thodg/libgit2

diff --git a/include/git2/rebase.h b/include/git2/rebase.h
index 6eb2794..c760fbe 100644
--- a/include/git2/rebase.h
+++ b/include/git2/rebase.h
@@ -68,6 +68,19 @@ GIT_EXTERN(int) git_rebase(
 	const git_signature *signature,
 	const git_rebase_options *opts);
 
+/**
+ * Aborts a rebase that is currently in progress, resetting the repository
+ * and working directory to their state before rebase began.
+ *
+ * @param repo The repository with the in-progress rebase
+ * @param signature The identity that is aborting the rebase
+ * @return Zero on success; GIT_ENOTFOUND if a rebase is not in progress,
+ *         -1 on other errors.
+ */
+GIT_EXTERN(int) git_rebase_abort(
+	git_repository *repo,
+	const git_signature *signature);
+
 /** @} */
 GIT_END_DECL
 #endif
diff --git a/src/rebase.c b/src/rebase.c
index 68d741d..38ced24 100644
--- a/src/rebase.c
+++ b/src/rebase.c
@@ -44,6 +44,18 @@ typedef enum {
 	GIT_REBASE_TYPE_MERGE = 2,
 } git_rebase_type_t;
 
+typedef struct {
+	git_rebase_type_t type;
+	char *state_path;
+
+	int head_detached : 1;
+
+	char *orig_head_name;
+	git_oid orig_head_id;
+} git_rebase_state;
+
+#define GIT_REBASE_STATE_INIT {0}
+
 static int rebase_state_type(
 	git_rebase_type_t *type_out,
 	char **path_out,
@@ -80,6 +92,84 @@ done:
 	return 0;
 }
 
+static int rebase_state(git_rebase_state *state, git_repository *repo)
+{
+	git_buf path = GIT_BUF_INIT, orig_head_name = GIT_BUF_INIT,
+		orig_head_id = GIT_BUF_INIT;
+	int state_path_len, error;
+
+	memset(state, 0x0, sizeof(git_rebase_state));
+
+	if ((error = rebase_state_type(&state->type, &state->state_path, repo)) < 0)
+		goto done;
+
+	if (state->type == GIT_REBASE_TYPE_NONE) {
+		giterr_set(GITERR_REBASE, "There is no rebase in progress");
+		return GIT_ENOTFOUND;
+	}
+
+	if ((error = git_buf_puts(&path, state->state_path)) < 0)
+		goto done;
+
+	state_path_len = git_buf_len(&path);
+
+	if ((error = git_buf_joinpath(&path, path.ptr, HEAD_NAME_FILE)) < 0 ||
+		(error = git_futils_readbuffer(&orig_head_name, path.ptr)) < 0)
+		goto done;
+
+	git_buf_rtrim(&orig_head_name);
+
+	if (strcmp(ORIG_DETACHED_HEAD, orig_head_name.ptr) == 0)
+		state->head_detached = 1;
+
+	git_buf_truncate(&path, state_path_len);
+
+	if ((error = git_buf_joinpath(&path, path.ptr, ORIG_HEAD_FILE)) < 0)
+		goto done;
+
+	if (!git_path_isfile(path.ptr)) {
+		/* Previous versions of git.git used 'head' here; support that. */
+		git_buf_truncate(&path, state_path_len);
+
+		if ((error = git_buf_joinpath(&path, path.ptr, HEAD_FILE)) < 0)
+			goto done;
+	}
+
+	if ((error = git_futils_readbuffer(&orig_head_id, path.ptr)) < 0)
+		goto done;
+
+	git_buf_rtrim(&orig_head_id);
+
+	if ((error = git_oid_fromstr(&state->orig_head_id, orig_head_id.ptr)) < 0)
+		goto done;
+
+	if (!state->head_detached)
+		state->orig_head_name = git_buf_detach(&orig_head_name);
+
+done:
+	git_buf_free(&path);
+	git_buf_free(&orig_head_name);
+	git_buf_free(&orig_head_id);
+	git_buf_free(&onto_id);
+	return error;
+}
+
+static void rebase_state_free(git_rebase_state *state)
+{
+	if (state == NULL)
+		return;
+
+	git__free(state->orig_head_name);
+	git__free(state->state_path);
+}
+
+static int rebase_finish(git_rebase_state *state)
+{
+	return git_path_isdir(state->state_path) ?
