Category Archives: cURL and libcurl

curl and/or libcurl related

a github wishlist

The curl project’s source code has been hosted on GitHub since March 2010. I wrote a blog post in 2013 about what I missed from the service back then and while it has improved significantly since then, there are still features I miss and flaws I think can be fixed.

For this reason, I’ve created and now maintain a dedicated git repository with feedback “items” that I think could enhance GitHub when used by a project like curl:

Useful feedback

The purpose of this repository is to allow each entry to be on-point and good feedback to GitHub. I do not expect GitHub to implement any of them, but the better we can present the case for every issue, the more likely I think it is that we can gain supporters for them.

What makes curl “special”

I don’t think curl is a unique project in the way we run and host it. But there are a few characteristics that maybe make it stand out a little from many other projects hosted on GitHub:

  • curl is written in C. It means it cannot be part of the “dependency” and related security checks etc that GitHub provides
  • we are git users but we are not GitHub exclusive: we allow participation in and contributions to the project without a GitHub presence
  • we are an old-style project where discussions, planning and arguments about project details are held on mailing lists (outside of GitHub)
  • we have strict ideas about how git commits should be done and how the messages should look like etc, so we cannot accept merges done with the buttons on the GitHub site

You can help

Feel free to help me polish the proposals, or even submit new ones, but I think they need to be focused and I will only accept issues there that I agree with.

Submit issues, pull-requests or bring up a discussion.

The most used software components in the world

I’ve previously said that curl is one of the most widely used software components in the world with its estimated over ten billion installations, and I’m getting questions about it every now and then.

— Is curl the most widely used software component in the world? If not, which one is?

We can’t know for sure which products are on the top list of the most widely deployed software components. There’s no method for us to count or estimate these numbers with a decent degree of certainty. We can only guess and make rough estimates – and it also depends on exactly what we count. And quite probably also depending on who‘s doing the counting.

First, let’s acknowledge that SQLite already hosts a page for mostly deployed software module, where they speculate on this topic (and which doesn’t even mention curl). Also, does this count number of devices running the code or number of installs? If we count devices, does virtual machines count? Is it the number of currently used installations or total number of installations done over the years?


The SQLite page suggests four contenders for the top-5 list and I think it is pretty good:

  • zlib (the original implementation)
  • libpng
  • libjpeg
  • sqlite

I will go out on a limb and say that the two image libraries in the list, while of course very widely used, are not typically used on devices without screens and in the IoT world of today, such devices are fairly common. Light bulbs, power switches, networking gear etc. I think it might imply that they are slightly less used than the others in the list. Secondarily, libjpeg seems to not actually be around, but there are a few other successors that are used? Ie not a single implementation.

All top components are Open Source (sqlite’s situation is special but they still call it open source), and I don’t think it is a coincidence.

Are there other contenders not mentioned here? I figure maybe some of the operating systems for the tiniest devices that ship in the billions could be there. But I’m not sure there’s any such obvious market dominant player. There are other compression libraries too, but I doubt they reach the levels of zlib at this moment.

Someone brings up the Linux kernel, which certainly is very well used, but all Android devices, servers, windows 10 etc probably don’t make the unit count go over 7 billion and I believe that in virtually all Linux these kernel installs, curl, zlib and sqlite also run…

Similarly to how SQLite forgot to mention curl, I might of course also have a blind eye for some other really well-used code block.

The finalists

We end up with three finalists:

  • zlib
  • sqlite
  • libcurl

I think it is impossible for us to rank these three in an order with any good certainty. If we look at that sqlite list of where it is used, we quickly recognize that zlib and libcurl are deployed in pretty much all of them as well. The three modules have a huge overlap and will all be installed in billions of devices, while of course there are also plenty that only install one or two of them.

I just can’t figure out the numbers that would rank these modules in the top-list.

The SQLite page says: our best guess is that SQLite is the second mostly widely deployed software library, after libz. They might of course be right. Or wrong. They also don’t specify or explain how they do that guess.


Whenever I’ve mentioned widely used components in the past, someone has brought up “libc” as a contender. But since there are many different libc implementations and they are typically done for specific platforms/operating systems, I don’t think any single of the libc implementations actually reach the top-5 list.

zlib in curl/sqlite

Many people says zlib, partly because curl uses it, but then I have to add that zlib is an optional dependency for curl and I know many, including large volume, users that ship products with libcurl that doesn’t use zlib at all. One very obvious and public example, is the curl.exe shipped in Windows 10 – that’s maybe one billion installs of curl that don’t bundle zlib.

