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Remote image size without upload

Using Obj-c / Cocoa -touch, I try to get the image size from the list of images, but I do not want to load them. Is there an easy way to do this? I found some solutions in other languages ​​such as this SO question , but I'm looking for an easier way.

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2 answers

Here is the UIImage category that I use for this. It is based on fastimage . One of the main warnings is that the NSURLConnectionDelegate is set to NSURL itself, and this can lead to collisions in certain situations. This is not complete yet (the file url is ignored, for example ...), but you can see where it goes.

Title:

#import <UIKit/UIKit.h>

typedef void (^UIImageSizeRequestCompleted) (NSURL* imgURL, CGSize size);

@interface UIImage (RemoteSize)

+ (void) requestSizeFor: (NSURL*) imgURL completion: (UIImageSizeRequestCompleted) completion;

@end

Source:

#import "UIImage+RemoteSize.h"

#import <objc/runtime.h>

static char *kSizeRequestDataKey = "NSURL.sizeRequestData";
static char *kSizeRequestTypeKey = "NSURL.sizeRequestType";
static char *kSizeRequestCompletionKey = "NSURL.sizeRequestCompletion";

typedef uint32_t dword;

@interface NSURL (RemoteSize)
@property (nonatomic, strong) NSMutableData* sizeRequestData;
@property (nonatomic, strong) NSString* sizeRequestType;
@property (nonatomic, copy) UIImageSizeRequestCompleted sizeRequestCompletion;
@end

@implementation NSURL (RemoteSize)

- (void) setSizeRequestCompletion: (UIImageSizeRequestCompleted) block {
    objc_setAssociatedObject(self, &kSizeRequestCompletionKey, block, OBJC_ASSOCIATION_COPY);
}

- (UIImageSizeRequestCompleted) sizeRequestCompletion {
    return objc_getAssociatedObject(self, &kSizeRequestCompletionKey);
}

- (void) setSizeRequestData:(NSMutableData *)sizeRequestData {
    objc_setAssociatedObject(self, &kSizeRequestDataKey, sizeRequestData, OBJC_ASSOCIATION_RETAIN);
}

- (NSMutableData*) sizeRequestData {
    return objc_getAssociatedObject(self, &kSizeRequestDataKey);
}

- (void) setSizeRequestType:(NSString *)sizeRequestType {
    objc_setAssociatedObject(self, &kSizeRequestTypeKey, sizeRequestType, OBJC_ASSOCIATION_RETAIN);
}

- (NSString*) sizeRequestType {
    return objc_getAssociatedObject(self, &kSizeRequestTypeKey);
}

#pragma mark - NSURLConnectionDelegate
- (void) connection: (NSURLConnection*) connection didReceiveResponse:(NSURLResponse *)response {
    [self.sizeRequestData setLength: 0];    //Redirected => reset data
}

- (void) connection: (NSURLConnection*) connection didReceiveData:(NSData *)data {
    NSMutableData* receivedData = self.sizeRequestData;

    if( !receivedData ) {
        receivedData = [NSMutableData data];
        self.sizeRequestData = receivedData;
    }

    [receivedData appendData: data];

    //Parse metadata
    const unsigned char* cString = [receivedData bytes];
    const NSInteger length = [receivedData length];

    const char pngSignature[8] = {137, 80, 78, 71, 13, 10, 26, 10};
    const char bmpSignature[2] = {66, 77};
    const char gifSignature[2] = {71, 73}; 
    const char jpgSignature[2] = {255, 216};

    if(!self.sizeRequestType ) {
        if( memcmp(pngSignature, cString, 8) == 0 ) {
            self.sizeRequestType = @"PNG";
        }
        else if( memcmp(bmpSignature, cString, 2) == 0 ) {
            self.sizeRequestType = @"BMP";
        }
        else if( memcmp(jpgSignature, cString, 2) == 0 ) {
            self.sizeRequestType = @"JPG";
        }
        else if( memcmp(gifSignature, cString, 2) == 0 ) {
            self.sizeRequestType = @"GIF";
        }
    }

    if( [self.sizeRequestType isEqualToString: @"PNG"] ) {
        char type[5];
        int offset = 8;

        dword chunkSize = 0;
        int chunkSizeSize = sizeof(chunkSize);

        if( offset+chunkSizeSize > length ) 
            return;

        memcpy(&chunkSize, cString+offset, chunkSizeSize);
        chunkSize = OSSwapInt32(chunkSize);
        offset += chunkSizeSize;

        if( offset + chunkSize > length ) 
            return;

        memcpy(&type, cString+offset, 4); type[4]='\0';
        offset += 4;

        if( strcmp(type, "IHDR") == 0 ) {   //Should always be first
            dword width = 0, height = 0;
            memcpy(&width, cString+offset, 4);
            offset += 4;
            width = OSSwapInt32(width);

            memcpy(&height, cString+offset, 4);
            offset += 4;
            height = OSSwapInt32(height);

            if( self.sizeRequestCompletion ) {
                self.sizeRequestCompletion(self, CGSizeMake(width, height));
            }

            self.sizeRequestCompletion = nil;

