How to decrease TCP connect() system call timeout? - bash

In command below I enable file /dev/tcp/10.10.10.1/80 both for reading and writing and associate it with file descriptor 3:
$ time exec 3<>/dev/tcp/10.10.10.1/80
bash: connect: Operation timed out
bash: /dev/tcp/10.10.10.1/80: Operation timed out
real 1m15.151s
user 0m0.000s
sys 0m0.000s
This automatically tries to perform TCP three-way handshake. If 10.10.10.1 is not reachable as in example above, then connect system call tries to connect for 75 seconds. Is this 75 second timeout determined by bash? Or is this system default? Last but not least, is there a way to decrease this timeout value?

It's not possible in Bash without modifying the source as already mentioned, although here is the workaround by using timeout command, e.g.:
$ timeout 1 bash -c "</dev/tcp/stackoverflow.com/80" && echo Port open. || echo Port closed.
Port open.
$ timeout 1 bash -c "</dev/tcp/stackoverflow.com/81" && echo Port open. || echo Port closed.
Port closed.
Using this syntax, the timeout command will kill the process after the given time.
See: timeout --help for more options.

It is determined by TCP. It can be decreased on a per-socket basis by application code.
NB The timeout only takes effect if there is no response at all. If there is a connection refusal, the error occurs immediately.

No: there is no way of changing timeout by using /dev/tcp/
Yes, you could change default timeout for TCP connection in any programming language.
But, bash is not a programming language!
You could have a look into source code (see: Bash Homepage), you may find lib/sh/netopen.c file where you could read in _netopen4 function:
s = socket(AF_INET, (typ == 't') ? SOCK_STREAM : SOCK_DGRAM, 0);
You could read this file carefully, there are no consideration of connection timeout.
Without patching bash sources, there is no way of changing connection timeout by a bash script.
Simple HTTP client using netcat (near pure bash)
There is a little sample HTTP client written in pure bash, but using netcat:
#!/bin/bash
tmpfile=$(mktemp -p $HOME .netbash-XXXXXX)
exec 7> >(nc -w 3 -q 0 stackoverflow.com 80 >$tmpfile)
exec 6<$tmpfile
rm $tmpfile
printf >&7 "GET %s HTTP/1.0\r\nHost: stackoverflow.com\r\n\r\n" \
/questions/24317341/how-to-decrease-tcp-connect-system-call-timeout
timeout=100;
while ! read -t .001 -u 6 status ; do read -t .001 foo;done
echo STATUS: $status
[ "$status" ] && [ -z "${status//HTTP*200 OK*}" ] || exit 1
echo HEADER:
while read -u 6 -a head && [ "${head//$'\r'}" ]; do
printf "%-20s : %s\n" ${head%:} "${head[*]:1}"
done
echo TITLE:
sed '/<title>/s/<[^>]*>//gp;d' <&6
exec 7>&-
exec 6<&-
This could render:
STATUS: HTTP/1.1 200 OK
HEADER:
Cache-Control : private
Content-Type : text/html; charset=utf-8
X-Frame-Options : SAMEORIGIN
X-Request-Guid : 46d55dc9-f7fe-425f-a560-fc49d885a5e5
Content-Length : 91642
Accept-Ranges : bytes
Date : Wed, 19 Oct 2016 13:24:35 GMT
Via : 1.1 varnish
Age : 0
Connection : close
X-Served-By : cache-fra1243-FRA
X-Cache : MISS
X-Cache-Hits : 0
X-Timer : S1476883475.343528,VS0,VE100
X-DNS-Prefetch-Control : off
Set-Cookie : prov=ff1129e3-7de5-9375-58ee-5f739eb73449; domain=.stackoverflow.com; expires=Fri, 01-Jan-2055 00:00:00 GMT; path=/; HttpOnly
TITLE:
bash - How to decrease TCP connect() system call timeout? - Stack Overflow
Some explanations:
We create first a temporary file (under private directory for security reason), bind and delete before using them.
$ tmpfile=$(mktemp -p $HOME .netbash-XXXXXX)
$ exec 7> >(nc -w 3 -q 0 stackoverflow.com 80 >$tmpfile)
$ exec 6<$tmpfile
$ rm $tmpfile
$ ls $tmpfile
ls: cannot access /home/user/.netbash-rKvpZW: No such file or directory
$ ls -l /proc/self/fd
lrwx------ 1 user user 64 Oct 19 15:20 0 -> /dev/pts/1
lrwx------ 1 user user 64 Oct 19 15:20 1 -> /dev/pts/1
lrwx------ 1 user user 64 Oct 19 15:20 2 -> /dev/pts/1
lr-x------ 1 user user 64 Oct 19 15:20 3 -> /proc/30237/fd
lr-x------ 1 user user 64 Oct 19 15:20 6 -> /home/user/.netbash-rKvpZW (deleted)
l-wx------ 1 user user 64 Oct 19 15:20 7 -> pipe:[2097453]
$ echo GET / HTTP/1.0$'\r\n\r' >&7
$ read -u 6 foo
$ echo $foo
HTTP/1.1 500 Domain Not Found
$ exec 7>&-
$ exec 6>&-

