HTTP 100 (Continue): meaning and handling

Status / error code:		Category:

Constant name:
Source:		Operating System:
Description: HTTP 100 acknowledges that the initial request headers were received and the request body may follow.

Could be also:
Constant	Type	OS
ERROR_TOO_MANY_SEMAPHORES	Win32 error	Windows
ENETDOWN	errno	Linux
EPROTO	errno	Mac
EADDRINUSE	errno	Windows
SYMBOLIC_INITIALIZATION_FAILED	BugCheck Code	Windows

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	HTTP_STATUS_SWITCH_PROTOCOLS

HTTP_STATUS_CONTINUE

HTTP 100 is used with the Expect: 100-continue mechanism. It allows a client to send request headers first and wait before sending a potentially large request body.

This response is informational, not a final success result. A server can still reject the request with a final status after examining the headers, so clients must continue to read the response stream.

The interim response is most useful with Expect: 100-continue, allowing a client to avoid sending a large request body before the server accepts the request headers. It is not the final outcome. After receiving 100, the client sends the body and waits for the normal final response status.

RFC 9110: HTTP Semantics

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