depot/third_party/nixpkgs/doc/build-helpers/fetchers.chapter.md

Fetchers

Building software with Nix often requires downloading source code and other files from the internet. To this end, we use functions that we call fetchers, which obtain remote sources via various protocols and services.

Nix provides built-in fetchers such as builtins.fetchTarball. Nixpkgs provides its own fetchers, which work differently:

• A built-in fetcher will download and cache files at evaluation time and produce a store path. A Nixpkgs fetcher will create a (fixed-output) derivation, and files are downloaded at build time.
• Built-in fetchers will invalidate their cache after tarball-ttl expires, and will require network activity to check if the cache entry is up to date. Nixpkgs fetchers only re-download if the specified hash changes or the store object is not available.
• Built-in fetchers do not use substituters. Derivations produced by Nixpkgs fetchers will use any configured binary cache transparently.

This significantly reduces the time needed to evaluate Nixpkgs, and allows Hydra to retain and re-distribute sources used by Nixpkgs in the public binary cache. For these reasons, Nix's built-in fetchers are not allowed in Nixpkgs.

The following table summarises the differences:

Fetchers	Download	Output	Cache	Re-download when
builtins.fetch*	evaluation time	store path	/nix/store, ~/.cache/nix	tarball-ttl expires, cache miss in ~/.cache/nix, output store object not in local store
pkgs.fetch*	build time	derivation	/nix/store, substituters	output store object not available

:::{.tip} pkgs.fetchFrom* helpers retrieve snapshots of version-controlled sources, as opposed to the entire version history, which is more efficient. pkgs.fetchgit by default also has the same behaviour, but can be changed through specific attributes given to it. :::

Caveats

Because Nixpkgs fetchers are fixed-output derivations, an output hash has to be specified, usually indirectly through a hash attribute. This hash refers to the derivation output, which can be different from the remote source itself!

This has the following implications that you should be aware of:

• Use Nix (or Nix-aware) tooling to produce the output hash.

• When changing any fetcher parameters, always update the output hash. Use one of the methods from . Otherwise, existing store objects that match the output hash will be re-used rather than fetching new content.

  :::{.note} A similar problem arises while testing changes to a fetcher's implementation. If the output of the derivation already exists in the Nix store, test failures can go undetected. The invalidateFetcherByDrvHash function helps prevent reusing cached derivations. :::

Updating source hashes

There are several ways to obtain the hash corresponding to a remote source. Unless you understand how the fetcher you're using calculates the hash from the downloaded contents, you should use the fake hash method.

1. []{#sec-pkgs-fetchers-updating-source-hashes-fakehash-method} The fake hash method: In your package recipe, set the hash to one of

   • ""
   • lib.fakeHash
   • lib.fakeSha256
   • lib.fakeSha512

   Attempt to build, extract the calculated hashes from error messages, and put them into the recipe.

   :::{.warning} You must use one of these four fake hashes and not some arbitrarily-chosen hash. See for details. :::

   :::{.example #ex-fetchers-update-fod-hash}

   Update source hash with the fake hash method

   Consider the following recipe that produces a plain file:

   { fetchurl }:
   fetchurl {
     url = "https://raw.githubusercontent.com/NixOS/nixpkgs/23.05/.version";
     hash = "sha256-ZHl1emidXVojm83LCVrwULpwIzKE/mYwfztVkvpruOM=";
   }
   

   A common mistake is to update a fetcher parameter, such as url, without updating the hash:

   { fetchurl }:
   fetchurl {
     url = "https://raw.githubusercontent.com/NixOS/nixpkgs/23.11/.version";
     hash = "sha256-ZHl1emidXVojm83LCVrwULpwIzKE/mYwfztVkvpruOM=";
   }
   

   This will produce the same output as before! Set the hash to an empty string:

   { fetchurl }:
   fetchurl {
     url = "https://raw.githubusercontent.com/NixOS/nixpkgs/23.11/.version";
     hash = "";
   }
   

   When building the package, use the error message to determine the correct hash:

