/*

     File: CanonicalRequest.m

 Abstract: A function for creating canonical HTTP/HTTPS requests.

  Version: 1.1

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 */

#import "CanonicalRequest.h"

#include <xlocale.h>

#pragma mark * URL canonicalization steps 

/*! A step in the canonicalisation process.

 *  \details The canonicalisation process is made up of a sequence of steps, each of which is 

 *  implemented by a function that matches this function pointer.  The function gets a URL 

 *  and a mutable buffer holding that URL as bytes.  The function can mutate the buffer as it 

 *  sees fit.  It typically does this by calling CFURLGetByteRangeForComponent to find the range 

 *  of interest in the buffer.  In that case bytesInserted is the amount to adjust that range, 

 *  and the function should modify that to account for any bytes it inserts or deletes.  If 

 *  the function modifies the buffer too much, it can return kCFNotFound to force the system 

 *  to re-create the URL from the buffer.

 *  \param url The original URL to work on.

 *  \param urlData The URL as a mutable buffer; the routine modifies this.

 *  \param bytesInserted The number of bytes that have been inserted so far the mutable buffer.

 *  \returns An updated value of bytesInserted or kCFNotFound if the URL must be reparsed.

 */

typedef CFIndex (*CanonicalRequestStepFunction)(NSURL *url, NSMutableData *urlData, CFIndex bytesInserted);

/*! The post-scheme separate should be "://"; if that's not the case, fix it.

 *  \param url The original URL to work on.

 *  \param urlData The URL as a mutable buffer; the routine modifies this.

 *  \param bytesInserted The number of bytes that have been inserted so far the mutable buffer.

 *  \returns An updated value of bytesInserted or kCFNotFound if the URL must be reparsed.

 */

static CFIndex FixPostSchemeSeparator(NSURL *url, NSMutableData *urlData, CFIndex bytesInserted)

{

    CFRange     range;

    uint8_t *   urlDataBytes;

    NSUInteger  urlDataLength;

    NSUInteger  cursor;

    NSUInteger  separatorLength;

    NSUInteger  expectedSeparatorLength;

    assert(url != nil);

    assert(urlData != nil);

    assert(bytesInserted >= 0);

    range = CFURLGetByteRangeForComponent( (CFURLRef) url, kCFURLComponentScheme, NULL);

    if (range.location != kCFNotFound) {

        assert(range.location >= 0);

        assert(range.length >= 0);

        urlDataBytes  = [urlData mutableBytes];

        urlDataLength = [urlData length];

        separatorLength = 0;

        cursor = (NSUInteger) range.location + (NSUInteger) bytesInserted + (NSUInteger) range.length;

        if ( (cursor < urlDataLength) && (urlDataBytes[cursor] == ':') ) {

            cursor += 1;

            separatorLength += 1;

            if ( (cursor < urlDataLength) && (urlDataBytes[cursor] == '/') ) {

                cursor += 1;

                separatorLength += 1;

                if ( (cursor < urlDataLength) && (urlDataBytes[cursor] == '/') ) {

                    cursor += 1;

                    separatorLength += 1;

                }

            }

        }

        #pragma unused(cursor)          // quietens an analyser warning

        expectedSeparatorLength = strlen("://");

        if (separatorLength != expectedSeparatorLength) {

            [urlData replaceBytesInRange:NSMakeRange((NSUInteger) range.location + (NSUInteger) bytesInserted + (NSUInteger) range.length, separatorLength) withBytes:"://" length:expectedSeparatorLength];

            bytesInserted = kCFNotFound;        // have to build everything now

        }

    }

    return bytesInserted;

}

/*! The scheme should be lower case; if it's not, make it so.

 *  \param url The original URL to work on.

 *  \param urlData The URL as a mutable buffer; the routine modifies this.

 *  \param bytesInserted The number of bytes that have been inserted so far the mutable buffer.

 *  \returns An updated value of bytesInserted or kCFNotFound if the URL must be reparsed.

