···

       
3
       
3
       
 
       
Building software with Nix often requires downloading source code and other files from the internet.

     

       
4
       
4
       
 
       
To this end, we use functions that we call _fetchers_, which obtain remote sources via various protocols and services.

     

       
5
       
5
       
 
       


     

       
6
       
6
       
-
       
Nix provides built-in fetchers such as [`builtins.fetchTarball`](https://nixos.org/manual/nix/stable/language/builtins.html#builtins-fetchTarball).

     

       
6
       
6
       
+
       
Nix provides built-in fetchers such as [`fetchTarball`](https://nixos.org/manual/nix/stable/language/builtins.html#builtins-fetchTarball).

     

       
7
       
7
       
 
       
Nixpkgs provides its own fetchers, which work differently:

     

       
8
       
8
       
 
       


     

       
9
       
9
       
 
       
- A built-in fetcher will download and cache files at evaluation time and produce a [store path](https://nixos.org/manual/nix/stable/glossary#gloss-store-path).

     

···

       
163
       
163
       
 
       
They are useful for creating files from Nix expression, and are all implemented as convenience wrappers around `writeTextFile`.

     

       
164
       
164
       
 
       


     

       
165
       
165
       
 
       
Each of these functions will cause a derivation to be produced.

     

       
166
       
166
       
-
       
When you coerce the result of each of these functions to a string with [string interpolation](https://nixos.org/manual/nix/stable/language/string-interpolation) or [`builtins.toString`](https://nixos.org/manual/nix/stable/language/builtins#builtins-toString), it will evaluate to the [store path](https://nixos.org/manual/nix/stable/store/store-path) of this derivation.

     

       
166
       
166
       
+
       
When you coerce the result of each of these functions to a string with [string interpolation](https://nixos.org/manual/nix/stable/language/string-interpolation) or [`toString`](https://nixos.org/manual/nix/stable/language/builtins#builtins-toString), it will evaluate to the [store path](https://nixos.org/manual/nix/stable/store/store-path) of this derivation.

     

       
167
       
167
       
 
       


     

       
168
       
168
       
 
       
:::: {.note}

     

       
169
       
169
       
 
       
Some of these functions will put the resulting files within a directory inside the [derivation output](https://nixos.org/manual/nix/stable/language/derivations#attr-outputs).

     
···

       
344
       
344
       
 
       
`allowSubstitutes` (Bool, _optional_)

     

       
345
       
345
       
 
       


     

       
346
       
346
       
 
       
: Whether to allow substituting from a binary cache.

     

       
347
       
347
       
-
       
  Passed through to [`allowSubstitutes`](https://nixos.org/manual/nix/stable/language/advanced-attributes#adv-attr-allowSubstitutes) of the underlying call to `builtins.derivation`.

     

       
347
       
347
       
+
       
  Passed through to [`allowSubstitutes`](https://nixos.org/manual/nix/stable/language/advanced-attributes#adv-attr-allowSubstitutes) of the underlying call to `derivation`.

     

       
348
       
348
       
 
       


     

       
349
       
349
       
 
       
  It defaults to `false`, as running the derivation's simple `builder` executable locally is assumed to be faster than network operations.

     

       
350
       
350
       
 
       
  Set it to true if the `checkPhase` step is expensive.

     
···

       
355
       
355
       
 
       


     

       
356
       
356
       
 
       
: Whether to prefer building locally, even if faster [remote build machines](https://nixos.org/manual/nix/stable/command-ref/conf-file#conf-substituters) are available.

     

       
357
       
357
       
 
       


     

       
358
       
358
       
-
       
  Passed through to [`preferLocalBuild`](https://nixos.org/manual/nix/stable/language/advanced-attributes#adv-attr-preferLocalBuild) of the underlying call to `builtins.derivation`.

     

       
358
       
358
       
+
       
  Passed through to [`preferLocalBuild`](https://nixos.org/manual/nix/stable/language/advanced-attributes#adv-attr-preferLocalBuild) of the underlying call to `derivation`.

     

       
359
       
359
       
 
       


     

       
360
       
360
       
 
       
  It defaults to `true` for the same reason `allowSubstitutes` defaults to `false`.

     

       
361
       
361
       
 
       


     

···

       
24
       
24
       
 
       


     

       
25
       
25
       
 
       
  libset =

     

       
26
       
26
       
 
       
    toplib:

     

       
27
       
27
       
-
       
    builtins.map (subsetname: {

     

       
27
       
27
       
+
       
    map (subsetname: {

     

       
28
       
28
       
 
       
      subsetname = subsetname;

     

       
29
       
29
       
 
       
      functions = libDefPos [ ] toplib.${subsetname};

     

       
30
       
30
       
-
       
    }) (builtins.map (x: x.name) libsets);

     

       
30
       
30
       
+
       
    }) (map (x: x.name) libsets);

     

       
31
       
31
       
 
       


     

       
32
       
32
       
 
       
  flattenedLibSubset =

     

       
33
       
33
       
 
       
    { subsetname, functions }:

     

       
34
       
34
       
-
       
    builtins.map (fn: {

     

       
34
       
34
       
+
       
    map (fn: {

     

       
35
       
35
       
 
       
      name = "lib.${subsetname}.${fn.name}";

     

       
36
       
36
       
 
       
      value = fn.location;

     

       
37
       
37
       
 
       
    }) functions;

     

       
38
       
38
       
 
       


     

       
39
       
39
       
-
       
  locatedlibsets = libs: builtins.map flattenedLibSubset (libset libs);

     

       
39
       
39
       
+
       
  locatedlibsets = libs: map flattenedLibSubset (libset libs);

     

       
40
       
40
       
 
       
  removeFilenamePrefix =

     

       
41
       
41
       
 
       
    prefix: filename:

     

