Category Archives: Network

Internet. Networking.

Workshop season six, episode three

November 14, 2024 Daniel Stenberg Leave a comment

One positive thing among many others at this version of the HTTP Workshop (day one, day two) is the fact that there have been several new faces showing up here. People who have not previously attended any HTTP Workshops. Getting fresh blood into the mix is great. A chance to maybe lower the average age of the attendees also feels welcome.

This half day was the final session for this time. Three topics were dealt with.

Do you speak HTTP? Getting your HTTP implementation to do right according to the specification can be a challenge. There is a whole range of existing tests for various areas of HTTP but there might still be a place to add HTTP semantic tests in particular for servers. Discussions brought about reflections around testing, doing tests, test formats, other tests, test infrastructure and more. I think the general sense was that yes it would be great. At least if someone else makes it happen…

Every HTTP stack is an intermediary – HTTP semantics is the (requirement for low-level) API. Yes. Lots of nodding around the huge table.

Workshop feedback and thoughts. What is a good cadence for future events, how long should the events be etc. This is probably the maximum amount of attendees we can handle using the same setup. This event was clearly better than several of the past ones in terms of diversity, but I will second our “workshop maestro” in that it could improve further still. We also discussed whether do-arranging together with IETF is good or bad, should it then be before or after IETF?

I think the consensus said that making it biannual event is good. The reasoning for keeping the event in Europe has been because a larger share of the European attendees come from smaller companies compared to the non-Europeans which to a larger degree come from larger companies that might have it easier to pay for longer trips.

My personal take

The HTTP Workshop is a one-of-a-kind event. At these events everything is about and around HTTP with an information density level that is super high. We get to learn how things actually work for people or that do not work. And that we are not alone in whatever struggles or HTTP challenges we have.

Networking with other doers here and absorbing every protocol detail being expressed, gives food for thoughts and lessons to take advantage from in years to come when we for sure are going to take HTTP transfers further. This is in many ways a kind of brain fertilizer event.

Did I mention I enjoyed it? I will certainly try to attend the next one.

Network, Web

The 2024 Workshop, day two

November 13, 2024 Daniel Stenberg Leave a comment

The fun continues. See day one.

In an office building close to the Waterloo station in London, around 40 persons again sat down at this giant table forming a big square that made it possible for us all to see each other. One by one there were brief presentations done with follow-up discussions. The discussions often reiterated old truths, brought up related topics and sometimes went deep down into the weeds about teeny weeny details of the involved protocol specs. The way we love it.

The people around the table represent Ericsson, Google, Microsoft, Apple, Meta, Akamai, Cloudflare, Fastly, Mozilla, Varnish. Caddy, Nginx, Haproxy, Tomcat, Adobe and curl and probably a few more I forget now. One could say with some level of certainty that a large portion of every day HTTP traffic in the world is managed by things managed by people present here.

This morning we all actually understood that the south entrance is actually the east one (yeah, that’s a so called internal joke) and most of us were sitting down, eager and prepared when the day started at 9:30 am.

Capsule. The capsule protocol (RFC 9297) is a way to, put simply, send UDP packets/datagrams over old style HTTP/1 or HTTP/2 proxies.

Cookies. With the 6265bis effort well on its way to ship as an updated RFC, there is an effort and intent to take yet another stab at improving and refreshing the cookie spec situation. In particular to better split off browser management and API related stuff from the more network-oriented over-the-wire details. You know yours truly never ceases an opportunity to voice his opinion on cookies… I approve of this attempt as well, as I think increasing clarity and improving the specification situation can’t but to help improve things.

Declarative web push. There’s an ongoing effort to improve web push – not to be confused with server push, so that it can be done easier and without needing JavaScript to manage it in the client side.

Reverse HTTP. There are origins who want to contact their CDNs without having to listening on any ports/sockets and still be able to provide content. That’s one of the use cases for Reverse HTTP and we got to learn details from internet drafts done on the topics for the last fifteen years and why it might still be a worthwhile effort and why the use cases still exist. But is there an enough demand to put it into HTTP?

Server Stack Detection. A discussion around how someone can detect the origin of the server stack of any given HTTP server implementation. Should there be a better way? What is the downside of introducing what would basically be the server version of the user-agent header field? Lots of productive discussions on how to avoid recreating problems of the past but in a reversed way.

MoQ: What is it and why is it not just HTTP/3? Was an educational session about the ongoing work done in this working group that is wrongly named and would appreciate more input from the general protocol community.

New HTTP stack. A description of the journey of a full HTTP stack rewrite: how components can be chained together and in which order and a follow-up discussion about if this should be included in documentation and if so in which way etc. Lessons included that the spec is one thing, the Internet is another. Maybe not an entirely new revelation.

Multiplexing in the year 2024. There are details in HTTP/2 multiplexing that does not really work, there are assumptions that are now hard to change. To introduce new protocols and features in the modern HTTP stack, things need to be done for both HTTP/2 and HTTP/3 that are similar but still different and it forces additional work and pain.

What if we create a way to do multiplexing over TCP, so called “over streams”, so that the HTTP/3 fallback over TCP could still be done using HTTP/3 framing. This would allow future new protocols to remain HTTP/3-only and just make the transport be either QUIC+UDP or Streams-over TCP+TLS. This triggered a lot of discussions, mostly positive and forward-looking but also a lot of concerns raised about additional work and yet another protocols component to write and implement that then needs to be supported until the end of times because things never truly go away completely.

I think this sounds like a fun challenge! Count me in.

End of day two. I need a beer or two to digest this.

Network, Web

The 2024 HTTP Workshop

November 13, 2024 Daniel Stenberg 2 Comments

Day one.

For the sixth time, this informal group of HTTP implementers and related “interested parties” unite in a room over a couple of days doing a HTTP Workshop. Nine years since that first event in Münster, Germany.

