Allow users to specify which downloader they want to use

Package Control.sublime-settings

@@ -123,6 +123,24 @@
 	// Additional packages to ignore when listing unmanaged packages.
 	"unmanaged_packages_ignore": [],
 
+	// The downloader backends that should be used for HTTP(S) requests, split
+	// by operating system to allow for configuration to be shared.
+	//
+	// Valid options include: "urllib", "curl", "wget", (Windows-only) "wininet"
+	//
+	// This setting allows Windows users to bypass wininet and use urllib
+	// instead if they machine or network presents trouble to wininet. Some
+	// OS X and Linux users have also reported better luck with certain proxies
+	// using curl or wget instead of urllib.
+	//
+	// The "curl" and "wget" options require the command line "curl" or "wget"
+	// program installed and present in the PATH.
+	"downloader_precedence": {
+		"windows": ["wininet"],
+		"osx": ["urllib"],
+		"linux": ["urllib", "curl", "wget"]
+	},
+
 	// Directories to ignore when creating a package
 	"dirs_to_ignore": [
 		".hg", ".git", ".svn", "_darcs", "CVS"

package_control/download_manager.py

@@ -2,6 +2,7 @@
 import socket
 from threading import Lock, Timer
 from contextlib import contextmanager
+import sys
 
 try:
     # Python 3
@@ -210,11 +211,34 @@ def fetch(self, url, error_message, prefer_cached=False):
 
         url = update_url(url, self.settings.get('debug'))
 
+        # We don't use sublime.platform() here since this is used for
+        # the crawler on packagecontrol.io also
+        if sys.platform == 'darwin':
+            platform = 'osx'
+        elif sys.platform == 'win32':
+            platform = 'windows'
+        else:
+            platform = 'linux'
+
+        downloader_precedence = self.settings.get('downloader_precedence', {})
+        downloader_list = downloader_precedence.get(platform, [])
+
+        if not isinstance(downloader_list, list) or len(downloader_list) == 0:
+            error_string = text.format(
+                u'''
+                No list of preferred downloaders specified in the
+                "downloader_precedence" setting for the platform "%s"
+                ''',
+                platform
+            )
+            show_error(error_string)
+            raise DownloaderException(error_string)
+
         # Make sure we have a downloader, and it supports SSL if we need it
         if not self.downloader or (is_ssl and not self.downloader.supports_ssl()):
-            for downloader_class in DOWNLOADERS:
+            for downloader_name in downloader_list:
                 try:
-                    downloader = downloader_class(self.settings)
+                    downloader = DOWNLOADERS[downloader_name](self.settings)
                     if is_ssl and not downloader.supports_ssl():
                         continue
                     self.downloader = downloader
@@ -225,10 +249,14 @@ def fetch(self, url, error_message, prefer_cached=False):
         if not self.downloader:
             error_string = text.format(
                 u'''
-                Unable to download %s due to no ssl module available and no
-                capable program found.
+                None of the preferred downloaders can download %s.
+
+                This is usually either because the ssl module is unavailable
+                and/or the command line curl or wget executables could not be
+                found in the PATH.
 
-                Please install curl or wget.
+                If you customized the "downloader_precedence" setting, please
+                verify your customization.
                 ''',
                 url
             )

package_control/downloaders/__init__.py

@@ -1,11 +1,15 @@
 import os
 
+from .urllib_downloader import UrlLibDownloader
+from .curl_downloader import CurlDownloader
+from .wget_downloader import WgetDownloader
+
+DOWNLOADERS = {
+    'urllib': UrlLibDownloader,
+    'curl': CurlDownloader,
+    'wget': WgetDownloader
+}
+
 if os.name == 'nt':
     from .wininet_downloader import WinINetDownloader
-    DOWNLOADERS = [WinINetDownloader]
-
-else:
-    from .urllib_downloader import UrlLibDownloader
-    from .curl_downloader import CurlDownloader
-    from .wget_downloader import WgetDownloader
-    DOWNLOADERS = [UrlLibDownloader, CurlDownloader, WgetDownloader]
+    DOWNLOADERS['wininet'] = WinINetDownloader

package_control/package_manager.py

@@ -71,6 +71,7 @@ def __init__(self):
             'channels',
             'debug',
             'dirs_to_ignore',
+            'downloader_precedence',
             'files_to_ignore',
             'files_to_include',
             'git_binary',