   $ nix-build
   (some output removed for clarity)
   error: hash mismatch in fixed-output derivation '/nix/store/7yynn53jpc93l76z9zdjj4xdxgynawcw-version.drv':
           specified: sha256-AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=
               got:    sha256-BZqI7r0MNP29yGH5+yW2tjU9OOpOCEvwWKrWCv5CQ0I=
   error: build of '/nix/store/bqdjcw5ij5ymfbm41dq230chk9hdhqff-version.drv' failed
   

   :::

2. Prefetch the source with nix-prefetch-<type> <URL>, where <type> is one of

   • url
   • git
   • hg
   • cvs
   • bzr
   • svn

   The hash is printed to stdout.

3. Prefetch by package source (with nix-prefetch-url '<nixpkgs>' -A <package>.src, where <package> is package attribute name). The hash is printed to stdout.

   This works well when you've upgraded the existing package version and want to find out new hash, but is useless if the package can't be accessed by attribute or the package has multiple sources (.srcs, architecture-dependent sources, etc).

4. Upstream hash: use it when upstream provides sha256 or sha512. Don't use it when upstream provides md5, compute sha256 instead.

   A little nuance is that nix-prefetch-* tools produce hashes with the nix32 encoding (a Nix-specific base32 adaptation), but upstream usually provides hexadecimal (base16) encoding. Fetchers understand both formats. Nixpkgs does not standardise on any one format.

   You can convert between hash formats with nix-hash.

5. Extract the hash from a local source archive with sha256sum. Use nix-prefetch-url file:///path/to/archive if you want the custom Nix base32 hash.

Obtaining hashes securely

It's always a good idea to avoid Man-in-the-Middle (MITM) attacks when downloading source contents. Otherwise, you could unknowingly download malware instead of the intended source, and instead of the actual source hash, you'll end up using the hash of malware. Here are security considerations for this scenario:

• http:// URLs are not secure to prefetch hashes.

• Upstream hashes should be obtained via a secure protocol.

• https:// URLs give you more protections when using nix-prefetch-* or for upstream hashes.

• https:// URLs are secure when using the fake hash method only if you use one of the listed fake hashes. If you use any other hash, the download will be exposed to MITM attacks even if you use HTTPS URLs.

  In more concrete terms, if you use any other hash, the --insecure flag will be passed to the underlying call to curl when downloading content.

[]{#fetchurl}

fetchurl

fetchurl returns a fixed-output derivation which downloads content from a given URL and stores the unaltered contents within the Nix store.

It uses {manpage}curl(1) internally, and allows its behaviour to be modified by specifying a few attributes in the argument to fetchurl (see the documentation for attributes curlOpts, curlOptsList, and netrcPhase).

The resulting store path is determined by the hash given to fetchurl, and also the name (or pname and version) values.

If neither name nor pname and version are specified when calling fetchurl, it will default to using the basename of url or the first element of urls. If pname and version are specified, fetchurl will use those values and will ignore name, even if it is also specified.

Inputs

fetchurl requires an attribute set with the following attributes:

url (String; optional)

The URL to download from.

:::{.note} Either url or urls must be specified, but not both. :::

All URLs of the format specified here are supported.

Default value: "".

urls (List of String; optional)

A list of URLs, specifying download locations for the same content. Each URL will be tried in order until one of them succeeds with some content or all of them fail. See to understand how this attribute affects the behaviour of fetchurl.

:::{.note} Either url or urls must be specified, but not both. :::

Default value: [].

hash (String; optional)

Hash of the derivation output of fetchurl, following the format for integrity metadata as defined by SRI. For more information, see .

:::{.note} It is recommended that you use the hash attribute instead of the other hash-specific attributes that exist for backwards compatibility.

If hash is not specified, you must specify outputHash and outputHashAlgo, or one of sha512, sha256, or sha1. :::

Default value: "".

outputHash (String; optional)

Hash of the derivation output of fetchurl in the format expected by Nix. See the documentation on the Nix manual for more information about its format.

:::{.note} It is recommended that you use the hash attribute instead.

