To make life with serval easier I compiled a bunch of scripts that can be used on any Linux-like system with
bash,
curl and
jq installed. Some inspiration was taken from other projects like
ibrdtn with its
dtntrigger application.
Detailed installation instructions for serval-dna and servalshellscripts can be found on their respective github pages.
This article is organized as follows:
- Example network setup
- Starting serval for the first time
- File related tasks (add and update of files)
- Append-only journals
- Text messaging and chatbot
- Automatic new content triggers
- Final words
1. Example network setup
For this article three hosts are used with the following layout:
n1 <-> n2 <-> n3
| Hostname |
IP |
SID |
| n1 |
10.0.0.20 |
CBDECA838535B64EF2868148E43020C124E01C2CC1E1CA356B171BCE68F79252 |
| n2 |
10.0.0.21 |
1CF665DAC21437B1841A1BC9BE34A11A075F985CFCBB3A0C28E8F0FEC9B25D3B |
| n3 |
10.0.0.22 |
00224C08CC240C36571791E8CBCB7EFEB29C551B585EA85815A369767AB55978 |
2. Starting serval for the first time
Repeat this on each node:
n1 ~ # mkdir servaldir
n1 ~ # cd servaldir
n1 ~/servaldir # start_serval -i
Starting daemon
INFO: Local date/time: 2017-05-19 13:04:03 +0200
INFO: Serval DNA version: START-3734-g9b7d8bf
WARN: conf.c:65:reload() config file /tmp/pycore.54650/n1.conf/serval.conf does not exist -- using all defaults
WARN: No network interfaces configured (empty 'interfaces' config option)
Setting interfaces to '*'
INFO: Local date/time: 2017-05-19 13:04:04 +0200
INFO: Serval DNA version: START-3734-g9b7d8bf
WARN: conf.c:65:reload() config file /tmp/pycore.54650/n1.conf/serval.conf does not exist -- using all defaults
Setting RESTAUTH to pum:pum123
Creating new identity
sid:CBDECA838535B64EF2868148E43020C124E01C2CC1E1CA356B171BCE68F79252
identity:8C7D1B972890EC7D8021926A508B363CE57D7658840C2B32C2995F847B99AF21
Restarting daemon
Going interactive
n1 ~/servaldir #
After this command you get an interactive shell with
SERVALINSTANCE_PATH set to your current directory.
Omitting the optional parameter to
start_serval you get back to your regular shell without the added environment variable.
The command starts serval, generates a new identity if none is present, adds a REST user and adds
ALL network interfaces to
servald.
Edit
start_serval script for different REST credentials or only specific interfaces (e.g.
wlan*).
3. File related tasks
Sharing a file with the
rhizome helper script is easy:
n2 ~/servaldir # echo "hallo world example" > /tmp/myfile
n2 ~/servaldir # rhizome put /tmp/myfile
n2 ~/servaldir #
Receiving on n1:
n1 ~/servaldir # rhizome list
+ 54D5A0C1FF192DDA671CC76DDF058D1835D55E35F17CDB87091A2A0771392BD2
+ 20 Bytes | 13:05:30 05/19/2017 | 13:05:30 05/19/2017
+ A: null* S: 1CF665DA* R: null*
n1 ~/servaldir # rhizome get 54D5A0C1FF192DDA671CC76DDF058D1835D55E35F17CDB87091A2A0771392BD2
hallo world example
n1 ~/servaldir #
Updating myfile in place on n2 again (BID of file required):
n2 ~/servaldir # echo "goodbye world example" > /tmp/myfile
n2 ~/servaldir # rhizome update /tmp/myfile 54D5A0C1FF192DDA671CC76DDF058D1835D55E35F17CDB87091A2A0771392BD2
n2 ~/servaldir #
Changing again to n1:
n1 ~/servaldir # rhizome list
+ 54D5A0C1FF192DDA671CC76DDF058D1835D55E35F17CDB87091A2A0771392BD2
+ 22 Bytes | 13:05:30 05/19/2017 | 13:09:37 05/19/2017
+ A: null* S: 1CF665DA* R: null*
n1 ~/servaldir # rhizome get 54D5A0C1FF192DDA671CC76DDF058D1835D55E35F17CDB87091A2A0771392BD2
goodbye world example
n1 ~/servaldir #
The bundle id has stayed the same but the number of bytes and the timestamp have changed.
4. Append-only journals
Having append only files shared is sometimes useful if you want to distribute for example sensor data such as a position log.
n2 ~/servaldir # journal append SENSORLOG coords "$(date +"%s") x: 23 y: 26"
n2 ~/servaldir #
n1 ~/servaldir # journal list SENSORLOG coords
service, bundle_id, author, size, name
SENSORLOG,4D46A163FBB3763607FAE345B1E4A475B72B7CE486D4F716CB80DB31DD65906B,null,23,coords
n1 ~/servaldir # journal show 4D46A163FBB3763607FAE345B1E4A475B72B7CE486D4F716CB80DB31DD65906B
1495192585 x: 23 y: 26
n1 ~/servaldir #
So far one entry, so lets add another position to our log on n2:
n2 ~/servaldir # journal append SENSORLOG coords "$(date +"%s") x: 24 y: 27"
n2 ~/servaldir #
Reading out the journal back on n1:
n1 ~/servaldir # journal show 4D46A163FBB3763607FAE345B1E4A475B72B7CE486D4F716CB80DB31DD65906B
1495192585 x: 23 y: 26
1495192825 x: 24 y: 27
n1 ~/servaldir #
5. Text messaging and chatbot
The chat bot can be used as a simple remote command trigger.
n3 ~/servaldir # cp ~/src/servalshellscripts/bot/chat-ng .n3 ~/servaldir # vim chat-ng
Change the script in the CONFIG and HOOKS sections. In this case ADMIN_SID is set to the SID of n1.
