Category Archives: cURL and libcurl

curl and/or libcurl related

cURL and libcurl, wolfSSL

curl up 2019 is over

(I will update this blog post with more links to videos and PDFs to presentations as they get published, so come back later in case your favorite isn’t linked already.)

The third curl developers conference, curl up 2019, is how history. We gathered in the lovely Charles University in central Prague where we sat down in an excellent class room. After the HTTP symposium on the Friday, we spent the weekend to dive in deeper in protocols and curl details.

I started off the Saturday by The state of the curl project (youtube). An overview of how we’re doing right now in terms of stats, graphs and numbers from different aspects and then something about what we’ve done the last year and a quick look at what’s not do good and what we could work on going forward.

James Fuller took the next session and his Newbie guide to contributing to libcurl presentation. Things to consider and general best practices to that could make your first steps into the project more likely to be pleasant!

Long term curl hacker Dan Fandrich (also known as “Daniel two” out of the three Daniels we have among our top committers) followed up with Writing an effective curl test where the detailed what different tests we have in curl, what they’re for and a little about how to write such tests.

Sign seen at the curl up dinner reception Friday night

After that I was back behind the desk in the classroom that we used for this event and I talked The Deprecation of legacy crap (Youtube). How and why we are removing things, some things we are removing and will soon remove and finally a little explainer on our new concept and handling of “experimental” features.

Igor Chubin then explained his new protect for us: curlator: a framework for console services (Youtube). It’s a way and tooling that makes it easier to provide access to shell and console oriented services over the web, using curl.

Me again. Governance, money in the curl project and someone offering commercial support (Youtube) was a presentation about how we intend for the project to join a legal entity SFC, and a little about money we have, what to spend it on and how I feel it is good to keep the project separate from any commercial support ventures any of us might do!

While the list above might seems like more than enough, the day wasn’t over. Christian Schmitz also did his presentation on Using SSL root certificate from Mac/Windows.

Our local hero organizer James Fuller then spoiled us completely when we got around to have dinner at a monastery with beer brewing monks and excellent food. Good food, good company and curl related dinner subjects. That’s almost heaven defined!

Sunday

Daylight saving time morning and you could tell. I’m sure it was not at all related to the beers from the night before…

James Fuller fired off the day by talking to us about Curlpipe (github), a DSL for building http execution pipelines.

The class room we used for the curl up presentations and discussions during Saturday and Sunday.

Robin Marx then put in the next gear and entertained us another hour with a protocol deep dive titled HTTP/3 (QUIC): the details (slides). For me personally this was a exactly what I needed as Robin clearly has kept up with more details and specifics in the QUIC and HTTP/3 protocols specifications than I’ve managed and his talk help the rest of the room get at least little bit more in sync with current development.

Jakub Nesetril and Lukáš Linhart from Apiary then talked us through what they’re doing and thinking around web based APIs and how they and their customers use curl: Real World curl usage at Apiary.

Then I was up again and I got to explain to my fellow curl hackers about HTTP/3 in curl. Internal architecture, 3rd party libs and APIs.

Jakub Klímek explained to us in very clear terms about current and existing problems in his talk IRIs and IDNs: Problems of non-ASCII countries. Some of the problems involve curl and while most of them have their clear explanations, I think we have to lessons to learn from this: URLs are still as messy and undocumented as ever before and that we might have some issues to fix in this area in curl.

To bring my fellow up to speed on the details of the new API introduced the last year I then made a presentation called The new URL API.

Clearly overdoing it for a single weekend, I then got the honors of doing the last presentation of curl up 2019 and for an audience that were about to die from exhaustion I talked Internals. A walk-through of the architecture and what libcurl does when doing a transfer.

Summary

I ended up doing seven presentations during this single weekend. Not all of them stellar or delivered with elegance but I hope they were still valuable to some. I did not steal someone else’s time slot as I would gladly have given up time if we had other speakers wanted to say something. Let’s aim for more non-Daniel talkers next time!

A weekend like this is such a boost for inspiration, for morale and for my ego. All the friendly faces with the encouraging and appreciating comments will keep me going for a long time after this.

