view mercurial/cext/manifest.c @ 47965:f9e6f2bb721d

rhg: Don’t compare ambiguous files one byte at a time

Even though the use of `BufReader` reduces the number of syscalls to read
the file from disk, `.bytes()` yields a separate `Result` for every byte.
Creating those results and dispatching on them is most likely costly.

Instead, this commit opts for simplicity by reading the entire file into memory
and comparing a single pair of byte strings. Note that memory already needs to
contain the entire previous contents of the file, as read from the filelog.
So with an extremely large file this doubles memory use but does not make it
grow by orders of magnitude.

At first I wrote code that still avoids reading the entire file into memory
and compares one buffer at a time with `BufReader`. Find this code below for
posterity. However its correctness is subtle. I ended up preferring the
simplicity of the obviously-correct single comparison.

```rust
let mut reader = BufReader::new(fobj);
let mut expected = &contents_in_p1[..];
loop {
    let buf = reader.fill_buf().when_reading_file(&fs_path)?;
    if buf.is_empty() {
        // Found EOF
        return Ok(expected.is_empty());
    } else if let Some(rest) = expected.drop_prefix(buf) {
        // What we read so far matches the expected content, continue reading
        let buf_len = buf.len();
        reader.consume(buf_len);
        expected = rest
    } else {
        // Found different content
        return Ok(false);
    }
}
```

Differential Revision: https://phab.mercurial-scm.org/D11412

/*
 * manifest.c - manifest type that does on-demand parsing.
 *
 * Copyright 2015, Google Inc.
 *
 * This software may be used and distributed according to the terms of
 * the GNU General Public License, incorporated herein by reference.
 */
#include <Python.h>

#include <assert.h>
#include <stdlib.h>
#include <string.h>

#include "charencode.h"
#include "util.h"

#define DEFAULT_LINES 100000

typedef struct {
	char *start;
	Py_ssize_t len; /* length of line including terminal newline */
	char hash_suffix;
	bool from_malloc;
	bool deleted;
} line;

typedef struct {
	PyObject_HEAD
	PyObject *pydata;
	Py_ssize_t nodelen;
	line *lines;
	int numlines; /* number of line entries */
	int livelines; /* number of non-deleted lines */
	int maxlines; /* allocated number of lines */
	bool dirty;
} lazymanifest;

#define MANIFEST_OOM -1
#define MANIFEST_NOT_SORTED -2
#define MANIFEST_MALFORMED -3
#define MANIFEST_BOGUS_FILENAME -4
#define MANIFEST_TOO_SHORT_LINE -5

/* get the length of the path for a line */
static Py_ssize_t pathlen(line *l)
{
	const char *end = memchr(l->start, '\0', l->len);
	return (end) ? (Py_ssize_t)(end - l->start) : l->len;
}

/* get the node value of a single line */
static PyObject *nodeof(Py_ssize_t nodelen, line *l, char *flag)
{
	char *s = l->start;
	Py_ssize_t llen = pathlen(l);
	Py_ssize_t hlen = l->len - llen - 2;
	PyObject *hash;
	if (llen + 1 + 40 + 1 > l->len) { /* path '\0' hash '\n' */
		PyErr_SetString(PyExc_ValueError, "manifest line too short");
		return NULL;
	}
	/* Detect flags after the hash first. */
	switch (s[llen + hlen]) {
	case 'l':
	case 't':
	case 'x':
		*flag = s[llen + hlen];
		--hlen;
		break;
	default:
		*flag = '\0';
		break;
	}

	if (hlen != 2 * nodelen) {
		PyErr_SetString(PyExc_ValueError, "invalid node length in manifest");
		return NULL;
	}
	hash = unhexlify(s + llen + 1, nodelen * 2);
	if (!hash) {
		return NULL;
	}
	if (l->hash_suffix != '\0') {
		char newhash[33];
		memcpy(newhash, PyBytes_AsString(hash), nodelen);
		Py_DECREF(hash);
		newhash[nodelen] = l->hash_suffix;
		hash = PyBytes_FromStringAndSize(newhash, nodelen + 1);
	}
	return hash;
}

