The usual treatment.  Run multiple times the fetch regress suite,
still fine.

(note to ease review: got_imsg_fetch_ref is already serialized as if
it were a struct object in send_fetch_ref.)

ok?

diff refs/heads/main refs/heads/w
commit - 2aea6fc2c2c95ba4968b598247e00edb6f91048b
commit + 05db677d577e42756e296c0262a02c65bfd614fb
blob - cce4cea87c0a4dcf12328d3491728a50bcce8f84
blob + 6a64f1edca2e533d797c2fc7ebd6e8d738023fa4
--- lib/got_lib_privsep.h
+++ lib/got_lib_privsep.h
@@ -384,7 +384,7 @@ struct got_imsg_fetch_have_ref {
 
 /* Structure for GOT_IMSG_FETCH_HAVE_REF data. */
 struct got_imsg_fetch_have_ref {
-	uint8_t id[SHA1_DIGEST_LENGTH];
+	struct got_object_id id;
 	size_t name_len;
 	/* Followed by name_len data bytes. */
 } __attribute__((__packed__));
@@ -433,7 +433,7 @@ struct got_imsg_fetch_ref {
 /* Structure for GOT_IMSG_FETCH_REF data. */
 struct got_imsg_fetch_ref {
 	/* Describes a reference which will be fetched. */
-	uint8_t refid[SHA1_DIGEST_LENGTH];
+	struct got_object_id refid;
 	/* Followed by reference name in remaining data of imsg buffer. */
 };
 
blob - 48bdc5abc37116465cd5276b7720b4809ef3079c
blob + 16a24da99f408f5487194b9f4ff88b84b5add165
--- lib/privsep.c
+++ lib/privsep.c
@@ -578,7 +578,7 @@ got_privsep_send_fetch_req(struct imsgbuf *ibuf, int f
 			return got_error_from_errno("imsg_create FETCH_HAVE_REF");
 
 		/* Keep in sync with struct got_imsg_fetch_have_ref! */
-		if (imsg_add(wbuf, id->sha1, sizeof(id->sha1)) == -1)
+		if (imsg_add(wbuf, id, sizeof(*id)) == -1)
 			return got_error_from_errno("imsg_add FETCH_HAVE_REF");
 		if (imsg_add(wbuf, &name_len, sizeof(name_len)) == -1)
 			return got_error_from_errno("imsg_add FETCH_HAVE_REF");
@@ -736,7 +736,7 @@ got_privsep_recv_fetch_progress(int *done, struct got_
 		}
 		break;
 	case GOT_IMSG_FETCH_REF:
-		if (datalen <= SHA1_DIGEST_LENGTH) {
+		if (datalen <= sizeof(**id)) {
 			err = got_error(GOT_ERR_PRIVSEP_MSG);
 			break;
 		}
@@ -745,9 +745,9 @@ got_privsep_recv_fetch_progress(int *done, struct got_
 			err = got_error_from_errno("malloc");
 			break;
 		}
-		memcpy((*id)->sha1, imsg.data, SHA1_DIGEST_LENGTH);
-		*refname = strndup(imsg.data + SHA1_DIGEST_LENGTH,
-		    datalen - SHA1_DIGEST_LENGTH);
+		memcpy(*id, imsg.data, sizeof(**id));
+		*refname = strndup(imsg.data + sizeof(**id),
+		    datalen - sizeof(**id));
 		if (*refname == NULL) {
 			err = got_error_from_errno("strndup");
 			break;
blob - 6e1ae2146ae101481c8223adead2d0fbc046ed00
blob + 77ba914fb971f5e412b57bd1633bda6ee0e1f26d
--- libexec/got-fetch-pack/got-fetch-pack.c
+++ libexec/got-fetch-pack/got-fetch-pack.c
@@ -281,7 +281,7 @@ send_fetch_ref(struct imsgbuf *ibuf, struct got_object
 		return got_error_from_errno("imsg_create FETCH_REF");
 
 	/* Keep in sync with struct got_imsg_fetch_ref definition! */
-	if (imsg_add(wbuf, refid->sha1, SHA1_DIGEST_LENGTH) == -1)
+	if (imsg_add(wbuf, refid, sizeof(*refid)) == -1)
 		return got_error_from_errno("imsg_add FETCH_REF");
 	if (imsg_add(wbuf, refname, reflen) == -1)
 		return got_error_from_errno("imsg_add FETCH_REF");
@@ -866,7 +866,7 @@ main(int argc, char **argv)
 			err = got_error_from_errno("malloc");
 			goto done;
 		}
-		memcpy(id->sha1, href.id, SHA1_DIGEST_LENGTH);
+		memcpy(id, &href.id, sizeof(*id));
 		err = got_pathlist_append(&have_refs, refname, id);
 		if (err) {
 			free(refname);