Subject: Re: [PATCH v2 6/6] t5556-http-auth: add test for HTTP auth hdr logic

From: Derrick Stolee <[email-masked]>
Date: Fri, 28 Oct 2022 11:08:28 -0400

On 10/21/22 1:08 PM, Matthew John Cheetham via GitGitGadget wrote:
> From: Matthew John Cheetham <[email-masked]>

> @@ -1500,6 +1500,8 @@ else
>  	endif
>  	BASIC_CFLAGS += $(CURL_CFLAGS)
>  
> +	TEST_PROGRAMS_NEED_X += test-http-server
> +
>  	REMOTE_CURL_PRIMARY = git-remote-http$X
>  	REMOTE_CURL_ALIASES = git-remote-https$X git-remote-ftp$X git-remote-ftps$X
>  	REMOTE_CURL_NAMES = $(REMOTE_CURL_PRIMARY) $(REMOTE_CURL_ALIASES)

This hunk is in the "else" block of "ifdef NO_CURL",
so this makes sense for why TEST_PROGRAMS_NEED_X is
augmented here, away from other instances.

> diff --git a/contrib/buildsystems/CMakeLists.txt b/contrib/buildsystems/CMakeLists.txt
> index 787738e6fa3..45251695ce0 100644
> --- a/contrib/buildsystems/CMakeLists.txt
> +++ b/contrib/buildsystems/CMakeLists.txt
> @@ -989,6 +989,19 @@ set(wrapper_scripts
>  set(wrapper_test_scripts
>  	test-fake-ssh test-tool)
>  
> +if(CURL_FOUND)
> +       list(APPEND wrapper_test_scripts test-http-server)
> +
> +       add_executable(test-http-server ${CMAKE_SOURCE_DIR}/t/helper/test-http-server.c)
> +       target_link_libraries(test-http-server common-main)
> +
> +       if(MSVC)
> +               set_target_properties(test-http-server
> +                                       PROPERTIES RUNTIME_OUTPUT_DIRECTORY_DEBUG ${CMAKE_BINARY_DIR}/t/helper)
> +               set_target_properties(test-http-server
> +                                       PROPERTIES RUNTIME_OUTPUT_DIRECTORY_RELEASE ${CMAKE_BINARY_DIR}/t/helper)
> +       endif()
> +endif()

And this file has the pattern of many "if(CURL_FOUND)"
blocks with isolated purposes, so it makes sense to
have this be an isolated change instead of grouped with
a different case.

> diff --git a/t/helper/.gitignore b/t/helper/.gitignore
> index 8c2ddcce95f..1a94ab6eed5 100644
> --- a/t/helper/.gitignore
> +++ b/t/helper/.gitignore
> @@ -1,2 +1,3 @@
>  /test-tool
>  /test-fake-ssh
> +test-http-server

Should this start with a "/" like the other entries?

> diff --git a/t/helper/test-credential-helper-replay.sh b/t/helper/test-credential-helper-replay.sh
> new file mode 100755
> index 00000000000..03e5e63dad6
> --- /dev/null
> +++ b/t/helper/test-credential-helper-replay.sh
> @@ -0,0 +1,14 @@
> +cmd=$1
> +teefile=$cmd-actual.cred
> +catfile=$cmd-response.cred
> +rm -f $teefile
> +while read line;
> +do
> +	if test -z "$line"; then
> +		break;
> +	fi
> +	echo "$line" >> $teefile
> +done
> +if test "$cmd" = "get"; then
> +	cat $catfile
> +fi

Should this be a helper method within another script, such
as t/lib-credential.sh or t/lib-httpd.sh? The read over
stdin will still work, as in this example:

read_chunk() {
	while read line; do
		case "$line" in
		--) break ;;
		*) echo "$line" ;;
		esac
	done
}

