As I mentioned before, the curl documentation needs improvement. As a first step I converted the man page for curl_easy_setopt into no less than 210(!) individual man pages. One new for each option the function supports.

The man page was originally (a few days ago) almost 3000 lines, and now with them all split up we end up with a lot more text. This because the new format encourages more text per option and each page now has to detail itself more. This should also make each option much easier to google/search and to link to when we help users understand the options.

I’ve made some server-side scripts to generate html versions of them all, I generate a list of all options we have and the examples we host on the web site now have all mentions of the options linked directly to these new pages.

The curl_easy_setopt man page will then get most explanations cut out and mainly be used as an index with the options grouped into logical sections to help users find the options they want to use. I could cut out almost 2500 lines.

The new man pages add about 7500 lines of documentation (excluding the headers in each file)…

cURL and libcurl, Open Source

curl the next few years

June 19, 2014 Daniel Stenberg

Roadmap of things Daniel Stenberg and Steve Holme want to work on next. It is intended to serve as a guideline for others for information, feedback and possible participation.

If you agree, disagree or would like to add stuff you want to work on, please join us on the curl-library list! This “roadmap” is likely to change over time. We’ll keep the updated ROADMAP in git.

New stuff – libcurl

http2 test suite
http2 multiplexing/pipelining
SPDY
SRV records
HTTPS to proxy
make sure there’s an easy handle passed in to curl_formadd(), curl_formget() and curl_formfree() by adding replacement functions and deprecating the old ones to allow custom mallocs and more
HTTP Digest authentication via Windows SSPI
GSSAPI authentication in the email protocols
add support for third-party SASL libraries such as Cyrus SASL – may need to move existing native and SSPI based authentication into vsasl folder after reworking HTTP and SASL code
SASL authentication in LDAP
Simplify the SMTP email interface so that programmers don’t have to construct the body of an email that contains all the headers, alternative content, images and attachments – maintain raw interface so that programmers that want to do this can
Allow the email protocols to return the capabilities before authenticating. This will allow an application to decide on the best authentication mechanism
Allow Windows threading model to be replaced by Win32 pthreads port
Implement a dynamic buffer size to allow SFTP to use much larger buffers and possibly allow the size to be customizable by applications. Use less memory when handles are not in use?

New stuff – curl

Embed a language interpreter (lua?). For that middle ground where curl isnâ€™t enough and a libcurl binding feels â€œtoo muchâ€. Build-time conditional of course.
Simplify the SMTP command line so that the headers and multi-part content don’t have to be constructed before calling curl

Improve

build for windows (considered hard by many users)
curl -h output (considered overwhelming to users)
we have Â > 160 command line options, is there a way to redo things to simplify or improve the situation as we are likely to keep adding features/options in the future too
docs (considered “bad” by users but how do we make it better?)
authentication framework (consider merging HTTP and SASL authentication to give one API for protocols to call)
Perform some of the clean up from the TODO document, removing old definitions and such like that are currently earmarked to be removed years ago

Remove

cmake support (nobody maintains it)
makefile.vc files as there is no point in maintaining two sets of Windows makefiles. Note: These are currently being used by the Windows autobuilds

cURL and libcurl, Open Source

The curl and libcurl 2014 survey

June 19, 2014 Daniel Stenberg 2 Comments

Reading through the answers to the curl project‘s survey “curl and libcurl 2014” is very interesting and educational.

After having lead and participated in this project for so long I have my own picture of what we’re good and bad at. That’s not exactly the same image I get when I read the survey responses. That’s of course the educating part and I really want to learn from this poll and see where to put in some efforts and attempt to improve. At the same time I’ve been working for a while to put together a roadmap for the project, and the survey will help guide us with that work as well.

The full generated summary of the answers can be found on the site, but I thought I do the extra effort here and try to extrapolate data, compare and try to get to the real story that lurks in the shadows.

Over the almost 10 days the poll was open, we received 194 responses. I was hoping for more participation, but on the other hand I don’t think more people would’ve given a much different view. My only concern would be that I’m not sure exactly how well we reached out.

