Revert "gpg-interface: prefer check_signature() for GPG verification"

This reverts commit 72b006f4bfd30b7c5037c163efaf279ab65bea9c, which
breaks the end-user experience when merging a signed tag without
having the public key.  We should report "can't check because we
have no public key", but the code with this change claimed that
there was no signature.

4 files changed, 75 insertions, 72 deletions

diff --git a/builtin/fmt-merge-msg.c b/builtin/fmt-merge-msg.c
index f7ed102d8b..a4615587fd 100644
--- a/builtin/fmt-merge-msg.c
+++ b/builtin/fmt-merge-msg.c
@@ -495,7 +495,6 @@ static void fmt_merge_msg_sigs(struct strbuf *out)
 		enum object_type type;
 		unsigned long size, len;
 		char *buf = read_object_file(oid, &type, &size);
-		struct signature_check sigc = { 0 };
 		struct strbuf sig = STRBUF_INIT;
 
 		if (!buf || type != OBJ_TAG)
@@ -504,12 +503,10 @@ static void fmt_merge_msg_sigs(struct strbuf *out)
 
 		if (size == len)
 			; /* merely annotated */
-		else if (!check_signature(buf, len, buf + len, size - len,
-					  &sigc)) {
-			strbuf_addstr(&sig, sigc.gpg_output);
-			signature_check_clear(&sigc);
-		} else
-			strbuf_addstr(&sig, "gpg verification failed.\n");
+		else if (verify_signed_buffer(buf, len, buf + len, size - len, &sig, NULL)) {
+			if (!sig.len)
+				strbuf_addstr(&sig, "gpg verification failed.\n");
+		}
 
 		if (!tag_number++) {
 			fmt_tag_signature(&tagbuf, &sig, buf, len);
diff --git a/gpg-interface.c b/gpg-interface.c
index 5134ce2780..131e7d529e 100644
--- a/gpg-interface.c
+++ b/gpg-interface.c
@@ -207,55 +207,6 @@ found_duplicate_status:
 	FREE_AND_NULL(sigc->key);
 }
 
-static int verify_signed_buffer(const char *payload, size_t payload_size,
-				const char *signature, size_t signature_size,
-				struct strbuf *gpg_output,
-				struct strbuf *gpg_status)
-{
-	struct child_process gpg = CHILD_PROCESS_INIT;
-	struct gpg_format *fmt;
-	struct tempfile *temp;
-	int ret;
-	struct strbuf buf = STRBUF_INIT;
-
-	temp = mks_tempfile_t(".git_vtag_tmpXXXXXX");
-	if (!temp)
-		return error_errno(_("could not create temporary file"));
-	if (write_in_full(temp->fd, signature, signature_size) < 0 ||
-	    close_tempfile_gently(temp) < 0) {
-		error_errno(_("failed writing detached signature to '%s'"),
-			    temp->filename.buf);
-		delete_tempfile(&temp);
-		return -1;
-	}
-
-	fmt = get_format_by_sig(signature);
-	if (!fmt)
-		BUG("bad signature '%s'", signature);
-
-	argv_array_push(&gpg.args, fmt->program);
-	argv_array_pushv(&gpg.args, fmt->verify_args);
-	argv_array_pushl(&gpg.args,
-			 "--status-fd=1",
-			 "--verify", temp->filename.buf, "-",
-			 NULL);
-
-	if (!gpg_status)
-		gpg_status = &buf;
-
-	sigchain_push(SIGPIPE, SIG_IGN);
-	ret = pipe_command(&gpg, payload, payload_size,
-			   gpg_status, 0, gpg_output, 0);
-	sigchain_pop(SIGPIPE);
-
-	delete_tempfile(&temp);
-
-	ret |= !strstr(gpg_status->buf, "\n[GNUPG:] GOODSIG ");
-	strbuf_release(&buf); /* no matter it was used or not */
-
-	return ret;
-}
-
 int check_signature(const char *payload, size_t plen, const char *signature,
 	size_t slen, struct signature_check *sigc)
 {
@@ -400,3 +351,51 @@ int sign_buffer(struct strbuf *buffer, struct strbuf *signature, const char *sig
 