       
42
       
42
       
 
       
    let

     
···

       
46
       
46
       
 
       
    in

     

       
47
       
47
       
 
       
    substr;

     

       
48
       
48
       
 
       


     

       
49
       
49
       
-
       
  removeNixpkgs = removeFilenamePrefix (builtins.toString nixpkgsPath);

     

       
49
       
49
       
+
       
  removeNixpkgs = removeFilenamePrefix (toString nixpkgsPath);

     

       
50
       
50
       
 
       


     

       
51
       
51
       
 
       
  liblocations = builtins.filter (elem: elem.value != null) (lib.lists.flatten (locatedlibsets lib));

     

       
52
       
52
       
 
       


     
···

       
59
       
59
       
 
       
      };

     

       
60
       
60
       
 
       
    };

     

       
61
       
61
       
 
       


     

       
62
       
62
       
-
       
  relativeLocs = (builtins.map fnLocationRelative liblocations);

     

       
62
       
62
       
+
       
  relativeLocs = (map fnLocationRelative liblocations);

     

       
63
       
63
       
 
       
  sanitizeId = builtins.replaceStrings [ "'" ] [ "-prime" ];

     

       
64
       
64
       
 
       


     

       
65
       
65
       
 
       
  urlPrefix = "https://github.com/NixOS/nixpkgs/blob/${revision}";

     

       
66
       
66
       
 
       
  jsonLocs = builtins.listToAttrs (

     

       
67
       
67
       
-
       
    builtins.map (

     

       
67
       
67
       
+
       
    map (

     

       
68
       
68
       
 
       
      { name, value }:

     

       
69
       
69
       
 
       
      {

     

       
70
       
70
       
 
       
        name = sanitizeId name;

     

       
71
       
71
       
 
       
        value =

     

       
72
       
72
       
 
       
          let

     

       
73
       
73
       
-
       
            text = "${value.file}:${builtins.toString value.line}";

     

       
74
       
74
       
-
       
            target = "${urlPrefix}/${value.file}#L${builtins.toString value.line}";

     

       
73
       
73
       
+
       
            text = "${value.file}:${toString value.line}";

     

       
74
       
74
       
+
       
            target = "${urlPrefix}/${value.file}#L${toString value.line}";

     

       
75
       
75
       
 
       
          in

     

       
76
       
76
       
 
       
          "[${text}](${target}) in `<nixpkgs>`";

     

       
77
       
77
       
 
       
      }

     

···

       
89
       
89
       
 
       
# ./example.nix

     

       
90
       
90
       
 
       


     

       
91
       
91
       
 
       
let

     

       
92
       
92
       
-
       
  nixpkgs = builtins.fetchTarball {

     

       
92
       
92
       
+
       
  nixpkgs = fetchTarball {

     

       
93
       
93
       
 
       
    url = "https://github.com/NixOS/nixpkgs/archive/94b2848559b12a8ed1fe433084686b2a81123c99.tar.gz";

     

       
94
       
94
       
 
       
    hash = "sha256-B4Q3c6IvTLg3Q92qYa8y+i4uTaphtFdjp+Ir3QQjdN0=";

     

       
95
       
95
       
 
       
  };

     

···

       
316
       
316
       
 
       
`importNpmLock` uses the following fetchers:

     

       
317
       
317
       
 
       


     

       
318
       
318
       
 
       
- `pkgs.fetchurl` for `http(s)` dependencies

     

       
319
       
319
       
-
       
- `builtins.fetchGit` for `git` dependencies

     

       
319
       
319
       
+
       
- `fetchGit` for `git` dependencies

     

       
320
       
320
       
 
       


     

       
321
       
321
       
 
       
It is possible to provide additional arguments to individual fetchers as needed:

     

       
322
       
322
       
 
       


     

···

       
374
       
374
       
 
       
  pname = "maven-demo";

     

       
375
       
375
       
 
       
  version = "1.0";

     

       
376
       
376
       
 
       


     

       
377
       
377
       
-
       
  src = builtins.fetchTarball "https://github.com/fzakaria/nixos-maven-example/archive/main.tar.gz";

     

       
377
       
377
       
+
       
  src = fetchTarball "https://github.com/fzakaria/nixos-maven-example/archive/main.tar.gz";

     

       
378
       
378
       
 
       
  buildInputs = [ maven ];

     

       
379
       
379
       
 
       


     

       
380
       
380
       
 
       
  buildPhase = ''

     
···

       
445
       
445
       
 
       
  pname = "maven-demo";

     

       
446
       
446
       
 
       
  version = "1.0";

     

       
447
       
447
       
 
       


     

       
448
       
448
       
-
       
  src = builtins.fetchTarball "https://github.com/fzakaria/nixos-maven-example/archive/main.tar.gz";

     

       
448
       
448
       
+
       
  src = fetchTarball "https://github.com/fzakaria/nixos-maven-example/archive/main.tar.gz";

     

       
449
       
449
       
 
       
  nativeBuildInputs = [ makeWrapper ];

     

       
450
       
450
       
 
       
  buildInputs = [ maven ];

     

       
451
       
451
       
 
       


     
···

       
538
       
538
       
 
       
  pname = "maven-demo";

     

       
539
       
539
       
 
       
  version = "1.0";

     

       
540
       
540
       
 
       


     

       
541
       
541
       
-
       
  src = builtins.fetchTarball "https://github.com/fzakaria/nixos-maven-example/archive/main.tar.gz";

     

       
541
       
541
       
+
       
  src = fetchTarball "https://github.com/fzakaria/nixos-maven-example/archive/main.tar.gz";

     

       
542
       
542
       
 
       
  nativeBuildInputs = [ makeWrapper ];

     

       
543
       
543
       
 
       
  buildInputs = [ maven ];

     

       
544
       
544