If you are someone like me, obsessed with networking and HTTP in particular this is certainly the place to be. Talking and discussing past lessons, coming changes and protocol dreams in several days with like-minded people is a blast. The people on these events are friends that I don’t always get to hang out with too often. Many of the attendees here have been involved in this community for a long time and have attended all or most of the past workshops as well. I have fortunately been able to attend all of them so far.

This time we are in London.

Let me tell you a little about the topics of day one – without spilling the beans about exactly who said what or what the company they came from. (I will add links to the presentations later once I know where to link to.)

Make Cleartext HTTP harder. The first discussion point of the day. While we have made HTTPS easier over recent years it can only take us so far. What if we considered means to make HTTP harder to use as the next level efforts to further reduce its use over the internet. The HSTS preload list is only growing. Should we instead convert it into a HSTS exclude list that can shrink over time? This triggered a looong a discussion in the group which brought back a lot of old arguments and reasoning from days I thought we had left behind long ago.

HTTP 2/3 abuses. A prominent implementer of a HTTP proxy/load balancer walked us through a whole series of different HTTP/2 and HTTP/3 protocols details that attackers can have been exploiting in recent years, with details about what can be done to mitigate such attacks. It made several other implementers mention how they take similar precautions and some other general discussions around the topics of what can be considered normal use of the protocol and what is not.

Idle connections & mobile: beneficial or harmful. 0-RTT instead of idle connections. There is a non-negligible cost associate with keeping connections alive for clients running on mobile phones. Would it be possible to instead move forward into a world when they are not kept alive but instead closed and 0-RTT opened again next time they are needed? Again the room woke up to a long discussion about the benefits and problems with doing this – which if it would be possible probably would save a lot of battery time on the average mobile phones.

QUIC pacing. We learned that it is very important for servers to implement decent QUIC pacing as it can increase performance up to 20 times compared to no pacing at all. What about using the flow control properly? What about changing the default buffer sizes for UDP sockets in the Linux kernel to something similar to TCP sockets in order to help the default case to perform better?

HTTP prioritization for product performance. The HTTP/2 way of doing prioritization was deemed a failure and too complicated a long time ago but in this presentation we were taught that there are definitely use cases and scenarios where the regular HTTP/3 priority setup is helpful and improves performs. Examples and descriptions for a popular and well used client were shown.

Allowing HTTP clients to use stale DNS data. What if HTTP clients would use stale data instead of having to wait for the DNS resolver response as a means to avoid having to wait a whole RTT to get the date that in a fair amount of the cases is the same as the stale data. Again a long discussion around TTLs for DNS queries and the fact that some clients are already doing this, in more or less explicit ways.

QUIC cache DSR. As the last talk of the the afternoon we got in the details of Direct Server Response for QUIC and how this can improve performance and problems and challenges involved with this. It then indirectly took us into a long sub-thread talking about HTTP caching, Vary headers and what could and should be done to improve things going forward. There seems to be an understanding that it would be good to improve the current situation but it is not entirely clear to this author exactly what that would entail.

When we then took a walk through the streets of London, only to have an awesome dinner during which we could all conclude that HTTP still is not ready. There is still work to be done. There are challenges left to overcome.

See you tomorrow for day two.

cURL and libcurl, Network

slow TCP connect on Windows

August 14, 2024 Daniel Stenberg 2 Comments

I have this tradition of mentioning occasional network related quirks on Windows on my blog so here we go again.

This round started with a bug report that said

curl is slow to connect to localhost on Windows

It is also demonstrably true. The person runs a web service on a local IPv4 port (and nothing on the IPv6 port), and it takes over 200 milliseconds to connect to it. You would expect it to take no less than a number of microseconds, as it does on just about all other systems out there.

The command

curl http://localhost:4567

Connecting

Buckle up, this is getting worse. But first, let’s take a look at this exact use case and what happens.

The hostname localhost first resolves to ::1 and 127.0.0.1 by curl. curl actually resolves this name “hardcoded”, so it does this extremely fast. Hardcoded meaning that it does not actually use DNS or any resolver functionality. It provides this result “fixed” for this hostname.

When curl has both IPv6 and IPv4 addresses to connect to and the host supports both IP families, it will first start the IPv6 attempt(s) and only if it did not succeed to connect over IPv6 after two hundred millisecond does it start the IPv4 attempts. This way of connecting is called Happy Eyeballs and is the de-facto and recommended way to connect to servers in a dual-stack since years back.

On all systems except Windows, where the IPv6 TCP connect attempt sends a SYN to a TCP port where nothing is listening, it gets a RST back immediately and returns failure. ECONNREFUSED is the most likely outcome of that.

On all systems except Windows, curl then immediately switches over to the IPv4 connect attempt instead that in modern systems succeeds within a small fraction of a millisecond. The failed IPv6 attempt is not noticeable to a user.

A TCP reminder

This is how a working TCP connect can be visualized like:

But when the TCP port in the server has no listener it actually performs like this

Connect failures on Windows

On Windows however, the story is different.

When the TCP SYN is sent to the port where nothing is listening and an RST is sent back to tell the client so, the client TCP stack does not return an error immediately.

Instead it decides that maybe the problem is transient and it will magically fix itself in the near future. It then waits a little and then keeps sending new SYN packets to see if the problem perhaps has fixed itself – until a maximum retry value is reached (set in the registry, this value defaults to 3 extra times).

Done on localhost, this retry-SYN process can easily take a few seconds and when done over a network, it can take even more seconds.

Since this behavior makes the leading IPv6 attempt not possible to fail within 200 milliseconds even when nothing is listening on that port, connecting to any service that is IPv4-only but has an IPv6 address by default delays curl’s connect success by two hundred milliseconds. On Windows.

Of course this does not only hurt curl. This is likely to delay connect attempts for countless applications and services for Windows users.

Non-responding is different

I want to emphasize that there is a big difference when trying to connect to a host where the SYN packet is simply not answered. When the server is not responding. Because then it could be a case of the packet gotten lost on the way so then the TCP stack has to resend the SYN again a couple of times (after a delay) to see if it maybe works this time.

