The key issue here is that FastHTTPUser uses a different underlying HTTP client (geventhttpclient) compared to HTTPUser (which relies on requests), so the cookies parameter syntax you’re used to won’t work directly. Here are two reliable, practical methods to set hardcoded cookies with FastHTTPUser:

Method 1: Manually Construct the Cookie Header (for one-off requests) #

Since cookies are transmitted via the Cookie HTTP header, you can build the header string yourself and include it in your request headers. This is ideal if you only need cookies for a single request.

from locust import task, FastHTTPUser

class LoadTestUser(FastHTTPUser):
    @task
    def send_post_request(self):
        # Define your cookies as a key-value dict
        my_cookies = {
            "session_id": "my-hardcoded-session-123",
            "user_auth_token": "xyz-abc-789"
        }
        
        # Convert the dict to a valid Cookie header string
        cookie_header = "; ".join([f"{key}={value}" for key, value in my_cookies.items()])
        
        # Build your request headers (include the Cookie header)
        request_headers = {
            "Content-Type": "application/json",
            "Cookie": cookie_header
        }
        
        # Your POST payload
        post_payload = {"action": "submit", "data": "test-content"}
        
        # Send the POST request
        response = self.client.post(
            url="/api/submit",
            json=post_payload,
            headers=request_headers
        )

Method 2: Persist Cookies to the Client (for all user requests) #

If you want the cookies to be automatically included in every request made by the user, you can populate the FastHTTPUser client’s cookies attribute (a SimpleCookie object) during the user’s initialization phase.

from locust import task, FastHTTPUser
from http.cookies import SimpleCookie

class LoadTestUser(FastHTTPUser):
    def on_start(self):
        # Runs once when the user starts (perfect for setup tasks)
        user_cookies = SimpleCookie()
        
        # Add your hardcoded cookie pairs
        user_cookies["session_id"] = "my-hardcoded-session-123"
        user_cookies["user_auth_token"] = "xyz-abc-789"
        
        # Attach the cookies to the client—they'll be sent with all subsequent requests
        self.client.cookies.update(user_cookies)
    
    @task
    def send_post_request(self):
        post_payload = {"action": "submit", "data": "test-content"}
        
        # No need to specify cookies here—they're automatically included
        response = self.client.post(
            url="/api/submit",
            json=post_payload
        )

Key Notes: #

• FastHTTPUser’s client does not support the cookies parameter that HTTPUser (requests-based) uses, so you can’t pass a dict directly to post() or get() like you did before.
• For dynamic cookies (e.g., retrieved from a login response), you can extract the Set-Cookie header from the login response and add it to the client’s cookies using the same SimpleCookie approach.

内容的提问来源于stack exchange，提问作者vnbal