separate diffs for easier reading (hopefully.)  the first one is
trivial, the second one seems so but it's slightly tricky because in
some structs the "tree_id" field is the struct in others the pointer
to the struct: got_imsg_commit_object embeds the struct while
got_commit_object dosen't.

ok?

-----------------------------------------------
commit 42c43229569244a64062c0b12fd11eef28120da8
from: Omar Polo <op@omarpolo.com>
date: Wed Feb  1 15:02:02 2023 UTC
 
 got_imsg_object: use struct instead of buffer for id
 
diff 38cd26a413a43dc0a7d5f80041fd705fe0d55773 42c43229569244a64062c0b12fd11eef28120da8
commit - 38cd26a413a43dc0a7d5f80041fd705fe0d55773
commit + 42c43229569244a64062c0b12fd11eef28120da8
blob - 151e0d73fa443289c8609863654c6bef6d128723
blob + 2817ac884ce25ec43a9812d10cca3e9dc017a4cf
--- lib/got_lib_privsep.h
+++ lib/got_lib_privsep.h
@@ -220,7 +220,7 @@ struct got_imsg_object {
  * Structure for GOT_IMSG_TREE_REQUEST and GOT_IMSG_OBJECT data.
  */
 struct got_imsg_object {
-	uint8_t id[SHA1_DIGEST_LENGTH];
+	struct got_object_id id;
 
 	/* These fields are the same as in struct got_object. */
 	int type;
blob - 970978560467422ed3a634b6c3b86e48e6b49fd0
blob + 1f118154617c4dae7a5a12d5531b577d6d906da7
--- lib/privsep.c
+++ lib/privsep.c
@@ -398,7 +398,7 @@ got_privsep_send_tree_req(struct imsgbuf *ibuf, int fd
 	if (wbuf == NULL)
 		return got_error_from_errno("imsg_create TREE_REQUEST");
 
-	if (imsg_add(wbuf, id->sha1, SHA1_DIGEST_LENGTH) == -1)
+	if (imsg_add(wbuf, id, sizeof(*id)) == -1)
 		return got_error_from_errno("imsg_add TREE_REQUEST");
 
 	if (pack_idx != -1) { /* tree is packed */
@@ -510,7 +510,7 @@ got_privsep_send_obj(struct imsgbuf *ibuf, struct got_
 
 	memset(&iobj, 0, sizeof(iobj));
 
-	memcpy(iobj.id, obj->id.sha1, sizeof(iobj.id));
+	memcpy(&iobj.id, &obj->id, sizeof(iobj.id));
 	iobj.type = obj->type;
 	iobj.flags = obj->flags;
 	iobj.hdrlen = obj->hdrlen;
@@ -1118,7 +1118,7 @@ got_privsep_get_imsg_obj(struct got_object **obj, stru
 	if (*obj == NULL)
 		return got_error_from_errno("calloc");
 
-	memcpy((*obj)->id.sha1, iobj->id, SHA1_DIGEST_LENGTH);
+	memcpy(&(*obj)->id, &iobj->id, sizeof(iobj->id));
 	(*obj)->type = iobj->type;
 	(*obj)->flags = iobj->flags;
 	(*obj)->hdrlen = iobj->hdrlen;

-----------------------------------------------
commit 0c1022cbc2057b7964c07168452299432782b57b (main)
from: Omar Polo <op@omarpolo.com>
date: Wed Feb  1 15:02:02 2023 UTC
 
 got_imsg_commit_object: use struct instead of buffer for id
 
diff 42c43229569244a64062c0b12fd11eef28120da8 0c1022cbc2057b7964c07168452299432782b57b
commit - 42c43229569244a64062c0b12fd11eef28120da8
commit + 0c1022cbc2057b7964c07168452299432782b57b
blob - 2817ac884ce25ec43a9812d10cca3e9dc017a4cf
blob + 1b4b7bc8fc2baddfd1f3353725f35bd6ac9af0cf
--- lib/got_lib_privsep.h
+++ lib/got_lib_privsep.h
@@ -233,7 +233,7 @@ struct got_imsg_commit_object {
 
