[PATCH 1 of 4 lazy-manifest] manifest.c: new extension code to lazily parse manifests

Augie Fackler raf at durin42.com
Thu Jan 8 20:34:58 UTC 2015


# HG changeset patch
# User Augie Fackler <augie at google.com>
# Date 1420748959 18000
#      Thu Jan 08 15:29:19 2015 -0500
# Node ID 788bb2dacad048f161dfed583d3a95f708e91d1e
# Parent  7ad155e13f0f51df8e986a0ec4e58ac9a0ccedbb
manifest.c: new extension code to lazily parse manifests

This lets us iterate manifests in order, but do a _lot_ less work in
the common case when we only care about a few manifest entries.

Many thanks to Mike Edgar for reviewing this in advance of it going
out to the list, which caught many things I missed.

diff --git a/mercurial/manifest.c b/mercurial/manifest.c
new file mode 100644
--- /dev/null
+++ b/mercurial/manifest.c
@@ -0,0 +1,846 @@
+/*
+ * manifest.c - manifest type that does on-demand parsing.
+ */
+#include <assert.h>
+#include <string.h>
+#include <stdlib.h>
+
+#include <Python.h>
+
+/* yay c89 */
+#define true 1
+#define false 0
+typedef unsigned char bool;
+
+const int kDefaultLinesSize = 100000;
+
+typedef struct {
+	char *start;
+	Py_ssize_t len; /* length of line not including terminal newline */
+	char hash_suffix;
+	bool hash_none;
+	bool from_malloc;
+	bool deleted;
+} line;
+
+typedef struct {
+	PyObject_HEAD PyObject *pydata;
+	line *lines;
+	int numlines;
+	int livelines;
+	int maxlines;
+	bool dirty;
+} lazymanifest;
+
+#define MANIFEST_OOM -1
+#define MANIFEST_NOT_SORTED -2
+#define MANIFEST_MALFORMED -3
+
+static int realloc_if_needed(lazymanifest * self)
+{
+	if (self->numlines == self->maxlines) {
+		self->maxlines *= 2;
+		self->lines = realloc(
+			self->lines, self->maxlines * sizeof(line));
+	}
+	return self->lines != NULL;
+}
+
+static int find_lines(lazymanifest * self, char *data, Py_ssize_t len)
+{
+	char *prev = NULL;
+	while (data) {
+		char *point = memchr(data, '\n', len);
+		if (point == NULL) {
+			if (prev == NULL) {
+				return 0;
+			} else {
+				return MANIFEST_MALFORMED;
+			}
+		}
+		if (point) {
+			point++; /* advance past newline */
+			if (!realloc_if_needed(self)) {
+				return MANIFEST_OOM; /* no memory */
+			}
+			if (prev != NULL && strcmp(prev, data) > -1) {
+				/* This data isn't sorted, so we have to abort. */
+				return MANIFEST_NOT_SORTED;
+			}
+			prev = data;
+			line *l = self->lines + ((self->numlines)++);
+			l->start = data;
+			l->len = point - data;
+			l->hash_suffix = '\0';
+			l->hash_none = false;
+			l->from_malloc = false;
+			l->deleted = false;
+			if (*point == '\0') {
+				break;
+			} else {
+				len = len - l->len;
+				data = point;
+			}
+		}
+	}
+	self->livelines = self->numlines;
+	return 0;
+}
+
+static int lzm_init_real(lazymanifest * self, PyObject * pydata) {
+	self->dirty = false;
+	char *data;
+	Py_ssize_t len;
+	int err = PyString_AsStringAndSize(pydata, &data, &len);
+	if (err == -1)
+		return -1;
+	self->pydata = pydata;
+	Py_INCREF(self->pydata);
+	int ret;
+	Py_BEGIN_ALLOW_THREADS
+	self->lines = (line *)malloc(kDefaultLinesSize * sizeof(line));
+	self->maxlines = kDefaultLinesSize;
+	self->numlines = 0;
+	if (self->lines == NULL)
+		ret = -2;
+	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;
+	default:
+		PyErr_Format(PyExc_ValueError,
+			     "Unknown problem parsing manifest.");
+	}
+	return ret == 0 ? 0 : -1;
+}
+
+static int lzm_init(lazymanifest * self, PyObject * args)
+{
+	PyObject *pydata;
+	if (!PyArg_ParseTuple(args, "S", &pydata)) {
+		return -1;
+	}
+	return lzm_init_real(self, pydata);
+}
+
+static void lzm_dealloc(lazymanifest * self)
+{
+	/* free any extra lines we had to allocate */
+	int i;
+	for (i = 0; i < self->numlines; i++) {
+		if (self->lines[i].from_malloc) {
+			free(self->lines[i].start);
