Godot 4 源码分析 - 文件读入编码处理

今天需要读入xml文件进行处理，结果读入一个带中文的文件时，出错了。当然程序还能运行，但编译器一直报错，而且XML解析也不正确

单步调试发现读入的内容出现乱码，具体逻辑：

String FileAccess::get_as_text(bool p_skip_cr) const {
	uint64_t original_pos = get_position();
	const_cast<FileAccess *>(this)->seek(0);

	String text = get_as_utf8_string(p_skip_cr);

	const_cast<FileAccess *>(this)->seek(original_pos);

	return text;
}

String FileAccess::get_as_utf8_string(bool p_skip_cr, String encoding) const {
	encoding = encoding.to_lower();
	Vector<uint8_t> sourcef;
	uint64_t len = get_length();
	sourcef.resize(len + 1);

	uint8_t *w = sourcef.ptrw();
	uint64_t r = get_buffer(w, len);
	ERR_FAIL_COND_V(r != len, String());
	w[len] = 0;

	String s((const char *)w);
	s.parse_utf8((const char *)w, -1, p_skip_cr);
	return s;
}

Error String::parse_utf8(const char *p_utf8, int p_len, bool p_skip_cr) {
	if (!p_utf8) {
		return ERR_INVALID_DATA;
	}

	String aux;

	int cstr_size = 0;
	int str_size = 0;

	/* HANDLE BOM (Byte Order Mark) */
	if (p_len < 0 || p_len >= 3) {
		bool has_bom = uint8_t(p_utf8[0]) == 0xef && uint8_t(p_utf8[1]) == 0xbb && uint8_t(p_utf8[2]) == 0xbf;
		if (has_bom) {
			//8-bit encoding, byte order has no meaning in UTF-8, just skip it
			if (p_len >= 0) {
				p_len -= 3;
			}
			p_utf8 += 3;
		}
	}

	bool decode_error = false;
	bool decode_failed = false;
	{
		const char *ptrtmp = p_utf8;
		const char *ptrtmp_limit = &p_utf8[p_len];
		int skip = 0;
		uint8_t c_start = 0;
		while (ptrtmp != ptrtmp_limit && *ptrtmp) {
			uint8_t c = *ptrtmp >= 0 ? *ptrtmp : uint8_t(256 + *ptrtmp);

			if (skip == 0) {
				if (p_skip_cr && c == '\r') {
					ptrtmp++;
					continue;
				}
				/* Determine the number of characters in sequence */
				if ((c & 0x80) == 0) {
					skip = 0;
				} else if ((c & 0xe0) == 0xc0) {
					skip = 1;
				} else if ((c & 0xf0) == 0xe0) {
					skip = 2;
				} else if ((c & 0xf8) == 0xf0) {
					skip = 3;
				} else if ((c & 0xfc) == 0xf8) {
					skip = 4;
				} else if ((c & 0xfe) == 0xfc) {
					skip = 5;
				} else {
					skip = 0;
					print_unicode_error(vformat("Invalid UTF-8 leading byte (%x)", c), true);
					decode_failed = true;
				}
				c_start = c;

				if (skip == 1 && (c & 0x1e) == 0) {
					print_unicode_error(vformat("Overlong encoding (%x ...)", c));
					decode_error = true;
				}
				str_size++;
			} else {
				if ((c_start == 0xe0 && skip == 2 && c < 0xa0) || (c_start == 0xf0 && skip == 3 && c < 0x90) || (c_start == 0xf8 && skip == 4 && c < 0x88) || (c_start == 0xfc && skip == 5 && c < 0x84)) {
					print_unicode_error(vformat("Overlong encoding (%x %x ...)", c_start, c));
					decode_error = true;
				}
				if (c < 0x80 || c > 0xbf) {
					print_unicode_error(vformat("Invalid UTF-8 continuation byte (%x ... %x ...)", c_start, c), true);
					decode_failed = true;
					skip = 0;
				} else {
					--skip;
				}
			}

			cstr_size++;
			ptrtmp++;
		}

		if (skip) {
			print_unicode_error(vformat("Missing %d UTF-8 continuation byte(s)", skip), true);
			decode_failed = true;
		}
	}

	if (str_size == 0) {
		clear();
		return OK; // empty string
	}

	resize(str_size + 1);
	char32_t *dst = ptrw();
	dst[str_size] = 0;

	int skip = 0;
	uint32_t unichar = 0;
	while (cstr_size) {
		uint8_t c = *p_utf8 >= 0 ? *p_utf8 : uint8_t(256 + *p_utf8);

		if (skip == 0) {
			if (p_skip_cr && c == '\r') {
				p_utf8++;
				continue;
			}
			/* Determine the number of characters in sequence */
			if ((c & 0x80) == 0) {
				*(dst++) = c;
				unichar = 0;
				skip = 0;
			} else if ((c & 0xe0) == 0xc0) {
				unichar = (0xff >> 3) & c;
				skip = 1;
			} else if ((c & 0xf0) == 0xe0) {
				unichar = (0xff >> 4) & c;
				skip = 2;
			} else if ((c & 0xf8) == 0xf0) {
				unichar = (0xff >> 5) & c;
				skip = 3;
			} else if ((c & 0xfc) == 0xf8) {
				unichar = (0xff >> 6) & c;
				skip = 4;
			} else if ((c & 0xfe) == 0xfc) {
				unichar = (0xff >> 7) & c;
				skip = 5;
			} else {
				*(dst++) = 0x20;
				unichar = 0;
				skip = 0;
			}
		} else {
			if (c < 0x80 || c > 0xbf) {
				*(dst++) = 0x20;
				skip = 0;
			} else {
				unichar = (unichar << 6) | (c & 0x3f);
				--skip;
				if (skip == 0) {
					if (unichar == 0) {
						print_unicode_error("NUL character", true);
						decode_failed = true;
						unichar = 0x20;
					}
					if ((unichar & 0xfffff800) == 0xd800) {
						print_unicode_error(vformat("Unpaired surrogate (%x)", unichar));
						decode_error = true;
					}
					if (unichar > 0x10ffff) {
						print_unicode_error(vformat("Invalid unicode codepoint (%x)", unichar));
						decode_error = true;
					}
					*(dst++) = unichar;
				}
			}
		}

