thodg/got

diff --git a/got/Makefile b/got/Makefile
index 810f98c..f3bd403 100644
--- a/got/Makefile
+++ b/got/Makefile
@@ -1,9 +1,10 @@
 .PATH:${.CURDIR}/../lib
 
 PROG=		got
-SRCS=		got.c delta.c diff.c diffreg.c error.c fileindex.c object.c \
-		opentemp.c path.c pack.c privsep.c reference.c repository.c \
-		sha1.c worktree.c zbuf.c
+SRCS=		got.c commit_graph.c delta.c diff.c diffreg.c error.c \
+		fileindex.c object.c object_idset.c opentemp.c path.c \
+		pack.c privsep.c reference.c repository.c sha1.c \
+		worktree.c zbuf.c
 
 CPPFLAGS = -I${.CURDIR}/../include -I${.CURDIR}/../lib
 LDADD = -lutil -lz
diff --git a/got/got.c b/got/got.c
index 4849992..aaa7c0a 100644
--- a/got/got.c
+++ b/got/got.c
@@ -33,6 +33,7 @@
 #include "got_repository.h"
 #include "got_worktree.h"
 #include "got_diff.h"
+#include "got_commit_graph.h"
 
 #ifndef nitems
 #define nitems(_a)	(sizeof((_a)) / sizeof((_a)[0]))
@@ -331,101 +332,43 @@ print_commit(struct got_commit_object *commit, struct got_object_id *id,
 	return err;
 }
 
-struct commit_queue_entry {
-	TAILQ_ENTRY(commit_queue_entry) entry;
-	struct got_object_id *id;
-	struct got_commit_object *commit;
-};
-
 static const struct got_error *
 print_commits(struct got_object *root_obj, struct got_object_id *root_id,
     struct got_repository *repo, int show_patch, int limit)
 {
 	const struct got_error *err;
-	struct got_commit_object *root_commit;
-	TAILQ_HEAD(, commit_queue_entry) commits;
-	struct commit_queue_entry *entry;
-
-	TAILQ_INIT(&commits);
+	struct got_commit_graph *graph;
+	int ncommits;
 
-	err = got_object_commit_open(&root_commit, repo, root_obj);
+	err = got_commit_graph_open(&graph, root_id, repo);
 	if (err)
 		return err;
-
-	entry = calloc(1, sizeof(*entry));
-	if (entry == NULL)
-		return got_error_from_errno();
-	entry->id = got_object_id_dup(root_id);
-	if (entry->id == NULL) {
-		err = got_error_from_errno();
-		free(entry);
+	err = got_commit_graph_iter_start(graph, root_id);
+	if (err)
 		return err;
-	}
-	entry->commit = root_commit;
-	TAILQ_INSERT_HEAD(&commits, entry, entry);
-
-	while (!TAILQ_EMPTY(&commits)) {
-		struct got_parent_id *pid;
-		struct got_object *obj;
-		struct got_commit_object *pcommit;
-		struct commit_queue_entry *pentry;
-
-		entry = TAILQ_FIRST(&commits);
-
-		err = print_commit(entry->commit, entry->id, repo, show_patch);
-		if (err)
-			break;
-
-		if (limit && --limit == 0)
-			break;
-
-		if (entry->commit->nparents == 0)
-			break;
-
-		/* Follow the first parent (TODO: handle merge commits). */
-		pid = SIMPLEQ_FIRST(&entry->commit->parent_ids);
-		err = got_object_open(&obj, repo, pid->id);
-		if (err)
-			break;
-		if (got_object_get_type(obj) != GOT_OBJ_TYPE_COMMIT) {
-			err = got_error(GOT_ERR_OBJ_TYPE);
-			break;
+	do {
+		struct got_commit_object *commit;
+		struct got_object_id *id;
+
+		err = got_commit_graph_iter_next(&commit, &id, graph);
+		if (err) {
+			if (err->code != GOT_ERR_ITER_NEED_MORE)
+				break;
+			err = got_commit_graph_fetch_commits(&ncommits,
+			    graph, 1, repo);
+			if (err)
+				break;
+			else
+				continue;
 		}
-
-		err = got_object_commit_open(&pcommit, repo, obj);
-		got_object_close(obj);
-		if (err)
+		if (commit == NULL)
 			break;
-