If outputHash is specified, you must also specify outputHashAlgo. :::

Default value: "".

outputHashAlgo (String; optional)

Algorithm used to generate the value specified in outputHash. See the documentation on the Nix manual for more information about the values it supports.

:::{.note} It is recommended that you use the hash attribute instead.

The value specified in outputHashAlgo will be ignored if outputHash isn't also specified. :::

Default value: "".

sha1 (String; optional)

SHA-1 hash of the derivation output of fetchurl in the format expected by Nix. See the documentation on the Nix manual for more information about its format.

:::{.note} It is recommended that you use the hash attribute instead. :::

Default value: "".

sha256 (String; optional)

SHA-256 hash of the derivation output of fetchurl in the format expected by Nix. See the documentation on the Nix manual for more information about its format.

:::{.note} It is recommended that you use the hash attribute instead. :::

Default value: "".

sha512 (String; optional)

SHA-512 hash of the derivation output of fetchurl in the format expected by Nix. See the documentation on the Nix manual for more information about its format.

:::{.note} It is recommended that you use the hash attribute instead. :::

Default value: "".

name (String; optional)

The symbolic name of the downloaded file when saved in the Nix store. See the fetchurl overview for details on how the name of the file is decided.

Default value: "".

pname (String; optional)

A base name, which will be combined with version to form the symbolic name of the downloaded file when saved in the Nix store. See the fetchurl overview for details on how the name of the file is decided.

:::{.note} If pname is specified, you must also specify version, otherwise fetchurl will ignore the value of pname. :::

Default value: "".

version (String; optional)

A version, which will be combined with pname to form the symbolic name of the downloaded file when saved in the Nix store. See the fetchurl overview for details on how the name of the file is decided.

Default value: "".

recursiveHash (Boolean; optional) []{#sec-pkgs-fetchers-fetchurl-inputs-recursiveHash}

If set to true, will signal to Nix that the hash given to fetchurl was calculated using the "recursive" mode. See the documentation on the Nix manual for more information about the existing modes.

By default, fetchurl uses "recursive" mode when the executable attribute is set to true, so you don't need to specify recursiveHash in this case.

Default value: false.

executable (Boolean; optional)

If true, sets the executable bit on the downloaded file.

Default value: false.

downloadToTemp (Boolean; optional) []{#sec-pkgs-fetchers-fetchurl-inputs-downloadToTemp}

If true, saves the downloaded file to a temporary location instead of the expected Nix store location. This is useful when used in conjunction with postFetch attribute, otherwise fetchurl will not produce any meaningful output.

The location of the downloaded file will be set in the $downloadedFile variable, which should be used by the script in the postFetch attribute. See to understand how to work with this attribute.

Default value: false.

postFetch (String; optional)

Script executed after the file has been downloaded successfully, and before fetchurl finishes running. Useful for post-processing, to check or transform the file in some way. See to understand how to work with this attribute.

Default value: "".

netrcPhase (String or Null; optional)

Script executed to create a {manpage}netrc(5) file to be used with {manpage}curl(1). The script should create the netrc file (note that it does not begin with a ".") in the directory it's currently running in ($PWD).

The script is executed during the setup done by fetchurl before it runs any of its code to download the specified content.

:::{.note} If specified, fetchurl will automatically alter its invocation of {manpage}curl(1) to use the netrc file, so you don't need to add anything to curlOpts or curlOptsList. :::

:::{.caution} Since netrcPhase needs to be specified in your source Nix code, any secrets that you put directly in it will be world-readable by design (both in your source code, and when the derivation gets created in the Nix store).

If you want to avoid this behaviour, see the documentation of netrcImpureEnvVars for an alternative way of dealing with these secrets. :::

Default value: null.

netrcImpureEnvVars (List of String; optional)

If specified, fetchurl will add these environment variable names to the list of impure environment variables, which will be passed from the environment of the calling user to the builder running the fetchurl code.

This is useful when used with netrcPhase to hide any secrets that are used in it, because the script in netrcPhase only needs to reference the environment variables with the secrets in them instead. However, note that these are called impure variables for a reason: the environment that starts the build needs to have these variables declared for everything to work properly, which means that additional setup is required outside what Nix controls.

