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![Taylor Blau](/assets/img/avatar_default.png)
We added an "object-info" capability to the v2 upload-pack protocol in
a2ba162cda
(object-info: support for retrieving object info,
2021-04-20). In the almost 3 years since, we have not added any
client-side support, and it does not appear to exist in other
implementations either (JGit understands the verb on the server side,
but not on the client side).
Since this largely unused code is accessible over the network by
default, it increases the attack surface of upload-pack. I don't know of
any particularly severe problem, but one issue is that because of the
request/response nature of the v2 protocol, it will happily read an
unbounded number of packets, adding each one to a string list (without
regard to whether they are objects we know about, duplicates, etc).
This may be something we want to improve in the long run, but in the
short term it makes sense to disable the feature entirely. We'll add a
config option as an escape hatch for anybody who wants to develop the
feature further.
A more gentle option would be to add the config option to let people
disable it manually, but leave it enabled by default. But given that
there's no client side support, that seems like the wrong balance with
security.
Disabling by default will slow adoption a bit once client-side support
does become available (there were some patches[1] in 2022, but nothing
got merged and there's been nothing since). But clients have to deal
with older servers that do not understand the option anyway (and the
capability system handles that), so it will just be a matter of servers
flipping their config at that point (and hopefully once any unbounded
allocations have been addressed).
[jk: this is a patch that GitHub has been running for several years, but
rebased forward and with a new commit message for upstream]
[1] https://lore.kernel.org/git/20220208231911.725273-1-calvinwan@google.com/
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
350 lines
8.3 KiB
C
350 lines
8.3 KiB
C
#include "git-compat-util.h"
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#include "repository.h"
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#include "config.h"
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#include "hash-ll.h"
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#include "pkt-line.h"
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#include "version.h"
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#include "ls-refs.h"
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#include "protocol-caps.h"
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#include "serve.h"
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#include "upload-pack.h"
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#include "bundle-uri.h"
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#include "trace2.h"
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static int advertise_sid = -1;
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static int advertise_object_info = -1;
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static int client_hash_algo = GIT_HASH_SHA1;
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static int always_advertise(struct repository *r UNUSED,
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struct strbuf *value UNUSED)
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{
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return 1;
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}
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static int agent_advertise(struct repository *r UNUSED,
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struct strbuf *value)
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{
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if (value)
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strbuf_addstr(value, git_user_agent_sanitized());
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return 1;
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}
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static int object_format_advertise(struct repository *r,
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struct strbuf *value)
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{
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if (value)
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strbuf_addstr(value, r->hash_algo->name);
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return 1;
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}
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static void object_format_receive(struct repository *r UNUSED,
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const char *algo_name)
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{
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if (!algo_name)
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die("object-format capability requires an argument");
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client_hash_algo = hash_algo_by_name(algo_name);
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if (client_hash_algo == GIT_HASH_UNKNOWN)
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die("unknown object format '%s'", algo_name);
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}
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static int session_id_advertise(struct repository *r, struct strbuf *value)
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{
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if (advertise_sid == -1 &&
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repo_config_get_bool(r, "transfer.advertisesid", &advertise_sid))
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advertise_sid = 0;
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if (!advertise_sid)
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return 0;
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if (value)
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strbuf_addstr(value, trace2_session_id());
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return 1;
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}
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static void session_id_receive(struct repository *r UNUSED,
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const char *client_sid)
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{
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if (!client_sid)
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client_sid = "";
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trace2_data_string("transfer", NULL, "client-sid", client_sid);
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}
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static int object_info_advertise(struct repository *r, struct strbuf *value UNUSED)
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{
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if (advertise_object_info == -1 &&
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repo_config_get_bool(r, "transfer.advertiseobjectinfo",
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&advertise_object_info)) {
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/* disabled by default */
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advertise_object_info = 0;
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}
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return advertise_object_info;
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}
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struct protocol_capability {
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/*
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* The name of the capability. The server uses this name when
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* advertising this capability, and the client uses this name to
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* specify this capability.
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*/
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const char *name;
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/*
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* Function queried to see if a capability should be advertised.
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* Optionally a value can be specified by adding it to 'value'.
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* If a value is added to 'value', the server will advertise this
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* capability as "<name>=<value>" instead of "<name>".
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*/
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int (*advertise)(struct repository *r, struct strbuf *value);
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/*
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* Function called when a client requests the capability as a command.
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* Will be provided a struct packet_reader 'request' which it should
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* use to read the command specific part of the request. Every command
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* MUST read until a flush packet is seen before sending a response.
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*
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* This field should be NULL for capabilities which are not commands.
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*/
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int (*command)(struct repository *r, struct packet_reader *request);
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/*
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* Function called when a client requests the capability as a
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* non-command. This may be NULL if the capability does nothing.
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*
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* For a capability of the form "foo=bar", the value string points to
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* the content after the "=" (i.e., "bar"). For simple capabilities
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* (just "foo"), it is NULL.