/* get the node hash and flags of a line as a tuple */
static PyObject *hashflags(Py_ssize_t nodelen, line *l)
{
	char flag;
	PyObject *hash = nodeof(nodelen, l, &flag);
	PyObject *flags;
	PyObject *tup;

	if (!hash)
		return NULL;
	flags = PyBytes_FromStringAndSize(&flag, flag ? 1 : 0);
	if (!flags) {
		Py_DECREF(hash);
		return NULL;
	}
	tup = PyTuple_Pack(2, hash, flags);
	Py_DECREF(flags);
	Py_DECREF(hash);
	return tup;
}

/* if we're about to run out of space in the line index, add more */
static bool realloc_if_full(lazymanifest *self)
{
	if (self->numlines == self->maxlines) {
		self->maxlines *= 2;
		self->lines = realloc(self->lines, self->maxlines * sizeof(line));
	}
	return !!self->lines;
}

/*
 * Find the line boundaries in the manifest that 'data' points to and store
 * information about each line in 'self'.
 */
static int find_lines(lazymanifest *self, char *data, Py_ssize_t len)
{
	char *prev = NULL;
	while (len > 0) {
		line *l;
		char *next;
		if (*data == '\0') {
			/* It's implausible there's no filename, don't
			 * even bother looking for the newline. */
			return MANIFEST_BOGUS_FILENAME;
		}
		next = memchr(data, '\n', len);
		if (!next) {
			return MANIFEST_MALFORMED;
		}
		if ((next - data) < 42) {
			/* We should have at least 42 bytes in a line:
			   1 byte filename
			   1 NUL
			   40 bytes of hash
			   so we can give up here.
			*/
			return MANIFEST_TOO_SHORT_LINE;
		}
		next++; /* advance past newline */
		if (prev && strcmp(prev, data) > -1) {
			/* This data isn't sorted, so we have to abort. */
			return MANIFEST_NOT_SORTED;
		}
		if (!realloc_if_full(self)) {
			return MANIFEST_OOM; /* no memory */
		}
		l = self->lines + ((self->numlines)++);
		l->start = data;
		l->len = next - data;
		l->hash_suffix = '\0';
		l->from_malloc = false;
		l->deleted = false;
		len = len - l->len;
		prev = data;
		data = next;
	}
	self->livelines = self->numlines;
	return 0;
}

static void lazymanifest_init_early(lazymanifest *self)
{
	self->pydata = NULL;
	self->lines = NULL;
	self->numlines = 0;
	self->maxlines = 0;
}

static int lazymanifest_init(lazymanifest *self, PyObject *args)
{
	char *data;
	Py_ssize_t nodelen, len;
	int err, ret;
	PyObject *pydata;

	lazymanifest_init_early(self);
	if (!PyArg_ParseTuple(args, "nS", &nodelen, &pydata)) {
		return -1;
	}
	if (nodelen != 20 && nodelen != 32) {
		/* See fixed buffer in nodeof */
		PyErr_Format(PyExc_ValueError, "Unsupported node length");
		return -1;
	}
	self->nodelen = nodelen;
	self->dirty = false;

	err = PyBytes_AsStringAndSize(pydata, &data, &len);
	if (err == -1)
		return -1;
	self->pydata = pydata;
	Py_INCREF(self->pydata);
	Py_BEGIN_ALLOW_THREADS
	self->lines = malloc(DEFAULT_LINES * sizeof(line));
	self->maxlines = DEFAULT_LINES;
	self->numlines = 0;
	if (!self->lines)
		ret = MANIFEST_OOM;
	else
		ret = find_lines(self, data, len);
	Py_END_ALLOW_THREADS
	switch (ret) {
	case 0:
		break;
	case MANIFEST_OOM:
		PyErr_NoMemory();
		break;
	case MANIFEST_NOT_SORTED:
		PyErr_Format(PyExc_ValueError,
			     "Manifest lines not in sorted order.");
		break;
	case MANIFEST_MALFORMED:
		PyErr_Format(PyExc_ValueError,
			     "Manifest did not end in a newline.");
		break;
	case MANIFEST_BOGUS_FILENAME:
		PyErr_Format(
			PyExc_ValueError,
			"Manifest had an entry with a zero-length filename.");
		break;
	case MANIFEST_TOO_SHORT_LINE:
		PyErr_Format(
			PyExc_ValueError,
			"Manifest had implausibly-short line.");
		break;
	default:
		PyErr_Format(PyExc_ValueError,
			     "Unknown problem parsing manifest.");
	}
	return ret == 0 ? 0 : -1;
}

