Connect fast-import to the remote-helper via pipe, adding 'bidi-import' capability

The fast-import commands 'cat-blob' and 'ls' can be used by
remote-helpers to retrieve information about blobs and trees that
already exist in fast-import's memory. This requires a channel from
fast-import to the remote-helper.

remote-helpers that use these features shall advertise the new
'bidi-import' capability to signal that they require the communication
channel.  When forking fast-import in transport-helper.c connect it to
a dup of the remote-helper's stdin-pipe. The additional file
descriptor is passed to fast-import via its command line
(--cat-blob-fd).  It follows that git and fast-import are connected to
the remote-helpers's stdin.

Because git can send multiple commands to the remote-helper on it's
stdin, it is required that helpers that advertise 'bidi-import' buffer
all input commands until the batch of 'import' commands is ended by a
newline before sending data to fast-import.  This is to prevent mixing
commands and fast-import responses on the helper's stdin.

Signed-off-by: Florian Achleitner <florian.achleitner.2.6.31@gmail.com>
Acked-by: David Michael Barr <b@rr-dav.id.au>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/transport-helper.c b/transport-helper.c
index cfe098849022fcc56bcb1a57d00e4c89e753492b..3523f1ff56b9cde4ccaf4bd75686bb4a69318c39 100644 (file)
--- a/transport-helper.c
+++ b/transport-helper.c
@@ -10,6 +10,7 @@
 #include "string-list.h"
 #include "thread-utils.h"
 #include "sigchain.h"
+#include "argv-array.h"
 
 static int debug;
 
@@ -19,6 +20,7 @@ struct helper_data {
        FILE *out;
        unsigned fetch : 1,
                import : 1,
+               bidi_import : 1,
                export : 1,
                option : 1,
                push : 1,
@@ -101,6 +103,7 @@ static void do_take_over(struct transport *transport)
 static struct child_process *get_helper(struct transport *transport)
 {
        struct helper_data *data = transport->data;
+       struct argv_array argv = ARGV_ARRAY_INIT;
        struct strbuf buf = STRBUF_INIT;
        struct child_process *helper;
        const char **refspecs = NULL;
@@ -122,11 +125,10 @@ static struct child_process *get_helper(struct transport *transport)
        helper->in = -1;
        helper->out = -1;
        helper->err = 0;
-       helper->argv = xcalloc(4, sizeof(*helper->argv));
-       strbuf_addf(&buf, "git-remote-%s", data->name);
-       helper->argv[0] = strbuf_detach(&buf, NULL);
-       helper->argv[1] = transport->remote->name;
-       helper->argv[2] = remove_ext_force(transport->url);
+       argv_array_pushf(&argv, "git-remote-%s", data->name);
+       argv_array_push(&argv, transport->remote->name);
+       argv_array_push(&argv, remove_ext_force(transport->url));
+       helper->argv = argv_array_detach(&argv, NULL);
        helper->git_cmd = 0;
        helper->silent_exec_failure = 1;
 
@@ -178,6 +180,8 @@ static struct child_process *get_helper(struct transport *transport)
                        data->push = 1;
                else if (!strcmp(capname, "import"))
                        data->import = 1;
+               else if (!strcmp(capname, "bidi-import"))
+                       data->bidi_import = 1;
                else if (!strcmp(capname, "export"))
                        data->export = 1;
                else if (!data->refspecs && !prefixcmp(capname, "refspec ")) {
@@ -241,8 +245,7 @@ static int disconnect_helper(struct transport *transport)
                close(data->helper->out);
                fclose(data->out);
                res = finish_command(data->helper);
-               free((char *)data->helper->argv[0]);
-               free(data->helper->argv);
+               argv_array_free_detached(data->helper->argv);
                free(data->helper);
                data->helper = NULL;
        }
@@ -376,14 +379,23 @@ static int fetch_with_fetch(struct transport *transport,
 static int get_importer(struct transport *transport, struct child_process *fastimport)
 {
        struct child_process *helper = get_helper(transport);
+       struct helper_data *data = transport->data;
+       struct argv_array argv = ARGV_ARRAY_INIT;
+       int cat_blob_fd, code;
        memset(fastimport, 0, sizeof(*fastimport));
        fastimport->in = helper->out;
-       fastimport->argv = xcalloc(5, sizeof(*fastimport->argv));
-       fastimport->argv[0] = "fast-import";
-       fastimport->argv[1] = "--quiet";
+       argv_array_push(&argv, "fast-import");
+       argv_array_push(&argv, "--quiet");
 
+       if (data->bidi_import) {
+               cat_blob_fd = xdup(helper->in);
+               argv_array_pushf(&argv, "--cat-blob-fd=%d", cat_blob_fd);
+       }
+       fastimport->argv = argv.argv;
        fastimport->git_cmd = 1;
-       return start_command(fastimport);
+
+       code = start_command(fastimport);
+       return code;
 }
 
 static int get_exporter(struct transport *transport,
@@ -438,11 +450,17 @@ static int fetch_with_import(struct transport *transport,
        }
 
        write_constant(data->helper->in, "\n");
+       /*
+        * remote-helpers that advertise the bidi-import capability are required to
+        * buffer the complete batch of import commands until this newline before
+        * sending data to fast-import.
+        * These helpers read back data from fast-import on their stdin, which could
+        * be mixed with import commands, otherwise.
+        */
 
        if (finish_command(&fastimport))
                die("Error while running fast-import");
-       free(fastimport.argv);
-       fastimport.argv = NULL;
+       argv_array_free_detached(fastimport.argv);
 
        /*
         * The fast-import stream of a remote helper that advertises