> diff --git a/t/helper/test-http-server.c b/t/helper/test-http-server.c

> @@ -0,0 +1,1134 @@
> +#include "config.h"
> +#include "run-command.h"
> +#include "strbuf.h"
> +#include "string-list.h"
> +#include "trace2.h"
> +#include "version.h"
> +#include "dir.h"
> +#include "date.h"
> +
> +#define TR2_CAT "test-http-server"
> +
> +static const char *pid_file;
> +static int verbose;
> +static int reuseaddr;
> +
> +static const char test_http_auth_usage[] =
> +"http-server [--verbose]\n"
> +"           [--timeout=<n>] [--init-timeout=<n>] [--max-connections=<n>]\n"
> +"           [--reuseaddr] [--pid-file=<file>]\n"
> +"           [--listen=<host_or_ipaddr>]* [--port=<n>]\n"
> +"           [--anonymous-allowed]\n"
> +"           [--auth=<scheme>[:<params>] [--auth-token=<scheme>:<token>]]*\n"
> +;

These are a lot of options to implement all at once. They are probably
simple enough, but depending on the implementation and tests, it might
be helpful to split this patch into smaller ones that introduce these
options along with the tests that exercise each. That will help
verify that they are being tested properly instead of needing to track
back and forth across the patch for each one.

> +
> +/* Timeout, and initial timeout */
> +static unsigned int timeout;
> +static unsigned int init_timeout;
> +
> +static void logreport(const char *label, const char *err, va_list params)
> +{
> +	struct strbuf msg = STRBUF_INIT;
> +
> +	strbuf_addf(&msg, "[%"PRIuMAX"] %s: ", (uintmax_t)getpid(), label);
> +	strbuf_vaddf(&msg, err, params);
> +	strbuf_addch(&msg, '\n');
> +
> +	fwrite(msg.buf, sizeof(char), msg.len, stderr);
> +	fflush(stderr);
> +
> +	strbuf_release(&msg);
> +}
> +
> +__attribute__((format (printf, 1, 2)))
> +static void logerror(const char *err, ...)
> +{
> +	va_list params;
> +	va_start(params, err);
> +	logreport("error", err, params);
> +	va_end(params);
> +}
> +
> +__attribute__((format (printf, 1, 2)))
> +static void loginfo(const char *err, ...)
> +{
> +	va_list params;
> +	if (!verbose)
> +		return;
> +	va_start(params, err);
> +	logreport("info", err, params);
> +	va_end(params);
> +}

I wonder how much of this we need or is just a nice thing. I would
err on the side of making things as simple as possible, but being
able to debug this test server may be important based on your
experience.

> +static void set_keep_alive(int sockfd)
> +{
> +	int ka = 1;
> +
> +	if (setsockopt(sockfd, SOL_SOCKET, SO_KEEPALIVE, &ka, sizeof(ka)) < 0) {
> +		if (errno != ENOTSOCK)
> +			logerror("unable to set SO_KEEPALIVE on socket: %s",
> +				strerror(errno));
> +	}
> +}
> +
> +//////////////////////////////////////////////////////////////////
> +// The code in this section is used by "worker" instances to service
> +// a single connection from a client.  The worker talks to the client
> +// on 0 and 1.
> +//////////////////////////////////////////////////////////////////

Use /* */ style comments. You can repeat the asterisks to get a
similar visual block.

> +
> +enum worker_result {
> +	/*
> +	 * Operation successful.
> +	 * Caller *might* keep the socket open and allow keep-alive.
> +	 */
> +	WR_OK       = 0,
> +	/*
> +	 * Various errors while processing the request and/or the response.
> +	 * Close the socket and clean up.
> +	 * Exit child-process with non-zero status.
> +	 */
> +	WR_IO_ERROR = 1<<0,
> +	/*
> +	 * Close the socket and clean up.  Does not imply an error.
> +	 */
> +	WR_HANGUP   = 1<<1,

nit: add a whitespace line between an item and the next
item's comment.

> +
> +	WR_STOP_THE_MUSIC = (WR_IO_ERROR | WR_HANGUP),
> +};

(I read, but have no comments on the http-server boilerplate.)

> +
> +enum auth_result {
> +	AUTH_UNKNOWN = 0,
> +	AUTH_DENY = 1,
> +	AUTH_ALLOW = 2,
> +};
> +
> +struct auth_module {
> +	const char *scheme;
> +	const char *challenge_params;

Later, I notice that you set challenge_params using an
xstrdup() so this shouldn't be const and you should
free it in any freeing code.

