[ DEBUG ]: 09:52:15 | system: Retrieving: dracut-kiwi-lib-9.17.23-lp150.1.1.x86_64.rpm [.error] [ DEBUG ]: 09:52:15 | system: Abort, retry, ignore? [a/r/i/...? shows all options] (a): a
[ INFO ]: Processing: [########################################] 100%
[ ERROR ]: 09:52:15 | KiwiInstallPhaseFailed: System package installation failed: Download (curl) error for 'http://download.opensuse.org/repositories/Virtualization:/Appliances:/Builder/openSUSE_Leap_15.0/x86_64/dracut-kiwi-lib-9.17.23-lp150.1.1.x86_64.rpm':
Error code: Curl error 60
Error message: SSL certificate problem: unable to get local issuer certificate

One of the pain points in trying to make the Meson build system work with Rust and Cargo is Cargo's use of build scripts, i.e. the build.rs that many Rust programs use for doing things before the main build. This post is about my exploration of what build.rs does.

Thanks to Nirbheek Chauhan for his comments and additions to a draft of this article!

TL;DR: build.rs is pretty ad-hoc and somewhat primitive, when compared to Meson's very nice, high-level patterns for build-time things.

I have the intuition that giving names to the things that are usually done in build.rs scripts, and creating abstractions for them, can make it easier later to implement those abstractions in terms of Meson. Maybe we can eliminate build.rs in most cases? Maybe Cargo can acquire higher-level concepts that plug well to Meson?

(That is... I think we can refactor our way out of this mess.)

What does build.rs do?

The first paragraph in the documentation for Cargo build scripts tells us this:

Some packages need to compile third-party non-Rust code, for example C libraries. Other packages need to link to C libraries which can either be located on the system or possibly need to be built from source. Others still need facilities for functionality such as code generation before building (think parser generators).

That is,

• Compiling third-party non-Rust code. For example, maybe there is a C sub-library that the Rust crate needs.

• Link to C libraries... located on the system... or built from source. For example, in gtk-rs, the sys crates link to libgtk-3.so, libcairo.so, etc. and need to find a way to locate those libraries with pkg-config.

• Code generation. In the C world this could be generating a parser with yacc; in the Rust world there are many utilities to generate code that is later used in your actual program.

In the next sections I'll look briefly at each of these cases, but in a different order.

Code generation

Here is an example, in how librsvg generates code for a couple of things that get autogenerated before compiling the main library:

• A perfect hash function (PHF) of attributes and CSS property names.
• A pair of lookup tables for SRGB linearization and un-linearization.

For example, this is main() in build.rs:

fn main() {
    generate_phf_of_svg_attributes();
    generate_srgb_tables();
}

And this is the first few lines of of the first function:

fn generate_phf_of_svg_attributes() {
    let path = Path::new(&env::var("OUT_DIR").unwrap()).join("attributes-codegen.rs");
    let mut file = BufWriter::new(File::create(&path).unwrap());

    writeln!(&mut file, "#[repr(C)]").unwrap();

    // ... etc
}

Generate a path like $OUT_DIR/attributes-codegen.rs, create a file with that name, a BufWriter for the file, and start outputting code to it.

Similarly, the second function:

fn generate_srgb_tables() {
    let linearize_table = compute_table(linearize);
    let unlinearize_table = compute_table(unlinearize);

    let path = Path::new(&env::var("OUT_DIR").unwrap()).join("srgb-codegen.rs");
    let mut file = BufWriter::new(File::create(&path).unwrap());

    // ...

    print_table(&mut file, "LINEARIZE", &linearize_table);
    print_table(&mut file, "UNLINEARIZE", &unlinearize_table);
}

Compute two lookup tables, create a file named $OUT_DIR/srgb-codegen.rs, and write the lookup tables to the file.

Later in the actual librsvg code, the generated files get included into the source code using the include! macro. For example, here is where attributes-codegen.rs gets included:

// attributes.rs

extern crate phf;  // crate for perfect hash function

// the generated file has the declaration for enum Attribute
include!(concat!(env!("OUT_DIR"), "/attributes-codegen.rs"));

One thing to note here is that the generated source files (attributes-codegen.rs, srgb-codegen.rs) get put in $OUT_DIR, a directory that Cargo creates for the compilation artifacts. The files do not get put into the original source directories with the rest of the library's code; the idea is to keep the source directories pristine.