            [connection cancel];
        }
    }
    else if( [self.sizeRequestType isEqualToString: @"BMP"] ) {
        int offset = 18;
        dword width = 0, height = 0;
        memcpy(&width, cString+offset, 4);
        offset += 4;

        memcpy(&height, cString+offset, 4);
        offset += 4;

        if( self.sizeRequestCompletion ) {
            self.sizeRequestCompletion(self, CGSizeMake(width, height));
        }

        self.sizeRequestCompletion = nil;

        [connection cancel];
    }
    else if( [self.sizeRequestType isEqualToString: @"JPG"] ) {
        int offset = 4;
        dword block_length = cString[offset]*256 + cString[offset+1];

        while (offset<length) {
            offset += block_length;

            if( offset >= length )
                break;
            if( cString[offset] != 0xFF )
                break;
            if( cString[offset+1] == 0xC0 ||
                cString[offset+1] == 0xC1 ||
                cString[offset+1] == 0xC2 ||
                cString[offset+1] == 0xC3 ||
                cString[offset+1] == 0xC5 ||
                cString[offset+1] == 0xC6 ||
                cString[offset+1] == 0xC7 ||
                cString[offset+1] == 0xC9 ||
                cString[offset+1] == 0xCA ||
                cString[offset+1] == 0xCB ||
                cString[offset+1] == 0xCD ||
                cString[offset+1] == 0xCE ||
                cString[offset+1] == 0xCF ) {

                dword width = 0, height = 0;

                height = cString[offset+5]*256 + cString[offset+6];
                width = cString[offset+7]*256 + cString[offset+8];

                if( self.sizeRequestCompletion ) {
                    self.sizeRequestCompletion(self, CGSizeMake(width, height));
                }

                self.sizeRequestCompletion = nil;

                [connection cancel];

            }
            else {
                offset += 2;
                block_length = cString[offset]*256 + cString[offset+1];
            }

        }
    }
    else if( [self.sizeRequestType isEqualToString: @"GIF"] ) {
        int offset = 6;
        dword width = 0, height = 0;
        memcpy(&width, cString+offset, 2);
        offset += 2;

        memcpy(&height, cString+offset, 2);
        offset += 2;

        if( self.sizeRequestCompletion ) {
            self.sizeRequestCompletion(self, CGSizeMake(width, height));
        }

        self.sizeRequestCompletion = nil;

        [connection cancel];
    }
}

- (void) connection: (NSURLConnection*) connection didFailWithError:(NSError *)error {
    if( self.sizeRequestCompletion ) 
        self.sizeRequestCompletion(self, CGSizeZero);
}

- (NSCachedURLResponse *)connection:(NSURLConnection *)connection willCacheResponse:(NSCachedURLResponse *)cachedResponse {
    return cachedResponse;
}

- (void) connectionDidFinishLoading: (NSURLConnection *)connection {
    // Basically, we failed to obtain the image size using metadata and the
    // entire image was downloaded...

    if(!self.sizeRequestData.length) {
        self.sizeRequestData = nil;
    }
    else {
        //Try parse to UIImage
        UIImage* image = [UIImage imageWithData: self.sizeRequestData];

        if( self.sizeRequestCompletion && image) {
            self.sizeRequestCompletion(self, [image size]);
            return;
        }
    }

    self.sizeRequestCompletion(self, CGSizeZero);
}

@end

@implementation UIImage (RemoteSize)

+ (void) requestSizeFor: (NSURL*) imgURL completion: (UIImageSizeRequestCompleted) completion {

    if( [imgURL isFileURL] ) {
        //Load from file stream
    }
    else {
        imgURL.sizeRequestCompletion = completion;

        NSURLRequest* request = [NSURLRequest requestWithURL: imgURL];
        NSURLConnection* conn = [NSURLConnection connectionWithRequest: request delegate: imgURL];
        [conn scheduleInRunLoop: [NSRunLoop mainRunLoop] forMode: NSDefaultRunLoopMode];
        [conn start];
    }
}

@end
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, NSUrlConnection HTTP- ( ), Content-Length: , . expectedContentLength NSURLResponse, . . .

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