Thank you to our awesome and lovely event sponsors – shown in the curl up logo below! Without you, this sort of happening would not happen.

curl up 2020

I will of course want to see another curl up next year. There are no plans yet and we don’t know where to host. I think it is valuable to move it around but I think it is even more valuable that we have a friend on the ground in that particular city to help us out. Once this year’s event has sunken in properly and a month or two has passed, the case for and organization of next year’s conference will commence. Stay tuned, and if you want to help hosting us do let me know!


cURL and libcurl

curl goes 180

The 180th public curl release is a patch release: 7.64.1. There’s been 49 days since 7.64.0 shipped. The first release since our 21st birthday last week. (Full changelog.)

Numbers

the 180th release
2 changes
49 days (total: 7,677)
116 bug fixes (total: 5,029)
184 commits (total: 24,111)
0 new public libcurl functions (total: 80)
2 new curl_easy_setopt() options (total: 267)
1 new curl command line option (total: 221)
49 contributors, 25 new (total: 1,929)
25 authors, 10 new (total: 669)
0 security fixes (total: 87)

News!

This is a patch release but we still managed to introduce some fun news in this version. We ship brand new alt-svc support which we encourage keen and curious users to enable in their builds and test out. We strongly discourage anyone from using that feature in production as we reserve ourselves the right to change it before removing the EXPERIMENTAL label. As mentioned in the blog post linked above, alt-svc is the official way to bootstrap into HTTP/3 so this is a fundamental stepping stone for supporting that protocol version in a future curl.

We also introduced brand new support for the Amiga-specific TLS backend AmiSSL, which is a port of OpenSSL to that platform.

Bug-fixes

With over a hundred bug-fixes landed in this period there are a lot to choose from, but some of the most most fun and important ones from my point of view include the following.

connection check crash

This was a rather bad regression that occasionally caused crashes when libcurl would scan its connection cache for a live connection to reuse. Most likely to trigger with the Schannel backend.

connection sharing crash

The example source code that uses a shared connection cache among many threads was another crash regression. It turned out a thread could accidentally get hold of a connection already in private use by another thread…

“Expire in…” logs removed

Having the harmless but annoying text there was a mistake to begin with. It was a debug-only line that accidentally was pushed and not discovered in time. It’s history now.

curl -M manual removed

The tutorial-like manual piece that was previously included in the -M (or –manual) built-in command documentation, is no longer included. The output shown is now just the curl.1 man page. The reason for this is that the tutorial has gone a bit stale and there is now better updated and better explained documentation elsewhere. Primarily perhaps in everything curl. The online version of that document will eventually also be removed.

TLS terminology cleanups

We now refer to the Windows TLS backend as “Schannel” and the Apple macOS one as “Secure Transport” in all curl code and documentation. Those are the official names and those are the names people in general know them as. No more use of the former names that sometimes made people confused.

Shaving off bytes and mallocs

We rearranged the layout of a few structs and changed to using bitfields instead of booleans and more. This way, we managed to shrink two of the primary internal structs by 5% and 11% with no functionality change or loss.

Similarly, we removed a few mallocs, even in the common code path, so now the number of allocs for my regular test download of 4GB data over a localhost HTTP server claims fewer allocs than ever before.

Next?

We estimate that there will be a 7.65.0 release to ship 56 days from now. Then we will remove some deprecated features, perhaps add something new and quite surely fix a whole bunch of more bugs. Who know what fun we will come up with at curl up this coming weekend?

Keep reporting. Keep posting pull-requests. We love them and you!

Brand new sticker shipment for curl up from our beloved sticker sponsor!


cURL and libcurl

Happy 21st, curl!

6 Comments

Another year has passed. The curl project is now 21 years old.

I think we can now say that it is a grown-up in most aspects. What have we accomplished in the project in these 21 years?

We’ve done 179 releases. Number 180 is just a week away.

We estimate that there are now roughly 6 billion curl installations world-wide. In phones, computers, TVs, cars, video games etc. With 4 billion internet users, that’s like 1.5 curl installation per Internet connected human on earth

669 persons have authored patches that was merged.

The curl source code now consists of 160,000 lines of code made in over 24,000 commits.

1,927 persons have helped out so far. With code, bug reports, advice, help and more.

The curl repository also hosts 429 man pages with a total of 36,900 lines of documentation. That count doesn’t even include the separate project Everything curl which is a dedicated book on curl with an additional 10,165 lines.