Almost all curl users use it for HTTP and HTTPS. Sure, we also use a lot of other protocols and in fact all supported protocols did up having at least two users according to the survey, but only a single digit percentage did not mark HTTP and HTTPS as protocols they use. The least used supported protocol gopher, is used among 1.5% of the users who responded.

FTPS and SFTP are basically equally much used and they are the 4th and 5th most used protocols. HTTP, HTTPS and FTP are clearly our most popular protocols.

Only one in five users use curl on a single platform. All others use it on two or more, and one if four use it on four or more with an unexpectedly high 11% saying they use it on 5 or more platforms! That’s a pretty strong message to me that our multi-platform strategy is important.

Our users have been with us for a long time. Half of the users have been using curl for five years or more! A fifth has been with us for 8 years or more! And yet there seems to be a healthy amount of newcomers finding us as 14% is within their first year.

The above numbers combined, I’m not surprised but only happy to see that 4 out of 5 users are also involved in other open source projects. curl is just one piece in a large ecosystem and I think it is good that we all participate in several projects so that we learn and cross-pollinate where possible!

Less than half of the respondents are subscribed to a curl mailing list, and curl-library is the most popular one. This also reflects in subscriber numbers on the actual mailing lists where curl-library with its 1400+ members has almost twice as many subscribers as curl-users. One way to view this is that we are old enough, established enough and working enough so that users don’t have to subscribe to our lists to keep up. The less optimistic way to see it could be that this is because we haven’t reached out good enough or that our mailing list culture/setup isn’t welcoming enough.

Perhaps most surprising to me: that several persons got upset and reacted strongly to the question about how good we treat “female and other minorities” in the project. To me there’s no doubt that female contributors are a minority in the curl community and I want to learn if we’re doing our best to be inclusive and open to all possible contributors. Or at least how good/bad people think we are doing.

29% of the respondents have contributed patches, meaning 56 individuals. I think that tells more about the ones who took part of the survey than it measures participation level among “regular users”.

Documentation

A big revelation for me was the question where I asked people to identify the “worst parts” of the project. The image here below is the look of the summary.

It quite clearly identifies “documentation” as the area in most need of improvements.

I don’t think the amount of docs is the problem. After discussing with people I think the primary issues are:

Some collections of docs are just too big and hard to find in, like the curl man page and the curl_easy_setopt man pages. We need to split them up and/or rearrange somehow to help people find the info they need. Work has started on this. I’ll follow up with details later.
We get slightly bad “reviews” on this when people confuse the libcurl bindings’ lack of docs to be our problem. Lots of libcurl bindings are not very good documented – but they are separate projects not controlled or documented by us. I don’t know what we can do to help that situation. Suggestions are very welcome!
We don’t have much step-by-step tutorials on how to get started and how to knit things together. We mostly provide reference manuals. I will appreciate help with improving this!

cURL

cURL and libcurl, Mozilla, Network, Web

Http2 interim meeting NYC

June 8, 2014 Daniel Stenberg 5 Comments

On June 5th, around thirty people sat down around a huge table in a conference room on the 4th floor in the Google offices in New York City, with a heavy rain pouring down outside.

It was time for another IETF http2 interim meeting. The attendees were all participants in the HTTPbis work group and came from a wide variety of companies and countries. The major browser vendors were represented there, and so were operators and big service providers and some proxy people. Most of the people who have been speaking up on the mailing list over the last year or so, unfortunately with a couple of people notably absent. (And before anyone asks, yes we are a group where the majority is old males like me.)

Most people present knew many of the others already, which helped to create a friendly familiar spirit and we quickly got started on the Thursday morning working our way through the rather long lits of issues to deal with. When we had our previous interim meeting in London, I think most of us though we would’ve been further along today but recent development and discussions on the list had actually brought back a lot of issues we though we were already done with and we now reiterated a whole slew of subjects. We weren’t allowed to take photographs indoors so you won’t see any pictures of this opportunity from me here.

