Not every network request sends a cookie to the browser. This primarily depends on the server's configuration and the browser's cookie policy.
1. Server Settings
Typically, when a user first visits a website, the server may include a Set-Cookie header in the response, causing the browser to store the cookie. In subsequent requests, the browser automatically attaches the cookie to the request header only if the request domain matches the cookie's domain. Additionally, if the server does not set a cookie for certain resources, the browser will not include the cookie in requests for those resources.
2. Browser Policies
Browsers also have their own policies to determine whether to send cookies. For example, browsers can be configured to block third-party cookies, meaning only first-party cookies (i.e., from the directly interacting site) are sent. Furthermore, users can choose to completely disable cookies via browser settings, ensuring no cookies are sent in any request.
3. Example
Suppose a user visits an online shopping website that sets a session cookie upon the user's first visit to maintain the login state. When the user browses different pages of the website, as long as these pages belong to the same domain, each HTTP request includes this session cookie. However, if the website includes content from other domains (such as ads or social media plugins), requests from those other domains may not include the original website's cookie unless a specific cross-origin policy is in place.
Summary Therefore, whether a cookie is sent with every network request depends on multiple factors, including how the server sets cookies, the browser's cookie policy, and whether the target resource matches the cookie's domain. Not all network requests send cookies, which helps protect user privacy and reduce unnecessary data transmission.