warc indexing: better handling of records with content-length to small, read first line to get to warc end (fixes indexing of warc in ikreymer/webarchiveplayer#14)

pywb/warc/archiveiterator.py

@@ -43,7 +43,14 @@ class ArchiveIterator(object):
     package which will create a properly chunked gzip file:
 
     warc2warc -Z myfile.{0} > myfile.{0}.gz
-    """
+"""
+
+    INC_RECORD = """\
+    WARNING: Record not followed by newline, perhaps Content-Length is invalid
+    Offset: {0}
+    Remainder: {1}
+"""
+
 
     def __init__(self, fileobj, no_record_parse=False,
                  verify_http=False):
@@ -130,15 +137,30 @@ class ArchiveIterator(object):
 
           count empty_size so that it can be substracted from
           the record length for uncompressed
+
+          if first line read is not blank, likely error in WARC/ARC,
+          display a warning
         """
         empty_size = 0
+        first_line = True
+
         while True:
             line = self.reader.readline()
             if len(line) == 0:
                 return None, empty_size
 
-            if line.rstrip() == '':
+            stripped = line.rstrip()
+
+            if stripped == '' or first_line:
                 empty_size += len(line)
+
+                if stripped != '':
+                    # if first line is not blank,
+                    # likely content-length was invalid, display warning
+                    err_offset = self.fh.tell() - self.reader.rem_length() - empty_size
+                    sys.stderr.write(self.INC_RECORD.format(err_offset, line))
+
+                first_line = False
                 continue
 
             return line, empty_size