Tag Archives: cURL and libcurl

cURL and libcurl

Shipping curl 7.21.5

I don’t usually post anything here when we do curl releases, pretty much because we do them bimonthly on a fairly steady schedule so there should be little surprise to anyone interested by the time they get public.

But hey, this is hard work and just to remind you all what’s going on I thought I’d throw in a mention of what we’ve spent the last two months doing. curl and libcurl 7.21.5 is released today.

The five notable changes introduced this time include:

The CURLOPT_SOCKOPTFUNCTION callback can now return information back to libcurl that the socket libcurl operates on is already connected. This is useful for applications that do a lot of fiddling on their own and possibly provide its own socket to start with using the CURLOPT_OPENSOCKETFUNCTION.

curl the tool got support for the –netrc-file option, that allows a user to point out a specific .netrc file instead of always forcing the user to use the fixed $HOME/.netrc one.

Brand new support for building libcurl with the cyassl library for SSL/TLS support. Previously curl only had support for the older OpenSSL emulation API that cyassl used to provide, but starting now we’re using cyassl directly and it is now a proper SSL citizen among the seven SSL libraries curl supports.

Since the previous release when we shipped the first support for TLS-SRP that required GnuTLS, the OpenSSL project accepted patches that introduced TLS-SRP into their official version as well and accordingly we have received patches that now allow users to use TLS-SRP with libcurl built against (a new enough) OpenSSL as well.

We have started to re-use two error codes a bit differently within libcurl, so that it now can return: CURLE_NOT_BUILT_IN (4) when an application tries to use a feature that was missing or was explicitly disabled at build-time and CURLE_UNKNOWN_OPTION (48) when the application has passed in an option that isn’t known or recognized.

And we’re counting more than 40 bugfixes worth mentioning. The most important ones are possibly:

If using the multi interface doing RTSP, libcurl could crash when trying to re-use a previous connection.

POP3 didn’t do TLS properly, it issued the wrong command to start TLS and it didn’t send the password correctly once it did switch to TLS!

When using the multi interface, there could be times when the timeout didn’t trigger so it wouldn’t close lingering connections even when asked to do so.

SFTP and SFP with the multi_socket interface were not working correctly and would very easily end up with stalled transfers due to the application being told to wait for the wrong action (or none at all).

If told to use the CCC command (which is used with FTP-SSL when the client asks the server to switch off from an SSL connection back to plain TCP again), curl would disable SSL on the connection but then use the wrong socket reader function and crash.

… but of course, if you’ve suffered from a particular bug in a previous release I’m sure you’ll consider the exact bug fix that corrects your problem to be the most important one!

Not to forget, the great people apart from yours truly that have contributed with code and insights since the previous release. Without them, the above list of changes and bugfixes just wouldn’t exist. The friends we have to thank are (in no particular order):

Mike Crowe, Kamil Dudka, Julien Chaffraix, Hoi-Ho Chan, Ben Noordhuis, Dan Fandrich, Henry Ludemann, Karl M, Manuel Massing, Marcus Sundberg, Stefan Krause, Todd A Ouska, Saqib Ali, Andre Guibert de Bruet, Tor Arntsen, Vincent Torri, Dave Reisner, Chris Smowton, Tinus van den Berg, Hongli Lai, Gisle Vanem, Andrei Benea, Mehmet Bozkurt

… and now back to working towards the next release. To be expected in roughly two months. Repeat.

cURL and libcurl, Open Source

curlyears plus equals one

BirthdaycakeThirteen years ago I released the first version of curl to the world – on March 20 1998. curl is now a teenage project and there’s no slowdown or end in sight.

So what does a project like ours introduce after having existed for so long? The recent year has been full of activities in the project, and here’s a run down with some of the stuff that has been going on:

We switched source code versioning system from CVS to git

gopher support got back into curl

support for RTMP was added

Two additional SSL libraries are now supported: PolarSSL and axTLS, making it a total of seven

70 persons provided code into the git repository, making the THANKS document now list 854 names.

About 1000 commits were made – out of a total of almost 14000 (counted from Dec 1999) so it makes this year slightly under average in terms of commit rate.

6 releases were shipped with a total of 179 bugfixes

1 security flaw was found and fixed

More than 4900 mails were posted to the curl mailing lists

We introduced a unit test system

Over 1400GB of data was downloaded from the curl web site

During the end of this period, 45% of our web visitors used Firefox, 23% used Chrome and less than 20% used IE. 75% were on Windows, 13% on Linux and 10% on Mac.

cURL

Network, Windows

localhost hack on Windows

There's no place like 127.0.0.1

Readers of my blog and friends in general know that I’m not really a Windows guy. I never use it and I never develop things explicitly for windows – but I do my best in making sure my portable code also builds and runs on windows. This blog post is about a new detail that I’ve just learned and that I think I could help shed the light on, to help my fellow hackers. The other day I was contacted by a user of libcurl because he was using it on Windows and he noticed that when wanting to transfer data from the loopback device (where he had a service of his own), and he accessed it using “localhost” in the URL passed to libcurl, he would spot a DNS request for the address of that host name while when he used regular windows tools he would not see that! After some mails back and forth, the details got clear:

Windows has a default /etc/hosts version (conveniently instead put at “c:\WINDOWS\system32\drivers\etc\hosts”) and that default  /etc/hosts alternative used to have an entry for “localhost” in it that would point to 127.0.0.1.

