* Start move towards SHA-256 hashes instead of MD5.

* Start cleaning up unique store path generation (they weren't always
  unique; in particular the suffix ("-aterm-2.2", "-builder.sh") was
  not part of the hash, therefore changes to the suffix would cause
  multiple store objects with the same hash).

src/libstore/normalise.cc

@@ -1137,7 +1137,7 @@ void NormalisationGoal::createClosure()
     /* Write the normal form.  This does not have to occur in the
        transaction below because writing terms is idem-potent. */
     ATerm nfTerm = unparseStoreExpr(nf);
-    Path nfPath = writeTerm(nfTerm, "-s");
+    Path nfPath = writeTerm(nfTerm, "s");
 
     /* Register each output path, and register the normal form.  This
        is wrapped in one database transaction to ensure that if we

src/libstore/store.cc

@@ -411,19 +411,34 @@ static void invalidatePath(const Path & path, Transaction & txn)
 }
 
 
+Path makeStorePath(const string & type,
+    Hash & hash, const string & suffix)
+{
+    /* e.g., "source:sha256:1abc...:/nix/store:foo.tar.gz" */
+    string s = type + ":sha256:" + (string) hash + ":"
+        + nixStore + ":" + suffix;
+
+    Hash nameHash = hashString(s, htSHA256);
+
+    printMsg(lvlError, format("name input: %1% -> %2%") % s % (string) nameHash);
+
+    return nixStore + "/" + (string) nameHash + "-" + suffix;
+}
+
+
 Path addToStore(const Path & _srcPath)
 {
     Path srcPath(absPath(_srcPath));
     debug(format("adding `%1%' to the store") % srcPath);
 
-    Hash h(htMD5);
+    Hash h(htSHA256);
     {
         SwitchToOriginalUser sw;
-        h = hashPath(srcPath, htMD5);
+        h = hashPath(srcPath, htSHA256);
     }
 
     string baseName = baseNameOf(srcPath);
-    Path dstPath = canonPath(nixStore + "/" + (string) h + "-" + baseName);
+    Path dstPath = makeStorePath("source", h, baseName);
 
     if (!readOnlyMode && !isValidPath(dstPath)) { 
 
@@ -443,6 +458,11 @@ Path addToStore(const Path & _srcPath)
             
             copyPath(srcPath, dstPath);
 
+            Hash h2 = hashPath(dstPath, htSHA256);
+            if (h != h2)
+                throw Error(format("contents of `%1%' changed while copying it to `%2%' (%3% -> %4%)")
+                    % srcPath % dstPath % (string) h % (string) h2);
+
             makePathReadOnly(dstPath);
             
             Transaction txn(nixDB);
@@ -457,11 +477,13 @@ Path addToStore(const Path & _srcPath)
 }
 
 
-void addTextToStore(const Path & dstPath, const string & s)
+Path addTextToStore(const string & suffix, const string & s)
 {
-    assertStorePath(dstPath);
+    Hash hash = hashString(s, htSHA256);
+
+    Path dstPath = makeStorePath("text", hash, suffix);
     
-    if (!isValidPath(dstPath)) {
+    if (!readOnlyMode && !isValidPath(dstPath)) {
 
         PathSet lockPaths;
         lockPaths.insert(dstPath);
@@ -482,6 +504,8 @@ void addTextToStore(const Path & dstPath, const string & s)
 
         outputLock.setDeletion(true);
     }
+
+    return dstPath;
 }
 
 

src/libstore/store.hh

@@ -81,14 +81,17 @@ void assertStorePath(const Path & path);
 /* Checks whether a path is valid. */ 
 bool isValidPath(const Path & path);
 
+/* Constructs a unique store path name. */
+Path makeStorePath(const string & type,
+    Hash & hash, const string & suffix);
+    
 /* Copy the contents of a path to the store and register the validity
    the resulting path.  The resulting path is returned. */
 Path addToStore(const Path & srcPath);
 
-/* Like addToStore, but the path of the output is given, and the
-   contents written to the output path is a regular file containing
-   the given string. */
-void addTextToStore(const Path & dstPath, const string & s);
+/* Like addToStore, but the contents written to the output path is a
+   regular file containing the given string. */
+Path addTextToStore(const string & suffix, const string & s);
 
 /* Delete a value from the nixStore directory. */
 void deleteFromStore(const Path & path);

src/libstore/storeexpr.cc

@@ -14,19 +14,9 @@ Hash hashTerm(ATerm t)
 
 Path writeTerm(ATerm t, const string & suffix)
 {
-    /* The id of a term is its hash. */
-    Hash h = hashTerm(t);
-
-    Path path = canonPath(nixStore + "/" + 
-        (string) h + suffix + ".store");
-
-    if (!readOnlyMode && !isValidPath(path)) {
-        char * s = ATwriteToString(t);
-        if (!s) throw Error(format("cannot write aterm to `%1%'") % path);
-        addTextToStore(path, string(s));
-    }
-    
-    return path;
+    char * s = ATwriteToString(t);
+    if (!s) throw Error("cannot print aterm");
+    return addTextToStore(suffix + ".store", string(s));
 }