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*/
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void (*receive)(struct repository *r, const char *value);
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};
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static struct protocol_capability capabilities[] = {
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{
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.name = "agent",
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.advertise = agent_advertise,
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},
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{
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.name = "ls-refs",
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.advertise = ls_refs_advertise,
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.command = ls_refs,
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},
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{
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.name = "fetch",
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.advertise = upload_pack_advertise,
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.command = upload_pack_v2,
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},
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{
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.name = "server-option",
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.advertise = always_advertise,
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},
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{
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.name = "object-format",
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.advertise = object_format_advertise,
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.receive = object_format_receive,
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},
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{
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.name = "session-id",
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.advertise = session_id_advertise,
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.receive = session_id_receive,
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},
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{
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.name = "object-info",
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.advertise = object_info_advertise,
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.command = cap_object_info,
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},
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{
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.name = "bundle-uri",
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.advertise = bundle_uri_advertise,
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.command = bundle_uri_command,
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},
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};
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void protocol_v2_advertise_capabilities(void)
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{
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struct strbuf capability = STRBUF_INIT;
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struct strbuf value = STRBUF_INIT;
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int i;
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/* serve by default supports v2 */
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packet_write_fmt(1, "version 2\n");
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for (i = 0; i < ARRAY_SIZE(capabilities); i++) {
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struct protocol_capability *c = &capabilities[i];
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if (c->advertise(the_repository, &value)) {
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strbuf_addstr(&capability, c->name);
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if (value.len) {
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strbuf_addch(&capability, '=');
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strbuf_addbuf(&capability, &value);
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}
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strbuf_addch(&capability, '\n');
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packet_write(1, capability.buf, capability.len);
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}
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strbuf_reset(&capability);
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strbuf_reset(&value);
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}
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packet_flush(1);
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strbuf_release(&capability);
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strbuf_release(&value);
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}
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static struct protocol_capability *get_capability(const char *key, const char **value)
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{
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int i;
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if (!key)
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return NULL;
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for (i = 0; i < ARRAY_SIZE(capabilities); i++) {
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struct protocol_capability *c = &capabilities[i];
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const char *out;
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if (!skip_prefix(key, c->name, &out))
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continue;
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if (!*out) {
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*value = NULL;
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return c;
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}
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if (*out++ == '=') {
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*value = out;
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return c;
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}
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}
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return NULL;
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}
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static int receive_client_capability(const char *key)
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{
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const char *value;
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const struct protocol_capability *c = get_capability(key, &value);
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if (!c || c->command || !c->advertise(the_repository, NULL))
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return 0;
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if (c->receive)
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c->receive(the_repository, value);
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return 1;
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}
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static int parse_command(const char *key, struct protocol_capability **command)
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{
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const char *out;
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if (skip_prefix(key, "command=", &out)) {
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const char *value;
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struct protocol_capability *cmd = get_capability(out, &value);
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if (*command)
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die("command '%s' requested after already requesting command '%s'",
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out, (*command)->name);
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if (!cmd || !cmd->advertise(the_repository, NULL) || !cmd->command || value)
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die("invalid command '%s'", out);
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*command = cmd;
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return 1;
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}
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return 0;
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}
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enum request_state {
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PROCESS_REQUEST_KEYS,
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PROCESS_REQUEST_DONE,
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};
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static int process_request(void)
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{
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enum request_state state = PROCESS_REQUEST_KEYS;
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struct packet_reader reader;
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int seen_capability_or_command = 0;
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struct protocol_capability *command = NULL;
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packet_reader_init(&reader, 0, NULL, 0,
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PACKET_READ_CHOMP_NEWLINE |
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PACKET_READ_GENTLE_ON_EOF |
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PACKET_READ_DIE_ON_ERR_PACKET);
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/*
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* Check to see if the client closed their end before sending another
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* request. If so we can terminate the connection.
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*/
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if (packet_reader_peek(&reader) == PACKET_READ_EOF)
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return 1;
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reader.options &= ~PACKET_READ_GENTLE_ON_EOF;
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while (state != PROCESS_REQUEST_DONE) {
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switch (packet_reader_peek(&reader)) {
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case PACKET_READ_EOF:
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BUG("Should have already died when seeing EOF");
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case PACKET_READ_NORMAL:
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if (parse_command(reader.line, &command) ||
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receive_client_capability(reader.line))
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seen_capability_or_command = 1;
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else
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die("unknown capability '%s'", reader.line);
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/* Consume the peeked line */
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packet_reader_read(&reader);
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break;
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case PACKET_READ_FLUSH:
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/*
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* If no command and no keys were given then the client
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* wanted to terminate the connection.
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*/
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if (!seen_capability_or_command)
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return 1;
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/*
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* The flush packet isn't consume here like it is in
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* the other parts of this switch statement. This is
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* so that the command can read the flush packet and
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* see the end of the request in the same way it would
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* if command specific arguments were provided after a
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* delim packet.
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*/
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state = PROCESS_REQUEST_DONE;
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break;
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case PACKET_READ_DELIM:
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/* Consume the peeked line */
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packet_reader_read(&reader);
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state = PROCESS_REQUEST_DONE;
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break;
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case PACKET_READ_RESPONSE_END:
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BUG("unexpected response end packet");
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}
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}
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if (!command)
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die("no command requested");
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if (client_hash_algo != hash_algo_by_ptr(the_repository->hash_algo))
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die("mismatched object format: server %s; client %s\n",
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the_repository->hash_algo->name,
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hash_algos[client_hash_algo].name);
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command->command(the_repository, &reader);
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return 0;
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}
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void protocol_v2_serve_loop(int stateless_rpc)
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{
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if (!stateless_rpc)
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protocol_v2_advertise_capabilities();
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/*
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* If stateless-rpc was requested then exit after
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* a single request/response exchange
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*/
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if (stateless_rpc) {
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process_request();
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} else {
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for (;;)
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if (process_request())
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break;
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}
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}
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