+		git_futils_rmdir_r(state->state_path, NULL, GIT_RMDIR_REMOVE_FILES) :
+		0;
+}
+
 static int rebase_setupfile(git_repository *repo, const char *filename, const char *fmt, ...)
 {
 	git_buf path = GIT_BUF_INIT,
@@ -330,3 +420,41 @@ done:
 	git_buf_free(&reflog);
 	return error;
 }
+
+int git_rebase_abort(git_repository *repo, const git_signature *signature)
+{
+	git_rebase_state state = GIT_REBASE_STATE_INIT;
+	git_reference *orig_head_ref = NULL;
+	git_commit *orig_head_commit = NULL;
+	int error;
+
+	assert(repo && signature);
+
+	if ((error = rebase_state(&state, repo)) < 0)
+		goto done;
+
+	error = state.head_detached ?
+		git_reference_create(&orig_head_ref, repo, GIT_HEAD_FILE,
+			 &state.orig_head_id, 1, signature, "rebase: aborting") :
+		git_reference_symbolic_create(
+			&orig_head_ref, repo, GIT_HEAD_FILE, state.orig_head_name, 1,
+			signature, "rebase: aborting");
+
+	if (error < 0)
+		goto done;
+
+	if ((error = git_commit_lookup(
+			&orig_head_commit, repo, &state.orig_head_id)) < 0 ||
+		(error = git_reset(repo, (git_object *)orig_head_commit,
+			GIT_RESET_HARD, NULL, signature, NULL)) < 0)
+		goto done;
+
+	error = rebase_finish(&state);
+
+done:
+	git_commit_free(orig_head_commit);
+	git_reference_free(orig_head_ref);
+	rebase_state_free(&state);
+
+	return error;
+}
diff --git a/tests/rebase/abort.c b/tests/rebase/abort.c
new file mode 100644
index 0000000..896eb48
--- /dev/null
+++ b/tests/rebase/abort.c
@@ -0,0 +1,148 @@
+#include "clar_libgit2.h"
+#include "git2/rebase.h"
+#include "merge.h"
+#include "posix.h"
+
+#include <fcntl.h>
+
+static git_repository *repo;
+
+// Fixture setup and teardown
+void test_rebase_abort__initialize(void)
+{
+	repo = cl_git_sandbox_init("rebase");
+}
+
+void test_rebase_abort__cleanup(void)
+{
+	cl_git_sandbox_cleanup();
+}
+
+static void test_abort(git_merge_head *branch, git_merge_head *onto)
+{
+	git_reference *head_ref, *branch_ref = NULL;
+	git_signature *signature;
+	git_status_list *statuslist;
+	git_reflog *reflog;
+	const git_reflog_entry *reflog_entry;
+
+	cl_git_pass(git_signature_new(&signature, "Rebaser", "rebaser@example.com", 1404157834, -400));
+	cl_git_pass(git_rebase_abort(repo, signature));
+
+	cl_assert_equal_i(GIT_REPOSITORY_STATE_NONE, git_repository_state(repo));
+
+	/* Make sure the refs are updated appropriately */
+	cl_git_pass(git_reference_lookup(&head_ref, repo, "HEAD"));
+
+	if (branch->ref_name == NULL)
+		cl_assert_equal_oid(git_merge_head_id(branch), git_reference_target(head_ref));
+	else {
+		cl_assert_equal_s("refs/heads/beef", git_reference_symbolic_target(head_ref));
+		cl_git_pass(git_reference_lookup(&branch_ref, repo, git_reference_symbolic_target(head_ref)));
+		cl_assert_equal_oid(git_merge_head_id(branch), git_reference_target(branch_ref));
+	}
+
+	git_status_list_new(&statuslist, repo, NULL);
+	cl_assert_equal_i(0, git_status_list_entrycount(statuslist));
+	git_status_list_free(statuslist);
+
+	/* Make sure the reflogs are updated appropriately */
+	cl_git_pass(git_reflog_read(&reflog, repo, "HEAD"));
+
+	cl_assert(reflog_entry = git_reflog_entry_byindex(reflog, 0));
+	cl_assert_equal_oid(git_merge_head_id(onto), git_reflog_entry_id_old(reflog_entry));
