replace_object: add mechanism to replace objects found in "refs/replace/"

[thirdparty/git.git] / replace_object.c

diff --git a/replace_object.c b/replace_object.c
new file mode 100644 (file)
index 0000000..b23e1cd
--- /dev/null
+++ b/replace_object.c
@@ -0,0 +1,111 @@
+#include "cache.h"
+#include "sha1-lookup.h"
+#include "refs.h"
+
+static struct replace_object {
+       unsigned char sha1[2][20];
+} **replace_object;
+
+static int replace_object_alloc, replace_object_nr;
+
+static const unsigned char *replace_sha1_access(size_t index, void *table)
+{
+       struct replace_object **replace = table;
+       return replace[index]->sha1[0];
+}
+
+static int replace_object_pos(const unsigned char *sha1)
+{
+       return sha1_pos(sha1, replace_object, replace_object_nr,
+                       replace_sha1_access);
+}
+
+static int register_replace_object(struct replace_object *replace,
+                                  int ignore_dups)
+{
+       int pos = replace_object_pos(replace->sha1[0]);
+
+       if (0 <= pos) {
+               if (ignore_dups)
+                       free(replace);
+               else {
+                       free(replace_object[pos]);
+                       replace_object[pos] = replace;
+               }
+               return 1;
+       }
+       pos = -pos - 1;
+       if (replace_object_alloc <= ++replace_object_nr) {
+               replace_object_alloc = alloc_nr(replace_object_alloc);
+               replace_object = xrealloc(replace_object,
+                                         sizeof(*replace_object) *
+                                         replace_object_alloc);
+       }
+       if (pos < replace_object_nr)
+               memmove(replace_object + pos + 1,
+                       replace_object + pos,
+                       (replace_object_nr - pos - 1) *
+                       sizeof(*replace_object));
+       replace_object[pos] = replace;
+       return 0;
+}
+
+static int register_replace_ref(const char *refname,
+                               const unsigned char *sha1,
+                               int flag, void *cb_data)
+{
+       /* Get sha1 from refname */
+       const char *slash = strrchr(refname, '/');
+       const char *hash = slash ? slash + 1 : refname;
+       struct replace_object *repl_obj = xmalloc(sizeof(*repl_obj));
+
+       if (strlen(hash) != 40 || get_sha1_hex(hash, repl_obj->sha1[0])) {
+               free(repl_obj);
+               warning("bad replace ref name: %s", refname);
+               return 0;
+       }
+
+       /* Copy sha1 from the read ref */
+       hashcpy(repl_obj->sha1[1], sha1);
+
+       /* Register new object */
+       if (register_replace_object(repl_obj, 1))
+               die("duplicate replace ref: %s", refname);
+
+       return 0;
+}
+
+static void prepare_replace_object(void)
+{
+       static int replace_object_prepared;
+
+       if (replace_object_prepared)
+               return;
+
+       for_each_replace_ref(register_replace_ref, NULL);
+       replace_object_prepared = 1;
+}
+
+/* We allow "recursive" replacement. Only within reason, though */
+#define MAXREPLACEDEPTH 5
+
+const unsigned char *lookup_replace_object(const unsigned char *sha1)
+{
+       int pos, depth = MAXREPLACEDEPTH;
+       const unsigned char *cur = sha1;
+
+       prepare_replace_object();
+
+       /* Try to recursively replace the object */
+       do {
+               if (--depth < 0)
+                       die("replace depth too high for object %s",
+                           sha1_to_hex(sha1));
+
+               pos = replace_object_pos(cur);
+               if (0 <= pos)
+                       cur = replace_object[pos]->sha1[1];
+       } while (0 <= pos);
+
+       return cur;
+}