Fix for #178

- make sure nsvg__addPath() hands only valid number of pointts (1+N*3)
- require moveTo path command before handling other commands
- require (sign+)digit for a valid path command coordinate
- allow to add bezier segment only after there’s at leat one point (now
also consistent with nsvg__lineTo)

src/nanosvg.h

@@ -225,11 +225,6 @@ static int nsvg__isdigit(char c)
 	return c >= '0' && c <= '9';
 }
 
-static int nsvg__isnum(char c)
-{
-	return strchr("0123456789+-.eE", c) != 0;
-}
-
 static NSVG_INLINE float nsvg__minf(float a, float b) { return a < b ? a : b; }
 static NSVG_INLINE float nsvg__maxf(float a, float b) { return a > b ? a : b; }
 
@@ -736,9 +731,11 @@ static void nsvg__lineTo(NSVGparser* p, float x, float y)
 
 static void nsvg__cubicBezTo(NSVGparser* p, float cpx1, float cpy1, float cpx2, float cpy2, float x, float y)
 {
-	nsvg__addPoint(p, cpx1, cpy1);
+	if (p->npts > 0) {
-	nsvg__addPoint(p, cpx2, cpy2);
+		nsvg__addPoint(p, cpx1, cpy1);
-	nsvg__addPoint(p, x, y);
+		nsvg__addPoint(p, cpx2, cpy2);
+		nsvg__addPoint(p, x, y);
+	}
 }
 
 static NSVGattrib* nsvg__getAttr(NSVGparser* p)
@@ -1040,6 +1037,10 @@ static void nsvg__addPath(NSVGparser* p, char closed)
 	if (closed)
 		nsvg__lineTo(p, p->pts[0], p->pts[1]);
 
+	// Expect 1 + N*3 points (N = number of cubic bezier segments).
+	if ((p->npts % 3) != 1)
+		return;
+
 	path = (NSVGpath*)malloc(sizeof(NSVGpath));
 	if (path == NULL) goto error;
 	memset(path, 0, sizeof(NSVGpath));
@@ -1458,6 +1459,15 @@ static int nsvg__parseUnits(const char* units)
 	return NSVG_UNITS_USER;
 }
 
+static int nsvg__isCoordinate(const char* s)
+{
+	// optional sign
+	if (*s == '-' || *s == '+')
+		s++;
+	// must have at least one digit
+	return nsvg__isdigit(*s);
+}
+
 static NSVGcoordinate nsvg__parseCoordinateRaw(const char* str)
 {
 	NSVGcoordinate coord = {0, NSVG_UNITS_USER};
@@ -1883,8 +1893,11 @@ static int nsvg__getArgsPerElement(char cmd)
 		case 'a':
 		case 'A':
 			return 7;
+		case 'z':
+		case 'Z':
+			return 0;
 	}
-	return 0;
+	return -1;
 }
 
 static void nsvg__pathMoveTo(NSVGparser* p, float* cpx, float* cpy, float* args, int rel)
@@ -2194,6 +2207,7 @@ static void nsvg__parsePath(NSVGparser* p, const char** attr)
 	float args[10];
 	int nargs;
 	int rargs = 0;
+	char initPoint;
 	float cpx, cpy, cpx2, cpy2;
 	const char* tmp[4];
 	char closedFlag;
@@ -2216,13 +2230,14 @@ static void nsvg__parsePath(NSVGparser* p, const char** attr)
 		nsvg__resetPath(p);
 		cpx = 0; cpy = 0;
 		cpx2 = 0; cpy2 = 0;
+		initPoint = 0;
 		closedFlag = 0;
 		nargs = 0;
 
 		while (*s) {
 			s = nsvg__getNextPathItem(s, item);
 			if (!*item) break;
-			if (nsvg__isnum(item[0])) {
+			if (cmd != '\0' && nsvg__isCoordinate(item)) {
 				if (nargs < 10)
 					args[nargs++] = (float)nsvg__atof(item);
 				if (nargs >= rargs) {
@@ -2235,6 +2250,7 @@ static void nsvg__parsePath(NSVGparser* p, const char** attr)
 							cmd = (cmd == 'm') ? 'l' : 'L';
 							rargs = nsvg__getArgsPerElement(cmd);
 							cpx2 = cpx; cpy2 = cpy;
+							initPoint = 1;
 							break;
 						case 'l':
 						case 'L':
@@ -2284,7 +2300,6 @@ static void nsvg__parsePath(NSVGparser* p, const char** attr)
 				}
 			} else {
 				cmd = item[0];
-				rargs = nsvg__getArgsPerElement(cmd);
 				if (cmd == 'M' || cmd == 'm') {
 					// Commit path.
 					if (p->npts > 0)
@@ -2293,7 +2308,11 @@ static void nsvg__parsePath(NSVGparser* p, const char** attr)
 					nsvg__resetPath(p);
 					closedFlag = 0;
 					nargs = 0;
-				} else if (cmd == 'Z' || cmd == 'z') {
+				} else if (initPoint == 0) {
+					// Do not allow other commands until initial point has been set (moveTo called once).
+					cmd = '\0';
+				}
+				if (cmd == 'Z' || cmd == 'z') {
 					closedFlag = 1;
 					// Commit path.
 					if (p->npts > 0) {
@@ -2309,6 +2328,12 @@ static void nsvg__parsePath(NSVGparser* p, const char** attr)
 					closedFlag = 0;
 					nargs = 0;
 				}
+				rargs = nsvg__getArgsPerElement(cmd);
+				if (rargs == -1) {
+					// Command not recognized
+					cmd = '\0';
+					rargs = 0;
+				}
 			}
 		}
 		// Commit path.