> +	struct string_list *tokens;
> +};
> +
> +static int allow_anonymous;
> +static struct auth_module **auth_modules = NULL;
> +static size_t auth_modules_nr = 0;
> +static size_t auth_modules_alloc = 0;

So, we are setting up a number of potential auth modules,
each of which has a scheme to match a request to the module,
and a list of tokens that would be considered worthy of the
AUTH_ALLOW result. Otherwise, if the scheme matches but no
token matches, we get AUTH_DENY. Finally, if no scheme matches
we get AUTH_UNKNOWN.

This concept might be worth a comment here around the data
structures before we get into how that is implemented.

> +static struct auth_module *get_auth_module(struct strbuf *scheme)
> +{
> +	int i;
> +	struct auth_module *mod;
> +	for (i = 0; i < auth_modules_nr; i++) {
> +		mod = auth_modules[i];
> +		if (!strcasecmp(mod->scheme, scheme->buf))
> +			return mod;
> +	}
> +
> +	return NULL;
> +}

Matching the input scheme against the list of modules.

Only complaint: there is no reason that 'scheme' needs t
be a strbuf, but could be a 'const char *' here.

> +static void add_auth_module(struct auth_module *mod)
> +{
> +	ALLOC_GROW(auth_modules, auth_modules_nr + 1, auth_modules_alloc);
> +	auth_modules[auth_modules_nr++] = mod;
> +}

nit: this could be located earlier, next to the list
definition, or delayed until it is needed. That would
allow get_auth_module() to be closer to its first use.

> +static int is_authed(struct req *req, const char **user, enum worker_result *wr)
> +{
> +	enum auth_result result = AUTH_UNKNOWN;
> +	struct string_list hdrs = STRING_LIST_INIT_NODUP;
> +	struct auth_module *mod;
> +
> +	struct string_list_item *hdr;
> +	struct string_list_item *token;
> +	const char *v;
> +	struct strbuf **split = NULL;
> +	int i;
> +	char *challenge;
> +
> +	/* ask all auth modules to validate the request */
> +	for_each_string_list_item(hdr, &req->header_list) {
> +		if (skip_iprefix(hdr->string, "Authorization: ", &v)) {
> +			split = strbuf_split_str(v, ' ', 2);
> +			if (!split[0] || !split[1]) continue;

For each valid request header...

> +			// trim trailing space ' '
> +			strbuf_setlen(split[0], split[0]->len - 1);
> +
> +			mod = get_auth_module(split[0]);
> +			if (mod) {

...get an appropriate module, if it exists...

> +
> +				for_each_string_list_item(token, mod->tokens) {
> +					if (!strcmp(split[1]->buf, token->string)) {
> +						result = AUTH_ALLOW;
> +						goto done;
> +					}
> +				}
> +
> +				if (result != AUTH_UNKNOWN)
> +					goto done;

...and report if we find a valid token.

Here, it seems I was wrong in my expectation of AUTH_DENY:
if a matching module exists but no token exists in that
module, then we keep searching other modules. 

> +			}
> +		}
> +	}
> +
> +done:
> +	switch (result) {
> +	case AUTH_ALLOW:
> +		trace2_printf("%s: auth '%s' ALLOW", TR2_CAT, mod->scheme);
> +		*user = "VALID_TEST_USER";
> +		*wr = WR_OK;
> +		break;
> +
> +	case AUTH_DENY:
> +		trace2_printf("%s: auth '%s' DENY", TR2_CAT, mod->scheme);
> +		/* fall-through */

I'm not sure that I see a case where this is possible. Maybe
we should have a 'result = AUTH_DENY' at the start of the
"if (mod)" block, followed by a 'goto done' in all cases
instead of "if (result != AUTH_UNKNOWN)"?

> +	case AUTH_UNKNOWN:
> +		if (allow_anonymous)
> +			break;

If we do not require auth, then we want to continue if there
is no matching authentication.