Related

Gearman worker in shell hangs as a zombie

I have a Gearman worker in a shell script started with perp in the following way:
runuid -s gds \
/usr/bin/gearman -h 127.0.0.1 -t 1000 -w -f gds-rel \
-- xargs /home/gds/gds-rel-worker.sh < /dev/null 2>/dev/null
The worker only does some input validation and calls another shell script run.sh that invokes bash, curl, Terragrunt, Terraform, Ansible and gcloud to provision and update resources in GCP like this:
./run.sh --release 1.2.3 2>&1 >> /var/log/gds-release
The script is intended to run unattended. The problem I have is that after the job finishes successfully (that's both shell scripts run.sh and gds-rel-worker.sh) the Gearman job remains executing, because the child process becomes zombie (see last line below).
root 144748 1 0 Apr29 ? 00:00:00 perpboot -d /etc/perp
root 144749 144748 0 Apr29 ? 00:00:00 \_ tinylog -k 8 -s 100000 -t -z /var/log/perp/perpd-root
root 144750 144748 0 Apr29 ? 00:00:00 \_ perpd /etc/perp
root 2492482 144750 0 May14 ? 00:00:00 \_ tinylog (gearmand) -k 10 -s 100000000 -t -z /var/log/perp/gearmand
gearmand 2492483 144750 0 May14 ? 00:00:08 \_ /usr/sbin/gearmand -L 127.0.0.1 -p 4730 --verbose INFO --log-file stderr --keepalive --keepalive-idle 120 --keepalive-interval 120 --keepalive-count 3 --round-robin --threads 36 --worker-wakeup 3 --job-retries 1
root 2531800 144750 0 May14 ? 00:00:00 \_ tinylog (gds-rel-worker) -k 10 -s 100000000 -t -z /var/log/perp/gds-rel-worker
gds 2531801 144750 0 May14 ? 00:00:00 \_ /usr/bin/gearman -h 127.0.0.1 -t 1000 -w -f gds-rel -- xargs /home/gds/gds-rel-worker.sh
gds 2531880 2531801 0 May14 ? 00:00:00 \_ [xargs] <defunct>
So far I have traced the problem to run.sh, because if I replace its call with something simpler (e.g. echo "Hello"; sleep 5) the worker does not hang. Unfortunately, I have no clue what is causing the problem. The script run.sh is rather long and complex, but has been working without a problem so far. Tracing the worker process I see this:
getpid() = 2531801
write(2, "gearman: ", 9) = 9
write(2, "gearman_worker_work", 19) = 19
write(2, " : ", 3) = 3
write(2, "gearman_wait(GEARMAN_TIMEOUT) ti"..., 151) = 151
write(2, "\n", 1) = 1
sendto(5, "\0REQ\0\0\0'\0\0\0\0", 12, MSG_NOSIGNAL, NULL, 0) = 12
recvfrom(5, "\0RES\0\0\0\n\0\0\0\0", 8192, MSG_NOSIGNAL, NULL, NULL) = 12
sendto(5, "\0REQ\0\0\0\4\0\0\0\0", 12, MSG_NOSIGNAL, NULL, 0) = 12
poll([{fd=5, events=POLLIN}, {fd=3, events=POLLIN}], 2, 1000) = 1 ([{fd=5, revents=POLLIN}])
sendto(5, "\0REQ\0\0\0'\0\0\0\0", 12, MSG_NOSIGNAL, NULL, 0) = 12
recvfrom(5, "\0RES\0\0\0\6\0\0\0\0\0RES\0\0\0(\0\0\0QH:terra-"..., 8192, MSG_NOSIGNAL, NULL, NULL) = 105
pipe([6, 7]) = 0
pipe([8, 9]) = 0
clone(child_stack=NULL, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, child_tidptr=0x7fea38480a50) = 2531880
close(6) = 0
close(9) = 0
write(7, "1.2.3\n", 18) = 6
close(7) = 0
read(8, "which: no terraform-0.14 in (/us"..., 1024) = 80
read(8, "Identity added: /home/gds/.ssh/i"..., 1024) = 54
read(8, 0x7fff6251f5b0, 1024) = ? ERESTARTSYS (To be restarted if SA_RESTART is set)
--- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=2531880, si_uid=1006, si_status=0, si_utime=0, si_stime=0} ---
read(8,
So the worker continues reading standard output even though the child has finished successfully and presumably closed it. Any ideas how to catch what causes this problem?
I was able to solve it. The script run.sh was starting ssh-agent, which opens a socket and since Gearman redirects all outputs the worker continued reading the open file descriptor even after the script successfully completed.
I found it by examining the open file descriptors for the Gearman worker process after it hang:
# ls -l /proc/2531801/fd/*
lr-x------. 1 gds devops 64 May 17 11:26 /proc/2531801/fd/0 -> /dev/null
l-wx------. 1 gds devops 64 May 17 11:26 /proc/2531801/fd/1 -> 'pipe:[9356665]'
l-wx------. 1 gds devops 64 May 17 11:26 /proc/2531801/fd/2 -> 'pipe:[9356665]'
lr-x------. 1 gds devops 64 May 17 11:26 /proc/2531801/fd/3 -> 'pipe:[9357481]'
l-wx------. 1 gds devops 64 May 17 11:26 /proc/2531801/fd/4 -> 'pipe:[9357481]'
lrwx------. 1 gds devops 64 May 17 11:26 /proc/2531801/fd/5 -> 'socket:[9357482]'
lr-x------. 1 gds devops 64 May 17 11:26 /proc/2531801/fd/8 -> 'pipe:[9369888]'
Then identified the processes using file node for the pipe in file descriptor 8 that German worker continued reading:
# lsof | grep 9369888
gearman 2531801 gds 8r FIFO 0,13 0t0 9369888 pipe
ssh-agent 2531899 gds 9w FIFO 0,13 0t0 9369888 pipe
And finally listed files opened by ssh-agent and found what stands behind file descriptor 3:
# ls -l /proc/2531899/fd/*
lrwx------. 1 root root 64 May 17 11:14 /proc/2531899/fd/0 -> /dev/null
lrwx------. 1 root root 64 May 17 11:14 /proc/2531899/fd/1 -> /dev/null
lrwx------. 1 root root 64 May 17 11:14 /proc/2531899/fd/2 -> /dev/null
lrwx------. 1 root root 64 May 17 11:14 /proc/2531899/fd/3 -> 'socket:[9346577]'
# lsof | grep 9346577
ssh-agent 2531899 gds 3u unix 0xffff89016fd34000 0t0 9346577 /tmp/ssh-0b14coFWhy40/agent.2531898 type=STREAM
As a solution I added kill of the ssh-agent before exit from run.sh script and now there are no jobs hanging due to zombie process.

