CNDB-11460 another fix for cqlsh unicode tests in TestCqlshUnicode (#1618)

CNDB-11460 another fix for cqlsh unicode tests in TestCqlshUnicode -
make a second read in read_until to get UTF-8 characters that are split
across reads.

Author: djatnieks

pylib/cqlshlib/test/run_cqlsh.py

@@ -249,6 +249,7 @@ def read_until(self, until, blksize=4096, timeout=None,
         cqlshlog.debug("Searching for %r" % (until.pattern,))
         got = self.readbuf
         self.readbuf = ''
+        empty_reads = 0
         with timing_out(timeout):
             while True:
                 val = self.read(blksize, ptty_timeout)
@@ -257,7 +258,13 @@ def read_until(self, until, blksize=4096, timeout=None,
                         val = val.replace(replace_target, '')
                 cqlshlog.debug("read %r from subproc" % (val,))
                 if val == '':
-                    raise EOFError("'until' pattern %r not found" % (until.pattern,))
+                    empty_reads += 1
+                    if empty_reads > 1:
+                        raise EOFError("'until' pattern %r not found" % (until.pattern,))
+                    # Read again to allow decoding of UTF-8 characters that span multiple reads
+                    continue
+
+                empty_reads = 0
                 got += val
                 m = until.search(got)
                 if m is not None: