LogDog: Fix archival Get/Tail implementations.

logdog/common/storage/storage.go

 // Copyright 2015 The LUCI Authors. All rights reserved.
 // Use of this source code is governed under the Apache License, Version 2.0
 // that can be found in the LICENSE file.
 
 package storage
 
 import (
         "errors"
         "time"
 
@@ skipping 43 matching lines @@
 // GetRequest is a request to retrieve a series of LogEntry records.
 type GetRequest struct {
         // Project is the project name of the stream.
         Project config.ProjectName
         // Path is the stream path to retrieve.
         Path types.StreamPath
         // Index is the entry's stream index.
         Index types.MessageIndex
 
         // Limit is the maximum number of records to return before stopping iteration.
-        // If zero, no maximum limit will be applied.
+        // If <= 0, no maximum limit will be applied.
         //
         // The Storage instance may return fewer records than the supplied Limit as an
         // implementation detail.
         Limit int
         // KeysOnly, if true, allows (but doesn't require) the Storage instance to
         // omit entry data in its get callback. For scanning operations, this can be
         // much cheaper/faster than full data queries.
         KeysOnly bool
 }
 
 // GetCallback is invoked for each record in the Get request. If it returns
 // false, iteration should stop.
-type GetCallback func(types.MessageIndex, []byte) bool
+//
+// The MessageIndex may be -1 if the message index isn't known. In this case,
+// the caller will have to unmarshal the log entry data to determine its index.
+type GetCallback func(*Entry) bool
 
 // Storage is an abstract LogDog storage implementation. Interfaces implementing
 // this may be used to store and retrieve log records by the collection service
 // layer.
 //
 // All of these methods must be synchronous and goroutine-safe.
 //
 // All methods may return errors.Transient errors if they encounter an error
 // that may be transient.
 type Storage interface {
@@ skipping 14 matching lines @@
         // requested based on availability or implementation details; consequently,
         // receiving fewer than requsted records does not necessarily mean that more
         // records are not available.
         //
         // Returns nil if retrieval executed successfully, ErrDoesNotExist if
         // the requested stream does not exist, and an error if an error occurred
         // during retrieval.
         Get(GetRequest, GetCallback) error
 
         // Tail retrieves the latest log in the stream. If the stream has no logs, it
-        // will return ErrDoesNotExist.
-        Tail(config.ProjectName, types.StreamPath) ([]byte, types.MessageIndex, error)
+        // will fail with ErrDoesNotExist.
+        //
+        // The MessageIndex may be -1 if the message index isn't known. In this case,
+        // the caller will have to unmarshal the log entry data to determine its
+        // index.
+        Tail(config.ProjectName, types.StreamPath) (*Entry, error)
 
         // Config installs the supplied configuration parameters into the storage
         // instance.
         Config(Config) error
 }