Execute a code for 5 seconds and then stop it

The goal of code is that, I want to make a random tcp traffic using iperf and capture it over 5, 10, 15, 20 seconds using tcpdump. In addition, capturing the throughput is also important for me. My problem is that, I would like to execute code1, code2, code3 and code4 for 5, 10, 15 and 20 seconds in bash. However I don't know how to put the mentioned condition for it. Here is my code:
for Test_duration in 5 10 15 20
do
echo “Test performing with $Test_duration duration”
sudo tcpdump -G 10 -W 2 -w /tmp/scripttest_$Test_duration -i h1-eth0 &
while true; do
#code1
time2=$(($RANDOM%20+1))&
pksize2=$(($RANDOM%1000+200))&
iperf -c 10.0.0.2 -t $time2 -r -l $pksize2 >> /media/sf_sharedsaeed/throughtput/iperthroughput_host2_$Test_duration.txt &\
#code2
time3=$(($RANDOM%20+1))&
pksize3=$(($RANDOM%1000+200))&
iperf -c 10.0.0.3 -t $time3 -r -l $pksize3 >> /media/sf_sharedsaeed/throughtput/iperthroughput_host3_$Test_duration.txt &\
#code3
time4=$(($RANDOM%20+1))&
pksize4=$(($RANDOM%1000+200))&
iperf -c 10.0.0.4 -t $time4 -r -l $pksize4 >> /media/sf_sharedsaeed/throughtput/iperthroughput_host4_$Test_duration.txt &\
#code4
time5=$(($RANDOM%20+1))&
pksize5=$(($RANDOM%1000+200))&
iperf -c 10.0.0.5 -t $time5 -r -l $pksize5 >> /media/sf_sharedsaeed/throughtput/iperthroughput_host5_$Test_duration.txt &\
done
done
Another constraint is that, code1, code2, code3 and code4 should be executed at the same time so, I used &.
Please help me what should I replace instead of while true; to have periodic execution of codes. Can any body help me?
You could do that by using a background subshell that creates a simple file lock on expiration that you detect from your while loops. Here is an example based on a simplified version of your code:
for Test_duration in 5 10 15 20
do
# TIMEOUT_LOCK will be your file lock
rm -f TIMEOUT_LOCK
# next command will run in a parallel subshell at the background
(sleep $Test_duration; touch TIMEOUT_LOCK) &
echo “Test performing with $Test_duration duration”
while true; do
# check whether current timeout (5 or 10 or 15 ...) has occured
if [ -f TIMEOUT_LOCK ]; then rm -f TIMEOUT_LOCK; break; fi
# do your stuff here - I'm just outputing dots and sleeping
echo -n "."
sleep 1
done
echo ""
done
The output of this code is:
“Test performing with 5 duration”
.....
“Test performing with 10 duration”
..........
“Test performing with 15 duration”
...............
“Test performing with 20 duration”
....................

expect redirect outputs giberish

I have backup.sh
#!/bin/bash
expect backup.exp
and backup.exp
#!/usr/bin/expect -f
#exp_internal 1
#log_user 0
set timeout 29
puts "----------------- [exec date +%Y.%m.%d\ %H:%M:%S] ------ exp start -----"
spawn -noecho ssh andrej#10.11.22.17
expect {
timeout { send_user "\n--- failed to get expected string---\n"; exit 1 }
eof { send_user "\nSSH failure\n"; exit 1 }
" andrej $ "
}
send "sudo bash\r"
send "ls -lh\r"
send exit\r
send exit\r
interact
puts "----------------- [exec date +%Y.%m.%d\ %H:%M:%S] ------ exp ende ------"
when I run
bash backup.sh >> backup.templog 2>&1
I get
----------------- 2015.09.02 18:48:29 ------ exp start -----
Last login: Wed Sep 2 18:48:24 2015 from 10.11.22.16
^[]0;andrej#centos7c:~/andrej^G^[[?1034h^[[01;32mandrej#centos7c ^[[01;34m18:48 andrej $ ^[[00msudo bash
^[]0;root#centos7c:/home/andrej/andrej^G^[[?1034h^[[01;31mroot#centos7c ^[[01;34m18:48 andrej $ ^[[00mls -lh
total 16K
-rw-rw-r--. 1 andrej andrej 13K Jun 30 19:04 iptables.sh
drwxrwxr-x. 2 andrej andrej 6 Jun 17 22:46 ^[[0m^[[01;34mmount^[[0m
^[]0;root#centos7c:/home/andrej/andrej^G^[[01;31mroot#centos7c ^[[01;34m18:48 andrej $ ^[[00mexit
exit
^[]0;andrej#centos7c:~/andrej^G^[[01;32mandrej#centos7c ^[[01;34m18:48 andrej $ ^[[00mexit
logout
Connection to 10.11.22.17 closed.
----------------- 2015.09.02 18:48:39 ------ exp ende ------
but when I do
bash backup.sh
, I get nice output that I need :
----------------- 2015.09.02 18:52:09 ------ exp start -----
Last login: Wed Sep 2 18:48:39 2015 from 10.11.22.16
andrej#centos7c 18:52 andrej $ sudo bash
root#centos7c 18:52 andrej $ ls -lh
total 16K
-rw-rw-r--. 1 andrej andrej 13K Jun 30 19:04 iptables.sh
drwxrwxr-x. 2 andrej andrej 6 Jun 17 22:46 mount
root#centos7c 18:52 andrej $ exit
exit
andrej#centos7c 18:52 andrej $ exit
logout
Connection to 10.11.22.17 closed.
----------------- 2015.09.02 18:52:20 ------ exp ende ------
How can I get rid of extra giberish when outputing to the log file when executing the script? I am using centos 7.1 in both server and client.
If you have any sugesstion please help me out. Thank you very much.
rewriting a but to address a couple of issues:
expect has 2 built-in methods to get the current datetime: timestamp (expect-specific) and clock (from Tcl)
I turn off output (log_user 0)
when it's important, I change the prompt and use an anchored regular expression to match it
I only output the results of the ls -lh command, which I suspect is your goal.
#!/usr/bin/expect -f
#exp_internal 1
set timeout 29
proc separator {msg} {
puts [format "----------------- %s ------ %s -----" [timestamp -format "%Y.%m.%d %T"] $msg]
}
separator "exp start"
log_user 0
spawn -noecho ssh andrej#10.11.22.17
expect {
timeout { send_user "\n--- failed to get expected string---\n"; exit 1 }
eof { send_user "\nSSH failure\n"; exit 1 }
" $ "
}
send "sudo bash\r"
expect " $ "
send "PS1='$'\r"
expect -re {\$$}
send "ls -lh\r"
expect -re {(.+)\r\n\$$}
puts $expect_out(1,string)
send "exit\r"
expect " $ "
send "exit\r"
expect eof
separator "exp ende"

