Backing up third-party sources with Conan

For recipes and build scripts for open source, publicly available libraries, it is common practice to download the sources from a canonical source, like Github releases, or project download web pages. Keeping a record of the origin of these files is useful for traceability purposes, however, it is often not guaranteed that the files will be available in the long term, and a user in the future building the same recipe from source may encounter a problem. Conan can thus be configured to transparently retrieve sources from a configured mirror, without modifying the recipes or conandata.yml. Additionally, these sources can be transparently uploaded alongside the packages via conan upload.

The sources backup feature is intended for storing the downloaded recipe sources in a file server in your own infrastructure, allowing future reproducibility of your builds even in the case where the original download URLs are no longer accessible.

The backup is triggered for calls to the download and get methods when a sha256 file signature is provided.

Configuration overview

This feature is controlled by a few global.conf items:

  • core.sources:download_cache: Local path to store the sources backups to. If not set, the default Conan home cache path will be used.

  • core.sources:download_urls: Ordered list of URLs that Conan will try to download the sources from, where origin represents the original URL passed to get/download from conandata.yml. This allows to control the fetch order, either ["origin", "https://your.backup/remote/"] to look into and fetch from your backup remote only if and when the original source is not present, or ["https://your.backup/remote/", "origin"] to prefer your backup server ahead of the recipes’ canonical links. Being a list, multiple remotes are also possible. ["origin"] by default

  • core.sources:upload_url: URL of the remote to upload the backups to when calling conan upload, which might or might not be different from any of the URLs defined for download. Empty by default

  • core.sources:exclude_urls: List of origins to skip backing up. If the URL passed to get/download starts with any of the origins included in this list, the source won’t be uploaded to the backup remote when calling conan upload. Empty by default

Usage

Let’s overview how the feature works by providing an example usage from beginning to end:

In summary, it looks something like:

  • A remote backup repository is set up. This should allow PUT and GET HTTP methods to modify and fetch its contents. If access credentials are desired (which is strongly recommended for uploading permissions), you can use the source_credentials.json feature. See below if you are in need for configuring your own.

  • The remote’s URL can then be set in core.sources:download_urls and core.sources:upload_url.

  • In your recipe’s source() method, ensure the relevant get/download calls supply the sha256 signature of the downloaded files.

  • Set core.sources:download_cache in your global.conf file if a custom location is desired, else the default cache folder will be used

  • Run Conan normally, creating packages etc.

  • Once some sources have been locally downloaded, the folder pointed to by core.sources:download_cache will contain, for each downloaded file:

    • A blob file (no extensions) with the name of the sha256 signature provided in get/download.

    • A .json file which will also have the name of the sha256 signature, that will contain information about which references and which mirrors this blob belongs to.

  • Calling conan upload will now optionally upload the backups for the matching references if core.sources:upload_url is set.

Note

See below for a guide on how to configure your own backup server

Setting up the necessary configs

The global.conf file should contain the core.sources:download_urls

global.conf

  1. core.sources:download_urls=["https://myteam.myorg.com/artifactory/backup-sources/", "origin"]

You might want to add extra confs based on your use case, as described in the beginning of this document.

Note

The recommended approach for dealing with the configuration of CI workers and developers in your organization is to install the configs using the conan config install command on a repository. Read more here

Run Conan as normal

With the above steps completed, Conan can now be used as normal, and for every downloaded source, Conan will first look into the folder indicated in core.sources:download_cache, and if not found there, will traverse core.sources:download_urls until it find the file or fails, and store a local copy in the same core.sources:download_cache location.

When the backup is fetched from the the backup remote, a message like what follows will be shown to the user:

The client will now print information regarding from which remote it was capable of downloading the sources

  1. $ conan create . --version=1.3
  3. ...
  5. ======== Installing packages ========
  6. zlib/1.3: Calling source() in /Users/ruben/.conan2/p/zlib0f4e45286ecd1/s/src
  7. zlib/1.3: Sources for ['https://zlib.net/fossils/zlib-1.3.tar.gz', 'https://github.com/madler/zlib/releases/download/v1.3/zlib-1.3.tar.gz']
  8.           found in remote backup https://myteam.myorg.com/artifactory/backup-sources
  10. -------- Installing package zlib/1.3 (1 of 1) --------
  12. ...

If we now again try to run this, we’ll find that no download is performed and the locally stored version of the files is used.

Upload the packages

Once a package has been created as shown above, when a call to conan upload zlib/1.3 -c is performed to upload the resulting binary to your Conan repository, it will also upload the source backups for that same reference to your backups remote if configured to do so, and future source downloads of this recipe will use the newly updated contents when necessary.

Note

See the packages list feature for a way to only upload the packages that have been built

In case there’s a need to upload backups for sources not linked to any package, or for packages that are already on the remote and would therefore be skipped during upload, the conan cache backup-upload command can be used to address this scenario.

Creating the backup repository

You can also set up your own remote backup repository instead of relying on an already available one. While an Artifactory generic repository (available for free with Artifactory CE) is recommend for this purpose, any simple server that allows PUT and GET HTTP methods to modify and fetch its contents is sufficient.

Read the following section for instructions on how to create a generic Artifactory backup repo and how to give it public read permissions, while keeping write access only for authorized agents