+		}
+	}
+	if (self->lines != NULL) {
+		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);
+}
+
+/* defined in parsers.c */
+PyObject *unhexlify(const char *str, int len);
+
+static size_t pathlen(line *l) {
+	return strnlen(l->start, l->len);
+}
+
+static PyObject *nodeof(line *l) {
+	if (l->hash_none) {
+		Py_INCREF(Py_None);
+		return Py_None;
+	}
+	char *s = l->start;
+	ssize_t llen = pathlen(l);
+	PyObject *hash = unhexlify(s + llen + 1, 40);
+	if (hash == NULL) {
+		return NULL;
+	}
+	if (l->hash_suffix != '\0') {
+		char newhash[21];
+		memcpy(newhash, PyString_AsString(hash), 20);
+		Py_DECREF(hash);
+		newhash[20] = l->hash_suffix;
+		hash = PyString_FromStringAndSize(newhash, 21);
+	}
+	return hash;
+}
+
+static PyObject *hashflags(line * l)
+{
+	char *s = l->start;
+	size_t plen = pathlen(l);
+	PyObject *hash = nodeof(l);
+	if (hash == NULL)
+		return NULL;
+	/* 40 for hash, 1 for null byte, 1 for newline */
+	size_t hplen = plen + 42;
+	Py_ssize_t flen = l->len - hplen;
+	PyObject *flags;
+	if (flen > 0) {
+		flags = PyString_FromStringAndSize(s + hplen - 1, flen);
+	} else {
+		flags = PyString_FromString("");
+	}
+	if (flags == NULL) {
+		Py_DECREF(hash);
+		return NULL;
+	}
+	PyObject *tup = PyTuple_Pack(2, hash, flags);
+	Py_DECREF(flags);
+	Py_DECREF(hash);
+	return tup;
+}
+
+PyObject *lmIter_iternext(PyObject * o)
+{
+	PyObject *ret = NULL, *path = NULL, *hash = NULL, *flags = NULL;
+	lmIter *self = (lmIter *)o;
+	Py_ssize_t index = self->pos++;
+	/* skip over deleted manifest entries */
+	while (index < self->m->numlines &&
+	       self->m->lines[index].deleted == true) {
+		index = ++(self->pos);
+	}
+	if (self->m->numlines <= index) {
+		goto bail;
+	}
+	line *l = &(self->m->lines[index]);
+	size_t pl = pathlen(l);
+	path = PyString_FromStringAndSize(l->start, pl);
+	hash = nodeof(l);
+	Py_ssize_t consumed = pl + 41;
+	if (l->len > (consumed + 1)) {
+		flags = PyString_FromStringAndSize(l->start + consumed,
+						   l->len - consumed - 1);
+	} else {
+		flags = PyString_FromString("");
+
+	}
+	if (flags == NULL) {
+		goto bail;
+	}
+	ret = PyTuple_Pack(3, path, hash, flags);
+bail:
+	Py_XDECREF(path);
+	Py_XDECREF(hash);
+	Py_XDECREF(flags);
+	return ret;
+}
+
+static PyTypeObject lazymanifestIterator = {
+	PyObject_HEAD_INIT(NULL)
+	0,                           /*ob_size */
+	"parsers.lazymanifest.iterator", /*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 */
+	/* tp_flags: Py_TPFLAGS_HAVE_ITER tells python to
+	   use tp_iter and tp_iternext fields. */
+	Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_ITER,
+	"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_iternext,                 /* tp_iternext: next() method */
+};
+
+static lazymanifest *lzm_copy(lazymanifest *self, PyObject *unused_args);
+
+static PyObject *lzm_GetIter(lazymanifest *self)
+{
+	lazymanifest *t = lzm_copy(self, NULL);
+	if (t == NULL) {
+		PyErr_NoMemory();
+		return NULL;
+	}
+	lmIter *i = PyObject_New(lmIter, &lazymanifestIterator);
+	if (i != NULL) {
+		i->m = t;
+		i->pos = 0;
+	} else {
+		Py_DECREF(t);
+		PyErr_NoMemory();
+	}
+	return (PyObject *)i;
+}
+
+/* __getitem__ and __setitem__ support */
+
+static Py_ssize_t lzm_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 *lzm_getitem(lazymanifest * self, PyObject * key)
+{
+	if (!PyString_Check(key)) {
+		PyErr_Format(PyExc_TypeError,
+			     "getitem: manifest keys must be a string.");
+		return NULL;
+	}
+	line needle = { PyString_AsString(key), 0 };
+	line *hit = bsearch(&needle, self->lines, self->numlines, sizeof(line),
+			    &linecmp);
+	if (hit == NULL || hit->deleted == true) {
+		PyErr_Format(PyExc_KeyError, "No such manifest entry.");
+		return NULL;
+	}
+	return hashflags(hit);
+}
+
