feat(cosmos): Add a "CapData" vstorage RPC endpoint

golang/cosmos/proto/agoric/vstorage/query.proto

@@ -9,11 +9,18 @@ option go_package = "github.com/Agoric/agoric-sdk/golang/cosmos/x/vstorage/types
 
 // Query defines the gRPC querier service
 service Query {
-  // Return an arbitrary vstorage datum.
+  // Return the raw string value of an arbitrary vstorage datum.
   rpc Data(QueryDataRequest) returns (QueryDataResponse) {
     option (google.api.http).get = "/agoric/vstorage/data/{path}";
   }
 
+  // Return a formatted representation of a vstorage datum that must be
+  // a valid StreamCell with CapData values, or standalone CapData.
+  rpc CapData(QueryCapDataRequest)
+    returns (QueryCapDataResponse) {
+      option (google.api.http).get = "/agoric/vstorage/capdata/{path}";
+  }
+
   // Return the children of a given vstorage path.
   rpc Children(QueryChildrenRequest)
     returns (QueryChildrenResponse) {
@@ -37,6 +44,51 @@ message QueryDataResponse {
   ];
 }
 
+// QueryCapDataRequest contains a path and formatting configuration.
+message QueryCapDataRequest {
+  string path = 1 [
+    (gogoproto.jsontag)    = "path",
+    (gogoproto.moretags)   = "yaml:\"path\""
+  ];
+  // mediaType must be an actual media type in the registry at
+  // https://www.iana.org/assignments/media-types/media-types.xhtml
+  // or a special value that does not conflict with the media type syntax.
+  // The only valid value is "JSON Lines", which is also the default.
+  string media_type = 2 [
+    (gogoproto.jsontag)    = "mediaType",
+    (gogoproto.moretags)   = "yaml:\"mediaType\""
+  ];
+  // itemFormat, if present, must be the special value "flat" to indicate that
+  // the deep structure of each item should be flattened into a single level
+  // with kebab-case keys (e.g., `{ "metrics": { "min": 0, "max": 88 } }` as
+  // `{ "metrics-min": 0, "metrics-max": 88 }`).
+  string item_format = 3 [
+    (gogoproto.jsontag)    = "itemFormat",
+    (gogoproto.moretags)   = "yaml:\"itemFormat\""
+  ];
+  // remotableValueFormat indicates how to transform references to opaque but
+  // distinguishable Remotables into readable embedded representations.
+  // * "object" represents each Remotable as an `{ id, allegedName }` object.
+  // * "string" represents each Remotable as a bracketed string such as `[Alleged: IST brand {}]`.
+  string remotable_value_format = 10 [
+    (gogoproto.jsontag)    = "remotableValueFormat",
+    (gogoproto.moretags)   = "yaml:\"remotableValueFormat\""
+  ];
+}
+
+// QueryCapDataResponse represents the result with the requested formatting,
+// reserving space for future metadata such as media type.
+message QueryCapDataResponse {
+  string block_height = 1 [
+    (gogoproto.jsontag)    = "blockHeight",
+    (gogoproto.moretags)   = "yaml:\"blockHeight\""
+  ];
+  string value = 10 [
+    (gogoproto.jsontag)    = "value",
+    (gogoproto.moretags)   = "yaml:\"value\""
+  ];
+}
+
 // QueryChildrenRequest is the vstorage path children query.
 message QueryChildrenRequest {
   string path = 1 [

golang/cosmos/x/vstorage/README.md

@@ -0,0 +1,52 @@
+# Virtual Storage
+
+This module manages "[IAVL](https://github.com/cosmos/iavl)" chain storage data with a hierarchical keyspace in which each key is a "[path](./types/path_keys.go)" composed of zero or more dot-separated nonempty segments in a restricted alphabet. It exposes gRPC endpoints to arbitrary external clients for reading data, and internal read/write interfaces for use by SwingSet (which itself manages further subtree-scoped attenuation).
+
+## Internal Go interface
+
+[Keeper](./keeper/keeper.go)
+* generic
+  * GetChildren
+  * GetEntry
+  * HasEntry
+  * HasStorage
+  * SetStorage[AndNotify]
+* StreamCell-oriented (a StreamCell captures a block height and an array of values)
+  * AppendStorageValue[AndNotify]
+* queue-oriented (a queue stores items at paths like "$prefix.$n", documenting
+  the n for the next item to be consumed at "$prefix.head" and the n for the next
+  next item to be pushed at "$prefix.tail" such that the queue is empty when both
+  head and tail store the same n)
+  * GetQueueLength
+  * PushQueueItem
+
+## Internal JSON interface
+
+This is used by the SwingSet "bridge".
+
+[Receive](./vstorage.go) with input `{ "method": "...", "args": [...] }`
+* generic
+  * method "entries", args path
+  * method "get"/"has", args path
+  * method "set"/"setWithoutNotify", args [[path, value?], ...]
+  * method "children", args path
+  * method "values", args path (returns values for children in the same order as method "children")
+  * method "size", args path (returns the count of children)
+* StreamCell-oriented
+  * method "append", args [[path, value?], ...]
+
+## External protobuf interface
+
+gRPC via [Querier](./keeper/keeper.go)
+and CometBFT method "abci_query" with params `{ "path": "/agoric.vstorage.Query/...", "data": "<hexadecimal representation of serialized protobuf>" }` via the same
+* /agoric.vstorage.Query/CapData
+* /agoric.vstorage.Query/Children
+* /agoric.vstorage.Query/Data
+
+## Arbitrary-response HTTP interface
+
+This depends upon appModule `LegacyQuerierHandler` functionality that is [removed from cosmos-sdk as of v0.47](https://github.com/cosmos/cosmos-sdk/blob/fa4d87ef7e6d87aaccc94c337ffd2fe90fcb7a9d/CHANGELOG.md#api-breaking-changes-3)
+
+[legacy querier](./keeper/querier.go)
+* /custom/vstorage/children/$path
+* /custom/vstorage/data/$path