Re: [PATCH] add http.maxReceiveSpeed to limit git-receive-pack receiving speed

From: Junio C Hamano <gitster@pobox.com>
Date: Aug 19, 2021, 18:28 UTC
Message-ID: <xmqq4kbl2sre.fsf@gitster.g>
In-Reply-To: <20210819091433.348-1-chenan.xxw@alibaba-inc.com>

Xia XiaoWen <haoyurenzhuxia@gmail.com> writes:

> Sometimes need to limit the receive speed of git `clone/fetch`
> because of the limited network bandwidth, otherwise will prevent
> other applications from using the network normally.

No subject in these two half-sentences.

    In order to avoid hogging all the available bandwidth, users may
    want to limit the speed to receive traffic for "git clone" or
    "git fetch".

perhaps.

> Add `http.maxReceiveSpeed` to limit `git-receive-pack` receiving

"limit `git-receive-pack`'s" or "limit receiving speedk of ..."

> speed, Can be overridden by `GIT_HTTP_MAX_RECEIVE_SPEED` eivironment
> variable.
>
> The default is unlimited, same if the value is 0 or negative. The

Let's error it out when the configuration gives a value that does not make sense instead. That way, we could in the future use some of these invalid values to signal special behaviour if we wanted to.

> default unit is Bytes/s, common unit suffixes of k, m, or g are supported.

OK.

> this configuration is valid for `clone`, `fetch`, `pull` commands of the

s/this/This/

> https protocol, and only supports libcurl 7.15.5 and above.

We are likely be raising the floor versions of libcURL to 7.16.0 or even 7.19.4 soonish. It probably would make it easier to allow it unconditionally (otherwise you'd probably need to implement error or warning messages when configuration is given but the libcURL version used is too old, etc.).

Show 14 quoted lines

> ---
>  http.c | 24 +++++++++++++++++++++++-
>  1 file changed, 23 insertions(+), 1 deletion(-)
>
> diff --git a/http.c b/http.c
> index 8119247149..12030cf3bc 100644
> --- a/http.c
> +++ b/http.c
> @@ -83,6 +83,9 @@ static const char *ssl_pinnedkey;
>  static const char *ssl_cainfo;
>  static long curl_low_speed_limit = -1;
>  static long curl_low_speed_time = -1;
> +#if LIBCURL_VERSION_NUM >= 0x070f05
> +static ssize_t curl_max_receive_speed = -1;

On cURL side, CURLOPT_MAX_RECV_SPEED_LARGE takes curl_off_t, which is typically off_t (which is signed).

I wonder if ssize_t is overkill for our purpose, though. Can't this be a plain vanilla "int" or perhaps "long", just like the variable defined above uses "long" for "speed"? Or is 2gb/s too low to be practical and we must use a 64-bit type?

Show 12 quoted lines

> +#endif
>  static int curl_ftp_no_epsv;
>  static const char *curl_http_proxy;
>  static const char *http_proxy_authmethod;
> @@ -361,7 +364,12 @@ static int http_options(const char *var, const char *value, void *cb)
>  		curl_low_speed_time = (long)git_config_int(var, value);
>  		return 0;
>  	}
> -
> +#if LIBCURL_VERSION_NUM >= 0x070f05
> +	if (!strcmp("http.maxreceivespeed", var)) {
> +		curl_max_receive_speed = git_config_ssize_t(var, value);

Check for nonsense values, so that we can later use them to mean something special. It is good to remember is that you can always loosen the rules after you give your software to your users, but it is very hard to tighten the rules. As you never need more than one way to specify "the default" (aka "unlimited"), reserving any non-positive value to mean the default is a design that is extensible poorly.

I.e. insert something like

		if (curl_max_receive_speed < 0)
			die("negatigve number for %s: %s", var, value);

here.

Show 12 quoted lines

> +		return 0;
> +	}
> +#endif
>  	if (!strcmp("http.noepsv", var)) {
>  		curl_ftp_no_epsv = git_config_bool(var, value);
>  		return 0;
> @@ -974,6 +982,12 @@ static CURL *get_curl_handle(void)
>  				 curl_low_speed_time);
>  	}
>  
> +#if LIBCURL_VERSION_NUM >= 0x070f05
> +	if (curl_max_receive_speed > 0)

The "result" handle was created anew in this function, so the distinction does not really matter in practrice, but since you are carefully initializing the variable to "-1" so that we can differentiate the case where it is unconfigured (hence we want to use the default) and it is set to zero (hence we want to use the default), it would be more consistent and future-proof if you also allowed 0 to be passed here, i.e.

	if (curl_max_receive_speed >= 0)

> +		curl_easy_setopt(result, CURLOPT_MAX_RECV_SPEED_LARGE,
> +				 curl_max_receive_speed);

This call, if you use anything but curl_off_t as the type for curl_max_receive_speed variable where it is declared, needs a cast, like in the example https://curl.se/libcurl/c/CURLOPT_MAX_RECV_SPEED_LARGE.html

Show 22 quoted lines

> +#endif
> +
>  	curl_easy_setopt(result, CURLOPT_MAXREDIRS, 20);
>  #if LIBCURL_VERSION_NUM >= 0x071301
>  	curl_easy_setopt(result, CURLOPT_POSTREDIR, CURL_REDIR_POST_ALL);
> @@ -1105,6 +1119,9 @@ void http_init(struct remote *remote, const char *url, int proactive_auth)
>  {
>  	char *low_speed_limit;
>  	char *low_speed_time;
> +#if LIBCURL_VERSION_NUM >= 0x070f05
> +	char *max_receive_speed;
> +#endif
>  	char *normalized_url;
>  	struct urlmatch_config config = { STRING_LIST_INIT_DUP };
>  
> @@ -1196,6 +1213,11 @@ void http_init(struct remote *remote, const char *url, int proactive_auth)
>  	low_speed_time = getenv("GIT_HTTP_LOW_SPEED_TIME");
>  	if (low_speed_time != NULL)
>  		curl_low_speed_time = strtol(low_speed_time, NULL, 10);
> +#if LIBCURL_VERSION_NUM >= 0x070f05
> +	max_receive_speed = getenv("GIT_HTTP_MAX_RECEIVE_SPEED");
> +	if (max_receive_speed && !git_parse_ssize_t(max_receive_speed, &curl_max_receive_speed))

Overlong line.

Unlike curl_max_receive_speed that must be visible and understandable long haul in this file, the temporary string variable lives only during these handful of lines and shortened name is easier to see and understand what is going on. Also, you can avoid repeated spelling out of the environment variable name by giving a constant for it near the top of this function, e.g.

	static const char mrs_env[] = "GIT_HTTP_MAX_RECEIVE_SPEED";

Then this part would become:

	if (mrs) {
		if (!git_parse_ssize_t(mrs, &curl_max_receive_speed))
			die(_("invalid number for %s: %s", mrs_env, mrs);
		if (curl_max_receive_speed < 0)
			die(_("negative number for %s: %s", mrs_env, mrs);
	}

> +		warning("failed to parse GIT_HTTP_MAX_RECEIVE_SPEED: %s", max_receive_speed);

Thanks.