cli: add `cat-file` command

Introduce a simple command that emulates `git cat-file`.

src/cli/cmd.h

@@ -25,6 +25,7 @@ extern const cli_cmd_spec cli_cmds[];
 extern const cli_cmd_spec *cli_cmd_spec_byname(const char *name);
 
 /* Commands */
+extern int cmd_cat_file(int argc, char **argv);
 extern int cmd_help(int argc, char **argv);
 
 #endif /* CLI_cmd_h__ */

src/cli/cmd_cat_file.c

+/*
+ * Copyright (C) the libgit2 contributors. All rights reserved.
+ *
+ * This file is part of libgit2, distributed under the GNU GPL v2 with
+ * a Linking Exception. For full terms see the included COPYING file.
+ */
+
+#include <git2.h>
+#include "cli.h"
+#include "cmd.h"
+
+#define COMMAND_NAME "cat-file"
+
+typedef enum {
+	DISPLAY_CONTENT = 0,
+	DISPLAY_EXISTS,
+	DISPLAY_PRETTY,
+	DISPLAY_SIZE,
+	DISPLAY_TYPE
+} display_t;
+
+static int show_help;
+static int display = DISPLAY_CONTENT;
+static char *type_name, *object_spec;
+
+static const cli_opt_spec opts[] = {
+	{ CLI_OPT_TYPE_SWITCH,    "help",    0, &show_help,   1,
+	  CLI_OPT_USAGE_HIDDEN | CLI_OPT_USAGE_STOP_PARSING, NULL,
+	  "display help about the " COMMAND_NAME " command" },
+
+	{ CLI_OPT_TYPE_SWITCH,     NULL,    't', &display,    DISPLAY_TYPE,
+	  CLI_OPT_USAGE_REQUIRED,  NULL,    "display the type of the object" },
+	{ CLI_OPT_TYPE_SWITCH,     NULL,    's', &display,    DISPLAY_SIZE,
+	  CLI_OPT_USAGE_CHOICE,    NULL,    "display the size of the object" },
+	{ CLI_OPT_TYPE_SWITCH,     NULL,    'e', &display,    DISPLAY_EXISTS,
+	  CLI_OPT_USAGE_CHOICE,    NULL,    "displays nothing unless the object is corrupt" },
+	{ CLI_OPT_TYPE_SWITCH,     NULL,    'p', &display,    DISPLAY_PRETTY,
+	  CLI_OPT_USAGE_CHOICE,    NULL,    "pretty-print the object" },
+	{ CLI_OPT_TYPE_ARG,       "type",    0, &type_name,   0,
+	  CLI_OPT_USAGE_CHOICE,   "type",   "the type of object to display" },
+	{ CLI_OPT_TYPE_ARG,       "object",  0, &object_spec, 0,
+	  CLI_OPT_USAGE_REQUIRED, "object", "the object to display" },
+	{ 0 },
+};
+
+static void print_help(void)
+{
+	cli_opt_usage_fprint(stdout, PROGRAM_NAME, COMMAND_NAME, opts);
+	printf("\n");
+
+	printf("Display the content for the given object in the repository.\n");
+	printf("\n");
+
+	printf("Options:\n");
+
+	cli_opt_help_fprint(stdout, opts);
+}
+
+static int print_odb(git_object *object, display_t display)
+{
+	git_odb *odb = NULL;
+	git_odb_object *odb_object = NULL;
+	const unsigned char *content;
+	git_object_size_t size;
+	int ret = 0;
+
+	/*
+	 * Our parsed blobs retain the raw content; all other objects are
+	 * parsed into a working representation.  To get the raw content,
+	 * we need to do an ODB lookup.  (Thankfully, this should be cached
+	 * in-memory from our last call.)
+	 */
+	if (git_object_type(object) == GIT_OBJECT_BLOB) {
+		content = git_blob_rawcontent((git_blob *)object);
+		size = git_blob_rawsize((git_blob *)object);
+	} else {
+		if (git_repository_odb(&odb, git_object_owner(object)) < 0 ||
+		    git_odb_read(&odb_object, odb, git_object_id(object)) < 0) {
