win-nasm: Use gstreamer mirror as primary source

nasm.us went down today and broke all our CI. Use the gstreamer mirror
as the primary source and fallback to nasm.us if that's down.

subprojects/win-nasm/download-binary.py

@@ -6,6 +6,7 @@ import ssl
 import zipfile
 import hashlib
 import urllib.request
+import urllib.error
 
 # Disable certificate checking because it always fails on Windows
 # We verify the checksum anyway.
@@ -13,12 +14,15 @@ ctx = ssl.create_default_context()
 ctx.check_hostname = False
 ctx.verify_mode = ssl.CERT_NONE
 
-base_url = 'https://www.nasm.us/pub/nasm/releasebuilds/{0}/{1}/nasm-{0}-{1}.zip'
+BASENAME = 'nasm-{}-{}.zip'
+UPSTREAM_URL = 'https://www.nasm.us/pub/nasm/releasebuilds/{}/{}/{}'
+GSTREAMER_URL = 'https://gstreamer.freedesktop.org/src/mirror/{}'
+
+version = sys.argv[1]
 arch = 'win64' if sys.argv[2] == 'x86_64' else 'win32'
-url = base_url.format(sys.argv[1], arch)
 zip_sha256 = sys.argv[3]
 source_dir = os.path.join(os.environ['MESON_SOURCE_ROOT'], os.environ['MESON_SUBDIR'])
-dest = os.path.basename(url)
+dest = BASENAME.format(version, arch)
 dest_path = os.path.join(source_dir, dest)
 
 def get_sha256(zipf):
@@ -35,10 +39,21 @@ if os.path.isfile(dest_path):
     else:
         print('{} checksum mismatch, redownloading'.format(dest))
 
-print('Downloading {} to {}'.format(url, dest))
-with open(dest_path, 'wb') as d:
-    f = urllib.request.urlopen(url, context=ctx)
-    d.write(f.read())
+for url in (GSTREAMER_URL.format(dest), UPSTREAM_URL.format(version, arch, dest)):
+    print('Downloading {} to {}'.format(url, dest))
+    try:
+        with open(dest_path, 'wb') as d:
+            f = urllib.request.urlopen(url, context=ctx)
+            d.write(f.read())
+        break
+    except urllib.error.URLError as ex:
+        print(ex)
+        print('Failed to download from {!r}, trying mirror...'.format(url))
+        continue
+else:
+    curdir = os.path.dirname(sys.argv[0])
+    print('Couldn\'t download {!r}! Try downloading it manually and '
+          'placing it into {!r}'.format(dest, curdir))
 
 found_sha256 = get_sha256(dest_path)
 if found_sha256 != zip_sha256: