http: allow users more control over user-agent

Users can now override the "product" portion of the user-agent (via
GIT_OPT_SET_USER_AGENT_PRODUCT). This continues to default to "git/2.0",
but users may define their own string, or may opt out of sending a
user-agent entirely (by passing an empty string). Similarly, users may
now also opt-out of sending any additional "comment" information by
setting the GIT_OPT_SET_USER_AGENT value to an empty string.

include/git2/common.h

@@ -228,7 +228,9 @@ typedef enum {
 	GIT_OPT_SET_SERVER_CONNECT_TIMEOUT,
 	GIT_OPT_GET_SERVER_CONNECT_TIMEOUT,
 	GIT_OPT_SET_SERVER_TIMEOUT,
-	GIT_OPT_GET_SERVER_TIMEOUT
+	GIT_OPT_GET_SERVER_TIMEOUT,
+	GIT_OPT_SET_USER_AGENT_PRODUCT,
+	GIT_OPT_GET_USER_AGENT_PRODUCT
 } git_libgit2_opt_t;
 
 /**
@@ -337,11 +339,35 @@ typedef enum {
  *
  *	* opts(GIT_OPT_SET_USER_AGENT, const char *user_agent)
  *
- *		> Set the value of the User-Agent header.  This value will be
- *		> appended to "git/1.0", for compatibility with other git clients.
+ *		> Set the value of the comment section of the User-Agent header.
+ *		> This can be information about your product and its version.
+ *		> By default this is "libgit2" followed by the libgit2 version.
  *		>
- *		> - `user_agent` is the value that will be delivered as the
- *		>   User-Agent header on HTTP requests.
+ *		> This value will be appended to User-Agent _product_, which
+ *		> is typically set to "git/2.0".
+ *		>
+ *		> Set to the empty string ("") to not send any information in the
+ *		> comment section, or set to NULL to restore the default.
+ *
+ *	* opts(GIT_OPT_GET_USER_AGENT, git_buf *out)
+ *
+ *		> Get the value of the User-Agent header.
+ *		> The User-Agent is written to the `out` buffer.
+ *
+ *	* opts(GIT_OPT_SET_USER_AGENT_PRODUCT, const char *user_agent_product)
+ *
+ *		> Set the value of the product portion of the User-Agent header.
+ *		> This defaults to "git/2.0", for compatibility with other git
+ *		> clients. It is recommended to keep this as git/<version> for
+ *		> compatibility with servers that do user-agent detection.
+ *		>
+ *		> Set to the empty string ("") to not send any user-agent string,
+ *		> or set to NULL to restore the default.
+ *
+ *	* opts(GIT_OPT_GET_USER_AGENT_PRODUCT, git_buf *out)
+ *
+ *		> Get the value of the User-Agent product header.
+ *		> The User-Agent product is written to the `out` buffer.
  *
  *	* opts(GIT_OPT_SET_WINDOWS_SHAREMODE, unsigned long value)
  *
@@ -377,11 +403,6 @@ typedef enum {
  *		>
  *		> - `ciphers` is the list of ciphers that are eanbled.
  *
- *	* opts(GIT_OPT_GET_USER_AGENT, git_buf *out)
- *
- *		> Get the value of the User-Agent header.
- *		> The User-Agent is written to the `out` buffer.
- *
  *	* opts(GIT_OPT_ENABLE_OFS_DELTA, int enabled)
  *
  *		> Enable or disable the use of "offset deltas" when creating packfiles,

src/libgit2/settings.c

@@ -51,11 +51,14 @@ extern int git_socket_stream__connect_timeout;
 extern int git_socket_stream__timeout;
 
 char *git__user_agent;
+char *git__user_agent_product;
 char *git__ssl_ciphers;
 
 static void settings_global_shutdown(void)
 {
 	git__free(git__user_agent);
+	git__free(git__user_agent_product);
+
 	git__free(git__ssl_ciphers);
 	git_repository__free_extensions();
 }
@@ -89,9 +92,16 @@ static int config_level_to_sysdir(int *out, int config_level)
 	return -1;
 }
 
+const char *git_settings__user_agent_product(void)
+{
+	return git__user_agent_product ? git__user_agent_product :
+		"git/2.0";
+}
+
 const char *git_settings__user_agent(void)
 {
-	return git__user_agent;
+	return git__user_agent ? git__user_agent :
+		"libgit2 " LIBGIT2_VERSION;
 }
 
 int git_libgit2_opts(int key, ...)
@@ -211,14 +221,65 @@ int git_libgit2_opts(int key, ...)
 		error = -1;
 #endif
 		break;
-	case GIT_OPT_SET_USER_AGENT:
-		git__free(git__user_agent);
-		git__user_agent = git__strdup(va_arg(ap, const char *));
-		if (!git__user_agent) {
-			git_error_set_oom();
-			error = -1;
-		}
 
+	case GIT_OPT_SET_USER_AGENT:
+		{
+			const char *new_agent = va_arg(ap, const char *);
+
+			git__free(git__user_agent);
+
+			if (new_agent) {
+				git__user_agent= git__strdup(new_agent);
+
+				if (!git__user_agent)
+					error = -1;
+			} else {
+				git__user_agent = NULL;
+			}
+		}
+		break;
+
+	case GIT_OPT_GET_USER_AGENT:
+		{
+			git_buf *out = va_arg(ap, git_buf *);
+			git_str str = GIT_STR_INIT;
+
+			if ((error = git_buf_tostr(&str, out)) < 0 ||
+			    (error = git_str_puts(&str, git_settings__user_agent())) < 0)
+				break;
+
+			error = git_buf_fromstr(out, &str);
+		}
+		break;
+
+	case GIT_OPT_SET_USER_AGENT_PRODUCT:
+		{
+			const char *new_agent = va_arg(ap, const char *);
+
+			git__free(git__user_agent_product);
+
+			if (new_agent) {
+				git__user_agent_product = git__strdup(new_agent);
+
+				if (!git__user_agent_product)
+					error = -1;
+			} else {
+				git__user_agent_product = NULL;
+			}
+		}
+		break;
+
+	case GIT_OPT_GET_USER_AGENT_PRODUCT:
+		{
+			git_buf *out = va_arg(ap, git_buf *);
+			git_str str = GIT_STR_INIT;
+
+			if ((error = git_buf_tostr(&str, out)) < 0 ||
+			    (error = git_str_puts(&str, git_settings__user_agent_product())) < 0)
+				break;
+
+			error = git_buf_fromstr(out, &str);
+		}
 		break;
 
 	case GIT_OPT_ENABLE_STRICT_OBJECT_CREATION:
@@ -245,19 +306,6 @@ int git_libgit2_opts(int key, ...)
 #endif
 		break;
 
-	case GIT_OPT_GET_USER_AGENT:
-		{
-			git_buf *out = va_arg(ap, git_buf *);
-			git_str str = GIT_STR_INIT;
-
-			if ((error = git_buf_tostr(&str, out)) < 0 ||
-			    (error = git_str_puts(&str, git__user_agent)) < 0)
-				break;
-
-			error = git_buf_fromstr(out, &str);
-		}
-		break;
-
 	case GIT_OPT_ENABLE_OFS_DELTA:
 		git_smart__ofs_delta_enabled = (va_arg(ap, int) != 0);
 		break;

src/libgit2/settings.h

@@ -10,5 +10,6 @@
 extern int git_settings_global_init(void);
 
 extern const char *git_settings__user_agent(void);
+extern const char *git_settings__user_agent_product(void);
 
 #endif

src/libgit2/transports/http.h

@@ -15,14 +15,4 @@
 
 extern bool git_http__expect_continue;
 
-GIT_INLINE(int) git_http__user_agent(git_str *buf)
-{
-	const char *ua = git_settings__user_agent();
-
-	if (!ua)
-		ua = "libgit2 " LIBGIT2_VERSION;
-
-	return git_str_printf(buf, "git/2.0 (%s)", ua);
-}
-
 #endif

src/libgit2/transports/httpclient.c

@@ -651,6 +651,30 @@ static int puts_host_and_port(git_str *buf, git_net_url *url, bool force_port)
 	return git_str_oom(buf) ? -1 : 0;
 }
 
+static int append_user_agent(git_str *buf)
+{
+	const char *product = git_settings__user_agent_product();
+	const char *comment = git_settings__user_agent();
+
+	GIT_ASSERT(product && comment);
+
+	if (!*product)
+		return 0;
+
+	git_str_puts(buf, "User-Agent: ");
+	git_str_puts(buf, product);
+
+	if (*comment) {
+		git_str_puts(buf, " (");
+		git_str_puts(buf, comment);
+		git_str_puts(buf, ")");
+	}
+
+	git_str_puts(buf, "\r\n");
+
+	return git_str_oom(buf) ? -1 : 0;
+}
+
 static int generate_connect_request(
 	git_http_client *client,
 	git_http_request *request)
@@ -665,9 +689,7 @@ static int generate_connect_request(
 	puts_host_and_port(buf, &client->server.url, true);
 	git_str_puts(buf, " HTTP/1.1\r\n");
 
-	git_str_puts(buf, "User-Agent: ");
-	git_http__user_agent(buf);
-	git_str_puts(buf, "\r\n");
+	append_user_agent(buf);
 
 	git_str_puts(buf, "Host: ");
 	puts_host_and_port(buf, &client->server.url, true);
@@ -711,9 +733,7 @@ static int generate_request(
 
 	git_str_puts(buf, " HTTP/1.1\r\n");
 
