[RFC] cat-file: add a --stdin-cmd mode
- From
John Cai <johncai86@gmail.com>
- Date
- Jan 21, 2022, 17:54 UTC
- Message-ID
- <20220121175405.45753-1-johncai86@gmail.com>
This RFC patch proposes a new flag --stdin-cmd that works with git-cat-file --batch. Similar to git-update-ref --stdin, it will accept commands and arguments from stdin.
The start of this idea was discussed in [1], where the original motivation was to be able to control when the buffer was flushed to stdout in --buffer mode.
However, this can actually be much more useful in situations when git-cat-file --batch is being used as a long lived backend query process. At GitLab, we use a pair of cat-file processes. One for iterating over object metadata with --batch-check, and the other to grab object contents with --batch. However, if we had --stdin-cmd, we could get rid of the second --batch-check process, and just have one progress where we can flip between getting object info, and getting object contents. This can lead to huge savings.
git cat-file --batch --stdin-cmd
$ <command> [arg1] [arg2] NL
We can also add a -z mode to allow for NUL-terminated lines
$ <command> [arg1] [arg2] NUL
This patch adds three commands: object, info, fflush
$ object <sha1> NL $ info <sha1> NL $ fflush NL
These three would be immediately useful in GitLab's context, but one can imagine this mode to be further extended for other things.
For instance, a non-trivial part of "cat-file --batch" time is spent on parsing its argument and seeing if it's a revision, ref etc. So we could add a command that only accepts a full-length 40 character SHA-1.
This would be the first step in adding such an interface to git-cat-file.
[1] https://lore.kernel.org/git/pull.1124.git.git.1636149400.gitgitgadget@gmail.com/
Helped-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com> Signed-off-by: John Cai <johncai86@gmail.com> --- builtin/cat-file.c | 137 +++++++++++++++++++++++++++++++++++++++++++- strvec.c | 23 ++++++++ strvec.h | 8 +++ t/t1006-cat-file.sh | 72 +++++++++++++++++++++++ 4 files changed, 239 insertions(+), 1 deletion(-)
diff --git a/builtin/cat-file.c b/builtin/cat-file.c index 7b3f42950e..2679b34b43 100644 --- a/builtin/cat-file.c +++ b/builtin/cat-file.c @@ -16,6 +16,7 @@ #include "packfile.h" #include "object-store.h" #include "promisor-remote.h" +#include "strvec.h" struct batch_options { int enabled; @@ -26,7 +27,10 @@ struct batch_options { int unordered; int cmdmode; /* may be 'w' or 'c' for --filters or --textconv */ const char *format; + int stdin_cmd; + int end_null; }; +static char line_termination = '\n'; static const char *force_path; @@ -508,6 +512,126 @@ static int batch_unordered_packed(const struct object_id *oid, data); } +enum batch_state { + /* Non-transactional state open for commands. */ + BATCH_STATE_OPEN, +}; + +static void parse_cmd_object(struct batch_options *opt, + const int argc, const char **argv, + struct strbuf *output, + struct expand_data *data) +{ + batch_one_object(argv[0], output, opt, data); +} + +static void parse_cmd_info(struct batch_options *opt, + const int argc, const char **argv, + struct strbuf *output, + struct expand_data *data) +{ + opt->print_contents = 0; + batch_one_object(argv[0], output, opt, data); +} + +static void parse_cmd_fflush(struct batch_options *opt, + const int argc, const char **argv, + struct strbuf *output, + struct expand_data *data) +{ + fflush(stdout); +} + +typedef void (*parse_cmd_fn_t)(struct batch_options *, const int, + const char **, struct strbuf *, + struct expand_data *); + +static const struct parse_cmd { + const char *prefix; + parse_cmd_fn_t fn; + unsigned args; + enum batch_state state; +} command[] = { + { "object", parse_cmd_object, 1, BATCH_STATE_OPEN }, + { "info", parse_cmd_info, 1, BATCH_STATE_OPEN }, + { "fflush", parse_cmd_fflush, 