+static int lzm_delitem(lazymanifest * self, PyObject * key)
+{
+	if (!PyString_Check(key)) {
+		PyErr_Format(PyExc_TypeError,
+			     "delitem: manifest keys must be a string.");
+		return -1;
+	}
+	line needle = { PyString_AsString(key), 0 };
+	line *hit = bsearch(&needle, self->lines, self->numlines, sizeof(line),
+			    &linecmp);
+	if (hit == NULL || hit->deleted == true) {
+		PyErr_Format(PyExc_KeyError,
+                             "Tried to delete nonexistent manifest entry.");
+		return -1;
+	}
+	self->dirty = true;
+	hit->deleted = true;
+	self->livelines--;
+	return 0;
+}
+
+static int lzm_setitem(lazymanifest * self, PyObject * key, PyObject * value)
+{
+	if (!PyString_Check(key)) {
+		PyErr_Format(PyExc_TypeError,
+                             "setitem: manifest keys must be a string.");
+		return -1;
+	}
+	if (value == NULL) {
+		return lzm_delitem(self, key);
+	}
+	if (!PyObject_IsInstance(value, (PyObject *) & PyTuple_Type)
+	    || PyTuple_Size(value) != 2) {
+		PyErr_Format(PyExc_TypeError,
+                             "Manifest values must be a tuple of (node, flags).");
+		return -1;
+	}
+	char *path;
+	Py_ssize_t plen;
+	if (PyString_AsStringAndSize(key, &path, &plen) == -1) {
+		return -1;
+	}
+
+	PyObject *pyhash = PyTuple_GetItem(value, 0);
+	char *hash = "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0";
+	char hashextra = '\0';
+	bool hashnone = false;
+	if (pyhash == Py_None) {
+		hashnone = true;
+	} else {
+		if (!PyString_Check(pyhash)) {
+			PyErr_Format(PyExc_TypeError,
+                                     "node must be a 20-byte string");
+			return -1;
+		}
+		Py_ssize_t hlen = PyString_Size(pyhash);
+		/* Some parts of the codebase try and set 21 or 22
+		 * byte "hash" values in order to perturb things for
+		 * status. We have to preserve at least the 21st
+		 * byte. Sigh.
+		 */
+		if (hlen != 20 && hlen != 21 && hlen != 22) {
+			PyErr_Format(PyExc_TypeError,
+                                     "node must be a 20-byte string");
+			return -1;
+		}
+		hash = PyString_AsString(pyhash);
+		if (hlen > 20) {
+			hashextra = hash[20];
+		}
+	}
+
+	PyObject *pyflags = PyTuple_GetItem(value, 1);
+	if (!PyString_Check(pyflags) || PyString_Size(pyflags) > 1) {
+		PyErr_Format(PyExc_TypeError,
+                             "flags must a 0 or 1 byte string");
+		return -1;
+	}
+	char *flags;
+	Py_ssize_t flen;
+	if (PyString_AsStringAndSize(pyflags, &flags, &flen) == -1) {
+		return -1;
+	}
+	/* 3 -> two null bytes and one newline */
+	size_t dlen = plen + 40 + flen + 3;
+	char *dest = malloc(dlen);
+	if (dest == NULL) {
+		PyErr_NoMemory();
+		return -1;
+	}
+	memcpy(dest, path, plen + 1);
+	int i;
+	for (i = 0; i < 20; i++) {
+		sprintf(dest + plen + 1 + (i * 2), "%02hhx", hash[i]);
+	}
+	sprintf(dest + plen + 41, "%s\n", flags);
+	line new = {
+		dest, /* start */
+		dlen - 1, /* total line length */
+		hashextra, /* extra byte, if any, on the hash */
+		hashnone, /* true if the hash is set to None */
+		true, /* is `start` a pointer we allocated? */
+		false, /* is this entry deleted? */
+	};
+	line *hit = bsearch(&new, self->lines, self->numlines,
+			    sizeof(line), &linecmp);
+	self->dirty = true;
+	if (hit != NULL) {
+		/* updating a line we already had */
+		if (hit->from_malloc) {
+			free(hit->start);
+		}
+		if (hit->deleted) {
+			self->livelines++;
+		}
+		memcpy(hit, &new, sizeof(line));
+	} else {
+		/* new line */
+		if (!realloc_if_needed(self)) {
+			PyErr_NoMemory();
+			return -1;
+		}
+		memcpy(self->lines + self->numlines++, &new, sizeof(line));
+		self->livelines++;
+		/* TODO: do a binary search and insert rather than
+		 * append and qsort. Also offer a batch-insert
+		 * interface, which should be a nice little
+		 * performance win.
