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fetchers: document requireFile

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Linus Heckemann 2023-02-05 15:33:51 +01:00
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27
doc/builders/fetchers.chapter.md
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@ -163,3 +163,30 @@ 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}
`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";
sha256 = "94bd34f85ee38d3ef59e5289ec7450b9443b924c55625661fffe66b03f2c8de2";
}
```
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
***
```