We did close many issues and I’ll just quickly mention some of the noteworthy ones here…

Extensions

We started out with the topic of “extensions”. Should we revert the decision from Zurich (where it was decided that we shouldn’t allow extensions in http2) or was the current state of the protocol the right one? The arguments for allowing extensions included that we’d keep getting requests for new things to add unless we have a way and that some of the recent stuff we’ve added really could’ve been done as extensions instead. An argument against it is that it makes things much simpler and reliable if we just document exactly what the protocol has and is, and removing “optional” behavior from the protocol has been one of the primary mantas along the design process.

The discussion went back and forth for a long time, and after almost three hours we had kind of a draw. Nobody was firmly against “the other” alternative but the two sides also seemed to have roughly the same amount of support. Then it was yet again time for the coin toss to guide us. Martin brought out an Australian coin and … the next protocol draft will allow extensions. Again. This also forces implementation to have to read and skip all unknown frames it receives compared to the existing situation where no unknown frames can ever occur.

BLOCKED as an extension

A rather given first candidate for an extension was the BLOCKED frame. At the time BLOCKED was added to the protocol it was explicitly added into the spec because we didn’t have extensions – and it is now being lifted out into one.

ALTSVC as an extension

What received slightly more resistance was the move to move out the ALTSVC frame as well. It was argued that the frame isn’t mandatory to support and therefore easily can be made into an extension.

Simplified padding

Another small change of the wire format since draft-12 was the removal of the high byte for padding to simplify. It reduces the amount you can pad a single frame but you can easily pad more using other means if you really have to, and there were numbers presented that said that 255 bytes were enough with HTTP 1.1 already so probably it will be enough for version 2 as well.

Schedule

There will be a new draft out really soon: draft -13. Martin, our editor of the spec, says he’ll be able to ship it in a week. That is intended to be the last draft, intended for implementation and it will then be expected to get deployed rather widely to allow us all in the industry to see how it works and be able to polish details or wordings that may still need it.

We had numerous vendors and HTTP stack implementers in the room and when we discussed schedule for when various products will be able to see daylight. If we all manage to stick to the plans. we may just have plenty of products and services that support http2 by the September/October time frame. If nothing major is found in this latest draft, we’re looking at RFC status not too far into 2015.

Meeting summary

I think we’re closing in for real now and I have good hopes for the protocol and our progress to a really wide scale deployment across the Internet. The HTTPbis group is an awesome crowd to work with and I had a great time. Our hosts took good care of us and made sure we didn’t lack any services or supplies. Extra thanks go to those of you who bought me dinners and to those who took me out to good beer places!

My http2 document

Yeah, it will now become somewhat out of date and my plan is to update it once the next draft ships. I’ll also do another http2 presentation already this week so I hope to also post an updated slide set soonish. Stay tuned!

Wireshark

My plan is to cooperate with the other Wireshark hackers and help making sure we have the next draft version supported in Wireshark really soon after its published.

curl and nghttp2

Most of the differences introduced are in the binary format so nghttp2 will need to be updated again – it is the library curl uses for the wire format of http2. The curl parts will need some adjustments, for example for Content-Encoding gzip that no longer is implicit but there should be little to do in the curl code for this draft bump.

Open Source, Technology

Hacking embedded day 2014

May 26, 2014 Daniel Stenberg

Once again our gracious sponsor Enea hosted an embedded hacking day arranged through foss-sthlm – the third time in three years at the same place with the same host. Fifty something happy hackers brought their boards, devices, screens, laptops and way too many cables to the place on a Saturday to spend it in the name of embedded systems. With no admission fee at all. Just bring your stuff, your skills and enjoy the day.

This happened on May 24th and on the outside of the windows we could identify one of the warmest and nicest spring/summer days so far this year in Stockholm. But hey, if you want to get some fun hacks done we mustn’t let those real-world things hamper us!

the room

All attendees were given a tshirt tshirt and then they found themselves a spot somewhere in the crowd and the socializing and hacking could start. I got the pleasure of loudly interrupting everyone once in a while to say welcome or point out that a talk was about to begin…

We also collected random fun hardware pieces donated to us by various people for a hardware raffle. More about that further down.