-		pentry = calloc(1, sizeof(*pentry));
-		if (pentry == NULL) {
-			err = got_error_from_errno();
-			got_object_commit_close(pcommit);
-			break;
-		}
-		pentry->id = got_object_id_dup(pid->id);
-		if (pentry->id == NULL) {
-			err = got_error_from_errno();
-			got_object_commit_close(pcommit);
+		err = print_commit(commit, id, repo, show_patch);
+		if (err || (limit && --limit == 0))
 			break;
-		}
-		pentry->commit = pcommit;
-		TAILQ_INSERT_TAIL(&commits, pentry, entry);
-
-		TAILQ_REMOVE(&commits, entry, entry);
-		got_object_commit_close(entry->commit);
-		free(entry->id);
-		free(entry);
-	}
-
-	while (!TAILQ_EMPTY(&commits)) {
-		entry = TAILQ_FIRST(&commits);
-		TAILQ_REMOVE(&commits, entry, entry);
-		got_object_commit_close(entry->commit);
-		free(entry->id);
-		free(entry);
-	}
+	} while (ncommits > 0);
 
+	got_commit_graph_close(graph);
 	return err;
 }
 
diff --git a/include/got_commit_graph.h b/include/got_commit_graph.h
new file mode 100644
index 0000000..1e63200
--- /dev/null
+++ b/include/got_commit_graph.h
@@ -0,0 +1,32 @@
+/*
+ * Copyright (c) 2018 Stefan Sperling <stsp@openbsd.org>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+
+struct got_commit_graph;
+
+const struct got_error *got_commit_graph_open(struct got_commit_graph **,
+    struct got_object_id *commit_id, struct got_repository *repo);
+void got_commit_graph_close(struct got_commit_graph *);
+
+const struct got_error *
+got_commit_graph_fetch_commits(int *, struct got_commit_graph *, int,
+    struct got_repository *);
+const struct got_error *got_commit_graph_iter_start(
+    struct got_commit_graph *, struct got_object_id *);
+const struct got_error *got_commit_graph_iter_next(struct got_commit_object **,
+    struct got_object_id **, struct got_commit_graph *);
+
+const struct got_commit_object *got_commit_graph_get_commit(
+    struct got_commit_graph *, struct got_object_id *);
diff --git a/include/got_error.h b/include/got_error.h
index ccb4b12..c833782 100644
--- a/include/got_error.h
+++ b/include/got_error.h
@@ -58,6 +58,7 @@
 #define GOT_ERR_PACK_OFFSET	42
 #define GOT_ERR_OBJ_EXISTS	43
 #define GOT_ERR_BAD_OBJ_ID	44
+#define GOT_ERR_ITER_NEED_MORE	45
 
 static const struct got_error {
 	int code;
@@ -105,6 +106,7 @@ static const struct got_error {
 	{ GOT_ERR_PACK_OFFSET,	"bad offset in pack file" },
 	{ GOT_ERR_OBJ_EXISTS,	"object already exists" },
 	{ GOT_ERR_BAD_OBJ_ID,	"bad object id" },
+	{ GOT_ERR_ITER_NEED_MORE,"more items needed to continue iteration" },
 };
 
 /*
diff --git a/lib/commit_graph.c b/lib/commit_graph.c
new file mode 100644
index 0000000..609fa34
--- /dev/null
+++ b/lib/commit_graph.c
@@ -0,0 +1,552 @@
+/*
+ * Copyright (c) 2018 Stefan Sperling <stsp@openbsd.org>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <sys/queue.h>
+#include <sys/stdint.h>
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sha1.h>
+#include <zlib.h>
+#include <ctype.h>
+
+#include "got_error.h"
+#include "got_object.h"
+#include "got_commit_graph.h"
+
+#include "got_lib_delta.h"
+#include "got_lib_zbuf.h"
+#include "got_lib_object.h"
+#include "got_lib_object_idset.h"
+
+struct got_commit_graph_node {
+	struct got_object_id id;
+
+	/*
+	 * Each graph node corresponds to a commit object.