IPv4 and IPv6 alike

I want to stress that this is not an issue tied to IPv6 or IPv4. The TCP stack seems to treat connect attempts done over either exactly the same. The reason I even mention the IP versions is because how this behavior works counter to Happy Eyeballs in the case where nothing listens to the IPv6 port.

Is resending SYN after RST “right” ?

According to this exhaustive resource I found on explaining this Windows TCP behavior, this is not in violation of RFC 793. One of the early TCP specifications from 1981.

It is surprising to users because no one else does it like this. I have not found any other systems or TCP stacks that behave this way.

Fixing?

There is no way for curl to figure out that this happens under the hood so we cannot just adjust the code to error out early on Windows as it does everywhere else.

Workarounds

There is a registry key in Windows called TcpMaxConnectRetransmissions that apparently can be tweaked to change this behavior. Of course it changes this for all applications so it is probably not wise to do this without a lot of extra verification that nothing breaks.

The two hundred millisecond Happy Eyeballs delay that curl exhibits can be mitigated by forcibly setting –happy-eyballs-timeout-ms to zero.

If you know the service is not using IPv6, you can tell curl to connect using IPv4 only, which then avoids trying and wasting time on the IPv6 sinkhole: –ipv4.

Without changing the registry and trying to connect to any random server out there where nothing is listening to the requested port, there is no decent workaround. You just have to accept that where other systems can return failure within a few milliseconds, Windows can waste multiple seconds.

Windows version

This behavior has been verified quite recently on modern Windows versions.

cURL and libcurl, Network, Web

HTTP/3 in curl mid 2024

June 10, 2024 Daniel Stenberg 8 Comments

Time for another checkup. Where are we right now with HTTP/3 support in curl for users?

I think curl’s situation is symptomatic for a lot of other HTTP tools and libraries. HTTP/3 has been and continues to be a much tougher deployment journey than HTTP/2 was.

curl supports four alternative HTTP/3 solutions

You can enable HTTP/3 for curl using one of these four different approaches. We provide multiple different ones to let “the market” decide and to allow different solutions to “compete” with each other so that users eventually can get the best one. The one they prefer. That saves us from the hard problem of trying to pick a winner early in the race.

More details about the four different approaches follow below.

Why is curl not using HTTP/3 already?

It already does if you build it yourself with the right set of third party libraries. Also, the curl for windows binaries provided by the curl project supports HTTP/3.

For Linux and other distributions and operating system packagers, a big challenge remains that the most widely used TLS library (OpenSSL) does not offer the widely accepted QUIC API that most other TLS libraries provide. (Remember that HTTP/3 uses QUIC which uses TLS 1.3 internally.) This lack of API prevents existing QUIC libraries to work with OpenSSL as their TLS solution forcing everyone who want to use a QUIC library to use another TLS library – because curl does not easily allows itself to get built using multiple TLS libraries . Having a separate TLS library for QUIC than for other TLS based protocols is not supported.

Debian tries an experiment to enable HTTP/3 in their shipped version of curl by switching to GnuTLS (and building with ngtcp2 + nghttp3).

HTTP/3 backends

To get curl to speak HTTP/3 there are three different components that need to be provided, apart from the adjustments in the curl code itself:

TLS 1.3 support for QUIC
A QUIC protocol library
An HTTP/3 protocol library

Illustrated

Below, you can see the four different HTTP/3 solutions supported by curl in different columns. All except the right-most solution are considered experimental.

From left to right:

the quiche library does both QUIC and HTTP/3 and it works with BoringSSL for TLS
msh3 is an HTTP/3 library that uses mquic for QUIC and either a fork family or Schannel for TLS
nghttp3 is an HTTP/3 library that in this setup uses OpenSSL‘s QUIC stack, which does both QUIC and TLS
nghttp3 for HTTP/3 using ngtcp2 for QUIC can use a range of different TLS libraries: fork family, GnuTLS and wolfSSL. (picotls is supported too, but curl itself does not support picotls for other TLS use)

ngtcp2 is ahead

ngtcp2 + nghttp3 was the first QUIC and HTTP/3 combination that shipped non-beta versions that work solidly with curl, and that is the primary reason it is the solution we recommend.

The flexibility in TLS solutions in that vertical is also attractive as this allows users a wide range of different libraries to select from. Unfortunately, OpenSSL has decided to not participate in that game so this setup needs another TLS library.

OpenSSL QUIC

OpenSSL 3.2 introduced a QUIC stack implementation that is not “beta”. As the second solution curl can use. In OpenSSL 3.3 they improved it further. Since early 2024 curl can get built and use this library for HTTP/3 as explained above.

However, the API OpenSSL provide for doing transfers is lacking. It lacks vital functionality that makes it inefficient and basically forces curl to sometimes busy-loop to figure out what to do next. This fact, and perhaps additional problems, make the OpenSSL QUIC implementation significantly slower than the competition. Another reason to advise users to maybe use another solution.

We keep communicating with the OpenSSL team about what we think needs to happen and what they need to provide in their API so that we can do QUIC efficiently. We hope they will improve their API going forward.

Stefan Eissing produced nice comparisons graph that I have borrowed from his Performance presentation (from curl up 2024. Stefan also blogged about h3 performance in curl earlier.). It compares three HTTP/3 curl backends against each other. (It does not include msh3 because it does not work good enough in curl.)

As you can see below, in several test setups OpenSSL is only achieving roughly half the performance of the other backends in both requests per second and raw transfer speed. This is on a localhost, so basically CPU bound transfers.

I believe OpenSSL needs to work on their QUIC performance in addition to providing an improved API.

quiche and msh3

quiche is still labeled beta and is only using BoringSSL which makes it harder to use in a lot of situations.

msh3 does not work at all right now in curl after a refactor a while ago.

HTTP/3 is a CPU hog

This is not news to anyone following protocol development. I have been repeating this over and over in every HTTP/3 presentation I have done – and I have done a few by now, but I think it is worth repeating and I also think Stefan’s graphs for this show the situation in a crystal clear way.

