useContractSchemaRpc: Parse schema based on module version (#45)

## Purpose

Make fetching/parsing of contract schema more precise based on the
module version information that is now exposed by the gRPC client.

This in turn also documents the relationship between module and schema
versions.

## Changes

Use module version to determine what custom sections to look for and add
comments explaining the expected results.

packages/wallet-connectors/src/WalletConnect.ts

@@ -122,7 +122,8 @@ function serializeUpdateContractMessage(
 }
 
 /**
- * Convert schema into the object format expected by the Mobile crypto library.
+ * Convert schema into the object format expected by the Mobile crypto library (function 'parameter_to_json')
+ * which decodes the parameter before presenting it to the user for approval.
  * @param schema The schema object.
  */
 function convertSchemaFormat(schema: Schema | undefined) {

samples/contractupdate/src/useContractSchemaRpc.ts

@@ -10,21 +10,31 @@ export interface SchemaRpcResult {
     schema: Schema;
 }
 
-function findCustomSections(m: WebAssembly.Module) {
+function findCustomSections(m: WebAssembly.Module, moduleVersion: number) {
     function getCustomSections(sectionName: string, schemaVersion: SchemaVersion | undefined) {
         const s = WebAssembly.Module.customSections(m, sectionName);
         return s.length === 0 ? undefined : { sectionName, schemaVersion, contents: s };
     }
-    // First look for embedded version, then v1, then v0. The "v"s being off by 1 is not an error.
-    return (
-        getCustomSections('concordium-schema', undefined) ||
-        getCustomSections('concordium-schema-v2', SchemaVersion.V1) ||
-        getCustomSections('concordium-schema-v1', SchemaVersion.V0)
-    );
+
+    // First look for section containing schema with embedded version, then "-v1" or "-v2" depending on the module version.
+    // See also comment in 'useContractSchemaRpc'.
+    switch (moduleVersion) {
+        case 0:
+            return (
+                getCustomSections('concordium-schema', undefined) || // always v0
+                getCustomSections('concordium-schema-v1', SchemaVersion.V0) // v0 (not a typo)
+            );
+        case 1:
+            return (
+                getCustomSections('concordium-schema', undefined) || // v1, v2, or v3
+                getCustomSections('concordium-schema-v2', SchemaVersion.V1) // v1 (not a typo)
+            );
+    }
+    return getCustomSections('concordium-schema', undefined); // expecting to find this section in future module versions
 }
 
-function findSchema(m: WebAssembly.Module): Result<SchemaRpcResult | undefined, string> {
-    const sections = findCustomSections(m);
+function findSchema(m: WebAssembly.Module, moduleVersion: 0 | 1): Result<SchemaRpcResult | undefined, string> {
+    const sections = findCustomSections(m, moduleVersion);
     if (!sections) {
         return ok(undefined);
     }
@@ -39,13 +49,25 @@ export function useContractSchemaRpc(rpc: ConcordiumGRPCClient, contract: Info)
     const [result, setResult] = useState<Result<SchemaRpcResult | undefined, string>>();
     useEffect(() => {
         ResultAsync.fromPromise(rpc.getModuleSource(new ModuleReference(contract.moduleRef)), errorString)
-            .andThen((r) => {
-                if (!r) {
+            .andThen(({ version, source }) => {
+                if (source.length === 0) {
                     return err('module source is empty');
                 }
-                return ResultAsync.fromPromise(WebAssembly.compile(r.source), errorString);
+                // The module can contain a schema in one of two different custom sections.
+                // The supported sections depend on the module version.
+                // The schema version can be either defined by the section name or embedded into the actual schema:
+                // - Both v0 and v1 modules support the section 'concordium-schema' where the schema includes the version.
+                //   - For v0 modules this is always a v0 schema.
+                //   - For v1 modules this can be a v1, v2, or v3 schema.
+                // - V0 modules additionally support section 'concordium-schema-v1' which always contain a v0 schema (not a typo).
+                // - V1 modules additionally support section 'concordium-schema-v2' which always contain a v1 schema (not a typo).
+                // The section 'concordium-schema' is the most common and is what the current tooling produces.
+                return ResultAsync.fromPromise(
+                    WebAssembly.compile(source).then((module) => ({ module, version })),
+                    errorString
+                );
             })
-            .andThen(findSchema)
+            .andThen(({ module, version }) => findSchema(module, version))
             .then(setResult);
     }, [contract, rpc]);
     return result;