Lighttpd

I think you might want to start with a "How to" on writing CGI. Your script should include something like printf "Status: 200\r\n" before printf "Content-type: text/plain\r\n\r\n"

The Common Gateway Interface (CGI) Version 1.1
https://datatracker.ietf.org/doc/html/rfc3875

You might want to include btmgmt --timeout 10 info in the command.
You can test btmgmt --timeout 10 info </dev/null 2>/dev/null to redirect stdin and stderr to /dev/null
If your system has /usr/bin/timeout, you might test with /usr/bin/timeout 10 btmgmt --timeout 10 info </dev/null 2>/dev/null

stdin and stdout of the CGI are pipes. stderr is a file IFF you specify server.breakagelog in your lighttpd.conf, or else it is the same as lighttpd stderr.

If you're expecting a streaming response, see server.stream-response-body

gstrauss wrote in RE: Bluez btmgmt output is discarded by CGI:

You might want to include btmgmt --timeout 10 info in the command.
You can test btmgmt --timeout 10 info </dev/null 2>/dev/null to redirect stdin and stderr to /dev/null
If your system has /usr/bin/timeout, you might test with /usr/bin/timeout 10 btmgmt --timeout 10 info </dev/null 2>/dev/null

stdin and stdout of the CGI are pipes. stderr is a file IFF you specify server.breakagelog in your lighttpd.conf, or else it is the same as lighttpd stderr.

If you're expecting a streaming response, see server.stream-response-body

I have added the --timeout 10 option to btmgmt and this didn't make any difference. Just to be sure that the text content isn't causing anything funny, I have written the output of the btmgmt info command into a text file and then used "cat" to output the contents, and this works fine, so this isn't related to the text content itself.

I didn't understand why I should be testing with stdout routed to /dev/null though. In case of the web server, stdout will be going to the web server and I should be seeing it in the browser, no?

This has gotta be related to how btmgmt writes things to stdout. When I use "btmgmt help", I can see the output. In this case, btmgmt is using printf equivalent to write to the terminal. If I use "btmgmt info", then btmgmt initiated a transaction with the bluez daemon and a callback is called when the response has been received. Anything written to the terminal in this callback isn't displayed in the CGI. But it is displayed when run from a terminal. So weird ...

Is btmgmt writing to stderr? btmgmt --timeout 10 info 2>&1

From the command line, /usr/bin/btmgmt info </dev/null produces no output, whereas /usr/bin/btmgmt info produces output (without </dev/null)

This is not an issue with lighttpd. Perhaps you should be using a different tools, such as btmon? I do not know. However, I do know that this isn't the place to get help with using btmgmt or btmon. Sorry.

gstrauss wrote in RE: Bluez btmgmt output is discarded by CGI:

Is btmgmt writing to stderr? btmgmt --timeout 10 info 2>&1

Based on strace output, btmgmt is writing to stdout:

write(1, "Index list with 0 items\n", 24Index list with 0 items
) = 24
epoll_ctl(3, EPOLL_CTL_MOD, 4, {EPOLLIN|EPOLLOUT, {u32=347506464, u64=93948462139168}}) = 0
epoll_ctl(3, EPOLL_CTL_DEL, 0, NULL)    = 0
epoll_ctl(3, EPOLL_CTL_DEL, 4, NULL)    = 0
epoll_ctl(3, EPOLL_CTL_DEL, 5, NULL)    = 0
close(5)                                = 0
close(3)                                = 0
close(4)                                = 0
exit_group(0)                           = ?
+++ exited with 0 +++
[ta@bonsai ~]$

taydin wrote in RE: Bluez btmgmt output is discarded by CGI:

gstrauss wrote in RE: Bluez btmgmt output is discarded by CGI:

Is btmgmt writing to stderr? btmgmt --timeout 10 info 2>&1

Based on strace output, btmgmt is writing to stdout:

[...]

OK, I see. So the web server is connecting btmgmt's stdin to /dev/null and that seems to prevent it from outputting anything when NOT using printf or equivalent.

No, the lighttpd mod_cgi runs CGI programs with stdin and stdout connected to pipes. man pipe
However, my example was that redirecting stdin to /dev/null changes btmgmt behavior, which is independent of lighttpd.