[PATCH v3] http: add custom hostname to IP address resolutions

[Christian Couder <christian.couder@gmail.com>]

Libcurl has a CURLOPT_RESOLVE easy option that allows
the result of hostname resolution in the following
format to be passed:

	[+]HOST:PORT:ADDRESS[,ADDRESS]

This way, redirects and everything operating against the
HOST+PORT will use the provided ADDRESS(s).

The following format is also allowed to stop using
hostname resolutions that have already been passed:

	-HOST:PORT

See https://curl.se/libcurl/c/CURLOPT_RESOLVE.html for
more details.

Let's add a corresponding "http.curloptResolve" config
option that takes advantage of CURLOPT_RESOLVE.

Each value configured for the "http.curloptResolve" key
is passed "as is" to libcurl through CURLOPT_RESOLVE, so
it should be in one of the above 2 formats. This keeps
the implementation simple and makes us consistent with
libcurl's CURLOPT_RESOLVE, and with curl's corresponding
`--resolve` command line option.

The implementation uses CURLOPT_RESOLVE only in
get_active_slot() which is called by all the HTTP
request sending functions.

Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
---

Changes since v2 are the following:

  - option renamed from "http.resolve" to "http.curloptResolve"
  - mention "libcurl" instead of "curl" in the commit message
  - mention "libculr" in the doc to make it easier to understand
    the new option name

Range diff:

1:  28c3bf9d02 ! 1:  3d689f8a6f http: add custom hostname to IP address resolutions
    @@ Commit message
         See https://curl.se/libcurl/c/CURLOPT_RESOLVE.html for
         more details.
     
    -    Let's add a corresponding "http.resolve" config option
    -    that takes advantage of CURLOPT_RESOLVE.
    +    Let's add a corresponding "http.curloptResolve" config
    +    option that takes advantage of CURLOPT_RESOLVE.
     
    -    Each value configured for the "http.resolve" key is
    -    passed "as is" to curl through CURLOPT_RESOLVE, so it
    -    should be in one of the above 2 formats. This keeps the
    -    implementation simple and makes us consistent with
    +    Each value configured for the "http.curloptResolve" key
    +    is passed "as is" to libcurl through CURLOPT_RESOLVE, so
    +    it should be in one of the above 2 formats. This keeps
    +    the implementation simple and makes us consistent with
         libcurl's CURLOPT_RESOLVE, and with curl's corresponding
         `--resolve` command line option.
     
    @@ Documentation/config/http.txt: http.version::
        - HTTP/2
        - HTTP/1.1
      
    -+http.resolve::
    -+  Hostname resolution information that will be used first when sending
    -+  HTTP requests.  This information should be in one of the following
    -+  formats:
    ++http.curloptResolve::
    ++  Hostname resolution information that will be used first by
    ++  libcurl when sending HTTP requests.  This information should
    ++  be in one of the following formats:
     +
     +  - [+]HOST:PORT:ADDRESS[,ADDRESS]
     +  - -HOST:PORT
    @@ http.c: static int http_options(const char *var, const char *value, void *cb)
                return 0;
        }
      
    -+  if (!strcmp("http.resolve", var)) {
    ++  if (!strcmp("http.curloptresolve", var)) {
     +          if (!value) {
     +                  return config_error_nonbool(var);
     +          } else if (!*value) {
    @@ t/t5551-http-fetch-smart.sh: test_expect_success 'client falls back from v2 to v
     +  BOGUS_HOST=gitbogusexamplehost.com &&
     +  BOGUS_HTTPD_URL=$HTTPD_PROTO://$BOGUS_HOST:$LIB_HTTPD_PORT &&
     +  test_must_fail git ls-remote "$BOGUS_HTTPD_URL/smart/repo.git" >/dev/null &&
    -+  git -c "http.resolve=$BOGUS_HOST:$LIB_HTTPD_PORT:127.0.0.1" ls-remote "$BOGUS_HTTPD_URL/smart/repo.git" >/dev/null
    ++  git -c "http.curloptResolve=$BOGUS_HOST:$LIB_HTTPD_PORT:127.0.0.1" ls-remote "$BOGUS_HTTPD_URL/smart/repo.git" >/dev/null
     +'
     +
      test_done


