Handling blank line in BufferedReader

Question

I am receiving this POST request from a client:

HTTP method: POST
Host: 127.0.0.1:52400
Connection: keep-alive
Content-Length: 18
Pragma: no-cache
Cache-Control: no-cache
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8
Origin: null
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_10_1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/38.0.2125.122 Safari/537.36
Content-Type: application/x-www-form-urlencoded
Accept-Encoding: gzip,deflate
Accept-Language: da-DK,da;q=0.8,en-US;q=0.6,en;q=0.4,es;q=0.2

fname=foof&pw=bar

I have a small and very simple Java Webserver running, getting this request from InputStream. From the BufferedReader I set data to a String, containing the request, like this:

for (String line; (line = in.readLine()) != null; ) {
    if (line.isEmpty()) break;
    header += line + "\n";
}

When I print header to the console, I get this:

POST / HTTP/1.1
Host: 127.0.0.1:52400
Connection: keep-alive
Content-Length: 18
Pragma: no-cache
Cache-Control: no-cache
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8
Origin: null
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_10_1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/38.0.2125.122 Safari/537.36
Content-Type: application/x-www-form-urlencoded
Accept-Encoding: gzip,deflate
Accept-Language: da-DK,da;q=0.8,en-US;q=0.6,en;q=0.4,es;q=0.2

The POST parameters are left out

I guess the problem occurs due to the blank line in the post-request.

How can I make sure the BufferedReader does read the request to the end, and not stopping at the blankline, all though stopping when the BufferedReader hits the end of the request.

Please ignore the lack of security in this example - I simply need to get the POST request into plain string representation for now.

Any help on this i appreciated, thanks! Jesper.

"I guess the problem occurs due to the blank line in the post-request." - have you verified this via unit test or sample request removing the blank line? — Smutje, Nov 17 '14 at 14:04
Probably related: http://stackoverflow.com/questions/13706466/how-do-i-tell-if-an-empty-line-has-been-read-in-with-a-bufferedreader — Smutje, Nov 17 '14 at 14:05
I don't think its blank line related issue. And readLine() doesn't returns string without trailing `\r\n`. Can you please post code how are you displaying lines? — brb tea, Nov 17 '14 at 14:36
@brbtea I have updated my for-loop. This gives me the exact result in the console, as shown. I need to get rid of the if-statement, in a clever way, because if I just remove it, the response from server is never sent. — Jesper Bruun Hansen, Nov 17 '14 at 15:01
Okay, the problem was solved by following this example http://stackoverflow.com/a/6329560/2804903 — Jesper Bruun Hansen, Nov 17 '14 at 16:17
`if (line.isEmpty()) break;` it was the issue, and you didn't post this in question. You will get empty line between headers and post parameters, and you are breaking loop there, so you will never reading post parameters. — brb tea, Nov 17 '14 at 17:39

score 0 · Answer 1 · answered Nov 17 '14 at 17:57

The problem is because you have a break in your for loop. When you reach the blank line, it hits the break and exits the loop, not adding any of the lines after that. Instead, you should use this:

for (String line; (line = in.readLine()) != null; ) {
    if (line.isEmpty()) continue;
    header += line + "\n";
}

By using continue instead of break, the loop will simply proceed to the next iteration, and the rest of the lines can be added.

More information can be found here

Handling blank line in BufferedReader

1 Answers1