MCP SSE client missing Accept header for text/event-stream #2651

Description

When connecting to remote MCP servers that use SSE (Server-Sent Events), nanobot does not send the required Accept header that includes both application/json and text/event-stream.

Affected MCP Servers

This issue affects Z.ai MCP servers:

• https://api.z.ai/api/mcp/web_search_prime/mcp
• https://api.z.ai/api/mcp/web_reader/mcp

These servers require:

Accept: application/json, text/event-stream

Current Behavior

Nanobot sends only Accept: application/json, causing the server to reject the connection with an error like:

Accept header must include both application/json and text/event-stream

Expected Behavior

Nanobot should send:

Accept: application/json, text/event-stream

Workaround

Using curl with the correct headers works:

curl -X POST "https://api.z.ai/api/mcp/web_reader/mcp" \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -H "Accept: application/json, text/event-stream" \
  -d "{\"jsonrpc\":\"2.0\",\"id\":1,\"method\":\"initialize\",\"params\":{...}}"

Environment

• nanobot v0.1.4.post6
• Ubuntu 22.04
• Config:

{
  "mcpServers": {
    "web-reader": {
      "type": "sse",
      "url": "https://api.z.ai/api/mcp/web_reader/mcp",
      "headers": {
        "Authorization": "Bearer YOUR_API_KEY"
      }
    }
  }
}

Related

• MCP Spec: https://modelcontextprotocol.io/specification/2025-03-26/basic/transports#http-with-sse