Commit 0348d842 authored by Daniel Shahaf's avatar Daniel Shahaf Committed by Chris Lamb

diffoscope.diff: Document feeders. (Closes: #863880)

Signed-off-by: Chris Lamb's avatarChris Lamb <>
parent 1fdbfd95
......@@ -242,6 +242,70 @@ class FIFOFeeder(threading.Thread):
raise self._exception
class _Feeder:
A 'feeder' is a specialized writer.
A 'feeder' is a callable that takes as argument a writeable file, and
writes to it. Feeders can transform the written data, truncate it,
checksum it, and so on. The callable must return True to represent that
the data had a terminating newline, and False otherwise.
Feeders are created by the functions make_feeder_from_raw_reader() and
empty_file_feeder(). The returned objects are closures, and are not
(currently?) instances of any particular class.
def empty_file_feeder():
Returns a feeder that simulates an empty file.
See _Feeder for feeders.
def feeder(f):
return False
return feeder
def make_feeder_from_raw_reader(in_file, filter=None):
Create a feeder that checksums, truncates, and transcodes the data. The
optional argument FILTER is a callable that gets passed each line, and
returns the line that should be used in its stead. (There is no facility
for FILTER to discard a line entirely.)
See _Feeder for feeders.
def feeder(out_file):
h = None
end_nl = False
max_lines = Config().max_diff_input_lines
line_count = 0
if max_lines < float("inf"):
h = hashlib.sha1()
for buf in in_file:
line_count += 1
out = filter(buf) if filter else buf
if h:
if line_count < max_lines:
end_nl = buf[-1] == '\n'
if h and line_count >= max_lines:
out_file.write("[ Too much input for diff (SHA1: {}) ]\n".format(
end_nl = True
return end_nl
return feeder
def diff(feeder1, feeder2):
tmpdir = get_temporary_directory().name
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