No response from [ -f /path/to/file ]

I am trying to get my Capistrano deploy script working, but it is not doing the symlinking as it is configured to do as shown below.
set :linked_files, %w{config/database.yml}
set :linked_dirs, %w{log tmp vendor/bundle public/system}
When it runs the related command, I get the following:
WARN [SKIPPING] No Matching Host for /usr/bin/env [ -f /path/to/shared/config/database.yml ]
If I run this command on the server, either through ssh or through logging onto the server and running the command, I get no response from the command.
user: ~
$ [ -f /path/to/shared/config/database.yml ]
user: ~
$
The file does exist in the specified location and has permissions.
user: ~
$ ll /path/to/shared/config/
total 4.0K
drwxrwxr-x 2 user group 33 Nov 30 10:58 .
drwxrwxr-x 7 user group 89 Nov 30 10:58 ..
-rwxrwxr-x 1 user group 805 Nov 30 10:58 database.yml
user: ~
Shouldn't this return a true or a false, instead of nothing? Is there a configuration I may have changed that suppresses the output? I get no response at all whether the file exists or not.
In your response to the actual question you ask, test (which is what [ is an alias for) does in fact not return output to stdout. It returns an exit code.
user: ~
$ [ -f /path/to/shared/config/database.yml ] # if the file exists
user: ~
$ echo $?
0
user: ~
$ [ -f /path/to/shared/config/database.yml ] # if the file does not exist
user: ~
$ echo $?
1
test -f /path/to/file (or [ -f /path/to/file ]) yields an exit code of 0 if the file exists or 1 if it does not. If you want to check that a file is there and echo the path to it, try:
[ -f /path/to/file ] && echo "/path/to/file"

