如何修复Google Apps Script向FastAPI发送PDF的POST请求报错

问题场景 #

通过Google Apps Script（GAS）将Google Drive中的PDF文件发送到自研FastAPI接口，接口负责提取PDF文本生成摘要并返回HTML文件。Swagger UI调用接口正常，但GAS调用时提示uploaded_file字段缺失。

现有代码 #

GAS代码 #

function process_PDF_file() {
  const PDF_fileId = "###"; // Google Drive中目标PDF的文件ID
  const url = "###"; // API接口地址

  const payload = {
    file: DriveApp.getFileById(PDF_fileId).getBlob()
  };
  let config = { muteHttpExceptions: true, payload };
  let response = UrlFetchApp.fetch(url, config);
  var data = JSON.parse(response.getContentText());
  Logger.log(data);
}

FastAPI路由代码 #

from fastapi import FastAPI, File

app = FastAPI()

@app.get("/")
async def root():
    return {"message": "Hello Summary Creator"}

@app.post("/file")
async def endpoint(uploaded_file: bytes = File()):
    content = uploaded_file
    filename = "temp.pdf"
    with open(filename, "wb") as f:
        f.write(content)
    main_routine()  # 自定义的摘要生成逻辑
    return {"Summary": f"{summary_download}"}

if __name__ == "__main__":
    import uvicorn
    uvicorn.run(app, host="127.0.0.1", port=8000)

报错信息 #

10:56:22 AM Info {detail=[{type=missing, url=https://errors.pydantic.dev/2.9/v/missing, input=null, loc=[body, uploaded_file], msg=Field required}]}

修复方案 #

核心问题 #

FastAPI的File()参数要求请求采用multipart/form-data格式，且字段名必须与接口参数名uploaded_file完全匹配。原GAS代码存在三个关键问题：

1. 默认使用GET请求，而接口是POST路由
2. 表单字段名用了file，与接口要求的uploaded_file不匹配
3. 未正确配置multipart/form-data请求头

修正后的GAS代码 #

function process_PDF_file() {
  const PDF_fileId = "###";
  const url = "###";

  // 获取PDF blob并指定文件名（可选但推荐）
  const pdfBlob = DriveApp.getFileById(PDF_fileId).getBlob().setName("uploaded.pdf");
  
  const payload = {
    uploaded_file: pdfBlob // 字段名与FastAPI参数名一致
  };
  
  const config = {
    method: "POST", // 明确指定POST方法
    muteHttpExceptions: true,
    contentType: false, // 让GAS自动处理multipart/form-data格式
    payload: payload
  };
  
  const response = UrlFetchApp.fetch(url, config);
  const data = JSON.parse(response.getContentText());
  Logger.log(data);
}

可选的FastAPI接口优化 #

为了更规范地处理文件上传（包括获取文件名等元数据），可以将接口参数改为UploadFile类型：

from fastapi import FastAPI, File, UploadFile

app = FastAPI()

@app.get("/")
async def root():
    return {"message": "Hello Summary Creator"}

@app.post("/file")
async def endpoint(uploaded_file: UploadFile = File(...)):
    // 读取文件内容
    content = await uploaded_file.read()
    // 使用上传的文件名，或自定义
    filename = uploaded_file.filename
    
    with open(filename, "wb") as f:
        f.write(content)
    
    main_routine()
    return {"Summary": summary_download}

if __name__ == "__main__":
    import uvicorn
    uvicorn.run(app, host="127.0.0.1", port=8000)

内容的提问来源于stack exchange，提问作者Mike B.