annotate mercurial/pathencode.c @ 17692:fb458b3e72fc

pathencode: skip encoding if input is already longer than maxstorepathlen

Calling basicencode may make the path longer, never shorter. If it's already
too long before, then we don't even need to basicencode it.

/*
 pathencode.c - efficient path name encoding

 Copyright 2012 Facebook

 This software may be used and distributed according to the terms of
 the GNU General Public License, incorporated herein by reference.
*/

/*
 * An implementation of the name encoding scheme used by the fncache
 * store.  The common case is of a path < 120 bytes long, which is
 * handled either in a single pass with no allocations or two passes
 * with a single allocation.  For longer paths, multiple passes are
 * required.
 */

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

#include "util.h"

/* state machine for the fast path */
enum path_state {
	START,   /* first byte of a path component */
	A,       /* "AUX" */
	AU,
	THIRD,   /* third of a 3-byte sequence, e.g. "AUX", "NUL" */
	C,       /* "CON" or "COMn" */
	CO,
	COMLPT,  /* "COM" or "LPT" */
	COMLPTn,
	L,
	LP,
	N,
	NU,
	P,       /* "PRN" */
	PR,
	LDOT,    /* leading '.' */
	DOT,     /* '.' in a non-leading position */
	H,       /* ".h" */
	HGDI,    /* ".hg", ".d", or ".i" */
	SPACE,
	DEFAULT, /* byte of a path component after the first */
};

/* state machine for dir-encoding */
enum dir_state {
	DDOT,
	DH,
	DHGDI,
	DDEFAULT,
};

static inline int isset(const uint32_t bitset[], char c)
{
	return bitset[((uint8_t)c) >> 5] & (1 << (((uint8_t)c) & 31));
}

static inline void charcopy(char *dest, Py_ssize_t *destlen, size_t destsize,
                            char c)
{
	if (dest) {
		assert(*destlen < destsize);
		dest[*destlen] = c;
	}
	(*destlen)++;
}

static inline void memcopy(char *dest, Py_ssize_t *destlen, size_t destsize,
                           const void *src, Py_ssize_t len)
{
	if (dest) {
		assert(*destlen + len < destsize);
		memcpy((void *)&dest[*destlen], src, len);
	}
	*destlen += len;
}

static inline void hexencode(char *dest, Py_ssize_t *destlen, size_t destsize,
			     uint8_t c)
{
	static const char hexdigit[] = "0123456789abcdef";

	charcopy(dest, destlen, destsize, hexdigit[c >> 4]);
	charcopy(dest, destlen, destsize, hexdigit[c & 15]);
}

/* 3-byte escape: tilde followed by two hex digits */
static inline void escape3(char *dest, Py_ssize_t *destlen, size_t destsize,
			   char c)
{
	charcopy(dest, destlen, destsize, '~');
	hexencode(dest, destlen, destsize, c);
}

static Py_ssize_t _encodedir(char *dest, size_t destsize,
                             const char *src, Py_ssize_t len)
{
	enum dir_state state = DDEFAULT;
	Py_ssize_t i = 0, destlen = 0;

	while (i < len) {
		switch (state) {
		case DDOT:
			switch (src[i]) {
			case 'd':
			case 'i':
				state = DHGDI;
				charcopy(dest, &destlen, destsize, src[i++]);
				break;
			case 'h':
				state = DH;
				charcopy(dest, &destlen, destsize, src[i++]);
				break;
			default:
				state = DDEFAULT;
				break;
			}
			break;
		case DH:
			if (src[i] == 'g') {
				state = DHGDI;
				charcopy(dest, &destlen, destsize, src[i++]);
			}
			else state = DDEFAULT;
			break;
		case DHGDI:
			if (src[i] == '/') {
				memcopy(dest, &destlen, destsize, ".hg", 3);
				charcopy(dest, &destlen, destsize, src[i++]);
			}
			state = DDEFAULT;
			break;
		case DDEFAULT:
			if (src[i] == '.')
				state = DDOT;
			charcopy(dest, &destlen, destsize, src[i++]);
			break;
		}
	}

	return destlen;
}

PyObject *encodedir(PyObject *self, PyObject *args)
{
	Py_ssize_t len, newlen;
	PyObject *pathobj, *newobj;
	char *path;

	if (!PyArg_ParseTuple(args, "O:encodedir", &pathobj))
		return NULL;

	if (PyString_AsStringAndSize(pathobj, &path, &len) == -1) {
		PyErr_SetString(PyExc_TypeError, "expected a string");
		return NULL;
	}