If I understand things correctly, the situation is similar in sqlite: it doesn’t always ship with a zlib dependency.

The poll

I asked my twitter followers which one of these three components they guess is the most widely used one. Very unscientifically and of course skewed towards libcurl (since I asked and I have a curl bias),

The over 2,000 respondents voted libcurl with a fairly high margin.

The datestamp shown in the image is when the poll went up and it was online for 24 hours.

What did I miss?

Did I miss a contender?

Have I overlooked some stats that make one of these win?

Updates: Since this was originally posted, I have had OpenSSL, expat and the Linux kernel proposed to me as additional finalists and possibly most-used components.


Image by PIRO4D from Pixabay

Hackad: curl use on TV

There’s this new TV-show on Swedish Television (SVT) called Hackad (“hacked” in English), which is about a team of white hat hackers showing the audience exactly how vulnerable lots of things, people and companies are and how they can be hacked using various means. In the show the hackers show how they hack into peoples accounts, their homes and their devices.

Generally this is done in a rather non-techy way as they mostly describe what they do in generic terms and not very specifically or with technical details. But in some short sequences the camera glances over a screen where source code or command lines are shown.

A little mr Robot like but in reality.

Similar to the fictional mr Robot, a readily available tool to use to accomplish what you want is of course… curl. In episode 4, we can easily spot curl command lines in several different shots.

Jesper Larsson is one of the hackers in the show and he responded on this blog post about them using curl, on Twitter:

Screenshots from episode 4

Lots of curl command lines
Markdown document with embedded curl command lines
Another snap of the same document showing more curl
David’s laptop when outside the house, showing a number of curl command lines, slightly blurry.

curl installations per capita

I’ve joked with friends and said that we should have a competition to see whom among us have the largest number of curl installations in their homes. This is of course somewhat based on that I claim that there are more than ten billion curl installations in the world. That’s more installations than humans. How many curl installations does an average person have?

Amusingly, someone also asked me this question at curl presentation I did recently.

I decided I would count my own installations to see what number I could possibly come up with, ignoring the discussion if I’m actually could be considered “average” in this regard or not. This counting includes a few assumptions and estimates, but this isn’t a game we can play with complete knowledge. But no crazy estimates, just reasonable ones!

I decided to count my entire household’s amount just to avoid having to decide exactly which devices to include or not. I’m counting everything that is “used regularly” in my house (things that haven’t been used within the last 12 months don’t count). We’re four persons in my household. Me, my wife and my two teenage kids.

Okay. Let the game begin. This is the Stenberg household count of October, 2021.

Computer Operating Systems

4: I have two kids who have one computer each at home. One Windows 10 and one macOS. They also have one ChromeOS laptop each for school.

3: My wife has no less than three laptops with Windows 10 for work and for home.

3: I have three computers I use regularly. One Windows 10 laptop and two Debian Linuxes (laptop + desktop).

1: We have a Windows 10 NUC connected to the living room TV.

Subtotal: 11 full fledged computers.

Computer applications

Tricky. In the Linux machines, the curl installation is often shared by all users so just because I use multiple tools (like git) that use curl doesn’t increase the installation count. Presumably this is also the same for most macOS and ChromeOS apps.

On Windows however, applications that use libcurl use their own private build (as Windows itself doesn’t provide libcurl, only the curl tool) so they would count as additional installations. But I’m not sure how much curl is used in the applications my family use on Windows. I don’t think my son for example plays any of those games in which I know they use curl.

I do however have (I counted!) 8 different VMs installed in my two primary development machines, running Windows, Linux (various distros for curl testing) and FreeBSD and they all have curl installed in them. I think they should count.

Subtotal: 8 (at least)

Phone and Tablet Operating Systems

2: Android phones. curl is part of AOSP and seem to be shipped bundled by most vendor Androids as well.

1: Android tablet

2: iPhones. curl has been part of iOS since the beginning.

