* Some refactoring.

src/util.cc

@@ -0,0 +1,94 @@
+#include "util.hh"
+
+
+string thisSystem = SYSTEM;
+string nixHomeDir = "/nix";
+string nixHomeDirEnvVar = "NIX";
+
+
+
+string absPath(string filename, string dir)
+{
+    if (filename[0] != '/') {
+        if (dir == "") {
+            char buf[PATH_MAX];
+            if (!getcwd(buf, sizeof(buf)))
+                throw Error("cannot get cwd");
+            dir = buf;
+        }
+        filename = dir + "/" + filename;
+        /* !!! canonicalise */
+        char resolved[PATH_MAX];
+        if (!realpath(filename.c_str(), resolved))
+            throw Error("cannot canonicalise path " + filename);
+        filename = resolved;
+    }
+    return filename;
+}
+
+
+static string printHash(unsigned char * buf)
+{
+    ostringstream str;
+    for (int i = 0; i < 16; i++) {
+        str.fill('0');
+        str.width(2);
+        str << hex << (int) buf[i];
+    }
+    return str.str();
+}
+
+    
+/* Verify that a reference is valid (that is, is a MD5 hash code). */
+bool isHash(const string & s)
+{
+    if (s.length() != 32) return false;
+    for (int i = 0; i < 32; i++) {
+        char c = s[i];
+        if (!((c >= '0' && c <= '9') ||
+              (c >= 'a' && c <= 'f')))
+            return false;
+    }
+    return true;
+}
+
+
+void checkHash(const string & s)
+{
+    if (!isHash(s)) throw BadRefError("invalid reference: " + s);
+}
+
+
+/* Compute the MD5 hash of a file. */
+string hashFile(string filename)
+{
+    unsigned char hash[16];
+    FILE * file = fopen(filename.c_str(), "rb");
+    if (!file)
+        throw BadRefError("file `" + filename + "' does not exist");
+    int err = md5_stream(file, hash);
+    fclose(file);
+    if (err) throw BadRefError("cannot hash file");
+    return printHash(hash);
+}
+
+
+
+/* Return the directory part of the given path, i.e., everything
+   before the final `/'. */
+string dirOf(string s)
+{
+    unsigned int pos = s.rfind('/');
+    if (pos == string::npos) throw Error("invalid file name");
+    return string(s, 0, pos);
+}
+
+
+/* Return the base name of the given path, i.e., everything following
+   the final `/'. */
+string baseNameOf(string s)
+{
+    unsigned int pos = s.rfind('/');
+    if (pos == string::npos) throw Error("invalid file name");
+    return string(s, pos + 1);
+}