In this time we have logged more than 4,900 bug-fixes, out of which 87 were security related problems.

We keep doing more and more CI builds, auto-builds, fuzzing and static code analyzing on our code day-to-day and non-stop. Each commit is now built and tested in over 50 different builds and environments and are checked by at least four different static code analyzers, spending upwards 20-25 CPU hours per commit.

We have had 2 curl developer conferences, with the third curl up about to happen this coming weekend in Prague, Czech Republic.

The curl project was created by me and I’m still the lead developer. Up until today, almost 60% of the commits in the project have my name on them. I have done most commits per month in the project every single month since August 2015, and in 186 months out of the 232 months for which we have logged data.

cURL and libcurl, Network, Web

Looking for the Refresh header

6 Comments

The other day someone filed a bug on curl that we don’t support redirects with the Refresh header. This took me down a rabbit hole of Refresh header research and I’ve returned to share with you what I learned down there.

tl;dr Refresh is not a standard HTTP header.

As you know, an HTTP redirect is specified to use a 3xx response code and a Location: header to point out the new URL (I use the term URL here but you know what I mean). This has been the case since RFC 1945 (HTTP/1.0). According to an old mail from Roy T Fielding (dated June 1996), Refresh “didn’t make it” into that spec. That was the first “real” HTTP specification. (And the HTTP we used before 1.0 didn’t even have headers!)

The little detail that it never made it into the 1.0 spec or any later one, doesn’t seem to have affected the browsers. Still today, browsers keep supporting the Refresh header as a sort of Location: replacement even though it seems to never have been present in a HTTP spec.

In good company

curl is not the only HTTP library that doesn’t support this non-standard header. The popular python library requests apparently doesn’t according to this bug from 2017, and another bug was filed about it already back in 2011 but it was just closed as “old” in 2014.

I’ve found no support in wget or wget2 either for this header.

I didn’t do any further extensive search for other toolkits’ support, but it seems that the browsers are fairly alone in supporting this header.

How common is the the Refresh header?

I decided to make an attempt to figure out, and for this venture I used the Rapid7 data trove. The method that data is collected with may not be the best – it scans the IPv4 address range and sends a HTTP request to each TCP port 80, setting the IP address in the Host: header. The result of that scan is 52+ million HTTP responses from different and current HTTP origins. (Exactly 52254873 responses in my 59GB data dump, dated end of February 2019).

Results from my scans

  • Location is used in 18.49% of the responses
  • Refresh is used in 0.01738% of the responses (exactly 9080 responses featured them)
  • Location is thus used 1064 times more often than Refresh
  • In 35% of the cases when Refresh is used, Location is also used
  • curl thus handles 99.9939% of the redirects in this test

Additional notes

  • When Refresh is the only redirect header, the response code is usually 200 (with 404 being the second most)
  • When both headers are used, the response code is almost always 30x
  • When both are used, it is common to redirect to the same target and it is also common for the Refresh header value to only contain a number (for the number of seconds until “refresh”).

Refresh from HTML content

Redirects can also be done by meta tags in HTML and sending the refresh that way, but I have not investigated how common as that isn’t strictly speaking HTTP so it is outside of my research (and interest) here.

In use, not documented, not in the spec

Just another undocumented corner of the web.

When I posted about these findings on the HTTPbis mailing list, it was pointed out that WHATWG mentions this header in their iana page. I say mention because calling that documenting would be a stretch…

It is not at all clear exactly what the header is supposed to do and it is not documented anywhere. It’s not exactly a redirect, but almost?

Will/should curl support it?

A decision hasn’t been made about it yet. With such a very low use frequency and since we’ve managed fine without support for it so long, maybe we can just maintain the situation and instead argue that we should just completely deprecate this header use from the web?

Updates

After this post first went live, I got some further feedback and data that are relevant and interesting.

  • Yoav Wiess created a patch for Chrome to count how often they see this header used in real life.
  • Eric Lawrence pointed out that IE had several incompatibilities in its Refresh parser back in the day.
  • Boris pointed out (in the comments below) the WHATWG documented steps for handling the header.
  • The use of <meta> tag refresh in contents is fairly high. The Chrome counter says almost 4% of page loads!
cURL and libcurl, Network, Open Source, Web

alt-svc in curl

2 Comments

The RFC 7838 was published already in April 2016. It describes the new HTTP header Alt-Svc, or as the title of the document says HTTP Alternative Services.