1: iOS tablet

Subtotal: 6

Phone and tablet apps

6 * 5: Youtube, Instagram. Spotify, Netflix, Google photos are installed in all of the mobile devices. Lots of other apps and games also use libcurl of course. I’ve decided to count low.

Subtotal: 30 – 40 yeah, the mobile apps really boost the amount.

TV, router, NAS, printer

1: an LG TV. This is tricky since I believe the TV operating system itself uses curl and I know individual apps do, and I strongly suspect they run their own builds so more or less every additional app on the TV run its own curl installation…

1: An ASUS wifi router I’m “fairly sure” includes curl

1: A Synology NAS I’m also fairly sure has curl

1: My printer/scanner is an HP model. I know from “sources” that pretty much every HP printer made has curl in them. I’m assuming mine does too.

Subtotal: 4 – 9


I have half a dozen wifi-enabled powerplugs in my house but to my disappointment I’ve not found any evidence that they use curl.

I have a Peugeot e2008 (electric) car, but there are no signs of curl installed in it and my casual Google searches also failed me. This could be one of the rarer car brands/models that don’t embed curl? Oh the irony.

My Peugeot e2008

I have a Fitbit Versa 3 watch, but I don’t think it runs curl. Again, my googling doesn’t show any signs of that, and I’ve found no traces of my Ember coffee cup using curl.

My fridge, washing machine, dish washer, stove and oven are all “dumb”, not network connected and not running curl. Gee, my whole kitchen is basically curl naked.

We don’t have game consoles in the household so we’re missing out on those possible curl installations. I also don’t have any bluray players or dedicated set-top/streaming boxes. We don’t have any smart speakers, smart lightbulbs or fancy networked audio-players. We have a single TV, a single car and have stayed away from lots of other “smart home” and IoT devices that could be running lots of curl.

Subtotal: lots of future potential!


11 + 8 + 6 + 30to40 + 4to9 = 59 to 74 CIPH (curl installations per household). If we go with the middle estimate, it means 66.

16.5 CIPC (curl installations per capita)

If the over 16 curl installations per person in just this household is an indication, I think it may suggest that my existing “ten billion installations” estimate is rather on the low side… If we say 10 is a fair average count and there are 5 billion Internet connected users, yeah then we’re at 50 billion installations

What’s your score?

Coming webinar: getting started with libcurl

Have you been curious about getting your feet wet with doing Internet transfers with libcurl but reasons (excuses?) have kept you away? Maybe it has felt as a too big step to take?

Fear not, on October 21 I’m doing a free webinar on Getting started with libcurl detailing useful first steps on how to get your initial application off the ground!

Sign up here!

The half-hour presentation will include details such as:

  • Basic fundamentals in the libcurl API and a look on the common data types and concepts.
  • Setting up and understanding a first libcurl transfer.
  • Differences between the two primary libcurl transfer interfaces: easy and multi.
  • A look at the most commonly used libcurl options
  • Suggestions on how and where to take the next steps

The plan is to make this presentation work independently of platform, compiler and IDE choice and it will focus on C/C++ code. Still, since most libcurl bindings are very “thin” and often mimics the C API fairly closely, it should be valuable and provide good information even for you who plan to write your libcurl-using applications in other languages.

We’ll also end the session with a Q&A-part of course so queue up your questions!

The presentation will be recorded and made available after the fact.


To participate on the live event, skip over and sign up for it.

The event will take place on October 21, 2021 at 10:00 PDT (check your time zone)


Image by Wokandapix from Pixabay

One new contributor every 3.4 days

In the curl project we keep track of and say thanks to every single contributor. That includes persons who report bugs or security problems, who run infrastructure for us, who assist in debugging or fixing problems as well as those who author code or edit the website. Those who have contributed to make curl to what it is.

Exactly today October 4th 2021, we reached 2,500 names in this list of contributors for the first time. 2,500 persons since the day curl was created back in March 1998. 2,500 contributors in 8599 days. This means that on average we’ve seen one new contributor helping out in the project every 3.44 days for almost twenty-four years. Not bad at all.

The 2,500th recorded contributor was Ryan Mast who brought pull-request 7809.

Thank you everyone who have helped us so far!

As can be seen on the graph below plotting the number of people in the THANKS file, the rate of newcomers have increased slowly over the years and we’ve added new names at the rate of about two hundred per year recently. There’s a chance that we will add the next 2,500 names to the list faster than twenty-four years. The latest 1,000 contributors have been added since the beginning of 2017, so in less than five years.

