使用Python-requests在JSF网站(SIGAA UnB)发起POST请求失败求助

我想在SIGAA UnB网站实现“选择院系、年份、学历后点击搜索”对应的POST请求。我用火狐开发者工具查看了POST请求详情，复制了请求头和请求体，提取了ID和会话Cookie，还把HTML响应导出到文件，但每次尝试都只返回初始页面，就像POST请求没生效一样，求指出缺失的部分。

原代码如下：

from bs4 import BeautifulSoup as BS4 
import requests

page = requests.Session()

# GET Method to search for Cookies and IDs
answer = page.get("https://sigaa.unb.br/sigaa/public/turmas/listar.jsf?aba=p-ensino")
my_cookie = answer.cookies
j_id = BS4(answer.text, "html.parser").find(id="javax.faces.ViewState")["value"]

post_header = {
    "Host": "sigaa.unb.br",
    "User-Agent": "Mozilla/5.0 (X11; Linux x86_64; rv:109.0) Gecko/20100101 Firefox/114.0",
    "Accept": "text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,*/*;q=0.8",
    "Accept-Language": "pt-BR,pt;q=0.8,en-US;q=0.5,en;q=0.3",
    "Accept-Encoding": "gzip, deflate, br",
    "Content-Type": "application/x-www-form-urlencoded",
    "Content-Length": "194",
    "Origin": "https://sigaa.unb.br",
    "Connection": "keep-alive",
    "Referer": "https://sigaa.unb.br/sigaa/public/turmas/listar.jsf?aba=p-ensino",
    "Cookie": str(my_cookie["JSESSIONID"]),
    "Upgrade-Insecure-Requests": "1",
    "Sec-Fetch-Dest": "document",
    "Sec-Fetch-Mode": "navigate",
    "Sec-Fetch-Site": "same-origin",
    "Sec-Fetch-User": "?1",
}

post_form = {
    "formTurma": "formTurma",
    "formTurma:inputNivel" :    "G",
    "formTurma:inputDepto" :    "673",
    "formTurma:inputAno" :  "2023",
    "formTurma:inputPeriodo" :  "1",
    "formTurma:j_id_jsp_1370969402_11" :    "Buscar",
    "javax.faces.ViewState": str(j_id),
}

answer = page.post("https://sigaa.unb.br/sigaa/public/turmas/listar.jsf?aba=p-ensino", data=post_form, headers=post_header, cookies=my_cookie)
profile_file = open("sigaa.html", "w")
profile_file.write(answer.text)

以下是导致请求失效的核心问题和修复方案：

• Cookie重复设置冲突：你已经用requests.Session()管理会话，它会自动保存和发送Cookie，但你又手动在请求头加了Cookie字段，还在POST时传了cookies=my_cookie，这会导致服务器收到重复或错误的Cookie信息。直接删掉请求头里的Cookie字段，POST时也不用传cookies参数，让Session自动处理即可。

• 硬编码Content-Length无效：Content-Length是根据请求体实际长度自动计算的，手动硬编码的数值如果和实际请求体长度不匹配，服务器会拒绝处理请求。直接移除请求头里的Content-Length字段。

• 动态按钮ID硬编码：formTurma:j_id_jsp_1370969402_11是JSF动态生成的按钮name属性，每次会话可能变化，不能硬编码。应该从初始GET请求的页面里解析——用BeautifulSoup找到显示文本为“Buscar”的按钮，提取它的name值。

• 冗余请求头可移除：Host字段requests会自动设置，不需要手动添加，可从请求头中移除。

from bs4 import BeautifulSoup as BS4 
import requests

page = requests.Session()

# 获取初始页面、Cookie和必要参数
target_url = "https://sigaa.unb.br/sigaa/public/turmas/listar.jsf?aba=p-ensino"
initial_response = page.get(target_url)
soup = BS4(initial_response.text, "html.parser")

# 提取ViewState
view_state = soup.find(id="javax.faces.ViewState")["value"]
# 提取搜索按钮的动态name属性
search_btn_name = soup.find("input", {"value": "Buscar"})["name"]

# 构造精简后的请求头
post_headers = {
    "User-Agent": "Mozilla/5.0 (X11; Linux x86_64; rv:109.0) Gecko/20100101 Firefox/114.0",
    "Accept": "text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,*/*;q=0.8",
    "Accept-Language": "pt-BR,pt;q=0.8,en-US;q=0.5,en;q=0.3",
    "Accept-Encoding": "gzip, deflate, br",
    "Content-Type": "application/x-www-form-urlencoded",
    "Origin": "https://sigaa.unb.br",
    "Connection": "keep-alive",
    "Referer": target_url,
    "Upgrade-Insecure-Requests": "1",
    "Sec-Fetch-Dest": "document",
    "Sec-Fetch-Mode": "navigate",
    "Sec-Fetch-Site": "same-origin",
    "Sec-Fetch-User": "?1",
}

# 构造请求体，使用动态获取的按钮name
post_data = {
    "formTurma": "formTurma",
    "formTurma:inputNivel": "G",
    "formTurma:inputDepto": "673",
    "formTurma:inputAno": "2023",
    "formTurma:inputPeriodo": "1",
    search_btn_name: "Buscar",
    "javax.faces.ViewState": view_state,
}

# 发送POST请求，Session自动管理Cookie
final_response = page.post(target_url, data=post_data, headers=post_headers)

# 保存响应内容
with open("sigaa.html", "w", encoding="utf-8") as output_file:
    output_file.write(final_response.text)

内容的提问来源于stack exchange，提问作者Raphides