HTTP 100 Continue vs 417 Expectation Failed
HTTP 100 (Continue) is a 1xx Informational response, while 417 (Expectation 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, 417 means that the server cannot meet the requirements of the Expect header.
Description
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.
When You See It
When a client sends an Expect: 100-continue header, the server responds with 100 before the client sends the body.
How to Fix
This is an interim response — no fix needed. The client should continue sending the request body.
Description
The server cannot meet the requirements of the Expect header.
When You See It
When the server doesn't support Expect: 100-continue.
How to Fix
Remove the Expect header from your request.
Key Differences
100 is a 1xx Informational response, while 417 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 417: The server cannot meet the requirements of the Expect header.
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 417 when when the server doesn't support Expect: 100-continue.
When to Use Which
For 100 (Continue): This is an interim response — no fix needed. The client should continue sending the request body. For 417 (Expectation Failed): Remove the Expect header from your request.