At least in those terms, Meson and Cargo agree that source directories should be kept clean of autogenerated files.

The Code Generation section of Cargo's documentation agrees:

In general, build scripts should not modify any files outside of OUT_DIR. It may seem fine on the first blush, but it does cause problems when you use such crate as a dependency, because there's an implicit invariant that sources in .cargo/registry should be immutable. cargo won't allow such scripts when packaging.

Now, some things to note here:

• Both the build.rs program and the actual library sources look at the $OUT_DIR environment variable for the location of the generated sources.

• The Cargo docs say that if the code generator needs input files, it can look for them based on its current directory, which will be the toplevel of your source package (i.e. your toplevel Cargo.toml).

Meson hates this scheme of things. In particular, Meson is very systematic about where it finds input files and sources, and where things like code generators are allowed to place their output.

The way Meson communicates these paths to code generators is via command-line arguments to "custom targets". Here is an example that is easier to read than the documentation:

gen = find_program('generator.py')

outputs = custom_target('generated',
  output : ['foo.h', 'foo.c'],
  command : [gen, '@OUTDIR@'],
  ...
)

This defines a target named 'generated', which will use the generator.py program to output two files, foo.h and foo.c. That Python program will get called with @OUTDIR@ as a command-line argument; in effect, meson will call /full/path/to/generator.py @OUTDIR@ explicitly, without any magic passed through environment variables.

If this looks similar to what Cargo does above with build.rs, it's because it is similar. It's just that Meson gives a name to the concept of generating code at build time (Meson's name for this is a custom target), and provides a mechanism to say which program is the generator, which files it is expected to generate, and how to call the program with appropriate arguments to put files in the right place.

In contrast, Cargo assumes that all of that information can be inferred from an environment variable.

In addition, if the custom target takes other files as input (say, so it can call yacc my-grammar.y), the custom_target() command can take an input: argument. This way, Meson can add a dependency on those input files, so that the appropriate things will be rebuilt if the input files change.

Now, Cargo could very well provide a small utility crate that build scripts could use to figure out all that information. Meson would tell Cargo to use its scheme of things, and pass it down to build scripts via that utility crate. I.e. to have

// build.rs

extern crate cargo_high_level;

let output = Path::new(cargo_high_level::get_output_path()).join("codegen.rs");
//                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ this, instead of:

let output = Path::new(&env::var("OUT_DIR").unwrap()).join("codegen.rs");

// let the build system know about generated dependencies
cargo_high_level::add_output(output);

A similar mechanism could be used for the way Meson likes to pass command-line arguments to the programs that deal with custom targets.

Linking to C libraries on the system

Some Rust crates need to link to lower-level C libraries that actually do the work. For example, in gtk-rs, there are high-level binding crates called gtk, gdk, cairo, etc. These use low-level crates called gtk-sys, gdk-sys, cairo-sys. Those -sys crates are just direct wrappers on top of the C functions of the respective system libraries: gtk-sys makes almost every function in libgtk-3.so available as a Rust-callable function.

System libraries sometimes live in a well-known part of the filesystem (/usr/lib64, for example); other times, like in Windows and MacOS, they could be anywhere. To find that location plus other related metadata (include paths for C header files, library version), many system libraries use pkg-config. At the highest level, one can run pkg-config on the command line, or from build scripts, to query some things about libraries. For example:

# what's the system's installed version of GTK?
$ pkg-config --modversion gtk+-3.0
3.24.4

# what compiler flags would a C compiler need for GTK?
$ pkg-config --cflags gtk+-3.0
-pthread -I/usr/include/gtk-3.0 -I/usr/include/at-spi2-atk/2.0 -I/usr/include/at-spi-2.0 -I/usr/include/dbus-1.0 -I/usr/lib64/dbus-1.0/include -I/usr/include/gtk-3.0 -I/usr/include/gio-unix-2.0/ -I/usr/include/libxkbcommon -I/usr/include/wayland -I/usr/include/cairo -I/usr/include/pango-1.0 -I/usr/include/harfbuzz -I/usr/include/pango-1.0 -I/usr/include/fribidi -I/usr/include/atk-1.0 -I/usr/include/cairo -I/usr/include/pixman-1 -I/usr/include/freetype2 -I/usr/include/libdrm -I/usr/include/libpng16 -I/usr/include/gdk-pixbuf-2.0 -I/usr/include/libmount -I/usr/include/blkid -I/usr/include/uuid -I/usr/include/glib-2.0 -I/usr/lib64/glib-2.0/include

