shallow: automatically clean up shallow tempfiles

We sometimes write tempfiles of the form "shallow_XXXXXX"
during fetch/push operations with shallow repositories.
Under normal circumstances, we clean up the result when we
are done. However, we do no take steps to clean up after
ourselves when we exit due to die() or signal death.

This patch teaches the tempfile creation code to register
handlers to clean up after ourselves. To handle this, we
change the ownership semantics of the filename returned by
setup_temporary_shallow. It now keeps a copy of the filename
itself, and returns only a const pointer to it.

We can also do away with explicit tempfile removal in the
callers. They all exit not long after finishing with the
file, so they can rely on the auto-cleanup, simplifying the
code.

Note that we keep things simple and maintain only a single
filename to be cleaned. This is sufficient for the current
caller, but we future-proof it with a die("BUG").

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/receive-pack.c

@@ -828,14 +828,10 @@ static void execute_commands(struct command *commands,
 		}
 	}
 
-	if (shallow_update) {
-		if (!checked_connectivity)
-			error("BUG: run 'git fsck' for safety.\n"
-			      "If there are errors, try to remove "
-			      "the reported refs above");
-		if (alt_shallow_file && *alt_shallow_file)
-			unlink(alt_shallow_file);
-	}
+	if (shallow_update && !checked_connectivity)
+		error("BUG: run 'git fsck' for safety.\n"
+		      "If there are errors, try to remove "
+		      "the reported refs above");
 }
 
 static struct command *read_head_info(struct sha1_array *shallow)
@@ -1087,10 +1083,6 @@ static void update_shallow_info(struct command *commands,
 			cmd->skip_update = 1;
 		}
 	}
-	if (alt_shallow_file && *alt_shallow_file) {
-		unlink(alt_shallow_file);
-		alt_shallow_file = NULL;
-	}
 	free(ref_status);
 }
 

commit.h

@@ -209,7 +209,7 @@ extern int write_shallow_commits(struct strbuf *out, int use_pack_protocol,
 extern void setup_alternate_shallow(struct lock_file *shallow_lock,
 				    const char **alternate_shallow_file,
 				    const struct sha1_array *extra);
-extern char *setup_temporary_shallow(const struct sha1_array *extra);
+extern const char *setup_temporary_shallow(const struct sha1_array *extra);
 extern void advertise_shallow_grafts(int);
 
 struct shallow_info {

fetch-pack.c

@@ -947,17 +947,6 @@ static void update_shallow(struct fetch_pack_args *args,
 	if (!si->shallow || !si->shallow->nr)
 		return;
 
-	if (alternate_shallow_file) {
-		/*
-		 * The temporary shallow file is only useful for
-		 * index-pack and unpack-objects because it may
-		 * contain more roots than we want. Delete it.
-		 */
-		if (*alternate_shallow_file)
-			unlink(alternate_shallow_file);
-		free((char *)alternate_shallow_file);
-	}
-
 	if (args->cloning) {
 		/*
 		 * remote is shallow, but this is a clone, there are

shallow.c

@@ -8,6 +8,7 @@
 #include "diff.h"
 #include "revision.h"
 #include "commit-slab.h"
+#include "sigchain.h"
 
 static int is_shallow = -1;
 static struct stat_validity shallow_stat;
@@ -206,27 +207,53 @@ int write_shallow_commits(struct strbuf *out, int use_pack_protocol,
 	return write_shallow_commits_1(out, use_pack_protocol, extra, 0);
 }
 
-char *setup_temporary_shallow(const struct sha1_array *extra)
+static struct strbuf temporary_shallow = STRBUF_INIT;
+
+static void remove_temporary_shallow(void)
 {
+	if (temporary_shallow.len) {
+		unlink_or_warn(temporary_shallow.buf);
+		strbuf_reset(&temporary_shallow);
+	}
+}
+
+static void remove_temporary_shallow_on_signal(int signo)
+{
+	remove_temporary_shallow();
+	sigchain_pop(signo);
+	raise(signo);
+}
+
+const char *setup_temporary_shallow(const struct sha1_array *extra)
+{
+	static int installed_handler;
 	struct strbuf sb = STRBUF_INIT;
 	int fd;
 
+	if (temporary_shallow.len)
+		die("BUG: attempt to create two temporary shallow files");
+
 	if (write_shallow_commits(&sb, 0, extra)) {
-		struct strbuf path = STRBUF_INIT;
-		strbuf_addstr(&path, git_path("shallow_XXXXXX"));
-		fd = xmkstemp(path.buf);
+		strbuf_addstr(&temporary_shallow, git_path("shallow_XXXXXX"));
+		fd = xmkstemp(temporary_shallow.buf);
+
+		if (!installed_handler) {
+			atexit(remove_temporary_shallow);
+			sigchain_push_common(remove_temporary_shallow_on_signal);
+		}
+
 		if (write_in_full(fd, sb.buf, sb.len) != sb.len)
 			die_errno("failed to write to %s",
-				  path.buf);
+				  temporary_shallow.buf);
 		close(fd);
 		strbuf_release(&sb);
-		return strbuf_detach(&path, NULL);
+		return temporary_shallow.buf;
 	}
 	/*
 	 * is_repository_shallow() sees empty string as "no shallow
 	 * file".
 	 */
-	return xstrdup("");
+	return temporary_shallow.buf;
 }
 
 void setup_alternate_shallow(struct lock_file *shallow_lock,

upload-pack.c

@@ -81,7 +81,7 @@ static void create_pack_file(void)
 	const char *argv[12];
 	int i, arg = 0;
 	FILE *pipe_fd;
-	char *shallow_file = NULL;
+	const char *shallow_file = NULL;
 
 	if (shallow_nr) {
 		shallow_file = setup_temporary_shallow(NULL);
@@ -242,11 +242,6 @@ static void create_pack_file(void)
 		error("git upload-pack: git-pack-objects died with error.");
 		goto fail;
 	}
-	if (shallow_file) {
-		if (*shallow_file)
-			unlink(shallow_file);
-		free(shallow_file);
-	}
 
 	/* flush the data */
 	if (0 <= buffered) {