 */

static CFIndex LowercaseScheme(NSURL *url, NSMutableData *urlData, CFIndex bytesInserted)

{

    CFRange     range;

    uint8_t *   urlDataBytes;

    CFIndex     i;

    assert(url != nil);

    assert(urlData != nil);

    assert(bytesInserted >= 0);

    range = CFURLGetByteRangeForComponent( (CFURLRef) url, kCFURLComponentScheme, NULL);

    if (range.location != kCFNotFound) {

        assert(range.location >= 0);

        assert(range.length >= 0);

        urlDataBytes = [urlData mutableBytes];

        for (i = range.location + bytesInserted; i < (range.location + bytesInserted + range.length); i++) {

            urlDataBytes[i] = (uint8_t) tolower_l(urlDataBytes[i], NULL);

        }

    }

    return bytesInserted;

}

/*! The host should be lower case; if it's not, make it so.

 *  \param url The original URL to work on.

 *  \param urlData The URL as a mutable buffer; the routine modifies this.

 *  \param bytesInserted The number of bytes that have been inserted so far the mutable buffer.

 *  \returns An updated value of bytesInserted or kCFNotFound if the URL must be reparsed.

 */

static CFIndex LowercaseHost(NSURL *url, NSMutableData *urlData, CFIndex bytesInserted)

    // The host should be lower case; if it's not, make it so.

{

    CFRange     range;

    uint8_t *   urlDataBytes;

    CFIndex     i;

    assert(url != nil);

    assert(urlData != nil);

    assert(bytesInserted >= 0);

    range = CFURLGetByteRangeForComponent( (CFURLRef) url, kCFURLComponentHost, NULL);

    if (range.location != kCFNotFound) {

        assert(range.location >= 0);

        assert(range.length >= 0);

        urlDataBytes = [urlData mutableBytes];

        for (i = range.location + bytesInserted; i < (range.location + bytesInserted + range.length); i++) {

            urlDataBytes[i] = (uint8_t) tolower_l(urlDataBytes[i], NULL);

        }

    }

    return bytesInserted;

}

/*! An empty host should be treated as "localhost" case; if it's not, make it so.

 *  \param url The original URL to work on.

 *  \param urlData The URL as a mutable buffer; the routine modifies this.

 *  \param bytesInserted The number of bytes that have been inserted so far the mutable buffer.

 *  \returns An updated value of bytesInserted or kCFNotFound if the URL must be reparsed.

 */

static CFIndex FixEmptyHost(NSURL *url, NSMutableData *urlData, CFIndex bytesInserted)

{

    CFRange     range;

    CFRange     rangeWithSeparator;

    assert(url != nil);

    assert(urlData != nil);

    assert(bytesInserted >= 0);

    range = CFURLGetByteRangeForComponent( (CFURLRef) url, kCFURLComponentHost, &rangeWithSeparator);

    if (range.length == 0) {

        NSUInteger  localhostLength;

        assert(range.location >= 0);

        assert(range.length >= 0);

        localhostLength = strlen("localhost");

        if (range.location != kCFNotFound) {

            [urlData replaceBytesInRange:NSMakeRange( (NSUInteger) range.location + (NSUInteger) bytesInserted, 0) withBytes:"localhost" length:localhostLength];

            bytesInserted += localhostLength;

        } else if ( (rangeWithSeparator.location != kCFNotFound) && (rangeWithSeparator.length == 0) ) {

            [urlData replaceBytesInRange:NSMakeRange((NSUInteger) rangeWithSeparator.location + (NSUInteger) bytesInserted, 0) withBytes:"localhost" length:localhostLength];

            bytesInserted += localhostLength;

        }

    }

    return bytesInserted;

}

/*! Transform an empty URL path to "/".  For example, "http://www.apple.com" becomes "http://www.apple.com/".

 *  \param url The original URL to work on.

 *  \param urlData The URL as a mutable buffer; the routine modifies this.

 *  \param bytesInserted The number of bytes that have been inserted so far the mutable buffer.

 *  \returns An updated value of bytesInserted or kCFNotFound if the URL must be reparsed.