2,500 contributors to curl

The thanks page on the website is usually synced at release time so it is always a little bit behind compared to what’s recorded in the curl git repository.


The graph bump back in 2005: it was a one-time sweep-up where I went through our entire history and made sure that all names of people who were previously mentioned and who had helped were added correctly to the document. Since then, we’ve kept better track and make sure to add new names as we go along.


We of course collect the names of the contributors primarily by the use of scripts, which is also the best way to avoid some slipping through.

  1. We always mention contributors and helpers in git commits, and they should be “marked” correctly for scripts to be able to extract them
  2. We keep a list of contributors per-release in the RELEASE-NOTES document. When we commit updates to RELEASE-NOTES, we use the fixed commit message ‘synced’ to have our tools use that as a marker.
  3. To get the updated list of contributors since the previous update of RELEASE-NOTES, we use the scripts/ script.
  4. At release time, we update THANKS withe the scripts/ script.

Post-Quantum curl

For some TLS connections you want the secrets you exchange over them to remain private for decades to come.

So what if someone in the future produces a computer system that can crack all the common current encryption algorithms in no time and they already have past secret communications stored?

Such a possible future computer system that might do this is believed to be the quantum computer. There are early and tiny versions of such machines already in existence, but they are far from strong enough to be cracking any strong ciphers today. The question is then how long it takes until they will be able to do that, and thus for how long recorded secret communications can expect to remain secret. 10 years? 20? 30?

If there’s a capable quantum computer made available in let’s say twenty years time, our currently most common TLS ciphers are then rendered next to worthless in twenty years. If you want your communication to remain private even after the introduction of quantum computers, you need post-quantum safe algorithms for your TLS data, and you need a post-quantum curl to use those ciphers for your transfers!

Post-quantum TLS

My colleagues at wolfSSL have recently been working on making sure that the library with the same name has support for a set of ciphers that are post-quantum safe. That work has been merged into wolfSSL’s git repository and will be part of a future pending release. That “future release” is hopefully just a few weeks off now.

In association with that, we’ve also made sure that curl built with wolfSSL can take advantage of these powers. The necessary curl changes for this have landed in git and will be part of the pending curl 7.80.0 release.

Use it with curl

To make your curl transfers post-quantum safe today, all you need to do is:

  1. make sure you have a wolfSSL build and install with the proper algorithms enabled
  2. build curl from git (or wait for the 7.80.0 release) and tell it to use wolfSSL for TLS
  3. specify a post-quantum curve when you invoke curl


curl --curve SABER_LEVEL5

The success of such a TLS 1.3 handshake with a server then of course also requires that you communicate with a server that conversely also supports quantum-safe algorithms. This not terribly common yet.


The primary curl pull-request for this feature was authored by Anthony Hu.

Image by Gerd Altmann from Pixabay

My weekly reports

I work a lot on my own. I mean, I plan a lot of what to do on a daily basis myself, I execute a lot of it myself and I push my code and changes to various git repositories, often solo. I work quite a lot.

In a lot of the cases, I work together with one or more persons in each individual case, but very often that’s one or a few different persons involved in each and every one.

Yet I work at a company with colleagues, friends, managers and sales people who occasionally wonder what I’ve been up to recently and what I’m working on right now.

Weekly reports

To share information, to combat my feeling of working in complete solitude and to better sync work with colleagues, I’ve been sending out a weekly report every Friday. It briefly explains what I did this week, what I blogged about and what I’m up to the next week.

I’ve done this on and off since I joined wolfSSL, and a while ago it dawned on me that since I do most of my work on open source code and in general in the open, I could just as well just make my “reports” available to the entire world. Or rather: those who care and are interested can find them and read them!

Minor details are still hush hush

Since I do commercial curl work with and for other companies, I need to not spill the beans on things like actual secrets and most company names will be anonymized. I hope that won’t interfere too much.


I decided to make it available on GitHub like this:

  • It allows me to edit the reports in plain markdown and commit it to git and yet have all the reports in one place for easy search and reference.
  • It allows me to have a discussion area on GitHub if anyone ever wants to discuss anything in the report with me.
  • It separates the reports from my blog.


