为何在Python Socket请求中需同时指定Host与HTTP Host头？

Great question—this is one of those things that seems redundant at first glance, but they’re actually handling two completely separate jobs, even though they share the same name. Let’s break it down clearly:

1. The Host in Socket Creation: For Building the Underlying Network Connection #

When you create a socket and pass a host (like example.com) and port, you’re telling your system:

• "Use DNS to turn this hostname into an actual IP address."
• "Open a TCP connection to that IP address on the specified port (usually 80 for plain HTTP, 443 for HTTPS)."

This is all about low-level network plumbing. The socket doesn’t know or care about HTTP—it just needs to find the right server machine on the internet and establish a line of communication. Without this step, you can’t send any data to the server at all.

2. The Host Header in the HTTP Request: For Routing to the Correct Website #

Once the TCP connection is up and running, the Host header is a requirement of the HTTP/1.1 protocol (and modern servers expect it even if you use older versions). Here’s why it’s non-negotiable:

• Most servers today are virtual hosts—a single physical server (with one IP address) hosts dozens or hundreds of different websites.
• When the server gets your HTTP request over the already-connected TCP line, it needs to know which of those websites you’re trying to access. The Host header is how it makes that call.

To make it concrete:

• You create a socket to example.com (which resolves to IP 93.184.216.34).
• But in your HTTP request, you set the Host header to test.com.
• If the server at 93.184.216.34 hosts both sites, it will return content for test.com instead of example.com.

Even if the server only hosts one website, including the Host header is still best practice to comply with HTTP standards.

内容的提问来源于stack exchange，提问作者jsstuball