When Windows 7 was released, Microsoft had removed the localhost entry from the /etc/hosts file. Reading sources on the net, it might be related to them supporting IPv6 for real but it’s not at all clear what the connection between those two actions would be.

getaddrinfo() in Windows has since then, and it is unclear exactly at which point in time it started to do this, been made to know about the specific string “localhost” and is documented to always return “all loopback addresses on the local computer”.

So, a custom resolver such as c-ares that doesn’t use Windows’ functions to resolve names but does it all by itself, that has been made to look in the /etc/host file etc now suddenly no longer finds “localhost” in a local file but ends up asking the DNS server for info about it… A case that is far from ideal. Most servers won’t have an entry for it and others might simply provide the wrong address.

I think we’ll have to give in and provide this hack in c-ares as well, just the way Windows itself does.

Oh, and as a bonus there’s even an additional hack mentioned in the getaddrinfo docs: On Windows Server 2003 and later if the pNodeName parameter points to a string equal to “..localmachine”, all registered addresses on the local computer are returned.

cURL and libcurl, libssh2, Network

Fosdem 2011: my libcurl talk on video

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Kai Engert was good enough to capture all the talks in the security devroom at Fosdem 2011, and while I’m seeding the full torrent I’ve made my own talk available as a direct download from here:

Fosdem 2011: security-room at 14:15 by Daniel Stenberg

The thing is about 107MB big, 640×480 resolution and is roughly 26 minutes playing time. WebM format.

cURL and libcurl, libssh2, Open Source

libcurl, seven SSL libs and one SSH lib

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I did a talk today at Fosdem with this title. The room only had 48 seats and it was completely packed with people standing everywhere it was possible around the seated guys.

The English slides from my talk are below. It was also recorded on video so I hope I’ll be able to post once it becomes available online

libcurl, seven SSL libraries and one SSH library
cURL and libcurl, Haxx, Open Source, Rockbox

Going to FOSDEM 2011

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Fosdem 2011We’re going to FOSDEM again. This year we’ll ship over the entire company (all three of us) and we’ll join up with a few fellow Rockbox hackers and spend a weekend in Brussels among thousands of fellow free software and open source hackers.

During this conference, 5-6 February, I’ve submitted a libcurl-related talk to the embedded-room that wasn’t accepted into the regular program, but I’ve agreed to still prepare it and I then might get a slot in case someone gets sick or something. A bit ungrateful as now I still have to prepare my slides for the talk but there’s a big risk that I’ve done it in vain! I’ve also submitted a suggestion for a second talk in the opensc/security room (also related to stuff in the curl project) but as of now (with but 16 days left) that schedule is yet to be announced so I don’t know if I’ll do a talk there or not.

So, I might do no talks. I might do two. I just don’t know. We’ll see.

If you’re a friend of mine and you’re going to FOSDEM this year, please let me know and we can meet and have a chat or whatever. I love getting faces to all the names, nicks and email addresses I otherwise only see of many people.

Update: My talk in the security room is titled “libcurl: Supporting seven SSL libraries and one SSH library” and will start at 14:15 on Saturday the 5th of February.

cURL and libcurl, Mail

“Hacking me”

2 Comments

If you ever wonder how clever it was of me to make an FTP tool that used the default anonymous password curl_by_daniel@... once upon a time and you want to know why I changed that to ftp@example.com instead? Here’s a golden snippet to just absorb and enjoy:

Date: Thu, 23 Dec 2010 22:56:00
From: iHack3r <hidden>
To: info@[my company]
Subject: Hacking me

To the idiot named Daniel, Please stop brute force attacking my FTP client. I do not appreciate it, i have an anonymous account set up for the general public to access my files that i want them to access, QUIT trying to hack the admin because 1. DISABLED unless i am leaving to go somewhere without my computer 2: THE PASSWORD is random letters and numbers.