Minimal web server using netcat

I'm trying to set up a minimal web server using netcat (nc). When the browser calls up localhost:1500, for instance, it should show the result of a function (date in the example below, but eventually it'll be a python or c program that yields some data).
My little netcat web server needs to be a while true loop in bash, possibly as simple as this:
while true ; do echo -e "HTTP/1.1 200 OK\n\n $(date)" | nc -l -p 1500 ; done
When I try this the browser shows the currently available data during the moment when nc starts. I want the browser displays the data during the moment the browser requests it, though. How can I achieve this?
Try this:
while true ; do nc -l -p 1500 -c 'echo -e "HTTP/1.1 200 OK\n\n $(date)"'; done
The -cmakes netcat execute the given command in a shell, so you can use echo. If you don't need echo, use -e. For further information on this, try man nc. Note, that when using echo there is no way for your program (the date-replacement) to get the browser request. So you probably finally want to do something like this:
while true ; do nc -l -p 1500 -e /path/to/yourprogram ; done
Where yourprogram must do the protocol stuff like handling GET, sending HTTP 200 etc.
I had the problem where I wanted to return the result of executing a bash command:
$ while true; do { echo -e 'HTTP/1.1 200 OK\r\n'; sh test; } | nc -l 8080; done
NOTE:
This command was taken from: http://www.razvantudorica.com/08/web-server-in-one-line-of-bash
This executes a bash script and returns the result to a browser client connecting to the server running this command on port 8080.
My script does this:
$ nano test
#!/bin/bash
echo "************PRINT SOME TEXT***************\n"
echo "Hello World!!!"
echo "\n"
echo "Resources:"
vmstat -S M
echo "\n"
echo "Addresses:"
echo "$(ifconfig)"
echo "\n"
echo "$(gpio readall)"
and my web browser is showing
************PRINT SOME TEXT***************
Hello World!!!
Resources:
procs -----------memory---------- ---swap-- -----io---- -system-- ----cpu----
r b swpd free buff cache si so bi bo in cs us sy id wa
0 0 0 314 18 78 0 0 2 1 306 31 0 0 100 0
Addresses:
eth0 Link encap:Ethernet HWaddr b8:27:eb:86:e8:c5
inet addr:192.168.1.83 Bcast:192.168.1.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:27734 errors:0 dropped:0 overruns:0 frame:0
TX packets:26393 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:1924720 (1.8 MiB) TX bytes:3841998 (3.6 MiB)
lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
UP LOOPBACK RUNNING MTU:65536 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:0 (0.0 B) TX bytes:0 (0.0 B)
GPIOs:
+----------+-Rev2-+------+--------+------+-------+
| wiringPi | GPIO | Phys | Name | Mode | Value |
+----------+------+------+--------+------+-------+
| 0 | 17 | 11 | GPIO 0 | IN | Low |
| 1 | 18 | 12 | GPIO 1 | IN | Low |
| 2 | 27 | 13 | GPIO 2 | IN | Low |
| 3 | 22 | 15 | GPIO 3 | IN | Low |
| 4 | 23 | 16 | GPIO 4 | IN | Low |
| 5 | 24 | 18 | GPIO 5 | IN | Low |
| 6 | 25 | 22 | GPIO 6 | IN | Low |
| 7 | 4 | 7 | GPIO 7 | IN | Low |
| 8 | 2 | 3 | SDA | IN | High |
| 9 | 3 | 5 | SCL | IN | High |
| 10 | 8 | 24 | CE0 | IN | Low |
| 11 | 7 | 26 | CE1 | IN | Low |
| 12 | 10 | 19 | MOSI | IN | Low |
| 13 | 9 | 21 | MISO | IN | Low |
| 14 | 11 | 23 | SCLK | IN | Low |
| 15 | 14 | 8 | TxD | ALT0 | High |
| 16 | 15 | 10 | RxD | ALT0 | High |
| 17 | 28 | 3 | GPIO 8 | ALT2 | Low |
| 18 | 29 | 4 | GPIO 9 | ALT2 | Low |
| 19 | 30 | 5 | GPIO10 | ALT2 | Low |
| 20 | 31 | 6 | GPIO11 | ALT2 | Low |
+----------+------+------+--------+------+-------+
Add -q 1 to the netcat command line:
while true; do
echo -e "HTTP/1.1 200 OK\n\n $(date)" | nc -l -p 1500 -q 1
done
The problem you are facing is that nc does not know when the web client is done with its request so it can respond to the request.
A web session should go something like this.
TCP session is established.
Browser Request Header: GET / HTTP/1.1
Browser Request Header: Host: www.google.com
Browser Request Header: \n #Note: Browser is telling Webserver that the request header is complete.
Server Response Header: HTTP/1.1 200 OK
Server Response Header: Content-Type: text/html
Server Response Header: Content-Length: 24
Server Response Header: \n #Note: Webserver is telling browser that response header is complete
Server Message Body: <html>sample html</html>
Server Message Body: \n #Note: Webserver is telling the browser that the requested resource is finished.
The server closes the TCP session.
Lines that begin with "\n" are simply empty lines without even a space and contain nothing more than a new line character.
I have my bash httpd launched by xinetd, xinetd tutorial. It also logs date, time, browser IP address, and the entire browser request to a log file, and calculates Content-Length for the Server header response.
user#machine:/usr/local/bin# cat ./bash_httpd
#!/bin/bash
x=0;
Log=$( echo -n "["$(date "+%F %T %Z")"] $REMOTE_HOST ")$(
while read I[$x] && [ ${#I[$x]} -gt 1 ];do
echo -n '"'${I[$x]} | sed -e's,.$,",'; let "x = $x + 1";
done ;
); echo $Log >> /var/log/bash_httpd
Message_Body=$(echo -en '<html>Sample html</html>')
echo -en "HTTP/1.0 200 OK\nContent-Type: text/html\nContent-Length: ${#Message_Body}\n\n$Message_Body"
To add more functionality, you could incorporate.
METHOD=$(echo ${I[0]} |cut -d" " -f1)
REQUEST=$(echo ${I[0]} |cut -d" " -f2)
HTTP_VERSION=$(echo ${I[0]} |cut -d" " -f3)
If METHOD = "GET" ]; then
case "$REQUEST" in
"/") Message_Body="HTML formatted home page stuff"
;;
/who) Message_Body="HTML formatted results of who"
;;
/ps) Message_Body="HTML formatted results of ps"
;;
*) Message_Body= "Error Page not found header and content"
;;
esac
fi
Happy bashing!
Another way to do this
while true; do (echo -e 'HTTP/1.1 200 OK\r\n'; echo -e "\n\tMy website has date function" ; echo -e "\t$(date)\n") | nc -lp 8080; done
