LogDog: Add signed GS URL fetching.

logdog/api/endpoints/coordinator/logs/v1/logs.proto

Index: logdog/api/endpoints/coordinator/logs/v1/logs.proto
diff --git a/logdog/api/endpoints/coordinator/logs/v1/logs.proto b/logdog/api/endpoints/coordinator/logs/v1/logs.proto
index 32a13e7620b779dc0079c0ba52626fa5b2fdda12..e894320be9e712ccfebe5c5a6171a9a46f647ea6 100644
--- a/logdog/api/endpoints/coordinator/logs/v1/logs.proto
+++ b/logdog/api/endpoints/coordinator/logs/v1/logs.proto
@@ -9,6 +9,7 @@ package logdog;
 import "github.com/luci/luci-go/logdog/api/endpoints/coordinator/logs/v1/state.proto";
 import "github.com/luci/luci-go/logdog/api/logpb/log.proto";
 import "google/protobuf/timestamp.proto";
+import "google/protobuf/duration.proto";
 
 // GetRequest is the request structure for the user Get endpoint.
 //
@@ -64,6 +65,13 @@ message GetRequest {
   // A contiguous request with Index 3 will return: [3, 4], stopping because
   // 5 is missing. A non-contiguous request will return [3, 4, 6, 7].
   bool non_contiguous = 7;
+
+  // If supplied and >0, return a signed version of the log stream's RecordIO
+  // entry protobuf URL. If signing URLs is not supported, the signed URL
+  // field in the response will be empty.
+  //
+  // The signed URL will have an expiration that is <= the requested expiration.

[Vadim Sh., 2016/11/30 21:03:52]

you mean >=?

[dnj, 2016/12/01 17:39:30]

I mean <=, as in if you request 24 days and the server caps at 1 day, you'll get
1 day.'

The expiration here is a duration, not a time, so it probably will always be <
in practice b/c of delay.

[Vadim Sh., 2016/12/01 19:32:12]

Oh, I thought it would return an URL that lives at least
"sign_entry_url_lifetime" (and possibly more). 

+  google.protobuf.Duration sign_entry_url_lifetime = 8;
 }
 
 // TailRequest is the request structure for the user Tail endpoint. It returns
@@ -106,6 +114,17 @@ message GetResponse {
 
   // Log represents the set of retrieved log records.
   repeated logpb.LogEntry logs = 4;
+
+  // Holds information about the log stream's signed entry URL.
+  message SignedEntryUrl {
+    // The signed URL value.
+    string value = 1;
+    // The time when this signed URL will expire.
+    google.protobuf.Timestamp expiration = 2;
+  }
+  // An optional signed log entry RecordIO protobuf URL, if requested via
+  // "sign_entry_url_lifetime".
+  SignedEntryUrl signed_entry_url = 5;
 }
 
 // QueryRequest is the request structure for the user Query endpoint.