feat: Switch file reading to use concrete endpoints

src/fsspec_xrootd/xrootd.py

@@ -2,6 +2,7 @@
 
 import asyncio
 import io
+import logging
 import os.path
 import warnings
 from collections import defaultdict
@@ -168,10 +169,21 @@ def __init__(
             If true, synchronous methods will not be available in this instance
         loop:
             Bring your own loop (for sync methods)
+        storage_options:
+            Options for the XRootD file system object. Includes (not limited to):
+            - locate_all_sources = True: bool
+                - Defaults to True. Finds all locations at which the file is hosted, and chooses
+                  from those. Does not let the redirector pick the first to respond.
+            - valid_sources = []: list
+                - If given and locate_all_sources is True, fsspec will only reject any file host
+                  not in this list. Entries should be of the form ie: `cmsxrootd-site1.fnal.gov`
+                  (no port number)
         """
         super().__init__(self, asynchronous=asynchronous, loop=loop, **storage_options)
         self.timeout = storage_options.get("timeout", XRootDFileSystem.default_timeout)
         self.hostid = hostid
+        self.locate_all_sources = storage_options.get("locate_all_sources", True)
+        self.valid_sources = storage_options.get("valid_sources", [])
         self._myclient = client.FileSystem("root://" + hostid)
         if not self._myclient.url.is_valid():
             raise ValueError(f"Invalid hostid: {hostid!r}")
@@ -702,23 +714,37 @@ def __init__(
         if not isinstance(path, str):
             raise ValueError(f"Path expected to be string, path: {path}")
 
-        self._myFile = client.File()
-        status, _n = self._myFile.open(
-            fs.unstrip_protocol(path),
-            self.mode,
-            timeout=self.timeout,
-        )
+        self.fs = fs
+
+        if "r" in mode and self.fs.locate_all_sources:
+            self._hosts = self._locate_sources(path)
+        else:
+            self._hosts = [fs.storage_options["hostid"]]
+
+        # Try hosts until you find an openable file
+        for _i_host in range(len(self._hosts)):
+            self._myFile = client.File()
+            status, _n = self._myFile.open(
+                fs.unstrip_protocol(path),
+                self.mode,
+                timeout=self.timeout,
+            )
+            if status.ok:
+                break
 
         if not status.ok:
             raise OSError(f"File did not open properly: {status.message}")
 
+        # Move hosts that tried and failed to self._dismissed_hosts
+        self._dismissed_hosts = self._hosts[:_i_host]
+        self._hosts = self._hosts[_i_host:]
+
         self.metaOffset = 0
         if "a" in mode:
             _stats, _deets = self._myFile.stat(timeout=self.timeout)
             self.metaOffset = _deets.size
 
         self.path = path
-        self.fs = fs
         self.mode = mode
         self.blocksize = (
             self.DEFAULT_BLOCK_SIZE if block_size in ["default", None] else block_size
@@ -760,6 +786,59 @@ def __init__(
             self.location = None
             self.offset = 0
 
+    def _locate_sources(self, logical_filename: str) -> list[str]:
+        """Find hosts that have the desired file.
+
+        Gets a list of hosts from the XRootD server that was provided when the
+        XRootDFile object was instantiated. Note that this implies it will only find
+        more hosts of the given file if self.fs is a redirector. Implementation of a
+        solution from the Pepper project in this issue:
+
+        (https://github.com/CoffeaTeam/fsspec-xrootd/issues/36).
+
+        If valid_sources is a non-empty list in fs.storage_options, will only return domain names
+        that are also in valid_sources
+
+        Parameters
+        ----------
+        logical_filename: The logical filename of the file. (ex: "//store/mc/other/stuff/file.root")
+
+        Returns
+        -------
+        List of domain names that host the file
+        """
+        myclient = self.fs._myclient
+        # From Pepper:
+        # The flag PrefName (to get domain names instead of IP addresses) does
+        # not exist in the Python bindings. However, MAKEPATH has the same value
+        status, loc = myclient.locate(logical_filename, client.flags.OpenFlags.MAKEPATH)
+        if loc is None:
+            raise OSError("XRootD error: " + status.message)
+        hosts = []
+        for r in loc:
+            if len(r.address.split(":")) > 1:
+                # Strip off the port number if necessary
+                clean_address = "".join(r.address.split(":")[:-1])
+            else:
+                clean_address = r.address
+            if (clean_address in self.fs.valid_sources) or (
+                len(self.fs.valid_sources) == 0
+            ):
+                hosts.append(clean_address)
+                logging.debug(f"Added host {clean_address} to _hosts")
+            else:
+                logging.debug(
+                    f"Host {clean_address} not in valid_sources {self.fs.valid_sources}"
+                )
+        if len(hosts) == 0:
+            err_msg = f"XRootD error: No hosts for file {logical_filename} found using XRootD server {self.fs.storage_options['hostid']}"
+            if len(self.fs.valid_sources) > 0:
+                vld_src_msg = f" and valid sources {self.fs.valid_sources}"
+                raise OSError(err_msg + vld_src_msg)
+            else:
+                raise OSError(err_msg)
+        return hosts
+
     def _fetch_range(self, start: int, end: int) -> Any:
         status, data = self._myFile.read(
             self.metaOffset + start, self.metaOffset + end - start, timeout=self.timeout