tests/test-debugcommands.t

hgweb: send proper HTTP response after uncaught exception

This patch fixes a bug where hgweb would send an incomplete HTTP
response.

If an uncaught exception is raised when hgweb is processing a request,
hgweb attempts to send a generic error response and log that exception.

The server defaults to chunked transfer coding. If an uncaught exception
occurred, it was sending the error response string / chunk properly.
However, RFC 7230 Section 4.1 mandates a 0 size last chunk be sent to
indicate end of the entity body. hgweb was failing to send this last
chunk. As a result, properly written HTTP clients would assume more data
was coming and they would likely time out waiting for another chunk to
arrive.

Mercurial's own test harness was paving over the improper HTTP behavior
by not attempting to read the response body if the status code was 500.
This incorrect workaround was added in ba6577a19656 and has been removed
with this patch.

  $ hg init debugrevlog
  $ cd debugrevlog
  $ echo a > a
  $ hg ci -Am adda
  adding a
  $ hg debugrevlog -m
  format : 1
  flags  : inline
  
  revisions     :  1
      merges    :  0 ( 0.00%)
      normal    :  1 (100.00%)
  revisions     :  1
      full      :  1 (100.00%)
      deltas    :  0 ( 0.00%)
  revision size : 44
      full      : 44 (100.00%)
      deltas    :  0 ( 0.00%)
  
  avg chain length  : 0
  compression ratio : 0
  
  uncompressed data size (min/max/avg) : 43 / 43 / 43
  full revision size (min/max/avg)     : 44 / 44 / 44
  delta size (min/max/avg)             : 0 / 0 / 0


Test internal debugstacktrace command

  $ cat > debugstacktrace.py << EOF
  > from mercurial.util import debugstacktrace, dst, sys
  > def f():
  >     dst('hello world')
  > def g():
  >     f()
  >     debugstacktrace(skip=-5, f=sys.stdout)
  > g()
  > EOF
  $ python debugstacktrace.py
  hello world at:
   debugstacktrace.py:7 in * (glob)
   debugstacktrace.py:5 in g
   debugstacktrace.py:3 in f
  stacktrace at:
   debugstacktrace.py:7 *in * (glob)
   debugstacktrace.py:6 *in g (glob)
   */util.py:* in debugstacktrace (glob)