-	git_str_puts(buf, "User-Agent: ");
-	git_http__user_agent(buf);
-	git_str_puts(buf, "\r\n");
+	append_user_agent(buf);
 
 	git_str_puts(buf, "Host: ");
 	puts_host_and_port(buf, request->url, false);

src/libgit2/transports/winhttp.c

@@ -746,6 +746,33 @@ static void CALLBACK winhttp_status(
 	}
 }
 
+static int user_agent(bool *exists, git_str *out)
+{
+	const char *product = git_settings__user_agent_product();
+	const char *comment = git_settings__user_agent();
+
+	GIT_ASSERT(product && comment);
+
+	if (!*product) {
+		*exists = false;
+		return 0;
+	}
+
+	git_str_puts(out, product);
+
+	if (*comment) {
+		git_str_puts(out, " (");
+		git_str_puts(out, comment);
+		git_str_puts(out, ")");
+	}
+
+	if (git_str_oom(out))
+		return -1;
+
+	*exists = true;
+	return 0;
+}
+
 static int winhttp_connect(
 	winhttp_subtransport *t)
 {
@@ -757,6 +784,7 @@ static int winhttp_connect(
 	int error = -1;
 	int default_timeout = TIMEOUT_INFINITE;
 	int default_connect_timeout = DEFAULT_CONNECT_TIMEOUT;
+	bool has_ua = true;
 	DWORD protocols =
 		WINHTTP_FLAG_SECURE_PROTOCOL_TLS1 |
 		WINHTTP_FLAG_SECURE_PROTOCOL_TLS1_1 |
@@ -787,11 +815,11 @@ static int winhttp_connect(
 		goto on_error;
 	}
 
-
-	if (git_http__user_agent(&ua) < 0)
+	if (user_agent(&has_ua, &ua) < 0)
 		goto on_error;
 
-	if (git_utf8_to_16_alloc(&wide_ua, git_str_cstr(&ua)) < 0) {
+	if (has_ua &&
+	    git_utf8_to_16_alloc(&wide_ua, git_str_cstr(&ua)) < 0) {
 		git_error_set(GIT_ERROR_OS, "unable to convert host to wide characters");
 		goto on_error;
 	}

tests/libgit2/core/useragent.c

@@ -1,17 +1,52 @@
 #include "clar_libgit2.h"
 #include "settings.h"
 
-void test_core_useragent__get(void)
+static git_buf default_ua = GIT_BUF_INIT;
+static git_buf default_product = GIT_BUF_INIT;
+
+void test_core_useragent__initialize(void)
 {
-	const char *custom_name = "super duper git";
-	git_str buf = GIT_STR_INIT;
-
-	cl_assert_equal_p(NULL, git_settings__user_agent());
-	cl_git_pass(git_libgit2_opts(GIT_OPT_SET_USER_AGENT, custom_name));
-	cl_assert_equal_s(custom_name, git_settings__user_agent());
-
-	cl_git_pass(git_libgit2_opts(GIT_OPT_GET_USER_AGENT, &buf));
-	cl_assert_equal_s(custom_name, buf.ptr);
-
-	git_str_dispose(&buf);
+	cl_git_pass(git_libgit2_opts(GIT_OPT_GET_USER_AGENT, &default_ua));
+	cl_git_pass(git_libgit2_opts(GIT_OPT_GET_USER_AGENT_PRODUCT, &default_product));
+}
+
+void test_core_useragent__cleanup(void)
+{
+	git_libgit2_opts(GIT_OPT_SET_USER_AGENT, NULL);
+	git_libgit2_opts(GIT_OPT_SET_USER_AGENT_PRODUCT, NULL);
+
+	git_buf_dispose(&default_ua);
+	git_buf_dispose(&default_product);
+}
+
+void test_core_useragent__get_default(void)
+{
+	cl_assert(default_ua.size);
+	cl_assert(default_ua.ptr);
+	cl_assert(git__prefixcmp(default_ua.ptr, "libgit2 ") == 0);
+
+	cl_assert(default_product.size);
+	cl_assert(default_product.ptr);
+	cl_assert(git__prefixcmp(default_product.ptr, "git/") == 0);
+}
+
+void test_core_useragent__set(void)
+{
+	cl_git_pass(git_libgit2_opts(GIT_OPT_SET_USER_AGENT, "foo bar 4.24"));
+	cl_assert_equal_s("foo bar 4.24", git_settings__user_agent());
+	cl_assert_equal_s(default_product.ptr, git_settings__user_agent_product());
+
+	cl_git_pass(git_libgit2_opts(GIT_OPT_SET_USER_AGENT_PRODUCT, "baz/2.2.3"));
+	cl_assert_equal_s("foo bar 4.24", git_settings__user_agent());
+	cl_assert_equal_s("baz/2.2.3", git_settings__user_agent_product());
+
+	cl_git_pass(git_libgit2_opts(GIT_OPT_SET_USER_AGENT, ""));
+	cl_git_pass(git_libgit2_opts(GIT_OPT_SET_USER_AGENT_PRODUCT, ""));
+	cl_assert_equal_s("", git_settings__user_agent());
+	cl_assert_equal_s("", git_settings__user_agent_product());
+
+	cl_git_pass(git_libgit2_opts(GIT_OPT_SET_USER_AGENT, NULL));
+	cl_git_pass(git_libgit2_opts(GIT_OPT_SET_USER_AGENT_PRODUCT, NULL));
+	cl_assert_equal_s(default_ua.ptr, git_settings__user_agent());
+	cl_assert_equal_s(default_product.ptr, git_settings__user_agent_product());
 }