feat(tvix/store/blobsvc): add from_addr

This allows constructing blob stores with a URL syntax at runtime,
by passing the --blob-service-addr arg.

We probably still want to have some builder pattern here, to allow
additional schemes to be registered.

Change-Id: Ie588ff7a7c6fb64c9474dfbd2e4bc5f168dfd778
Reviewed-on: https://cl.tvl.fyi/c/depot/+/8742
Reviewed-by: tazjin <tazjin@tvl.su>
Tested-by: BuildkiteCI

tvix/store/src/blobservice/sled.rs

@@ -28,6 +28,36 @@ impl SledBlobService {
 }
 
 impl BlobService for SledBlobService {
+    /// Constructs a [SledBlobService] from the passed [url::Url]:
+    /// - scheme has to be `sled://`
+    /// - there may not be a host.
+    /// - a path to the sled needs to be provided (which may not be `/`).
+    fn from_url(url: &url::Url) -> Result<Self, Error> {
+        if url.scheme() != "sled" {
+            return Err(crate::Error::StorageError("invalid scheme".to_string()));
+        }
+
+        if url.has_host() {
+            return Err(crate::Error::StorageError(format!(
+                "invalid host: {}",
+                url.host().unwrap()
+            )));
+        }
+
+        // TODO: expose compression and other parameters as URL parameters, drop new and new_temporary?
+        if url.path().is_empty() {
+            Self::new_temporary().map_err(|e| Error::StorageError(e.to_string()))
+        } else {
+            if url.path() == "/" {
+                Err(crate::Error::StorageError(
+                    "cowardly refusing to open / with sled".to_string(),
+                ))
+            } else {
+                Self::new(url.path().into()).map_err(|e| Error::StorageError(e.to_string()))
+            }
+        }
+    }
+
     #[instrument(skip(self), fields(blob.digest=%digest))]
     fn has(&self, digest: &B3Digest) -> Result<bool, Error> {
         match self.db.contains_key(digest.to_vec()) {
@@ -127,3 +157,77 @@ impl BlobWriter for SledBlobWriter {
         }
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use tempfile::TempDir;
+
+    use super::BlobService;
+    use super::SledBlobService;
+
+    /// This uses a wrong scheme.
+    #[test]
+    fn test_invalid_scheme() {
+        let url = url::Url::parse("http://foo.example/test").expect("must parse");
+
+        assert!(SledBlobService::from_url(&url).is_err());
+    }
+
+    /// This uses the correct scheme, and doesn't specify a path (temporary sled).
+    #[test]
+    fn test_valid_scheme_temporary() {
+        let url = url::Url::parse("sled://").expect("must parse");
+
+        assert!(SledBlobService::from_url(&url).is_ok());
+    }
+
+    /// This sets the path to a location that doesn't exist, which should fail (as sled doesn't mkdir -p)
+    #[test]
+    fn test_nonexistent_path() {
+        let tmpdir = TempDir::new().unwrap();
+
+        let mut url = url::Url::parse("sled://foo.example").expect("must parse");
+        url.set_path(tmpdir.path().join("foo").join("bar").to_str().unwrap());
+
+        assert!(SledBlobService::from_url(&url).is_err());
+    }
+
+    /// This uses the correct scheme, and specifies / as path (which should fail
+    // for obvious reasons)
+    #[test]
+    fn test_invalid_path_root() {
+        let url = url::Url::parse("sled:///").expect("must parse");
+
+        assert!(SledBlobService::from_url(&url).is_err());
+    }
+
+    /// This uses the correct scheme, and sets a tempdir as location.
+    #[test]
+    fn test_valid_scheme_path() {
+        let tmpdir = TempDir::new().unwrap();
+
+        let mut url = url::Url::parse("sled://").expect("must parse");
+        url.set_path(tmpdir.path().to_str().unwrap());
+
+        assert!(SledBlobService::from_url(&url).is_ok());
+    }
+
+    /// This sets a host, rather than a path, which should fail.
+    #[test]
+    fn test_invalid_host() {
+        let url = url::Url::parse("sled://foo.example").expect("must parse");
+
+        assert!(SledBlobService::from_url(&url).is_err());
+    }
+
+    /// This sets a host AND a valid path, which should fail
+    #[test]
+    fn test_invalid_host_and_path() {
+        let tmpdir = TempDir::new().unwrap();
+
+        let mut url = url::Url::parse("sled://foo.example").expect("must parse");
+        url.set_path(tmpdir.path().to_str().unwrap());
+
+        assert!(SledBlobService::from_url(&url).is_err());
+    }
+}