2 files changed, 37 insertions, 10 deletions
diff --git a/src/libutil/util.cc b/src/libutil/util.cc
index be0a9bf317d1..5cda9a0677b5 100644
--- a/src/libutil/util.cc
+++ b/src/libutil/util.cc
@@ -413,6 +413,17 @@ void createSymlink(const Path & target, const Path & link)
 }
 
 
+void replaceSymlink(const Path & target, const Path & link)
+{
+    Path tmp = canonPath(dirOf(link) + "/.new_" + baseNameOf(link));
+
+    createSymlink(target, tmp);
+
+    if (rename(tmp.c_str(), link.c_str()) != 0)
+        throw SysError(format("renaming ‘%1%’ to ‘%2%’") % tmp % link);
+}
+
+
 LogType logType = ltPretty;
 Verbosity verbosity = lvlInfo;
 
@@ -931,16 +942,16 @@ string runProgram(Path program, bool searchPath, const Strings & args,
     checkInterrupt();
 
     /* Create a pipe. */
-    Pipe stdout, stdin;
-    stdout.create();
-    if (!input.empty()) stdin.create();
+    Pipe out, in;
+    out.create();
+    if (!input.empty()) in.create();
 
     /* Fork. */
     Pid pid = startProcess([&]() {
-        if (dup2(stdout.writeSide, STDOUT_FILENO) == -1)
+        if (dup2(out.writeSide, STDOUT_FILENO) == -1)
             throw SysError("dupping stdout");
         if (!input.empty()) {
-            if (dup2(stdin.readSide, STDIN_FILENO) == -1)
+            if (dup2(in.readSide, STDIN_FILENO) == -1)
                 throw SysError("dupping stdin");
         }
 
@@ -956,16 +967,16 @@ string runProgram(Path program, bool searchPath, const Strings & args,
         throw SysError(format("executing ‘%1%’") % program);
     });
 
-    stdout.writeSide.close();
+    out.writeSide.close();
 
     /* FIXME: This can deadlock if the input is too long. */
     if (!input.empty()) {
-        stdin.readSide.close();
-        writeFull(stdin.writeSide, input);
-        stdin.writeSide.close();
+        in.readSide.close();
+        writeFull(in.writeSide, input);
+        in.writeSide.close();
     }
 
-    string result = drainFD(stdout.readSide);
+    string result = drainFD(out.readSide);
 
     /* Wait for the child to finish. */
     int status = pid.wait(true);
@@ -1076,6 +1087,15 @@ string chomp(const string & s)
 }
 
 
+string trim(const string & s, const string & whitespace)
+{
+    auto i = s.find_first_not_of(whitespace);
+    if (i == string::npos) return "";
+    auto j = s.find_last_not_of(whitespace);
+    return string(s, i, j == string::npos ? j : j - i + 1);
+}
+
+
 string statusToString(int status)
 {
     if (!WIFEXITED(status) || WEXITSTATUS(status) != 0) {
diff --git a/src/libutil/util.hh b/src/libutil/util.hh
index 20330fb7699e..7d20351eec2e 100644
--- a/src/libutil/util.hh
+++ b/src/libutil/util.hh
@@ -110,6 +110,9 @@ Paths createDirs(const Path & path);
 /* Create a symlink. */
 void createSymlink(const Path & target, const Path & link);
 
+/* Atomically create or replace a symlink. */
+void replaceSymlink(const Path & target, const Path & link);
+
 
 template<class T, class A>
 T singleton(const A & a)
@@ -334,6 +337,10 @@ string concatStringsSep(const string & sep, const StringSet & ss);
 string chomp(const string & s);
 
 
+/* Remove whitespace from the start and end of a string. */
+string trim(const string & s, const string & whitespace = " \n\r\t");
+
+
 /* Convert the exit status of a child as returned by wait() into an
    error string. */
 string statusToString(int status);