http: add support for specifying the SSL version

Teach git about a new option, "http.sslVersion", which permits one
to specify the SSL version to use when negotiating SSL connections.
The setting can be overridden by the GIT_SSL_VERSION environment
variable.

Signed-off-by: Elia Pinto <gitter.spiros@gmail.com>
Helped-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/config.txt

@@ -1576,6 +1576,29 @@ http.saveCookies::
 	If set, store cookies received during requests to the file specified by
 	http.cookieFile. Has no effect if http.cookieFile is unset.
 
+http.sslVersion::
+	The SSL version to use when negotiating an SSL connection, if you
+	want to force the default.  The available and default version
+	depend on whether libcurl was built against NSS or OpenSSL and the
+	particular configuration of the crypto library in use. Internally
+	this sets the 'CURLOPT_SSL_VERSION' option; see the libcurl
+	documentation for more details on the format of this option and
+	for the ssl version supported. Actually the possible values of
+	this option are:
+
+	- sslv2
+	- sslv3
+	- tlsv1
+	- tlsv1.0
+	- tlsv1.1
+	- tlsv1.2
+
++
+Can be overridden by the 'GIT_SSL_VERSION' environment variable.
+To force git to use libcurl's default ssl version and ignore any
+explicit http.sslversion option, set 'GIT_SSL_VERSION' to the
+empty string.
+
 http.sslCipherList::
   A list of SSL ciphers to use when negotiating an SSL connection.
   The available ciphers depend on whether libcurl was built against

contrib/completion/git-completion.bash

@@ -2118,6 +2118,7 @@ _git_config ()
 		http.postBuffer
 		http.proxy
 		http.sslCipherList
+		http.sslVersion
 		http.sslCAInfo
 		http.sslCAPath
 		http.sslCert

http.c

@@ -37,6 +37,20 @@ static int curl_ssl_verify = -1;
 static int curl_ssl_try;
 static const char *ssl_cert;
 static const char *ssl_cipherlist;
+static const char *ssl_version;
+static struct {
+	const char *name;
+	long ssl_version;
+} sslversions[] = {
+	{ "sslv2", CURL_SSLVERSION_SSLv2 },
+	{ "sslv3", CURL_SSLVERSION_SSLv3 },
+	{ "tlsv1", CURL_SSLVERSION_TLSv1 },
+#if LIBCURL_VERSION_NUM >= 0x072200
+	{ "tlsv1.0", CURL_SSLVERSION_TLSv1_0 },
+	{ "tlsv1.1", CURL_SSLVERSION_TLSv1_1 },
+	{ "tlsv1.2", CURL_SSLVERSION_TLSv1_2 },
+#endif
+};
 #if LIBCURL_VERSION_NUM >= 0x070903
 static const char *ssl_key;
 #endif
@@ -190,6 +204,8 @@ static int http_options(const char *var, const char *value, void *cb)
 	}
 	if (!strcmp("http.sslcipherlist", var))
 		return git_config_string(&ssl_cipherlist, var, value);
+	if (!strcmp("http.sslversion", var))
+		return git_config_string(&ssl_version, var, value);
 	if (!strcmp("http.sslcert", var))
 		return git_config_string(&ssl_cert, var, value);
 #if LIBCURL_VERSION_NUM >= 0x070903
@@ -364,9 +380,24 @@ static CURL *get_curl_handle(void)
 	if (http_proactive_auth)
 		init_curl_http_auth(result);
 
+	if (getenv("GIT_SSL_VERSION"))
+		ssl_version = getenv("GIT_SSL_VERSION");
+	if (ssl_version && *ssl_version) {
+		int i;
+		for (i = 0; i < ARRAY_SIZE(sslversions); i++) {
+			if (!strcmp(ssl_version, sslversions[i].name)) {
+				curl_easy_setopt(result, CURLOPT_SSLVERSION,
+						 sslversions[i].ssl_version);
+				break;
+			}
+		}
+		if (i == ARRAY_SIZE(sslversions))
+			warning("unsupported ssl version %s: using default",
+				ssl_version);
+	}
+
 	if (getenv("GIT_SSL_CIPHER_LIST"))
 		ssl_cipherlist = getenv("GIT_SSL_CIPHER_LIST");
-
 	if (ssl_cipherlist != NULL && *ssl_cipherlist)
 		curl_easy_setopt(result, CURLOPT_SSL_CIPHER_LIST,
 				ssl_cipherlist);