基于Predictive Parsing的ABNF语法分析器（八）——AbnfParser文法解析器之带星号的情形（如char-val, prose-val）
赖俊
带星号*表示重复的次数，例如*A表示A可以重复0至任意多次，*3A表示A可以重复0次、1次、2次或3次，4*A表示A至少要重复4次。我们先来看最简单的情形*A，ABNF的语法定义中char-val和prose-val都属于这种。
/*
This file is one of the component a Context-free Grammar Parser Generator,
which accept a piece of text as the input, and generates a parser
for the inputted context-free grammar.
Copyright (C) 2013, Junbiao Pan (Email: panjunbiao@gmail.com)
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
// char-val = DQUOTE *(%x20-21 / %x23-7E) DQUOTE
// DQUOTE = %x22
protected CharVal char_val() throws IOException, MatchException {
String char_val = "";
// char-val是双引号开始的
assertMatch(is.peek(), 0x22);
// 把这个双引号消化掉 :)
is.read();
// 双引号后面跟着的0x20-21、0x23-7E都属于合法的字符，读入之
while (match(is.peek(), 0x20, 0x21) || match(is.peek(), 0x23, 0x7E)) {
char_val += (char)is.read();
}
// 如果不是跟着0x20-21、0x23-7E，则必须是双引号，否则异常
assertMatch(is.peek(), 0x22);
is.read();
// 返回这个字符串
return new CharVal(char_val);
}
// char-val = DQUOTE *(%x20-21 / %x23-7E) DQUOTE
// DQUOTE = %x22
@Test
public void testChar_val() throws Exception {
Tester<CharVal> tester = new Tester<CharVal>() {
@Override
public CharVal test(AbnfParser parser) throws MatchException, IOException {
return parser.char_val();
}
};
String input;
input = "";
// 用来虐待char_var()方法的各种case，自己看吧
Assert.assertEquals(input, AbnfParserFactory.newInstance("\"" + input + "\"").char_val().toString());
input = String.valueOf((char)0x20);
Assert.assertEquals(input, AbnfParserFactory.newInstance("\"" + input + "\"").char_val().toString());
input = String.valueOf((char)0x21);
Assert.assertEquals(input, AbnfParserFactory.newInstance("\"" + input + "\"").char_val().toString());
input = String.valueOf((char)0x23);
Assert.assertEquals(input, AbnfParserFactory.newInstance("\"" + input + "\"").char_val().toString());
input = String.valueOf((char)0x7E);
Assert.assertEquals(input, AbnfParserFactory.newInstance("\"" + input + "\"").char_val().toString());
input = String.valueOf((char)0x20) + String.valueOf((char)0x20);
Assert.assertEquals(input, AbnfParserFactory.newInstance("\"" + input + "\"").char_val().toString());
input = String.valueOf((char)0x21) + String.valueOf((char)0x21);
Assert.assertEquals(input, AbnfParserFactory.newInstance("\"" + input + "\"").char_val().toString());
input = String.valueOf((char)0x23) + String.valueOf((char)0x23);
Assert.assertEquals(input, AbnfParserFactory.newInstance("\"" + input + "\"").char_val().toString());
input = String.valueOf((char)0x7E) + String.valueOf((char)0x7E);
Assert.assertEquals(input, AbnfParserFactory.newInstance("\"" + input + "\"").char_val().toString());
input = "AbCd1234#$%^~!@#$%^&*()`-=_+[]\\{}|,./<>?;:'";
Assert.assertEquals(input, AbnfParserFactory.newInstance("\"" + input + "\"").char_val().toString());
Assert.assertEquals(input, AbnfParserFactory.newInstance("\"" + input + "\"A").char_val().toString());
Assert.assertEquals(input, AbnfParserFactory.newInstance("\"" + input + "\"\"").char_val().toString());
//
Assertion.assertMatchException("", tester, 1, 1);
Assertion.assertMatchException("" + (char)0x19, tester, 1, 1);
// 这个case可以发现我们这个解析器的缺陷，
// 例如当一个输入流是只有一个双引号开头，没有双引号结尾的情况下，
// char_var()方法会抛出异常（这一点是可以接受的），
// 但读指针却无法到双引号之前了（也就是说这个算法不支持回溯）
Assertion.assertMatchException("\"", tester, 2, 1);
Assertion.assertMatchException("\"a", tester, 3, 1);
Assertion.assertMatchException("B", tester, 1, 1);
}
// prose-val = "<" *(%x20-3D / %x3F-7E) ">"
// prose_val()方法和char_val()方法很类似，请自行阅读
protected ProseVal prose_val() throws IOException, MatchException {
String proseval = "";
assertMatch(is.peek(), '<');
is.read();
while (match(is.peek(), 0x20, 0x3D) || match(is.peek(), 0x3F, 0x7E)) {
proseval += (char)is.read();
}
assertMatch(is.peek(), '>');
is.read();
return new ProseVal(proseval);
}
// prose-val = "<" *(%x20-3D / %x3F-7E) ">"
@Test
public void testProse_val() throws Exception {
Tester<String> tester = new Tester<String>() {
@Override
public String test(AbnfParser parser) throws MatchException, IOException {
return parser.prose_val().toString();
}
};
String input;
input = String.valueOf(new char[] {'<', '>'});
Assert.assertEquals(input, AbnfParserFactory.newInstance(input).prose_val().toString());
input = String.valueOf(new char[] {'<', 0x20, '>'});
Assert.assertEquals(input, AbnfParserFactory.newInstance(input).prose_val().toString());
input = String.valueOf(new char[] {'<', 0x3D, '>'});
Assert.assertEquals(input, AbnfParserFactory.newInstance(input).prose_val().toString());
input = String.valueOf(new char[] {'<', 0x3F, '>'});
Assert.assertEquals(input, AbnfParserFactory.newInstance(input).prose_val().toString());
input = String.valueOf(new char[] {'<', 0x7E, '>'});
Assert.assertEquals(input, AbnfParserFactory.newInstance(input).prose_val().toString());
input = String.valueOf(new char[] {'<', 0x20, 0x3D, 0x3F, 0x7E, '>'});
Assert.assertEquals(input, AbnfParserFactory.newInstance(input).prose_val().toString());
Assert.assertEquals("<>", AbnfParserFactory.newInstance("<>>").prose_val().toString());
Assertion.assertMatchException("<" + (char) 0x19 + ">", tester, 2, 1);
Assertion.assertMatchException("<" + (char) 0x7F + ">", tester, 2, 1);
Assertion.assertMatchException("<" + (char)0x20 + (char)0x19 + ">", tester, 3, 1);
}
本系列文章索引：基于预测的ABNF文法分析器
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