+		 */
+		qsort(self->lines, self->numlines, sizeof(line), &linecmp);
+	}
+	return 0;
+}
+
+static PyMappingMethods lzm_mapping_methods = {
+	(lenfunc)lzm_size,             /* mp_length */
+	(binaryfunc)lzm_getitem,       /* mp_subscript */
+	(objobjargproc)lzm_setitem,    /* mp_ass_subscript */
+};
+
+/* sequence methods (important or __contains__ builds an iterator */
+
+static int lzm_contains(lazymanifest * self, PyObject * key)
+{
+	if (!PyString_Check(key)) {
+		PyErr_Format(PyExc_TypeError,
+			     "contains: manifest keys must be a string.");
+		return 0;
+	}
+	line needle = { PyString_AsString(key), 0 };
+	line *hit = bsearch(&needle, self->lines, self->numlines, sizeof(line),
+			    &linecmp);
+	if (hit == NULL || hit->deleted == true) {
+		return 0;
+	}
+	return 1;
+}
+
+static PySequenceMethods lzm_seq_meths = {
+	(lenfunc)lzm_size, /* sq_length */
+	0, /* sq_concat */
+	0, /* sq_repeat */
+	0, /* sq_item */
+	0, /* sq_slice */
+	0, /* sq_ass_item */
+	0, /* sq_ass_slice */
+	(objobjproc)lzm_contains, /* sq_contains */
+	0, /* sq_inplace_concat */
+	0, /* sq_inplace_repeat */
+};
+
+
+/* Other methods (copy, diff, etc) */
+static PyTypeObject lazymanifestType;
+
+static int compact(lazymanifest *self) {
+	if (!self->dirty)
+		return 0;
+	int i;
+	ssize_t need = 0;
+	for (i = 0; i < self->numlines; i++) {
+		if (self->lines[i].deleted == false) {
+			need += self->lines[i].len;
+		}
+	}
+	char *dest = malloc(need);
+	if (dest == NULL) {
+		return -1;
+	}
+	ssize_t copied = 0;
+	int real = 0;
+	for (i = 0; i < self->numlines; i++) {
+		line *src = self->lines + i;
+		char *tofree = NULL;
+		if (src->from_malloc) {
+			tofree = src->start;
+		}
+		if (src->deleted == false) {
+			ssize_t c = src->len;
+			memcpy(dest + copied, src->start, c);
+			line new = {
+				dest + copied, /* start */
+				c, /* total line length */
+				src->hash_suffix, /* extra byte, if any, on the hash */
+				src->hash_none, /* true if the hash is set to None */
+				false, /* is `start` a pointer we allocated? */
+				false, /* is this entry deleted? */
+			};
+			line *l = (self->lines) + real;
+			memcpy(l, &new, sizeof(line));
+			real++;
+			copied += c;
+		}
+		if (tofree)
+			free(tofree);
+	}
+	PyObject *pydata = PyString_FromStringAndSize(dest, copied);
+	if (pydata == NULL)
+		return -1;
+	char *realdest;
+	int err = PyString_AsStringAndSize(pydata, &realdest, &copied);
+	if (err == -1)
+		return -1;
+	/* Right now, lines contain pointers into a block we just had
+	   Python copy. Fix up the pointers so that they point into
+	   the Python string we just built.