# and which libraries?
$ pkg-config --libs gtk+-3.0
-lgtk-3 -lgdk-3 -lpangocairo-1.0 -lpango-1.0 -latk-1.0 -lcairo-gobject -lcairo -lgdk_pixbuf-2.0 -lgio-2.0 -lgobject-2.0 -lglib-2.0

There is a pkg-config crate which build.rs can use to call this, and communicate that information to Cargo. The example in the crate's documentation is for asking pkg-config for the foo package, with version at least 1.2.3:

extern crate pkg_config;

fn main() {
    pkg_config::Config::new().atleast_version("1.2.3").probe("foo").unwrap();
}

And the documentation says,

After running pkg-config all appropriate Cargo metadata will be printed on stdout if the search was successful.

Wait, what?

Indeed, printing specially-formated stuff on stdout is how build.rs scripts communicate back to Cargo about their findings. To quote Cargo's docs on build scripts; the following is talking about the stdout of build.rs:

Any line that starts with cargo: is interpreted directly by Cargo. This line must be of the form cargo:key=value, like the examples below:

# specially recognized by Cargo
cargo:rustc-link-lib=static=foo
cargo:rustc-link-search=native=/path/to/foo
cargo:rustc-cfg=foo
cargo:rustc-env=FOO=bar
# arbitrary user-defined metadata
cargo:root=/path/to/foo
cargo:libdir=/path/to/foo/lib
cargo:include=/path/to/foo/include

One can use the stdout of a build.rs program to add additional command-line options for rustc, or set environment variables for it, or add library paths, or specific libraries.

Meson hates this scheme of things. I suppose it would prefer to do the pkg-config calls itself, and then pass that information down to Cargo, you guessed it, via command-line options or something well-defined like that. Again, the example cargo_high_level crate I proposed above could be used to communicate this information from Meson to Cargo scripts. Meson also doesn't like this because it would prefer to know about pkg-config-based libraries in a declarative fashion, without having to run a random script like build.rs.

Building C code from Rust

Finally, some Rust crates build a bit of C code and then link that into the compiled Rust code. I have no experience with that, but the respective build scripts generally use the cc crate to call a C compiler and pass options to it conveniently. I suppose Meson would prefer to do this instead, or at least to have a high-level way of passing down information to Cargo.

In effect, Meson has to be in charge of picking the C compiler. Having the thing-to-be-built pick on its own has caused big problems in the past: GObject-Introspection made the same mistake years ago when it decided to use distutils to detect the C compiler; gtk-doc did as well. When those tools are used, we still deal with problems with cross-compilation and when the system has more than one C compiler in it.

Snarky comments about the Unix philosophy

If part of the Unix philosophy is that shit can be glued together with environment variables and stringly-typed stdout... it's a pretty bad philosophy. All the cases above boil down to having a well-defined, more or less strongly-typed way to pass information between programs instead of shaking proverbial tree of the filesystem and the environment and seeing if something usable falls down.

Would we really have to modify all build.rs scripts for this?

Probably. Why not? Meson already has a lot of very well-structured knowledge of how to deal with multi-platform compilation and installation. Re-creating this knowledge in ad-hoc ways in build.rs is not very pleasant or maintainable.

Related work

• Cargo internals thread on using a declarative format to specify external dependencies

• Run pkg-config from declarative dependencies in Cargo.toml

Setelah disiapkan beberapa lama, akhirnya buku dan ebook Active Directory Berbasis Linux Samba 4 secara resmi dirilis dan sudah bisa didapatkan via Google Play maupun melalui Tokopedia dan Bukalapak.

Active Directory Berbasis Linux Samba 4 ini merupakan versi update dari rilis sebelumnya, dengan perbaikan-perbaikan materi dan penyesuaiannya dengan perkembangan terkini.