> +		for (i = 0; i < auth_modules_nr; i++) {
> +			mod = auth_modules[i];
> +			if (mod->challenge_params)
> +				challenge = xstrfmt("WWW-Authenticate: %s %s",
> +						    mod->scheme,
> +						    mod->challenge_params);
> +			else
> +				challenge = xstrfmt("WWW-Authenticate: %s",
> +						    mod->scheme);
> +			string_list_append(&hdrs, challenge);
> +		}
> +		*wr = send_http_error(1, 401, "Unauthorized", -1, &hdrs, *wr);

However, here is the critical piece about how servers will
start to act with the new WWW-Authenticate header usage in
the Git credential helper interface. This will be critical
in the testing for Git to retry the credential helper while
passing these authentications schemes from the installed
modules.

> +	}
> +
> +	strbuf_list_free(split);
> +	string_list_clear(&hdrs, 0);
> +
> +	return result == AUTH_ALLOW ||
> +	      (result == AUTH_UNKNOWN && allow_anonymous);

Did it work? Or did it not need to work? I'm interested to
investigate the case that the client sent an authentication
header that matches a module but doesn't match any tokens,
but we allow anonymous access, anyway. Is that a 400? Or
is that a 401?

> +static enum worker_result dispatch(struct req *req)
> +{
> +	enum worker_result wr = WR_OK;
> +	const char *user = NULL;
> +
> +	if (!is_authed(req, &user, &wr))
> +		return wr;

If we are not authed, send the 401 response.

> +	if (is_git_request(req))
> +		return do__git(req, user);

If we are authed, then pass through to the Git response.

> +	return send_http_error(1, 501, "Not Implemented", -1, NULL,
> +			       WR_OK | WR_HANGUP);

If the Git request fails, we don't care. This is a test.
Just pass a 500-level error and the client will barf,
letting us know that something went wrong.

> +static void kill_some_child(void)

> +static void check_dead_children(void)

These technically sound methods have unfortunate names.
Using something like "connection" over "child" might
alleviate some of the horror. (I initially wanted to
suggest "subprocess" but you compare live_children to
max_connections in the next method, so connection seemed
appropriate.)

> +static struct strvec cld_argv = STRVEC_INIT;
> +static void handle(int incoming, struct sockaddr *addr, socklen_t addrlen)
> +{
> +	struct child_process cld = CHILD_PROCESS_INIT;
> +
> +	if (max_connections && live_children >= max_connections) {
> +		kill_some_child();
> +		sleep(1);  /* give it some time to die */
> +		check_dead_children();
> +		if (live_children >= max_connections) {
> +			close(incoming);
> +			logerror("Too many children, dropping connection");
> +			return;
> +		}
> +	}

Do we anticipate exercising concurrent requests in our
tests? Perhaps it's not worth putting a cap on the
connection count so we can keep the test helpers simple.

> +	if (addr->sa_family == AF_INET) {
> +		char buf[128] = "";
> +		struct sockaddr_in *sin_addr = (void *) addr;
> +		inet_ntop(addr->sa_family, &sin_addr->sin_addr, buf, sizeof(buf));
> +		strvec_pushf(&cld.env, "REMOTE_ADDR=%s", buf);
> +		strvec_pushf(&cld.env, "REMOTE_PORT=%d",
> +				 ntohs(sin_addr->sin_port));
> +#ifndef NO_IPV6
> +	} else if (addr->sa_family == AF_INET6) {
> +		char buf[128] = "";
> +		struct sockaddr_in6 *sin6_addr = (void *) addr;
> +		inet_ntop(AF_INET6, &sin6_addr->sin6_addr, buf, sizeof(buf));
> +		strvec_pushf(&cld.env, "REMOTE_ADDR=[%s]", buf);
> +		strvec_pushf(&cld.env, "REMOTE_PORT=%d",
> +				 ntohs(sin6_addr->sin6_port));
> +#endif
> +	}
> +
> +	strvec_pushv(&cld.args, cld_argv.v);
> +	cld.in = incoming;
> +	cld.out = dup(incoming);
> +
> +	if (cld.out < 0)
> +		logerror("could not dup() `incoming`");
> +	else if (start_command(&cld))
> +		logerror("unable to fork");
> +	else
> +		add_child(&cld, addr, addrlen);
> +}
> +

I scanned the socket creation code, but my eyes were
glazing over. I'm definitely in the camp of "if it works,
that's enough for our tests." If we start to rely on this
test harness in more places, we can improve any shortcomings
as they arise.

