ostree-repo-resolve-rev: Add function to accept a partial checksum

This patch adds a function that will parse a partial checksum when
resolving a refspec.  If the inputted refspec matches a truncated
existing checksum, it will return that checksum to be parsed.  If
multiple truncated checksums match the partial refspec, it is not
unique and will return false.  This addition is inspired by the same
functionality in Docker, which allows a user to reference a specific
commit without typing the entire checksum.

partial checksums: Add function to abstract comparison

This modifies the list_objects and list_objects_at functions
to take an additional argument for the string that a commit starts
with.  If this string arg is not null, it will only list commit
objects beginning with that string.  This allows for a new function
ostree_repo_list_commit_objects_starting_with to pass a partial string
and return a list of all matching commits.  This improves on the
previous strategy of listing refs because it will list all commit objects,
even ones in past history.  This update also includes bugfixes on
error handling and string comparison, and changes the output structure
of resolve_partial_checksum. The new strcuture will no longer return FALSE
without error.  Also, the hashtable foreach now uses iter.  Also
includes modified test file

src/libostree/ostree-repo-refs.c

@@ -347,6 +347,75 @@ resolve_refspec (OstreeRepo     *self,
   return ret;
 }
 
+/**
+ * ostree_repo_resolve_partial_checksum:
+ * @self: Repo
+ * @refspec: A refspec
+ * @full_checksum (out) (transfer full): A full checksum corresponding to the truncated ref given
+ * @error: Error
+ *
+ * Look up the existing refspec checksums.  If the given ref is a unique truncated beginning
+ * of a valid checksum it will return that checksum in the parameter @full_checksum
+ */
+static gboolean
+ostree_repo_resolve_partial_checksum (OstreeRepo   *self,
+                                      const char   *refspec,
+                                      char        **full_checksum,
+                                      GError      **error)
+{
+  gboolean ret = FALSE;
+  s_unref_hashtable GHashTable *ref_list = NULL;
+  gs_free char *ret_rev = NULL;
+  guint length;
+  const char *checksum = NULL;
+  OstreeObjectType objtype;
+  GHashTableIter hashiter;
+  gpointer key, value;
+  GVariant *first_commit;
+
+  g_return_val_if_fail (error == NULL || *error == NULL, FALSE);
+
+  /* this looks through all objects and adds them to the ref_list if:
+     a) they are a commit object AND
+     b) the obj checksum starts with the partual checksum defined by "refspec" */
+  if (!ostree_repo_list_commit_objects_starting_with (self, refspec, &ref_list, NULL, error))
+    goto out;
+
+  length = g_hash_table_size (ref_list);
+
+  g_hash_table_iter_init (&hashiter, ref_list);
+  if (g_hash_table_iter_next (&hashiter, &key, &value))
+    first_commit = (GVariant*) key;
+  else
+    first_commit = NULL;
+
+  if (first_commit) 
+    ostree_object_name_deserialize (first_commit, &checksum, &objtype);
+
+  /* length more than one - multiple commits match partial refspec: is not unique */
+  if (length > 1)
+    {
+      g_set_error (error, G_IO_ERROR, G_IO_ERROR_FAILED,
+                   "Refspec %s not unique", refspec);
+      goto out;
+    }
+    
+  /* length is 1 - a single matching commit gives us our revision */
+  else if (length == 1)
+    {
+      ret_rev = g_strdup (checksum);
+    }
+
+  /* Note: if length is 0, then code will return TRUE
+     because there is no error, but it will return full_checksum = NULL
+     to signal to continue parsing */
+
+  ret = TRUE;
+  ot_transfer_out_value (full_checksum, &ret_rev);
+ out:
+  return ret;
+}
+
 /**
  * ostree_repo_resolve_rev:
  * @self: Repo
@@ -374,8 +443,15 @@ ostree_repo_resolve_rev (OstreeRepo     *self,
     {
       ret_rev = g_strdup (refspec);
     }
-  else
+
+  else if (!ostree_repo_resolve_partial_checksum (self, refspec, &ret_rev, error))
+    goto out;
+
+  if (!ret_rev)
     {
+      if (error != NULL && *error != NULL)
+        goto out;
+
       if (g_str_has_suffix (refspec, "^"))
         {
           gs_free char *parent_refspec = NULL;

src/libostree/ostree-repo.c

@@ -990,12 +990,14 @@ list_loose_objects_at (OstreeRepo             *self,
                        GHashTable             *inout_objects,
                        const char             *prefix,
                        int                     dfd,
+                       const char             *commit_starting_with,
                        GCancellable           *cancellable,
                        GError                **error)
 {
   gboolean ret = FALSE;
   DIR *d = NULL;
   struct dirent *dent;
+  GVariant *key, *value;
 
   d = fdopendir (dfd);
   if (!d)
@@ -1030,21 +1032,33 @@ list_loose_objects_at (OstreeRepo             *self,
       else
         continue;
 
-      if ((dot - name) == 62)
+      if ((dot - name) != 62)
+        continue;
+
+      memcpy (buf, prefix, 2);
+      memcpy (buf + 2, name, 62);
+      buf[sizeof(buf)-1] = '\0';
+
+      /* if we passed in a "starting with" argument, then
+         we only want to return .commit objects with a checksum
+         that matches the commit_starting_with argument */
+      if (commit_starting_with)
         {
-          GVariant *key, *value;
+          /* object is not a commit, do not add to array */
+          if (objtype != OSTREE_OBJECT_TYPE_COMMIT)
+              continue;
 
