[PATCH v2 1/2] remote-curl: accept all encodings supported by curl

[Brandon Williams <bmwill@google.com>]

Configure curl to accept all encodings which curl supports instead of
only accepting gzip responses.

This fixes an issue when using an installation of curl which is built
without the "zlib" feature. Since aa90b9697 (Enable info/refs gzip
decompression in HTTP client, 2012-09-19) we end up requesting "gzip"
encoding anyway despite libcurl not being able to decode it.  Worse,
instead of getting a clear error message indicating so, we end up
falling back to "dumb" http, producing a confusing and difficult to
debug result.

Since curl doesn't do any checking to verify that it supports the a
requested encoding, instead set the curl option `CURLOPT_ENCODING` with
an empty string indicating that curl should send an "Accept-Encoding"
header containing only the encodings supported by curl.

Reported-by: Anton Golubev <anton.golubev@gmail.com>
Signed-off-by: Brandon Williams <bmwill@google.com>
---

Version 2 of this series just tweaks the commit message and the test per
Jonathan's suggestion.

 http.c                      |  2 +-
 remote-curl.c               |  2 +-
 t/t5551-http-fetch-smart.sh | 13 +++++++++----
 3 files changed, 11 insertions(+), 6 deletions(-)

diff --git a/http.c b/http.c
index fed13b216..709150fc7 100644
--- a/http.c
+++ b/http.c
@@ -1788,7 +1788,7 @@ static int http_request(const char *url,
 
 	curl_easy_setopt(slot->curl, CURLOPT_URL, url);
 	curl_easy_setopt(slot->curl, CURLOPT_HTTPHEADER, headers);
-	curl_easy_setopt(slot->curl, CURLOPT_ENCODING, "gzip");
+	curl_easy_setopt(slot->curl, CURLOPT_ENCODING, "");
 
 	ret = run_one_slot(slot, &results);
 
diff --git a/remote-curl.c b/remote-curl.c
index ceb05347b..565bba104 100644
--- a/remote-curl.c
+++ b/remote-curl.c
@@ -684,7 +684,7 @@ static int post_rpc(struct rpc_state *rpc)
 	curl_easy_setopt(slot->curl, CURLOPT_NOBODY, 0);
 	curl_easy_setopt(slot->curl, CURLOPT_POST, 1);
 	curl_easy_setopt(slot->curl, CURLOPT_URL, rpc->service_url);
-	curl_easy_setopt(slot->curl, CURLOPT_ENCODING, "gzip");
+	curl_easy_setopt(slot->curl, CURLOPT_ENCODING, "");
 
 	if (large_request) {
 		/* The request body is large and the size cannot be predicted.
diff --git a/t/t5551-http-fetch-smart.sh b/t/t5551-http-fetch-smart.sh
index f5721b4a5..913089b14 100755
--- a/t/t5551-http-fetch-smart.sh
+++ b/t/t5551-http-fetch-smart.sh
@@ -26,14 +26,14 @@ setup_askpass_helper
 cat >exp <<EOF
 > GET /smart/repo.git/info/refs?service=git-upload-pack HTTP/1.1
 > Accept: */*
-> Accept-Encoding: gzip
+> Accept-Encoding: ENCODINGS
 > Pragma: no-cache
 < HTTP/1.1 200 OK
 < Pragma: no-cache
 < Cache-Control: no-cache, max-age=0, must-revalidate
 < Content-Type: application/x-git-upload-pack-advertisement
 > POST /smart/repo.git/git-upload-pack HTTP/1.1
-> Accept-Encoding: gzip
+> Accept-Encoding: ENCODINGS
 > Content-Type: application/x-git-upload-pack-request
 > Accept: application/x-git-upload-pack-result
 > Content-Length: xxx
@@ -79,8 +79,13 @@ test_expect_success 'clone http repository' '
 		/^< Date: /d
 		/^< Content-Length: /d
 		/^< Transfer-Encoding: /d
-	" >act &&
-	test_cmp exp act
+	" >actual &&
+	sed -e "s/^> Accept-Encoding: .*/> Accept-Encoding: ENCODINGS/" \
+			actual >actual.smudged &&
+	test_cmp exp actual.smudged &&
+
+	grep "Accept-Encoding:.*gzip" actual >actual.gzip &&
+	test_line_count = 2 actual.gzip
 '
 
 test_expect_success 'fetch changes via http' '
-- 
2.17.0.441.gb46fe60e1d-goog