	newlen = len ? _encodedir(NULL, 0, path, len + 1) : 1;

	if (newlen == len + 1) {
		Py_INCREF(pathobj);
		return pathobj;
	}

	newobj = PyString_FromStringAndSize(NULL, newlen);

	if (newobj) {
		PyString_GET_SIZE(newobj)--;
		_encodedir(PyString_AS_STRING(newobj), newlen, path,
			   len + 1);
	}

	return newobj;
}

static Py_ssize_t _encode(const uint32_t twobytes[8], const uint32_t onebyte[8],
			  char *dest, Py_ssize_t destlen, size_t destsize,
			  const char *src, Py_ssize_t len,
			  int encodedir)
{
	enum path_state state = START;
	Py_ssize_t i = 0;

	/*
	 * Python strings end with a zero byte, which we use as a
	 * terminal token as they are not valid inside path names.
	 */

	while (i < len) {
		switch (state) {
		case START:
			switch (src[i]) {
			case '/':
				charcopy(dest, &destlen, destsize, src[i++]);
				break;
			case '.':
				state = LDOT;
				escape3(dest, &destlen, destsize, src[i++]);
				break;
			case ' ':
				state = DEFAULT;
				escape3(dest, &destlen, destsize, src[i++]);
				break;
			case 'a':
				state = A;
				charcopy(dest, &destlen, destsize, src[i++]);
				break;
			case 'c':
				state = C;
				charcopy(dest, &destlen, destsize, src[i++]);
				break;
			case 'l':
				state = L;
				charcopy(dest, &destlen, destsize, src[i++]);
				break;
			case 'n':
				state = N;
				charcopy(dest, &destlen, destsize, src[i++]);
				break;
			case 'p':
				state = P;
				charcopy(dest, &destlen, destsize, src[i++]);
				break;
			default:
				state = DEFAULT;
				break;
			}
			break;
		case A:
			if (src[i] == 'u') {
				state = AU;
				charcopy(dest, &destlen, destsize, src[i++]);
			}
			else state = DEFAULT;
			break;
		case AU:
			if (src[i] == 'x') {
				state = THIRD;
				i++;
			}
			else state = DEFAULT;
			break;
		case THIRD:
			state = DEFAULT;
			switch (src[i]) {
			case '.':
			case '/':
			case '\0':
				escape3(dest, &destlen, destsize, src[i - 1]);
				break;
			default:
				i--;
				break;
			}
			break;
		case C:
			if (src[i] == 'o') {
				state = CO;
				charcopy(dest, &destlen, destsize, src[i++]);
			}
			else state = DEFAULT;
			break;
		case CO:
			if (src[i] == 'm') {
				state = COMLPT;
				i++;
			}
			else if (src[i] == 'n') {
				state = THIRD;
				i++;
			}
			else state = DEFAULT;
			break;
		case COMLPT:
			switch (src[i]) {
			case '1': case '2': case '3': case '4': case '5':
			case '6': case '7': case '8': case '9':
				state = COMLPTn;
				i++;
				break;
			default:
				state = DEFAULT;
				charcopy(dest, &destlen, destsize, src[i - 1]);
				break;
			}
			break;
		case COMLPTn:
			state = DEFAULT;
			switch (src[i]) {
			case '.':
			case '/':
			case '\0':
				escape3(dest, &destlen, destsize, src[i - 2]);
				charcopy(dest, &destlen, destsize, src[i - 1]);
				break;
			default:
				memcopy(dest, &destlen, destsize,
					&src[i - 2], 2);
				break;
			}
			break;
		case L:
			if (src[i] == 'p') {
				state = LP;
				charcopy(dest, &destlen, destsize, src[i++]);
			}
			else state = DEFAULT;
			break;
		case LP:
			if (src[i] == 't') {
				state = COMLPT;
				i++;
			}
			else state = DEFAULT;
			break;
		case N:
			if (src[i] == 'u') {
				state = NU;
				charcopy(dest, &destlen, destsize, src[i++]);
			}
			else state = DEFAULT;
			break;
		case NU:
			if (src[i] == 'l') {
				state = THIRD;
				i++;
			}
			else state = DEFAULT;
			break;
		case P:
			if (src[i] == 'r') {
				state = PR;
				charcopy(dest, &destlen, destsize, src[i++]);
			}
			else state = DEFAULT;
			break;
		case PR:
			if (src[i] == 'n') {
				state = THIRD;
				i++;
			}
			else state = DEFAULT;
			break;
		case LDOT:
			switch (src[i]) {
			case 'd':
			case 'i':
				state = HGDI;
				charcopy(dest, &destlen, destsize, src[i++]);
				break;
			case 'h':
				state = H;
				charcopy(dest, &destlen, destsize, src[i++]);
				break;
			default:
				state = DEFAULT;
				break;
			}
			break;
		case DOT:
			switch (src[i]) {
			case '/':
			case '\0':
				state = START;
				memcopy(dest, &destlen, destsize, "~2e", 3);
				charcopy(dest, &destlen, destsize, src[i++]);
				break;
			case 'd':
			case 'i':
				state = HGDI;
				charcopy(dest, &destlen, destsize, '.');
				charcopy(dest, &destlen, destsize, src[i++]);
				break;
			case 'h':
				state = H;
				memcopy(dest, &destlen, destsize, ".h", 2);
				i++;
				break;
			default:
				state = DEFAULT;
				charcopy(dest, &destlen, destsize, '.');
				break;
			}
			break;
		case H:
			if (src[i] == 'g') {
				state = HGDI;
				charcopy(dest, &destlen, destsize, src[i++]);
			}
			else state = DEFAULT;
			break;
		case HGDI:
			if (src[i] == '/') {
				state = START;
				if (encodedir)
					memcopy(dest, &destlen, destsize, ".hg",
						3);
				charcopy(dest, &destlen, destsize, src[i++]);
			}
			else state = DEFAULT;
			break;
		case SPACE:
			switch (src[i]) {
			case '/':
			case '\0':
				state = START;
				memcopy(dest, &destlen, destsize, "~20", 3);
				charcopy(dest, &destlen, destsize, src[i++]);
				break;
			default:
				state = DEFAULT;
				charcopy(dest, &destlen, destsize, ' ');
				break;
			}
			break;
		case DEFAULT:
			while (isset(onebyte, src[i])) {
				charcopy(dest, &destlen, destsize, src[i++]);
				if (i == len)
					goto done;
			}
			switch (src[i]) {
			case '.':
				state = DOT;
				i++;
				break;
			case ' ':
				state = SPACE;
				i++;
				break;
			case '/':
				state = START;
				charcopy(dest, &destlen, destsize, '/');
				i++;
				break;
			default:
				if (isset(onebyte, src[i])) {
					do {
						charcopy(dest, &destlen,
							 destsize, src[i++]);
					} while (i < len &&
						 isset(onebyte, src[i]));
				}
				else if (isset(twobytes, src[i])) {
					char c = src[i++];
					charcopy(dest, &destlen, destsize, '_');
					charcopy(dest, &destlen, destsize,
						 c == '_' ? '_' : c + 32);
				}
				else
					escape3(dest, &destlen, destsize,
						src[i++]);
				break;
			}
			break;
		}
	}
done:
	return destlen;
}