 Documentation/config/http.txt | 16 ++++++++++++++++
 http.c                        | 18 ++++++++++++++++++
 t/t5551-http-fetch-smart.sh   |  7 +++++++
 3 files changed, 41 insertions(+)

diff --git a/Documentation/config/http.txt b/Documentation/config/http.txt
index 7003661c0d..179d03e57b 100644
--- a/Documentation/config/http.txt
+++ b/Documentation/config/http.txt
@@ -98,6 +98,22 @@ http.version::
 	- HTTP/2
 	- HTTP/1.1
 
+http.curloptResolve::
+	Hostname resolution information that will be used first by
+	libcurl when sending HTTP requests.  This information should
+	be in one of the following formats:
+
+	- [+]HOST:PORT:ADDRESS[,ADDRESS]
+	- -HOST:PORT
+
++
+The first format redirects all requests to the given `HOST:PORT`
+to the provided `ADDRESS`(s). The second format clears all
+previous config values for that `HOST:PORT` combination.  To
+allow easy overriding of all the settings inherited from the
+system config, an empty value will reset all resolution
+information to the empty list.
+
 http.sslVersion::
 	The SSL version to use when negotiating an SSL connection, if you
 	want to force the default.  The available and default version
diff --git a/http.c b/http.c
index 229da4d148..8beacb95cc 100644
--- a/http.c
+++ b/http.c
@@ -128,6 +128,8 @@ static struct curl_slist *pragma_header;
 static struct curl_slist *no_pragma_header;
 static struct string_list extra_http_headers = STRING_LIST_INIT_DUP;
 
+static struct curl_slist *host_resolutions;
+
 static struct active_request_slot *active_queue_head;
 
 static char *cached_accept_language;
@@ -393,6 +395,18 @@ static int http_options(const char *var, const char *value, void *cb)
 		return 0;
 	}
 
+	if (!strcmp("http.curloptresolve", var)) {
+		if (!value) {
+			return config_error_nonbool(var);
+		} else if (!*value) {
+			curl_slist_free_all(host_resolutions);
+			host_resolutions = NULL;
+		} else {
+			host_resolutions = curl_slist_append(host_resolutions, value);
+		}
+		return 0;
+	}
+
 	if (!strcmp("http.followredirects", var)) {
 		if (value && !strcmp(value, "initial"))
 			http_follow_config = HTTP_FOLLOW_INITIAL;
@@ -1131,6 +1145,9 @@ void http_cleanup(void)
 	curl_slist_free_all(no_pragma_header);
 	no_pragma_header = NULL;
 
+	curl_slist_free_all(host_resolutions);
+	host_resolutions = NULL;
+
 	if (curl_http_proxy) {
 		free((void *)curl_http_proxy);
 		curl_http_proxy = NULL;
@@ -1211,6 +1228,7 @@ struct active_request_slot *get_active_slot(void)
 	if (curl_save_cookies)
 		curl_easy_setopt(slot->curl, CURLOPT_COOKIEJAR, curl_cookie_file);
 	curl_easy_setopt(slot->curl, CURLOPT_HTTPHEADER, pragma_header);
+	curl_easy_setopt(slot->curl, CURLOPT_RESOLVE, host_resolutions);
 	curl_easy_setopt(slot->curl, CURLOPT_ERRORBUFFER, curl_errorstr);
 	curl_easy_setopt(slot->curl, CURLOPT_CUSTOMREQUEST, NULL);
 	curl_easy_setopt(slot->curl, CURLOPT_READFUNCTION, NULL);
diff --git a/t/t5551-http-fetch-smart.sh b/t/t5551-http-fetch-smart.sh
index f92c79c132..4a8dbb7eee 100755
--- a/t/t5551-http-fetch-smart.sh
+++ b/t/t5551-http-fetch-smart.sh
@@ -567,4 +567,11 @@ test_expect_success 'client falls back from v2 to v0 to match server' '
 	grep symref=HEAD:refs/heads/ trace
 '
 
+test_expect_success 'passing hostname resolution information works' '
+	BOGUS_HOST=gitbogusexamplehost.com &&
+	BOGUS_HTTPD_URL=$HTTPD_PROTO://$BOGUS_HOST:$LIB_HTTPD_PORT &&
+	test_must_fail git ls-remote "$BOGUS_HTTPD_URL/smart/repo.git" >/dev/null &&
+	git -c "http.curloptResolve=$BOGUS_HOST:$LIB_HTTPD_PORT:127.0.0.1" ls-remote "$BOGUS_HTTPD_URL/smart/repo.git" >/dev/null
+'
+
 test_done
-- 
2.36.1.20.g51170867bd