+	 */
+	for (i = 0; i < real; i++) {
+		int offset = (self->lines[i].start) - dest;
+		self->lines[i].start = realdest + offset;
+	}
+	Py_DECREF(self->pydata);
+	free(dest);
+	self->pydata = pydata;
+	Py_INCREF(self->pydata);
+	self->numlines = real;
+	self->livelines = real;
+	self->dirty = false;
+	return 0;
+}
+
+static PyObject *lzm_text(lazymanifest * self, PyObject * unused_args)
+{
+	if (compact(self) != 0) {
+		PyErr_NoMemory();
+		return NULL;
+	}
+	Py_INCREF(self->pydata);
+	return self->pydata;
+}
+
+static lazymanifest *lzm_copy(lazymanifest * self, PyObject * unused_args)
+{
+	lazymanifest *copy = NULL;
+	if (compact(self) != 0) {
+		goto nomem;
+	}
+	copy = PyObject_New(lazymanifest, &lazymanifestType);
+	if (copy == NULL) {
+		goto nomem;
+	}
+	copy->numlines = self->numlines;
+	copy->livelines = self->livelines;
+	copy->dirty = false;
+	copy->lines = malloc(self->maxlines * sizeof(line));
+	if (copy->lines == NULL) {
+		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 *lzm_filtercopy(lazymanifest * self, PyObject *matchfn)
+{
+	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 data */
+	compact(self);
+	lazymanifest *tmp = PyObject_New(lazymanifest, &lazymanifestType);
+	tmp->lines = (line *)malloc(self->maxlines * sizeof(line));
+	tmp->maxlines = self->maxlines;
+	tmp->livelines = 0;
+	tmp->numlines = 0;
+	tmp->pydata = self->pydata;
+	Py_INCREF(self->pydata);
+	Py_INCREF(matchfn);
+	int i;
+	for (i = 0; i < self->numlines; i++) {
+		PyObject *arg = PyString_FromString(self->lines[i].start);
+		PyObject *arglist = PyTuple_Pack(1, arg);
+		PyObject *result = PyObject_CallObject(matchfn, arglist);
+		/* if the callback raised an exception, just let it
+		 * through and give up */
+		if (result == NULL) {
+			free(tmp->lines);
+			tmp->lines = NULL;
+			Py_DECREF(matchfn);
+			Py_DECREF(self->pydata);
+			return NULL;
+		}
+		if (PyObject_IsTrue(result)) {
+			assert(!(self->lines[i].from_malloc));
+			tmp->lines[tmp->numlines++] = self->lines[i];
+			tmp->livelines++;
+		}
+		Py_DECREF(arglist);
+		Py_DECREF(arg);
+		Py_DECREF(result);
+	}
+	Py_DECREF(matchfn);
+	compact(tmp);
+	return tmp;
+}
+
+static PyObject *lzm_diff(lazymanifest * self, lazymanifest * other)
+{
+	if (!PyObject_IsInstance((PyObject *)other,
+				 (PyObject *)&lazymanifestType)) {
+		PyErr_Format(PyExc_TypeError, "other must be a lazymanifest");
+		return NULL;
+	}
+	PyObject *emptyTup = NULL, *ret = NULL;
+	PyObject *es = PyString_FromString("");
+	if (es == NULL) {
+		goto nomem;
+	}
+	emptyTup = PyTuple_Pack(2, Py_None, es);
+	Py_DECREF(es);
+	if (emptyTup == NULL) {
+		goto nomem;
+	}
+	ret = PyDict_New();
+	if (ret == NULL) {
+		goto nomem;
+	}
+	int sneedle = 0, oneedle = 0;
+	while (sneedle != self->numlines || oneedle != other->numlines) {
+		line *left = self->lines + sneedle;
+		line *right = other->lines + oneedle;
+		int result;
+		/* If we're looking at a deleted entry and it's not
+		 * the end of the manifest, just skip it. */
+		if (left->deleted && sneedle < self->numlines) {
+			sneedle++;
+			continue;
+		}
+		if (right->deleted && oneedle < other->numlines) {
+			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);
+		}
+		PyObject *key = result <= 0 ?
+			PyString_FromString(left->start) : PyString_FromString(right->start);
+		if (key == NULL)
+			goto nomem;
+		if (result < 0) {
+			PyObject *tup = hashflags(left);
+			if (tup == NULL) {
+				goto nomem;
+			}
+			PyObject *outer = PyTuple_Pack(2, tup, emptyTup);
+			Py_DECREF(tup);
+			if (outer == NULL) {
+				goto nomem;
+			}
+			PyDict_SetItem(ret, key, outer);
+			Py_DECREF(outer);
+			sneedle++;
+		} else if (result > 0) {
+			PyObject *tup = hashflags(right);
+			if (tup == NULL) {
+				goto nomem;
+			}
+			PyObject *outer = PyTuple_Pack(2, emptyTup, tup);
+			Py_DECREF(tup);
+			if (outer == NULL) {
+				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
+			    || left->hash_none != right->hash_none) {
+				PyObject *l = hashflags(left);
+				if (l == NULL) {
+					goto nomem;
+				}
+				PyObject *r = hashflags(right);
+				if (r == NULL) {
+					Py_DECREF(l);
+					goto nomem;
+				}
+				PyObject *outer = PyTuple_Pack(2, l, r);
