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![Jeff King](/assets/img/avatar_default.png)
When upload-pack advertises refs, it dereferences any tags it sees, and shows the resulting sha1 to the client. It does this by calling deref_tag. That function must load and parse each tag object to find the sha1 of the tagged object. However, it also ends up parsing the tagged object itself, which is not strictly necessary for upload-pack's use. Each tag produces two object loads (assuming it is not a recursive tag), when it could get away with only a single one. Dropping the second load halves the effort we spend. The downside is that we are no longer verifying the resulting object by loading it. In particular: 1. We never cross-check the "type" field given in the tag object with the type of the pointed-to object. If the tag says it points to a tag but doesn't, then we will keep peeling and realize the error. If the tag says it points to a non-tag but actually points to a tag, we will stop peeling and just advertise the pointed-to tag. 2. If we are missing the pointed-to object, we will not realize (because we never even look it up in the object db). However, both of these are errors in the object database, and both will be detected if a client actually requests the broken objects in question. So we are simply pushing the verification away from the advertising stage, and down to the actual fetching stage. On my test repo with 120K refs, this drops the time to advertise the refs from ~3.2s to ~2.0s. Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>
170 lines
3.9 KiB
C
170 lines
3.9 KiB
C
#include "cache.h"
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#include "tag.h"
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#include "commit.h"
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#include "tree.h"
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#include "blob.h"
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#define PGP_SIGNATURE "-----BEGIN PGP SIGNATURE-----"
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#define PGP_MESSAGE "-----BEGIN PGP MESSAGE-----"
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const char *tag_type = "tag";
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struct object *deref_tag(struct object *o, const char *warn, int warnlen)
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{
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while (o && o->type == OBJ_TAG)
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if (((struct tag *)o)->tagged)
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o = parse_object(((struct tag *)o)->tagged->sha1);
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else
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o = NULL;
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if (!o && warn) {
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if (!warnlen)
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warnlen = strlen(warn);
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error("missing object referenced by '%.*s'", warnlen, warn);
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}
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return o;
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}
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struct object *deref_tag_noverify(struct object *o)
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{
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while (o && o->type == OBJ_TAG) {
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o = parse_object(o->sha1);
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if (o && o->type == OBJ_TAG && ((struct tag *)o)->tagged)
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o = ((struct tag *)o)->tagged;
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else
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o = NULL;
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}
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return o;
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}
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struct tag *lookup_tag(const unsigned char *sha1)
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{
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struct object *obj = lookup_object(sha1);
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if (!obj)
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return create_object(sha1, OBJ_TAG, alloc_tag_node());
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if (!obj->type)
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obj->type = OBJ_TAG;
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if (obj->type != OBJ_TAG) {
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error("Object %s is a %s, not a tag",
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sha1_to_hex(sha1), typename(obj->type));
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return NULL;
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}
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return (struct tag *) obj;
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}
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static unsigned long parse_tag_date(const char *buf, const char *tail)
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{
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const char *dateptr;
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while (buf < tail && *buf++ != '>')
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/* nada */;
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if (buf >= tail)
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return 0;
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dateptr = buf;
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while (buf < tail && *buf++ != '\n')
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/* nada */;
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if (buf >= tail)
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return 0;
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/* dateptr < buf && buf[-1] == '\n', so strtoul will stop at buf-1 */
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return strtoul(dateptr, NULL, 10);
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}
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int parse_tag_buffer(struct tag *item, const void *data, unsigned long size)
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{
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unsigned char sha1[20];
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char type[20];
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const char *bufptr = data;
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const char *tail = bufptr + size;
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const char *nl;
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if (item->object.parsed)
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return 0;
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item->object.parsed = 1;
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if (size < 64)
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return -1;
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if (memcmp("object ", bufptr, 7) || get_sha1_hex(bufptr + 7, sha1) || bufptr[47] != '\n')
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return -1;
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bufptr += 48; /* "object " + sha1 + "\n" */
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if (prefixcmp(bufptr, "type "))
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return -1;
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bufptr += 5;
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nl = memchr(bufptr, '\n', tail - bufptr);
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if (!nl || sizeof(type) <= (nl - bufptr))
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return -1;
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strncpy(type, bufptr, nl - bufptr);
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type[nl - bufptr] = '\0';
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bufptr = nl + 1;
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if (!strcmp(type, blob_type)) {
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item->tagged = &lookup_blob(sha1)->object;
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} else if (!strcmp(type, tree_type)) {
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item->tagged = &lookup_tree(sha1)->object;
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} else if (!strcmp(type, commit_type)) {
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item->tagged = &lookup_commit(sha1)->object;
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} else if (!strcmp(type, tag_type)) {
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item->tagged = &lookup_tag(sha1)->object;
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} else {
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error("Unknown type %s", type);
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item->tagged = NULL;
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}
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if (bufptr + 4 < tail && !prefixcmp(bufptr, "tag "))
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; /* good */
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else
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return -1;
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bufptr += 4;
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nl = memchr(bufptr, '\n', tail - bufptr);
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if (!nl)
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return -1;
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item->tag = xmemdupz(bufptr, nl - bufptr);
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bufptr = nl + 1;
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if (bufptr + 7 < tail && !prefixcmp(bufptr, "tagger "))
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item->date = parse_tag_date(bufptr, tail);
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else
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item->date = 0;
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return 0;
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}
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int parse_tag(struct tag *item)
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{
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enum object_type type;
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void *data;
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unsigned long size;
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int ret;
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if (item->object.parsed)
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return 0;
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data = read_sha1_file(item->object.sha1, &type, &size);
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if (!data)
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return error("Could not read %s",
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sha1_to_hex(item->object.sha1));
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if (type != OBJ_TAG) {
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free(data);
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return error("Object %s not a tag",
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sha1_to_hex(item->object.sha1));
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}
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ret = parse_tag_buffer(item, data, size);
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free(data);
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return ret;
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}
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/*
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* Look at a signed tag object, and return the offset where
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* the embedded detached signature begins, or the end of the
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* data when there is no such signature.
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*/
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size_t parse_signature(const char *buf, unsigned long size)
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{
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char *eol;
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size_t len = 0;
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while (len < size && prefixcmp(buf + len, PGP_SIGNATURE) &&
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prefixcmp(buf + len, PGP_MESSAGE)) {
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eol = memchr(buf + len, '\n', size - len);
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len += eol ? eol - (buf + len) + 1 : size - len;
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}
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return len;
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}
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