Make ASIDownloadCache's expiryDateForRequest a static method on ASIHT…

…TPRequest so that the code can be reused.

The functionality is common enough that it may be advantageous for
a third party looking at the request headers to use this method to
calculate the request's expiry date.

Unit tests:

  No new tests.

Documentation:

  Documented the new method +expiryDateForRequest:maxAge:

Classes/ASIDownloadCache.m

@@ -105,31 +105,7 @@ - (void)updateExpiryForRequest:(ASIHTTPRequest *)request maxAge:(NSTimeInterval)
 
 - (NSDate *)expiryDateForRequest:(ASIHTTPRequest *)request maxAge:(NSTimeInterval)maxAge
 {
-	NSMutableDictionary *responseHeaders = [NSMutableDictionary dictionaryWithDictionary:[request responseHeaders]];
-
-	// If we weren't given a custom max-age, lets look for one in the response headers
-	if (!maxAge) {
-		NSString *cacheControl = [[responseHeaders objectForKey:@"Cache-Control"] lowercaseString];
-		if (cacheControl) {
-			NSScanner *scanner = [NSScanner scannerWithString:cacheControl];
-			[scanner scanUpToString:@"max-age" intoString:NULL];
-			if ([scanner scanString:@"max-age" intoString:NULL]) {
-				[scanner scanString:@"=" intoString:NULL];
-				[scanner scanDouble:&maxAge];
-			}
-		}
-	}
-
-	// RFC 2612 says max-age must override any Expires header
-	if (maxAge) {
-		return [[NSDate date] addTimeInterval:maxAge];
-	} else {
-		NSString *expires = [responseHeaders objectForKey:@"Expires"];
-		if (expires) {
-			return [ASIHTTPRequest dateFromRFC1123String:expires];
-		}
-	}
-	return nil;
+  return [ASIHTTPRequest expiryDateForRequest:request maxAge:maxAge];
 }
 
 - (void)storeResponseForRequest:(ASIHTTPRequest *)request maxAge:(NSTimeInterval)maxAge

Classes/ASIHTTPRequest.h

@@ -873,6 +873,11 @@ typedef void (^ASIDataBlock)(NSData *data);
 // And also by ASIS3Request
 + (NSString *)base64forData:(NSData *)theData;
 
+// Returns the expiration date for the request.
+// Calculated from the Expires response header property, unless maxAge is non-zero or
+// there exists a non-zero max-age property in the Cache-Control response header.
++ (NSDate *)expiryDateForRequest:(ASIHTTPRequest *)request maxAge:(NSTimeInterval)maxAge;
+
 // Returns a date from a string in RFC1123 format
 + (NSDate *)dateFromRFC1123String:(NSString *)string;
 

Classes/ASIHTTPRequest.m

@@ -4824,6 +4824,35 @@ + (NSString*)base64forData:(NSData*)theData {
     return [[[NSString alloc] initWithData:data encoding:NSASCIIStringEncoding] autorelease];
 }
 
++ (NSDate *)expiryDateForRequest:(ASIHTTPRequest *)request maxAge:(NSTimeInterval)maxAge
+{
+	NSDictionary *responseHeaders = [request responseHeaders];
+
+	// If we weren't given a custom max-age, lets look for one in the response headers
+	if (!maxAge) {
+		NSString *cacheControl = [[responseHeaders objectForKey:@"Cache-Control"] lowercaseString];
+		if (cacheControl) {
+			NSScanner *scanner = [NSScanner scannerWithString:cacheControl];
+			[scanner scanUpToString:@"max-age" intoString:NULL];
+			if ([scanner scanString:@"max-age" intoString:NULL]) {
+				[scanner scanString:@"=" intoString:NULL];
+				[scanner scanDouble:&maxAge];
+			}
+		}
+	}
+
+	// RFC 2612 says max-age must override any Expires header
+	if (maxAge) {
+		return [[NSDate date] addTimeInterval:maxAge];
+	} else {
+		NSString *expires = [responseHeaders objectForKey:@"Expires"];
+		if (expires) {
+			return [ASIHTTPRequest dateFromRFC1123String:expires];
+		}
+	}
+	return nil;
+}
+
 // Based on hints from http://stackoverflow.com/questions/1850824/parsing-a-rfc-822-date-with-nsdateformatter
 + (NSDate *)dateFromRFC1123String:(NSString *)string
 {