Default value: [].

curlOpts (String; optional)

If specified, this value will be appended to the invocation of {manpage}curl(1) when downloading the URL(s) given to fetchurl. Multiple arguments can be separated by spaces normally, but values with whitespaces will be interpreted as multiple arguments (instead of a single value), even if the value is escaped. See curlOptsList for a way to pass values with whitespaces in them.

Default value: "".

curlOptsList (List of String; optional)

If specified, each element of this list will be passed as an argument to the invocation of {manpage}curl(1) when downloading the URL(s) given to fetchurl. This allows passing values that contain spaces, with no escaping needed.

Default value: [].

showURLs (Boolean; optional)

If set to true, this will stop fetchurl from downloading anything at all. Instead, it will output a list of all the URLs it would've used to download the content (after resolving mirror:// URLs, for example). This is useful for debugging.

Default value: false.

meta (Attribute Set; optional)

Specifies any meta-attributes for the derivation returned by fetchurl.

Default value: {}.

passthru (Attribute Set; optional)

Specifies any extra passthru attributes for the derivation returned by fetchurl. Note that fetchurl defines passthru attributes of its own. Attributes specified in passthru can override the default attributes returned by fetchurl.

Default value: {}.

preferLocalBuild (Boolean; optional)

This is the same attribute as defined in the Nix manual. It is true by default because making a remote machine download the content just duplicates network traffic (since the local machine might download the results from the derivation anyway), but this could be useful in cases where network access is restricted on local machines.

Default value: true.

nativeBuildInputs (List of Attribute Set; optional)

Additional packages needed to download the content. This is useful if you need extra packages for postFetch or netrcPhase, for example. Has the same semantics as in . See to understand how this can be used with postFetch.

Default value: [].

Passthru outputs

fetchurl also defines its own passthru attributes:

url (String)

The same url attribute passed in the argument to fetchurl.

Examples

:::{.example #ex-fetchers-fetchurl-nixpkgs-version}

Using fetchurl to download a file

The following package downloads a small file from a URL and shows the most common way to use fetchurl:

{ fetchurl }:
fetchurl {
  url = "https://raw.githubusercontent.com/NixOS/nixpkgs/23.11/.version";
  hash = "sha256-BZqI7r0MNP29yGH5+yW2tjU9OOpOCEvwWKrWCv5CQ0I=";
}

After building the package, the file will be downloaded and place into the Nix store:

$ nix-build
(output removed for clarity)
/nix/store/4g9y3x851wqrvim4zcz5x2v3zivmsq8n-version

$ cat /nix/store/4g9y3x851wqrvim4zcz5x2v3zivmsq8n-version
23.11

:::

:::{.example #ex-fetchers-fetchurl-nixpkgs-version-multiple-urls}

Using fetchurl to download a file with multiple possible URLs

The following package adapts to use multiple URLs. The first URL was crafted to intentionally return an error to illustrate how fetchurl will try multiple URLs until it finds one that works (or all URLs fail).

{ fetchurl }:
fetchurl {
  urls = [
    "https://raw.githubusercontent.com/NixOS/nixpkgs/23.11/does-not-exist"
    "https://raw.githubusercontent.com/NixOS/nixpkgs/23.11/.version"
  ];
  hash = "sha256-BZqI7r0MNP29yGH5+yW2tjU9OOpOCEvwWKrWCv5CQ0I=";
}

After building the package, both URLs will be used to download the file:

$ nix-build
(some output removed for clarity)
trying https://raw.githubusercontent.com/NixOS/nixpkgs/23.11/does-not-exist
(some output removed for clarity)
curl: (22) The requested URL returned error: 404

trying https://raw.githubusercontent.com/NixOS/nixpkgs/23.11/.version
(some output removed for clarity)
/nix/store/n9asny31z32q7sdw6a8r1gllrsfy53kl-does-not-exist

