v1d: Log client write error

[dridi]

Some scenarios like hitting send_timeout because of a dripping write leaves no clue that an error occurred from the client request logs alone.

This introduces a client counterpart for:

FetchError backend write error: %d (%s) (%s)

Refs 49e44e390488c57c03d8111fcd43e245933bc151

[dridi]

Bugwash:

• add SLT_DeliveryError
• use it for "backend write error"
• introduce "client write error"
• collect feedback from production

[nigoroll]

bugwash:

• The error is in the session VSL, but due to the impracticality of -g session, it is not particularly useful
• SLT_Error is not a particularly good tag for this, because it is currently used for internal errors which can usually be addressed with VCL or changing parameters
• we have FetchError, should add a DeliveryError tag and then use the former consistently for VFPs, and the latter for VDPs

[dridi]

SLT_Error is not a particularly good tag for this, because it is currently used for internal errors which can usually be addressed with VCL or changing parameters

nitpick: this can be addressed with send_timeout for that case, but point taken, there is nothing we can do when the client disconnects.

[dridi]

I'd like to cover this during bugwash today, before we send this to production.

[daghf]

bionic failure,

cache/cache_expire.c: In function 'exp_inbox':
cache/cache_expire.c:282:61: error: format '%ld' expects argument of type 'long int', but argument 6 has type 'VCL_INT {aka long long int}' [-Werror=format=]
   VSLb(&ep->vsl, SLT_ExpKill, "EXP_Removed x=%ju t=%.0f h=%ld",
                                                           ~~^
                                                           %lld
cache/cache_expire.c:284:7:
       oc->hits);
       ~~~~~~~~                                               
cache/cache_expire.c: In function 'exp_expire':
cache/cache_expire.c:360:61: error: format '%ld' expects argument of type 'long int', but argument 6 has type 'VCL_INT {aka long long int}' [-Werror=format=]
   VSLb(&ep->vsl, SLT_ExpKill, "EXP_Expired x=%ju t=%.0f h=%ld",
                                                           ~~^
                                                           %lld
cache/cache_expire.c:362:7:
       oc->hits);
       ~~~~~~~~                                               
  CC       cache/varnishd-cache_fetch_proc.o
cache/cache_expire.c: At top level:
cc1: error: unrecognized command line option '-Wno-nullability-completeness' [-Werror]
cc1: error: unrecognized command line option '-Wno-missing-variable-declarations' [-Werror]
cc1: error: unrecognized command line option '-Wno-system-headers-Wno-thread-safety' [-Werror]
cc1: all warnings being treated as errors

[bsdphk]

goes after march-15 release

[nigoroll]

during bugwash, @bsdphk brought up the question if this could affect vsl clients, and while it does not look like it, git grep suggests that we should change some other places where FetchError is referred.

[bsdphk]

after march15 release