+				Py_DECREF(l);
+				Py_DECREF(r);
+				if (outer == NULL) {
+					goto nomem;
+				}
+				PyDict_SetItem(ret, key, outer);
+				Py_DECREF(outer);
+			}
+			sneedle++;
+			oneedle++;
+		}
+		Py_DECREF(key);
+	}
+	Py_DECREF(emptyTup);
+	return ret;
+nomem:
+	PyErr_NoMemory();
+	Py_XDECREF(ret);
+	Py_XDECREF(emptyTup);
+	return NULL;
+}
+
+static PyMethodDef lzm_methods[] = {
+	{"copy", (PyCFunction)lzm_copy, METH_NOARGS,
+	 "Make a copy of this lazymanifest."},
+	{"filtercopy", (PyCFunction)lzm_filtercopy, METH_O,
+	 "Make a copy of this manifest filtered by matchfn."},
+	{"diff", (PyCFunction)lzm_diff, METH_O,
+	 "Compare this lazymanifest to another one."},
+	{"text", (PyCFunction)lzm_text, METH_NOARGS,
+	 "Encode this manifest to text."},
+	{NULL},
+};
+
+static PyTypeObject lazymanifestType = {
+	PyObject_HEAD_INIT(NULL)
+	0,                                                /* ob_size */
+	"parsers.lazymanifest",                           /* tp_name */
+	sizeof(lazymanifest),                             /* tp_basicsize */
+	0,                                                /* tp_itemsize */
+	(destructor)lzm_dealloc,                          /* tp_dealloc */
+	0,                                                /* tp_print */
+	0,                                                /* tp_getattr */
+	0,                                                /* tp_setattr */
+	0,                                                /* tp_compare */
+	0,                                                /* tp_repr */
+	0,                                                /* tp_as_number */
+	&lzm_seq_meths,                                   /* tp_as_sequence */
+	&lzm_mapping_methods,                             /* tp_as_mapping */
+	0,                                                /* tp_hash */
+	0,                                                /* tp_call */
+	0,                                                /* tp_str */
+	0,                                                /* tp_getattro */
+	0,                                                /* tp_setattro */
+	0,                                                /* tp_as_buffer */
+	Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_SEQUENCE_IN, /* tp_flags */
+	"TODO(augie)",                                    /* tp_doc */
+	0,                                                /* tp_traverse */
+	0,                                                /* tp_clear */
+	0,                                                /* tp_richcompare */
+	0,                                             /* tp_weaklistoffset */
+	(getiterfunc)lzm_GetIter,                         /* tp_iter */
+	0,                                                /* tp_iternext */
+	lzm_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)lzm_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);
+}
diff --git a/mercurial/parsers.c b/mercurial/parsers.c
--- a/mercurial/parsers.c
+++ b/mercurial/parsers.c
@@ -71,7 +71,7 @@ static inline int hexdigit(const char *p
 /*
  * Turn a hex-encoded string into binary.
  */
-static PyObject *unhexlify(const char *str, int len)
+PyObject *unhexlify(const char *str, int len)
 {
 	PyObject *ret;
 	char *d;
@@ -2233,6 +2233,7 @@ static PyMethodDef methods[] = {
 };
 
 void dirs_module_init(PyObject *mod);
+void manifest_module_init(PyObject *mod);
 
 static void module_init(PyObject *mod)
 {
@@ -2247,6 +2248,7 @@ static void module_init(PyObject *mod)
 	PyModule_AddStringConstant(mod, "versionerrortext", versionerrortext);
 
 	dirs_module_init(mod);
+	manifest_module_init(mod);
 
 	indexType.tp_new = PyType_GenericNew;
 	if (PyType_Ready(&indexType) < 0 ||
diff --git a/setup.py b/setup.py
--- a/setup.py
+++ b/setup.py
@@ -491,6 +491,7 @@ extmodules = [
     Extension('mercurial.mpatch', ['mercurial/mpatch.c'],
               depends=common_depends),
     Extension('mercurial.parsers', ['mercurial/dirs.c',
+                                    'mercurial/manifest.c',
                                     'mercurial/parsers.c',
                                     'mercurial/pathencode.c'],
               depends=common_depends),
diff --git a/tests/test-manifest.py b/tests/test-manifest.py
