HTTP response without content-length doesn't work

Swamp Thing · Jan 22, 2024

I am trying out the web server feature on a NodeMCU ESP8266 board. If I include a Content-Length line in the response header, it works perfectly.

But if I omit the content-length, then Chrome and Firefox fail to display the page. Chrome displays a blank page, and Firefox says "Connection was reset".

This is the HTTP response as received on Telnet:

Code:

HTTP/1.1 200 OK
Content-Type: text/html
Connection: close

<html><body>Hello</body></html>
Connection closed by foreign host.

(There is a "\r\n" at the end of each line and after the header).

Curl and Wget also report "connection closed" errors.

My understanding is that if content-length is not specified, then closing the connection is a valid way to signal end of data. Especially with "connection: close". So what is the problem?

harborsparrow · Jan 22, 2024

The Content-Length header is mandatory for messages with entity bodies, unless the message is transported using chunked encoding. Some info on chunked encoding is here: https://en.wikipedia.org/wiki/Chunked_transfer_encoding

HTTP response without content-length doesn't work

1. What does it mean when an HTTP response doesn't have a Content-Length header?

2. Why might an HTTP response not include a Content-Length header?

3. What issues can occur if an HTTP response lacks a Content-Length header?

4. How can a server correctly handle responses without a Content-Length header?

5. What are the best practices for developers dealing with HTTP responses without Content-Length headers?

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