Hey Phillip, First of all thank you for the thorough review—it really helps someone who’s learning how to contribute! On 27 Jan 2022, at 6:25, Phillip Wood wrote: > Hi John > > On 25/01/2022 22:50, John Cai wrote: >> 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@xxxxxxxxx/ >> >> Helped-by: Ævar Arnfjörð Bjarmason <avarab@xxxxxxxxx> >> Signed-off-by: John Cai <johncai86@xxxxxxxxx> >> --- >> Changes from v1: >> >> - changed option name to batch-command. >> - changed command function interface to receive the whole line after the command >> name to put the onus of parsing arguments to each individual command function. >> - pass in whole line to batch_one_object in both parse_cmd_object and >> parse_cmd_info to support spaces in the object reference. >> - removed addition of -z to include in a separate patch series >> - added documentation. > > I've left some comments below, they're mostly small details, I like the new option name and the changes you've made to the command parsing. > >> --- >> Documentation/git-cat-file.txt | 15 +++++ >> builtin/cat-file.c | 114 ++++++++++++++++++++++++++++++++- >> strvec.c | 23 +++++++ >> strvec.h | 8 +++ >> t/t1006-cat-file.sh | 32 +++++++++ >> 5 files changed, 191 insertions(+), 1 deletion(-) >> >> diff --git a/Documentation/git-cat-file.txt b/Documentation/git-cat-file.txt >> index bef76f4dd0..8aefa45e4c 100644 >> --- a/Documentation/git-cat-file.txt >> +++ b/Documentation/git-cat-file.txt >> @@ -96,6 +96,21 @@ OPTIONS >> need to specify the path, separated by whitespace. See the >> section `BATCH OUTPUT` below for details. >> +-batch-command:: > > is this missing a '-'? > >> + Enter a command mode that reads from stdin. May not be combined with any >> + other options or arguments except `--textconv` or `--filters`, in which >> + case the input lines also need to specify the path, separated by >> + whitespace. See the section `BATCH OUTPUT` below for details. >> + >> +object <object>:: >> + Print object contents for object reference <object> >> + >> +info <object>:: >> + Print object info for object reference <object> >> + >> +flush:: >> + Flush to stdout immediately when used with --buffer >> + >> --batch-all-objects:: >> Instead of reading a list of objects on stdin, perform the >> requested batch operation on all objects in the repository and >> diff --git a/builtin/cat-file.c b/builtin/cat-file.c >> index 7b3f42950e..30794284d5 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; > > Now that the option has been renamed it would be nice to rename the corresponding variable to match I was trying to find a good name. There is already a cmdmode variable. I’m thinking stdin_cmd is not such a bad name since we are receiving commands from stdin. suggestions welcome! > >> + int end_null; > > If you're not adding '-z' here then you don't need this or the addition below. > >> }; >> +static char line_termination = '\n'; >> static const char *force_path; >> @@ -508,6 +512,102 @@ static int batch_unordered_packed(const struct object_id *oid, >> data); >> } >> +enum batch_state { >> + /* Non-transactional state open for commands. */ >> + BATCH_STATE_OPEN, >> +}; > > I forgot to ask what the idea behind the batch state is last time - what's it for? This is to support transactional semantics for commands we want to support in the future, but since this is already a biggish change, we can leave this out of this series. > >> +static void parse_cmd_object(struct batch_options *opt, >> + const char *line, >> + struct strbuf *output, >> + struct expand_data *data) >> +{ >> + opt->print_contents = 1; >> + batch_one_object(line, output, opt, data); >> +} >> + >> +static void parse_cmd_info(struct batch_options *opt, >> + const char *line, >> + struct strbuf *output, >> + struct expand_data *data) >> +{ >> + opt->print_contents = 0; >> + batch_one_object(line, output, opt, data); >> +} >> + >> +static void parse_cmd_fflush(struct batch_options *opt, >> + const char *line, >> + struct strbuf *output, >> + struct expand_data *data) >> +{ >> + fflush(stdout); >> +} >> + >> +typedef void (*parse_cmd_fn_t)(struct batch_options *, const char *, >> + struct strbuf *, struct expand_data *); >> + >> +static const struct parse_cmd { >> + const char *prefix; >> + parse_cmd_fn_t fn; >> + unsigned args; > > This is now a flag so maybe 'takes_args' would better describe its