> +//////////////////////////////////////////////////////////////////
> +// This section is executed by both the primary instance and all
> +// worker instances.  So, yes, each child-process re-parses the
> +// command line argument and re-discovers how it should behave.
> +//////////////////////////////////////////////////////////////////
> +
> +int cmd_main(int argc, const char **argv)
> +{
> +	int listen_port = 0;
> +	struct string_list listen_addr = STRING_LIST_INIT_NODUP;
> +	int worker_mode = 0;
> +	int i;
> +	struct auth_module *mod = NULL;
> +
> +	trace2_cmd_name("test-http-server");
> +	setup_git_directory_gently(NULL);
> +
> +	for (i = 1; i < argc; i++) {
> +		const char *arg = argv[i];
> +		const char *v;
> +
> +		if (skip_prefix(arg, "--listen=", &v)) {
> +			string_list_append(&listen_addr, xstrdup_tolower(v));
> +			continue;
> +		}
> +		if (skip_prefix(arg, "--port=", &v)) {
> +			char *end;
> +			unsigned long n;
> +			n = strtoul(v, &end, 0);
> +			if (*v && !*end) {
> +				listen_port = n;
> +				continue;
> +			}
> +		}
> +		if (!strcmp(arg, "--worker")) {
> +			worker_mode = 1;
> +			trace2_cmd_mode("worker");
> +			continue;
> +		}
> +		if (!strcmp(arg, "--verbose")) {
> +			verbose = 1;
> +			continue;
> +		}
> +		if (skip_prefix(arg, "--timeout=", &v)) {
> +			timeout = atoi(v);
> +			continue;
> +		}
> +		if (skip_prefix(arg, "--init-timeout=", &v)) {
> +			init_timeout = atoi(v);
> +			continue;
> +		}
> +		if (skip_prefix(arg, "--max-connections=", &v)) {
> +			max_connections = atoi(v);
> +			if (max_connections < 0)
> +				max_connections = 0; /* unlimited */
> +			continue;
> +		}
> +		if (!strcmp(arg, "--reuseaddr")) {
> +			reuseaddr = 1;
> +			continue;
> +		}
> +		if (skip_prefix(arg, "--pid-file=", &v)) {
> +			pid_file = v;
> +			continue;
> +		}

ok, most of these arguments are actually about the per-connection
subprocesses.

> +		if (skip_prefix(arg, "--allow-anonymous", &v)) {
> +			allow_anonymous = 1;
> +			continue;
> +		}

Here is how we choose to allo anonymous access.

> +		if (skip_prefix(arg, "--auth=", &v)) {
> +			struct strbuf **p = strbuf_split_str(v, ':', 2);
> +
> +			if (!p[0]) {
> +				error("invalid argument '%s'", v);
> +				usage(test_http_auth_usage);
> +			}
> +
> +			// trim trailing ':'
> +			if (p[1])
> +				strbuf_setlen(p[0], p[0]->len - 1);
> +
> +			if (get_auth_module(p[0])) {
> +				error("duplicate auth scheme '%s'\n", p[0]->buf);
> +				usage(test_http_auth_usage);
> +			}
> +
> +			mod = xmalloc(sizeof(struct auth_module));
> +			mod->scheme = xstrdup(p[0]->buf);
> +			mod->challenge_params = p[1] ? xstrdup(p[1]->buf) : NULL;

Here, you xstrdup() into a 'const char *', but you are really
passing ownership so it shouldn't be conts.

> +			mod->tokens = xmalloc(sizeof(struct string_list));

nit: this could also be "CALLOC_ARRAY(mod->tokens, 1);"

> +			string_list_init_dup(mod->tokens);
> +
> +			add_auth_module(mod);
> +
> +			strbuf_list_free(p);
> +			continue;

Ok, we gain the auth schemes from the command line.

