Cache path info lookups in SQLite

This re-implements the binary cache database in C++, allowing it to be
used by other Store backends, in particular the S3 backend.

src/libutil/hash.cc

@@ -33,7 +33,7 @@ Hash::Hash(HashType type)
     else if (type == htSHA1) hashSize = sha1HashSize;
     else if (type == htSHA256) hashSize = sha256HashSize;
     else if (type == htSHA512) hashSize = sha512HashSize;
-    else throw Error("unknown hash type");
+    else abort();
     assert(hashSize <= maxHashSize);
     memset(hash, 0, maxHashSize);
 }
@@ -64,6 +64,12 @@ bool Hash::operator < (const Hash & h) const
 }
 
 
+std::string Hash::to_string(bool base32) const
+{
+    return printHashType(type) + ":" + (base32 ? printHash32(*this) : printHash(*this));
+}
+
+
 const string base16Chars = "0123456789abcdef";
 
 
@@ -78,15 +84,28 @@ string printHash(const Hash & hash)
 }
 
 
+Hash parseHash(const string & s)
+{
+    string::size_type colon = s.find(':');
+    if (colon == string::npos)
+        throw BadHash(format("invalid hash ‘%s’") % s);
+    string hts = string(s, 0, colon);
+    HashType ht = parseHashType(hts);
+    if (ht == htUnknown)
+        throw BadHash(format("unknown hash type ‘%s’") % hts);
+    return parseHash16or32(ht, string(s, colon + 1));
+}
+
+
 Hash parseHash(HashType ht, const string & s)
 {
     Hash hash(ht);
     if (s.length() != hash.hashSize * 2)
-        throw Error(format("invalid hash ‘%1%’") % s);
+        throw BadHash(format("invalid hash ‘%1%’") % s);
     for (unsigned int i = 0; i < hash.hashSize; i++) {
         string s2(s, i * 2, 2);
         if (!isxdigit(s2[0]) || !isxdigit(s2[1]))
-            throw Error(format("invalid hash ‘%1%’") % s);
+            throw BadHash(format("invalid hash ‘%1%’") % s);
         std::istringstream str(s2);
         int n;
         str >> std::hex >> n;
@@ -103,6 +122,7 @@ const string base32Chars = "0123456789abcdfghijklmnpqrsvwxyz";
 string printHash32(const Hash & hash)
 {
     size_t len = hash.base32Len();
+    assert(len);
 
     string s;
     s.reserve(len);
@@ -139,7 +159,7 @@ Hash parseHash32(HashType ht, const string & s)
         for (digit = 0; digit < base32Chars.size(); ++digit) /* !!! slow */
             if (base32Chars[digit] == c) break;
         if (digit >= 32)
-            throw Error(format("invalid base-32 hash ‘%1%’") % s);
+            throw BadHash(format("invalid base-32 hash ‘%1%’") % s);
         unsigned int b = n * 5;
         unsigned int i = b / 8;
         unsigned int j = b % 8;
@@ -161,7 +181,7 @@ Hash parseHash16or32(HashType ht, const string & s)
         /* base-32 representation */
         hash = parseHash32(ht, s);
     else
-        throw Error(format("hash ‘%1%’ has wrong length for hash type ‘%2%’")
+        throw BadHash(format("hash ‘%1%’ has wrong length for hash type ‘%2%’")
             % s % printHashType(ht));
     return hash;
 }
@@ -322,7 +342,7 @@ string printHashType(HashType ht)
     else if (ht == htSHA1) return "sha1";
     else if (ht == htSHA256) return "sha256";
     else if (ht == htSHA512) return "sha512";
-    else throw Error("cannot print unknown hash type");
+    else abort();
 }
 
 

src/libutil/hash.hh

@@ -7,6 +7,9 @@
 namespace nix {
 
 
+MakeError(BadHash, Error);
+
+
 enum HashType : char { htUnknown, htMD5, htSHA1, htSHA256, htSHA512 };
 
 
@@ -26,12 +29,15 @@ struct Hash
 
     HashType type;
 
-    /* Create an unusable hash object. */
+    /* Create an unset hash object. */
     Hash();
 
     /* Create a zero-filled hash object. */
     Hash(HashType type);
 
+    /* Check whether a hash is set. */
+    operator bool () const { return type != htUnknown; }
+
     /* Check whether two hash are equal. */
     bool operator == (const Hash & h2) const;
 
@@ -52,12 +58,16 @@ struct Hash
     {
         return (hashSize * 8 - 1) / 5 + 1;
     }
+
+    std::string to_string(bool base32 = true) const;
 };
 
 
 /* Convert a hash to a hexadecimal representation. */
 string printHash(const Hash & hash);
 
+Hash parseHash(const string & s);
+
 /* Parse a hexadecimal representation of a hash code. */
 Hash parseHash(HashType ht, const string & s);
 

src/libutil/util.cc

@@ -403,6 +403,18 @@ Path createTempDir(const Path & tmpRoot, const Path & prefix,
 }
 
 
+Path getCacheDir()
+{
+    Path cacheDir = getEnv("XDG_CACHE_HOME");
+    if (cacheDir.empty()) {
+        Path homeDir = getEnv("HOME");
+        if (homeDir.empty()) throw Error("$XDG_CACHE_HOME and $HOME are not set");
+        cacheDir = homeDir + "/.cache";
+    }
+    return cacheDir;
+}
+
+
 Paths createDirs(const Path & path)
 {
     Paths created;

src/libutil/util.hh

@@ -102,6 +102,9 @@ void deletePath(const Path & path, unsigned long long & bytesFreed);
 Path createTempDir(const Path & tmpRoot = "", const Path & prefix = "nix",
     bool includePid = true, bool useGlobalCounter = true, mode_t mode = 0755);
 
+/* Return the path to $XDG_CACHE_HOME/.cache. */
+Path getCacheDir();
+
 /* Create a directory and all its parents, if necessary.  Returns the
    list of created directories, in order of creation. */
 Paths createDirs(const Path & path);