Getting ERR_INVALID_HTTP_RESPONSE using web server code in Land of Lisp with clisp on OS X

Question

I'm reading Land of Lisp (it's 10 years old, but so is clisp, so it seems up to date enough). I'm on Chapter 13, where you write a web server. It just opens the client socket as standard-output, then uses princ and format t to write out to the client. The full source code of the web server is at http://landoflisp.com/webserver.lisp.

I'm having the same problem with both my typed in code and downloading the webserver.lisp from the website and running it. When I go to the site in Chrome, I get ERR_INVALID_HTTP_RESPONSE. In Safari I get can't open page. When I try to go to the site in Firefox, I get the expected page, but all of the html tags are just rendered as text. When I try interacting with the site in curl, I'm getting a closing % in the output that I'm not sure where it's coming from.

> curl http://localhost:8080/greeting
<html><form>What is your name?<input name='name' /></form></html>%

I know it's not the best HTML, but it does the same if I add body tags and declare doctype html at the start too. The % in the curl response isn't there in the princ, and I get a % when I try going to other URL's for the server like localhost:8080 or localhost:8080/greeting?name=Lewis.

I don't actually plan to use this web server for much of anything, but the rest of the book seems involved in making an app that uses it, and I'ld like to finish the book, so it would be nice if I could at least get the web server working with at least one browser.

Oh, normal web pages like www.google.com have a % at the end of the output too when I do command-line curl is OS X, so I guess that fact isn't relevant. Well, google does, but microsoft.com doesn't. Not sure where it comes from. — Lewis Cawthorne
– Lewis Cawthorne, Commented Apr 4, 2019 at 23:03
I think this is related to your problem groups.google.com/forum/#!topic/land-of-lisp/afwjs0eic94 — Martin Buchmann
– Martin Buchmann, Commented Apr 5, 2019 at 14:57
@MartinBuchmann: for more conformance write CR LF at the end of a line. For security: never call read-from-string without *read-eval* being nil. — Rainer Joswig
– Rainer Joswig, Commented Apr 5, 2019 at 21:02
Hmm.. I tried adding (format t "HTTP/1.1 200 OK~%") before the other output in a progn block, but it didn't fix anything. — Lewis Cawthorne
– Lewis Cawthorne, Commented Apr 6, 2019 at 2:57
If you are on UNIX ~% will write a linefeed. The end of a HTTP line is cr and then lf. Not just lf alone. Write a return character and then a linefeed character. — Rainer Joswig
– Rainer Joswig, Commented Apr 6, 2019 at 5:44

Lewis Cawthorne · Accepted Answer · 2019-04-06 15:23:09Z

1

Looks like this fixed it, as per the discussion above pointing to the forum. We needed an "HTTP 1.1 200 OK" followed by a \r\n, then a \r\n on a newline by itself, then the page. That got it working right in both Firefox and Chrome. I just added this to the request handler:

(format t "HTTP/1.1 200 OK~C~C" #\return #\linefeed)
(format t "~C~C" #\return #\linefeed)

Thanks for all the help in the discussion getting me to this answer!

answered Apr 6, 2019 at 15:23

Lewis Cawthorne

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