static void lazymanifest_dealloc(lazymanifest *self)
{
	/* free any extra lines we had to allocate */
	int i;
	for (i = 0; self->lines && (i < self->numlines); i++) {
		if (self->lines[i].from_malloc) {
			free(self->lines[i].start);
		}
	}
	free(self->lines);
	self->lines = NULL;
	if (self->pydata) {
		Py_DECREF(self->pydata);
		self->pydata = NULL;
	}
	PyObject_Del(self);
}

/* iteration support */

typedef struct {
	PyObject_HEAD lazymanifest *m;
	Py_ssize_t pos;
} lmIter;

static void lmiter_dealloc(PyObject *o)
{
	lmIter *self = (lmIter *)o;
	Py_DECREF(self->m);
	PyObject_Del(self);
}

static line *lmiter_nextline(lmIter *self)
{
	do {
		self->pos++;
		if (self->pos >= self->m->numlines) {
			return NULL;
		}
		/* skip over deleted manifest entries */
	} while (self->m->lines[self->pos].deleted);
	return self->m->lines + self->pos;
}

static PyObject *lmiter_iterentriesnext(PyObject *o)
{
	lmIter *self = (lmIter *)o;
	Py_ssize_t pl;
	line *l;
	char flag;
	PyObject *ret = NULL, *path = NULL, *hash = NULL, *flags = NULL;
	l = lmiter_nextline(self);
	if (!l) {
		goto done;
	}
	pl = pathlen(l);
	path = PyBytes_FromStringAndSize(l->start, pl);
	hash = nodeof(self->m->nodelen, l, &flag);
	if (!path || !hash) {
		goto done;
	}
	flags = PyBytes_FromStringAndSize(&flag, flag ? 1 : 0);
	if (!flags) {
		goto done;
	}
	ret = PyTuple_Pack(3, path, hash, flags);
done:
	Py_XDECREF(path);
	Py_XDECREF(hash);
	Py_XDECREF(flags);
	return ret;
}

#ifdef IS_PY3K
#define LAZYMANIFESTENTRIESITERATOR_TPFLAGS Py_TPFLAGS_DEFAULT
#else
#define LAZYMANIFESTENTRIESITERATOR_TPFLAGS Py_TPFLAGS_DEFAULT \
	| Py_TPFLAGS_HAVE_ITER
#endif

static PyTypeObject lazymanifestEntriesIterator = {
	PyVarObject_HEAD_INIT(NULL, 0) /* header */
	"parsers.lazymanifest.entriesiterator", /*tp_name */
	sizeof(lmIter),                  /*tp_basicsize */
	0,                               /*tp_itemsize */
	lmiter_dealloc,                  /*tp_dealloc */
	0,                               /*tp_print */
	0,                               /*tp_getattr */
	0,                               /*tp_setattr */
	0,                               /*tp_compare */
	0,                               /*tp_repr */
	0,                               /*tp_as_number */
	0,                               /*tp_as_sequence */
	0,                               /*tp_as_mapping */
	0,                               /*tp_hash */
	0,                               /*tp_call */
	0,                               /*tp_str */
	0,                               /*tp_getattro */
	0,                               /*tp_setattro */
	0,                               /*tp_as_buffer */
	LAZYMANIFESTENTRIESITERATOR_TPFLAGS, /* tp_flags */
	"Iterator for 3-tuples in a lazymanifest.",  /* tp_doc */
	0,                               /* tp_traverse */
	0,                               /* tp_clear */
	0,                               /* tp_richcompare */
	0,                               /* tp_weaklistoffset */
	PyObject_SelfIter,               /* tp_iter: __iter__() method */
	lmiter_iterentriesnext,          /* tp_iternext: next() method */
};

static PyObject *lmiter_iterkeysnext(PyObject *o)
{
	Py_ssize_t pl;
	line *l = lmiter_nextline((lmIter *)o);
	if (!l) {
		return NULL;
	}
	pl = pathlen(l);
	return PyBytes_FromStringAndSize(l->start, pl);
}