purpose. > >> + enum batch_state state; >> +} commands[] = { >> + { "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; >> + 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(commands); i++) { >> + const char *prefix = commands[i].prefix; >> + char c; >> + const char *cmd_name; > > skip_prefix() sets this to the end of the name so maybe 'cmd_end' would be clearer? > >> + if (!skip_prefix(input.buf, prefix, &cmd_name)) >> + continue; >> + /* >> + * If the command has arguments, verify that it's >> + * followed by a space. Otherwise, it shall be followed >> + * by a line terminator. >> + */ >> + c = commands[i].args ? ' ' : line_termination; >> + if (input.buf[strlen(prefix)] != c) > > Now that you're using skip_prefix() you can write this as > if (*cmd_end != c) > >> + continue; >> + >> + cmd = &commands[i]; >> + break; >> + } >> + if (!cmd) >> + die("unknown command: %s", input.buf); >> + >> + p = input.buf + strlen(cmd->prefix) + 1; > > This can be simplified to > p = cmd_end + 1; > >> + const char *pos = strstr(p, &line_termination); > > This isn't needed without '-z'. If it were required then using strchrnul() would prevent a NULL pointer dereference when the last input line does not end with a terminator. I think we typically call a pointer to the end of the line 'eol' or 'end'. Also variables should be declared at the top of the function. > >> + switch (state) { >> + case BATCH_STATE_OPEN: >> + break; >> + } >> + cmd->fn(opt, xstrndup(p, pos-p), output, data); > > Is there a reason this is passing a copy of the string? > >> + } >> + strbuf_release(&input); >> +} >> + >> static int batch_objects(struct batch_options *opt) >> { >> struct strbuf input = STRBUF_INIT; >> @@ -515,6 +615,7 @@ 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 +691,8 @@ 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 && > > If you moved the 'if (stdin_cmd)' block above this block we could loose this change. I'm not sure if that is possible without looking at the whole function though. > >> + strbuf_getline(&input, stdin) != EOF) { >> if (data.split_on_whitespace) { >> /* >> * Split at first whitespace, tying off the beginning >> @@ -608,6 +710,9 @@ 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; >> @@ -636,6 +741,7 @@ static int batch_option_callback(const struct option *opt, >> bo->enabled = 1; >> bo->print_contents = !strcmp(opt->long_name, "batch"); >> + bo->stdin_cmd = !strcmp(opt->long_name, "batch-command"); >> bo->format = arg; >> return 0; >> @@ -683,6 +789,10 @@ int cmd_cat_file(int argc, const char **argv, const char *prefix) >> N_("like --batch, but don't emit <contents>"), >> PARSE_OPT_OPTARG | PARSE_OPT_NONEG, >> batch_option_callback), >> + OPT_CALLBACK_F(0, "batch-command", &batch, N_(""), >> + N_("enters batch mode that accepts commands"), >> + PARSE_OPT_NOARG | PARSE_OPT_NONEG, >> + batch_option_callback), >> OPT_CMDMODE(0, "batch-all-objects", &opt, >> N_("with --batch[-check]: ignores stdin, batches all known objects"), 'b'), >> /* Batch-specific options */ >> @@ -738,6 +848,8 @@ 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 >> [...] > > We don't need any strvec changes now that we don't split the input lines to --bactch-command > >> +F='%s\0' > > This isn't used now > >> +test_expect_success 'batch-command unknown command' ' >> + echo unknown_command >cmd && >> + test_expect_code 128 git cat-file --batch-command < 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 'batch-command calling object works' ' >> + echo "object $sha1" | git cat-file --batch-command >actual && >> + echo "$sha1 blob $size" >expect && >> + echo `git cat-file -p "$sha1"` >>expect && >> + test_cmp expect actual >> +' >> + >> +test_expect_success 'batch-command calling info works' ' >> + echo "info $sha1" | git cat-file --batch-command >actual && >> + echo "$sha1 blob $size" >expect && >> + test_cmp expect actual >> +' > > I had a quick look at this test file and there is a loop at the top that runs some --batch tests on various inputs, I wonder if these two tests could go in there. > >> +test_expect_success 'batch-command fflush works' ' >> + printf "fflush\n" > cmd && >> + test_expect_code 0 git cat-file --batch-command < cmd 2>err >> +' > > It'd be nice to check this actually flushes the output. could you give me some ideas on how to do this? > > Best Wishes > > Phillip > >> test_done