HTTP/3 is slow in terms of transfer performance when you are CPU bound. In most cases of course, users are not CPU bound because typically networks are the bottlenecks and instead the limited bandwidth to the remote site is what limits the speed on a particular transfer.

HTTP/3 is typically faster to completing a handshake, thanks to QUIC, so a HTTP/3 transfer can often get the first byte transmitted sooner than any other HTTP version (over TLS) can.

To show how this looks with more of Stefan’s pictures, let’s first show the faster handshakes from his machine somewhere in Germany. These tests were using a curl 8.8.0-DEV build, from a while before curl 8.8.0 was released.

Nope, we cannot explain why google.com actually turned out worse with HTTP/3. It can be added that curl.se is hosted by Fastly’s CDN, so this is really comparing curl against three different CDN vendors’ implementations.

Again: these are CPU bound transfers so what this image really shows is the enormous amounts of extra CPU work that is required to push these transfers through. As long as you are not CPU bound, your transfers should of course run at the same speeds as they do with the older HTTP versions.

These comparisons show curl’s treatment of these protocols as they are not generic protocol comparisons (if such are even possible). We cannot rule out that curl might have some issues or weird solutions in the code that could explain part of this. I personally suspect that while we certainly always have areas for improvement remaining, I don’t think we have any significant performance blockers lurking. We cannot be sure though.

OpenSSL-QUIC stands out here as well, in the not so attractive end.

HTTP/3 deployments

w3techs, Mozilla and Cloudflare data all agree that somewhere around 28-30% of the web traffic is HTTP/3 right now. This is a higher rate than HTTP/1.1 for browser traffic.

An interesting detail about this 30% traffic share is that all the big players and CDNs (Google, Facebook, Cloudflare, Akamai, Fastly, Amazon etc) run HTTP/3, and I would guess that they combined normally have a much higher share of all the web traffic than 30%. Meaning that there is a significant amount of browser web traffic that could use HTTP/3 but still does not. Unfortunately I don’t have the means to figure out explanations for this.

HTTPS stack overview

In case you need a reminder, here is how an HTTPS stack works.

Network

The Gemini protocol seen by this HTTP client person

May 28, 2023 Daniel Stenberg 10 Comments

There is again a pull-request submitted to the curl project to bring support for the Gemini protocol. It seems like a worthwhile effort that I support, even if it is also a lot of work involved and it might take some time before it reaches the state in which it can be merged. A previous attempt at doing this was abandoned a while ago.

This renewed interest made me take a fresh tour through the current Gemini protocol spec and I decided to write down some observations for you. So here I am. These are comments based on my reading of the 0.16.1 version of the protocol spec. I have implemented Internet application protocols client side for some thirty years. I have not actually implemented the Gemini protocol.

Motivations for existence

Gemini is the result of a kind of a movement that tries to act against some developments they think are wrong on the current web. Gemini is not only a new wire protocol, but also features a new documentation format and more. They also say its not “the web” at all but a new thing. As a sign of this, the protocol is designed by the pseudonymous “Solderpunk” – and the IETF or other suitable or capable organizations have not been involved – and it shows.

Counter surveillance

Gemini has no cookies, no negotiations, no authentication, no compression and basically no (other) headers either in a stated effort to prevent surveillance and tracking. It instead insists on using TLS client certificates (!) for keeping state between requests.

A Gemini response from a server is just a two-digit response code, a single media type and the binary payload. Nothing else.

Reduce complexity

They insist that thanks to reduced complexity it enables more implementations, both servers and clients, and that seems logical. The reduced complexity however also makes it less visually pleasing to users and by taking shortcuts in the protocol, it risks adding complexities elsewhere instead. Its quite similar to going back to GOPHER.

Form over content

This value judgement is repeated among Gemini fans. They think “the web” favors form over content and they say Gemini intentionally is the opposite. It seems to be true because Gemini documents certainly are never visually very attractive. Like GOPHER.

But of course, the protocol is also so simple that it lacks the power to do a lot of things you can otherwise do on the web.

The spec

The only protocol specification is a single fairly short page that documents the over-the-wire format mostly in plain English (undoubtedly featuring interpretation conflicts), includes the URL format specification (very briefly) and oddly enough also features the text/gemini media type: a new document format that is “a kind of lightweight hypertext format, which takes inspiration from gophermaps and from Markdown“.

The spec says “Although not finalised yet, further changes to the specification are likely to be relatively small.” The protocol itself however has no version number or anything and there is no room for doing a Gemini v2 in a forward-compatible way. This way of a “living document” seems to be popular these days, even if rather problematic for implementers.

Gopher revival

The Gemini protocol reeks of GOPHER and HTTP/0.9 vibes. Application protocol style anno mid 1990s with TLS on top. Designed to serve single small text documents from servers you have a relation to.

Short-lived connections

The protocol enforces closing the connection after every response, forcibly making connection reuse impossible. This is terrible for performance if you ever want to get more than one resource off a server. I also presume (but there is no mention of this in the spec) that they discourage use of TLS session ids/tickets for subsequent transfers (since they can be used for tracking), making subsequent transfers even slower.

We know from HTTP and a primary reason for the introduction of HTTP/1.1 back in 1997 that doing short-lived bursty TCP connections makes it almost impossible to reach high transfer speeds due to the slow-starts. Also, re-doing the TCP and TLS handshakes over and over could also be seen a plain energy waste.

The main reason they went with this design seem to be to avoid having a way to signal the size of payloads or do some kind of “chunked” transfers. Easier to document and to implement: yes. But also slower and more wasteful.

Serving an average HTML page using a number of linked resources/images over this protocol is going to be significantly slower than with HTTP/1.1 or later. Especially for servers far away. My guess is that people will not serve “normal” HTML content over this protocol.

Gemini only exists done over TLS. There is no clear text version.

GET-only

There are no other methods or ways to send data to the server besides the query component of the URL. There are no POST or PUT equivalents. There is basically only a GET method. In fact, there is no method at all but it is implied to be “GET”.

