With use bytes turned off:

SV = PV(0x1c71c9e8) at 0x1c202710
  REFCNT = 1
  FLAGS = (PADMY,POK,pPOK,UTF8)
  PV = 0x1cab9940 "\0\0\3\302\261---\nCONTENT_LENGTH:
[etc]

[download]

With use bytes turned on:

SV = PV(0xbfdd1e8) at 0xb734730
  REFCNT = 1
  FLAGS = (PADMY,POK,pPOK)
  PV = 0xbfeb710 "\0\0\3\261---\nCONTENT_LENGTH: 
[etc]

[download]

With use bytes turned off and with calling utf8::downgrade on the string before dumping:

SV = PV(0xd5ed9e8) at 0xd0d3710
  REFCNT = 1
  FLAGS = (PADMY,POK,pPOK)
  PV = 0xd98b100 "\0\0\3\261---\nCONTENT_LENGTH:
[etc]

[download]

Calls to Encode::is_utf8 are also tracking those values as noted by the dump.

aHA.

Resorted to reading the code in pp_pack.c, discovered that the UTFness of a packed string appears to be based on the UTFness of its components (which makes sense). The second string I'm packing here came from the Net::Async::FastCGI::Request stdin data, and was UTF8-flagged. So the question turns into how to convince that module to forget about encodings in its I/O - the code I'm building here is just relaying bits from one place to another and shouldn't be touching them.

In reply to Re^2: use bytes vs packed data by RDOlson
in thread use bytes vs packed data by RDOlson

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