Apa itu Linux Samba 4?

Samba provides file and print services for various Microsoft Windows clients and can integrate with a Microsoft Windows Server domain, either as a Domain Controller (DC) or as a domain member. As of version 4, it supports Active Directory and Microsoft Windows NT domains.

Jadi Samba 4 adalah software yang berjalan pada sistem Linux yang menyediakan layanan Active Directory, Domain Controller, File dan Print Sharing dan dapat diintegrasikan dengan sistem berbasis Windows, baik dengan Windows Server maupun Windows Client. Meski memiliki basis Linux, saat klien Windows berkomunikasi dengan Samba 4, si Windows tidak merasa jika ia berhubungan dengan Linux, karena Samba 4 mimicry sifat-sifat Windows server, sehingga klien Windows maupun Windows Server akan merasa berhubungan dengan sesama sistem operasi Windows.

Ebook dan buku Active Directory Berbasis Samba 4 ini cocok bagi perusahaan yang ingin tetap memberikan layanan Active Directory dan PDC/BDC berbasis Windows namun ingin menggunakan kapabilitas Linux, selain tentunya bisa menghilangkan kebutuhan lisensi Windows Server.

Disusun dalam bentuk tutorial tahap demi tahap, buku dan ebook ini merupakan buku panduan yang digunakan untuk training dengan judul yang sama pada layanan training Excellent.

Link

• Ebook pada Google Play Book
• Buku Cetak pada Tokopedia
• Buku Cetak pada Bukalapak

Catatan

Status untuk buku cetak tertulis “Preorder” namun karena sudah diproses cetak pekan lalu, bukunya sudah bisa dikirim mulai pekan depan.

Fixes and updates applied with this second minor version improved and extended the main functions, let’s see what’s new.

If you are new to the zypper-upgraderepo plugin, give a look to the previous article to better understand the mission and the basic usage.

Repository check

The first important change is inherent the way to check a valid repository:

• the HTTP request sent is HEAD instead of GET in order to have a more lightweight answer from the server, being the HTML page not included in the packet;
• the request point directly to the repodata.xml file instead of the folder, that because some server security setting could hide the directory listing and send back a 404 error although the repository works properly.

Check just a few repos

Most of the times we want to check the whole repository’s list at once, but sometimes we want to check few of them to see whether or not they are finally available or ready to be upgraded without looping through the whole list again and again. That’s where the –only-repo switch followed by a list of comma-separated numbers comes in help.

–only-repo switch

All repo by default

The disabled repositories now are shown by default and a new column highlights which of them are enabled or not, keeping their number in sync with the zypper lr output. To see only the enabled ones just use the switch –only-enabled.

Table view

Report view

Beside the table view, the switch –report introduce a new pleasant view using just two columns and spanning the right cell to more rows in order to improve the number of info and the reading quality.

Report view

Other changes

The procedure which tries to discover an alternative URL now dives back and forth the directory list in order to explore the whole tree of folders wherever the access is allowed by the server itself. The side effect is a general improvement also in repo downgrade.

The output in upgrade mode is now verbose and shows a table similar to the checking one, giving details about the changed URLs in the details column.

The server timeout error is now handled through the switch –timeout which allows tweaking the time before to consider an error any late answer from the server itself.

Final thoughts and what’s next

This plugin is practically completed, achieving all the goals needed for its main purpose no other relevant changes are scheduled, so I started thinking of other projects to work in my spare time.

Among them, there is one I am interested in: bring the power of openSUSE software search page to the command line.

However, there are some problems:

• This website doesn’t implement any web API so will be a lot of scraping job;
• There are missing packages while switching from the global research (selecting All distribution) to the specific distribution;
• Packages from Packman are not included.

I have already got some ideas to solve them and did lay down several lines of code, so let’s see what happens!

Merujuk pada pemberitaan di https://blog.documentfoundation.org/blog/2019/02/19/first-libreoffice-asia-conference/ tentang acara Konferensi LibreOffice Asia yang pertama kali, berikut terjemahan dari media rilis tersebut:

Konferensi LibreOffice Asia yang pertama kali akan diadakan pada 25-26 Mei 2019 di Nihonbashi, Tokyo, Jepang

Ini adalah konferensi LibreOffice yang pertama menjangkau Asia, area yang memiliki pertumbuhan perangkat lunak berbasis FOSS yang sangat pesat.

