Summary
relay/channel/gemini/relay-gemini.go	Modified logic to append GeminiChatContent only if its Parts slice is non-empty in CovertGemini2OpenAI.

Poem

In Gemini’s relay, the code now checks twice,
No empty messages—just content precise.
Only with parts does a message get through,
Filtering the empty, letting meaning accrue.
A hop and a skip, the payload’s now neat—
The relay’s more clever, and messages sweet!

---

📜 Recent review details

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📥 Commits

Reviewing files that changed from the base of the PR and between 0b9b21e and a87d427.

📒 Files selected for processing (1)

• relay/channel/gemini/relay-gemini.go (1 hunks)

🔇 Additional comments (1)

relay/channel/gemini/relay-gemini.go (1)

377-379: Excellent fix for the empty content issue!

This conditional check effectively prevents the root cause of the 400 Bad Request errors by filtering out messages with empty Parts arrays before they're sent to the Gemini API. The solution is minimal, targeted, and maintains backward compatibility while addressing the specific issue described in the PR objectives.

✨ Finishing Touches

• 📝 Generate Docstrings

---

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[QingyeSC]

感谢大佬的帮助，也遇到类似问题

[tbphp]

经过一天更广的用于多场景测试，确定parts相关问题已经修复，且多个复杂场景都使用正常。