> +		}
> +		if (skip_prefix(arg, "--auth-token=", &v)) {
> +			struct strbuf **p = strbuf_split_str(v, ':', 2);
> +			if (!p[0]) {
> +				error("invalid argument '%s'", v);
> +				usage(test_http_auth_usage);
> +			}
> +
> +			if (!p[1]) {
> +				error("missing token value '%s'\n", v);
> +				usage(test_http_auth_usage);
> +			}
> +
> +			// trim trailing ':'

Use /* */ (Aside: I'm surprised we don't have a build option in
DEVELOPER=1 that catches the use of these comments.)

> +			strbuf_setlen(p[0], p[0]->len - 1);
> +
> +			mod = get_auth_module(p[0]);
> +			if (!mod) {
> +				error("auth scheme not defined '%s'\n", p[0]->buf);
> +				usage(test_http_auth_usage);
> +			}
> +
> +			string_list_append(mod->tokens, p[1]->buf);
> +			strbuf_list_free(p);
> +			continue;
> +		}

And the token lists. It is important that the scheme is added
before any token is added.

> +		fprintf(stderr, "error: unknown argument '%s'\n", arg);
> +		usage(test_http_auth_usage);
> +	}
> +
> +	/* avoid splitting a message in the middle */
> +	setvbuf(stderr, NULL, _IOFBF, 4096);
> +
> +	if (listen_port == 0)
> +		listen_port = DEFAULT_GIT_PORT;
> +
> +	/*
> +	 * If no --listen=<addr> args are given, the setup_named_sock()
> +	 * code will use receive a NULL address and set INADDR_ANY.
> +	 * This exposes both internal and external interfaces on the
> +	 * port.
> +	 *
> +	 * Disallow that and default to the internal-use-only loopback
> +	 * address.
> +	 */
> +	if (!listen_addr.nr)
> +		string_list_append(&listen_addr, "127.0.0.1");
> +
> +	/*
> +	 * worker_mode is set in our own child process instances
> +	 * (that are bound to a connected socket from a client).
> +	 */
> +	if (worker_mode)
> +		return worker();
> +
> +	/*
> +	 * `cld_argv` is a bit of a clever hack. The top-level instance
> +	 * of test-http-server does the normal bind/listen/accept stuff.
> +	 * For each incoming socket, the top-level process spawns
> +	 * a child instance of test-http-server *WITH* the additional
> +	 * `--worker` argument. This causes the child to set `worker_mode`
> +	 * and immediately call `worker()` using the connected socket (and
> +	 * without the usual need for fork() or threads).
> +	 *
> +	 * The magic here is made possible because `cld_argv` is static
> +	 * and handle() (called by service_loop()) knows about it.
> +	 */
> +	strvec_push(&cld_argv, argv[0]);
> +	strvec_push(&cld_argv, "--worker");
> +	for (i = 1; i < argc; ++i)
> +		strvec_push(&cld_argv, argv[i]);
> +
> +	/*
> +	 * Setup primary instance to listen for connections.
> +	 */
> +	return serve(&listen_addr, listen_port);
> +}

And complete the thing with some boilerplate.

This was a lot to read, and the interesting bits are all mixed in
with the http server code, which is less interesting to what we
are trying to accomplish. It would be beneficial to split this
into one or two patches before we actually introduce the tests.

The most important thing that I think would be helpful is to
isolate all the authentication behavior into its own patch so
we can see how those connections from the command-line arguments
affect the behavior of the server responses.

I think ideally we would have the following split:

 1. All server boilerblate. All requests 500 not-implemented.

 2. Add Git fall-through with no authentication. Add the tests
    that are intended to allow anonymous auth.

 3. Add authentication data structures read from command-line,
    but not processed at all in the logic.

 4. Act on the authentication data structures to alter the
    requests. Add the tests that use these authentication
    schemes.

I could easily see a case for combining 1&2 as well as 3&4,
for slightly larger but more completely-testable changes at
every step.

>From what I read, I don't think there is much to change in
the end result of the code, but it definitely was hard to read
the important things when surrounded by many lines of
boilerplate.

> diff --git a/t/t5556-http-auth.sh b/t/t5556-http-auth.sh

I'm going to pause here and come back to the test script in
a separate reply.

Thanks,
-Stolee