Amazon Product Advertising API + Alamofire

AmazonProduct.swift

//
//  AmazonProduct.swift
//  Requires SHXMLParser for parsing Amazon's XML responses (https://github.com/simhanature/SHXMLParser)
//
//  Created by Cory Alder on 2015-01-11.
//  Copyright (c) 2015 Davander Mobile Corporation. All rights reserved.
//
// partly inspired by RWMAmazonProductAdvertisingManager

import Alamofire
import Foundation
import SHXMLParser

enum AmazonProductAdvertising: String {
    case StandardRegion = "webservices.amazon.com"
    case AWSAccessKey = "AWSAccessKeyId"
    case TimestampKey = "Timestamp"
    case SignatureKey = "Signature"
    case VersionKey = "Version"
    case AssociateTagKey = "AssociateTag"
    case CurrentVersion = "2011-08-01"
}

let AWSDateISO8601DateFormat3 = "yyyy-MM-dd'T'HH:mm:ss.SSS'Z'"


func amazonRequest(parameters: [String: AnyObject]? = nil, serializer ser: AmazonSerializer?) -> Alamofire.Request {
    
    let serializer: AmazonSerializer = {
        if let s = ser {
            return s
        } else {
            let s = AmazonSerializer(key: aws_key_default, secret: aws_secret_default)
            s.useSSL = false
            return s
        }
    }()
    
    let URL = serializer.endpointURL()
    
    let e = Alamofire.ParameterEncoding.Custom(serializer.serializerBlock())
    
    let mutableURLRequest = NSMutableURLRequest(URL: URL)
    
    mutableURLRequest.HTTPMethod = Alamofire.Method.GET.rawValue
    
    let encoded: URLRequestConvertible  = e.encode(mutableURLRequest, parameters: parameters).0
    
    return Alamofire.request(encoded)
}

class AmazonSerializer {
    
    let accessKey: String
    let secret: String
    
    var region: String = AmazonProductAdvertising.StandardRegion.rawValue
    var formatPath: String = "/onca/xml"
    var useSSL = true
    
    init(key: String, secret sec: String) {
        self.secret = sec
        self.accessKey = key
    }
    
    func endpointURL() -> NSURL {
        let scheme = useSSL ? "https" : "http"
        let URL = NSURL(string: "\(scheme)://\(region)\(formatPath)")
        return URL!
    }
    
    func serializerBlock() -> (URLRequestConvertible, [String: AnyObject]?) -> (NSMutableURLRequest, NSError?) {
        return { (req, params) -> (NSMutableURLRequest, NSError?) in
            
            // TODO: if params == nil error out ASAP
            
            var mutableParameters = params!
            
            let timestamp = AmazonSerializer.ISO8601FormatStringFromDate(NSDate())
            
            if mutableParameters[AmazonProductAdvertising.AWSAccessKey.rawValue] == nil {
                mutableParameters[AmazonProductAdvertising.AWSAccessKey.rawValue] = self.accessKey
            }
            
            
            mutableParameters[AmazonProductAdvertising.VersionKey.rawValue] = AmazonProductAdvertising.CurrentVersion.rawValue;
            mutableParameters[AmazonProductAdvertising.TimestampKey.rawValue] = timestamp;
            
            var canonicalStringArray = [String]()
        
            // alphabetize
            let sortedKeys = Array(mutableParameters.keys).sort {$0 < $1}
            
            for key in sortedKeys {
                canonicalStringArray.append("\(key)=\(mutableParameters[key]!)")
            }
            
            let canonicalString = canonicalStringArray.joinWithSeparator("&")
            
            let encodedCanonicalString = CFURLCreateStringByAddingPercentEscapes(
                nil,
                canonicalString,
                nil,
                ":,",//"!*'();:@&=+$,/?%#[]",
                CFStringBuiltInEncodings.UTF8.rawValue
            )
            
            let method = req.URLRequest.HTTPMethod
            
            let signature = "\(method)\n\(self.region)\n\(self.formatPath)\n\(encodedCanonicalString)"
            
            let encodedSignatureData = signature.hmacSHA256(self.secret)
            var encodedSignatureString = encodedSignatureData.base64EncodedString()
            
            encodedSignatureString = CFURLCreateStringByAddingPercentEscapes(
                nil,
                encodedSignatureString,
                nil,
                "+=",//"!*'();:@&=+$,/?%#[]",
                CFStringBuiltInEncodings.UTF8.rawValue
            ) as String
            
