Avoid skipping parsing Dr. Drang’s JSON Feed, which can’t be detected that it’s a JSON Feed with only partial data, since it has the version element at the end. Add a test for this.

Frameworks/Account/LocalAccount/LocalAccountRefresher.swift

@@ -102,7 +102,7 @@ extension LocalAccountRefresher: DownloadSessionDelegate {
 		
 		if data.count > 4096 {
 			let parserData = ParserData(url: feed.url, data: data)
-			return FeedParser.canParse(parserData)
+			return FeedParser.mightBeAbleToParseBasedOnPartialData(parserData)
 		}
 		
 		return true		

Frameworks/RSParser/Feeds/FeedParser.swift

@@ -18,7 +18,7 @@ public struct FeedParser {
 	public static func canParse(_ parserData: ParserData) -> Bool {
 
 		let type = feedType(parserData)
-		
+
 		switch type {
 		case .jsonFeed, .rssInJSON, .rss, .atom:
 			return true
@@ -27,6 +27,18 @@ public struct FeedParser {
 		}
 	}
 
+	public static func mightBeAbleToParseBasedOnPartialData(_ parserData: ParserData) -> Bool {
+
+		let type = feedType(parserData, isPartialData: true)
+
+		switch type {
+		case .jsonFeed, .rssInJSON, .rss, .atom, .unknown:
+			return true
+		default:
+			return false
+		}
+	}
+
 	public static func parse(_ parserData: ParserData) throws -> ParsedFeed? {
 
 		// This is generally fast enough to call on the main thread —

Frameworks/RSParser/Feeds/FeedType.swift

@@ -20,7 +20,7 @@ public enum FeedType {
 
 private let minNumberOfBytesRequired = 128
 
-public func feedType(_ parserData: ParserData) -> FeedType {
+public func feedType(_ parserData: ParserData, isPartialData: Bool = false) -> FeedType {
 
 	// Can call with partial data — while still downloading, for instance.
 	// If there’s not enough data, return .unknown. Ask again when there’s more data.
@@ -47,5 +47,15 @@ public func feedType(_ parserData: ParserData) -> FeedType {
 		return .atom
 	}
 
+	if isPartialData && nsdata.isProbablyJSON() {
+		// Might not be able to detect a JSON Feed without all data.
+		// Dr. Drang’s JSON Feed (see althis.json and allthis-partial.json in tests)
+		// has, at this writing, the JSON version element at the end of the feed,
+		// which is totally legal — but it means not being able to detect
+		// that it’s a JSON Feed without all the data.
+		// So this returns .unknown instead of .notAFeed.
+		return .unknown
+	}
+
 	return .notAFeed
 }

Frameworks/RSParser/RSParser.xcodeproj/project.pbxproj

@@ -64,6 +64,7 @@
 		845213281FCB4042003B6E93 /* RSHTMLTag.h in Headers */ = {isa = PBXBuildFile; fileRef = 845213261FCB4042003B6E93 /* RSHTMLTag.h */; settings = {ATTRIBUTES = (Public, ); }; };
 		845213291FCB4042003B6E93 /* RSHTMLTag.m in Sources */ = {isa = PBXBuildFile; fileRef = 845213271FCB4042003B6E93 /* RSHTMLTag.m */; };
 		84566D941FD0ABFB00103322 /* allthis.json in Resources */ = {isa = PBXBuildFile; fileRef = 84566D931FD0ABFB00103322 /* allthis.json */; };
+		84566D961FD1FC1800103322 /* allthis-partial.json in Resources */ = {isa = PBXBuildFile; fileRef = 84566D951FD1FC1800103322 /* allthis-partial.json */; };
 		84628AAD1FCA10AE00566A9B /* allthis.atom in Resources */ = {isa = PBXBuildFile; fileRef = 84628AAC1FCA10AE00566A9B /* allthis.atom */; };
 		848674D21FCE7BF600802D1F /* macworld.rss in Resources */ = {isa = PBXBuildFile; fileRef = 848674D11FCE7BF500802D1F /* macworld.rss */; };
 		849A03D01F0081EA00122600 /* DaringFireball.html in Resources */ = {isa = PBXBuildFile; fileRef = 849A03C51F0081EA00122600 /* DaringFireball.html */; };
@@ -166,6 +167,7 @@
 		845213261FCB4042003B6E93 /* RSHTMLTag.h */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; path = RSHTMLTag.h; sourceTree = "<group>"; };
 		845213271FCB4042003B6E93 /* RSHTMLTag.m */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.objc; path = RSHTMLTag.m; sourceTree = "<group>"; };
 		84566D931FD0ABFB00103322 /* allthis.json */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = text.json; path = allthis.json; sourceTree = "<group>"; };
+		84566D951FD1FC1800103322 /* allthis-partial.json */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = text.json; path = "allthis-partial.json"; sourceTree = "<group>"; };
 		84628AAC1FCA10AE00566A9B /* allthis.atom */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = text.xml; path = allthis.atom; sourceTree = "<group>"; };
 		848674D11FCE7BF500802D1F /* macworld.rss */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = text; path = macworld.rss; sourceTree = "<group>"; };
 		849A03C51F0081EA00122600 /* DaringFireball.html */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = text.html; path = DaringFireball.html; sourceTree = "<group>"; };
@@ -365,6 +367,7 @@
 				849A03CE1F0081EA00122600 /* sixcolors.html */,
 				84628AAC1FCA10AE00566A9B /* allthis.atom */,
 				84566D931FD0ABFB00103322 /* allthis.json */,
+				84566D951FD1FC1800103322 /* allthis-partial.json */,
 				849A03CF1F0081EA00122600 /* Subs.opml */,
 			);
 			path = Resources;
@@ -546,6 +549,7 @@
 				849A03DA1F0081EA00122600 /* Subs.opml in Resources */,
 				849A03D61F0081EA00122600 /* manton.rss in Resources */,
 				849A03D11F0081EA00122600 /* DaringFireball.rss in Resources */,
+				84566D961FD1FC1800103322 /* allthis-partial.json in Resources */,
 				849A03D01F0081EA00122600 /* DaringFireball.html in Resources */,
 				84566D941FD0ABFB00103322 /* allthis.json in Resources */,
 				84628AAD1FCA10AE00566A9B /* allthis.atom in Resources */,

Frameworks/RSParser/RSParserTests/FeedParserTypeTests.swift

@@ -127,6 +127,18 @@ class FeedParserTypeTests: XCTestCase {
 		XCTAssertTrue(type == .jsonFeed)
 	}
 
+	// MARK: Unknown
+
+	func testPartialAllThisUnknownFeedType() {
+
+		// In the case of this feed, the partial data isn’t enough to detect that it’s a JSON Feed.
+		// The type detector should return .unknown rather than .notAFeed.
+		
+		let d = parserData("allthis-partial", "json", "http://leancrew.com/allthis/")
+		let type = feedType(d, isPartialData: true)
+		XCTAssertEqual(type, .unknown)
+	}
+
 	// MARK: Performance
 	
 	func testFeedTypePerformance() {