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Guillaume Bouchard 5a34a473dd builtins.readFile: do not truncate content
This closes #3026 by allowing `builtins.readFile` to read a file with a
wrongly reported file size, for example, files in `/proc` may report a
file size of 0. Reading file in `/proc` is not a good enough motivation,
however I do think it just makes nix more robust by allowing more file
to be read.  Especially, I do considerer the previous behavior to be
dangerous because nix was previously reading truncated files. Examples
of file system which incorrectly report file size may be network file
system or dynamic file system (for performance reason, a dynamic file
system such as FUSE may generate the content of the file on demand).

```
nix-repl> builtins.readFile "/proc/version"
""
```

With this commit:

```
nix-repl> builtins.readFile "/proc/version"
"Linux version 5.6.7 (nixbld@localhost) (gcc version 9.3.0 (GCC)) #1-NixOS SMP Thu Apr 23 08:38:27 UTC 2020\n"
```

Here is a summary of the behavior changes:

- If the reported size is smaller, previous implementation
was silently returning a truncated file content. The new implementation
is returning the correct file content.

- If a file had a bigger reported file size, previous implementation was
failing with an exception, but the new implementation is returning the
correct file content. This change of behavior is coherent with this pull
request.

Open questions

- The behavior is unchanged for correctly reported file size, however
performances may vary because it uses the more complex sink interface.
Considering that sink is used a lot, I don't think this impacts the
performance a lot.
- `builtins.readFile` on an infinite file, such as `/dev/random` may
fill the memory.
- it does not support adding file to store, such as `${/proc/version}`.
2020-04-29 14:50:52 +02:00
.github Remove build and binaryTarball since they're included in installerScript 2020-03-13 15:56:25 +01:00
config update config/config.{sub,guess} 2018-08-13 20:00:17 +00:00
contrib function-trace: always show the trace 2019-09-18 23:23:21 +02:00
corepkgs Move some corepkgs into the nix binary 2020-03-11 16:57:48 +01:00
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m4 autoconf: Fix C++17 detection not working on Ubuntu 16.04. 2019-07-03 04:32:25 +02:00
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perl nix-perl: Fix segfault in queryPathInfo) 2020-03-10 11:00:17 +01:00
scripts installer: Fix terminal colors. 2020-03-24 21:15:01 -07:00
src builtins.readFile: do not truncate content 2020-04-29 14:50:52 +02:00
tests Merge pull request #3458 from zimbatm/nix-user-conf-dir 2020-04-15 13:00:28 +02:00
.dir-locals.el .dir-locals.el: Set additional lambda indentation to zero 2020-02-20 07:56:35 +01:00
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Makefile.config.in Misc changes from the flakes branch 2020-03-24 14:34:47 +01:00
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Nix, the purely functional package manager

Nix is a new take on package management that is fairly unique. Because of its purity aspects, a lot of issues found in traditional package managers don't appear with Nix.

To find out more about the tool, usage and installation instructions, please read the manual, which is available on the Nix website at https://nixos.org/nix/manual.

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Take a look at the Hacking Section of the manual. It helps you to get started with building Nix from source.

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