pathencode: simplify basicencode

mercurial/pathencode.c

@@ -1,532 +1,525 b''
 /*
  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;
 
-	if (len < 5 || memcmp(src, "data/", 5) != 0) {
-		memcopy(dest, &destlen, destsize, src, len);
-		return destlen;
-	}
-
-	memcopy(dest, &destlen, destsize, "data/", 5);
-
 	return _encode(twobytes, onebyte, dest, destlen, destsize,
-		       src + 5, len - 5, 1);
+		       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;
 	}
 
 	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;
 }