Talk

To spice up the day of hacking, we offered some talks. First out was…

Bluetooth and Low Power radio byÂ Mats Karlsson and during this session we got to learn a bunch about hacking extremely low power devices and doing radio for them with Arduinos and more.

Mats talks bluetooth

We hadn’t much more than started but the clock showed lunch time and we were served lunch!

Contest

Readers of my blog and previous attendees of any of the embedded hacking days I’ve been organizing should be familiar with the embedded Linux contests I’ve made.

Lately I’ve added a new twist to my setup and I tested it previously when I visited foss-gbg and ran a contest there.

Basically it is a complicated maze/track that you walk through by answering questions, and when you reach the goal you have collected a set of words along the way. Those words should then be rearranged to form a question and that final question should be answered as fast as possible.

Daniel explains

Since I already blogged and publicized my previous “Parallell Spaghetti Decode” contest I of course had a new map this time and I altered the set questions a bit as well, even if participants in the latter can find similarities in the previous one. This kind of contest is a bit complicated so for this I hand out the play field and the questions on two pieces of paper to each participant.

After only a little over seven minutes we had a winner, Yann Vernier, who could walk home with a brand new Nexus 7 32GB. The prize was, as so much else this day, donated by Enea.

Hardware Raffle

I donated my Arduino Nano (never even unpacked) and a Raspberry Pi with SD-card that I never use. Enea pooled in with a Parallella board and we got an RFduino and a Texas Instrument Stellaris ARM-based little round robot. The Parallella board was the by far most popular device (as expected really) with the Stellaris board as second. Only 12 people signed up for the Rpi…

Parallella board

Everyone who was interested in one of the 5 devices signed up on a list, marking each thing of interest.

. Stellaris

We then put little pieces of paper with numbers on them in a big bowl and I got to draw 5 numbers (representing different individuals) who then won the devices. It of course turned out we did it in a complicated way that I had did some minor mistakes in to add to the fun. In the end I believe it was at least a fair process that didn’t give any favors or weight in any particular way. I believe we got 5 happy winners.

Workshop

“How to select hardware” was the name of the workshop I lead. Basically it was a one hour group discussion around how to buy, find, order, deal with, not do, avoid when looking for hardware for your (hobby) project. Discussions around brands, companies, sites, buying from China or Ebay, reading reviews, writing reviews, how people do when they buy things when building stuff of their own.

Workshop attendees

I think we had some good talks and lots of people shared their experiences, stories and some horror stories. Hopefully we all brought a little something with us back from that…

muffins

After that we refilled our coffee mugs and indulged in the huge and tasty muffins that magically had appeared.

Something we had learned from previous events was to not “pack” too many talks and other things during the day but to also allow everyone to really spend time on getting things done and to just stroll around and talk with others.

Instead of a third slot for a talk or another workshop we had a little wishlist in our wiki for the day, and as a result I managed to bully BjÃ¶rn Stenberg to the room where he then described his automated system for his warming cupboard (vÃ¤rmeskÃ¥p) which basically is a place to dry clothes. BjÃ¶rn has perfected his cupboard’s ability to dry clothes and also shut off/tell him when they are dry and not waste energy by keep on warming using damp sensors, Arduinos and more.

Bjorn's controller box

With that we were in the final sprint for the day. The last commits were made. The final bragging comments described blinking leds. Cables were detached. Bags were filled will electronics. People started to drop off.

Only a few brave souls stayed to the very end. And they celebrated in style.

JÃ¤mtlands IPA

I had a great day, and I received several positive comments and feedback from participants. I hope we’ll run a similar event again soon, it’d be great to keep this an annual tradition.

The pictures in this blog post are taken by: me, Jon Aldama, Annica Spangholt, Magnus Sandberg and JÃ¤mtlands bryggerier. Thanks! More pictures can also be found in Enea’s blog posting and in the Google+ event.