 */

static CFIndex FixEmptyPath(NSURL *url, NSMutableData *urlData, CFIndex bytesInserted)

{

    CFRange     range;

    CFRange     rangeWithSeparator;

    assert(url != nil);

    assert(urlData != nil);

    assert(bytesInserted >= 0);

    range = CFURLGetByteRangeForComponent( (CFURLRef) url, kCFURLComponentPath, &rangeWithSeparator);

    // The following is not a typo.  We use rangeWithSeparator to find where to insert the 

    // "/" and the range length to decide whether we /need/ to insert the "/".

    if ( (rangeWithSeparator.location != kCFNotFound) && (range.length == 0) ) {

        assert(range.location >= 0);

        assert(range.length >= 0);

        assert(rangeWithSeparator.location >= 0);

        assert(rangeWithSeparator.length >= 0);

        [urlData replaceBytesInRange:NSMakeRange( (NSUInteger) rangeWithSeparator.location + (NSUInteger) bytesInserted, 0) withBytes:"/" length:1];

        bytesInserted += 1;

    }

    return bytesInserted;

}

/*! If the user specified the default port (80 for HTTP, 443 for HTTPS), remove it from the URL.

 *  \details Actually this code is disabled because the equivalent code in the default protocol  

 *  handler has also been disabled; some setups depend on get the port number in the URL, even if it 

 *  is the default.

 *  \param url The original URL to work on.

 *  \param urlData The URL as a mutable buffer; the routine modifies this.

 *  \param bytesInserted The number of bytes that have been inserted so far the mutable buffer.

 *  \returns An updated value of bytesInserted or kCFNotFound if the URL must be reparsed.

 */

__attribute__((unused)) static CFIndex DeleteDefaultPort(NSURL *url, NSMutableData *urlData, CFIndex bytesInserted) 

{

    NSString *  scheme;

    BOOL        isHTTP;

    BOOL        isHTTPS;

    CFRange     range;

    uint8_t *   urlDataBytes;

    NSString *  portNumberStr;

    int         portNumber;

    assert(url != nil);

    assert(urlData != nil);

    assert(bytesInserted >= 0);

    scheme = [[url scheme] lowercaseString];

    assert(scheme != nil);

    isHTTP  = [scheme isEqual:@"http" ];

    isHTTPS = [scheme isEqual:@"https"];

    range = CFURLGetByteRangeForComponent( (CFURLRef) url, kCFURLComponentPort, NULL);

    if (range.location != kCFNotFound) {

        assert(range.location >= 0);

        assert(range.length >= 0);

        urlDataBytes = [urlData mutableBytes];

        portNumberStr = [[NSString alloc] initWithBytes:&urlDataBytes[range.location + bytesInserted] length:(NSUInteger) range.length encoding:NSUTF8StringEncoding];

        if (portNumberStr != nil) {

            portNumber = [portNumberStr intValue];

            if ( (isHTTP && (portNumber == 80)) || (isHTTPS && (portNumber == 443)) ) {

                // -1 and +1 to account for the leading ":"

                [urlData replaceBytesInRange:NSMakeRange((NSUInteger) range.location + (NSUInteger) bytesInserted - 1, (NSUInteger) range.length + 1) withBytes:NULL length:0];

                bytesInserted -= (range.length + 1);

            }

        }

    }

    return bytesInserted;

}

#pragma mark * Other request canonicalization

/*! Canonicalise the request headers.

 *  \param request The request to canonicalise.

 */

static void CanonicaliseHeaders(NSMutableURLRequest * request)

{

    // If there's no content type and the request is a POST with a body, add a default 

    // content type of "application/x-www-form-urlencoded".

    if ( ([request valueForHTTPHeaderField:@"Content-Type"] == nil) 

      && ([[request HTTPMethod] caseInsensitiveCompare:@"POST"] == NSOrderedSame) 

      && (([request HTTPBody] != nil) || ([request HTTPBodyStream] != nil)) ) {

        [request setValue:@"application/x-www-form-urlencoded" forHTTPHeaderField:@"Content-Type"];

    }

    // If there's no "Accept" header, add a default.