#ifdef IS_PY3K
#define LAZYMANIFESTKEYSITERATOR_TPFLAGS Py_TPFLAGS_DEFAULT
#else
#define LAZYMANIFESTKEYSITERATOR_TPFLAGS Py_TPFLAGS_DEFAULT \
	| Py_TPFLAGS_HAVE_ITER
#endif

static PyTypeObject lazymanifestKeysIterator = {
	PyVarObject_HEAD_INIT(NULL, 0) /* header */
	"parsers.lazymanifest.keysiterator", /*tp_name */
	sizeof(lmIter),                  /*tp_basicsize */
	0,                               /*tp_itemsize */
	lmiter_dealloc,                  /*tp_dealloc */
	0,                               /*tp_print */
	0,                               /*tp_getattr */
	0,                               /*tp_setattr */
	0,                               /*tp_compare */
	0,                               /*tp_repr */
	0,                               /*tp_as_number */
	0,                               /*tp_as_sequence */
	0,                               /*tp_as_mapping */
	0,                               /*tp_hash */
	0,                               /*tp_call */
	0,                               /*tp_str */
	0,                               /*tp_getattro */
	0,                               /*tp_setattro */
	0,                               /*tp_as_buffer */
	LAZYMANIFESTKEYSITERATOR_TPFLAGS, /* tp_flags */
	"Keys iterator for a lazymanifest.",  /* tp_doc */
	0,                               /* tp_traverse */
	0,                               /* tp_clear */
	0,                               /* tp_richcompare */
	0,                               /* tp_weaklistoffset */
	PyObject_SelfIter,               /* tp_iter: __iter__() method */
	lmiter_iterkeysnext,             /* tp_iternext: next() method */
};

static lazymanifest *lazymanifest_copy(lazymanifest *self);

static PyObject *lazymanifest_getentriesiter(lazymanifest *self)
{
	lmIter *i = NULL;
	lazymanifest *t = lazymanifest_copy(self);
	if (!t) {
		PyErr_NoMemory();
		return NULL;
	}
	i = PyObject_New(lmIter, &lazymanifestEntriesIterator);
	if (i) {
		i->m = t;
		i->pos = -1;
	} else {
		Py_DECREF(t);
		PyErr_NoMemory();
	}
	return (PyObject *)i;
}

static PyObject *lazymanifest_getkeysiter(lazymanifest *self)
{
	lmIter *i = NULL;
	lazymanifest *t = lazymanifest_copy(self);
	if (!t) {
		PyErr_NoMemory();
		return NULL;
	}
	i = PyObject_New(lmIter, &lazymanifestKeysIterator);
	if (i) {
		i->m = t;
		i->pos = -1;
	} else {
		Py_DECREF(t);
		PyErr_NoMemory();
	}
	return (PyObject *)i;
}

/* __getitem__ and __setitem__ support */

static Py_ssize_t lazymanifest_size(lazymanifest *self)
{
	return self->livelines;
}

static int linecmp(const void *left, const void *right)
{
	return strcmp(((const line *)left)->start,
		      ((const line *)right)->start);
}

static PyObject *lazymanifest_getitem(lazymanifest *self, PyObject *key)
{
	line needle;
	line *hit;
	if (!PyBytes_Check(key)) {
		PyErr_Format(PyExc_TypeError,
			     "getitem: manifest keys must be a string.");
		return NULL;
	}
	needle.start = PyBytes_AsString(key);
	hit = bsearch(&needle, self->lines, self->numlines, sizeof(line),
		      &linecmp);
	if (!hit || hit->deleted) {
		PyErr_Format(PyExc_KeyError, "No such manifest entry.");
		return NULL;
	}
	return hashflags(self->nodelen, hit);
}

static int lazymanifest_delitem(lazymanifest *self, PyObject *key)
{
	line needle;
	line *hit;
	if (!PyBytes_Check(key)) {
		PyErr_Format(PyExc_TypeError,
			     "delitem: manifest keys must be a string.");
		return -1;
	}
	needle.start = PyBytes_AsString(key);
	hit = bsearch(&needle, self->lines, self->numlines, sizeof(line),
		      &linecmp);
	if (!hit || hit->deleted) {
		PyErr_Format(PyExc_KeyError,
			     "Tried to delete nonexistent manifest entry.");
		return -1;
	}
	self->dirty = true;
	hit->deleted = true;
	self->livelines--;
	return 0;
}

