Handle gRPC compressed payloads

src/util/protobuf.ts

@@ -1,4 +1,8 @@
 import parseRawProto from 'rawprotoparse';
+import { gunzipSync, inflateSync } from 'zlib';
+
+const GZIP_MAGIC_BYTES = '1f8b';
+const DEFLATE_MAGIC_BYTES = new Set<string>(['7801', '785e', '789c', '78da', '7820', '787d', '78bb', '78f9']);
 
 export function isProbablyProtobuf(input: Uint8Array) {
     // Protobuf data starts with a varint, consisting of a field
@@ -38,12 +42,24 @@ export const extractProtobufFromGrpc = (input: Buffer) => {
     const protobufMessasges: Buffer[] = [];
 
     while (input.length > 0) {
-        if (input.readInt8() != 0) {
-            throw new Error("Compressed gRPC messages not yet supported")
+        const compressionFlag = input.readInt8();
+        const length = input.readInt32BE(1);
+        let message = input.slice(5, 5 + length);
+
+        if (compressionFlag != 0) {
+            // TODO: In theory we should check consistency of actual content encoding
+            // with 'grpc-encoding' header, but we do not have access to it in this context
+            const magicBytes = message.toString('hex', 0, 2);
+            if (magicBytes == GZIP_MAGIC_BYTES) {
+                message = gunzipSync(message);
+            } else if (DEFLATE_MAGIC_BYTES.has(magicBytes)) {
+                message = inflateSync(message);
+            } else {
+                throw new Error(`Unknown gRPC compression scheme, magic bytes = '${magicBytes}'`);
+            }
         }
 
-        const length = input.readInt32BE(1);
-        protobufMessasges.push(input.slice(5, 5 + length));
+        protobufMessasges.push(message);
         input = input.subarray(5 + length);
     }