为何HTTP/2中404等状态码的头部省略文本描述？

Great question! This comes down to intentional design decisions in HTTP/2 that prioritize efficiency and simplify machine-to-machine communication, ditching redundant components from the older HTTP/1.x spec. Here's a breakdown:

• Reason phrases are a legacy from HTTP/1.x
  In HTTP/1.1, status codes like 404 were paired with human-readable reason phrases (e.g., "Not Found") because early versions of HTTP were more focused on being human-friendly. But these phrases are completely unnecessary for machines—client applications only need the numeric status code to understand the response's meaning.

• HTTP/2's binary framing eliminates redundancy
  Unlike HTTP/1.x's text-based format, HTTP/2 uses a binary framing layer to transmit data. This design was built to cut down on overhead and speed up transfers. Reason phrases count as redundant data here, so the spec simply removes them entirely. Servers don't send them, and clients don't expect or parse them.

• The HTTP/2 spec explicitly mandates this
  RFC 7540 (the official HTTP/2 standard) clearly states that status codes are transmitted as numeric values only, with no accompanying reason phrase. This simplifies the protocol by removing potential inconsistencies—for example, different HTTP/1.1 servers might return variations like "NOT FOUND" or "Not Found", but the numeric 404 is universally consistent.

• Client-side handling keeps user experience intact
  Even though the reason phrase is missing from the HTTP/2 response, modern clients (like browsers or tools like curl) will still display the familiar human-readable text when needed. They map the numeric status code to a standard reason phrase internally, so users don't notice the difference.

To put it simply: HTTP/2 cuts the fluff that machines don't need, while still ensuring humans get the context they require through client-side mapping.

内容的提问来源于stack exchange，提问作者Example person