Build from source

The curl project creates source code that can be built to produce the two products curl and libcurl. The conversion from source code to binaries is often referred to as "building". You build curl and libcurl from source.

The curl project doesn't provide any built binaries at all, it only ships the source code. The binaries which can be found on the download page of the curl web and installed from other places on the Internet are all built and provided to the world by other friendly people and organizations.

The source code consists of a large number of files containing C code. Generally speaking, the same set of files are used to build binaries for all platforms and computer architectures that curl supports. curl can be built and run on a vast number of different platforms. If you use a rare operating system yourself, chances are that building curl from source is the easiest or perhaps the only way to get curl.

Making it easy to build curl is a priority to the curl project, although we don't always necessarily succeed!

git vs tarballs

When release tarballs are created, a few files are generated and included in the final release file. Those generated files are not present in the git repository, because they are generated and there is no need to store them in git.

So, if you want to build curl from git you need to generate some of those files yourself before you can build. On Linux and Unix systems, do this by running ./buildconf and on Windows you run buildconf.bat.

On Linux and Unix-like systems

There are two distinctly different ways to build curl on Linux and other Unix-like systems. There's the one using the configure script and there's the CMake approach.

There are two different build environments to cater for people's different opinions and tastes. The configure based build is arguably the more mature and more complete build system and should probably be considered the default one.

Autotools

The "Autotools" is a collection of different tools that used together generate the configure script. The configure script is run by the user who wants to build curl and it does a whole bunch of things:

  • it checks for features and functions present in your system

  • it offers command-line options so that you as a builder can decide what to enable and disable in the build. Features and protocols, etc., can be toggled on/off. Or even compiler warning levels and more.

  • it offers command-line options to let the builder point to specific installation paths for various third-party dependencies that curl can be built to use.

  • specifies on which file path the generated installation should be placed when ultimately the build is made and "make install" is invoked

In the most basic usage, just running ./configure in the source directory is enough. When the script completes, it outputs a summary of what options it has detected/enabled and what features that are still disabled, some of them possibly because it failed to detect the presence of necessary third-party dependencies that are needed for those functions to work.

Then you invoke make to build the entire thing and make install to install curl, libcurl and associated things. make install requires that you have the correct rights in your system to create and write files in the installation directory or you will get some errors.

cross-compiling

Cross-compiling means that you build the source on one architecture but the output is created to be run on a different one. For example, you could build the source on a Linux machine but have the output work to run on a Windows machine.

For cross-compiling to work, you need a dedicated compiler and build system setup for the particular target system for which you want to build. How to get and install that system is not covered in this book.

Once you have a cross compiler, you can instruct configure to use that compiler instead of the "native" compiler when it builds curl so that the end result then can be moved over and used on the other machine.

CMake

TBD

static linking

TBD

On Windows

TBD

make

TBD

CMake

TBD

other compilers

TBD

On other systems

TBD

Porting curl to non-supported systems

TBD

Select TLS backend

The configure based build offers the user to select from a wide variety of different TLS libraries when building. You select them by using the correct command line options.

The default OpenSSL configure check will also detect and use BoringSSL or libressl.

  • GnuTLS: --without-ssl --with-gnutls.
  • Cyassl: --without-ssl --with-cyassl
  • NSS: --without-ssl --with-nss
  • PolarSSL: --without-ssl --with-polarssl
  • mbedTLS: --without-ssl --with-mbedtls
  • axTLS: --without-ssl --with-axtls
  • schannel: --without-ssl --with-winssl
  • secure transport: --with-winssl --with-darwinssl

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