[rostopic] Fix rostopic echo for non rosmsg field

[wkentaro]

Close #908

[dirk-thomas]

If you run roslaunch rospy_tutorials talker_listener.launch and rostopic echo /chatter --nostr it prints:

data: <string length: 25>

Therefore I would expect rostopic echo /chatter --nostr -n 1 to print:

<string length: 25>

but it actually prints:

None

[dirk-thomas]

What about this instead:

return '<string length: %s>' % len(val)

[wkentaro]

Nice.

[dirk-thomas]

Here I don't see how we could print the type information (<array type: ??? ...>):

return '<array length: %s>' % len(val)

[wkentaro]

With 47adb6d,

% rostopic echo /rosout/msg --nostr
<string length: 24>
---

% rostopic echo /rosout/topics --noarr
<array type: string, length: 2>
---

[wkentaro]

With 9dd94cf,

Before

% rostopic echo /rosout --nostr -n1
header:
  seq: 13891
  stamp:
    secs: 1475187530
    nsecs: 501231908
  frame_id: <string length: 0>
level: 2
name: <string length: 9>
msg: <string length: 41>
file: <string length: 11>
function: <string length: 8>
line: 43
topics: <string length: 2>

After

% rostopic echo /rosout --nostr -n1
header:
  seq: 14060
  stamp:
    secs: 1475187547
    nsecs: 301131010
  frame_id: <string length: 0>
level: 2
name: <string length: 9>
msg: <string length: 41>
file: <string length: 11>
function: <string length: 8>
line: 43
topics: <array type: string, length: 2>
---

[dirk-thomas]

The current patch duplicates a lot of code / logic. I would recommend to create a function like this:

def _value_transform(type_information, val, echo_nostr, echo_noarr):
    if echo_noarr and '[' in type_information:
        return '<array type: %s, length: %s>' % \
            (type_information.rstrip('[]'), len(val))
    elif echo_nostr and type_information == 'string':
        return '<string length: %s>' % len(val)
    elif echo_nostr and type_information == 'string[]':
        return '<array type: string, length: %s>' % len(val)
    return None

and call it from the two locations accordingly.

[dirk-thomas]

This looks good to me. Thank you for providing this patch so fast.

[mikepurvis]

Thanks for the quick turnaround, all.