$ cat /nix/store/n9asny31z32q7sdw6a8r1gllrsfy53kl-does-not-exist
23.11

However, note that the name of the file was derived from the first URL (this is further explained in the fetchurl overview). To ensure the result will have the same name regardless of which URLs are used, we can modify the package:

{ fetchurl }:
fetchurl {
  name = "nixpkgs-version";
  urls = [
    "https://raw.githubusercontent.com/NixOS/nixpkgs/23.11/does-not-exist"
    "https://raw.githubusercontent.com/NixOS/nixpkgs/23.11/.version"
  ];
  hash = "sha256-BZqI7r0MNP29yGH5+yW2tjU9OOpOCEvwWKrWCv5CQ0I=";
}

After building the package, the result will have the name we specified:

$ nix-build
(output removed for clarity)
/nix/store/zczb6wl3al6jm9sm5h3pr6nqn0i5ji9z-nixpkgs-version

:::

:::{.example #ex-fetchers-fetchurl-nixpkgs-version-postfetch}

Manipulating the content downloaded by fetchurl

It might be useful to manipulate the content downloaded by fetchurl directly in its derivation. In this example, we'll adapt to append the result of running the hello package to the contents we download, purely to illustrate how to manipulate the content.

{ fetchurl, hello, lib }:
fetchurl {
  url = "https://raw.githubusercontent.com/NixOS/nixpkgs/23.11/.version";

  nativeBuildInputs = [ hello ];

  downloadToTemp = true;
  postFetch = ''
    ${lib.getExe hello} >> $downloadedFile
    mv $downloadedFile $out
  '';

  hash = "sha256-ceooQQYmDx5+0nfg40uU3NNI2yKrixP7HZ/xLZUNv+w=";
}

After building the package, the resulting file will have "Hello, world!" appended to it:

$ nix-build
(output removed for clarity)
/nix/store/ifi6pp7q0ag5h7c5v9h1c1c7bhd10c7f-version

$ cat /nix/store/ifi6pp7q0ag5h7c5v9h1c1c7bhd10c7f-version
23.11
Hello, world!

Note that the hash specified in the package is different than the hash specified in , because the contents of the output have changed (even though the actual file that was downloaded is the same). See for more details on how to work with the hash attribute when the output changes. :::

fetchzip

Returns a fixed-output derivation which downloads an archive from a given URL and decompresses it.

Despite its name, fetchzip is not limited to .zip files but can also be used with various compressed tarball formats by default. This can extended by specifying additional attributes, see to understand how to do that.

Inputs

fetchzip requires an attribute set, and most attributes are passed to the underlying call to fetchurl.

The attributes below are treated differently by fetchzip when compared to what fetchurl expects:

name (String; optional)

Works as defined in fetchurl, but has a different default value than fetchurl.

Default value: "source".

nativeBuildInputs (List of Attribute Set; optional)

Works as defined in fetchurl, but it is also augmented by fetchzip to include packages to deal with additional archives (such as .zip).

Default value: [].

postFetch (String; optional)

Works as defined in fetchurl, but it is also augmented with the code needed to make fetchzip work.

:::{.caution} It is only safe to modify files in $out in postFetch. Consult the implementation of fetchzip for anything more involved. :::

Default value: "".

stripRoot (Boolean; optional)

If true, the decompressed contents are moved one level up the directory tree.

This is useful for archives that decompress into a single directory which commonly includes some values that change with time, such as version numbers. When this is the case (and stripRoot is true), fetchzip will remove this directory and make the decompressed contents available in the top-level directory.

shows what this attribute does.

This attribute is not passed through to fetchurl.

Default value: true.

extension (String or Null; optional)

If set, the archive downloaded by fetchzip will be renamed to a filename with the extension specified in this attribute.

This is useful when making fetchzip support additional types of archives, because the implementation may use the extension of an archive to determine whether they can decompress it. If the URL you're using to download the contents doesn't end with the extension associated with the archive, use this attribute to fix the filename of the archive.

This attribute is not passed through to fetchurl.

Default value: null.

recursiveHash (Boolean; optional)

Works as defined in fetchurl, but its default value is different than for fetchurl.