The request is also size-limited to a 1024 byte URL so even using the query method, a Gemini client cannot send much data to a server. More on the URL further down.

Query

There is a mechanism for a server to send back a single-line prompt asking for “text input” which a client then can pass to it in the URL query component in a follow-up request. But there is no extra meta data or syntax, just a single line text prompt (no longer than 1024 bytes) and free form “text” sent back.

There is nothing written about how a client should deal with the existing query part in this situation. Like if you want to send a query and answer the prompt. Or how to deal with the fact that the entire URL, including the now added query part, still needs to fit within the URL size limit.

Better use a short host name and a short path name to be able to send as much data as possible.

TOFU

the strongly RECOMMENDED approach is to implement a lightweight “TOFU” certificate-pinning system which treats self-signed certificates as first- class citizens.
(From the Gemini protocol spec 0.16.1 section 4.2)

Trust on first use (TOFU) as a concept works fairly well when you interface a limited set of servers with which you have some relationship. Therefore it often works fine for SSH for example. (I say “fine” for even with ssh, people often have the habit of just saying yes and accepting changed keys even when they perhaps should not.)

There are multiple problems with doing TOFU for a client/server document browsing system like Gemini.

A challenge is of course that on the first visit a client cannot spot an impostor, and neither can it when the server updates its certificates down the line. Maybe an attacker did it? It trains users on just saying “yes” when asked if they should trust it. Since you as a user might not have a clue about how runs that particular server or whatever the reason is why the certificate changes.

The concept of storing certificates to compare against later is a scaling challenge in multiple dimensions:

Certificates need to be stored for a long time (years?)
Each host name + port number combination has its own certificate. In a world that goes beyond thousands of Gemini hosts, this becomes a challenge for clients to deal with in a convenient (and fast) manner.
Presumably each user on a system has its own certificate store. What user A trusts, user B does not necessarily have to trust.
Does each Gemini client keep its own certificate store? Do they share? Who can update? How do they update the store? What’s the file format? A common db somehow?
When storing the certificates, you might also want to do like modern SSH does: not store the host names in cleartext as it is a rather big privacy leak showing exactly which servers you have visited.

I strongly suspect that many existing Gemini clients avoid this huge mess by simply not verifying the server certificates at all or by just storing the certificates temporarily in memory.

You can opt to store a hash or fingerprint of the certificate instead of the whole one, but that does not change things much.

I think insisting on TOFU is one of Gemini’s weakest links and I cannot see how this system can ever scale to a larger audience or even just many servers. I foresee that they need to accept Certificate Authorities or use DANE in a future.

Gemini Proxying

By insisting on passing on the entire URL in the requests, it is primarily a way to solve name based virtual hosting, but it is also easy for a Gemini server to act as a proxy for other servers. On purpose. And maybe I should write “easy”.

Since Gemini is (supposed to be) end-to-end TLS, proxying requests to another server is not actually possible while also maintaining security. The proxy would have to for example respond with the certificate retrieved from the remote server (in addition to its own) but the spec mentions nothing of this so we can guess existing clients and proxies don’t do it. I think this can be fixed by just adjusting the spec. But would add some rather kludgy complexity for a maybe a not too exciting feature.

Proxying to gopher:// URLs should be possible with the existing wording because there is no TLS to the server end. It could also proxy http:// URLs too but risk having to download the entire thing first before it can send the response.

URLs

The Gemini URL scheme is explained in 138 words, which is of course very terse and assumes quite a lot. It includes “This scheme is syntactically compatible with the generic URI syntax defined in RFC 3986“.

The spec then goes on to explain that the URL needs be UTF-8 encoded when sent over the wire, which I find peculiar because a normal RFC 3986 URL is just a set of plain octets. A Gemini client thus needs to know the charset that was used for or to assume for the original URL in order to convert it to UTF-8.

Example: if there is a %C5 in the URL and the charset was ISO-8859-1. That means the octet is a LATIN CAPITAL LETTER A WITH RING ABOVE. The UTF-8 version of said character is the two-byte sequence 0xC3 0x85. But if the original charset instead was ISO-8859-6, the same %C5 octet means ARABIC LETTER ALEF WITH HAMZA BELOW, encoded as 0xD8 0xA5 in UTF-8.

To me this does not rhyme well with reduced complexity. This conversion alone will cause challenges when done in curl because applications pass an RFC 3986 URL to the library and it does not currently have enough information on how to convert that to UTF-8. Not to mention that libcurl completely lacks UTF-8 conversion functions.

This makes me suspect that the intention is probably that only the host name in the URL should be UTF-8 encoded for IDN reasons and the rest should be left as-is? The spec could use a few more words to explain this.

One of the Gemini clients that I checked out to see how they do this, in order to better understand the spec, even use the punycode version of the host name quoting “Pending possible Gemini spec change”. What is left to UTF-8 then? That client did not UTF-8 encode anything of the URL, which adds to my suspicion that people don’t actually follow this spec detail but rather just interoperate…

The UTF-8 converted version of the URL must not be longer than 1024 bytes when included in a Gemini request.

The fact that the URL size limit is for the UTF-8 encoded version of the URL makes it hard to error out early because the source version of the URL might be shorter than 1024 bytes only to have it grow past the size limit in the encoding phase.

Origin

The document is carelessly thinking “host name” is a good authority boundary to TLS client certificates, totally ignoring the fact that “the web” learned this lesson long time ago. It needs to restrict it to the host name plus port number. Not doing that opens up Gemini for rather bad security flaws. This can be fixed by improving the spec.

Media type

The text/gemini media type should simply be moved out the protocol spec and be put elsewhere. It documents content that may or may not be transferred over Gemini. Similarly, we don’t document HTML in the HTTP spec.

Misunderstandings?

I am fairly sure that once I press publish on this blog post, some people will insist that I have misunderstood parts or most of the protocol spec. I think that is entirely plausible and kind of my point: the spec is written in such an open-ended way that it will not avoid this. We basically cannot implement this protocol by only reading the spec.

Future?

