missing field content HTTP 400 - Codex

Quick fix

Replace content:null with an empty string in CC Switch to fix strict upstream rejections.

Symptom

Error outputCopy

messages[1]: missing field `content` at line 1 column 34911

Cause

When forwarding via cc-switch (v3.19.x - v3.20.0) Responses→Chat conversion path (`apiFormat=openai_chat`) to third-party upstreams that strictly parse JSON Schema (e.g., Agnes, Yunzhou Public Welfare), title generation sub-requests initiated by Codex Desktop or multi-turn tool call scenarios trigger HTTP 400 errors.

The root cause lies in flaws in the internal conversion logic of cc-switch: 1. In `responses_message_item_to_chat_message`, when the input message item lacks a `content` field, the code executes `.unwrap_or(Value::Null)`, resulting in `"content": null` in the output JSON. 2. In `collapse_system_messages_to_head`, for messages where role is system but content is not a string (null or array), the merging logic does not match, causing the message to be retained and passed through unchanged. 3. In `flush_pending_tool_calls`, fixed production includes assistant messages containing `"content": null`.

Although OpenAI specification allows `content` to be null in tool_calls scenarios, many non-OpenAI upstreams (e.g., gateways based on serde) directly error out upon encountering null values with "missing field content" or "invalid content" during deserialization.

Fix

1. 1

   Modify the conversion logic in cc-switch source code to replace all occurrences producing `content: null` with an empty string. Specific locations involved: 1. `responses_message_item_to_chat_message`: Change `unwrap_or(Value::Null)` to `unwrap_or(Value::String(String::new()))`. 2. `collapse_system_messages_to_head`: Ensure system messages with non-string content are correctly handled or discarded to prevent passing through null. 3. `flush_pending_tool_calls`: Change the fixed `content: null` to an empty string.

   // src-tauri/src/proxy/providers/transform_codex_chat.rs
   // 修复点 1: responses_message_item_to_chat_message
    let content = item
        .get("content")
        .map(|value| responses_content_to_chat_content(chat_role, value))
        .unwrap_or(Value::Null);
    let content = item
        .get("content")
        .map(|value| responses_content_to_chat_content(chat_role, value))
        .unwrap_or(Value::String(String::new()));
   
   // 修复点 2 & 3: 确保 flush_pending_tool_calls 和 collapse_system_messages_to_head 不输出 null content

2. 2

   If you cannot modify the source code immediately, use a local reverse proxy (such as Nginx or a simple Node.js/Python script) to intercept outbound requests from cc-switch, replace all `"content": null` in the JSON body with `"content": ""`, and then forward to the upstream. This serves as a temporary mitigation.

Affected Versions

ToolCodex

Version3.19.0 - 3.20.0

PlatformsWindowsmacOSLinux

Source Issues

This page is distilled from 2 real issues

• #6033[BUG] Codex /responses→Chat 转换输出 content:null，严格上游(Agnes)报 400 "missing field content"
• #6918使用codex 和ccswitch配置时 codex 返回报错了

FAQ

Why does Claude Code not have this issue?

Claude Code typically uses Anthropic's native API format or different conversion paths; its request body structure handles null content more tolerantly, or its internal message building logic avoids generating empty system messages. This issue primarily affects scenarios using Codex and passing through Responses→Chat conversion.

Will I get this error if my upstream is the official OpenAI API?

No. The official OpenAI API has explicit compatibility handling for `content: null` (especially in tool_calls scenarios). Therefore, only third-party gateways or self-built upstreams that are very strict about JSON deserialization and do not support null values will trigger this error.

Are there other options besides modifying the source code?

Yes. You can use a local reverse proxy as middleware to automatically replace `content: null` with `content: ""` in the request body. This was mentioned in Issue #6033 as an effective temporary mitigation measure.

Related problems

Codex connecting to Kimi reports HTTP 400 tool schema validation failureUpgrade cc-switch to v3.18.0+; if the error persists, wait for the MFJS schema cleaning feature to go live.7 issues mergedHTTP 400 Invalid JSON /responsesChange meta.apiFormat of the Codex provider to openai_responses so requests are forwarded straight through.2 issues merged401 Unauthorized: Incorrect API key providedAfter switching to OpenAI Official or turning the proxy off, clear the leftover third-party OPENAI_API_KEY from ~/.codex/auth.json and restart Codex.2 issues merged