使用Python模拟Latex转图片API请求遭拒绝的问题排查

我在模拟一个将LaTeX代码转换为图片的API请求，浏览器中发送的请求完全正常，但用Python模拟时服务器拒绝连接，求排查解决。

浏览器中正常的请求信息 #

POST /default/latex2image HTTP/2
Host: e1kf0882p7.execute-api.us-east-1.amazonaws.com
Content-Length: 96
Sec-Ch-Ua: " Not A;Brand";v="99", "Chromium";v="104"
Accept: application/json, text/javascript, */*; q=0.01
Content-Type: application/x-www-form-urlencoded; charset=UTF-8
Sec-Ch-Ua-Mobile: ?0
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/104.0.5112.81 Safari/537.36
Sec-Ch-Ua-Platform: "Windows"
Origin: https://latex2image.joeraut.com
Sec-Fetch-Site: cross-site
Sec-Fetch-Mode: cors
Sec-Fetch-Dest: empty
Referer: https://latex2image.joeraut.com/
Accept-Encoding: gzip, deflate
Accept-Language: es-ES,es;q=0.9

{"latexInput":"\\begin{align*}\
{1}\
\\end{align*}\
",
"outputFormat":"PNG",
"outputScale":"125%"}

我的Python代码 #

pload = {
"latexInput":"{0}",
"outputFormat":"PNG",
"outputScale":"125%"
}

header = {
"Content-Length": "96",
"Sec-Ch-Ua": "Not A;Brand;v=99, Chromium;v=104",
"Accept": "application/json, text/javascript, */*; q=0.01",
"Content-Type": "application/x-www-form-urlencoded; charset=UTF-8",
"Sec-Ch-Ua-Mobile":"?0",
"User-Agent": "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/104.0.5112.81 Safari/537.36",
"Sec-Ch-Ua-Platform": "Windows",
"Origin": "https://latex2image.joeraut.com",
"Sec-Fetch-Site": "cross-site",
"Sec-Fetch-Mode": "cors",
"Sec-Fetch-Dest": "empty",
"Referer": "https://latex2image.joeraut.com/",
"Accept-Encoding": "gzip, deflate",
"Accept-Language": "es-ES,es;q=0.9",
}
r = requests.post("http://e1kf0882p7.execute-api.us-east-1.amazonaws.com", data=pload, headers=header)
print(r.text)
print(r.status_code)

运行后出现的错误 #

requests.exceptions.ConnectionError: HTTPConnectionPool(host='e1kf0882p7.execute-api.us-east-1.amazonaws.com', 
port=80): Max retries exceeded with url: / (Caused by NewConnectionError('<urllib3.connection.HTTPConnection object at 0x00000259A4D20670>: Failed to establish a new connection: [WinError 10061] No se puede establecer una 
conexión ya que el equipo de destino denegó expresamente dicha conexión'))

问题排查与解决 #

1. 请求URL错误 #

浏览器请求的完整路径是/default/latex2image，且使用HTTPS协议（HTTP/2），但你的代码仅指定了域名，未添加路径，且用了HTTP协议。AWS API Gateway默认只开放HTTPS端口443，HTTP端口80通常关闭，这是连接被拒绝的核心原因。

修正后的URL应为：https://e1kf0882p7.execute-api.us-east-1.amazonaws.com/default/latex2image

2. 手动设置Content-Length无效且易出错 #

你手动指定的Content-Length: 96和实际请求体长度不匹配时，服务器会因校验失败拒绝请求。requests库会自动计算并设置该字段，直接删除这个头即可。

3. 请求体格式不匹配 #

浏览器发送的是JSON格式请求体，但你用data=pload发送的是表单编码格式，和请求头描述存在矛盾。应使用json=pload发送JSON格式请求，同时将Content-Type改为application/json。

修正后的代码 #

import requests

pload = {
    "latexInput": "\\begin{align*}\n{1}\n\\end{align*}\n",
    "outputFormat": "PNG",
    "outputScale": "125%"
}

header = {
    "Sec-Ch-Ua": "\" Not A;Brand\";v=\"99\", \"Chromium\";v=\"104\"",
    "Accept": "application/json, text/javascript, */*; q=0.01",
    "Content-Type": "application/json",
    "Sec-Ch-Ua-Mobile": "?0",
    "User-Agent": "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/104.0.5112.81 Safari/537.36",
    "Sec-Ch-Ua-Platform": "\"Windows\"",
    "Origin": "https://latex2image.joeraut.com",
    "Sec-Fetch-Site": "cross-site",
    "Sec-Fetch-Mode": "cors",
    "Sec-Fetch-Dest": "empty",
    "Referer": "https://latex2image.joeraut.com/",
    "Accept-Encoding": "gzip, deflate",
    "Accept-Language": "es-ES,es;q=0.9",
}

r = requests.post("https://e1kf0882p7.execute-api.us-east-1.amazonaws.com/default/latex2image", json=pload, headers=header)
print(r.text)
print(r.status_code)

内容的提问来源于stack exchange，提问作者David pociello quadrado