It is impossible to tell if this will fly for real or not. This is not a protocol designed for the masses to replace anything at high volumes. That is of course totally fine and it can still serve its community perfectly fine. There seems to be interest enough to keep the protocol and ecosystem alive for the moment at least. Possibly for a long time into the future as well.

What I would change

As I believe you might have picked up by now, I am not a big fan of this protocol but I still believe it can work and serve its community. If anyone would ask me, here are a few things I would consider changing in order to take it up a few notches.

Split the spec into three separate ones: protocol, URL syntax, media type. Expand the protocol parts with more exact syntax descriptions and examples to supplement the English.
Clarify the client certificate use to be origin based, not host name.
Drop the TOFU idea, it makes for a too weak security story that does not scale and introduces massive complexities for clients.
Clarify the UTF-8 encoding requirement for URLs. It is confusing and possibly bringing in a lot of complexity. Simplify?
Clarify how proxying is actually supposed to work in regards to TLS and secure connections. Maybe drop the proxy idea completely to keep the simplicity.
Consider a way to re-use connections, even if that means introducing some kind of “chunks” HTTP-style.

Discussion

Hacker news

Network, Open Source, Web

trurl manipulates URLs

April 3, 2023 Daniel Stenberg 2 Comments

trurl is a tool in a similar spirit of tr but for URLs. Here, tr stands for translate or transpose.

trurl is a small command line tool that parses and manipulates URLs, designed to help shell script authors everywhere.

URLs are tricky to parse and there are numerous security problems in software because of this. trurl wants to help soften this problem by taking away the need for script and command line authors everywhere to re-invent the wheel over and over.

trurl uses libcurl’s URL parser and will thus parse and understand URLs exactly the same as curl the command line tool does – making it the perfect companion tool.

I created trurl on March 31, 2023.

Some command line examples

Given just a URL (even without scheme), it will parse it and output a normalized version:

$ trurl ex%61mple.com/
http://example.com/

The above command will guess on a http:// scheme when none was provided. The guess has basic heuristics, like for example FTP server host names often starts with ftp:

$ trurl ftp.ex%61mple.com/
ftp://ftp.example.com/

A user can output selected components of a provided URL. Like if you only want to extract the path or the query components from it.:

$ trurl https://curl.se/?search=foobar --get '{path}'
/

Or both (with extra text intermixed):

$ trurl https://curl.se/?search=foobar --get 'p: {path} q: {query}'
p: / q: search=foobar

A user can create a URL by providing the different components one by one and trurl outputs the URL:

$ trurl --set scheme=https --set host=fool.wrong
https://fool.wrong/

Reset a specific previously populated component by setting it to nothing. Like if you want to clear the user component:

$ trurl https://daniel@curl.se/--set user=
https://curl.se/

trurl tells you the full new URL when the first URL is redirected to a second relative URL:

$ trurl https://curl.se/we/are/here.html --redirect "../next.html"
https://curl.se/we/next.html

trurl provides easy-to-use options for adding new segments to a URL’s path and query components. Not always easily done in shell scripts:

$ trurl https://curl.se/we/are --append path=index.html
https://curl.se/we/are/index.html

$ trurl https://curl.se?info=yes --append query=user=loggedin
https://curl.se/?info=yes&user=loggedin

trurl can work on a single URL or any amount of URLs passed on to it. The modifications and extractions are then performed on them all, one by one.

$ trurl https://curl.se localhost example.com 
https://curl.se/
http://localhost/
http://example.com/

trurl can read URLs to work on off a file or from stdin, and works on them in a streaming fashion suitable for filters etc.

$ cat many-urls.yxy | trurl --url-file -
...

More or different

trurl was born just a few days ago, this is what we have made it do so far. There is a high probability that it will change further going forward before it settles on exactly how things ideally should work.

It also means that we are extra open for and welcoming to feedback, ideas and pull-requests. With some luck, this could become a new everyday tool for all of us.

Tell us on GitHub!

cURL and libcurl, Network, Security

QUIC and HTTP/3 with wolfSSL

August 15, 2022 Daniel Stenberg 2 Comments

Disclaimer: I work for wolfSSL but I don’t speak for wolfSSL. I state my own opinions and I try to be as honest and transparent as possible. As always.

QUIC API

Back in the summer of 2020 I blogged about QUIC support coming in wolfSSL. That work never actually took off, primarily I believe because the team kept busy with other projects and tasks that had more customer focus and interest and yeah, there was not really any noticeable customer demand for QUIC with wolfSSL.

Time passed.

On July 21 2022, Stefan Eissing submitted his work on introducing a QUIC API and after reviews and updates, it was merged into the wolfSSL master branch on August 9th.

The QUIC API is planned to appear “for real” in a coming wolfSSL release version. Until then, we can play with what is available in git.

Let me be clear here: the good people at wolfSSL has not decided to write a full QUIC implementation, because that would be insane when so many good alternatives are already being worked on. This is just a set of new functions to allow wolfSSL to be used as TLS component when a QUIC stack is created.

Having QUIC support in wolfSSL is just one (but important) step along the way as it makes it possible to use wolfSSL to build a QUIC implementation but there are some more steps needed to turn this baby into full HTTP/3.

ngtcp2

Luckily, ngtcp2 exists and it is an established QUIC implementation that was written to be TLS agnostic from the beginning. This “only” needs adaptions provided to make sure it can be built and used with wolSSL as the TLS provider.

Stefan brought wolfSSL support to ngtcp2 in this PR. Merged on August 13th.

nghttp3

nghttp3 is the HTTP/3 library that uses ngtcp2 for QUIC, so once ngtcp2 supports wolfSSL we can use nghttp3 to do HTTP/3.

curl

curl can (as one of the available options) get built to use nghttp3 for HTTP/3, and if we just make sure we use an underlying ngtcp2 built to use a wolfSSL version with QUIC support, we can now do proper curl HTTP/3 transfers powered by wolfSSL.

Stefan made it possible to build curl with the wolfSSL+ngtcp2 combo in this PR. Merged on August 15th.