Thanks also to Jon, Annica and Sofie for the hard hosting work during the event. It made everything run smooth and without any bumps!

cURL and libcurl, libssh2, Network, Open Source

Why SFTP is still slow in curl

May 14, 2014 Daniel Stenberg

Okay, there’s no point in denying this fact: SFTP transfers in curl and libcurl are much slower than if you just do them with your ordinary OpenSSH sftp command line tool or similar. The difference in performance can even be quite drastic.

Why is this so and what can we do about it? And by “we” I fully get that you dear reader think that I or someone else already deeply involved in the curl project should do it.

Background

I once blogged a lengthy post on how I modified libssh2 to do SFTP transfers much faster. curl itself uses libssh2 to do SFTP so there’s at least a good start. The problem is only that the speedup we did in libssh2 was because of SFTP’s funny protocol design so we had to:

send off requests for a (large) set of data blocks at once, each block being N kilobytes big
using a several hundred kilobytes big buffer (when downloading the received data would be stored in the big buffer)
then return as soon as there’s one block (or more) that has returned from the server with data
over time and in a loop, there are then blocks constantly in transit and a number of blocks always returning. By sending enough outgoing requests in the “outgoing pipe”, the “incoming pipe” and CPU can be kept fairly busy.
never wait until the entire receive buffer is complete before we go on, but instead use a sliding buffer so that we avoid “halting points” in the transfer

This is more or less what the sftp tool does. We’ve also done experiments with using libssh2 directly and then we can reach quite decent transfer speeds.

libcurl

The libcurl transfer core is basically the same no matter which protocol that is being transferred. For a normal download this is what it does:

waits for data to become available
read as much data as possible into a 16KB buffer
send the data to the application
goto 1

So, there are two problems with this approach when it comes to the SFTP problems as described above.

The first one is that a 16KB buffer is very small in SFTP terms and immediately becomes a bottle neck in itself. In several of my experiments I could see how a buffer of 128, 256 or even 512 kilobytes would be needed to get high bandwidth high latency transfers to really fly.

The second being that with a fixed buffer it will come to a point every 16KB byte where it needs to wait for that specific response to come back before it can continue and ask for the next 16KB of data. That “sync point” is really not helping performance either – especially not when it happens so often as every 16KB.

A solution?

For someone who just wants a quick-fix and who builds their own libcurl, rebuild with CURL_MAX_WRITE_SIZE set to 256000 or something like that and you’ll get a notable boost. But that’s neither a nice nor clean fix.

A proper fix should first of all only be applied for SFTP transfers, thus deciding at run-time if it is necessary or not. Then it should dynamically provide a larger buffer and thirdly, for upload it should probably make the buffer “sliding” as in the libssh2 example code sftp_write_sliding.c.

This is also already mentioned in the TODO document as “Modified buffer size approach“.

There’s clearly room for someone to step forward and help us improve in this area. Welcome!

Mozilla, Network, Open Source, Web

licensed to get shared

May 6, 2014 Daniel Stenberg

As my http2 presentation is about to get its 16,000th viewer over at Slideshare I just have to take a moment and reflect over that fact.

Sixteen thousand viewers. I’ve uploaded slides there before over the years but no other presentation has gotten even close to this amount of attention even though some of them have been collecting views for years by now.

I wrote my http2 explained document largely due to the popularity of my presentation and the stream of questions and curiosity that brought to life. Within just a couple of days, that 27 page document had been downloaded more than 2,000 times and by now over 5000 times. This is almost 7MB of PDF which I believe raises the bar for the ordinary casual browser to not download it without having an interest and intention to at least glance through it. Of course I realize a large portion of said downloads are never really read.