HTTP Alternative Services

An alternative service in HTTP lingo is a quite simply another server instance that can provide the same service and act as the same origin as the original one. The alternative service can run on another port, on another host name, on another IP address, or over another HTTP version.

An HTTP server can inform a client about the existence of such alternatives by returning this Alt-Svc header. The header, which has an expiry time, tells the client that there’s an optional alternative to this service that is hosted on that host name, that port number using that protocol. If that client is a browser, it can connect to the alternative in the background and if that works out fine, continue to use that host for the rest of the time that alternative is said to work.

In reality, this header becomes a little similar to the DNS records SRV or URI: it points out a different route to the server than what the A/AAAA records for it say.

The Alt-Svc header came into life as an attempt to help out with HTTP/2 load balancing, since with the introduction of HTTP/2 clients would suddenly use much more persistent and long-living connections instead of the very short ones used for traditional HTTP/1 web browsing which changed the nature of how connections are done. This way, a system that is about to go down can hint the clients on how to continue using the service, elsewhere.

Alt-Svc: h2="backup.example.com:443"; ma=2592000;

HTTP upgrades

Once that header was published, the by then already existing and deployed Google QUIC protocol switched to using the Alt-Svc header to hint clients (read “Chrome users”) that “hey, this service is also available over gQUIC“. (Prior to that, they used their own custom alternative header that basically had the same meaning.)

This is important because QUIC is not TCP. Resources on the web that are pointed out using the traditional HTTPS:// URLs, still imply that you connect to them using TCP on port 443 and you negotiate TLS over that connection. Upgrading from HTTP/1 to HTTP/2 on the same connection was “easy” since they were both still TCP and TLS. All we needed then was to use the ALPN extension and voila: a nice and clean version negotiation.

To upgrade a client and server communication into a post-TCP protocol, the only official way to it is to first connect using the lowest common denominator that the HTTPS URL implies: TLS over TCP, and only once the server tells the client what more there is to try, the client can go on and try out the new toys.

For HTTP/3, this is the official way for HTTP servers to tell users about the availability of an HTTP/3 upgrade option.

curl

I want curl to support HTTP/3 as soon as possible and then as I’ve mentioned above, understanding Alt-Svc is a key prerequisite to have a working “bootstrap”. curl needs to support Alt-Svc. When we’re implementing support for it, we can just as well support the whole concept and other protocol versions and not just limit it to HTTP/3 purposes.

curl will only consider received Alt-Svc headers when talking HTTPS since only then can it know that it actually speaks with the right host that has the authority enough to point to other places.

Experimental

This is the first feature and code that we merge into curl under a new concept we do for “experimental” code. It is a way for us to mark this code as: we’re not quite sure exactly how everything should work so we allow users in to test and help us smooth out the quirks but as a consequence of this we might actually change how it works, both behavior and API wise, before we make the support official.

We strongly discourage anyone from shipping code marked experimental in production. You need to explicitly enable this in the build to get the feature. (./configure –enable-alt-svc)

But at the same time we urge and encourage interested users to test it out, try how it works and bring back your feedback, criticism, praise, bug reports and help us make it work the way we’d like it to work so that we can make it land as a “normal” feature as soon as possible.

Ship

The experimental alt-svc code has been merged into curl as of commit 98441f3586 (merged March 3rd 2019) and will be present in the curl code starting in the public release 7.64.1 that is planned to ship on March 27, 2019. I don’t have any time schedule for when to remove the experimental tag but ideally it should happen within just a few release cycles.

alt-svc cache

The curl implementation of alt-svc has an in-memory cache of known alternatives. It can also both save that cache to a text file and load that file back into memory. Saving the alt-svc cache to disk allows it to survive curl invokes and to truly work the way it was intended. The cache file stores the expire timestamp per entry so it doesn’t matter if you try to use a stale file.

curl –alt-svc

Caveat: I now talk about how a feature works that I’ve just above said might change before it ships. With the curl tool you ask for alt-svc support by pointing out the alt-svc cache file to use. Or pass a “” (empty name) to make it not load or save any file. It makes curl load an existing cache from that file and at the end, also save the cache to that file.

curl also already since a long time features fancy connection options such as –resolve and –connect-to, which both let a user control where curl connects to, which in many cases work a little like a static poor man’s alt-svc. Learn more about those in my curl another host post.

libcurl options for alt-svc

We start out the alt-svc support for libcurl with two separate options. One sets the file name to the alt-svc cache on disk (CURLOPT_ALTSVC), and the other control various aspects of how libcurl should behave in regards to alt-svc specifics (CURLOPT_ALTSVC_CTRL).

