Mercurial > hg
view mercurial/bdiff.c @ 36367:043e77f3be09
sshpeer: return framed file object when needed
Currently, wireproto.wirepeer has a default implementation of
_submitbatch() and sshv1peer has a very similar implementation.
The main difference is that sshv1peer is aware of the total amount
of bytes it can read whereas the default implementation reads the
stream until no more data is returned. The default implementation
works for HTTP, since there is a known end to HTTP responses (either
Content-Length or 0 sized chunk).
This commit teaches sshv1peer to use our just-introduced "cappedreader"
class for wrapping a file object to limit the number of bytes that
can be read. We do this by introducing an argument to specify whether
the response is framed. If set, we returned a cappedreader instance
instead of the raw pipe.
_call() always has framed responses. So we set this argument
unconditionally and then .read() the entirety of the result.
Strictly speaking, we don't need to use cappedreader in this case
and can inline frame decoding/read logic. But I like when things
are consistent. The overhead should be negligible.
_callstream() and _callcompressable() are special: whether framing
is used depends on the specific command. So, we define a set
of commands that have framed response. It currently only
contains "batch."
As a result of this change, the one-off implementation of
_submitbatch() in sshv1peer can be removed since it is now
safe to .read() the response's file object until end of stream.
cappedreader takes care of not overrunning the frame.
Differential Revision: https://phab.mercurial-scm.org/D2380
author | Gregory Szorc <gregory.szorc@gmail.com> |
---|---|
date | Wed, 21 Feb 2018 08:35:48 -0800 |
parents | 50868145a8de |
children | 068e774ae29e |
line wrap: on
line source
/* bdiff.c - efficient binary diff extension for Mercurial Copyright 2005, 2006 Matt Mackall <mpm@selenic.com> This software may be used and distributed according to the terms of the GNU General Public License, incorporated herein by reference. Based roughly on Python difflib */ #include <limits.h> #include <stdlib.h> #include <string.h> #include "bdiff.h" #include "bitmanipulation.h" #include "compat.h" /* Hash implementation from diffutils */ #define ROL(v, n) ((v) << (n) | (v) >> (sizeof(v) * CHAR_BIT - (n))) #define HASH(h, c) ((c) + ROL(h, 7)) struct pos { int pos, len; }; int bdiff_splitlines(const char *a, ssize_t len, struct bdiff_line **lr) { unsigned hash; int i; const char *p, *b = a; const char *const plast = a + len - 1; struct bdiff_line *l; /* count the lines */ i = 1; /* extra line for sentinel */ for (p = a; p < plast; p++) if (*p == '\n') i++; if (p == plast) i++; *lr = l = (struct bdiff_line *)calloc(i, sizeof(struct bdiff_line)); if (!l) return -1; /* build the line array and calculate hashes */ hash = 0; for (p = a; p < plast; p++) { hash = HASH(hash, *p); if (*p == '\n') { l->hash = hash; hash = 0; l->len = p - b + 1; l->l = b; l->n = INT_MAX; l++; b = p + 1; } } if (p == plast) { hash = HASH(hash, *p); l->hash = hash; l->len = p - b + 1; l->l = b; l->n = INT_MAX; l++; } /* set up a sentinel */ l->hash = 0; l->len = 0; l->l = a + len; return i - 1; } static inline int cmp(struct bdiff_line *a, struct bdiff_line *b) { return a->hash != b->hash || a->len != b->len || memcmp(a->l, b->l, a->len); } static int equatelines(struct bdiff_line *a, int an, struct bdiff_line *b, int bn) { int i, j, buckets = 1, t, scale; struct pos *h = NULL; /* build a hash table of the next highest power of 2 */ while (buckets < bn + 1) buckets *= 2; /* try to allocate a large hash table to avoid collisions */ for (scale = 4; scale; scale /= 2) { h = (struct pos *)calloc(buckets, scale * sizeof(struct pos)); if (h) break; } if (!h) return 0; buckets = buckets * scale - 1; /* clear the hash table */ for (i = 0; i <= buckets; i++) { h[i].pos = -1; h[i].len = 0; } /* add lines to the hash table chains */ for (i = 0; i < bn; i++) { /* find the equivalence class */ for (j = b[i].hash & buckets; h[j].pos != -1; j = (j + 1) & buckets) if (!cmp(b + i, b + h[j].pos)) break; /* add to the head of the equivalence class */ b[i].n = h[j].pos; b[i].e = j; h[j].pos = i; h[j].len++; /* keep track of popularity */ } /* compute popularity threshold */ t = (bn >= 31000) ? bn / 1000 : 1000000 / (bn + 1); /* match items in a to their equivalence class in b */ for (i = 0; i < an; i++) { /* find the equivalence class */ for (j = a[i].hash & buckets; h[j].pos != -1; j = (j + 1) & buckets) if (!cmp(a + i, b + h[j].pos)) break; a[i].e = j; /* use equivalence class for quick compare */ if (h[j].len <= t) a[i].n = h[j].pos; /* point to head of match list */ else a[i].n = -1; /* too popular */ } /* discard hash tables */ free(h); return 1; } static int longest_match(struct bdiff_line *a, struct bdiff_line *b, struct pos *pos, int a1, int a2, int b1, int b2, int *omi, int *omj) { int mi = a1, mj = b1, mk = 0, i, j, k, half, bhalf; /* window our search on large regions to better bound worst-case performance. by choosing a window at the end, we reduce skipping overhead on the b chains. */ if (a2 - a1 > 30000) a1 = a2 - 30000; half = (a1 + a2 - 1) / 2; bhalf = (b1 + b2 - 1) / 2; for (i = a1; i < a2; i++) { /* skip all lines in b after the current block */ for (j = a[i].n; j >= b2; j = b[j].n) ; /* loop through all lines match a[i] in b */ for (; j >= b1; j = b[j].n) { /* does this extend an earlier match? */ for (k = 1; j - k >= b1 && i - k >= a1; k++) { /* reached an earlier match? */ if (pos[j - k].pos == i - k) { k += pos[j - k].len; break; } /* previous line mismatch? */ if (a[i - k].e != b[j - k].e) break; } pos[j].pos = i; pos[j].len = k; /* best match so far? we prefer matches closer to the middle to balance recursion */ if (k > mk) { /* a longer match */ mi = i; mj = j; mk = k; } else if (k == mk) { if (i > mi && i <= half && j > b1) { /* same match but closer to half */ mi = i; mj = j; } else if (i == mi && (mj > bhalf || i == a1)) { /* same i but best earlier j */ mj = j; } } } } if (mk) { mi = mi - mk + 1; mj = mj - mk + 1; } /* expand match to include subsequent popular lines */ while (mi + mk < a2 && mj + mk < b2 && a[mi + mk].e == b[mj + mk].e) mk++; *omi = mi; *omj = mj; return mk; } static struct bdiff_hunk *recurse(struct bdiff_line *a, struct bdiff_line *b, struct pos *pos, int a1, int a2, int b1, int b2, struct bdiff_hunk *l) { int i, j, k; while (1) { /* find the longest match in this chunk */ k = longest_match(a, b, pos, a1, a2, b1, b2, &i, &j); if (!k) return l; /* and recurse on the remaining chunks on either side */ l = recurse(a, b, pos, a1, i, b1, j, l); if (!l) return NULL; l->next = (struct bdiff_hunk *)malloc(sizeof(struct bdiff_hunk)); if (!l->next) return NULL; l = l->next; l->a1 = i; l->a2 = i + k; l->b1 = j; l->b2 = j + k; l->next = NULL; /* tail-recursion didn't happen, so do equivalent iteration */ a1 = i + k; b1 = j + k; } } int bdiff_diff(struct bdiff_line *a, int an, struct bdiff_line *b, int bn, struct bdiff_hunk *base) { struct bdiff_hunk *curr; struct pos *pos; int t, count = 0; /* allocate and fill arrays */ t = equatelines(a, an, b, bn); pos = (struct pos *)calloc(bn ? bn : 1, sizeof(struct pos)); if (pos && t) { /* generate the matching block list */ curr = recurse(a, b, pos, 0, an, 0, bn, base); if (!curr) return -1; /* sentinel end hunk */ curr->next = (struct bdiff_hunk *)malloc(sizeof(struct bdiff_hunk)); if (!curr->next) return -1; curr = curr->next; curr->a1 = curr->a2 = an; curr->b1 = curr->b2 = bn; curr->next = NULL; } free(pos); /* normalize the hunk list, try to push each hunk towards the end */ for (curr = base->next; curr; curr = curr->next) { struct bdiff_hunk *next = curr->next; if (!next) break; if (curr->a2 == next->a1 || curr->b2 == next->b1) while (curr->a2 < an && curr->b2 < bn && next->a1 < next->a2 && next->b1 < next->b2 && !cmp(a + curr->a2, b + curr->b2)) { curr->a2++; next->a1++; curr->b2++; next->b1++; } } for (curr = base->next; curr; curr = curr->next) count++; return count; } void bdiff_freehunks(struct bdiff_hunk *l) { struct bdiff_hunk *n; for (; l; l = n) { n = l->next; free(l); } }