/* Do a binary search for the insertion point for new, creating the
 * new entry if needed. */
static int internalsetitem(lazymanifest *self, line *new)
{
	int start = 0, end = self->numlines;
	while (start < end) {
		int pos = start + (end - start) / 2;
		int c = linecmp(new, self->lines + pos);
		if (c < 0)
			end = pos;
		else if (c > 0)
			start = pos + 1;
		else {
			if (self->lines[pos].deleted)
				self->livelines++;
			if (self->lines[pos].from_malloc)
				free(self->lines[pos].start);
			start = pos;
			goto finish;
		}
	}
	/* being here means we need to do an insert */
	if (!realloc_if_full(self)) {
		PyErr_NoMemory();
		return -1;
	}
	memmove(self->lines + start + 1, self->lines + start,
		(self->numlines - start) * sizeof(line));
	self->numlines++;
	self->livelines++;
finish:
	self->lines[start] = *new;
	self->dirty = true;
	return 0;
}

static int lazymanifest_setitem(
	lazymanifest *self, PyObject *key, PyObject *value)
{
	char *path;
	Py_ssize_t plen;
	PyObject *pyhash;
	Py_ssize_t hlen;
	char *hash;
	PyObject *pyflags;
	char *flags;
	Py_ssize_t flen;
	Py_ssize_t dlen;
	char *dest;
	int i;
	line new;
	if (!PyBytes_Check(key)) {
		PyErr_Format(PyExc_TypeError,
			     "setitem: manifest keys must be a string.");
		return -1;
	}
	if (!value) {
		return lazymanifest_delitem(self, key);
	}
	if (!PyTuple_Check(value) || PyTuple_Size(value) != 2) {
		PyErr_Format(PyExc_TypeError,
			     "Manifest values must be a tuple of (node, flags).");
		return -1;
	}
	if (PyBytes_AsStringAndSize(key, &path, &plen) == -1) {
		return -1;
	}

	pyhash = PyTuple_GetItem(value, 0);
	if (!PyBytes_Check(pyhash)) {
		PyErr_Format(PyExc_TypeError,
			     "node must be a %zi bytes string", self->nodelen);
		return -1;
	}
	hlen = PyBytes_Size(pyhash);
	if (hlen != self->nodelen) {
		PyErr_Format(PyExc_TypeError,
			     "node must be a %zi bytes string", self->nodelen);
		return -1;
	}
	hash = PyBytes_AsString(pyhash);

	pyflags = PyTuple_GetItem(value, 1);
	if (!PyBytes_Check(pyflags) || PyBytes_Size(pyflags) > 1) {
		PyErr_Format(PyExc_TypeError,
			     "flags must a 0 or 1 bytes string");
		return -1;
	}
	if (PyBytes_AsStringAndSize(pyflags, &flags, &flen) == -1) {
		return -1;
	}
	if (flen == 1) {
		switch (*flags) {
		case 'l':
		case 't':
		case 'x':
			break;
		default:
			PyErr_Format(PyExc_TypeError, "invalid manifest flag");
			return -1;
		}
	}
	/* one null byte and one newline */
	dlen = plen + hlen * 2 + 1 + flen + 1;
	dest = malloc(dlen);
	if (!dest) {
		PyErr_NoMemory();
		return -1;
	}
	memcpy(dest, path, plen + 1);
	for (i = 0; i < hlen; i++) {
		/* Cast to unsigned, so it will not get sign-extended when promoted
		 * to int (as is done when passing to a variadic function)
		 */
		sprintf(dest + plen + 1 + (i * 2), "%02x", (unsigned char)hash[i]);
	}
	memcpy(dest + plen + 2 * hlen + 1, flags, flen);
	dest[plen + 2 * hlen + 1 + flen] = '\n';
	new.start = dest;
	new.len = dlen;
	new.hash_suffix = '\0';
	if (hlen > 20) {
		new.hash_suffix = hash[20];
	}
	new.from_malloc = true;     /* is `start` a pointer we allocated? */
	new.deleted = false;        /* is this entry deleted? */
	if (internalsetitem(self, &new)) {
		return -1;
	}
	return 0;
}

static PyMappingMethods lazymanifest_mapping_methods = {
	(lenfunc)lazymanifest_size,             /* mp_length */
	(binaryfunc)lazymanifest_getitem,       /* mp_subscript */
	(objobjargproc)lazymanifest_setitem,    /* mp_ass_subscript */
};

