DM 8208 Improve error handling on external task failure

[tgoldina]

Testing:
Use http://localhost:8080/firefly/demo/ffapi-highlevel-charttest.html (last div) and firefly/python/SamplePythonLauncher.py to test. (In order for Firefly to access python launcher, python.exe property should be set. You can set this property in ~/gradle/build.config.

Example:
python.exe= "/path/to/myPythonLauncher.py"

These are the error conditions I have tested. (The error message appears in the last div, if everything works fine, histogram shows up - no error.)

1. missing property for launcher executable:
   Error: java.lang.IllegalArgumentException: The python launcher path is not an executable: @python.exe@

2. misspelled launcher:
   Error: java.lang.IllegalArgumentException: py.exe property is not defined

3. missing launcher executable:
   Error: edu.caltech.ipac.firefly.server.query.DataAccessException: Unable to get data from external task: Failed to obtain data. /Users/tatianag/dev/miniconda/bin/python: can't open file '/Users/tatianag/dev/pynotebooks/myLauncher.py': [Errno 2] No such file or directory

4. no permission to read:
   Error: edu.caltech.ipac.firefly.server.query.DataAccessException: Unable to get data from external task: Failed to obtain data. /Users/tatianag/dev/miniconda/bin/python: can't open file '/Users/tatianag/dev/pynotebooks/myLauncher.py': [Errno 13] Permission denied

5. Invalid JSON returned:
   Error: edu.caltech.ipac.firefly.server.query.DataAccessException: JsonFromExternalTask Can not parse returned JSON: Unexpected character (n) at position 0.

6. Error in python (missing json import):
   Error: edu.caltech.ipac.firefly.server.query.DataAccessException: Unable to get data from external task: Failed to obtain data. Traceback (most recent call last): File "/Users/tatianag/dev/pynotebooks/myLauncher.py", line 162, in print json.dumps(status) NameError: name 'json' is not defined

7. Syntax error in python:
   Error: edu.caltech.ipac.firefly.server.query.DataAccessException: Unable to get data from external task: Failed to obtain data. File "/Users/tatianag/dev/pynotebooks/myLauncher.py", line 64 iimport json ^ SyntaxError: invalid syntax

[loitly]

I was able to test several of the exceptions. They are handled as described. I think the variable python.exe is a bit confusing. I expect it to be the path to python, and not the launcher. Please look at the one code comment I made. I think it could be problematic.

[loitly]

I think this may affect other cases where result has .error only. By adding this, it will not fall in to this block.

[tgoldina]

I think I just changed it back to how it used to be before 10/21.

As we talked today, this code is handling JSON wrapper of possibly non-JSON result. The wrapping is done in ServCommand processRequest:33 and 53 and the wrapper always has 'success' field set either to true or false. Hence, checking has(result,'0.success') is a way to tell if JSON result is wrapped.

The advantage of checking for 'success' field is that now we can pass arrays as JSON result.

Just a note: when we change how we wrap JSON result in ServCommand.java, we need to change jsonRequest in JsonUtil.js, namely this precise code.