Default value: true.

downloadToTemp (Boolean; optional)

Works as defined in fetchurl, but its default value is different than for fetchurl.

Default value: true.

extraPostFetch DEPRECATED

This attribute is deprecated. Please use postFetch instead.

This attribute is not passed through to fetchurl.

Examples

::::{.example #ex-fetchers-fetchzip-simple-striproot}

Using fetchzip to output contents directly

The following recipe shows how to use fetchzip to decompress a .tar.gz archive:

{ fetchzip }:
fetchzip {
  url = "https://github.com/NixOS/patchelf/releases/download/0.18.0/patchelf-0.18.0.tar.gz";
  hash = "sha256-3ABYlME9R8klcpJ7MQpyFEFwHmxDDEzIYBqu/CpDYmg=";
}

This archive has all its contents in a directory named patchelf-0.18.0. This means that after decompressing, you'd have to enter this directory to see the contents of the archive. However, fetchzip makes this easier through the attribute stripRoot (enabled by default).

After building the recipe, the derivation output will show all the files in the archive at the top level:

$ nix-build
(output removed for clarity)
/nix/store/1b7h3fvmgrcddvs0m299hnqxlgli1yjw-source

$ ls /nix/store/1b7h3fvmgrcddvs0m299hnqxlgli1yjw-source
aclocal.m4  completions  configure.ac  m4           Makefile.in  patchelf.spec     README.md  tests
build-aux   configure    COPYING       Makefile.am  patchelf.1   patchelf.spec.in  src        version

If stripRoot is set to false, the derivation output will be the decompressed archive as-is:

{ fetchzip }:
fetchzip {
  url = "https://github.com/NixOS/patchelf/releases/download/0.18.0/patchelf-0.18.0.tar.gz";
  hash = "sha256-uv3FuKE4DqpHT3yfE0qcnq0gYjDNQNKZEZt2+PUAneg=";
  stripRoot = false;
}

:::{.caution} The hash changed! Whenever changing attributes of a Nixpkgs fetcher, remember to invalidate the hash, otherwise you won't get the results you're expecting! :::

After building the recipe:

$ nix-build
(output removed for clarity)
/nix/store/2hy5bxw7xgbgxkn0i4x6hjr8w3dbx16c-source

$ ls /nix/store/2hy5bxw7xgbgxkn0i4x6hjr8w3dbx16c-source
patchelf-0.18.0

::::

::::{.example #ex-fetchers-fetchzip-rar-archive}

Using fetchzip to decompress a .rar file

The unrar package provides a setup hook to decompress .rar archives during the unpack phase, which can be used with fetchzip to decompress those archives:

{ fetchzip, unrar }:
fetchzip {
  url = "https://archive.org/download/SpaceCadet_Plus95/Space_Cadet.rar";
  hash = "sha256-fC+zsR8BY6vXpUkVd6i1jF0IZZxVKVvNi6VWCKT+pA4=";
  stripRoot = false;
  nativeBuildInputs = [ unrar ];
}

Since this particular .rar file doesn't put its contents in a directory inside the archive, stripRoot must be set to false.

After building the recipe, the derivation output will show the decompressed files:

$ nix-build
(output removed for clarity)
/nix/store/zpn7knxfva6rfjja2gbb4p3l9w1f0d36-source

$ ls /nix/store/zpn7knxfva6rfjja2gbb4p3l9w1f0d36-source
FONT.DAT      PINBALL.DAT  PINBALL.EXE	PINBALL2.MID  TABLE.BMP    WMCONFIG.EXE
MSCREATE.DIR  PINBALL.DOC  PINBALL.MID	Sounds	     WAVEMIX.INF

::::

fetchpatch

fetchpatch works very similarly to fetchurl with the same arguments expected. It expects patch files as a source and performs normalization on them before computing the checksum. For example, it will remove comments or other unstable parts that are sometimes added by version control systems and can change over time.