/* sequence methods (important or __contains__ builds an iterator) */

static int lazymanifest_contains(lazymanifest *self, PyObject *key)
{
	line needle;
	line *hit;
	if (!PyBytes_Check(key)) {
		/* Our keys are always strings, so if the contains
		 * check is for a non-string, just return false. */
		return 0;
	}
	needle.start = PyBytes_AsString(key);
	hit = bsearch(&needle, self->lines, self->numlines, sizeof(line),
		      &linecmp);
	if (!hit || hit->deleted) {
		return 0;
	}
	return 1;
}

static PySequenceMethods lazymanifest_seq_meths = {
	(lenfunc)lazymanifest_size, /* sq_length */
	0, /* sq_concat */
	0, /* sq_repeat */
	0, /* sq_item */
	0, /* sq_slice */
	0, /* sq_ass_item */
	0, /* sq_ass_slice */
	(objobjproc)lazymanifest_contains, /* sq_contains */
	0, /* sq_inplace_concat */
	0, /* sq_inplace_repeat */
};


/* Other methods (copy, diff, etc) */
static PyTypeObject lazymanifestType;

/* If the manifest has changes, build the new manifest text and reindex it. */
static int compact(lazymanifest *self)
{
	int i;
	ssize_t need = 0;
	char *data;
	line *src, *dst;
	PyObject *pydata;
	if (!self->dirty)
		return 0;
	for (i = 0; i < self->numlines; i++) {
		if (!self->lines[i].deleted) {
			need += self->lines[i].len;
		}
	}
	pydata = PyBytes_FromStringAndSize(NULL, need);
	if (!pydata)
		return -1;
	data = PyBytes_AsString(pydata);
	if (!data) {
		return -1;
	}
	src = self->lines;
	dst = self->lines;
	for (i = 0; i < self->numlines; i++, src++) {
		char *tofree = NULL;
		if (src->from_malloc) {
			tofree = src->start;
		}
		if (!src->deleted) {
			memcpy(data, src->start, src->len);
			*dst = *src;
			dst->start = data;
			dst->from_malloc = false;
			data += dst->len;
			dst++;
		}
		free(tofree);
	}
	Py_DECREF(self->pydata);
	self->pydata = pydata;
	self->numlines = self->livelines;
	self->dirty = false;
	return 0;
}

static PyObject *lazymanifest_text(lazymanifest *self)
{
	if (compact(self) != 0) {
		PyErr_NoMemory();
		return NULL;
	}
	Py_INCREF(self->pydata);
	return self->pydata;
}

static lazymanifest *lazymanifest_copy(lazymanifest *self)
{
	lazymanifest *copy = NULL;
	if (compact(self) != 0) {
		goto nomem;
	}
	copy = PyObject_New(lazymanifest, &lazymanifestType);
	if (!copy) {
		goto nomem;
	}
	lazymanifest_init_early(copy);
	copy->nodelen = self->nodelen;
	copy->numlines = self->numlines;
	copy->livelines = self->livelines;
	copy->dirty = false;
	copy->lines = malloc(self->maxlines *sizeof(line));
	if (!copy->lines) {
		goto nomem;
	}
	memcpy(copy->lines, self->lines, self->numlines * sizeof(line));
	copy->maxlines = self->maxlines;
	copy->pydata = self->pydata;
	Py_INCREF(copy->pydata);
	return copy;
nomem:
	PyErr_NoMemory();
	Py_XDECREF(copy);
	return NULL;
}