0, BATCH_STATE_OPEN }, +}; + +static void batch_objects_stdin_cmd(struct batch_options *opt, + struct strbuf *output, + struct expand_data *data) +{ + struct strbuf input = STRBUF_INIT; + enum batch_state state = BATCH_STATE_OPEN; + + /* Read each line dispatch its command */ + while (!strbuf_getwholeline(&input, stdin, line_termination)) { + int i; + const struct parse_cmd *cmd = NULL; + struct strvec args = STRVEC_INIT; + size_t n; + const char *p; + + if (*input.buf == line_termination) + die("empty command in input"); + else if (isspace(*input.buf)) + die("whitespace before command: %s", input.buf); + + for (i = 0; i < ARRAY_SIZE(command); i++) { + const char *prefix = command[i].prefix; + char c; + + if (!starts_with(input.buf, prefix)) + continue; + + /* + * If the command has arguments, verify that it's + * followed by a space. Otherwise, it shall be followed + * by a line terminator. + */ + c = command[i].args ? ' ' : line_termination; + if (input.buf[strlen(prefix)] != c) + continue; + + cmd = &command[i]; + break; + } + if (!cmd) + die("unknown command: %s", input.buf); + + /* + * Read additional arguments. Do not raise an error in + * case there is an early EOF to let the command + * handle missing arguments with a proper error message + */ + p = input.buf + strlen(cmd->prefix) + 1; + if (*p == line_termination || !*p) { + n = 0; + } else { + const char *pos = strstr(p, "\n"); + char *str = xstrndup(p, pos - p); + + n = strvec_split_delim(&args, str, ' ', - 1); + free(str); + } + + if (n < cmd->args) + die("%s: too few arguments", cmd->prefix); + if (n > cmd->args) + die("%s: too many arguments", cmd->prefix); + + switch (state) { + case BATCH_STATE_OPEN: + /* TODO: command state management */ + break; + } + cmd->fn(opt, args.nr, args.v, output, data); + strvec_clear(&args); + } + + strbuf_release(&input); +} + static int batch_objects(struct batch_options *opt) { struct strbuf input = STRBUF_INIT; @@ -515,6 +639,7 @@ static int batch_objects(struct batch_options *opt) struct expand_data data; int save_warning; int retval = 0; + const int stdin_cmd = opt->stdin_cmd; if (!opt->format) opt->format = "%(objectname) %(objecttype) %(objectsize)"; @@ -590,7 +715,8 @@ static int batch_objects(struct batch_options *opt) save_warning = warn_on_object_refname_ambiguity; warn_on_object_refname_ambiguity = 0; - while (strbuf_getline(&input, stdin) != EOF) { + while (!stdin_cmd && + strbuf_getline(&input, stdin) != EOF) { if (data.split_on_whitespace) { /* * Split at first whitespace, tying off the beginning @@ -608,6 +734,9 @@ static int batch_objects(struct batch_options *opt) batch_one_object(input.buf, &output, opt, &data); } + if (stdin_cmd) + batch_objects_stdin_cmd(opt, &output, &data); + strbuf_release(&input); strbuf_release(&output); warn_on_object_refname_ambiguity = save_warning; @@ -685,6 +814,10 @@ int cmd_cat_file(int argc, const char **argv, const char *prefix) batch_option_callback), OPT_CMDMODE(0, "batch-all-objects", &opt, N_("with --batch[-check]: ignores stdin, batches all known objects"), 'b'), + OPT_BOOL(0, "stdin-cmd", &batch.stdin_cmd, + N_("with --batch[-check]: enters stdin 'command mode")), + OPT_BOOL('z', NULL, &batch.end_null, N_("with --stdin-cmd, use NUL termination")), + /* Batch-specific options */ OPT_GROUP(N_("Change or optimize batch output")), OPT_BOOL(0, "buffer", &batch.buffer_output, N_("buffer --batch output")), @@ -738,6 +871,8 @@ int cmd_cat_file(int argc, const char **argv, const char *prefix) /* Batch defaults */ if (batch.buffer_output < 0) batch.buffer_output = batch.all_objects; + if (batch.end_null) + line_termination = '\0'; /* Return early if we're in batch mode? */ if (batch.enabled) { diff --git a/strvec.c b/strvec.c index 61a76ce6cb..7dca04bf7a 100644 --- a/strvec.c +++ b/strvec.c @@ -85,6 +85,29 @@ void