• relative: Similar to using git-diff's --relative flag, only keep changes inside the specified directory, making paths relative to it.
• stripLen: Remove the first stripLen components of pathnames in the patch.
• decode: Pipe the downloaded data through this command before processing it as a patch.
• extraPrefix: Prefix pathnames by this string.
• excludes: Exclude files matching these patterns (applies after the above arguments).
• includes: Include only files matching these patterns (applies after the above arguments).
• revert: Revert the patch.

Note that because the checksum is computed after applying these effects, using or modifying these arguments will have no effect unless the hash argument is changed as well.

Most other fetchers return a directory rather than a single file.

fetchDebianPatch

A wrapper around fetchpatch, which takes:

• patch and hash: the patch's filename, and its hash after normalization by fetchpatch ;
• pname: the Debian source package's name ;
• version: the upstream version number ;
• debianRevision: the Debian revision number if applicable ;
• the area of the Debian archive: main (default), contrib, or non-free.

Here is an example of fetchDebianPatch in action:

{ lib
, fetchDebianPatch
, buildPythonPackage
}:

buildPythonPackage rec {
  pname = "pysimplesoap";
  version = "1.16.2";
  src = <...>;

  patches = [
    (fetchDebianPatch {
      inherit pname version;
      debianRevision = "5";
      name = "Add-quotes-to-SOAPAction-header-in-SoapClient.patch";
      hash = "sha256-xA8Wnrpr31H8wy3zHSNfezFNjUJt1HbSXn3qUMzeKc0=";
    })
  ];

  # ...
}

Patches are fetched from sources.debian.org, and so must come from a package version that was uploaded to the Debian archive. Packages may be removed from there once that specific version isn't in any suite anymore (stable, testing, unstable, etc.), so maintainers should use copy-tarballs.pl to archive the patch if it needs to be available longer-term.

fetchsvn

Used with Subversion. Expects url to a Subversion directory, rev, and hash.

fetchgit

Used with Git. Expects url to a Git repo, rev, and hash. rev in this case can be full the git commit id (SHA1 hash) or a tag name like refs/tags/v1.0.

Additionally, the following optional arguments can be given: fetchSubmodules = true makes fetchgit also fetch the submodules of a repository. If deepClone is set to true, the entire repository is cloned as opposing to just creating a shallow clone. deepClone = true also implies leaveDotGit = true which means that the .git directory of the clone won't be removed after checkout.

If only parts of the repository are needed, sparseCheckout can be used. This will prevent git from fetching unnecessary blobs from server, see git sparse-checkout for more information:

{ stdenv, fetchgit }:

stdenv.mkDerivation {
  name = "hello";
  src = fetchgit {
    url = "https://...";
    sparseCheckout = [
      "directory/to/be/included"
      "another/directory"
    ];
    hash = "sha256-AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=";
  };
}

fetchfossil

Used with Fossil. Expects url to a Fossil archive, rev, and hash.

fetchcvs

Used with CVS. Expects cvsRoot, tag, and hash.

fetchhg

Used with Mercurial. Expects url, rev, and hash.

A number of fetcher functions wrap part of fetchurl and fetchzip. They are mainly convenience functions intended for commonly used destinations of source code in Nixpkgs. These wrapper fetchers are listed below.

fetchFromGitea

fetchFromGitea expects five arguments. domain is the gitea server name. owner is a string corresponding to the Gitea user or organization that controls this repository. repo corresponds to the name of the software repository. These are located at the top of every Gitea HTML page as owner/repo. rev corresponds to the Git commit hash or tag (e.g v1.0) that will be downloaded from Git. Finally, hash corresponds to the hash of the extracted directory. Again, other hash algorithms are also available but hash is currently preferred.

fetchFromGitHub

fetchFromGitHub expects four arguments. owner is a string corresponding to the GitHub user or organization that controls this repository. repo corresponds to the name of the software repository. These are located at the top of every GitHub HTML page as owner/repo. rev corresponds to the Git commit hash or tag (e.g v1.0) that will be downloaded from Git. Finally, hash corresponds to the hash of the extracted directory. Again, other hash algorithms are also available, but hash is currently preferred.

