Y: parse ASCIIZ fields better

 - strip everything after ASCII NULL character before decoding
 - ignore all non-ascii decodable bytes, but show warnings

obspy/io/y/core.py

@@ -12,6 +12,7 @@
                         unicode_literals)
 from future.builtins import *  # NOQA
 
+import warnings
 from struct import unpack
 
 import numpy as np
@@ -23,6 +24,11 @@
 from obspy.core.util import AttribDict
 
 
+INVALID_CHAR_MSG = (
+    "Invalid non-ASCII characters in Y file header detected (%s). "
+    "These were ignored.")
+
+
 def __parse_tag(fh):
     """
     Reads and parses a single tag.
@@ -56,6 +62,33 @@ def __parse_tag(fh):
     return endian, tag_type, next_tag, next_same
 
 
+def _parse_tag_blankpadded_and_asciiz_parts(parts, blankpadded, asciiz):
+    blankpadded_dict = AttribDict()
+    for i, key in blankpadded.items():
+        part = parts[i]
+        try:
+            part = part.decode('ascii', errors="strict")
+        except UnicodeError as e:
+            warnings.warn(INVALID_CHAR_MSG % str(e), UserWarning)
+            part = part.decode('ascii', errors="ignore")
+        blankpadded_dict[key] = part.strip()
+    asciiz_dict = AttribDict()
+    for i, key in asciiz.items():
+        part = parts[i]
+        # strip everything from first ASCII NULL (if present)
+        # before decoding
+        term_index = part.find(b"\x00")
+        if term_index != -1:
+            part = part[:term_index]
+        try:
+            part = part.decode("ascii", errors="strict")
+        except UnicodeError as e:
+            warnings.warn(INVALID_CHAR_MSG % str(e), UserWarning)
+            part = part.decode("ascii", errors="ignore")
+        asciiz_dict[key] = part
+    return blankpadded_dict, asciiz_dict
+
+
 def _is_y(filename):
     """
     Checks whether a file is a Nanometrics Y file or not.
@@ -153,20 +186,23 @@ def _read_y(filename, headonly=False, **kwargs):  # @UnusedVariable
                 # UCHAR DataFormat[7] (ASCIIZ)
                 #   DataFormat is some text describing the data format recorded
                 #   at the station.
-                data = fh.read(next_tag)
-                parts = [p.decode('ascii', errors='ignore') for p in
-                         unpack(b'5s2s3s51s61s31s51s7s', data[8:])]
-                trace.stats.station = parts[0].strip()
-                trace.stats.location = parts[1].strip()
-                trace.stats.channel = parts[2].strip()
+                parts = unpack(b'5s2s3s51s61s31s51s7s', fh.read(next_tag)[8:])
+                blankpadded = {
+                    0: "station",
+                    1: "location",
+                    2: "channel"}
                 # extra
-                params = AttribDict()
-                params.network_id = parts[3].rstrip('\x00')
-                params.side_name = parts[4].rstrip('\x00')
-                params.comment = parts[5].rstrip('\x00')
-                params.sensor_type = parts[6].rstrip('\x00')
-                params.data_format = parts[7].rstrip('\x00')
-                trace.stats.y.tag_station_info = params
+                asciiz = {
+                    3: "network_id",
+                    4: "side_name",
+                    5: "comment",
+                    6: "sensor_type",
+                    7: "data_format"}
+                blankpadded_dict, asciiz_dict = \
+                    _parse_tag_blankpadded_and_asciiz_parts(
+                        parts, blankpadded, asciiz)
+                trace.stats.update(blankpadded_dict)
+                trace.stats.y.tag_station_info = asciiz_dict
             elif tag_type == 2:
                 # TAG_STATION_LOCATION
                 # UCHAR Update[8]
@@ -235,15 +271,20 @@ def _read_y(filename, headonly=False, **kwargs):  # @UnusedVariable
                 trace.stats.sampling_rate = parts[4]
                 # extra
                 params = AttribDict()
+                blankpadded = {8: "chan_flags"}
+                asciiz = {6: "sens_units",
+                          7: "calib_units"}
+                blankpadded_dict, asciiz_dict = \
+                    _parse_tag_blankpadded_and_asciiz_parts(
+                        parts, blankpadded, asciiz)
+                params.update(blankpadded_dict)
+                params.update(asciiz_dict)
                 params.start_valid_time = parts[0]
                 params.end_valid_time = parts[1]
                 params.sensitivity = parts[2]
                 params.sens_freq = parts[3]
                 params.sample_rate = parts[4]
                 params.max_clk_drift = parts[5]
-                params.sens_units = parts[6].rstrip(b'\x00').decode()
-                params.calib_units = parts[7].rstrip(b'\x00').decode()
-                params.chan_flags = parts[8].strip()
                 params.update_flag = parts[9]
                 trace.stats.y.tag_station_parameters = params
             elif tag_type == 4:
@@ -289,14 +330,19 @@ def _read_y(filename, headonly=False, **kwargs):  # @UnusedVariable
                 trace.stats.starttime = UTCDateTime(parts[0])
                 count = parts[2]
                 # extra
+                asciiz_dict = {
+                    6: "format",
+                    7: "format_version"}
+                _, asciiz_dict = \
+                    _parse_tag_blankpadded_and_asciiz_parts(
+                        parts, {}, asciiz_dict)
                 params = AttribDict()
+                params.update(asciiz_dict)
                 params.endtime = UTCDateTime(parts[1])
                 params.num_samples = parts[2]
                 params.dc_offset = parts[3]
                 params.max_amplitude = parts[4]
                 params.min_amplitude = parts[5]
-                params.format = parts[6].rstrip(b'\x00').decode()
-                params.format_version = parts[7].rstrip(b'\x00').decode()
                 trace.stats.y.tag_series_info = params
             elif tag_type == 6:
                 # TAG_SERIES_DATABASE