-          memcpy (buf, prefix, 2);
+          /* commit checksum does not match "starting with", do not add to array */     
-          memcpy (buf + 2, name, 62);
+          if (!g_str_has_prefix (buf, commit_starting_with))
-          buf[sizeof(buf)-1] = '\0';
+            continue;
-
-          key = ostree_object_name_serialize (buf, objtype);
-          value = g_variant_new ("(b@as)",
-                                 TRUE, g_variant_new_strv (NULL, 0));
-          /* transfer ownership */
-          g_hash_table_replace (inout_objects, key,
-                                g_variant_ref_sink (value));
         }
+
+        key = ostree_object_name_serialize (buf, objtype);
+        value = g_variant_new ("(b@as)",
+                               TRUE, g_variant_new_strv (NULL, 0));
+        /* transfer ownership */
+        g_hash_table_replace (inout_objects, key,
+                              g_variant_ref_sink (value));
     }
 
   ret = TRUE;
@@ -1057,6 +1071,7 @@ list_loose_objects_at (OstreeRepo             *self,
 static gboolean
 list_loose_objects (OstreeRepo                     *self,
                     GHashTable                     *inout_objects,
+                    const char                     *commit_starting_with,
                     GCancellable                   *cancellable,
                     GError                        **error)
 {
@@ -1084,7 +1099,8 @@ list_loose_objects (OstreeRepo                     *self,
         }
       /* Takes ownership of dfd */
       if (!list_loose_objects_at (self, inout_objects, buf, dfd,
-                                  cancellable, error))
+                                       commit_starting_with,
+                                       cancellable, error))
         goto out;
     }
 
@@ -1702,11 +1718,11 @@ ostree_repo_list_objects (OstreeRepo                  *self,
 
   if (flags & OSTREE_REPO_LIST_OBJECTS_LOOSE)
     {
-      if (!list_loose_objects (self, ret_objects, cancellable, error))
+      if (!list_loose_objects (self, ret_objects, NULL, cancellable, error))
         goto out;
       if (self->parent_repo)
         {
-          if (!list_loose_objects (self->parent_repo, ret_objects, cancellable, error))
+          if (!list_loose_objects (self->parent_repo, ret_objects, NULL, cancellable, error))
             goto out;
         }
     }
@@ -1722,6 +1738,53 @@ ostree_repo_list_objects (OstreeRepo                  *self,
   return ret;
 }
 
+/**
+ * ostree_repo_list_commit_objects_starting_with:
+ * @self: Repo
+ * @start: List commits starting with this checksum
+ * @out_commits: Array of GVariants
+ * @cancellable: Cancellable
+ * @error: Error
+ *
+ * This function synchronously enumerates all commit objects starting
+ * with @start, returning data in @out_commits.
+ *
+ * Returns: %TRUE on success, %FALSE on error, and @error will be set
+ */
+gboolean
+ostree_repo_list_commit_objects_starting_with (OstreeRepo                  *self,
+                                               const char                  *start,
+                                               GHashTable                 **out_commits,
+                                               GCancellable                *cancellable,
+                                               GError                     **error)
+{
+  gboolean ret = FALSE;
+  gs_unref_hashtable GHashTable *ret_commits = NULL;
+
+  g_return_val_if_fail (error == NULL || *error == NULL, FALSE);
+  g_return_val_if_fail (self->inited, FALSE);
+
+  ret_commits = g_hash_table_new_full (ostree_hash_object_name, g_variant_equal,
+                                       (GDestroyNotify) g_variant_unref,
+                                       (GDestroyNotify) g_variant_unref);
+
+  if (!list_loose_objects (self, ret_commits, start, cancellable, error))
+        goto out;
+
+
+  if (self->parent_repo)
+    {
+      if (!list_loose_objects (self->parent_repo, ret_commits, start,
+                               cancellable, error))
+        goto out;
+    }
+
+  ret = TRUE;
+  ot_transfer_out_value (out_commits, &ret_commits);
+ out:
+  return ret;
+}
+
 /**
  * ostree_repo_read_commit:
  * @self: Repo

src/libostree/ostree-repo.h

@@ -446,6 +446,12 @@ gboolean ostree_repo_list_objects (OstreeRepo                  *self,
                                    GCancellable                *cancellable,
                                    GError                     **error);
 
+gboolean ostree_repo_list_commit_objects_starting_with ( OstreeRepo                  *self,
+                                                         const char                  *start,
+                                                         GHashTable                 **out_commits,
+                                                         GCancellable                *cancellable,
+                                                         GError                     **error);
+
 gboolean ostree_repo_list_static_delta_names (OstreeRepo                  *self,
                                               GPtrArray                  **out_deltas,
                                               GCancellable                *cancellable,

tests/test-basic.sh

@@ -34,6 +34,15 @@ $OSTREE rev-parse 'test2^'
 $OSTREE rev-parse 'test2^^' 2>/dev/null && (echo 1>&2 "rev-parse test2^^ unexpectedly succeeded!"; exit 1)
 echo "ok rev-parse"
 
+checksum=$($OSTREE rev-parse test2)
+partial=${checksum:0:6} 
+echo "partial:" $partial
+echo "corresponds to:" $checksum
+$OSTREE rev-parse test2 > checksum
+$OSTREE rev-parse $partial > partial-results
+assert_file_has_content checksum $(cat partial-results)
+echo "ok shortened checksum"
+
 (cd repo && ostree rev-parse test2)
 echo "ok repo-in-cwd"