I’m quite sure that we will have reason to slightly adjust these when the HTTP/3 support comes closer to actually merging.

cURL and libcurl, wolfSSL

commercial curl support!

If you want commercial support, ports of curl to other operating systems or just instant help to fix your curl related problems, we’re here to help. Get in touch now! This is the premiere. This has not been offered by me or anyone else before.

I’m not sure I need to say it, but I personally have authored almost 60% of all commits in the curl source code during my more than twenty years in the project. I started the project, I’ve designed its architecture etc. There is simply no one around with my curl experience and knowledge of curl internals. You can’t buy better curl expertise.

curl has become one of the world’s most widely used software components and is the transfer engine doing a large chunk of all non-browser Internet transfers in the world today. curl has reached this level of success entirely without anyone offering commercial services around it. Still, not every company and product made out there has a team of curl experts and in this demanding time and age we know there are times when you rather hire the right team to help you out.

We are the curl experts that can help you and your team. Contact us for all and any support questions at support@wolfssl.com.

What about the curl project?

I’m heading into this new chapter of my life and the curl project with the full knowledge that this blurs the lines between my job and my spare time even more than before. But fear not!

The curl project is free and open and will remain independent of any commercial enterprise helping out customers. I realize me offering companies and organizations to deal with curl problems and solving curl issues for compensation creates new challenges and questions where boundaries go, if for nothing else for me personally. I still think this is worth pursuing and I’m sure we can figure out and handle whatever minor issues this can lead to.

My friends, the community, the users and harsh critiques on twitter will all help me stay true and honest. I know this. This should end up a plus for the curl project in general as well as for me personally. More focus, more work and more money involved in curl related activities should improve the project.

It is with great joy and excitement I take on this new step.

cURL and libcurl

curl 7.64.0 – like there’s no tomorrow

I know, has there been eight weeks since the previous release already? But yes it has – I double-checked! And then as the laws of nature dictates, there has been yet another fresh curl version released out into the wild.

Numbers

the 179th release
5 changes
56 days (total: 7,628)
76 bug fixes (total: 4,913)
128 commits (total: 23,927)
0 new public libcurl functions (total: 80)
3 new curl_easy_setopt() options (total: 265)
1 new curl command line option (total: 220)
56 contributors, 29 new (total: 1,904)
32 authors, 13 new (total: 658)
  3 security fixes (total: 87)

Security fixes

This release we have no less than three different security related fixes. I’ll describe them briefly here, but for the finer details I advice you to read the dedicated pages and documentation we’ve written for each one of them.

CVE-2018-16890 is a bug where the existing range check in the NTLM code is wrong, which allows a malicious or broken NTLM server to send a header to curl that will make it read outside a buffer and possibly crash or otherwise misbehave.

CVE-2019-3822 is related to the previous but with much worse potential effects. Another bad range check actually allows a sneaky NTLMv2 server to be able to send back crafted contents that can overflow a local stack based buffer. This is potentially in the worst case a remote code execution risk. I think this might be the worst security issue found in curl in a long time. A small comfort is that by disabling NTLM, you will avoid it until patched.

CVE-2019-3823 is a potential read out of bounds of a heap based buffer in the SMTP code. It is fairly hard to trigger and it will mostly cause a crash when it does.

Changes

  1. curl now supports Mike West’s cookie update known as draft-ietf-httpbis-cookie-alone. It basically means that cookies that are set as “secure” has to be set over HTTPS to be allow to override a previous secure cookie. Safer cookies.
  2. The –resolve option as well as CURLOPT_RESOLVE now support specifying a wildcard as port number.
  3. libcurl can now send trailing headers in chunked uploads using the new options.
  4. curl now offers options to enable HTTP/0.9 responses, The default is still enabled, but the plan is to deprecate that and in 6 months time switch over the to default to off.
  5. curl now uses higher resolution timer accuracy on windows.