Berlin, 18 Februari 2019 – Setelah kesuksesan besar Konferensi LibreOffice Indonesia pada tahun 2018, para anggota dari komunitas Asia memutuskan untuk mengangkat isu ini di 2019 dengan Konferensi LibreOffice Asia yang pertama kali di Nihonbashi – pusat kota Tokyo, Jepang – pada 25-26 Mei 2019.

Sebagai salah satu penyelenggara, Naruhiko Ogasawara, anggota dari komunitas LibreOffice Jepang dan The Document Foundation, tidak bisa menyembunyikan kegembiraannya. “Saat kami mengadakan LibreOffice Mini Conference Japan 2013 sebagai acara lokal, kami hanya sedikit mengetahui tentang komunitas-komunitas di belahan lain Asia,” ucap Naruhiko. “Kemudian tahun ini kami menghadiri LibreOffice Conference dan acara di Asia lainnya seperti openSUSE Asia, COSUP, dan lain sebagainya. Kami menyadari bahwa banyak rekan-rekan kami yang aktif dan bahwa komunitas kami harus belajar banyak dari mereka. Kami bangga dapat mengadakan Konferensi Asia yang pertama dengan rekan-rekan kami untuk lebih memperkuat kemitraan tersebut.

“Ini lompatan takdir yang nyata,” ucap Franklin Weng, salah seorang anggota dari Asia di Dewan Direksi The Document Foundation. “Asia adalah daerah yang perkembangannya sangat pesat dalam mengadopsi ODF dan LibreOffice, tetapi ekosistem kami untuk LibreOffice dan FOSS belum cukup baik. Dalam konferensi ini kami tidak hanya mencoba membuat ekosistem FOSS di Asia lebih baik, tetapi juga untuk mendorong anggota komunitas Asia menunjukkan potensi mereka.”

Beberapa anggota inti dari The Document Foundation akan menghadiri konferensi ini, termasuk Italo Vignoli, pimpinan tim pemasaran dan hubungan masyarakat dan wakil ketua Komite Sertifikasi LibreOffice, dan Lothar Becker, juga wakil ketua Komite Sertifikasi. Selain itu, akan ada anggota komunitas dari Indonesia, Korea Selatan, Taiwan, Jepang dan mungkin China yang hadir.

Poin dari konferensi ini meliputi:

• Workshop bisnis – yang akan dipandu oleh Lothar Becker dan Italo Vignoli, ketua dan wakil ketua Komite Sertifikasi LibreOffice dari The Document Foundation. Lothar dan Italo akan membahas tentang layanan bisnis – apa yang mendasar dari layanan bisnis LibreOffice, status bisnis LibreOffice saat ini di Eropa, Asia dan wilayah geografis lainnya, dan bagaimana kita dapat saling mendukung, dan lain sebagainya.

• CJK Hackfest – yang akan dipimpin oleh Mark Hung, seorang Pengembang LibreOffice Tersertifikasi di Taiwan, untuk membahas dan meretas masalah CJK di LibreOffice.

• Wawancara Sertifikasi – Wawancara Sertifikasi LibreOffice kedua di Asia akan diadakan selama LibreOffice Asia Conference, yang dipandu oleh Italo Vignoli dan Lothar Becker, ketua dan wakil ketua Komite Sertifikasi LibreOffice saat ini. Sejauh ini total 4 atau 5 kandidat akan diwawancarai untuk Profesional Migrasi Bersertifikat LibreOffice dan Pelatih Bersertifikat LibreOffice.

• Sertifikasi Lokal Asia untuk LibreOffice – yang akan dipandu oleh Franklin Weng dan Eric Sun, dua anggota TDF dari Taiwan, yang akan memperkenalkan ide-ide agar memiliki keterampilan LibreOffice dan sertifikasi pelatih di Asia.

Call for proposal akan segera diluncurkan pada bulan Februari. Selain topik di atas, topik terkait LibreOffice dan ODF lainnya juga diterima.