mem-pool: add convenience functions for strdup and strndup

fast-import had a special mem_pool_strdup() convenience function that I
want to be able to use from the new merge algorithm I am writing.  Move
it from fast-import to mem-pool, and also add a mem_pool_strndup()
while at it that I also want to use.

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

fast-import.c

@@ -526,14 +526,6 @@ static unsigned int hc_str(const char *s, size_t len)
 	return r;
 }
 
-static char *pool_strdup(const char *s)
-{
-	size_t len = strlen(s) + 1;
-	char *r = mem_pool_alloc(&fi_mem_pool, len);
-	memcpy(r, s, len);
-	return r;
-}
-
 static void insert_mark(struct mark_set *s, uintmax_t idnum, struct object_entry *oe)
 {
 	while ((idnum >> s->shift) >= 1024) {
@@ -615,7 +607,7 @@ static struct branch *new_branch(const char *name)
 		die("Branch name doesn't conform to GIT standards: %s", name);
 
 	b = mem_pool_calloc(&fi_mem_pool, 1, sizeof(struct branch));
-	b->name = pool_strdup(name);
+	b->name = mem_pool_strdup(&fi_mem_pool, name);
 	b->table_next_branch = branch_table[hc];
 	b->branch_tree.versions[0].mode = S_IFDIR;
 	b->branch_tree.versions[1].mode = S_IFDIR;
@@ -2806,7 +2798,7 @@ static void parse_new_tag(const char *arg)
 
 	t = mem_pool_alloc(&fi_mem_pool, sizeof(struct tag));
 	memset(t, 0, sizeof(struct tag));
-	t->name = pool_strdup(arg);
+	t->name = mem_pool_strdup(&fi_mem_pool, arg);
 	if (last_tag)
 		last_tag->next_tag = t;
 	else

mem-pool.c

@@ -102,6 +102,24 @@ void *mem_pool_calloc(struct mem_pool *mem_pool, size_t count, size_t size)
 	return r;
 }
 
+char *mem_pool_strdup(struct mem_pool *pool, const char *str)
+{
+	size_t len = strlen(str) + 1;
+	char *ret = mem_pool_alloc(pool, len);
+
+	return memcpy(ret, str, len);
+}
+
+char *mem_pool_strndup(struct mem_pool *pool, const char *str, size_t len)
+{
+	char *p = memchr(str, '\0', len);
+	size_t actual_len = (p ? p - str : len);
+	char *ret = mem_pool_alloc(pool, actual_len+1);
+
+	ret[actual_len] = '\0';
+	return memcpy(ret, str, actual_len);
+}
+
 int mem_pool_contains(struct mem_pool *mem_pool, void *mem)
 {
 	struct mp_block *p;

mem-pool.h

@@ -41,6 +41,12 @@ void *mem_pool_alloc(struct mem_pool *pool, size_t len);
  */
 void *mem_pool_calloc(struct mem_pool *pool, size_t count, size_t size);
 
+/*
+ * Allocate memory from the memory pool and copy str into it.
+ */
+char *mem_pool_strdup(struct mem_pool *pool, const char *str);
+char *mem_pool_strndup(struct mem_pool *pool, const char *str, size_t len);
+
 /*
  * Move the memory associated with the 'src' pool to the 'dst' pool. The 'src'
  * pool will be empty and not contain any memory. It still needs to be free'd