HTTP 100 Continue vs 412 Precondition Failed
HTTP 100 (Continue) is a 1xx Informational response, while 412 (Precondition Failed) is a 4xx Client Error response. 100 indicates that the server has received the request headers and the client should proceed to send the request body. This lets the client know it can continue with the request or abort if the headers were rejected. In contrast, 412 means that one or more conditions in the request headers (If-Match, If-Unmodified-Since) evaluated to false.
Descripción
The server has received the request headers and the client should proceed to send the request body. This lets the client know it can continue with the request or abort if the headers were rejected.
Cuándo lo verás
When a client sends an Expect: 100-continue header, the server responds with 100 before the client sends the body.
Cómo solucionarlo
This is an interim response — no fix needed. The client should continue sending the request body.
Descripción
One or more conditions in the request headers (If-Match, If-Unmodified-Since) evaluated to false.
Cuándo lo verás
When using conditional requests with ETags and the resource has changed.
Cómo solucionarlo
Refresh the ETag/Last-Modified value and retry with updated preconditions.
Diferencias clave
100 is a 1xx Informational response, while 412 is a 4xx Client Error response.
HTTP 100: The server has received the request headers and the client should proceed to send the request body. This lets the client know it can continue with the request or abort if the headers were rejected.
HTTP 412: One or more conditions in the request headers (If-Match, If-Unmodified-Since) evaluated to false.
You encounter 100 when when a client sends an Expect: 100-continue header, the server responds with 100 before the client sends the body.
You encounter 412 when when using conditional requests with ETags and the resource has changed.
Cuándo usar cada uno
For 100 (Continue): This is an interim response — no fix needed. The client should continue sending the request body. For 412 (Precondition Failed): Refresh the ETag/Last-Modified value and retry with updated preconditions.