fileadder: track the data length instead of measuring it with strlen

replaceCalls() ended with strlen(&buffer[pos]), so the length recorded for a
file was the distance to its first 0x00 byte rather than the file size. The
byte just past the content happens to be zero today, which is the only reason
the numbers come out right.

Nothing in html/ contains a 0x00 today, so this is latent, but it is a trap
waiting for the first gzipped or binary asset: gzip puts a zero in the fourth
byte of its header. A gzipped style.css lands in the index as 3 bytes, and
since addr advances by that same value the next file is placed 3 bytes in and
overwrites what came before it. Two gzipped files in html/ are enough to see
it: both come out as 3 bytes and the second sits 1356 bytes inside the first.

Pass the length in and return the adjusted one. The substitution shortens
#{function} to #{NNN}, so the delta is known without measuring. The loops are
bounded by the length as well, which also covers -n, where nothing had put a
terminator in the buffer for strlen to find in the first place.

No output change: the image built from an unmodified html/ is byte for byte
the same before and after, and html_data.h is identical.

tools/fileadder.c

@@ -173,17 +173,17 @@ int addidx(const char *name, int addr, int len)
 /*
  * Replaces calls of the type #{function} in .html files being added
  * It is assumed that the possibly expanded string will fit into the buffer
- * Returns the new length of the string
+ * Takes the length of the data and returns its new length
  */
-int replaceCalls(int pos)
+int replaceCalls(int pos, int len)
 {
 	int i = 0;
 	char function_buf[256];
 
-	while (buffer[pos + i]) {
-		if ((buffer[pos + i]) == '#' && (buffer[pos + i + 1] == '{')) {
+	while (i < len) {
+		if (buffer[pos + i] == '#' && i + 1 < len && buffer[pos + i + 1] == '{') {
 			int j = 2;
-			while (buffer[pos + i + j]) {
+			while (i + j < len) {
 				if (buffer[pos + i + j] == '}')
 					break;
 				function_buf[j - 2] = buffer[pos + i + j];
@@ -196,12 +196,13 @@ int replaceCalls(int pos)
 
 			}
 			function_buf[j - 2] = '\0';
-			if (!buffer[pos + i + j])
-				return i + j;
+			if (i + j >= len)
+				return len;
 			// Because the buffers overlap we cannot use strcpy
-			memmove(&buffer[pos + i + 5], &buffer[pos + i + j], strlen(&buffer[pos + i + j]) + 1);
+			memmove(&buffer[pos + i + 5], &buffer[pos + i + j], len - (i + j));
 			sprintf(&buffer[pos + i + 2], "%03d", callNum);
 			buffer[pos + i + 5] = '}';
+			len -= j - 5;
 			i += 6;
 			fbuf_p += snprintf(&fbuf[fbuf_p], DEF_SIZE - fbuf_p, "  %s,\n", function_buf);
 			xbuf_p += snprintf(&xbuf[xbuf_p], DEF_SIZE - xbuf_p, "extern uint16_t %s(void);\n", function_buf);
@@ -210,7 +211,7 @@ int replaceCalls(int pos)
 		i++;
 	}
 
-	return strlen(&buffer[pos]);
+	return len;
 }
 
 
@@ -308,6 +309,7 @@ int main(int argc, char **argv)
 				continue;
 
 			size_t data_read = addfile(pathbuffer, addr);
+			size_t file_len = data_read;
 			if (data_read) {
 				if (arguments.add_zero) {
 					buffer[addr + data_read + 1] = '\0';
@@ -316,7 +318,7 @@ int main(int argc, char **argv)
 				printf("Data inserted from %s at 0x%x, size: %ld\n", pathbuffer, addr, data_read);
 			}
 			int old_len = data_read;
-			data_read = replaceCalls(addr);
+			data_read = replaceCalls(addr, file_len);
 			if (old_len > data_read)
 				memset(buffer + addr + data_read, 0, old_len - data_read);
 			addidx(in_file->d_name, addr, data_read);