The command to execute as normal user is
meshms send $1 "PUBLIC" >/dev/null and as admin
meshms send $1 "ADMIN: $(df -h / | tail -n1)" >/dev/null.
This means that the admin gets the current free disk space as a reply and anyone else only the string “PUBLIC”.
n3 ~/servaldir # ./chatbot-ng
Now lets send a message to n3 from n2:
n2 ~/servaldir # meshms send 00224C08CC240C36571791E8CBCB7EFEB29C551B585EA85815A369767AB55978 "hello"
{
"http_status_code": 201,
"http_status_message": "Message sent",
"meshms_status_code": 1,
"meshms_status_message": "Updated"
}
n2 ~/servaldir # meshms list
# header: ["_id","their_sid","read","last_message","read_offset"]
[0,"00224C08CC240C36571791E8CBCB7EFEB29C551B585EA85815A369767AB55978",false,18,0]
n2 ~/servaldir # meshms msgs 00224C08CC240C36571791E8CBCB7EFEB29C551B585EA85815A369767AB55978
{
"read_offset":0,
"latest_ack_offset":8,
"header":["type","my_offset","their_offset","token","text","delivered","read","timestamp","ack_offset"],
"rows":[
["<",17,18,"AhII","PUBLIC",true,false,1495193503,null],
["ACK",8,3,"AQgI",null,true,false,null,8],
[">",8,0,"AQgA","hello",true,false,1495193462,null]
]
}
n2 ~/servaldir # meshms read 00224C08CC240C36571791E8CBCB7EFEB29C551B585EA85815A369767AB55978
{
"http_status_code": 201,
"http_status_message": "Read offset updated",
"meshms_status_code": 1,
"meshms_status_message": "Updated"
}
n2 ~/servaldir #
After sending the message we checked for new conversations, listed the messages in the conversation with n3 and afterwards marked all messages as read.
Now the same from n1:
n1 ~/servaldir # meshms send 00224C08CC240C36571791E8CBCB7EFEB29C551B585EA85815A369767AB55978 "hello"
{
"http_status_code": 201,
"http_status_message": "Message sent",
"meshms_status_code": 1,
"meshms_status_message": "Updated"
}
n1 ~/servaldir # meshms msgs 00224C08CC240C36571791E8CBCB7EFEB29C551B585EA85815A369767AB55978
{
"read_offset":58,
"latest_ack_offset":8,
"header":["type","my_offset","their_offset","token","text","delivered","read","timestamp","ack_offset"],
"rows":[
["<",17,58,"AjoI","ADMIN: /dev/sda1 26G 22G 2.3G 91% /",true,true,1495193708,null],
["ACK",8,3,"AQgI",null,true,false,null,8],
[">",8,0,"AQgA","hello",true,false,1495193695,null]
]
}
n1 ~/servaldir # meshms read 00224C08CC240C36571791E8CBCB7EFEB29C551B585EA85815A36967AB55978
{
"http_status_code": 201,
"http_status_message": "Read offset updated",
"meshms_status_code": 1,
"meshms_status_message": "Updated"
}
Here the reply message is different and contains the output of the disk free command.
Meanwhile the output of
chatbot-ng on n3 should look like this:
n1 ~/servaldir # ./chatbot-ng
Fri May 19 13:31:03 CEST 2017 | 1CF665* : hello
Fri May 19 13:34:56 CEST 2017 | ADMIN(CBDECA*) : hello
6. Automatic new content triggers
In the following example we want to process any new SENSOR journals that n1 receives as soon as possible.
First we need a script to handle new content, therefore we create a file named
/tmp/sensorevent with the following content:
#!/bin/sh
SERVICE=$1
NAME=$2
BID=$3
journal show $BID | wc -l > /tmp/$SERVICE-$NAME.numcoords
Now make it executable and start
rtrigger on n1:
n1 ~/servaldir # chmod a+x /tmp/sensorevent
n1 ~/servaldir # rtrigger /tmp/sensorevent SENSORLOG coord*
CMD: /tmp/sensorevent
SERVICE FILTER: SENSORLOG
FILE FILTER: coord*
This filters only for files of SERVICE ‘
SENSORLOG’ and with a filename matchig the regex ‘
coord*’.
Now lets append something to our log again on n2:
n2 ~/servaldir # journal append SENSORLOG coords "$(date +"%s") x: 25 y: 27"
n2 ~/servaldir # journal append SENSORLOG coords "$(date +"%s") x: 25 y: 26"
Switching back to the console of n1:
[...]
CMD: /tmp/sensorevent
SERVICE FILTER: SENSORLOG
FILE FILTER: coord*
TRIGGER (Fri May 19 13:50:09 CEST 2017): SENSORLOG coords 4D46A163FBB3763607FAE345B1E4A475B72B7CE486D4F716CB80DB31DD65906B
Executing /tmp/sensorevent
TRIGGER (Fri May 19 13:50:26 CEST 2017): SENSORLOG coords 4D46A163FBB3763607FAE345B1E4A475B72B7CE486D4F716CB80DB31DD65906B
Executing /tmp/sensorevent
Checking the output files on n1:
n1 ~/servaldir # ls -1 /tmp/SENSORLOG*
/tmp/SENSORLOG-coords.numcoords
n1 ~/servaldir # cat /tmp/SENSORLOG-coords.numcoords
4
n1 ~/servaldir #
7. Final words
This quite lengthy article hopefully gave some insight how serval can easily be used in sensor networks and for various automation tasks. By writing some simple shell glue code existing applications can benefit from delay-tolerant networking features.
The wrappers provided in
servalshellscripts are nowhere near complete and probably contain quite a few bugs but still make rapid prototyping of DTN apps in our lab much easier.