    if ([request valueForHTTPHeaderField:@"Accept"] == nil) {

        [request setValue:@"*/*" forHTTPHeaderField:@"Accept"];

    }

    // If there's not "Accept-Encoding" header, add a default.

    if ([request valueForHTTPHeaderField:@"Accept-Encoding"] == nil) {

        [request setValue:@"gzip, deflate" forHTTPHeaderField:@"Accept-Encoding"];

    }

    // If there's not an "Accept-Language" headre, add a default.  This is quite bogus; ideally we 

    // should derive the correct "Accept-Language" value from the langauge that the app is running 

    // in.  However, that's quite difficult to get right, so rather than show some general purpose 

    // code that might fail in some circumstances, I've decided to just hardwire US English. 

    // If you use this code in your own app you can customise it as you see fit.  One option might be 

    // to base this value on -[NSBundle preferredLocalizations], so that the web page comes back in 

    // the language that the app is running in.

    if ([request valueForHTTPHeaderField:@"Accept-Language"] == nil) {

        [request setValue:@"en-us" forHTTPHeaderField:@"Accept-Language"];

    }

}

#pragma mark * API

extern NSMutableURLRequest * CanonicalRequestForRequest(NSURLRequest *request)

{

    NSMutableURLRequest *   result;

    NSString *              scheme;

    assert(request != nil);

    // Make a mutable copy of the request.

    result = [request mutableCopy];

    // First up check that we're dealing with HTTP or HTTPS.  If not, do nothing (why were we 

    // we even called?).

    scheme = [[[request URL] scheme] lowercaseString];

    assert(scheme != nil);

    if ( ! [scheme isEqual:@"http" ] && ! [scheme isEqual:@"https"]) {

        assert(NO);

    } else {

        CFIndex         bytesInserted;

        NSURL *         requestURL;

        NSMutableData * urlData;

        static const CanonicalRequestStepFunction kStepFunctions[] = {

            FixPostSchemeSeparator, 

            LowercaseScheme, 

            LowercaseHost, 

            FixEmptyHost, 

            // DeleteDefaultPort,       -- The built-in canonicalizer has stopped doing this, so we don't do it either.

            FixEmptyPath

        };

        size_t          stepIndex;

        size_t          stepCount;

        // Canonicalise the URL by executing each of our step functions.

        bytesInserted = kCFNotFound;

        urlData = nil;

        requestURL = [request URL];

        assert(requestURL != nil);

        stepCount = sizeof(kStepFunctions) / sizeof(*kStepFunctions);

        for (stepIndex = 0; stepIndex < stepCount; stepIndex++) {

            // If we don't have valid URL data, create it from the URL.

            assert(requestURL != nil);

            if (bytesInserted == kCFNotFound) {

                NSData *    urlDataImmutable;

                urlDataImmutable = CFBridgingRelease( CFURLCreateData(NULL, (CFURLRef) requestURL, kCFStringEncodingUTF8, true) );

                assert(urlDataImmutable != nil);

                urlData = [urlDataImmutable mutableCopy];

                assert(urlData != nil);

                bytesInserted = 0;

            }

            assert(urlData != nil);

            // Run the step.

            bytesInserted = kStepFunctions[stepIndex](requestURL, urlData, bytesInserted);

            // Note: The following logging is useful when debugging this code.  Change the 

            // if expression to YES to enable it.

            if (NO) {

                fprintf(stderr, "  [%zu] %.*s\n", stepIndex, (int) [urlData length], (const char *) [urlData bytes]);

            }

            // If the step invalidated our URL (or we're on the last step, whereupon we'll need 

            // the URL outside of the loop), recreate the URL from the URL data.

            if ( (bytesInserted == kCFNotFound) || ((stepIndex + 1) == stepCount) ) {

                requestURL = CFBridgingRelease( CFURLCreateWithBytes(NULL, [urlData bytes], (CFIndex) [urlData length], kCFStringEncodingUTF8, NULL) );

                assert(requestURL != nil);

                urlData = nil;

            }

        }

        [result setURL:requestURL];

        // Canonicalise the headers.

        CanonicaliseHeaders(result);

    }

    return result;

}