Available HTTP/3 components

With this new ecosystem addition, the chart of HTTP/3 components for curl did not get any easier to parse!

If you start by selecting which HTTP/3 library (or maybe I should call it HTTP/3 vertical) to use when building, there are three available options to go with: quiche, msh3 or nghttp3. Depending on that choice, the QUIC library is given. quiche does QUIC as well, but the two other HTTP/3 libraries use dedicated QUIC libraries (msquic and ngtcp2 respectively).

Depending on which QUIC solution you use, there is a limited selection of TLS libraries to use. The image above shows TLS libraries that curl also supports for other protocols, meaning that if you pick one of those you can still use that curl build to for example do HTTPS for HTTP version 1 or 2.

TLS options

If you instead rather pick TLS library first, only quictls and BoringSSL are supported by all QUIC libraries (quictls is an OpenSSL fork with a BoringSSL-like QUIC API patched in). If you rather build curl to use Schannel (that’s the native Windows TLS API), GnuTLS or wolfSSL you have also indirectly chosen which QUIC and HTTP/3 libraries to use.

Picotls

ngtcp2 supports Picotls shown in orange in the image above because that is a TLS 1.3-only library that is not supported for other TLS operations within curl. If you build curl and opt to go with a ngtcp2 build using Picotls for QUIC, you would need to have use an second TLS library for other TLS-using protocols. This is possible, but is rarely what users prefer.

No OpenSSL option

It should probably be especially highlighted that the plain vanilla OpenSSL is not an available option. Primarily because they decided that the already created API was not good enough for them so they will instead work on implementing their own QUIC library to be released at some point in the future. That also implies that if we want to build curl to do HTTP/3 with OpenSSL in the future, we probably need to add support for a forth QUIC library – and someone would also have to write a HTTP/3 library to use OpenSSL for QUIC.

Why wolfSSL adding QUIC is good for HTTP/3

People in general want to build applications and infrastructure using released, official and supported libraries and the sad truth is that there is a clear shortage in such TLS libraries with QUIC support.

In your typical current Linux distribution, quictls and BoringSSL are usually not viable options. The first since it is an OpenSSL fork not many even ship as a package and the second because it is done by Google for Google and they don’t do releases and generally care little for outside-Google users.

For the situations where those two TLS options are out of the game, the image above shows you the grim reality: your HTTP/3 options are limited. On Windows you can go with msh3 since it can use Schannel there, but on non-Windows you can only use ngtcp2/nghttp3 and before this wolfSSL support the only TLS option was GnuTLS.

For many embedded solutions, or even FIPS requirements, wolfSSL is now the only viable option for doing HTTP/3 with curl.

cURL and libcurl, Network, Open Source

The dream of auto-detecting proxies

August 12, 2022 Daniel Stenberg 1 Comment

curl, along with every other Internet tool with aspirations, supports proxies. A proxy is a (usually known) middle-man in a network operation; instead of going directly to the remote end server, the client goes via a proxy.

curl has supported proxies since the day it was born.

Which proxy?

Applications that do Internet transfers often would like to automatically be able to do their transfers even when users are trapped in an environment where they use a proxy. To figure out the proxy situation automatically.

Many proxy users have to use their proxy to do Internet transfers.

A library to detect which proxy?

The challenge to figure out the proxy situation is of course even bigger if your applications can run on multiple platforms. macOS, Windows and Linux have completely different ways of storing and accessing the necessary information.

libproxy

libproxy is a well-known library used for exactly this purpose. The first feature request to add support for this into libcurl that I can find, was filed in December 2007 (I also blogged about it) and it has been popping up occasionally over the years since then.

In August 2016, David Woodhouse submitted a patch for curl that implemented support for libproxy (the PR version is here). I was skeptical then primarily because of the lack of tests and docs in libproxy (and that the project seemed totally unresponsive to bug reports). Subsequently we did not merge that pull request.

Almost six years later, in June 2022, Jan Brummer revived David’s previous work and submitted a fresh pull request to add libproxy support in curl. Another try.

The proxy library dream is clearly still very much alive. There are also a fair amount of applications and systems today that are built to use libproxy to figure out the proxy and then tell curl about it.

What is unfortunately also still present, is the unsatisfying state of libproxy. It seems to have changed and improved somewhat since the last time I looked at it (6 years ago), but there several warning signs remaining that make me hesitate.

This is not a dependency I want to encourage curl users to lean and depend upon.

I greatly appreciate the idea of a libproxy but I do not like the (state of the) implementation.

My responsibility

Or rather, the responsibility I think we have as curl maintainers. We ship a product that is used and depended upon by an almost unfathomable amount of users, tools, products and devices.

Our job is to help guide our users so that the entire product, including third party dependencies, become an as safe and secure solution as possible. I am not saying that we can take full responsibility for the security of code outside of our own domain, but I think we should recognize that what we condone and recommend will be used. People read our support for library X as some level of approval.

We should only add support for third party libraries that meets a certain quality threshold. This threshold or bar maybe is (unfortunately) not written down anywhere but is still mostly a soft “gut feeling” based on human reviews of the situation.

What to do

I think the sensible thing to do first, before trying to get curl to use libproxy, is to make sure that there is a library for proxies that we can and want to lean on. That library can be the libproxy of today but it could also be something else.

Some areas in need of attention in libproxy that I recently also highlighted in the curl PR, that would take it closer to meeting the requirements we can ask of a dependency:

Improve the project with docs. We cannot safely rely on a library and its APIs if we don’t know exactly what to expect.
There needs to be at least basic tests that verify its functionality. We cannot fix and improve the library safely if we cannot check that it still works and behaves as expected. Tests is the only reliable way to make sure of this.
Add CI jobs that build the project and run those tests. To help the project better verify that things don’t break along the way.
Consider improving the API. To be fair, it is extremely simple now, but it’s also so simple that that it becomes ineffective and quirky in some use cases.
Allow for external URL parser and URL retrieving etc to avoid blocking, double-parsing and to reuse caches properly. It would be ridiculous for curl to use a library that has its own separate (semi-broken) HTTP transfer and its own (synchronous) name resolving process.

