Resolving html entities with NSXMLParser on iPhone

Question 1

Resolving html entities with NSXMLParser on iPhone

iphone parsing nsxmlparser html-entities

Roberto · Mar 3, 2010 · Viewed 10.7k times · Source

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After exploring several alternatives, it appears that NSXMLParser will not support entities other than the standard entities <, >, ', " and &

The code below fails resulting in an NSXMLParserUndeclaredEntityError.


// Create a dictionary to hold the entities and NSString equivalents
// A complete list of entities and unicode values is described in the HTML DTD
// which is available for download http://www.w3.org/TR/xhtml1/DTD/xhtml-lat1.ent


NSDictionary *entityMap = [NSDictionary dictionaryWithObjectsAndKeys: 
                     [NSString stringWithFormat:@"%C", 0x00E8], @"egrave",
                     [NSString stringWithFormat:@"%C", 0x00E0], @"agrave", 
                     ...
                     ,nil];

NSXMLParser *parser = [[NSXMLParser alloc] initWithData:data];
[parser setDelegate:self];
[parser setShouldResolveExternalEntities:YES];
[parser parse];

// NSXMLParser delegate method
- (NSData *)parser:(NSXMLParser *)parser resolveExternalEntityName:(NSString *)entityName systemID:(NSString *)systemID {
    return [[entityMap objectForKey:entityName] dataUsingEncoding: NSUTF8StringEncoding];
}

Attempts to declare the entities by prepending the HTML document with ENTITY declarations will pass, however the expanded entities are not passed back to parser:foundCharacters and the è and à characters are dropped.

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"
[
  <!ENTITY agrave "à">
  <!ENTITY egrave "è">
]>

In another experiment, I created a completely valid xml document with an internal DTD

<?xml version="1.0" standalone="yes" ?>
<!DOCTYPE author [
    <!ELEMENT author (#PCDATA)>
    <!ENTITY js "Jo Smith">
]>
<author>&lt; &js; &gt;</author>

I implemented the parser:foundInternalEntityDeclarationWithName:value:; delegate method and it is clear that the parser is getting the entity data, however the parser:foundCharacters is only called for the pre-defined entities.

2010-03-20 12:53:59.871 xmlParsing[1012:207] Parser Did Start Document
2010-03-20 12:53:59.873 xmlParsing[1012:207] Parser foundElementDeclarationWithName: author model: 
2010-03-20 12:53:59.873 xmlParsing[1012:207] Parser foundInternalEntityDeclarationWithName: js value: Jo Smith
2010-03-20 12:53:59.874 xmlParsing[1012:207] didStartElement: author type: (null)
2010-03-20 12:53:59.875 xmlParsing[1012:207] parser foundCharacters Before: 
2010-03-20 12:53:59.875 xmlParsing[1012:207] parser foundCharacters After: <
2010-03-20 12:53:59.876 xmlParsing[1012:207] parser foundCharacters Before: <
2010-03-20 12:53:59.876 xmlParsing[1012:207] parser foundCharacters After: < 
2010-03-20 12:53:59.877 xmlParsing[1012:207] parser foundCharacters Before: < 
2010-03-20 12:53:59.878 xmlParsing[1012:207] parser foundCharacters After: <  
2010-03-20 12:53:59.879 xmlParsing[1012:207] parser foundCharacters Before: <  
2010-03-20 12:53:59.879 xmlParsing[1012:207] parser foundCharacters After: <  >
2010-03-20 12:53:59.880 xmlParsing[1012:207] didEndElement: author with content: <  >
2010-03-20 12:53:59.880 xmlParsing[1012:207] Parser Did End Document

I found a link to a tutorial on Using the SAX Interface of LibXML. The xmlSAXHandler that is used by NSXMLParser allows for a getEntity callback to be defined. After calling getEntity, the expansion of the entity is passed to the characters callback.

NSXMLParser is missing functionality here. What should happen is that the NSXMLParser or its delegate store the entity definitions and provide them to the xmlSAXHandler getEntity callback. This is clearly not happening. I will file a bug report.

In the meantime, the earlier answer of performing a string replacement is perfectly acceptable if your documents are small. Check out the SAX tutorial mentioned above along with the XMLPerformance sample app from Apple to see if implementing the libxml parser on your own is worthwhile.

This has been fun.

Question 2

I think I read every single web page relating to this problem but I still cannot find a solution to it, so here I am.

I have an HTML web page which is not under my control and I need to parse it from my iPhone application. Here is a sample of the web page I'm talking about:

<HTML>
  <HEAD>
    <META http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
  </HEAD>
  <BODY>
    <LI class="bye bye" rel="hello 1">
      <H5 class="onlytext">
        <A name="morning_part">morning</A>
      </H5>
      <DIV class="mydiv">
        <SPAN class="myclass">something about you</SPAN> 
        <SPAN class="anotherclass">
          <A href="http://www.google.it">Bye Bye &egrave; un saluto</A>
        </SPAN>
      </DIV>
    </LI>
  </BODY>
</HTML>

I'm using NSXMLParser and it is going well till it find the è html entity. It calls foundCharacters: for "Bye Bye" and then it calls resolveExternalEntityName:systemID:: with an entityName of "egrave". In this method i'm just returning the character "è" trasformed in an NSData, the foundCharacters is called again adding the string "è" to the previous one "Bye Bye " and then the parser raise the NSXMLParserUndeclaredEntityError error.

I have no DTD and I cannot change the html file I'm parsing. Do you have any ideas on this problem?

Update (12/03/2010). After the suggestion of Griffo I ended up with something like this:

data = [self replaceHtmlEntities:data];
NSXMLParser *parser = [[NSXMLParser alloc] initWithData:data];
[parser setDelegate:self];
[parser parse];

where replaceHtmlEntities:(NSData *) is something like this:

- (NSData *)replaceHtmlEntities:(NSData *)data {
    
    NSString *htmlCode = [[NSString alloc] initWithData:data encoding:NSISOLatin1StringEncoding];
    NSMutableString *temp = [NSMutableString stringWithString:htmlCode];
    
    [temp replaceOccurrencesOfString:@"&amp;" withString:@"&" options:NSLiteralSearch range:NSMakeRange(0, [temp length])];
    [temp replaceOccurrencesOfString:@"&nbsp;" withString:@" " options:NSLiteralSearch range:NSMakeRange(0, [temp length])];
    ...
    [temp replaceOccurrencesOfString:@"&Agrave;" withString:@"À" options:NSLiteralSearch range:NSMakeRange(0, [temp length])];

    NSData *finalData = [temp dataUsingEncoding:NSISOLatin1StringEncoding];
    return finalData;
    
}

But I am still looking the best way to solve this problem. I will try TouchXml in the next days but I still think that there should be a way to do this using NSXMLParser API, so if you know how, feel free to write it here.

Resolving html entities with NSXMLParser on iPhone

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