Do a dance to handle the docker "hijack" message

impls/node-protocolv2/client.ts

@@ -71,7 +71,24 @@ const handles = new Map<
 >();
 
 for await (const line of rl) {
-  const { id, init, payload, proc } = JSON.parse(line);
+  const { id, init, payload, proc } = (() => {
+    try {
+      return JSON.parse(line);
+    } catch (e) {
+      // Sometimes docker injects this into the stream:
+      // {"hijack":true,"stream":true,"stdin":true,"stdout":true,"stderr":true}{"type": "invoke", ...
+      const match = e.message.match(/line (\d*) column (\d*)/);
+      if (!!match) {
+        const offset = parseInt(match['2'], 10);
+        const first = JSON.parse(line.substring(0, offset));
+        assert(
+          'hijack' in first,
+          'The only syntax errors that we expect are that Docker jams stuff into the stream',
+        );
+        return JSON.parse(line.substring(offset));
+      }
+    }
+  })();
 
   switch (proc) {
     case 'kv.set': {

impls/node/client.ts

@@ -61,7 +61,24 @@ const rl = readline.createInterface({
 
 const handles = new Map<string, Pushable<unknown>>();
 for await (const line of rl) {
-  const { id, init, payload, proc } = JSON.parse(line);
+  const { id, init, payload, proc } = (() => {
+    try {
+      return JSON.parse(line);
+    } catch (e) {
+      // Sometimes docker injects this into the stream:
+      // {"hijack":true,"stream":true,"stdin":true,"stdout":true,"stderr":true}{"type": "invoke", ...
+      const match = e.message.match(/line (\d*) column (\d*)/);
+      if (!!match) {
+        const offset = parseInt(match['2'], 10);
+        const first = JSON.parse(line.substring(0, offset));
+        assert(
+          'hijack' in first,
+          'The only syntax errors that we expect are that Docker jams stuff into the stream',
+        );
+        return JSON.parse(line.substring(offset));
+      }
+    }
+  })();
 
   switch (proc) {
     case 'kv.set': {

impls/python/src/river_python_test/client.py

@@ -72,7 +72,16 @@ async def process_commands() -> None:
             if not line:
                 break
 
-            action = json.loads(line)
+            try:
+                action = json.loads(line)
+            except json.JSONDecodeError as e:
+                # Sometimes docker injects this into the stream:
+                # {"hijack":true,"stream":true,"stdin":true,"stdout":true,"stderr":true}{"type": "invoke", ...
+                offset = e.colno - 1
+                first = json.loads(line[0:offset])
+                assert "hijack" in first
+                action = json.loads(line[offset:])
+
             if not action:
                 print("FATAL: invalid command", line)
                 sys.exit(1)