POST请求下Flask重定向后渲染大量数据触发连接重置问题

现象说明 #

• 在POST请求流程中，通过flask.redirect（使用307状态码）跳转后，调用flask.render_template向客户端返回大量记录时，会出现ERR_CONNECTION_RESET连接重置错误
• 若跳过重定向步骤，直接调用返回render_template的函数，无论返回数据量大小，均不会出现连接重置问题
• 当number_records≥500时，该错误在Chromium浏览器中必现，在Firefox浏览器中随机出现

运行环境 #

• Python 3.10.9
• Flask 2.0.3
• Chromium 107.0.5304.121
• Firefox 108.0.1

复现代码 #

from flask import Flask, render_template_string, redirect, url_for

# ERR_CONNECTION_RESET depends on number_records
number_records = 100    # no error observed
number_records = 500
number_records = 1000

# data used in templates
choices = ["choice_1", "choice_2", "choice_3"]
dn = {}
for i in range(1, number_records+1):
    dn[i] = "name_%d" %(i)

# flask app
app = Flask(__name__)

@app.route("/")
def main():
    tmpl1 = """
<!doctype html>
<html>
  <head><title>Test main</title></head>
  <body>
    <hr>
    <form method=POST action=manage_names>
      <h1>Select the names</h1>
      <table id="t_names">
        <thead>
          <tr>
            <th>Select</th>
            <th>name</th>
          </tr>
        </thead>
        {% for k, v in dn.items() %}
        <tbody>
          <tr>
            <td>
              <input type="checkbox" name="select" value="{{ k }}" checked></input>
            </td>
            <td>{{ v }}</td>
          </tr>
        </tbody>
        {% endfor %}
      <br>
      </table>
      <br>
      <button type=submit name=submit-button value=submit method=POST>submit</button>
    </form>
  </body>
</html>
"""
    return render_template_string(tmpl1, dn=dn)

@app.route("/manage_names", methods=["POST"])
def _manage_names():
    # no code for tests
    return redirect(url_for("_set_choices"), code=307)

@app.route("/set_choices", methods=["POST"])
def _set_choices():
    tmpl2 = """
<!doctype html>
  <html>
  <head><title>Test ERR_CONNECTION_RESET</title></head>
  <body>
    <hr>
    <form method=POST action=manage_choices><h1>Set the choices</h1>
      <table id="t_choices" class="choice">
        <thead>
          <tr>
            <th>name</th>
            <th>choice</th>
          </tr>
        </thead>
        {% for k, v in dn.items() %}
        <tbody>
          <tr>
            <td>{{ v }}</td>
            <td>
              <input type="hidden" name="id" value="{{ k }}"/>
              <select name="choice" id="{{ k }}">
                {% for c in choices %}
                <option>{{ c }}</option>
                {% endfor %}
              </select>
            </td>
          </tr>
        </tbody>
        {% endfor %}
        <br>
      </table>
      <br>
    <button type=submit name=submit-button value=submit method=POST>submit</button>
    </form>
  </body>
</html>
"""
    return render_template_string(tmpl2, dn=dn, choices=choices)

@app.route("/manage_choices", methods=["POST"])
def _manage_choices():
    # For tests
    return redirect("/")

if __name__ == '__main__':
    app.run(debug=True)

内容的提问来源于stack exchange，提问作者fcpp1