oid: provide type lookups by enum value or name

src/libgit2/oid.h

@@ -66,6 +66,47 @@ GIT_INLINE(size_t) git_oid_hexsize(git_oid_t type)
 	return 0;
 }
 
+GIT_INLINE(const char *) git_oid_type_name(git_oid_t type)
+{
+	switch (type) {
+	case GIT_OID_SHA1:
+		return "sha1";
+
+#ifdef GIT_EXPERIMENTAL_SHA256
+	case GIT_OID_SHA256:
+		return "sha256";
+#endif
+	}
+
+	return "unknown";
+}
+
+GIT_INLINE(git_oid_t) git_oid_type_fromstr(const char *name)
+{
+	if (strcmp(name, "sha1") == 0)
+		return GIT_OID_SHA1;
+
+#ifdef GIT_EXPERIMENTAL_SHA256
+	if (strcmp(name, "sha256") == 0)
+		return GIT_OID_SHA256;
+#endif
+
+	return 0;
+}
+
+GIT_INLINE(git_oid_t) git_oid_type_fromstrn(const char *name, size_t len)
+{
+	if (len == CONST_STRLEN("sha1") && strncmp(name, "sha1", len) == 0)
+		return GIT_OID_SHA1;
+
+#ifdef GIT_EXPERIMENTAL_SHA256
+	if (len == CONST_STRLEN("sha256") && strncmp(name, "sha256", len) == 0)
+		return GIT_OID_SHA256;
+#endif
+
+	return 0;
+}
+
 GIT_INLINE(git_hash_algorithm_t) git_oid_algorithm(git_oid_t type)
 {
 	switch (type) {

tests/libgit2/core/oid.c

@@ -192,3 +192,22 @@ void test_core_oid__fmt_substr_sha1(void)
 	git_oid_fmt_substr(buf, &id_sha1, 5, 6);
 	cl_assert_equal_s(buf, "12eea6");
 }
+
+void test_core_oid__type_lookup(void)
+{
+	cl_assert_equal_i(GIT_OID_SHA1, git_oid_type_fromstr("sha1"));
+	cl_assert_equal_i(GIT_OID_SHA1, git_oid_type_fromstrn("sha1...", 4));
+	cl_assert_equal_s("sha1", git_oid_type_name(GIT_OID_SHA1));
+
+#ifdef GIT_EXPERIMENTAL_SHA256
+	cl_assert_equal_i(GIT_OID_SHA256, git_oid_type_fromstr("sha256"));
+	cl_assert_equal_i(GIT_OID_SHA256, git_oid_type_fromstrn("sha256...", 6));
+	cl_assert_equal_s("sha256", git_oid_type_name(GIT_OID_SHA256));
+#endif
+
+	cl_assert_equal_i(0, git_oid_type_fromstr("sha42"));
+	cl_assert_equal_i(0, git_oid_type_fromstrn("sha1", 3));
+	cl_assert_equal_i(0, git_oid_type_fromstrn("sha1...", 5));
+	cl_assert_equal_s("unknown", git_oid_type_name(0));
+	cl_assert_equal_s("unknown", git_oid_type_name(42));
+}