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Clean up potential race condition with downloading and parsing extra …
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…files for

icons. Fixes #3.
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@leonbreedt
leonbreedt committed Oct 27, 2015
1 parent 432d85d commit 850218c
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Showing 2 changed files with 50 additions and 47 deletions.
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97 changes: 50 additions & 47 deletions FavIcon/FavIcon.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -80,60 +80,65 @@ public enum IconDownloadResult {

/// Responsible for detecting all of the different icons supported by a given site.
public class FavIcons {
/// Interrogates a base URL, attempting to determine all of the supported icons.
/// It will check whether known file names exist, and if present, it will parse
/// the Google and Microsoft specific JSON and XML files to find files if necessary.
/// It will also attempt to parse the response of the `url` as HTML to try and find
/// relevant `<link>` elements.
/// Scans a base URL, attempting to determine all of the supported icons that can
/// be used for favicon purposes.
///
/// It will do the following to determine possible icons that can be used:
/// - Check whether or not `/favicon.ico` exists.
/// - If the base URL returns an HTML page, parse the `<head>` section and check for `<link>`
/// and `<meta>` tags that reference icons using Apple, Microsoft and Google
/// conventions.
/// - If _Web Application Manifest JSON_ (`manifest.json`) files are referenced, or
/// _Microsoft browser configuration XML_ (`browserconfig.xml`) files
/// are referenced, download and parse them to check if they reference icons.
///
/// All of this work is performed in a background queue.
///
/// - Parameters:
/// - url: The URL to interrogate for the presence of icons.
/// - completion: The callback to invoke when detection has completed. The caller
/// must not make any assumptions about which dispatch queue the completion
/// will be invoked on.
/// - Returns: The list of `DetectedIcon`s representing the icons that were found.
/// - url: The base URL to scan.
/// - completion: A callback to invoke when the scan has completed. The callback will be invoked
/// from a background queue.
/// - Returns: An array of `DetectedIcon`s for the icons that were found.
public static func detect(url: NSURL, completion: [DetectedIcon] -> Void) {
let operations = [
let detectionOperations = [
DownloadTextOperation(url: url),
CheckURLExistsOperation(url: NSURL(string: "/favicon.ico", relativeToURL: url)!.absoluteURL),
CheckURLExistsOperation(url: NSURL(string: "/browserconfig.xml", relativeToURL: url)!.absoluteURL)
]

executeURLOperations(operations) { results in
executeURLOperations(detectionOperations) { detectionResults in
var icons: [DetectedIcon] = []
var additionalDownloads: [(URLRequestOperation, URLResult -> Void)] = []

var manifestIcons: [DetectedIcon] = []
var browserConfigIcons: [DetectedIcon] = []
var additionalFileQueue: NSOperationQueue? = nil

switch results[0] {
switch detectionResults[0] {
case .TextDownloaded(let actualURL, let text, let contentType):
if contentType == "text/html" {
let document = HTMLDocument(string: text)

// Check for Web App manifest, trigger download and processing if required.
// 1. Extract any icons referenced by <link> or other elements from the HTML.
icons.appendContentsOf(extractHTMLHeadIcons(document, baseURL: actualURL))

// Check for Web App Manifest, if present, additional download and processing to do.
for link in document.query("/html/head/link") {
if let rel = link.attributes["rel"]?.lowercaseString where rel == "manifest",
let href = link.attributes["href"],
let manifestURL = NSURL(string: href, relativeToURL: url)
{
additionalFileQueue = NSOperationQueue()

executeURLOperations([DownloadTextOperation(url: manifestURL.absoluteURL)], queue: additionalFileQueue) { manifestResults in
switch manifestResults[0] {
additionalDownloads.append((DownloadTextOperation(url: manifestURL), { manifestResult in
switch manifestResult {
case .TextDownloaded( _, let manifestJSON, _):
manifestIcons = extractManifestJSONIcons(manifestJSON, baseURL: actualURL)
icons.appendContentsOf(extractManifestJSONIcons(manifestJSON, baseURL: actualURL))
break
default:
break
}
}
}))
}
}

// Check for Microsoft browser configuration XML, trigger download and processing if present and not disabled.
var browserConfigURL: NSURL? = operations[2].urlRequest.URL
switch results[2] {
// Check for Microsoft browser configuration XML, if present, additional download and processing to do.
var browserConfigURL: NSURL? = detectionOperations[2].urlRequest.URL
switch detectionResults[2] {
case .Success(let actualURL):
browserConfigURL = actualURL
break
Expand All @@ -152,46 +157,44 @@ public class FavIcons {
}
}
}

if let browserConfigURL = browserConfigURL {
if additionalFileQueue == nil {
additionalFileQueue = NSOperationQueue()
}

executeURLOperations([DownloadTextOperation(url: browserConfigURL)], queue: additionalFileQueue) { browserConfigResults in
switch browserConfigResults[0] {
additionalDownloads.append((DownloadTextOperation(url: browserConfigURL), { browserConfigResult in
switch browserConfigResult {
case .TextDownloaded( _, let browserConfigXML, _):
let document = XMLDocument(string: browserConfigXML)
browserConfigIcons = extractBrowserConfigXMLIcons(document, baseURL: actualURL)
icons.appendContentsOf(extractBrowserConfigXMLIcons(document, baseURL: actualURL))
break
default:
break
}
}
}))
}

// Extract any icons referenced by <link> or other elements from the HTML.
icons.appendContentsOf(extractHTMLHeadIcons(document, baseURL: actualURL))
}
break
default: break
}

switch results[1] {
switch detectionResults[1] {
case .Success(let actualURL):
icons.append(DetectedIcon(url: actualURL, type: .FavIcon))
break
default: break
}

if additionalFileQueue != nil {
additionalFileQueue?.waitUntilAllOperationsAreFinished()
additionalFileQueue = nil
icons.appendContentsOf(manifestIcons)
icons.appendContentsOf(browserConfigIcons)
if additionalDownloads.count > 0 {
let additionalOperations = additionalDownloads.map { $0.0 }
let additionalCompletions = additionalDownloads.map { $0.1 }

executeURLOperations(additionalOperations) { additionalResults in
for (index, result) in additionalResults.enumerate() {
additionalCompletions[index](result)
}

completion(icons)
}
} else {
completion(icons)
}

completion(icons)
}
}

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