new file mode 100644
--- /dev/null
+++ b/tests/test-manifest.py
@@ -0,0 +1,215 @@
+import binascii
+import unittest
+import itertools
+
+import silenttestrunner
+
+from mercurial import parsers
+
+HASH_1 = '1' * 40
+HASH_2 = 'f' * 40
+HASH_3 = '1234567890abcdef0987654321deadbeef0fcafe'
+A_SHORT_MANIFEST = (
+    'bar/baz/qux.py\0%(hash2)s%(flag2)s\n'
+    'foo\0%(hash1)s%(flag1)s\n'
+    ) % {'hash1': HASH_1,
+         'flag1': '',
+         'hash2': HASH_2,
+         'flag2': 'l',
+         }
+
+HUGE_MANIFEST_ENTRIES = 200001
+
+A_HUGE_MANIFEST = ''.join(sorted(
+    'file%d\0%s%s\n' % (i, h, f) for i, h, f in
+    itertools.izip(xrange(200001),
+                   itertools.cycle((HASH_1, HASH_2)),
+                   itertools.cycle(('', 'x', 'l')))))
+
+class testmanifest(unittest.TestCase):
+    def testEmptyManifest(self):
+        m = parsers.lazymanifest('')
+        self.assertEqual(0, len(m))
+        self.assertEqual([], list(m))
+
+    def testManifest(self):
+        m = parsers.lazymanifest(A_SHORT_MANIFEST)
+        want = [
+            ('bar/baz/qux.py', binascii.unhexlify(HASH_2), 'l'),
+            ('foo', binascii.unhexlify(HASH_1), ''),
+            ]
+        self.assertEqual(len(want), len(m))
+        self.assertEqual(want, list(m))
+        self.assertEqual((binascii.unhexlify(HASH_1), ''), m['foo'])
+        self.assertRaises(KeyError, lambda : m['wat'])
+        self.assertEqual((binascii.unhexlify(HASH_2), 'l'),
+                         m['bar/baz/qux.py'])
+
+    def testSetItem(self):
+        want = binascii.unhexlify(HASH_1), ''
+
+        m = parsers.lazymanifest('')
+        m['a'] = want
+        self.assertIn('a', m)
+        self.assertEqual(want, m['a'])
+        self.assertEqual('a\0' + HASH_1 + '\n', m.text())
+
+        m = parsers.lazymanifest(A_SHORT_MANIFEST)
+        m['a'] = want
+        self.assertEqual(want, m['a'])
+        self.assertEqual('a\0' + HASH_1 + '\n' + A_SHORT_MANIFEST,
+                         m.text())
+        m2 = m.copy()
+        del m
+        del m2 # make sure we don't double free() anything
+
+    def testCompaction(self):
+        unhex = binascii.unhexlify
+        h1, h2 = unhex(HASH_1), unhex(HASH_2)
+        m = parsers.lazymanifest(A_SHORT_MANIFEST)
+        m['alpha'] = h1, ''
+        m['beta'] = h2, ''
+        del m['foo']
+        want = 'alpha\0%s\nbar/baz/qux.py\0%sl\nbeta\0%s\n' % (
+            HASH_1, HASH_2, HASH_2)
+        self.assertEqual(want, m.text())
+        self.assertEqual(3, len(m))
+        self.assertEqual((h1, ''), m['alpha'])
+        self.assertEqual((h2, ''), m['beta'])
+        self.assertRaises(KeyError, lambda : m['foo'])
+        w = [('alpha', h1, ''), ('bar/baz/qux.py', h2, 'l'), ('beta', h2, '')]
+        self.assertEqual(w, list(m))
+
+    def testSetGetNodeSuffix(self):
+        clean = parsers.lazymanifest(A_SHORT_MANIFEST)
+        m = parsers.lazymanifest(A_SHORT_MANIFEST)
+        h, f = m['foo']
+        want = h + 'a', f
+        # Merge code wants to set 21-byte fake hashes at times
+        m['foo'] = want
+        self.assertEqual(want, m['foo'])
+        self.assertEqual([('bar/baz/qux.py', binascii.unhexlify(HASH_2), 'l'),
+                          ('foo', binascii.unhexlify(HASH_1) + 'a', '')],
+                         list(m))
+        # Sometimes it even tries a 22-byte fake hash, but we can
+        # return 21 and it'll work out
+        m['foo'] = want[0] + '+', f
+        self.assertEqual(want, m['foo'])
+        # make sure the suffix survives a copy
+        m2 = m.filtercopy(lambda x: x == 'foo')
+        self.assertEqual(want, m2['foo'])
+        m2 = m.copy()
+        self.assertEqual(want, m2['foo'])
+        # suffix with iteration
+        self.assertEqual([('bar/baz/qux.py', binascii.unhexlify(HASH_2), 'l'),
+                          ('foo', want[0], '')], list(m))
+        # shows up in diff
+        self.assertEqual({'foo': (want, (h, ''))}, m.diff(clean))
+        self.assertEqual({'foo': ((h, ''), want)}, clean.diff(m))
+
+    def testFilterCopyException(self):
+        m = parsers.lazymanifest(A_SHORT_MANIFEST)
+        def filt(path):
