test-tool: learn to act as a drop-in replacement for iconv

It is convenient to assume that everybody who wants to build & test Git
has access to a working `iconv` executable (after all, we already pretty
much require libiconv).

However, that limits esoteric test scenarios such as Git for Windows',
where an end user installation has to ship with `iconv` for the sole
purpose of being testable. That payload serves no other purpose.

So let's just have a test helper (to be able to test Git, the test
helpers have to be available, after all) to act as `iconv` replacement.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Makefile

@@ -820,6 +820,7 @@ TEST_BUILTINS_OBJS += test-hash-speed.o
 TEST_BUILTINS_OBJS += test-hash.o
 TEST_BUILTINS_OBJS += test-hashmap.o
 TEST_BUILTINS_OBJS += test-hexdump.o
+TEST_BUILTINS_OBJS += test-iconv.o
 TEST_BUILTINS_OBJS += test-json-writer.o
 TEST_BUILTINS_OBJS += test-lazy-init-name-hash.o
 TEST_BUILTINS_OBJS += test-match-trees.o

t/helper/test-iconv.c

@@ -0,0 +1,47 @@
+#include "test-tool.h"
+#include "git-compat-util.h"
+#include "strbuf.h"
+#include "gettext.h"
+#include "parse-options.h"
+#include "utf8.h"
+
+int cmd__iconv(int argc, const char **argv)
+{
+	struct strbuf buf = STRBUF_INIT;
+	char *from = NULL, *to = NULL, *p;
+	size_t len;
+	int ret = 0;
+	const char * const iconv_usage[] = {
+		N_("test-helper --iconv [<options>]"),
+		NULL
+	};
+	struct option options[] = {
+		OPT_STRING('f', "from-code", &from, "encoding", "from"),
+		OPT_STRING('t', "to-code", &to, "encoding", "to"),
+		OPT_END()
+	};
+
+	argc = parse_options(argc, argv, NULL, options,
+			iconv_usage, 0);
+
+	if (argc > 1 || !from || !to)
+		usage_with_options(iconv_usage, options);
+
+	if (!argc) {
+		if (strbuf_read(&buf, 0, 2048) < 0)
+			die_errno("Could not read from stdin");
+	} else if (strbuf_read_file(&buf, argv[0], 2048) < 0)
+		die_errno("Could not read from '%s'", argv[0]);
+
+	p = reencode_string_len(buf.buf, buf.len, to, from, &len);
+	if (!p)
+		die_errno("Could not reencode");
+	if (write(1, p, len) < 0)
+		ret = !!error_errno("Could not write %"PRIuMAX" bytes",
+				    (uintmax_t)len);
+
+	strbuf_release(&buf);
+	free(p);
+
+	return ret;
+}

t/helper/test-tool.c

@@ -37,6 +37,7 @@ static struct test_cmd cmds[] = {
 	{ "hashmap", cmd__hashmap },
 	{ "hash-speed", cmd__hash_speed },
 	{ "hexdump", cmd__hexdump },
+	{ "iconv", cmd__iconv },
 	{ "json-writer", cmd__json_writer },
 	{ "lazy-init-name-hash", cmd__lazy_init_name_hash },
 	{ "match-trees", cmd__match_trees },

t/helper/test-tool.h

@@ -31,6 +31,7 @@ int cmd__getcwd(int argc, const char **argv);
 int cmd__hashmap(int argc, const char **argv);
 int cmd__hash_speed(int argc, const char **argv);
 int cmd__hexdump(int argc, const char **argv);
+int cmd__iconv(int argc, const char **argv);
 int cmd__json_writer(int argc, const char **argv);
 int cmd__lazy_init_name_hash(int argc, const char **argv);
 int cmd__match_trees(int argc, const char **argv);