Bug-fixes

Check out the full change log to see the whole list. Here are some of the bug fixes I consider to be most noteworthy:

  • We re-implemented the code coverage support for autotools builds due to a license problem. It turned out the previously used macro was GPLv2 licensed in an unusual way for autoconf macros.
  • We make sure –xattr never stores URLs with credentials, following the security problem reported on a related tool. Not considered a security problem since this is actually what the user asked for, but still done like this for added safety.
  • With -J, curl should not be allowed to append to the file. It could lead to curl appending to a file that was in the download directory since before.
  • –tls-max didn’t work correctly on macOS when built to use Secure Transport.
  • A couple of improvements in the libssh-powered SSH backend.
  • Adjusted the build for OpenSSL 3.0.0 (the coming future version).
  • We no longer refer to Schannel as “winssl” anywhere. winssl is dead. Long live Schannel!
  • When built with mbedTLS, ignore SIGPIPE accordingly!
  • Test cases were adjusted and verified to work fine up until February 2037.
  • We fixed several parsing errors in the URL parser, mostly related to IPv6 addresses. Regressions introduced in 7.62.0.

Next

The next release cycle will be one week shorter and we expect to ship next release on March 27 – just immediately after curl turns 22 years old. There are already several changes in the pipe so we expect that to become 7.65.0.

We love your help and support! File bugs you experience or see, submit pull requests for the features or corrections you work on!

cURL and libcurl, Work

I’m on team wolfSSL

4 Comments

Let me start by saying thank you to all and everyone who sent me job offers or otherwise reached out with suggestions and interesting career moves. I received more than twenty different offers and almost every one of those were truly good options that I could have said yes to and still pulled home a good job. What a luxury challenge to have to select something from that! Publicly announcing me leaving Mozilla turned out a great ego-boost.

I took some time off to really reflect and contemplate on what I wanted from my next career step. What would the right next move be?

I love working on open source. Internet protocols, and transfers and doing libraries written in C are things considered pure fun for me. Can I get all that and yet keep working from home, not sacrifice my wage and perhaps integrate working on curl better in my day to day job?

I talked to different companies. Very interesting companies too, where I have friends and people who like me and who really wanted to get me working for them, but in the end there was one offer with a setup that stood out. One offer for which basically all check marks in my wish-list were checked.

wolfSSL

On February 5, 2019 I’m starting my new job at wolfSSL. My short and sweet period as unemployed is over and now it’s full steam ahead again! (Some members of my family have expressed that they haven’t really noticed any difference between me having a job and me not having a job as I spend all work days the same way nevertheless: in front of my computer.)

Starting now, we offer commercial curl support and various services for and around curl that companies and organizations previously really haven’t been able to get. Time I do not spend on curl related activities for paying customers I will spend on other networking libraries in the wolfSSL “portfolio”. I’m sure I will be able to keep busy.

I’ve met Larry at wolfSSL physically many times over the years and every year at FOSDEM I’ve made certain to say hello to my wolfSSL friends in their booth they’ve had there for years. They’re truly old-time friends.

wolfSSL is mostly a US-based company – I’m the only Swede on the team and the only one based in Sweden. My new colleagues all of course know just as well as you that I’m prevented from traveling to the US. All coming physical meetings with my work mates will happen in other countries.

commercial curl support!

We offer all sorts of commercial support for curl. I’ll post separately with more details around this.

cURL and libcurl, Network

HTTP/3 talk on video

Yesterday, I had attracted audience enough to fill up the largest presentation room GOTO 10 has, which means about one hundred interested souls.

The subject of the day was HTTP/3. The event was filmed with a mevo camera and I captured the presentation directly from my laptop as well, and I then stitched together the two sources into this final version late last night. As you’ll notice, the sound isn’t awesome and the rest of the “production” isn’t exactly top notch either, but hey, I don’t think it matters too much.

I’ll talk about HTTP/3 (Photo by Jon Åslund)
I’m Daniel Stenberg. I was handed a medal from the Swedish king in 2017 for my work on… (Photo by OpenTokix)
HTTP/2 vs HTTP/3 (Photo by OpenTokix)
Some of the challenges to deploy HTTP/3 are…. (Photo by Jonathan Sulo)

The slide set can also be viewed on slideshare.