From 02e717651c88c48afeb66ef85f1f868ba9b08dfb Mon Sep 17 00:00:00 2001
From: Ilya Kharabet <ilyakharabet@gmail.com>
Date: Tue, 2 Mar 2021 12:26:23 +0300
Subject: [PATCH] Make file download requests chunked (#75)

---
 .../FigmaExport/Loaders/ImagesLoader.swift    | 10 ----------
 .../FigmaExport/Output/FileDownloader.swift   | 20 ++++++++++++-------
 .../Extensions/Array+chunked.swift            |  9 +++++++++
 3 files changed, 22 insertions(+), 17 deletions(-)
 create mode 100644 Sources/FigmaExportCore/Extensions/Array+chunked.swift

diff --git a/Sources/FigmaExport/Loaders/ImagesLoader.swift b/Sources/FigmaExport/Loaders/ImagesLoader.swift
index 3b18a27c..60e07313 100644
--- a/Sources/FigmaExport/Loaders/ImagesLoader.swift
+++ b/Sources/FigmaExport/Loaders/ImagesLoader.swift
@@ -214,13 +214,3 @@ private extension String {
     }
 
 }
-
-// MARK: - Array Utils
-
-private extension Array {
-    func chunked(into size: Int) -> [[Element]] {
-        stride(from: 0, to: count, by: size).map {
-            Array(self[$0 ..< Swift.min($0 + size, count)])
-        }
-    }
-}
diff --git a/Sources/FigmaExport/Output/FileDownloader.swift b/Sources/FigmaExport/Output/FileDownloader.swift
index 60720765..07827042 100644
--- a/Sources/FigmaExport/Output/FileDownloader.swift
+++ b/Sources/FigmaExport/Output/FileDownloader.swift
@@ -14,22 +14,26 @@ final class FileDownloader {
     func fetch(files: [FileContents]) throws -> [FileContents] {
         let group = DispatchGroup()
         var errors: [Error] = []
-        
+
         var newFiles = [FileContents]()
 
         let remoteFileCount = files.filter { $0.sourceURL != nil }.count
         var downloaded = 0
 
+        let semaphore = DispatchSemaphore(value: session.configuration.httpMaximumConnectionsPerHost - 1)
+
         files.forEach { file in
             guard let remoteURL = file.sourceURL else {
                 newFiles.append(file)
                 return
             }
 
-            group.enter()
             let task = session.downloadTask(with: remoteURL) { localURL, _, error in
-                defer { group.leave() }
-                
+                defer {
+                    semaphore.signal()
+                    group.leave()
+                }
+
                 guard let fileURL = localURL, error == nil else {
                     errors.append(error!)
                     return
@@ -44,15 +48,17 @@ final class FileDownloader {
                 downloaded += 1
                 self.logger.info("Downloaded \(downloaded)/\(remoteFileCount)")
             }
-            
+
+            group.enter()
+            semaphore.wait()
             task.resume()
         }
         group.wait()
-        
+
         if !errors.isEmpty {
             throw ErrorGroup(all: errors)
         }
-        
+
         return newFiles
     }
 }
diff --git a/Sources/FigmaExportCore/Extensions/Array+chunked.swift b/Sources/FigmaExportCore/Extensions/Array+chunked.swift
new file mode 100644
index 00000000..017409bf
--- /dev/null
+++ b/Sources/FigmaExportCore/Extensions/Array+chunked.swift
@@ -0,0 +1,9 @@
+import Foundation
+
+public extension Array {
+    func chunked(into size: Int) -> [[Element]] {
+        stride(from: 0, to: count, by: size).map {
+            Array(self[$0 ..< Swift.min($0 + size, count)])
+        }
+    }
+}