Set compression to curl defaults

[neheb]

While zlib is mandatory for transmission, it is not mandatory for curl.

A libcurl that has been compiled with no support for zlib will return no data if compressed responses are set to on.

In the basic case this prevents the port checking functionality from working properly. It also prevents web seeding from working as well.

[mikedld]

Instead of unconditionally refusing to accept compressed responses, I'd rather check whether curl_version_info() indicates support for CURL_VERSION_LIBZ feature. Obsiously, not on each and every request :)

[cfpp2p]

@neheb @mikedld

tells curl to fill in the blanks with what it was compiled to support

ref: https://trac.transmissionbt.com/changeset/8658

curl_easy_setopt(e, CURLOPT_ENCODING, "");

[neheb]

Isn't curl_easy_setopt(e, CURLOPT_ENCODING, ""); a default setting?

[cfpp2p]

Isn't curl_easy_setopt(e, CURLOPT_ENCODING, ""); a default setting?

@neheb
Documentation seems ambiguous
curl/curl#785

Looking at source for curl-7.58.0

configure defines HAVE_LIBZ

content_encoding.c

/* supported content encodings table. */
static const content_encoding * const encodings[] = {
  &identity_encoding,
#ifdef HAVE_LIBZ
  &deflate_encoding,
  &gzip_encoding,
#endif
#ifdef HAVE_BROTLI
  &brotli_encoding,
#endif
  NULL
};

static const content_encoding deflate_encoding = {
  "deflate",
  NULL,
  deflate_init_writer,
  deflate_unencode_write,
  deflate_close_writer,
  sizeof(zlib_params)
};

static const content_encoding gzip_encoding = {
  "gzip",
  "x-gzip",
  gzip_init_writer,
  gzip_unencode_write,
  gzip_close_writer,
  sizeof(zlib_params)
};

[neheb]

So the default is whatever is supported by curl. What's the point in manually specifying it then. Or even doing checks?

[V-E-O]

@neheb According to latest doc from libcurl https://curl.haxx.se/libcurl/c/CURLOPT_ACCEPT_ENCODING.html, in default the encoding is NULL which means not sending an Accept-Encoding header. In most cases, it works well except for some weird servers arbitrarily sending compressed data if no Accept-Encoding.

[neheb]

Nice and clean. I like it. Force pushed a new commit.

This has the side benefit of also supporting brotli compression if curl is compiled with it.

[neheb]

@mikedld any complaints? I feel that there's no point to doing LIBZ checks since curl does it anyway.

[cfpp2p]

@neheb
NULL is not the same as ""
What you want is:

curl_easy_setopt(e, CURLOPT_ENCODING, "");

Tested each way. The results are as follows

curl_easy_setopt(e, CURLOPT_ENCODING, "");

GET /51414 HTTP/1.1
User-Agent: Transmission/2.93
Host: portcheck.transmissionbt.com
Accept: */*
Accept-Encoding: deflate, gzip, br


NULL (did NOT set CURLOPT_ENCODING at ALL!)

GET /51414 HTTP/1.1
User-Agent: Transmission/2.93
Host: portcheck.transmissionbt.com
Accept: */*


curl_easy_setopt(e, CURLOPT_ENCODING, "gzip;q=1.0, deflate, identity");

GET /51414 HTTP/1.1
User-Agent: Transmission/2.93
Host: portcheck.transmissionbt.com
Accept: */*
Accept-Encoding: gzip;q=1.0, deflate, identity

[neheb]

that's exactly what i force pushed...

[cfpp2p]

OK, sorry, looks good. I didn't see that.

[cfpp2p]

both transmission's remote.c and show.c already are using

curl_easy_setopt(curl, CURLOPT_ENCODING, "");
/* "" tells curl to fill in the blanks with what it was compiled to support */

[mikedld]

Looks good now. I didn't dive into the documentation deep enough when I suggested to add a feature check ;)

[mikedld]

Thanks for the input @cfpp2p, as always!