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authorEelco Dolstra <edolstra@gmail.com>2018-03-28T11·32+0200
committerEelco Dolstra <edolstra@gmail.com>2018-05-30T11·42+0200
commit7d21863bb3f3d4c42b273a8648a65bec83fe0b60 (patch)
tree252f7d24ef82026ed3ce9c8318c5f1287374581f /src/libutil
parent5a654fd7dd0bf58470e0a15d451cf36ce0c62beb (diff)
Make <nix/fetchurl.nix> run in constant memory
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).
Diffstat (limited to 'src/libutil')
-rw-r--r--src/libutil/util.cc17
-rw-r--r--src/libutil/util.hh2
2 files changed, 19 insertions, 0 deletions
diff --git a/src/libutil/util.cc b/src/libutil/util.cc
index 22753f4b7eca..6bc64ae75a42 100644
--- a/src/libutil/util.cc
+++ b/src/libutil/util.cc
@@ -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;
diff --git a/src/libutil/util.hh b/src/libutil/util.hh
index af97b76d90bc..fc25d27758c7 100644
--- a/src/libutil/util.hh
+++ b/src/libutil/util.hh
@@ -103,6 +103,8 @@ void readFile(const Path & path, Sink & sink);
 /* Write a string to a file. */
 void writeFile(const Path & path, const string & s, mode_t mode = 0666);
 
+void writeFile(const Path & path, Source & source, mode_t mode = 0666);
+
 /* Read a line from a file descriptor. */
 string readLine(int fd);