Common mistakes when using libcurl

I’ve been traveling this road for a while. Here’s my collection of 15 of the most common mistakes and issues people will run into when writing applications and services that use libcurl. I’ve also done recorded presentations on this topic that you can watch if you prefer that medium.

Most of these issues are shared among application authors independently of what language the program is written in – as libcurl bindings tend to be very thin and more or less expose the API in the same way the C API does. Some mistakes are however C and C++ specific.

15 mistakes to look out for when using libcurl

1. Skipping the documentation!

Nothing in my list here is magic, hidden or unknown. Everything is documented and well-known. The by far most common mistakes are done by people not reading up, rushing a bit too fast and sometimes making a little too many assumptions. Of course there’s also occasional copy-and-pasting from bad examples going on. The web is full of questionable source snippets to get inspiration from.

We spend a significant amount of time and energy on making sure the documentation is accurate, detailed and thorough. Many mistakes can be avoided by simply reading up a little more first!

All the several hundred man pages and more are available in the libcurl section of the curl web site.

2. Failure to check return codes

This sounds like such an obvious thing but we keep seeing this happen over and over again: users write code that uses libcurl functions but they don’t check the return codes.

If libcurl detects an error it will return an error code. Whenever libcurl doesn’t do what you expected it to do, it very often turns out to have returned an error code to the application that explains the behavior. We work hard at making sure libcurl functions return the correct return codes!

The libcurl examples we host on the curl web site (and ship in curl tarballs) are mostly done without error checks – for the sole purpose of making them smaller and easier to read as that removes code that isn’t strictly about libcurl.

3. Forgetting the verbose option

CURLOPT_VERBOSE is the libcurl user’s best friend. Whenever your transfer fails or somehow doesn’t do what you expected it to, switching on verbose mode should be one of the first actions as it often gives you a lot of clues about what’s going on under the hood.

Of course, you can also go further and use CURLOPT_DEBUGFUNCTION to get every more details, but usually you can save that for the more complicated issues.

4. There’s a global init function

You really should call curl_global_init() expclicitly and early on and understand that it isn’t thread-safe. (We’re working on that.)

libcurl will detect if you missed to call it, and then call it itself, but that’s not a practice we recommend since then you’ll have a harder time to do it thread-safe.

And there’s a corresponding curl_global_cleanup() to call when all your libcurl use is done.

5. Consider the redirects

HTTP/1.1 301 Moved Permanently
Server: M4gic server/3000
Retry-After: 0
Content-Length: 0
Accept-Ranges: bytes
Date: Thu, 07 May 2020 08:59:56 GMT
Connection: close

When you let libcurl handle redirects, consider limiting to what protocols you should allow redirects (CURLOPT_REDIR_PROTOCOLS), and of course you must remember that crafty users will figure out ways to redirect responses to potentially malicious servers given the chance.

Do not set custom HTTP methods on requests that follow redirects.

6. Let users set (parts of) the URL

Don’t do that. Unless you have considered the consequences and make sure you deal with them appropriately.

If you really insist that you need to let your users set the URL, restrict and carefully filter exact what parts and with what they can change it to.

The reason is of course that libcurl often supports other protocols than the one(s) you had in mind when you write your application. And users can do other crafty things to make host names point to other servers (which of course TLS based protocols will reject), abuse free-form URL input fields to pass on unexpected data (sometimes including newlines and other creative things) to your servers or have your application talk to malicious servers.

You can limit what protocols your application supports with CURLOPT_PROTOCOLS and you can parse URLs with the curl_url_set() function family before you pass them to curl to make sure given URLs make sense!

7. Setting HTTP method

Setting the custom HTTP request method with CURLOPT_CUSTOMREQUEST is most often done completely unnecessary, frequently causing problems and only very rarely actually done correctly.

The primarily problems with setting this option are:

  1. if you also ask libcurl to follow redirects, this custom method will be used in follow-up requests as well, even if the server indicate wanting a different one in the HTTP response code
  2. it doesn’t actually change libcurl’s behavior or expectations, it only changes the string libcurl sends in the request.

8. Disabled certificate checks

libcurl allows applications to disable TLS certificate checks with the two options CURLOPT_SSL_VERIFYPEER and CURLOPT_SSL_VERIFYHOST. This is powerful and at times very handy while developing and/or experimenting. It is also a very bad thing to ship in your product or deploy in your live service.

