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Make <nix/fetchurl.nix> run in constant memory

Browse source 
E.g.

  nix-build --store ~/my-nix/ -E 'import <nix/fetchurl.nix> { url = https://cache.nixos.org/nar/0nwi996rgq4b914qyx0mv2wq4k80hjac7xilikavagw7kxmn2iiv.nar.xz; sha256 = "0nwi996rgq4b914qyx0mv2wq4k80hjac7xilikavagw7kxmn2iiv"; }'

now runs in 17 MiB (was 70 MiB), while

  nix-build --store ~/my-nix/ -E 'import <nix/fetchurl.nix> { url = https://cache.nixos.org/nar/0nwi996rgq4b914qyx0mv2wq4k80hjac7xilikavagw7kxmn2iiv.nar.xz; sha256 = "0d2fxljdih3nc5dqx41hjzic3141ajil94m8kdbpryq569dpsbvb"; unpack = true; }'

runs in 17 MiB (was 346 MiB).
This commit is contained in:
Eelco Dolstra 2018-03-28 13:32:44 +02:00
parent 5a654fd7dd
commit 7d21863bb3
No known key found for this signature in database
GPG key ID: 8170B4726D7198DE
3 changed files with 60 additions and 33 deletions
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17
src/libutil/util.cc
View file

@ -328,6 +328,23 @@ void writeFile(const Path & path, const string & s, mode_t mode)
}
void writeFile(const Path & path, Source & source, mode_t mode)
{
AutoCloseFD fd = open(path.c_str(), O_WRONLY | O_TRUNC | O_CREAT | O_CLOEXEC, mode);
if (!fd)
throw SysError(format("opening file '%1%'") % path);
std::vector<unsigned char> buf(64 * 1024);
while (true) {
try {
auto n = source.read(buf.data(), buf.size());
writeFull(fd.get(), (unsigned char *) buf.data(), n);
} catch (EndOfFile &) { break; }
}
}
string readLine(int fd)
{
string s;