A solid proxy library?

The current libproxy is not even a lot of code, it could perhaps make more sense to just plainly write a new library based on how you would want a library like this to work – and use all the knowledge, magic and experience from libproxy to get the technical parts done correctly. A libproxy-next-generation.

But

This would require that someone really wanted to see this development take place and happen. It would take someone to take lead in the project and push for changes (like perhaps the 5 bullets I listed above). The best would be if someone who would like to use this kind of setup could sponsor a developer half/full time for a while to get a good head start on this.

Based on history, seeing we have had this known use case and this library around for well over a decade and this is the best we have accomplished so far, I am not optimistic that we can turn this ship around. Until then, we simply cannot allow curl to use this dependency.

cURL and libcurl, Network, Security

IPFS and their gateways

August 10, 2022 Daniel Stenberg 7 Comments

The InterPlanetary File System (IPFS) is according to the Wikipedia description: “a protocol, hypermedia and file sharing peer-to-peer network for storing and sharing data in a distributed file system.”. It works a little like bittorrent and you typically access content on it using a very long hash in an ipfs:// URL. Like this:

ipfs://bafybeigagd5nmnn2iys2f3doro7ydrevyr2mzarwidgadawmamiteydbzi

HTTP Gateways

I guess partly because IPFS is a rather new protocol not widely supported by many clients yet, people came up with the concept of IPFS “gateways”. (Others might have called it a proxy, because that is what it really is.)

This gateway is an HTTP server that runs on a machine that also knows how to speak and access IPFS. By sending the right HTTP request to the gateway, that includes the IPFS hash you are interested in, the gateway can respond with the contents from the IPFS hash.

This way, you just need an ordinary HTTP client to access IPFS. I think it is pretty clever. But as always, the devil is in the details.

Rewrite ipfs:// into https://

The quest for IPFS aficionados have seemingly become to add support for IPFS using this gateway approach to multiple widely used applications that know how to speak HTTP(S). Just rewrite the URL internally from IPFS to HTTPS.

ffmpeg got “native” IPFS support this way, and there is ongoing work to implement the same kind of URL rewrite for curl. (into curl, not libcurl)

So far so good I guess.

The URL rewrite

The IPFS “URL rewrite” is done in such so that the example IPFS URL is converted into “https://$gateway/$hash”. The transfer is done by the client as if it was a plain old HTTPS transfer.

What if the gateway is not local?

This approach has its biggest benefit of course when you can actually use a remote IPFS gateway. I presume most random ordinary users who want to access IPFS does not actually want to download, install and run an IPFS gateway on their machine to use this new power. They might very well appreciate the idea and convenience of accessing a remote IPFS gateway.

After all, the gateways are using HTTPS so at least the transfers are secure, right?

Leading people behind IPFS are even running public IPFS gateways for anyone to use. Both dweb.link and ipfs.io have been mentioned and suggested for default use. Possibly they are the same physical host as they appear to have the same IP addresses (owned by Protocol Labs, one of the big proponents behind IPFS).

The IPFS project also provides a list of public gateways.

No gateway set, use a default!

In an attempt to make this even easier for users, ffmpeg is made to use a built-in default gateway if none is set by the user.

I would expect very few users to actually have an IPFS gateway set. And even fewer to actually specify a local one.

So, when users want to watch a video using ffmpeg and an ipfs:// URL what happens?

The gateway sees it all

The remote gateway, that is administered by someone, somewhere, gets to see the full incoming request, and all traffic (video, whatever) that is sent back to the client (ffmpeg in this example) goes via the gateway. Sure, the client accesses the gateway via HTTPS so nobody can tamper with the traffic along the way, but the gateway is in full control and can inspect and tamper with the data as much as it likes. And there is no way for the client to know or detect if it is happening.

I am not involved in ffmpeg, nor do I have any insights into how the discussions evolved and were done around this subject, but for curl I have put my foot down and said that we must not blindly use and trust any default remote gateway like this. I believe it is our responsibility to not lure users into this traffic-monitoring setup.

Make sure you trust the gateway you use.

The curl way

curl will probably output an error message if there was no gateway set when an ipfs:// URL is used, and inform the user that it needs a gateway set to function and probably also show a URL for a page that contains more information about what this means and how to specify a gateway.

Bouncing gateways!

During the work of making the IPFS support for curl (which I review and comment on, not written or authored myself) I have also learned that some of the IPFS gateways even do regular HTTP 30x redirects to bounce over the client to another gateway.

Meaning: not only do you use and rely a total rando’s gateway on the Internet for your traffic. That gateway might even, on its own discretion, redirect you over to another host. Possibly run somewhere else, monitored by a separate team.

I have insisted, in the PR for ipfs support to curl, that the IPFS URL handling code should not automatically follow such gateway redirects, as I believe that adds even more risk to the user so if a user wants to allow this operation, it should be opt-in.

Imagine rising use of this

I would imagine that the ones hosting a popular default gateway either becomes overloaded and slow, or they need to scale up. If they scale up, they risk to leak traffic even wider. Scaling up also makes the operation more expensive, leading to incentives to make money somehow to finance it. Will the cookie car in the form of a massive data trove perhaps then be used/sold?

Users of these gateways get no promises, no rights, no contracts.

Other IPFS privacy concerns

Brave, the browser, has actual native IPFS support (not using any gateway) and they have an informative page called How does IPFS Impact my Privacy?

Final verdict

I am not dissing the idea nor implementation of IPFS itself. I think using HTTP gateways to access IPFS is a good idea in general as it makes the network more accessible. It is just a fragile solution that easily misleads users to do things they maybe shouldn’t. So maybe a little too accessible?

Credits

Image by Hans Schwarzkopf from Pixaba

Follow-up

I poked the ffmpeg project over Twitter, there was immediate reaction and there is already a proposed patch for ffmpeg that removes the use of a default IPFS gateway. “it’s a security risk”