html - 当 NSURLResponse 对于 textEncodingName 返回 nil 时检测 HTML 编码

Question

我正在使用此调用加载网站 HTML -

    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];
    [request setValue:@"utf-8" forHTTPHeaderField:@"Accept-Encoding"];
    [request setValue:@"text/html" forHTTPHeaderField:@"Accept"];
    [NSURLConnection sendAsynchronousRequest:request
                                       queue:[NSOperationQueue currentQueue]
                           completionHandler:^(NSURLResponse *response, NSData *data, NSError *error) { ... }

然后，要将 NSData 转换为 NSString，我需要知道编码，所以我调用 -

NSString *textEncoding = [response textEncodingName];

来自代码块，但在未指定“Content-Encoding” header 字段的网站上返回 nil。

如果我不知道编码，[[NSString alloc] initWithData:data encoding:responseEncoding] 不会给我可读的 HTML。

如何检测不发送“Content-Encoding” header 字段的网站的正确编码？

Answer 1

可以尝试不同的编码并查看哪种编码会产生可读的文本 -

static int encodingPriority[] = {
    NSUTF8StringEncoding,
    NSASCIIStringEncoding,
    NSISOLatin1StringEncoding,
    NSISOLatin2StringEncoding,
    NSUnicodeStringEncoding,
    NSWindowsCP1251StringEncoding,
    NSWindowsCP1252StringEncoding,
    NSWindowsCP1253StringEncoding,
    NSWindowsCP1254StringEncoding,
    NSWindowsCP1250StringEncoding,
    NSNEXTSTEPStringEncoding,
    NSJapaneseEUCStringEncoding,
    NSNonLossyASCIIStringEncoding,
    NSShiftJISStringEncoding,          /* kCFStringEncodingDOSJapanese */
    NSISO2022JPStringEncoding,        /* ISO 2022 Japanese encoding for e-mail */
    NSMacOSRomanStringEncoding,
    NSUTF16BigEndianStringEncoding,
    NSUTF16LittleEndianStringEncoding,
    NSUTF32StringEncoding,
    NSUTF32BigEndianStringEncoding,
    NSUTF32LittleEndianStringEncoding
};

#define REQUIRED_HTML_STRING    @"<html"

- (NSString *)htmlStringForUnknownEncodingData:(NSData *)data detectedEncoding:(NSStringEncoding *)detectedEncoding
{
    NSStringEncoding encoding;
    NSString *html;

    for (int i = 0; i < sizeof(encodingPriority); i++) {
        encoding = encodingPriority[i];

        // try this encoding
        html = [[NSString alloc] initWithData:data encoding:encoding];

        // we need to find a text, because bad encoding will return an unreadable text
        if (html && [html rangeOfString:REQUIRED_HTML_STRING options:NSCaseInsensitiveSearch].location != NSNotFound) {
            *detectedEncoding = encoding;
            return html;
        }
    }
    return nil;
}

然后，要检测 NSData 中的 HTML 使用哪种编码，请调用 -

NSStringEncoding encoding;
html = [self htmlStringForUnknownEncodingData:data detectedEncoding:&encoding];

if (html)
    NSLog("Encoding detected!");
else
    NSLog("No encoding detected");