[PATCH 4/4] httpd: Support caching via ETag header

[Denys Vlasenko]

I applied patch 4 as well with some edits.
Please test current git.
Thank you.

On Sat, Aug 15, 2020 at 11:05 PM Denys Vlasenko
<vda.linux at googlemail.com> wrote:
>
> On Sun, Aug 9, 2020 at 12:24 AM Sergey Ponomarev <stokito at gmail.com> wrote:
> >
> > If server respond with ETag then next time client (browser) resend it via If-None-Match header.
> > Then httpd will check if file wasn't modified and if not return 304 Not Modified status code.
> > The ETag value is constructed from file's last modification date in unix epoch and it's size:
> > "hex(last_mod)-hex(file_size)" e.g. "5e132e20-417" (with quotes).
> > That means that it's not completely reliable as hash functions but fair enough.
> > The same form of ETag is used by Nginx so load balancing of static content is safe.
> >
> > Signed-off-by: Sergey Ponomarev <stokito at gmail.com>
> > ---
> >  networking/httpd.c | 73 ++++++++++++++++++++++++++++++++++++++++++++--
> >  1 file changed, 70 insertions(+), 3 deletions(-)
> >
> > diff --git a/networking/httpd.c b/networking/httpd.c
> > index 1cea33ddd..cc3f757aa 100644
> > --- a/networking/httpd.c
> > +++ b/networking/httpd.c
> > @@ -215,6 +215,17 @@
> >  //config:      Makes httpd send files using GZIP content encoding if the
> >  //config:      client supports it and a pre-compressed <file>.gz exists.
> >  //config:
> > +//config:config FEATURE_HTTPD_ETAG
> > +//config:      bool "Support caching via ETag header"
> > +//config:      default y
> > +//config:      depends on HTTPD
> > +//config:      help
> > +//config:      If server respond with ETag then next time client (browser) resend it via If-None-Match header.
> > +//config:      Then httpd will check if file wasn't modified and if not return 304 Not Modified status code.
> > +//config:      The ETag value is constructed from file's last modification date in unix epoch and it's size:
> > +//config:      "hex(last_mod)-hex(file_size)" e.g. "5e132e20-417" (with quotes).
> > +//config:      That means that it's not completely reliable as hash functions but fair enough.
>
> $ make
>   GEN     networking/Config.in
> scripts/kconfig/conf -s Config.in
> networking/Config.in:294 error: Overlong line
> networking/Config.in:295 error: Overlong line
> networking/Config.in:296 error: Overlong line
> networking/Config.in:298 error: Overlong line
> networking/Config.in:306 error: Overlong line
> networking/Config.in:307 error: Overlong line
> #
> # using defaults found in .config
>
>
> > +//config:
> >  //config:config FEATURE_HTTPD_LAST_MODIFIED
> >  //config:      bool "Add Last-Modified header to response"
> >  //config:      default y
> > @@ -266,6 +277,7 @@
> >
> >  #include "libbb.h"
> >  #include "common_bufsiz.h"
> > +#include <inttypes.h>
>
> libbb.h includes inttypes.h
>
> > +/*
> > + * ETag is "hex(last_mod)-hex(file_size)" e.g. "5e132e20-417"
> > + */
> > +static char *make_etag(void)
> > +{
> > +       return xasprintf("\"%" PRIx64 "-%" PRIx64 "\"", last_mod, file_size);
> > +}
> > +
>
> networking/httpd.c: In function 'make_etag':
> networking/httpd.c:1082:19: error: format '%llx' expects argument of
> type 'long long unsigned int', but argument 2 has type 'time_t {aka
> long int}' [-Werror=format=]
>   return xasprintf("\"%" PRIx64 "-%" PRIx64 "\"", last_mod, file_size);
>                    ^~~~~