Let's test it with 2 HTTP request using curl
In this example, 172.16.2.6 is the server IP Address.
Server Side
admin#server:~$ while true; do (echo -e 'HTTP/1.1 200 OK\r\n'; echo -e "\n\tMy website has date function" ; echo -e "\t$(date)\n") | nc -lp 8080; done
GET / HTTP/1.1 Host: 172.16.2.6:8080 User-Agent: curl/7.48.0 Accept:
*/*
GET / HTTP/1.1 Host: 172.16.2.6:8080 User-Agent: curl/7.48.0 Accept:
*/*
Client Side
user#client:~$ curl 172.16.2.6:8080
My website has date function
Tue Jun 13 18:00:19 UTC 2017
user#client:~$ curl 172.16.2.6:8080
My website has date function
Tue Jun 13 18:00:24 UTC 2017
user#client:~$
If you want to execute another command, feel free to replace $(date).
I had the same need/problem but nothing here worked for me (or I didn't understand everything), so this is my solution.
I post my minimal_http_server.sh (working with my /bin/bash (4.3.11) but not /bin/sh because of the redirection):
rm -f out
mkfifo out
trap "rm -f out" EXIT
while true
do
cat out | nc -l 1500 > >( # parse the netcat output, to build the answer redirected to the pipe "out".
export REQUEST=
while read -r line
do
line=$(echo "$line" | tr -d '\r\n')
if echo "$line" | grep -qE '^GET /' # if line starts with "GET /"
then
REQUEST=$(echo "$line" | cut -d ' ' -f2) # extract the request
elif [ -z "$line" ] # empty line / end of request
then
# call a script here
# Note: REQUEST is exported, so the script can parse it (to answer 200/403/404 status code + content)
./a_script.sh > out
fi
done
)
done
And my a_script.sh (with your need):
#!/bin/bash
echo -e "HTTP/1.1 200 OK\r"
echo "Content-type: text/html"
echo
date
mkfifo pipe;
while true ;
do
#use read line from pipe to make it blocks before request comes in,
#this is the key.
{ read line<pipe;echo -e "HTTP/1.1 200 OK\r\n";echo $(date);
} | nc -l -q 0 -p 8080 > pipe;
done
Here is a beauty of a little bash webserver, I found it online and forked a copy and spruced it up a bit - it uses socat or netcat I have tested it with socat -- it is self-contained in one-script and generates its own configuration file and favicon.
By default it will start up as a web enabled file browser yet is easily configured by the configuration file for any logic. For files it streams images and music (mp3's), video (mp4's, avi, etc) -- I have tested streaming various file types to Linux,Windows and Android devices including a smartwatch!
I think it streams better than VLC actually. I have found it useful for transferring files to remote clients who have no access beyond a web browser e.g. Android smartwatch without needing to worry about physically connecting to a USB port.
If you want to try it out just copy and paste it to a file named bashttpd, then start it up on the host with $> bashttpd -s
Then you can go to any other computer (presuming the firewall is not blocking inbound tcp connections to port 8080 -- the default port, you can change the port to whatever you want using the global variables at the top of the script). http://bashttpd_server_ip:8080
#!/usr/bin/env bash
#############################################################################
###########################################################################
### bashttpd v 1.12
###
### Original author: Avleen Vig, 2012
### Reworked by: Josh Cartwright, 2012
### Modified by: A.M.Danischewski, 2015
### Issues: If you find any issues leave me a comment at
### http://scriptsandoneliners.blogspot.com/2015/04/bashttpd-self-contained-bash-webserver.html
###
### This is a simple Bash based webserver. By default it will browse files and allows for
### retrieving binary files.
###
### It has been tested successfully to view and stream files including images, mp3s,
### mp4s and downloading files of any type including binary and compressed files via
### any web browser.
###
### Successfully tested on various browsers on Windows, Linux and Android devices (including the
### Android Smartwatch ZGPAX S8).
###
### It handles favicon requests by hardcoded favicon image -- by default a marathon
### runner; change it to whatever you want! By base64 encoding your favorit favicon
### and changing the global variable below this header.
###
### Make sure if you have a firewall it allows connections to the port you plan to
### listen on (8080 by default).
###
### By default this program will allow for the browsing of files from the
### computer where it is run.
###
### Make sure you are allowed connections to the port you plan to listen on
### (8080 by default). Then just drop it on a host machine (that has bash)
### and start it up like this:
###
### $192.168.1.101> bashttpd -s
###
### On the remote machine you should be able to browse and download files from the host
### server via any web browser by visiting:
###
### http://192.168.1.101:8080
###
#### This program requires (to work to full capacity) by default:
### socat or netcat (w/ '-e' option - on Ubuntu netcat-traditional)
### tree - useful for pretty directory listings
### If you are using socat, you can type: bashttpd -s
###
### to start listening on the LISTEN_PORT (default is 8080), you can change
### the port below.
### E.g. nc -lp 8080 -e ./bashttpd ## <-- If your nc has the -e option.
### E.g. nc.traditional -lp 8080 -e ./bashttpd
### E.g. bashttpd -s -or- socat TCP4-LISTEN:8080,fork EXEC:bashttpd
###
### Copyright (C) 2012, Avleen Vig <avleen#gmail.com>
###
### Permission is hereby granted, free of charge, to any person obtaining a copy of
### this software and associated documentation files (the "Software"), to deal in
### the Software without restriction, including without limitation the rights to
### use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
### the Software, and to permit persons to whom the Software is furnished to do so,
### subject to the following conditions:
###
### The above copyright notice and this permission notice shall be included in all
### copies or substantial portions of the Software.
###
### THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
### IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
### FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
### COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
### IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
### CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
###
###########################################################################