strvec_split(struct strvec *array, const char *to_split) } } +size_t strvec_split_delim(struct strvec *array, const char *string, + int delim, int maxsplit) +{ + size_t count = 0; + const char *p = string, *end; + + for (;;) { + count++; + if (maxsplit >= 0 && count > maxsplit) { + strvec_push(array, p); + return count; + } + end = strchr(p, delim); + if (end) { + strvec_push_nodup(array, xmemdupz(p, end - p)); + p = end + 1; + } else { + strvec_push(array, p); + return count; + } + } +} + void strvec_clear(struct strvec *array) { if (array->v != empty_strvec) { diff --git a/strvec.h b/strvec.h index 9f55c8766b..c474918b91 100644 --- a/strvec.h +++ b/strvec.h @@ -73,6 +73,14 @@ void strvec_pop(struct strvec *); /* Splits by whitespace; does not handle quoted arguments! */ void strvec_split(struct strvec *, const char *); +/** + * strvec_split_delim() is a split function that behaves more like its + * string_list_split() cousin than the whitespace-splitting + * strvec_split(). + */ +size_t strvec_split_delim(struct strvec *array, const char *string, + int delim, int maxsplit); + /** * Free all memory associated with the array and return it to the * initial, empty state. diff --git a/t/t1006-cat-file.sh b/t/t1006-cat-file.sh index 145eee11df..8f339746ec 100755 --- a/t/t1006-cat-file.sh +++ b/t/t1006-cat-file.sh @@ -964,4 +964,76 @@ test_expect_success 'cat-file --batch-all-objects --batch-check ignores replace' test_cmp expect actual ' +F='%s\0' + +test_expect_success 'stdin-cmd not enough arguments' ' + echo "object " >cmd && + test_expect_code 128 git cat-file --batch --stdin-cmd < cmd 2>err && + grep -E "^fatal:.*too few arguments" err +' + +test_expect_success 'stdin-cmd too many arguments' ' + echo "object foo bar" >cmd && + test_expect_code 128 git cat-file --batch --stdin-cmd < cmd 2>err && + grep -E "^fatal:.*too many arguments" err +' + +test_expect_success 'stdin-cmd unknown command' ' + echo unknown_command >cmd && + test_expect_code 128 git cat-file --batch --stdin-cmd < cmd 2>err && + grep -E "^fatal:.*unknown command.*" err && + test_expect_code 128 git cat-file --batch --stdin-cmd -z < cmd 2>err && + grep -E "^fatal:.*unknown command.*" err +' + +test_expect_success 'setup object data' ' + content="Object Data" && + size=$(strlen "$content") && + sha1=$(echo_without_newline "$content" | git hash-object -w --stdin) +' + +test_expect_success 'stdin-cmd calling object works' ' + echo "object $sha1" | git cat-file --batch --stdin-cmd >actual && + echo "$sha1 blob $size" >expect && + echo `git cat-file -p "$sha1"` >>expect && + test_cmp expect actual +' + +test_expect_success 'stdin-cmd -z calling object works' ' + printf $F "object $sha1" | git cat-file --batch --stdin-cmd -z >actual && + echo "$sha1 blob $size" >expect && + echo `git cat-file -p "$sha1"` >>expect && + test_cmp expect actual +' + +test_expect_success 'setup object data' ' + content="Object Data" && + size=$(strlen "$content") && + sha1=$(echo_without_newline "$content" | git hash-object -w --stdin) +' + +test_expect_success 'stdin-cmd calling object works' ' + echo "object $sha1" | git cat-file --batch --stdin-cmd >actual && + echo "$sha1 blob $size" >expect && + echo `git cat-file -p "$sha1"` >>expect && + test_cmp expect actual +' + +test_expect_success 'stdin-cmd -z calling object works' ' + printf $F "object $sha1" | git cat-file --batch --stdin-cmd -z >actual && + echo "$sha1 blob $size" >expect && + echo `git cat-file -p "$sha1"` >>expect && + test_cmp expect actual +' + +test_expect_success 'stdin-cmd fflush works' ' + printf "fflush\n" > cmd && + test_expect_code 0 git cat-file --batch --stdin-cmd < cmd 2>err +' + +test_expect_success 'stdin-cmd -z fflush works' ' + printf $F 'fflush' > cmd && + test_expect_code 0 git cat-file --batch --stdin-cmd -z < cmd 2>err +' + test_done
-- 2.34.1