+	 * Graph vertices are modelled with two separate adjacency lists:
+	 * Adjacencies of a graph node are either parent (older) commits,
+	 * and child (younger) commits.
+	 */
+	struct got_commit_object *commit; /* contains list of parents */
+	int nchildren;
+	SIMPLEQ_HEAD(, got_parent_id) child_ids;
+
+	/* Used during graph iteration. */
+	TAILQ_ENTRY(got_commit_graph_node) entry;
+};
+
+struct got_commit_graph {
+	/* The set of all commits we have traversed. */
+	struct got_object_idset *node_ids;
+
+	/* The commit at which traversal began (youngest commit in node_ids). */
+	struct got_commit_graph_node *head_node;
+
+	/*
+	 * A set of object IDs of known parent commits which we have not yet
+	 * traversed. Each commit ID in this set represents a branch in commit
+	 * history: Either the first-parent branch of the head node, or another
+	 * branch corresponding to a traversed merge commit for which we have
+	 * not traversed a branch point commit yet.
+	 *
+	 * Whenever we add a commit with a matching ID to the graph, we remove
+	 * its corresponding element from this set, and add new elements for
+	 * each of that commit's parent commits which were not traversed yet.
+	 *
+	 * When API users ask us to fetch more commits, we fetch commits from
+	 * all currently open branches. This allows API users to process
+	 * commits in linear order even though the history contains branches.
+	 */
+	struct got_object_idset *open_branches;
+
+	/* The next commit to return when the API user asks for one. */
+	struct got_commit_graph_node *iter_node;
+
+	TAILQ_HEAD(, got_commit_graph_node) iter_candidates;
+};
+
+static struct got_commit_graph *
+alloc_graph(void)
+{
+	struct got_commit_graph *graph;
+
+	graph = calloc(1, sizeof(*graph));
+	if (graph == NULL)
+		return NULL;
+
+	graph->node_ids = got_object_idset_alloc();
+	if (graph->node_ids == NULL) {
+		free(graph);
+		return NULL;
+	}
+
+	graph->open_branches = got_object_idset_alloc();
+	if (graph->open_branches == NULL) {
+		got_object_idset_free(graph->node_ids);
+		free(graph);
+		return NULL;
+	}
+
+	TAILQ_INIT(&graph->iter_candidates);
+	return graph;
+}
+
+#if 0
+static int
+is_head_node(struct got_commit_graph_node *node)
+{
+	return node->nchildren == 0;
+}
+
+static int
+is_merge_point(struct got_commit_graph_node *node)
+{
+	return node->commit->nparents > 1;
+}
+
+int
+is_branch_point(struct got_commit_graph_node *node)
+{
+	return node->nchildren > 1;
+}
+#endif
+
+static int
+is_root_node(struct got_commit_graph_node *node)
+{
+	return node->commit->nparents == 0;
+}
+
+static const struct got_error *
+parse_commit_time(int64_t *time, struct got_commit_object *commit)
+{
+	const struct got_error *err = NULL;
+	const char *errstr;
+	char *committer, *space;
+
+	*time = 0;
+
+	committer = strdup(commit->committer);
+	if (committer == NULL)
+		return got_error_from_errno();
+
+	/* Strip off trailing timezone indicator. */
+	space = strrchr(committer, ' ');
+	if (space == NULL) {
