将标头发送到客户端后，无法设置标头

Question

我正在创建一个api，该api将使用nodejs中的python shell调用python脚本。然而，当我运行api时，api返回错误"；在将标头发送到客户端之后无法设置标头"；。下面是api的代码。

app.post(
"/uploadFacial",
multer({
storage: storage
}).single('upload'), function(req, res) {
console.log(req.file.filename);
var userid = req.body.upload[1];
console.log("User id: "+userid);
var success = true;
var message = '';
var subStringUserId = userid.substring(1,userid.length-1);
var dir = "./users/"+subStringUserId;
//res.setHeader("Content-Type", "application/json");

console.log(dir);
if (!fs.existsSync(dir)){
fs.mkdirSync(dir);
success = false;
message = 'Cannot detect the person.Please add name in the textbox provided below to save the person.';
res.status(200).json({message: message,success:success});
res.end();
}else {
console.log("in else");
var options={
mode:'text',
encoding:'utf-8',
pythonOptions:['-u'],
scriptPath:'./',
pythonPath:'',
args:[subStringUserId,req.file.filename]
}
var facialScript = new PythonShell('face_detect.py',options)
facialScript.on('message',(response)=>{
console.log(response);
res.status(200).send(response);
//res.end();

})
facialScript.on('error',(err)=>{
console.log(err);
})
}
});

如果需要，下面是python代码

from deepface import DeepFace
from os.path import join, dirname, realpath
import os, sys
import json

PARENT_DIR = join(dirname(realpath(__file__)), './users/')
TEST_DIR = join(dirname(realpath(__file__)), './uploads/')
print(json.dumps({'success':False,'message':'Cannot detect at moment.Please try later'})) #this is only for debugging
user_id = sys.argv[1] 

img_name = sys.argv[2]

db = os.path.join(PARENT_DIR, user_id)
img = os.path.join(TEST_DIR, img_name)
try:
df=DeepFace.find(img_path=img,db_path=db, model_name = "Facenet")
if(df.size==0):
print(json.dumps({'message': 'Cannot detect the person.Please add name in the textbox provided below to save the person.','success':False}))
else:
print(json.dumps({'success':True,'message':os.path.splitext(os.path.basename(df['identity'][0]))[0]}))        


except Exception as e: 
#logger.error('Failed to upload to ftp: '+ str(e))
a = 1

这是错误

throw new ERR_HTTP_HEADERS_SENT('set');
^
Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client
at ServerResponse.setHeader (_http_outgoing.js:470:11)
at ServerResponse.header (/Users/priyamvora/Node/Drishti/ImageUploadTest/node_modules/express/lib/response.js:771:10)
at ServerResponse.send (/Users/priyamvora/Node/Drishti/ImageUploadTest/node_modules/express/lib/response.js:170:12)
at PythonShell.facialScript.on (/Users/priyamvora/Node/Drishti/ImageUploadTest/multipart.js:129:27)
at PythonShell.emit (events.js:182:13)
at /Users/priyamvora/Node/Drishti/ImageUploadTest/node_modules/python-shell/index.js:324:22
at Array.forEach (<anonymous>)
at PythonShell.receiveInternal (/Users/priyamvora/Node/Drishti/ImageUploadTest/node_modules/python-shell/index.js:322:15)
at PythonShell.receive (/Users/priyamvora/Node/Drishti/ImageUploadTest/node_modules/python-shell/index.js:296:21)
at Socket.emit (events.js:182:13)

请尽早提供帮助。

Answer 1

如果执行了此If循环，则会发送响应

if (!fs.existsSync(dir)){
fs.mkdirSync(dir);
success = false;
message = 'Cannot detect the person.Please add name in the textbox provided below to save the person.';
res.status(200).json({message: message,success:success});
res.end();

一个响应试图发送以下代码太

var facialScript = new PythonShell('face_detect.py',options)
facialScript.on('message',(response)=>{
console.log(response);
res.status(200).send(response);
//res.end();

})

它不包括在else循环中。

Answer 2

这是因为；消息"；事件侦听器被触发不止一次，这就是为什么res.status(200).send(response);行执行不止一次导致此问题的原因。尝试将事件侦听器的结果累积在一个变量中，并发送响应(仅一次(。类似这样的东西：

let result="";
facialScript.on('message',(response)=>{
result=result+response;//assuming that response is string you can change this as per your convenience .

})
facialScript.on("end",()=>{
res.send(result);
})

此外，如果用于标识目录是否存在的条件，则必须删除内部的res.status(200).json({message: message,success:success});！！