UIWebView+SmartJS.h

//
//  UIWebView+SmartJS.h
//
//  Created by Jon Olson on 12/27/08.
//  Copyright 2008-2009 Ballistic Pigeon, LLC. All rights reserved.
//

#import <Foundation/Foundation.h>

extern NSString * const SmartJSErrorDomain;

enum {
	SmartJSSyntaxError = -1,
	SmartJSTypeError = -2,
	SmartJSRangeError = -3,
	SmartJSURIError = -4,
	SmartJSReferenceError = -5,
	SmartJSEvalError = -100000L
};

@interface UIWebView (SmartJS)

- (NSString *)stringByEvaluatingJavaScriptFromString:(NSString *)string error:(NSError **)error;

@end

UIWebView+SmartJS.m

//
//  UIWebView+SmartJS.m
//
//  Created by Jon Olson on 12/27/08.
//  Copyright 2008-2009 Ballistic Pigeon, LLC. All rights reserved.
//

#import "UIWebView+SmartJS.h"

NSString * const SmartJSErrorDomain = @"com.ballisticpigeon.smartjavascript.SmartJSErrorDomain";


// Naïve but correct implementation.
// It would be substantially better to do all the replacements in one pass
// This requires dealing natively with Unicode (or at least UTF8)
// There's also the questions of how many times we end up copying the string (4 right now, maybe?)
// We are still linear time, though, inasmuch as we do our replacment exactly 4 times
// On the whole, this is a mess best solved by a proper regular expression processor
static NSString *EscapeStringAsJavascriptCode(NSString *string) {
	NSMutableString *mutable = [[string mutableCopyWithZone:nil] autorelease];

	[mutable replaceOccurrencesOfString:@"\"" withString:@"\\\"" options:0 range:NSMakeRange(0, [string length])];
	[mutable replaceOccurrencesOfString:@"\\" withString:@"\\\\" options:0 range:NSMakeRange(0, [string length])];
	[mutable replaceOccurrencesOfString:@"\r" withString:@"\\r" options:0 range:NSMakeRange(0, [string length])];
	[mutable replaceOccurrencesOfString:@"\n" withString:@"\\n" options:0 range:NSMakeRange(0, [string length])];
	
	return [NSString stringWithFormat:@"\"%@\"", mutable];
}

static NSString const *safeJSFormat = @"(function() { try { return 'success:' + eval(%@); } catch (e) { return 'error:' + e.name + ':' + e.message})()";

@implementation UIWebView (SmartJS)

- (NSString *)stringByEvaluatingJavaScriptFromString:(NSString *)string error:(NSError **)error {
	NSString *code = [NSString stringWithFormat:(NSString *)safeJSFormat, string];
	
	NSString *result = [self stringByEvaluatingJavaScriptFromString:code]; // This should ALWAYS work
	
	NSRange faultStatusRange = [result rangeOfString:@":"];
	if (faultStatusRange.location == NSNotFound)
		[NSException raise:@"SmartJSResultParseException" format:@"Unable to parse the result from SmartJavaScript evaluator. This indicates a bug in the SmartJavaScript extension. The resulting text was: %@", result];
	
	NSString *faultStatus = [result substringToIndex:faultStatusRange.location-1];
	NSString *body = [result substringFromIndex:faultStatusRange.location+1];
	
	if ([faultStatus isEqualToString:@"success"]) {
		*error = nil; // No error
		return body; // Return their requested result
	}
	
	NSRange errorNameRange = [body rangeOfString:@":"];
	if (errorNameRange.location == NSNotFound)
		[NSException raise:@"SmartJSResultParseException" format:@"Unable to parse the result from SmartJavaScript evaluator. This indicates a bug in the SmartJavaScript extension. The resulting text was: %@", result]; // Return the full result as the : detected earlier could have been part of whatever unparsable string was returned
	
	NSString *errorName = [result substringToIndex:errorNameRange.location-1];
	NSString *errorDescription = [result substringFromIndex:errorNameRange.location+1];
	
	NSDictionary *errorUserInfo = [NSDictionary dictionaryWithObjectsAndKeys:errorName, NSLocalizedDescriptionKey, errorDescription, NSLocalizedFailureReasonErrorKey, nil];
	
	if ([errorName isEqualToString:@"SyntaxError"])
		*error = [NSError errorWithDomain:SmartJSErrorDomain code:SmartJSSyntaxError userInfo:errorUserInfo];
	else if ([errorName isEqualToString:@"TypeError"])
		*error = [NSError errorWithDomain:SmartJSErrorDomain code:SmartJSTypeError userInfo:errorUserInfo];
	else if ([errorName isEqualToString:@"RangeError"])
		*error = [NSError errorWithDomain:SmartJSErrorDomain code:SmartJSRangeError userInfo:errorUserInfo];
	else if ([errorName isEqualToString:@"URIError"])
		*error = [NSError errorWithDomain:SmartJSErrorDomain code:SmartJSURIError userInfo:errorUserInfo];
	else if ([errorName isEqualToString:@"ReferenceError"])
		*error = [NSError errorWithDomain:SmartJSErrorDomain code:SmartJSReferenceError userInfo:errorUserInfo];
	else
		*error = [NSError errorWithDomain:SmartJSErrorDomain code:SmartJSEvalError userInfo:errorUserInfo];
	
	return nil;
}

@end