+		err = got_error(GOT_ERR_BAD_OBJ_DATA);
+		goto done;
+	}
+	*space = '\0';
+
+	/* Timestamp is separated from committer name + email by space. */
+	space = strrchr(committer, ' ');
+	if (space == NULL) {
+		err = got_error(GOT_ERR_BAD_OBJ_DATA);
+		goto done;
+	}
+
+	*time = strtonum(space + 1, 0, INT64_MAX, &errstr);
+	if (errstr)
+		err = got_error(GOT_ERR_BAD_OBJ_DATA);
+
+done:
+	free(committer);
+	return err;
+}
+
+static const struct got_error *
+compare_commits(int *cmp, struct got_commit_object *c1,
+    struct got_commit_object *c2)
+{
+	const struct got_error *err;
+	int64_t t1, t2;
+
+	err = parse_commit_time(&t1, c1);
+	if (err)
+		return err;
+	err = parse_commit_time(&t2, c2);
+	if (err)
+		return err;
+
+	if (t1 == t2)	
+		*cmp = 0;
+	else if (t1 < t2)
+		*cmp = -1;
+	else
+		*cmp = 1;
+
+	return NULL;
+}
+
+static const struct got_error *
+add_iteration_candidate(struct got_commit_graph *graph,
+    struct got_commit_graph_node *node)
+{
+	struct got_commit_graph_node *n;
+	
+	if (TAILQ_EMPTY(&graph->iter_candidates)) {
+		TAILQ_INSERT_TAIL(&graph->iter_candidates, node, entry);
+		return NULL;
+	}
+
+	TAILQ_FOREACH(n, &graph->iter_candidates, entry) {
+		const struct got_error *err;
+		int cmp;
+		err = compare_commits(&cmp, node->commit, n->commit);
+		if (err)
+			return err;
+		if (cmp <= 0)
+			continue;
+		TAILQ_INSERT_BEFORE(n, node, entry);
+		break;
+	}
+
+	return NULL;
+}
+
+static const struct got_error *
+add_node(struct got_commit_graph_node **new_node,
+    struct got_commit_graph *graph, struct got_object_id *commit_id,
+    struct got_commit_object *commit, struct got_object_id *child_commit_id)
+{
+	const struct got_error *err = NULL;
+	struct got_commit_graph_node *node, *existing_node;
+
+	*new_node = NULL;
+
+	node = calloc(1, sizeof(*node));
+	if (node == NULL)
+		return got_error_from_errno();
+
+	memcpy(&node->id, commit_id, sizeof(node->id));
+	node->commit = commit;
+	SIMPLEQ_INIT(&node->child_ids);
+
+	err = got_object_idset_add((void **)(&existing_node),
+	    graph->node_ids, &node->id, node);
+	if (err == NULL) {
+		struct got_parent_id *pid;
+
+		err = add_iteration_candidate(graph, node);
+		if (err)
+			return err;
+
+		err = got_object_idset_remove(graph->open_branches, commit_id);
+		if (err && err->code != GOT_ERR_NO_OBJ)
+			return err;
+		SIMPLEQ_FOREACH(pid, &commit->parent_ids, entry) {
+			if (got_object_idset_get(graph->node_ids, pid->id))
+				continue; /* parent already traversed */
+			err = got_object_idset_add(NULL, graph->open_branches,
+			    pid->id, node);
+			if (err && err->code != GOT_ERR_OBJ_EXISTS)
+				return err;
+		}
+		*new_node = node;
+	} else if (err->code == GOT_ERR_OBJ_EXISTS) {
+		err = NULL;
+		free(node);
+		node = existing_node;
+	} else {
+		free(node);
+		return err;
+	}
+
+	if (child_commit_id) {
+		struct got_parent_id *child, *cid;
+
+		/* Prevent linking to self. */
+		if (got_object_id_cmp(commit_id, child_commit_id) == 0)