-iHack3r

The password was changed at Feb 13 2007 in curl version 7.16.2, but there are a surprisingly large amount of older curls still around out there…

Update: as the person responded again after having read this blog post and still didn’t get it, I felt the urge to speak up in even more clear terms:

I didn’t have anything to do with any “hacker attack” on any site. Not yours, and not anyone else’s. The fact that almost-my-email address appeared in your logs is because I wrote the FTP client. It is a general FTP client that is being used by a very very large amount of people all over the world. If I ever would attack a site, why on earth would I send along my real name or email address?

cURL and libcurl, Network

Byte ranges for FTP

In the IETF ftpext2 working group there have been some talks around clients’ and servers’ ability to do and support “ranged” file transfers, that is transferring only a piece of any given file. FTP supports the REST command and has done so since the dawn of man (RFC765 – June 1980), and using that command, a client can set the starting point for a transfer but there is no way to set the end point. HTTP has supported the Range: header since the first HTTP 1.1 spec back in January 1997, and that supports both a start and an end point. The HTTP header does in fact support multiple ranges within the same header, but let’s not overdo it here!

Currently, to avoid getting an entire file a client would simply close the data connection when it has got all the data it wants. The unfortunate reality is that some servers don’t notice clients doing this, so in order for this to work reliably a client also has to send ABOR, and after this command has been sent there is no way for the client to reliably figure out the state of the control connection so it has to get closed as well (which is crap in case more files are to be transferred to or from the same host). It primarily becomes unreliable because when ABOR is sent, the client gets one or two responses back due to a race condition between the closing and the actual end of transfer etc, and it isn’t possible to tell exactly how to continue.

A solution for the future is being worked on. I’ve joined up the effort to write a spec that will suggest a new FTP command that sets the end point for a transfer in the same vein REST sets the start point. For the moment, we’ve named our suggested command RANG (as short for range). “We” in this context means Tatsuhiro Tsujikawa, Anthony Bryan and myself but we of course hope to get further valuable feedback by the great ftpext2 people.

There already are use cases that want range request for FTP. The people behind metalinks for example want to download the same file from many servers, and then it makes sense to be able to download little pieces from different sources.

The people who found the libcurl bugs I linked to above use libcurl as part of the Fedora/Redhat installer Anaconda, and if I understand things right they use this feature to just get the beginning of some files to check them out and avoid having to download the full file before it knows it truly wants it. Thus it saves lots of bandwidth.

In short, the use-cases for ranged FTP retrievals are quite likely pretty much the same ones as they are for HTTP!

The first RANG draft is now available.

cURL and libcurl, Network

Scalable application layer transfers

At FSCONS 2010 I had the pleasure to do a talk about how to make your client-side networking applications really scale when upping the number of simultaneous connections. Including some details that libcurl will support you all the way!

My talk was named “Scalable application layer transfers” and the slides from it is available online. See below. Hopefully the video recording of it will appear later and I’ll post a  follow-up then. A little extra bonus material as background would be my poll vs select vs event-based article.

As I mentioned in a previous post, the room was shock full when I started preparing my equipment for the talk since the session before me was a keynote, but by the time I actually starter presenting there were only the limited set of hardcore geeks left.

In the FSCONS program there were several talks over the weekend about women in FOSS and so on, while I on the other hand certainly only contributed to enforcing the stereotypes by being white, male, middle-aged, very techy and I delivered my two speeches for audiences in which I believe not a single woman attended. Whether I am part of the problem or the solution we can discuss in a separate post later on… 🙂

Scalable application layer transfers

cURL and libcurl, Licensing, Open Source

Living With Open Source

.SEAs a session during the Internetdagarna conference (orginized by .SE), Björn Stenberg, Daniel Melin and I joined up to talk about open source with the title “Living With Open Source” (“Att Leva med Öppen Källkod” in the language of the brave: Swedish) on October 27. We did a 90 minute session split up between the three of us. The session was in Swedish and it was recorded so I expect that it will be made available online soon for those who are curious but didn’t attend.

Bjorn Stenberg during "att leva med Öppen kallkod"

Björn (on the picture above) started off by talking about how to work with Open Source as a user when using Open Source components. How to deal with changes, sending upstream, the cost of keeping changes private etc.

Talare - Att leva med öppen källkodDaniel Melin continued and talked about open source licensing. It is quite clearly an area that people find tricky and mysterious, judging from the many questions that followed. I think large parts of the audience wasn’t very advanced or well versed into open source details so then of course there is a lot to learn and to talk about. I think we all felt that we tried to cover quite a lot that together with the questions was hard to fit within the given time.

I ended our triplet by talking about open source from a producer’s viewpoint, how we view things in a typical open source project and I used a lot of details and factual points from the cURL project.

The audience consisted of perhaps 50 people. We had a rather nerdy subject and we had tough competition from five other parallel sessions, with some of them featuring Internet and other local celebrities.

Over all, I think we did good. The idea that held our three talks together I think was fine, we kept the schedule pretty good, the audience seemed to enjoy it and I had a great time. And we got a really nice lunch afterwards!

Att leva med Öppen Källkod