The Tips of allHeaderFields in NSURLResponse

Posted on Edited on In Word count in article: 1.6k Reading time ≈ 1 mins.

这两天提交 APP Store 被拒审了，排查之后发现是 NSHTTPURLResponse 中的 allHeaderFields 的一个坑。

根据 RFC2616 的描述，header 中的字段是大小写不敏感的，也就是，你写 Foo 和 foo 或者是 fOo 是一样的，但是苹果在的实现是，当你 set 的时候，是按照你写的 key-value 来，当你再次设置的时候，是按照大小写不敏感的方式来查找 set，之后在设置进去。

In Objective-C, the returned dictionary of headers is case-preserving during the set operation (unless the key already exists with a different case), and case-insensitive when looking up keys.
For example, if you set the header X-foo, and then later set the header X-Foo, the dictionary’s key is be X-foo, but the value comes from the X-Foo header.

而苹果在 iOS 13 新增了一个方法，这个方法将会用大小写不敏感的方式来查找 key，然后返回对应的 value。

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/*!
    @method valueForHTTPHeaderField:
    @abstract Returns the value which corresponds to the given header
    field. Note that, in keeping with the HTTP RFC, HTTP header field
    names are case-insensitive.
    @param field the header field name to use for the lookup
    (case-insensitive).
    @result the value associated with the given header field, or nil if
    there is no value associated with the given header field.
 */
- (nullable NSString *)valueForHTTPHeaderField:(NSString *)field API_AVAILABLE(macos(10.15), ios(13.0), watchos(6.0), tvos(13.0));

实际测试如下

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NSHTTPURLResponse *res = [[NSHTTPURLResponse alloc] initWithURL:[NSURL URLWithString:@"https://www.baidu.com"] statusCode:200 HTTPVersion:@"1.1" headerFields:@{@"foo": @"2", @"Foo": @"3", @"FOo": @"4", @"bar": @"1", @"Bar": @"2"}];

NSLog(@"%@", res.allHeaderFields);

NSLog(@"%@", [res valueForHTTPHeaderField:@"fOO"]);

其输出结果是

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{
    Bar = 2;
    FOo = 4;
}

4

这么看的话，似乎和文档描述的并不太一样，最后打印出来的 key 是 FOo 也就是最后添加进去的，而 Bar 也是最后添加进去的，key 会覆盖，value 也会覆盖。。。。