To use a different GitHub instance, use githubBase (defaults to "github.com").

fetchFromGitHub uses fetchzip to download the source archive generated by GitHub for the specified revision. If leaveDotGit, deepClone or fetchSubmodules are set to true, fetchFromGitHub will use fetchgit instead. Refer to its section for documentation of these options.

fetchFromGitLab

This is used with GitLab repositories. It behaves similarly to fetchFromGitHub, and expects owner, repo, rev, and hash.

To use a specific GitLab instance, use domain (defaults to "gitlab.com").

fetchFromGitiles

This is used with Gitiles repositories. The arguments expected are similar to fetchgit.

fetchFromBitbucket

This is used with BitBucket repositories. The arguments expected are very similar to fetchFromGitHub above.

fetchFromSavannah

This is used with Savannah repositories. The arguments expected are very similar to fetchFromGitHub above.

fetchFromRepoOrCz

This is used with repo.or.cz repositories. The arguments expected are very similar to fetchFromGitHub above.

fetchFromSourcehut

This is used with sourcehut repositories. Similar to fetchFromGitHub above, it expects owner, repo, rev and hash, but don't forget the tilde (~) in front of the username! Expected arguments also include vc ("git" (default) or "hg"), domain and fetchSubmodules.

If fetchSubmodules is true, fetchFromSourcehut uses fetchgit or fetchhg with fetchSubmodules or fetchSubrepos set to true, respectively. Otherwise, the fetcher uses fetchzip.

requireFile

requireFile allows requesting files that cannot be fetched automatically, but whose content is known. This is a useful last-resort workaround for license restrictions that prohibit redistribution, or for downloads that are only accessible after authenticating interactively in a browser. If the requested file is present in the Nix store, the resulting derivation will not be built, because its expected output is already available. Otherwise, the builder will run, but fail with a message explaining to the user how to provide the file. The following code, for example:

requireFile {
  name = "jdk-${version}_linux-x64_bin.tar.gz";
  url = "https://www.oracle.com/java/technologies/javase-jdk11-downloads.html";
  hash = "sha256-lL00+F7jjT71nlKJ7HRQuUQ7kkxVYlZh//5msD8sjeI=";
}

results in this error message:

***
Unfortunately, we cannot download file jdk-11.0.10_linux-x64_bin.tar.gz automatically.
Please go to https://www.oracle.com/java/technologies/javase-jdk11-downloads.html to download it yourself, and add it to the Nix store
using either
  nix-store --add-fixed sha256 jdk-11.0.10_linux-x64_bin.tar.gz
or
  nix-prefetch-url --type sha256 file:///path/to/jdk-11.0.10_linux-x64_bin.tar.gz

***

This function should only be used by non-redistributable software with an unfree license that we need to require the user to download manually. It produces packages that cannot be built automatically.

fetchtorrent

fetchtorrent expects two arguments. url which can either be a Magnet URI (Magnet Link) such as magnet:?xt=urn:btih:dd8255ecdc7ca55fb0bbf81323d87062db1f6d1c or an HTTP URL pointing to a .torrent file. It can also take a config argument which will craft a settings.json configuration file and give it to transmission, the underlying program that is performing the fetch. The available config options for transmission can be found here

{ fetchtorrent }:

fetchtorrent {
  config = { peer-limit-global = 100; };
  url = "magnet:?xt=urn:btih:dd8255ecdc7ca55fb0bbf81323d87062db1f6d1c";
  sha256 = "";
}

Parameters

• url: Magnet URI (Magnet Link) such as magnet:?xt=urn:btih:dd8255ecdc7ca55fb0bbf81323d87062db1f6d1c or an HTTP URL pointing to a .torrent file.

• backend: Which bittorrent program to use. Default: "transmission". Valid values are "rqbit" or "transmission". These are the two most suitable torrent clients for fetching in a fixed-output derivation at the time of writing, as they can be easily exited after usage. rqbit is written in Rust and has a smaller closure size than transmission, and the performance and peer discovery properties differs between these clients, requiring experimentation to decide upon which is the best.

• config: When using transmission as the backend, a json configuration can be supplied to transmission. Refer to the upstream documentation for information on how to configure.