wrap: Add fallback urls

It can happen that a server is temporaly down, tarballs often have
many mirrors available so we should be able to add at least one fallback
mirror in wrap files.

docs/markdown/Wrap-dependency-system-manual.md

@@ -72,9 +72,11 @@ revision = head
 
 ### Specific to wrap-file
 - `source_url` - download url to retrieve the wrap-file source archive
+- `source_fallback_url` - fallback URL to be used when download from `source_url` fails *Since: 0.55.0*
 - `source_filename` - filename of the downloaded source archive
 - `source_hash` - sha256 checksum of the downloaded source archive
 - `patch_url` - download url to retrieve an optional overlay archive
+- `patch_fallback_url` - fallback URL to be used when download from `patch_url` fails *Since: 0.55.0*
 - `patch_filename` - filename of the downloaded overlay archive
 - `patch_hash` - sha256 checksum of the downloaded overlay archive
 - `lead_directory_missing` - for `wrap-file` create the leading

docs/markdown/snippets/wrap_fallback.md

@@ -0,0 +1,4 @@
+## Wrap fallback URL
+
+Wrap files can now define `source_fallback_url` and `patch_fallback_url` to be
+used in case the main server is temporaly down.

mesonbuild/wrap/wrap.py

@@ -331,7 +331,8 @@ class Resolver:
         else:
             try:
                 resp = urllib.request.urlopen(urlstring, timeout=REQ_TIMEOUT)
-            except urllib.error.URLError:
+            except urllib.error.URLError as e:
+                mlog.log(str(e))
                 raise WrapException('could not get {} is the internet available?'.format(urlstring))
         with contextlib.closing(resp) as resp:
             try:
@@ -371,15 +372,23 @@ class Resolver:
         if dhash != expected:
             raise WrapException('Incorrect hash for {}:\n {} expected\n {} actual.'.format(what, expected, dhash))
 
-    def download(self, what: str, ofname: str) -> None:
+    def download(self, what: str, ofname: str, fallback=False) -> None:
         self.check_can_download()
-        srcurl = self.wrap.get(what + '_url')
+        srcurl = self.wrap.get(what + ('_fallback_url' if fallback else '_url'))
         mlog.log('Downloading', mlog.bold(self.packagename), what, 'from', mlog.bold(srcurl))
-        dhash, tmpfile = self.get_data(srcurl)
-        expected = self.wrap.get(what + '_hash')
-        if dhash != expected:
-            os.remove(tmpfile)
-            raise WrapException('Incorrect hash for {}:\n {} expected\n {} actual.'.format(what, expected, dhash))
+        try:
+            dhash, tmpfile = self.get_data(srcurl)
+            expected = self.wrap.get(what + '_hash')
+            if dhash != expected:
+                os.remove(tmpfile)
+                raise WrapException('Incorrect hash for {}:\n {} expected\n {} actual.'.format(what, expected, dhash))
+        except WrapException:
+            if not fallback:
+                if what + '_fallback_url' in self.wrap.values:
+                    return self.download(what, ofname, fallback=True)
+                mlog.log('A fallback URL could be specified using',
+                         mlog.bold(what + '_fallback_url'), 'key in the wrap file')
+            raise
         os.rename(tmpfile, ofname)
 
     def get_file_internal(self, what: str) -> str:

run_unittests.py

@@ -6517,11 +6517,13 @@ c = ['{0}']
             [wrap-file]
             directory = foo
 
-            source_url = file://{}
+            source_url = http://server.invalid/foo
+            source_fallback_url = file://{}
             source_filename = foo.tar.xz
             source_hash = {}
 
-            patch_url = file://{}
+            patch_url = http://server.invalid/foo
+            patch_fallback_url = file://{}
             patch_filename = foo-patch.tar.xz
             patch_hash = {}
             """.format(source_filename, source_hash, patch_filename, patch_hash))