static lazymanifest *lazymanifest_filtercopy(
	lazymanifest *self, PyObject *matchfn)
{
	lazymanifest *copy = NULL;
	int i;
	if (!PyCallable_Check(matchfn)) {
		PyErr_SetString(PyExc_TypeError, "matchfn must be callable");
		return NULL;
	}
	/* compact ourselves first to avoid double-frees later when we
	 * compact tmp so that it doesn't have random pointers to our
	 * underlying from_malloc-data (self->pydata is safe) */
	if (compact(self) != 0) {
		goto nomem;
	}
	copy = PyObject_New(lazymanifest, &lazymanifestType);
	if (!copy) {
		goto nomem;
	}
	lazymanifest_init_early(copy);
	copy->nodelen = self->nodelen;
	copy->dirty = true;
	copy->lines = malloc(self->maxlines * sizeof(line));
	if (!copy->lines) {
		goto nomem;
	}
	copy->maxlines = self->maxlines;
	copy->numlines = 0;
	copy->pydata = self->pydata;
	Py_INCREF(copy->pydata);
	for (i = 0; i < self->numlines; i++) {
		PyObject *arglist = NULL, *result = NULL;
		arglist = Py_BuildValue(PY23("(s)", "(y)"),
					self->lines[i].start);
		if (!arglist) {
			goto bail;
		}
		result = PyObject_CallObject(matchfn, arglist);
		Py_DECREF(arglist);
		/* if the callback raised an exception, just let it
		 * through and give up */
		if (!result) {
			goto bail;
		}
		if (PyObject_IsTrue(result)) {
			assert(!(self->lines[i].from_malloc));
			copy->lines[copy->numlines++] = self->lines[i];
		}
		Py_DECREF(result);
	}
	copy->livelines = copy->numlines;
	return copy;
nomem:
	PyErr_NoMemory();
bail:
	Py_XDECREF(copy);
	return NULL;
}

static PyObject *lazymanifest_diff(lazymanifest *self, PyObject *args)
{
	lazymanifest *other;
	PyObject *pyclean = NULL;
	bool listclean;
	PyObject *emptyTup = NULL, *ret = NULL;
	PyObject *es;
	int sneedle = 0, oneedle = 0;
	if (!PyArg_ParseTuple(args, "O!|O", &lazymanifestType, &other, &pyclean)) {
		return NULL;
	}
	listclean = (!pyclean) ? false : PyObject_IsTrue(pyclean);
	es = PyBytes_FromString("");
	if (!es) {
		goto nomem;
	}
	emptyTup = PyTuple_Pack(2, Py_None, es);
	Py_DECREF(es);
	if (!emptyTup) {
		goto nomem;
	}
	ret = PyDict_New();
	if (!ret) {
		goto nomem;
	}
	while (sneedle != self->numlines || oneedle != other->numlines) {
		line *left = self->lines + sneedle;
		line *right = other->lines + oneedle;
		int result;
		PyObject *key;
		PyObject *outer;
		/* If we're looking at a deleted entry and it's not
		 * the end of the manifest, just skip it. */
		if (sneedle < self->numlines && left->deleted) {
			sneedle++;
			continue;
		}
		if (oneedle < other->numlines && right->deleted) {
			oneedle++;
			continue;
		}
		/* if we're at the end of either manifest, then we
		 * know the remaining items are adds so we can skip
		 * the strcmp. */
		if (sneedle == self->numlines) {
			result = 1;
		} else if (oneedle == other->numlines) {
			result = -1;
		} else {
			result = linecmp(left, right);
		}
		key = result <= 0 ?
			PyBytes_FromString(left->start) :
			PyBytes_FromString(right->start);
		if (!key)
			goto nomem;
		if (result < 0) {
			PyObject *l = hashflags(self->nodelen, left);
			if (!l) {
				goto nomem;
			}
			outer = PyTuple_Pack(2, l, emptyTup);
			Py_DECREF(l);
			if (!outer) {
				goto nomem;
			}
			PyDict_SetItem(ret, key, outer);
			Py_DECREF(outer);
			sneedle++;
		} else if (result > 0) {
			PyObject *r = hashflags(self->nodelen, right);
			if (!r) {
				goto nomem;
			}
			outer = PyTuple_Pack(2, emptyTup, r);
			Py_DECREF(r);
			if (!outer) {
				goto nomem;
			}
			PyDict_SetItem(ret, key, outer);
			Py_DECREF(outer);
			oneedle++;
		} else {
			/* file exists in both manifests */
			if (left->len != right->len
			    || memcmp(left->start, right->start, left->len)
			    || left->hash_suffix != right->hash_suffix) {
				PyObject *l = hashflags(self->nodelen, left);
				PyObject *r;
				if (!l) {
					goto nomem;
				}
				r = hashflags(self->nodelen, right);
				if (!r) {
					Py_DECREF(l);
					goto nomem;
				}
				outer = PyTuple_Pack(2, l, r);
				Py_DECREF(l);
				Py_DECREF(r);
				if (!outer) {
					goto nomem;
				}
				PyDict_SetItem(ret, key, outer);
				Py_DECREF(outer);
			} else if (listclean) {
				PyDict_SetItem(ret, key, Py_None);
			}
			sneedle++;
			oneedle++;
		}
		Py_DECREF(key);
	}
	Py_DECREF(emptyTup);
	return ret;
nomem:
	PyErr_NoMemory();
	Py_XDECREF(ret);
	Py_XDECREF(emptyTup);
	return NULL;
}