Disabling the certificate check effectively removes the TLS protection from the connections!

Searching for these option names using source code search engines or just on github will show you hundreds or thousands of applications that leave these checks disabled. Don’t be like them!

9. Assume zero terminated data in callbacks

libcurl has a series of different callbacks in its API. Some of these callbacks delivers data to the application and that data is then typically offered with a pointer and a size of that data.

The documentation very clearly stipulates that this data is not zero terminated – you cannot and should not use C functions on the data that works on “C strings” (that assume a terminating, trailing, zero byte). It seems especially common when the data that is delivered is something like HTTP headers, which is text based data and seems to lure people into assuming a zero terminator.

10. C++ strings are not C strings

libcurl is a C library with a C API for maximum portability and availability, yet a large portion of libcurl users are actually writing their programs in C++.

This is not a problem. You can use the libcurl API perfectly fine from C++.

Passing “strings” to libcurl must however be done with the C approach: you pass a pointer to a zero terminated buffer. If you pass a reference to a C++ string object, libcurl will not know what it is and it will not get or use the string correctly. It will fail in mysterious ways!

Something like this:

// Keep the URL as a C++ string object
std::string str("");

// Pass it to curl as a C string!
curl_easy_setopt(curl, CURLOPT_URL, str.c_str());

11. Threading mistakes

libcurl is thread-safe, but there are some basic rules and limitations that you need to follow and adhere to, as detailed in the document linked to:

  1. curl_global_init is not thread-safe
  2. you must not use any libcurl handle concurrently
  3. if you use older TLS libraries, you must setup mutex locks

12. Understanding CURLOPT_NOSIGNAL

Signals is a Unix concept where an asynchronous notification is sent to a process or to a specific thread within the same process in order to notify it of an event that occurred.

What does libcurl use signals for?

When using the synchronous name resolver, libcurl uses alarm() to abort slow name resolves (if a timeout is set), which ultimately sends a SIGALARM to the process and is caught by libcurl

By default, libcurl installs its own sighandler while running, and restores the original one again on return – for SIGALARM and SIGPIPE.

Closing TLS (with OpenSSL etc) can trigger a SIGPIPE if the connection is dead.

Unless CURLOPT_NOSIGNAL is set! (default)


It prevents libcurl from triggering signals

When disabled, it prevents libcurl from installing its own sighandler and…

Generated signals must then be handled by the libcurl-using application itself

13. Forgetting -DCURL_STATICLIB

Creating and using libcurl statically is easy and convenient and seems especially popular on Windows

It requires the CURL_STATICLIB define to be set when building your application! This is a little unusual requirement and pattern which is probably why people often miss this.

Omission to use that define causes linker errors:
unknown symbol __imp__curl_easy_init

This requirement is present because Windows need __declspec to be present or absent in the headers depending on how it links.

Static builds mean chasing deps

libcurl can use many 3rd party dependencies

When linking statically, all those need to be provided to the linker, so the curl build scripts (as well as your application linking) usually need manual help to find them all

14. C++ methods

C++ class methods look very much like functions, but C++ class methods cannot be used as callbacks with libcurl

… since they assume a ‘this’ pointer to the current object and a C program doesn’t pass on such a pointer.

Static class member functions work though. You can thus work around this limitation with a trick like this:

// f is the pointer to your object.
static size_t YourClass::func(void *buffer, size_t sz, size_t n, void *f){
  // Call non-static member function.
// This is how you pass pointer to the static function:
curl_easy_setopt(hcurl, CURLOPT_XFERINFOFUNCTION, YourClass::func);
curl_easy_setopt(hcurl, CURLOPT_XEFRINFODATA, this);

15.Write callback invokes

Data is delivered from libcurl to the callback CURLOPT_WRITEFUNCTION

This callback might be called none, one, two or many times. Never assume you will get a certain amount of calls. The number of invokes is independent of the data amount and vary rather because of network, server, kernel or other reasons. Don’t assume the same invocation pattern will repeat!

curl’s first twenty years on the mac

September 25, 2001 is the official release date for Mac OS X 10.1. Exactly twenty years ago today.