 /* Structure for GOT_IMSG_COMMIT data. */
 struct got_imsg_commit_object {
-	uint8_t tree_id[SHA1_DIGEST_LENGTH];
+	struct got_object_id tree_id;
 	size_t author_len;
 	time_t author_time;
 	time_t author_gmtoff;
@@ -247,7 +247,7 @@ struct got_imsg_commit_object {
 	 * Followed by author_len + committer_len data bytes
 	 */
 
-	/* Followed by 'nparents' SHA1_DIGEST_LENGTH length strings */
+	/* Followed by 'nparents' struct got_object_id */
 
 	/*
 	 * Followed by 'logmsg_len' bytes of commit log message data in
blob - 1f118154617c4dae7a5a12d5531b577d6d906da7
blob + d40d65ea1e93b234a672d9edd3fef1c550898939
--- lib/privsep.c
+++ lib/privsep.c
@@ -1203,15 +1203,14 @@ got_privsep_send_commit(struct imsgbuf *ibuf, struct g
 	size_t logmsg_len = strlen(commit->logmsg);
 
 	total = sizeof(*icommit) + author_len + committer_len +
-	    commit->nparents * SHA1_DIGEST_LENGTH;
+	    commit->nparents * sizeof(struct got_object_id);
 
 	buf = malloc(total);
 	if (buf == NULL)
 		return got_error_from_errno("malloc");
 
 	icommit = (struct got_imsg_commit_object *)buf;
-	memcpy(icommit->tree_id, commit->tree_id->sha1,
-	    sizeof(icommit->tree_id));
+	memcpy(&icommit->tree_id, commit->tree_id, sizeof(icommit->tree_id));
 	icommit->author_len = author_len;
 	icommit->author_time = commit->author_time;
 	icommit->author_gmtoff = commit->author_gmtoff;
@@ -1227,8 +1226,8 @@ got_privsep_send_commit(struct imsgbuf *ibuf, struct g
 	memcpy(buf + len, commit->committer, committer_len);
 	len += committer_len;
 	STAILQ_FOREACH(qid, &commit->parent_ids, entry) {
-		memcpy(buf + len, &qid->id, SHA1_DIGEST_LENGTH);
-		len += SHA1_DIGEST_LENGTH;
+		memcpy(buf + len, &qid->id, sizeof(qid->id));
+		len += sizeof(qid->id);
 	}
 
 	if (imsg_compose(ibuf, GOT_IMSG_COMMIT, 0, 0, -1, buf, len) == -1) {
@@ -1263,7 +1262,7 @@ get_commit_from_imsg(struct got_commit_object **commit
 	icommit = imsg->data;
 	if (datalen != sizeof(*icommit) + icommit->author_len +
 	    icommit->committer_len +
-	    icommit->nparents * SHA1_DIGEST_LENGTH)
+	    icommit->nparents * sizeof(struct got_object_id))
 		return got_error(GOT_ERR_PRIVSEP_LEN);
 
 	if (icommit->nparents < 0)
@@ -1276,8 +1275,8 @@ get_commit_from_imsg(struct got_commit_object **commit
 		return got_error_from_errno(
 		    "got_object_commit_alloc_partial");
 
-	memcpy((*commit)->tree_id->sha1, icommit->tree_id,
-	    SHA1_DIGEST_LENGTH);
+	memcpy((*commit)->tree_id, &icommit->tree_id,
+	    sizeof(icommit->tree_id));
 	(*commit)->author_time = icommit->author_time;
 	(*commit)->author_gmtoff = icommit->author_gmtoff;
 	(*commit)->committer_time = icommit->committer_time;
@@ -1342,7 +1341,7 @@ get_commit_from_imsg(struct got_commit_object **commit
 		if (err)
 			break;
 		memcpy(&qid->id, imsg->data + len +
-		    i * SHA1_DIGEST_LENGTH, sizeof(qid->id));
+		    i * sizeof(qid->id), sizeof(qid->id));
 		STAILQ_INSERT_TAIL(&(*commit)->parent_ids, qid, entry);
 		(*commit)->nparents++;
 	}