static PyMethodDef lazymanifest_methods[] = {
	{"iterkeys", (PyCFunction)lazymanifest_getkeysiter, METH_NOARGS,
	 "Iterate over file names in this lazymanifest."},
	{"iterentries", (PyCFunction)lazymanifest_getentriesiter, METH_NOARGS,
	 "Iterate over (path, nodeid, flags) tuples in this lazymanifest."},
	{"copy", (PyCFunction)lazymanifest_copy, METH_NOARGS,
	 "Make a copy of this lazymanifest."},
	{"filtercopy", (PyCFunction)lazymanifest_filtercopy, METH_O,
	 "Make a copy of this manifest filtered by matchfn."},
	{"diff", (PyCFunction)lazymanifest_diff, METH_VARARGS,
	 "Compare this lazymanifest to another one."},
	{"text", (PyCFunction)lazymanifest_text, METH_NOARGS,
	 "Encode this manifest to text."},
	{NULL},
};

#ifdef IS_PY3K
#define LAZYMANIFEST_TPFLAGS Py_TPFLAGS_DEFAULT
#else
#define LAZYMANIFEST_TPFLAGS Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_SEQUENCE_IN
#endif

static PyTypeObject lazymanifestType = {
	PyVarObject_HEAD_INIT(NULL, 0) /* header */
	"parsers.lazymanifest",                           /* tp_name */
	sizeof(lazymanifest),                             /* tp_basicsize */
	0,                                                /* tp_itemsize */
	(destructor)lazymanifest_dealloc,                 /* tp_dealloc */
	0,                                                /* tp_print */
	0,                                                /* tp_getattr */
	0,                                                /* tp_setattr */
	0,                                                /* tp_compare */
	0,                                                /* tp_repr */
	0,                                                /* tp_as_number */
	&lazymanifest_seq_meths,                          /* tp_as_sequence */
	&lazymanifest_mapping_methods,                    /* tp_as_mapping */
	0,                                                /* tp_hash */
	0,                                                /* tp_call */
	0,                                                /* tp_str */
	0,                                                /* tp_getattro */
	0,                                                /* tp_setattro */
	0,                                                /* tp_as_buffer */
	LAZYMANIFEST_TPFLAGS,                             /* tp_flags */
	"TODO(augie)",                                    /* tp_doc */
	0,                                                /* tp_traverse */
	0,                                                /* tp_clear */
	0,                                                /* tp_richcompare */
	0,                                             /* tp_weaklistoffset */
	(getiterfunc)lazymanifest_getkeysiter,                /* tp_iter */
	0,                                                /* tp_iternext */
	lazymanifest_methods,                             /* tp_methods */
	0,                                                /* tp_members */
	0,                                                /* tp_getset */
	0,                                                /* tp_base */
	0,                                                /* tp_dict */
	0,                                                /* tp_descr_get */
	0,                                                /* tp_descr_set */
	0,                                                /* tp_dictoffset */
	(initproc)lazymanifest_init,                      /* tp_init */
	0,                                                /* tp_alloc */
};

void manifest_module_init(PyObject * mod)
{
	lazymanifestType.tp_new = PyType_GenericNew;
	if (PyType_Ready(&lazymanifestType) < 0)
		return;
	Py_INCREF(&lazymanifestType);

	PyModule_AddObject(mod, "lazymanifest",
			   (PyObject *)&lazymanifestType);
}