+            if path == 'foo':
+                assert False
+            return True
+        self.assertRaises(AssertionError, m.filtercopy, filt)
+
+    def testSetGetNodeNone(self):
+        clean = parsers.lazymanifest(A_SHORT_MANIFEST)
+        m = parsers.lazymanifest(A_SHORT_MANIFEST)
+        h, f = m['foo']
+        want = None, f
+        m['foo'] = want
+        self.assertEqual(want, m['foo'])
+        # none with iteration
+        self.assertEqual([('bar/baz/qux.py', binascii.unhexlify(HASH_2), 'l'),
+                          ('foo', None, '')], list(m))
+        # none with copies
+        m2 = m.filtercopy(lambda x: x == 'foo')
+        self.assertEqual(want, m2['foo'])
+        m2 = m.copy()
+        self.assertEqual(want, m2['foo'])
+        # shows up in diff
+        self.assertEqual({'foo': (want, (h, ''))}, m.diff(clean))
+        self.assertEqual({'foo': ((h, ''), want)}, clean.diff(m))
+
+    def testRemoveItem(self):
+        m = parsers.lazymanifest(A_SHORT_MANIFEST)
+        del m['foo']
+        self.assertRaises(KeyError, lambda : m['foo'])
+        self.assertEqual(1, len(m))
+        self.assertEqual(1, len(list(m)))
+
+    def testManifestDiff(self):
+        MISSING = (None, '')
+        addl = 'z-only-in-left\0' + HASH_1 + '\n'
+        addr = 'z-only-in-right\0' + HASH_2 + 'x\n'
+        left = parsers.lazymanifest(
+            A_SHORT_MANIFEST.replace(HASH_1, HASH_3 + 'x') + addl)
+        right = parsers.lazymanifest(A_SHORT_MANIFEST + addr)
+        want = {
+            'foo': ((binascii.unhexlify(HASH_3), 'x'),
+                    (binascii.unhexlify(HASH_1), '')),
+            'z-only-in-left': ((binascii.unhexlify(HASH_1), ''), MISSING),
+            'z-only-in-right': (MISSING, (binascii.unhexlify(HASH_2), 'x')),
+            }
+        self.assertEqual(want, left.diff(right))
+
+        want = {
+            'bar/baz/qux.py': (MISSING, (binascii.unhexlify(HASH_2), 'l')),
+            'foo': (MISSING, (binascii.unhexlify(HASH_3), 'x')),
+            'z-only-in-left': (MISSING, (binascii.unhexlify(HASH_1), '')),
+            }
+        self.assertEqual(want, parsers.lazymanifest('').diff(left))
+
+        want = {
+            'bar/baz/qux.py': ((binascii.unhexlify(HASH_2), 'l'), MISSING),
+            'foo': ((binascii.unhexlify(HASH_3), 'x'), MISSING),
+            'z-only-in-left': ((binascii.unhexlify(HASH_1), ''), MISSING),
+            }
+        self.assertEqual(want, left.diff(parsers.lazymanifest('')))
+        copy = right.copy()
+        del copy['z-only-in-right']
+        del right['foo']
+        want = {
+            'foo': (MISSING, (binascii.unhexlify(HASH_1), '')),
+            'z-only-in-right': ((binascii.unhexlify(HASH_2), 'x'), MISSING),
+            }
+        self.assertEqual(want, right.diff(copy))
+
+        short = parsers.lazymanifest(A_SHORT_MANIFEST)
+        pruned = short.copy()
+        del pruned['foo']
+        want = {
+            'foo': ((binascii.unhexlify(HASH_1), ''), MISSING),
+            }
+        self.assertEqual(want, short.diff(pruned))
+        want = {
+            'foo': (MISSING, (binascii.unhexlify(HASH_1), '')),
+            }
+        self.assertEqual(want, pruned.diff(short))
+
+    def testReversedLines(self):
+        backwards = ''.join(
+            l + '\n' for l in reversed(A_SHORT_MANIFEST.split('\n')) if l)
+        try:
+            parsers.lazymanifest(backwards)
+            self.fail('Should have raised ValueError')
+        except ValueError, v:
+            self.assertEqual('Manifest lines not in sorted order.', v.message)
+
+    def testNoTerminalNewline(self):
+        try:
+            parsers.lazymanifest(A_SHORT_MANIFEST + 'wat')
+            self.fail('Should have raised ValueError')
+        except ValueError, v:
+            self.assertEqual('Manifest did not end in a newline.', v.message)
+
+    def testHugeManifest(self):
+        m = parsers.lazymanifest(A_HUGE_MANIFEST)
+        self.assertEqual(HUGE_MANIFEST_ENTRIES, len(m))
+        self.assertEqual(len(m), len(list(m)))
+
+if __name__ == '__main__':
+    silenttestrunner.main(__name__)


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