+			return got_error(GOT_ERR_BAD_OBJ_ID);
+
+		/* Prevent double-linking to the same child. */
+		SIMPLEQ_FOREACH(cid, &node->child_ids, entry) {
+			if (got_object_id_cmp(cid->id, child_commit_id) == 0)
+				return got_error(GOT_ERR_BAD_OBJ_ID);
+		}
+
+		child = calloc(1, sizeof(*child));
+		if (child == NULL)
+			return got_error_from_errno();
+		child->id = got_object_id_dup(child_commit_id);
+		if (child->id == NULL) {
+			err = got_error_from_errno();
+			free(child);
+			return err;
+		}
+		SIMPLEQ_INSERT_TAIL(&node->child_ids, child, entry);
+		node->nchildren++;
+	}
+
+	return err;
+}
+
+const struct got_error *
+got_commit_graph_open(struct got_commit_graph **graph,
+    struct got_object_id *commit_id, struct got_repository *repo)
+{
+	const struct got_error *err = NULL;
+	struct got_object *obj;
+	struct got_commit_object *commit;
+
+	*graph = NULL;
+
+	err = got_object_open(&obj, repo, commit_id);
+	if (err)
+		return err;
+	if (got_object_get_type(obj) != GOT_OBJ_TYPE_COMMIT) {
+		err = got_error(GOT_ERR_OBJ_TYPE);
+		got_object_close(obj);
+		return err;
+	}
+
+	err = got_object_commit_open(&commit, repo, obj);
+	got_object_close(obj);
+	if (err)
+		return err;
+
+	*graph = alloc_graph();
+	if (*graph == NULL) {
+		got_object_commit_close(commit);
+		return got_error_from_errno();
+	}
+
+	err = add_node(&(*graph)->head_node, *graph, commit_id, commit, NULL);
+	if (err) {
+		got_commit_graph_close(*graph);
+		*graph = NULL;
+		return err;
+	}
+	
+	return NULL;
+}
+
+static const struct got_error *
+open_commit(struct got_commit_object **commit, struct got_object_id *id,
+    struct got_repository *repo)
+{
+	const struct got_error *err;
+	struct got_object *obj;
+
+	err = got_object_open(&obj, repo, id);
+	if (err)
+		return err;
+	if (got_object_get_type(obj) != GOT_OBJ_TYPE_COMMIT) {
+		err = got_error(GOT_ERR_OBJ_TYPE);
+		goto done;
+	}
+
+	err = got_object_commit_open(commit, repo, obj);
+done:
+	got_object_close(obj);
+	return err;
+}
+
+struct got_commit_graph_branch {
+	struct got_object_id parent_id;
+	struct got_commit_graph_node *node;
+};
+
+struct gather_branches_arg {
+	struct got_commit_graph_branch *branches;
+	int nbranches;
+};
+
+static void
+gather_branches(struct got_object_id *id, void *data, void *arg)
+{
+	struct gather_branches_arg *a = arg;
+	memcpy(&a->branches[a->nbranches].parent_id, id, sizeof(*id));
+	a->branches[a->nbranches].node = data;
+	a->nbranches++;
+}
+
+const struct got_error *
+fetch_commits_from_open_branches(int *ncommits,
+    struct got_commit_graph *graph, struct got_repository *repo)
+{
+	const struct got_error *err;
+	struct got_commit_graph_branch *branches;
+	struct gather_branches_arg arg;
+	int i;
+
+	*ncommits = 0;
+
+	arg.nbranches = got_object_idset_num_elements(graph->open_branches);
+	if (arg.nbranches == 0)
+		return NULL;
+
+	/*
+	 * Adding nodes to the graph might change the graph's open
+	 * branches state. Create a local copy of the current state.
