如何理解Chrome DevTools中的请求标头？

Question

I've sent a http request with custom headers to a localhost page, and the result is as follow image.

I used php to print out the requests. The printed requests are my custom requests as expect, but the other one in Chrome network tab is different. We can take User-Agent as an example. Why are they different? Which one should I believe?

P.S.

Maybe I cause some misunderstandings.

1. I use selenium webdriver to control the browser to visit a website
2. the UA is not from a Nexus, you can consider it as a custom value like "My UA"

The procedure is like [WebDriver] -> [Browser] -> [WebSite].

I guess maybe it is because that the chrome browser shows the default headers, and webdriver post the modified headers to browser to change them, and finally website server received the merged modified headers.

Answer 1

The user agent header contains a string describing your browser. Accessing a web page from different browsers will provide different values for the user agent header. According to the right image, you accessed the page from Google Chrome on a Mac - this appears to be true, because you are using the Chrome developer tools. According to the left image, you accessed the page from a Nexus mobile device. If the screenshot on the left is, in fact, from a Nexus mobile, then there is no problem; this is the expected behavior of the user agent header. If the image on the left is from your Chrome browser as well, then I would assume that there is some sort of problem with your custom headers.