		cstr_size--;
		p_utf8++;
	}
	if (skip) {
		*(dst++) = 0x20;
	}

	if (decode_failed) {
		return ERR_INVALID_DATA;
	} else if (decode_error) {
		return ERR_PARSE_ERROR;
	} else {
		return OK;
	}
}

其实已经读入到w里，但String::parse_utf8出错。

回头看了一下，原目标文件为GB2312编码。而Godot的FileAccess不支持别的编码。

那就加上，在不影响原有逻辑的基础上，小动一下：

ClassDB::bind_method(D_METHOD("get_as_text", "skip_cr", "encoding"), &FileAccess::get_as_text, DEFVAL(false), DEFVAL("utf-8"));

String FileAccess::get_as_text(bool p_skip_cr, String encoding) const {
	uint64_t original_pos = get_position();
	const_cast<FileAccess *>(this)->seek(0);

	String text = get_as_utf8_string(p_skip_cr, encoding);

	const_cast<FileAccess *>(this)->seek(original_pos);

	return text;
}

String FileAccess::get_as_utf8_string(bool p_skip_cr, String encoding) const {
	encoding = encoding.to_lower();
	Vector<uint8_t> sourcef;
	uint64_t len = get_length();
	sourcef.resize(len + 1);

	uint8_t *w = sourcef.ptrw();
	uint64_t r = get_buffer(w, len);
	ERR_FAIL_COND_V(r != len, String());
	w[len] = 0;

	if (encoding == "gb2312") {
		std::string str((const char *)w);
		String s(str);
		return s;
	}
	
	String s((const char *)w);
	s.parse_utf8((const char *)w, -1, p_skip_cr);
	return s;
}

GDScript中调用：

	var xml : Xml = Xml.new("D:\\ExenObj\\Exe\\DrGraph\\Files\\Demo.sch")
	xml.Read("gb2312");

class Xml:
	var RootNode: XmlNode = null
	var FileName: String = ""
	func _init(fileName: String) -> void:
		FileName = fileName
	
	func Read(encoding: String = "utf-8") -> void:
		if FileAccess.file_exists(FileName):			
			var fs = FileAccess.open(FileName, FileAccess.READ)
			var text = fs.get_as_text(false, encoding)
			var textStart = Helper.RegMatchAt(text, "<[^!?]")
			var pos = 0;
			if textStart.length() > 0:
				pos = text.find(textStart)
			if pos > 0:
				var header = text.substr(0, pos - 1)			
				text = text.substr(pos)
				var from = 0
				while pos > 0:
					pos = header.find("<!", from)
					if pos == -1:
						break
					from = pos + 1
					pos = header.find("\n", from)
					var str = header.substr(from, pos - from)
					var entityName = Helper.RegMatchAt(str, "Cbw.*?(?= )")
					var value = Helper.RegMatchAt(str, "(?<=').*?(?=')")
					if entityName.length() > 0 and value.length() > 0:
						print(entityName, " = ", value)
			RootNode = XmlNode.new("root");
			RootNode.xml = self;
			RootNode.from_string(text)
			fs.close()

如此，恢复正常。XML文本内容解析为图形效果

<CbwObjects>
	<TLine name="Line967">
		<Points>
			<Point x="258" y="868"/>
			<Point x="606" y="1043"/>
		</Points>
	</TLine>
	<TLine name="Line968">
		<Points>
			<Point x="329" y="698"/>
			<Point x="142" y="864"/>
		</Points>
	</TLine>
	<TRectangle name="Rect147">
		<Points>
			<Point x="433" y="804"/>
			<Point x="712" y="917"/>
		</Points>
	</TRectangle>
	<TRectangle name="Rect148">
		<Points>
			<Point x="378" y="638"/>
			<Point x="461" y="764"/>
		</Points>
	</TRectangle>
	<TRectangle name="Rect149">
		<Points>
			<Point x="105" y="651"/>
			<Point x="201" y="826"/>
		</Points>
	</TRectangle>
	<TRectangle name="Rect150">
		<Points>
			<Point x="139" y="1011"/>
			<Point x="341" y="866"/>
		</Points>
	</TRectangle>
	<TRectangle name="Rect151">
		<Points>
			<Point x="847" y="832"/>
			<Point x="939" y="1043"/>
		</Points>
	</TRectangle>
	<TRectangle name="Rect152">
		<Points>
			<Point x="850" y="635"/>
			<Point x="985" y="710"/>
		</Points>
	</TRectangle>
	<TEllipse name="Ellipse74">
		<Points>
			<Point x="551.451219512195" y="644.367464840815"/>
			<Point x="788" y="762"/>
		</Points>
	</TEllipse>
	<TLine name="Line799" pen="&CbwPen0;">
		<Points>
			<Point x="230" y="46"/>
			<Point x="417" y="284"/>
		</Points>
	</TLine>
</CbwObjects>