Someone on stack overflow says that error is typically caused by a callback returning the wrong / unexpected number of bytes.
These callbacks are at http.c line 2069 and line 299.
Not sure how either of these functions could return the wrong number of bytes (assuming you're not downloading a page directly to disk, with not enough room on disk, which is really unlikely).
Very first line computes the number of bytes to return.
If the bug were here I might put in some prints to see the arguments and the bytes returned.

Or you might use git to back up a couple weeks,
although nothing we've done in the past month has touched that file, so that's a longshot.

git checkout df7c3d74890026fc1acbfabdbb5a7b82c12cbc4d

It will yammer about a detatched head.
Rebuild and test. But make sure you

git checkout master

to get back to current code.

Karl Dahlke