#############################################################################
### CHANGE THIS TO WHERE YOU WANT THE CONFIGURATION FILE TO RESIDE
declare -r BASHTTPD_CONF="/tmp/bashttpd.conf"
### CHANGE THIS IF YOU WOULD LIKE TO LISTEN ON A DIFFERENT PORT
declare -i LISTEN_PORT=8080
## If you are on AIX, IRIX, Solaris, or a hardened system redirecting
## to /dev/random will probably break, you can change it to /dev/null.
declare -a DUMP_DEV="/dev/random"
## Just base64 encode your favorite favicon and change this to whatever you want.
declare -r FAVICON="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"
declare -i DEBUG=1
declare -i VERBOSE=0
declare -a REQUEST_HEADERS
declare REQUEST_URI=""
declare -a HTTP_RESPONSE=(
[200]="OK"
[400]="Bad Request"
[403]="Forbidden"
[404]="Not Found"
[405]="Method Not Allowed"
[500]="Internal Server Error")
declare DATE=$(date +"%a, %d %b %Y %H:%M:%S %Z")
declare -a RESPONSE_HEADERS=(
"Date: $DATE"
"Expires: $DATE"
"Server: Slash Bin Slash Bash"
)
function warn() { ((${VERBOSE})) && echo "WARNING: $#" >&2; }
function chk_conf_file() {
[ -r "${BASHTTPD_CONF}" ] || {
cat >"${BASHTTPD_CONF}" <<'EOF'
#
# bashttpd.conf - configuration for bashttpd
#
# The behavior of bashttpd is dictated by the evaluation
# of rules specified in this configuration file. Each rule
# is evaluated until one is matched. If no rule is matched,
# bashttpd will serve a 500 Internal Server Error.
#
# The format of the rules are:
# on_uri_match REGEX command [args]
# unconditionally command [args]
#
# on_uri_match:
# On an incoming request, the URI is checked against the specified
# (bash-supported extended) regular expression, and if encounters a match the
# specified command is executed with the specified arguments.
#
# For additional flexibility, on_uri_match will also pass the results of the
# regular expression match, ${BASH_REMATCH[#]} as additional arguments to the
# command.
#
# unconditionally:
# Always serve via the specified command. Useful for catchall rules.
#
# The following commands are available for use:
#
# serve_file FILE
# Statically serves a single file.
#
# serve_dir_with_tree DIRECTORY
# Statically serves the specified directory using 'tree'. It must be
# installed and in the PATH.
#
# serve_dir_with_ls DIRECTORY
# Statically serves the specified directory using 'ls -al'.
#
# serve_dir DIRECTORY
# Statically serves a single directory listing. Will use 'tree' if it is
# installed and in the PATH, otherwise, 'ls -al'
#
# serve_dir_or_file_from DIRECTORY
# Serves either a directory listing (using serve_dir) or a file (using
# serve_file). Constructs local path by appending the specified root
# directory, and the URI portion of the client request.
#
# serve_static_string STRING
# Serves the specified static string with Content-Type text/plain.
#
# Examples of rules:
#
# on_uri_match '^/issue$' serve_file "/etc/issue"
#
# When a client's requested URI matches the string '/issue', serve them the
# contents of /etc/issue
#
# on_uri_match 'root' serve_dir /
#
# When a client's requested URI has the word 'root' in it, serve up
# a directory listing of /
#
# DOCROOT=/var/www/html
# on_uri_match '/(.*)' serve_dir_or_file_from "$DOCROOT"
# When any URI request is made, attempt to serve a directory listing
# or file content based on the request URI, by mapping URI's to local
# paths relative to the specified "$DOCROOT"
#
#unconditionally serve_static_string 'Hello, world! You can configure bashttpd by modifying bashttpd.conf.'
DOCROOT=/
on_uri_match '/(.*)' serve_dir_or_file_from
# More about commands:
#
# It is possible to somewhat easily write your own commands. An example
# may help. The following example will serve "Hello, $x!" whenever
# a client sends a request with the URI /say_hello_to/$x:
#
# serve_hello() {
# add_response_header "Content-Type" "text/plain"
# send_response_ok_exit <<< "Hello, $2!"
# }
# on_uri_match '^/say_hello_to/(.*)$' serve_hello
#
# Like mentioned before, the contents of ${BASH_REMATCH[#]} are passed
# to your command, so its possible to use regular expression groups
# to pull out info.
#
# With this example, when the requested URI is /say_hello_to/Josh, serve_hello
# is invoked with the arguments '/say_hello_to/Josh' 'Josh',
# (${BASH_REMATCH[0]} is always the full match)
EOF
warn "Created bashttpd.conf using defaults. Please review and configure bashttpd.conf before running bashttpd again."
# exit 1
}
}
function recv() { ((${VERBOSE})) && echo "< $#" >&2; }
function send() { ((${VERBOSE})) && echo "> $#" >&2; echo "$*"; }
function add_response_header() { RESPONSE_HEADERS+=("$1: $2"); }
function send_response_binary() {
local code="$1"
local file="${2}"
local transfer_stats=""
local tmp_stat_file="/tmp/_send_response_$$_"
send "HTTP/1.0 $1 ${HTTP_RESPONSE[$1]}"
for i in "${RESPONSE_HEADERS[#]}"; do
send "$i"
done
send
if ((${VERBOSE})); then
## Use dd since it handles null bytes
dd 2>"${tmp_stat_file}" < "${file}"
transfer_stats=$(<"${tmp_stat_file}")
echo -en ">> Transferred: ${file}\n>> $(awk '/copied/{print}' <<< "${transfer_stats}")\n" >&2
rm "${tmp_stat_file}"
else
## Use dd since it handles null bytes
dd 2>"${DUMP_DEV}" < "${file}"
fi
}
function send_response() {
local code="$1"
send "HTTP/1.0 $1 ${HTTP_RESPONSE[$1]}"
for i in "${RESPONSE_HEADERS[#]}"; do
send "$i"
done
send
while IFS= read -r line; do
send "${line}"