Mac OS X 10.1

This was the first macOS release from Apple that bundled curl. It was a complete surprise to me as well when I realized this had happened. Nobody had told me about it ahead of time. I don’t even recall anymore how I figured this out, as I’m not a mac user and I’ve never had any direct contact with the peeps at Apple Inc who were and are responsible for shipping curl on that platform. Not before then and not after that either.

The general consensus at the time seemed to be that Apple replaced Wget with curl due to licensing reasons as Wget had been included in their previous OS X release. Wget is licensed under GPL and curl comes under an MIT-like license. I’m not sure if they shipped libcurl too already at that point.

Various Apple products have been using libcurl over the years on several of their operating systems.

We ship source, they build and ship binaries

Apple downloaded our source code tarball, built curl from it and shipped it. (They also made the exact code they used available.) If I remember this correctly, they built curl against OpenSSL and shipped a version of that as well in the beginning.

In later macOS releases (you know they later changed the name of their OS from being Mac OS X to macOS), they’ve switched curl to use different TLS backends over time. At one point they converted over to using Secure Transport (their own native TLS library) only to somewhat later switch again and then to libressl – which is what the current most recent macOS version uses for curl’s default TLS backend.

curl 7.7.2

The original cURL logo

The original curl version they bundled in that first release had been released by us in April earlier that same year. It was our 55th curl release but curl was only a little over three years old at the time. It was a young project and it was just in the beginning phase of what it would become.

Early, not first

Apple was certainly early with shipping curl bundled with their operating system but they were not first. curl was already then provided to several Linux distributions. Apple might’ve been one if the first to ship it by default though.

I remember that it felt awesome and as some sort of recognition and acknowledgement of what we’ve done.

Other operating systems

During the early 2000s lots of operating systems would ultimately one by one start to package and provide curl for their platforms. Linux distributions and BSD flavors of course, but soon the legacy Unixes would also follow. If it wasn’t offered by the primary vendor, third party providers would very soon offer packages,


The third party license screen in iOS (click on the image shown on the right here for the full resolution version) includes the curl license, showing that Apple use it in iPhones and iPads. I don’t know for what.


Apple has kept updating curl in their subsequent operating updates and has done a somewhat reasonable job at keeping up with our releases. In their most up-to-date macOS version 11.5.2 (release date: August 11, 2021) they ship curl 7.64.1, released from us on 2019-03-27. Our 181st release. It has twenty-two known vulnerabilities.

This can be compared to Windows 10 which keeps shipping OS updates very frequently but is seemingly stuck with curl 7.55.1, released in August 2017.

Futile attempts to help

For a while I reported security issues we found (that would be relevant) to Apple product security ahead of time before our releases went public, to give them time to react and ship fixes, the same way we send alerts to free operating systems.

I stopped doing that because 1. the Apple security people always complained on me for giving them too short time to react (something like two weeks, which is also the maximum notification time allowed by others) and 2. Apple never released any quick updates as a reaction to my notifications anyway. It took them months or years, making my efforts pointless. Basically they were just rude.

Nothing in return

Neither me personally nor the project have ever gotten anything or any compensation from Apple. Nothing. Nada. Perhaps Apple using curl early on was somewhat of a stamp of approval for some, which helped persuade others that curl is a tool to trust. Perhaps.

Apple has not sponsored the project, not paid for feature development, not helped us with hardware and never paid for support. They don’t cooperate with us to help us fix Apple-specific issues nor do they ever report problems to us (which we know they must find occasionally). Apple users who run into problems with curl on Apple’s operating systems regularly contact the curl project to get us to help fix Apple’s products. For free of course. We never even get a thank you.

I have a mac these days (purchased with my own money) that I use to debug and test mac-specific issues and problems on.

Apple is of course far from alone is this almost predatory behavior, but this post is about curl’s twenty years of serving Apple customers. Also: yes curl is open source and the license allows them to do this. We continue to ship a product that runs perfectly on macOS and other Apple operating systems. They continue to ship curl bundled with their operating systems.


The curl project has no drastic course-altering changes planned ahead and we’re not going away, so I believe the tool and library have the potential to continue being used on Apple products going forward as well. Possibly for a long time ahead. I have zero knowledge or visibility into that, so it’s just guessing on my part based on what’s been done in the past twenty years.