Thread: intermittent problems with station service

Thanks, Philip.

I turned on debug and continued to get the xml parsing error, but no
additional information. The invalid start byte error you got seems to be
less common, I haven't seen it in a while.

The specific error message I get is:
Downloading
http://service.iris.edu/fdsnws/station/1/query?network=SB&channel=HH%2A%2CBH%2A&level=channel&startbefore=2024-04-09T09%3A48%3A01.603000&endafter=2024-04-09T11%3A48%3A01.603000
with requesting gzip compression
Downloaded
http://service.iris.edu/fdsnws/station/1/query?network=SB&channel=HH%2A%2CBH%2A&level=channel&startbefore=2024-04-09T09%3A48%3A01.603000&endafter=2024-04-09T11%3A48%3A01.603000
with HTTP code: 200
could not retrieve channels for datacenter IRIS: Network = SB Start tag
expected, '<' not found, line 1, column 1 (<string>, line 1) Traceback
(most recent call last):
File "/home/jdw/Dropbox/SWAT/JustTesting.py", line 29, in <module>
Channels = DCclient.get_stations(startbefore=FileStart,
endafter=FileEnd,
File
"/home/jdw/.local/lib/python3.10/site-packages/obspy/clients/fdsn/client.py",
line 756, in get_stations
inventory = read_inventory(data_stream, format='STATIONXML')
File "/home/jdw/.local/lib/python3.10/site-packages/decorator.py", line
232, in fun
return caller(func, *(extras + args), **kw)
File
"/home/jdw/.local/lib/python3.10/site-packages/obspy/core/util/decorator.py",
line 297, in _map_example_filename
return func(*args, **kwargs)
File
"/home/jdw/.local/lib/python3.10/site-packages/obspy/core/inventory/inventory.py",
line 91, in read_inventory
return _generic_reader(path_or_file_object, _read, format=format,
File
"/home/jdw/.local/lib/python3.10/site-packages/obspy/core/util/base.py",
line 624, in _generic_reader
generic = callback_func(pathname_or_url, **kwargs)
File "/home/jdw/.local/lib/python3.10/site-packages/decorator.py", line
232, in fun
return caller(func, *(extras + args), **kw)
File
"/home/jdw/.local/lib/python3.10/site-packages/obspy/core/util/decorator.py",
line 142, in uncompress_file
return func(filename, *args, **kwargs)
File
"/home/jdw/.local/lib/python3.10/site-packages/obspy/core/inventory/inventory.py",
line 100, in _read
inventory, format = _read_from_plugin('inventory', filename,
format=format,
File
"/home/jdw/.local/lib/python3.10/site-packages/obspy/core/util/base.py",
line 423, in _read_from_plugin
list_obj = read_format(filename, **kwargs)
File
"/home/jdw/.local/lib/python3.10/site-packages/obspy/io/stationxml/core.py",
line 152, in _read_stationxml
root = etree.parse(path_or_file_object).getroot()
File "src/lxml/etree.pyx", line 3541, in lxml.etree.parse
File "src/lxml/parser.pxi", line 1896, in lxml.etree._parseDocument
File "src/lxml/parser.pxi", line 1916, in lxml.etree._parseMemoryDocument
File "src/lxml/parser.pxi", line 1803, in lxml.etree._parseDoc
File "src/lxml/parser.pxi", line 1144, in lxml.etree._BaseParser._parseDoc
File "src/lxml/parser.pxi", line 618, in
lxml.etree._ParserContext._handleParseResultDoc
File "src/lxml/parser.pxi", line 728, in lxml.etree._handleParseResult
File "src/lxml/parser.pxi", line 657, in lxml.etree._raiseParseError
File "<string>", line 1
lxml.etree.XMLSyntaxError: Start tag expected, '<' not found, line 1,
column 1

-- John


On Wed, May 29, 2024 at 10:27 AM Philip Crotwell <crotwell<at>seis.sc.edu>
wrote:

Hi

Not sure I have anything useful to add, but I too have seen random,
unrepeatable errors with the fdsn web services. Often retrying the failed
query succeeds immediately afterwards, so I do not think this is a data
problem. If anything, it feels like maybe a threading race condition type
of error, and the reproducibility problem is exacerbated, I assume, by
there being more than one instance of the web service behind the load
balancer. And of course it can be really hard to find and resolve these
sorts of issues unless you can recover the actual raw response to the query.

One thing you might try is getting debug output from obspy, like

DCclient = Client('IRIS', debug=True)

This might provide additional information if you can catch one of the
errors with it enabled.

I tried and caught this. Immediately afterwards, it ran fine, so .

Downloaded http://service.iris.edu/fdsnws/event/1/application.wadl
https://urldefense.com/v3/__http://service.iris.edu/fdsnws/event/1/application.wadl__;!!IKRxdwAv5BmarQ!bwcZrxC4BwireDnr1AghrLVfeX-SeBZLuM6h_avmtz0_5wzqxYdZ9le7MY9gP0DDGSbZCh-r0zCpQLMPstlPNZRx$>
with HTTP code: 200
Uncompressing gzipped response for
http://service.iris.edu/fdsnws/dataselect/1/application.wadl
https://urldefense.com/v3/__http://service.iris.edu/fdsnws/dataselect/1/application.wadl__;!!IKRxdwAv5BmarQ!bwcZrxC4BwireDnr1AghrLVfeX-SeBZLuM6h_avmtz0_5wzqxYdZ9le7MY9gP0DDGSbZCh-r0zCpQLMPshKNb7zr$>
Downloaded http://service.iris.edu/fdsnws/dataselect/1/application.wadl
https://urldefense.com/v3/__http://service.iris.edu/fdsnws/dataselect/1/application.wadl__;!!IKRxdwAv5BmarQ!bwcZrxC4BwireDnr1AghrLVfeX-SeBZLuM6h_avmtz0_5wzqxYdZ9le7MY9gP0DDGSbZCh-r0zCpQLMPshKNb7zr$>
with HTTP code: 200
Traceback (most recent call last):
File "/Users/crotwell/Code/GitHub/obspy/JustTesting.py", line 21, in
<module>
DCclient = Client('IRIS', debug=True)
^^^^^^^^^^^^^^^^^^^^^^^^^^
File
"/opt/homebrew/Caskroom/miniforge/base/envs/obspy/lib/python3.12/site-packages/obspy/clients/fdsn/client.py",
line 277, in __init__
self._discover_services()
File
"/opt/homebrew/Caskroom/miniforge/base/envs/obspy/lib/python3.12/site-packages/obspy/clients/fdsn/client.py",
line 1584, in _discover_services
decoded_wadl = wadl.decode('utf-8')
^^^^^^^^^^^^^^^^^^^^
UnicodeDecodeError: 'utf-8' codec can't decode byte 0x8b in position 1:
invalid start byte

Doubt this is very helpful, but at least you know you are not the only one?

Philip


On Tue, May 28, 2024 at 10:23 PM John West (via SAGE) <
webservices-bounce<at>lists.ds.iris.edu> wrote:

Hi!

I'm calling the station service using the obspy client.get_stations()
method, and getting randomly distributed badly formed XML.

Typical error message is something like: "Start tag expected, '<' not
found, line 1, column 1 (<string>, line 1)"

I've also had a few errors with: "Not a gzipped file (b'a\r')"

The attached sample Python code sometimes runs without error, and
sometimes generates multiple errors during a run. The errors are NOT in the
same places, they appear for different networks on each run.

Any ideas?

Thanks!
-- John

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