done
}
function send_response_ok_exit() { send_response 200; exit 0; }
function send_response_ok_exit_binary() { send_response_binary 200 "${1}"; exit 0; }
function fail_with() { send_response "$1" <<< "$1 ${HTTP_RESPONSE[$1]}"; exit 1; }
function serve_file() {
local file="$1"
local CONTENT_TYPE=""
case "${file}" in
*\.css)
CONTENT_TYPE="text/css"
;;
*\.js)
CONTENT_TYPE="text/javascript"
;;
*)
CONTENT_TYPE=$(file -b --mime-type "${file}")
;;
esac
add_response_header "Content-Type" "${CONTENT_TYPE}"
CONTENT_LENGTH=$(stat -c'%s' "${file}")
add_response_header "Content-Length" "${CONTENT_LENGTH}"
## Use binary safe transfer method since text doesn't break.
send_response_ok_exit_binary "${file}"
}
function serve_dir_with_tree() {
local dir="$1" tree_vers tree_opts basehref x
## HTML 5 compatible way to avoid tree html from generating favicon
## requests in certain browsers, such as browsers in android smartwatches. =)
local no_favicon=" <link href=\"data:image/x-icon;base64,${FAVICON}\" rel=\"icon\" type=\"image/x-icon\" />"
local tree_page=""
local base_server_path="/${2%/}"
[ "$base_server_path" = "/" ] && base_server_path=".."
local tree_opts="--du -h -a --dirsfirst"
add_response_header "Content-Type" "text/html"
# The --du option was added in 1.6.0. "/${2%/*}"
read _ tree_vers x < <(tree --version)
tree_page=$(tree -H "$base_server_path" -L 1 "${tree_opts}" -D "${dir}")
tree_page=$(sed "5 i ${no_favicon}" <<< "${tree_page}")
[[ "${tree_vers}" == v1.6* ]]
send_response_ok_exit <<< "${tree_page}"
}
function serve_dir_with_ls() {
local dir="$1"
add_response_header "Content-Type" "text/plain"
send_response_ok_exit < \
<(ls -la "${dir}")
}
function serve_dir() {
local dir="$1"
# If `tree` is installed, use that for pretty output.
which tree &>"${DUMP_DEV}" && \
serve_dir_with_tree "$#"
serve_dir_with_ls "$#"
fail_with 500
}
function urldecode() { [ "${1%/}" = "" ] && echo "/" || echo -e "$(sed 's/%\([[:xdigit:]]\{2\}\)/\\\x\1/g' <<< "${1%/}")"; }
function serve_dir_or_file_from() {
local URL_PATH="${1}/${3}"
shift
URL_PATH=$(urldecode "${URL_PATH}")
[[ $URL_PATH == *..* ]] && fail_with 400
# Serve index file if exists in requested directory
[[ -d "${URL_PATH}" && -f "${URL_PATH}/index.html" && -r "${URL_PATH}/index.html" ]] && \
URL_PATH="${URL_PATH}/index.html"
if [[ -f "${URL_PATH}" ]]; then
[[ -r "${URL_PATH}" ]] && \
serve_file "${URL_PATH}" "$#" || fail_with 403
elif [[ -d "${URL_PATH}" ]]; then
[[ -x "${URL_PATH}" ]] && \
serve_dir "${URL_PATH}" "$#" || fail_with 403
fi
fail_with 404
}
function serve_static_string() {
add_response_header "Content-Type" "text/plain"
send_response_ok_exit <<< "$1"
}
function on_uri_match() {
local regex="$1"
shift
[[ "${REQUEST_URI}" =~ $regex ]] && \
"$#" "${BASH_REMATCH[#]}"
}
function unconditionally() { "$#" "$REQUEST_URI"; }
function main() {
local recv=""
local line=""
local REQUEST_METHOD=""
local REQUEST_HTTP_VERSION=""
chk_conf_file
[[ ${UID} = 0 ]] && warn "It is not recommended to run bashttpd as root."
# Request-Line HTTP RFC 2616 $5.1
read -r line || fail_with 400
line=${line%%$'\r'}
recv "${line}"
read -r REQUEST_METHOD REQUEST_URI REQUEST_HTTP_VERSION <<< "${line}"
[ -n "${REQUEST_METHOD}" ] && [ -n "${REQUEST_URI}" ] && \
[ -n "${REQUEST_HTTP_VERSION}" ] || fail_with 400
# Only GET is supported at this time
[ "${REQUEST_METHOD}" = "GET" ] || fail_with 405
while IFS= read -r line; do
line=${line%%$'\r'}
recv "${line}"
# If we've reached the end of the headers, break.
[ -z "${line}" ] && break
REQUEST_HEADERS+=("${line}")
done
}
if [[ ! -z "{$1}" ]] && [ "${1}" = "-s" ]; then
socat TCP4-LISTEN:${LISTEN_PORT},fork EXEC:"${0}"
else
main
source "${BASHTTPD_CONF}"
fail_with 500
fi
LOL, a super lame hack, but at least curl and firefox accepts it:
while true ; do (dd if=/dev/zero count=10000;echo -e "HTTP/1.1\n\n $(date)") | nc -l 1500 ; done
You better replace it soon with something proper!
Ah yes, my nc were not exactly the same as yours, it did not like the -p option.
If you're using Apline Linux, the BusyBox netcat is slightly different:
while true; do nc -l -p 8080 -e sh -c 'echo -e "HTTP/1.1 200 OK\n\n$(date)"'; done
And another way using printf:
while true; do nc -l -p 8080 -e sh -c "printf 'HTTP/1.1 200 OK\n\n%s' \"$(date)\""; done
while true; do (echo -e 'HTTP/1.1 200 OK\r\nConnection: close\r\n';) | timeout 1 nc -lp 8080 ; done
Closes connection after 1 sec, so curl doesn't hang on it.
Type in nc -h and see if You have -e option available. If yes, You can create a script, for example:
script.sh
echo -e "HTTP/1.1 200 OK\n\n $(date)"
and run it like this:
while true ; do nc -l -p 1500 -e script.sh; done
Note that -e option needs to be enabled at compilation to be available.
I think the problem that all the solution listed doesn't work, is intrinsic in the nature of http service, the every request established is with a different client and the response need to be processed in a different context, every request must fork a new instance of response...
The current solution I think is the -e of netcat but I don't know why doesn't work... maybe is my nc version that I test on openwrt...
with socat it works....
I try this https://github.com/avleen/bashttpd
and it works, but I must run the shell script with this command.
socat tcp-l:80,reuseaddr,fork EXEC:bashttpd &
The socat and netcat samples on github doesn't works for me, but the socat that I used works.
Actually, the best way to close gracefully the connection is to send the Content-Length header like following. Client (like curl will close the connection after receiving the data.
DATA="Date: $(date)";
LENGTH=$(echo $DATA | wc -c);
echo -e "HTTP/1.1 200 OK\nContent-Length: ${LENGTH}\n\n${DATA}" | nc -l -p 8000;
On OSX you can use :
while true; do echo -e "HTTP/1.1 200 OK\n\n $(date)" | nc -l localhost 1500 ; done

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