+			ret = cli_error_git();
+			goto done;
+		}
+
+		content = git_odb_object_data(odb_object);
+		size = git_odb_object_size(odb_object);
+	}
+
+	switch (display) {
+	case DISPLAY_SIZE:
+		if (printf("%" PRIu64 "\n", size) < 0)
+			ret = cli_error_os();
+		break;
+	case DISPLAY_CONTENT:
+		if (p_write(fileno(stdout), content, (size_t)size) < 0)
+			ret = cli_error_os();
+		break;
+	default:
+		GIT_ASSERT(0);
+	}
+
+done:
+	git_odb_object_free(odb_object);
+	git_odb_free(odb);
+	return ret;
+}
+
+static int print_type(git_object *object)
+{
+	if (printf("%s\n", git_object_type2string(git_object_type(object))) < 0)
+		return cli_error_os();
+
+	return 0;
+}
+
+static int print_pretty(git_object *object)
+{
+	const git_tree_entry *entry;
+	size_t i, count;
+
+	/*
+	 * Only trees are stored in an unreadable format and benefit from
+	 * pretty-printing.
+	 */
+	if (git_object_type(object) != GIT_OBJECT_TREE)
+		return print_odb(object, DISPLAY_CONTENT);
+
+	for (i = 0, count = git_tree_entrycount((git_tree *)object); i < count; i++) {
+		entry = git_tree_entry_byindex((git_tree *)object, i);
+
+		if (printf("%06o %s %s\t%s\n",
+		           git_tree_entry_filemode_raw(entry),
+		           git_object_type2string(git_tree_entry_type(entry)),
+		           git_oid_tostr_s(git_tree_entry_id(entry)),
+		           git_tree_entry_name(entry)) < 0)
+			return cli_error_os();
+	}
+
+	return 0;
+}
+
+int cmd_cat_file(int argc, char **argv)
+{
+	git_repository *repo = NULL;
+	git_object *object = NULL;
+	git_object_t type;
+	cli_opt invalid_opt;
+	int giterr, ret = 0;
+
+	if (cli_opt_parse(&invalid_opt, opts, argv + 1, argc - 1, CLI_OPT_PARSE_GNU))
+		return cli_opt_usage_error(COMMAND_NAME, opts, &invalid_opt);
+
+	if (show_help) {
+		print_help();
+		return 0;
+	}
+
+	if (git_repository_open_ext(&repo, ".", GIT_REPOSITORY_OPEN_FROM_ENV, NULL) < 0)
+		return cli_error_git();
+
+	if ((giterr = git_revparse_single(&object, repo, object_spec)) < 0) {
+		if (display == DISPLAY_EXISTS && giterr == GIT_ENOTFOUND)
+			ret = 1;
+		else
+			ret = cli_error_git();
+
+		goto done;
+	}
+
+	if (type_name) {
+		git_object *peeled;
+
+		if ((type = git_object_string2type(type_name)) == GIT_OBJECT_INVALID) {
+			ret = cli_error_usage("invalid object type '%s'", type_name);
+			goto done;
+		}
+
+		if (git_object_peel(&peeled, object, type) < 0) {
+			ret = cli_error_git();
+			goto done;
+		}
+
+		git_object_free(object);
+		object = peeled;
+	}
+
+	switch (display) {
+	case DISPLAY_EXISTS:
+		ret = 0;
+		break;
+	case DISPLAY_TYPE:
+		ret = print_type(object);
+		break;
+	case DISPLAY_PRETTY:
+		ret = print_pretty(object);
+		break;
+	default:
+		ret = print_odb(object, display);
+		break;
+	}
+
+done:
+	git_object_free(object);
+	git_repository_free(repo);
+	return ret;
+}

src/cli/main.c

@@ -28,6 +28,7 @@ const cli_opt_spec cli_common_opts[] = {
 };
 
 const cli_cmd_spec cli_cmds[] = {
+	{ "cat-file", cmd_cat_file, "Display an object in the repository" },
 	{ "help",     cmd_help,     "Display help information" },
 	{ NULL }
 };