            let newCanonicalString = "\(encodedCanonicalString)&\(AmazonProductAdvertising.SignatureKey.rawValue)=\(encodedSignatureString)"
            
            let absString = req.URLRequest.URL!.absoluteString
            
            let urlString = req.URLRequest.URL?.query != nil ? "\(absString)&\(newCanonicalString)" : "\(absString)?\(newCanonicalString)"
            
            let request = req.URLRequest.mutableCopy() as! NSMutableURLRequest
            request.URL = NSURL(string: urlString)
            
            return (request, nil)
        }
    }

    
    private class func ISO8601FormatStringFromDate(date: NSDate) -> NSString {
        let dateFormatter = NSDateFormatter()
        dateFormatter.timeZone = NSTimeZone(name: "GMT")
        dateFormatter.dateFormat = AWSDateISO8601DateFormat3//"YYYY-MM-dd'T'HH:mm:ss'Z'"
        dateFormatter.locale = NSLocale(localeIdentifier: "en_US_POSIX")
        return dateFormatter.stringFromDate(date)
    }


}


// XML ResponseSerializer


extension Request {
    class func XMLResponseSerializer() -> GenericResponseSerializer<Dictionary<String,AnyObject>> {
        
        return GenericResponseSerializer {
            request, response, data in
            
            guard data != nil else {
                let failureReason = "Data could not be serialized. Input data was nil."
                let error = Error.errorWithCode(.DataSerializationFailed, failureReason: failureReason)
                return .Failure(data, error)
            }
            
            let parser = SHXMLParser()
            
            if let document = parser.parseData(data) as? [String: AnyObject] {
                return .Success(document)
            } else {
                let failureReason = "Data could not be serialized. for some unknwon reason"
                let error = Error.errorWithCode(.DataSerializationFailed, failureReason: failureReason)
                return .Failure(data, error as NSError)
            }
            
        }
    }
    
    public func responseXML(completionHandler: (NSURLRequest?, NSHTTPURLResponse?, Dictionary<String, AnyObject>?, ErrorType?) -> Void) -> Self {
        let ser = Request.XMLResponseSerializer()
        
        return response(queue: dispatch_get_main_queue(), responseSerializer: ser) {
            req, res, xmlResult in
            
            switch xmlResult {
            case .Failure( _, let err): completionHandler(req, res, nil, err)
            case .Success(let xml): completionHandler(req, res, xml, nil)
            }
            
        }
    }
}

Example.swift

let associate_tag_default = "weio-20"
let aws_key_default = "your amazon key"
let aws_secret_default = "your amazon secret"

let asin = "B00DVDMRX6" // an amazon id to search for

let serializer = AmazonSerializer(key: aws_key_default, secret: aws_secret_default)

let amazonParams = [
    "Service" : "AWSECommerceService",
    "Operation" : "ItemLookup",
    "ResponseGroup" : "Images,ItemAttributes",
    "IdType" : "ASIN",
    "ItemId" : asin,
    "AssociateTag" : associate_tag_default,
    "Condition" : "All"
]
        
amazonRequest(parameters: amazonParams, serializer: serializer).responseXML { (req, res, data, error) -> Void in
    println("Got results! \(data)")
}

Thanks!

Why did you remove the hmacSHA256 in the last revision?

I am having a lot of trouble getting this working.. Could you please update it to the latest version of swift or maybe a working example that we can open and run in Xcode?

I am reading this code and I am wondering if it still works with out the hmacsha256. I will be trying it later.

Thanks!
Though I ended up not using Alamofire it did helped a lot to understand the concept.

On line 112 you are missing the extension to string in order to hash the code.
I've added it from another source and it worked great! (just for other reference).

extension String {
    func hmacSHA256(key: String) -> String {
        let cKey = key.cString(using: String.Encoding.utf8)
        let cData = self.cString(using: String.Encoding.utf8)
        var result = [CUnsignedChar](repeating: 0, count: Int(CC_SHA256_DIGEST_LENGTH))
        CCHmac(CCHmacAlgorithm(kCCHmacAlgSHA256), cKey!, Int(strlen(cKey!)), cData!, Int(strlen(cData!)), &result)
        let hmacData:NSData = NSData(bytes: result, length: (Int(CC_SHA256_DIGEST_LENGTH)))
        let hmacBase64 = hmacData.base64EncodedString(options: NSData.Base64EncodingOptions.lineLength76Characters)
        return String(hmacBase64)
    }
}

Did anyone manage to get this running?

It looks so useful! Unable to get it running on xcode 9.1 swift 3, so many errors :-(

Hey can you update it to swift 4