+	 */
+	branches = calloc(arg.nbranches, sizeof(*branches));
+	if (branches == NULL)
+		return got_error_from_errno();
+	arg.nbranches = 0; /* reset; gather_branches() will increment */
+	arg.branches = branches;
+	got_object_idset_for_each(graph->open_branches, gather_branches, &arg);
+
+	for (i = 0; i < arg.nbranches; i++) {
+		struct got_object_id *commit_id;
+		struct got_commit_graph_node *child_node, *new_node;
+		struct got_commit_object *commit;
+
+		commit_id = &branches[i].parent_id;
+		child_node = branches[i].node;
+
+		err = open_commit(&commit, commit_id, repo);
+		if (err)
+			break;
+
+		err = add_node(&new_node, graph, commit_id, commit,
+		    &child_node->id);
+		if (err) {
+			if (err->code != GOT_ERR_OBJ_EXISTS)
+				break;
+			err = NULL;
+		}
+		if (new_node)
+			(*ncommits)++;
+		else
+			got_object_commit_close(commit);
+	}
+
+	free(branches);
+	return err;
+}
+
+const struct got_error *
+got_commit_graph_fetch_commits(int *nfetched, struct got_commit_graph *graph,
+    int limit, struct got_repository *repo)
+{
+	const struct got_error *err;
+	int total = 0, ncommits;
+
+	*nfetched = 0;
+
+	while (total < limit) {
+		err = fetch_commits_from_open_branches(&ncommits, graph, repo);
+		if (err)
+			return err;
+		if (ncommits == 0)
+			break;
+		total += ncommits;
+	}
+
+	*nfetched = total;
+	return NULL;
+}
+
+static void
+free_graph_node(struct got_object_id *id, void *data, void *arg)
+{
+	struct got_commit_graph_node *node = data;
+	got_object_commit_close(node->commit);
+	while (!SIMPLEQ_EMPTY(&node->child_ids)) {
+		struct got_parent_id *child = SIMPLEQ_FIRST(&node->child_ids);
+		SIMPLEQ_REMOVE_HEAD(&node->child_ids, entry);
+		free(child);
+	}
+	free(node);
+}
+
+void
+got_commit_graph_close(struct got_commit_graph *graph)
+{
+	got_object_idset_free(graph->open_branches);
+	got_object_idset_for_each(graph->node_ids, free_graph_node, NULL);
+	got_object_idset_free(graph->node_ids);
+	free(graph);
+}
+
+const struct got_error *
+got_commit_graph_iter_start(struct got_commit_graph *graph,
+    struct got_object_id *id)
+{
+	struct got_commit_graph_node *start_node, *node;
+	struct got_parent_id *pid;
+
+	start_node = got_object_idset_get(graph->node_ids, id);
+	if (start_node == NULL)
+		return got_error(GOT_ERR_NO_OBJ);
+
+	graph->iter_node = start_node;
+
+	while (!TAILQ_EMPTY(&graph->iter_candidates)) {
+		node = TAILQ_FIRST(&graph->iter_candidates);
+		TAILQ_REMOVE(&graph->iter_candidates, node, entry);
+	}
+
+	/* Put all known parents of this commit on the candidate list. */
+	SIMPLEQ_FOREACH(pid, &start_node->commit->parent_ids, entry) {
+		node = got_object_idset_get(graph->node_ids, pid->id);
+		if (node) {
+			const struct got_error *err;
+			err = add_iteration_candidate(graph, node);
+			if (err)
+				return err;
+		}
+	}
+
+	return NULL;
+}
+
+const struct got_error *
+got_commit_graph_iter_next(struct got_commit_object **commit,
+    struct got_object_id **id, struct got_commit_graph *graph)
+{
+	struct got_commit_graph_node *node;
+
+	if (graph->iter_node == NULL) {
+		/* We are done interating, or iteration was not started. */
+		*commit = NULL;
+		*id = NULL;
+		return NULL;
+	}
+
+	if (TAILQ_EMPTY(&graph->iter_candidates)) {
+		if (is_root_node(graph->iter_node) &&
+		    got_object_idset_num_elements(graph->open_branches) == 0) {
+			*commit = graph->iter_node->commit;
+			*id = &graph->iter_node->id;
+			/* We are done interating. */
+			graph->iter_node = NULL;
+			return NULL;
+		}
+		return got_error(GOT_ERR_ITER_NEED_MORE);
+	}
+
+	*commit = graph->iter_node->commit;
+	*id = &graph->iter_node->id;
+	node = TAILQ_FIRST(&graph->iter_candidates);
+	TAILQ_REMOVE(&graph->iter_candidates, node, entry);
+	graph->iter_node = node;
+	return NULL;
+}
+
+const struct got_commit_object *
+got_commit_graph_get_commit(struct got_commit_graph *graph,
+    struct got_object_id *id)
+{
+	struct got_commit_graph_node *node;
+	node = got_object_idset_get(graph->node_ids, id);
+	return node ? node->commit : NULL;
+}