static Py_ssize_t basicencode(char *dest, size_t destsize,
			      const char *src, Py_ssize_t len)
{
	static const uint32_t twobytes[8] = { 0, 0, 0x87fffffe };

	static const uint32_t onebyte[8] = {
		1, 0x2bff3bfa, 0x68000001, 0x2fffffff,
	};

	Py_ssize_t destlen = 0;

	return _encode(twobytes, onebyte, dest, destlen, destsize,
		       src, len, 1);
}

static const Py_ssize_t maxstorepathlen = 120;

/*
 * We currently implement only basic encoding.
 *
 * If a name is too long to encode due to Windows path name limits,
 * this function returns None.
 */
PyObject *pathencode(PyObject *self, PyObject *args)
{
	Py_ssize_t len, newlen;
	PyObject *pathobj, *newobj;
	char *path;

	if (!PyArg_ParseTuple(args, "O:pathencode", &pathobj))
		return NULL;

	if (PyString_AsStringAndSize(pathobj, &path, &len) == -1) {
		PyErr_SetString(PyExc_TypeError, "expected a string");
		return NULL;
	}

	if (len > maxstorepathlen) {
		newobj = Py_None;
		Py_INCREF(newobj);
		return newobj;
	}

	newlen = len ? basicencode(NULL, 0, path, len + 1) : 1;

	if (newlen <= maxstorepathlen + 1) {
		if (newlen == len + 1) {
			Py_INCREF(pathobj);
			return pathobj;
		}

		newobj = PyString_FromStringAndSize(NULL, newlen);

		if (newobj) {
			PyString_GET_SIZE(newobj)--;
			basicencode(PyString_AS_STRING(newobj), newlen, path,
				    len + 1);
		}
	} else {
		newobj = Py_None;
		Py_INCREF(newobj);
	}

	return newobj;
}