Someone suggested to me (possibly in jest) that I should convert these into ebooks and “charge 1 USD a piece to get some profit out of them”. I really won’t and I would have a struggle to do that. It has been said before but in my case it is indeed true: I stand on the shoulders of giants. I’ve just collected information and written down texts that mostly are ideas, suggestions and conclusions others have already made in various other forums, lists or documents. I wouldn’t feel right charging for that nor depriving anyone the rights and freedoms to create derivatives and continue building on what I’ve done. I’m just the curator and janitor here. Besides, I already have an awesome job at an awesome company that allows me to work full time on open source – every day.

The next phase started thanks to the open license. A friendly volunteer named Vladimir Lettiev showed up and translated the entire document into Russian and now suddenly the reach of the text is vastly expanded into a territory where it previously just couldn’t penetrate. With using people’s native languages, information can really trickle down to a much larger audience. Especially in regions that aren’t very Englishified.

cURL and libcurl, Open Source, Security

#MeraKrypto

April 29, 2014 Daniel Stenberg

A whole range of significant Swedish network organizations (ISOC, SNUS, DFRI and SUNET) organized a full-day event today, managed by the great mr Olle E Johansson. The event, called “MeraKrypto” (MoreCrypto would be the exact translation), was a day with introductions to TLS and a lot of talks around TLS and other encryption and security related topics.

I was there and held a talk on the topic of “curl and TLS” and I basically talked some basics around what curl and libcurl are, how we do TLS, some common problems and hwo verifying the server cert is a common usage mistake and then I continued on to quickly mention how http2 and TLS relate..See my slides below, but please be aware that as usual you may not grasp the whole thing only by the (English) slides. The event was fully booked so there was around one hundred peeps in the audience and there were a lot of interested minds that asked good questions proving they really understood the topics.

The discussion almost got heated during the talk about how companies do MITMing of SSL sessions and this guy from Bluecoat pretty much single-handedly argued for the need for this and how “it fills a useful purpose”.

It was a great afternoon!

The event was streamed live and recorded on video. I’ll post a link as soon as it gets available to me.

curl and TLS #MeraKrypto from Daniel Stenberg

Open Source

Wireshark dissector work

April 24, 2014 Daniel Stenberg

Recently I cloned the Wireshark git repository and started updating the http2 dissector. That’s the piece of code that gets called to analyze a stream of data that Wireshark thinks is http2.

The current http2 dissector was left at draft-09 state, while the current draft at the time was number 11 and there have been several changes on the binary format since so any reasonably updated client or server would send or receive byte streams that Wireshark couldn’t properly display.

I never wrote any dissector code before but I must say Wireshark didn’t disappoint. It was straight forward and mostly downright easy to fix most of the wrong details. I’m not pretending to be a master at this nor is the dissector code anywhere near “finished” yet but I still enjoyed the API and how to write a thing like this.

I’ve since dissected plain-text http2 streams that I’ve done with curl+nghttp2 and I’ve also used the SSLKEYLOGFILE trick with Firefox to automatically decrypt the TLS session and have the dissector figure out the underlying http2 parts.

If there’s any little snag to mention, it is the fact that they insist on getting patches submitted directly to gerrit instead of any mailing list or similar. This required me to create a gerrit account, and really figure out how to push my stuff from git to there, instead of the more traditional and simpler approach of just sending my patch to a mailing list or possibly submitting it to a bug/patch tracker somewhere with my browser.

Call me old-style but in fact the hip way of today with a pull-request github style would also have been much easier. Here’s what my gerrit submission looks like. But I get it, gerrit does push a little more work over to the submitter and I figure that once a submitter such as myself finally has fixed all the nits in the patch it is very easy for the project to actually merge it. I actually got someone else to help me point out how to even find the link to view the code review after the first one was submitted on the site… (when I post this, my patch has not yet been accepted or merged into the wireshark git repo)

Here’s a basic screenshot showing a trace of Firefox requesting https://nghttp2.org using http2. Click it for the full thing.

.. and what happens this morning my time? There’s a brand new http2 draft-12 out with more changes on the on-the-wire format! Well to be honest, that really wasn’t a surprise. I’ll get the new stuff supported too, but I’ll do that in a separate patch as I prefer to hold off until I see a live stream by at least one implementation to test against.