+	cl_assert_equal_oid(git_merge_head_id(branch), git_reflog_entry_id_new(reflog_entry));
+	cl_assert_equal_s("rebase: aborting", git_reflog_entry_message(reflog_entry));
+
+	git_reflog_free(reflog);
+	git_reference_free(head_ref);
+	git_reference_free(branch_ref);
+	git_signature_free(signature);
+}
+
+void test_rebase_abort__merge(void)
+{
+	git_reference *branch_ref, *onto_ref;
+	git_signature *signature;
+	git_merge_head *branch_head, *onto_head;
+
+	cl_git_pass(git_reference_lookup(&branch_ref, repo, "refs/heads/beef"));
+	cl_git_pass(git_reference_lookup(&onto_ref, repo, "refs/heads/master"));
+
+	cl_git_pass(git_merge_head_from_ref(&branch_head, repo, branch_ref));
+	cl_git_pass(git_merge_head_from_ref(&onto_head, repo, onto_ref));
+
+	cl_git_pass(git_signature_new(&signature, "Rebaser", "rebaser@example.com", 1404157834, -400));
+
+	cl_git_pass(git_rebase(repo, branch_head, NULL, onto_head, signature, NULL));
+	cl_assert_equal_i(GIT_REPOSITORY_STATE_REBASE_MERGE, git_repository_state(repo));
+
+	test_abort(branch_head, onto_head);
+
+	git_signature_free(signature);
+
+	git_merge_head_free(branch_head);
+	git_merge_head_free(onto_head);
+
+	git_reference_free(branch_ref);
+	git_reference_free(onto_ref);
+}
+
+void test_rebase_abort__detached_head(void)
+{
+	git_oid branch_id;
+	git_reference *onto_ref;
+	git_signature *signature;
+	git_merge_head *branch_head, *onto_head;
+
+	git_oid_fromstr(&branch_id, "b146bd7608eac53d9bf9e1a6963543588b555c64");
+	cl_git_pass(git_reference_lookup(&onto_ref, repo, "refs/heads/master"));
+
+	cl_git_pass(git_merge_head_from_id(&branch_head, repo, &branch_id));
+	cl_git_pass(git_merge_head_from_ref(&onto_head, repo, onto_ref));
+
+	cl_git_pass(git_signature_new(&signature, "Rebaser", "rebaser@example.com", 1404157834, -400));
+
+	cl_git_pass(git_rebase(repo, branch_head, NULL, onto_head, signature, NULL));
+	cl_assert_equal_i(GIT_REPOSITORY_STATE_REBASE_MERGE, git_repository_state(repo));
+
+	test_abort(branch_head, onto_head);
+
+	git_signature_free(signature);
+
+	git_merge_head_free(branch_head);
+	git_merge_head_free(onto_head);
+
+	git_reference_free(onto_ref);
+}
+
+void test_rebase_abort__old_style_head_file(void)
+{
+	git_reference *branch_ref, *onto_ref;
+	git_signature *signature;
+	git_merge_head *branch_head, *onto_head;
+
+	cl_git_pass(git_reference_lookup(&branch_ref, repo, "refs/heads/beef"));
+	cl_git_pass(git_reference_lookup(&onto_ref, repo, "refs/heads/master"));
+
+	cl_git_pass(git_merge_head_from_ref(&branch_head, repo, branch_ref));
+	cl_git_pass(git_merge_head_from_ref(&onto_head, repo, onto_ref));
+
+	cl_git_pass(git_signature_new(&signature, "Rebaser", "rebaser@example.com", 1404157834, -400));
+
+	cl_git_pass(git_rebase(repo, branch_head, NULL, onto_head, signature, NULL));
+	cl_assert_equal_i(GIT_REPOSITORY_STATE_REBASE_MERGE, git_repository_state(repo));
+
+	p_rename("rebase-merge/.git/rebase-merge/orig-head",
+		"rebase-merge/.git/rebase-merge/head");
+
+	test_abort(branch_head, onto_head);
+
+	git_signature_free(signature);
+
+	git_merge_head_free(branch_head);
+	git_merge_head_free(onto_head);
+
+	git_reference_free(branch_ref);
+	git_reference_free(onto_ref);
+}