switch to dedicated rpc

build/bazel/remote/execution/v2/remote_execution.proto

@@ -430,6 +430,13 @@ service ContentAddressableStorage {
   rpc GetTree(GetTreeRequest) returns (stream GetTreeResponse) {
     option (google.api.http) = { get: "/v2/{instance_name=**}/blobs/{root_digest.hash}/{root_digest.size_bytes}:getTree" };
   }
+
+  // Fetch the list of dictionaries use in Zstd compression.
+  //
+  // Server must implement this RPC method iff the `ZSTD_DICT` compressor is supported.
+  rpc GetZstdDictionaries(GetZstdDictionariesRequest) returns (GetZstdDictionariesResponse) {
+    option (google.api.http) = { get: "/v2/{instance_name=**}/blobs:zstdDictionaries" };
+  }
 }
 
 // The Capabilities service may be used by remote execution clients to query
@@ -1814,6 +1821,39 @@ message GetTreeResponse {
   string next_page_token = 2;
 }
 
+message GetZstdDictionariesRequest {
+  // The instance of the execution system to operate against. A server may
+  // support multiple instances of the execution system (with their own workers,
+  // storage, caches, etc.). The server MAY require use of this field to select
+  // between them in an implementation-defined fashion, otherwise it can be
+  // omitted.
+  string instance_name = 1;
+
+  // The digest functions supported by the client.
+  // Must be one of the server's supported digest functions listed in
+  // [CacheCapabilities.digest_functions][build.bazel.remote.execution.v2.CacheCapabilities.digest_functions].
+  DigestFunction.Value digest_function = 2;
+}
+
+message GetZstdDictionariesResponse {
+  message Dictionary {
+    uint32 id = 1;
+    Digest digest = 2;
+  }
+
+  // The dictionary ID that clients SHOULD use when uploading
+  // objects into the Content Addressable Storage. An entry for
+  // this dictionary ID MUST be present in `dictionaries`.
+  uint32 default_dictionary_id = 1;
+
+  // Dictionaries that may be used by the server when returning
+  // objects stored in the Content Addressable Storage. The key
+  // corresponds to a dictionary ID, as described in RFC 8878,
+  // section 5, while the value refers to a dictionary
+  // as described in RFC 8878, chapter 6.
+  repeated Dictionary dictionaries = 2;
+}
+
 // A request message for
 // [Capabilities.GetCapabilities][build.bazel.remote.execution.v2.Capabilities.GetCapabilities].
 message GetCapabilitiesRequest {
@@ -1823,15 +1863,6 @@ message GetCapabilitiesRequest {
   // between them in an implementation-defined fashion, otherwise it can be
   // omitted.
   string instance_name = 1;
-
-  // All the digest functions supported by the client.
-  // Server should consider which digest functions the client supports to use
-  // the correct Digest in the
-  // [ServerCapabilities][build.bazel.remote.execution.v2.ServerCapabilities]
-  // response.
-  // If there is no overlapping between client's and server's supported digest
-  // functions, then server MAY omit the digest fields in the response.
-  repeated DigestFunction.Value digest_functions = 1;
 }
 
 // A response message for
@@ -2009,40 +2040,18 @@ message Compressor {
 
     // Zstandard compression with dictionary.
     //
-    // When this is used, the server MUST advertise the dictionaries by
-    // including
-    // [ZstdDictionaries][build.bazel.remote.execution.v2.ZstdDictionaries]
-    // digest in CacheCapabilities.
+    // Servers which support this compressor MUST implements
+    // [ContentAddressableStorage.GetZstdDictionaries][build.bazel.remote.execution.v2.ContentAddressableStorage.GetZstdDictionaries].
+    //
+    // Clients which support this compressor SHOULD call `GetZstdDictionaries`
+    // rpc to obtain the dictionaries from the server to be used for
+    // ZSTD compression/decompression.
     ZSTD_DICT = 4;
   }
 }
 
-message ZstdDictionaries {
-  message Dictionary {
-    uint32 id 1;
-    Digest digest 2;
-  }
-
-  // The dictionary ID that clients SHOULD use when uploading
-  // objects into the Content Addressable Storage. An entry for
-  // this dictionary ID MUST be present in `dictionaries`.
-  uint32 default_dictionary_id = 1;
-
-  // Dictionaries that may be used by the server when returning
-  // objects stored in the Content Addressable Storage. The key
-  // corresponds to a dictionary ID, as described in RFC 8878,
-  // section 5, while the value refers to a dictionary
-  // as described in RFC 8878, chapter 6.
-  repeated Dictionary dictionaries = 2;
-}
-
 // Capabilities of the remote cache system.
 message CacheCapabilities {
-  message QualifiedDigest {
-    Digest digest = 1;
-    DigestFunction.value digest_function = 2;
-  }
-
   // All the digest functions supported by the remote cache.
   // Remote cache may support multiple digest functions simultaneously.
   repeated DigestFunction.Value digest_functions = 1;
@@ -2074,21 +2083,6 @@ message CacheCapabilities {
   // [BatchUpdateBlobs][build.bazel.remote.execution.v2.ContentAddressableStorage.BatchUpdateBlobs]
   // requests.
   repeated Compressor.Value supported_batch_update_compressors = 7;
-
-  // The digest of the
-  // [ZstdDictionaries][build.bazel.remote.execution.v2.ZstdDictionaries]
-  // that contains all the dictionaries supported by the remote cache.
-  //
-  // Digest function used should be one of the digest functions that both
-  // client and server support, as specified in digest_functions field in
-  // [CacheCapabilities.digest_functions][build.bazel.remote.execution.v2.CacheCapabilities.digest_functions]
-  // and
-  // [GetCapabilitiesRequest.digest_functions][build.bazel.remote.execution.v2.GetCapabilitiesRequest.digest_functions].
-  //
-  // If there is no overlapping between client's and server's supported
-  // dictionaries, then server MAY omit the dictionaries field in the
-  // response.
-  QualifiedDigest zstd_dictionaries = 8;
 }
 
 // Capabilities of the remote execution system.