 	return 0;
 }
+
+int verify_signed_buffer(const char *payload, size_t payload_size,
+			 const char *signature, size_t signature_size,
+			 struct strbuf *gpg_output, struct strbuf *gpg_status)
+{
+	struct child_process gpg = CHILD_PROCESS_INIT;
+	struct gpg_format *fmt;
+	struct tempfile *temp;
+	int ret;
+	struct strbuf buf = STRBUF_INIT;
+
+	temp = mks_tempfile_t(".git_vtag_tmpXXXXXX");
+	if (!temp)
+		return error_errno(_("could not create temporary file"));
+	if (write_in_full(temp->fd, signature, signature_size) < 0 ||
+	    close_tempfile_gently(temp) < 0) {
+		error_errno(_("failed writing detached signature to '%s'"),
+			    temp->filename.buf);
+		delete_tempfile(&temp);
+		return -1;
+	}
+
+	fmt = get_format_by_sig(signature);
+	if (!fmt)
+		BUG("bad signature '%s'", signature);
+
+	argv_array_push(&gpg.args, fmt->program);
+	argv_array_pushv(&gpg.args, fmt->verify_args);
+	argv_array_pushl(&gpg.args,
+			 "--status-fd=1",
+			 "--verify", temp->filename.buf, "-",
+			 NULL);
+
+	if (!gpg_status)
+		gpg_status = &buf;
+
+	sigchain_push(SIGPIPE, SIG_IGN);
+	ret = pipe_command(&gpg, payload, payload_size,
+			   gpg_status, 0, gpg_output, 0);
+	sigchain_pop(SIGPIPE);
+
+	delete_tempfile(&temp);
+
+	ret |= !strstr(gpg_status->buf, "\n[GNUPG:] GOODSIG ");
+	strbuf_release(&buf); /* no matter it was used or not */
+
+	return ret;
+}
diff --git a/gpg-interface.h b/gpg-interface.h
index 93cc3aff5c..3e624ec289 100644
--- a/gpg-interface.h
+++ b/gpg-interface.h
@@ -46,6 +46,15 @@ size_t parse_signature(const char *buf, size_t size);
 int sign_buffer(struct strbuf *buffer, struct strbuf *signature,
 		const char *signing_key);
 
+/*
+ * Run "gpg" to see if the payload matches the detached signature.
+ * gpg_output, when set, receives the diagnostic output from GPG.
+ * gpg_status, when set, receives the status output from GPG.
+ */
+int verify_signed_buffer(const char *payload, size_t payload_size,
+			 const char *signature, size_t signature_size,
+			 struct strbuf *gpg_output, struct strbuf *gpg_status);
+
 int git_gpg_config(const char *, const char *, void *);
 void set_signing_key(const char *);
 const char *get_signing_key(void);
diff --git a/log-tree.c b/log-tree.c
index aa6b038adb..1e56df62a7 100644
--- a/log-tree.c
+++ b/log-tree.c
@@ -448,22 +448,22 @@ static void show_signature(struct rev_info *opt, struct commit *commit)
 {
 	struct strbuf payload = STRBUF_INIT;
 	struct strbuf signature = STRBUF_INIT;
-	struct signature_check sigc = { 0 };
+	struct strbuf gpg_output = STRBUF_INIT;
 	int status;
 
 	if (parse_signed_commit(commit, &payload, &signature) <= 0)
 		goto out;
 
-	status = check_signature(payload.buf, payload.len, signature.buf,
-				 signature.len, &sigc);
-	if (status && sigc.result == 'N')
-		show_sig_lines(opt, status, "No signature\n");
-	else {
-		show_sig_lines(opt, status, sigc.gpg_output);
-		signature_check_clear(&sigc);
-	}
+	status = verify_signed_buffer(payload.buf, payload.len,
+				      signature.buf, signature.len,
+				      &gpg_output, NULL);
+	if (status && !gpg_output.len)
+		strbuf_addstr(&gpg_output, "No signature\n");
+
+	show_sig_lines(opt, status, gpg_output.buf);
 
  out:
+	strbuf_release(&gpg_output);
 	strbuf_release(&payload);
 	strbuf_release(&signature);
 }
@@ -496,7 +496,6 @@ static int show_one_mergetag(struct commit *commit,
 	struct object_id oid;
 	struct tag *tag;
 	struct strbuf verify_message;
-	struct signature_check sigc = { 0 };
 	int status, nth;
 	size_t payload_size, gpg_message_offset;
 
@@ -525,13 +524,12 @@ static int show_one_mergetag(struct commit *commit,
 	status = -1;
 	if (extra->len > payload_size) {
 		/* could have a good signature */
-		if (!check_signature(extra->value, payload_size,
-				     extra->value + payload_size,
-				     extra->len - payload_size, &sigc)) {
-			strbuf_addstr(&verify_message, sigc.gpg_output);
-			signature_check_clear(&sigc);
+		if (!verify_signed_buffer(extra->value, payload_size,
+					  extra->value + payload_size,
+					  extra->len - payload_size,
+					  &verify_message, NULL))
 			status = 0; /* good */
-		} else if (verify_message.len <= gpg_message_offset)
+		else if (verify_message.len <= gpg_message_offset)
 			strbuf_addstr(&verify_message, "No signature\n");
 		/* otherwise we couldn't verify, which is shown as bad */
 	}