mcp_tool usage is not writing files to disk

[cristianbote]

Description

I have encounter a few issues when opencode delegates and uses the tools I guess, and the result says that it wrote files but actually it didnt. Here's an example:

A: Now let me apply both edits.
Tool Use: mcp_edit({"filePath":"/path/to/file","oldString":"<redacted>","newString":"<redacted>"})
Tool Use: mcp_edit({"filePath":"/path/to/other/file","oldString":"<redacted>","newString":"<redacted>"})
H: Tool Result for toolu_01CX5nnnVVZLpTi3ENWWsLVu: Edit applied successfully.
Tool Result for toolu_01CPgBDWWaBvLcKmXyiQWEz4: Edit applied successfully.

Only to notice that the two files were not edited at all. Sometimes though opencode writes the files fine without the mcp_edit or mcp_write.

Steps to reproduce

1. Start opencode
2. Prompt to edit files
3. Try until opencode delegates to mcp_tool
4. Check the result

Operating system

macOS

Plugin version

1.3.1

OpenCode version

1.2.27

Debug logs

[cristianbote]

heya, so used opus on opencode to debug this and it seems the issue was this:

diff --git a/src/transforms.ts b/src/transforms.ts
index 260f278..4175c5e 100644
--- a/src/transforms.ts
+++ b/src/transforms.ts
@@ -1,4 +1,5 @@
 const TOOL_PREFIX = "mcp_"
+const SSE_EVENT_BOUNDARIES = ["\r\n\r\n", "\n\n"]
 
 export function transformBody(
   body: BodyInit | null | undefined,
@@ -51,7 +52,29 @@ export function transformBody(
 }
 
 export function stripToolPrefix(text: string): string {
-  return text.replace(/"name"\s*:\s*"mcp_([^"]+)"/g, '"name": "$1"')
+  return text
+    .replace(/"name"\s*:\s*"mcp_([^"]+)"/g, '"name": "$1"')
+    .replace(/(\bTool Use:\s*)mcp_([A-Za-z0-9_-]+)/g, "$1$2")
+}
+
+function getEventBoundary(buffer: string): {
+  index: number
+  delimiterLength: number
+} | null {
+  let match: { index: number; delimiterLength: number } | null = null
+
+  for (const delimiter of SSE_EVENT_BOUNDARIES) {
+    const index = buffer.indexOf(delimiter)
+    if (index === -1) {
+      continue
+    }
+
+    if (!match || index < match.index) {
+      match = { index, delimiterLength: delimiter.length }
+    }
+  }
+
+  return match
 }
 
 export function transformResponseStream(response: Response): Response {
@@ -67,10 +90,13 @@ export function transformResponseStream(response: Response): Response {
   const stream = new ReadableStream({
     async pull(controller) {
       for (;;) {
-        const boundary = buffer.indexOf("\n\n")
-        if (boundary !== -1) {
-          const completeEvent = buffer.slice(0, boundary + 2)
-          buffer = buffer.slice(boundary + 2)
+        const boundary = getEventBoundary(buffer)
+        if (boundary) {
+          const completeEvent = buffer.slice(
+            0,
+            boundary.index + boundary.delimiterLength,
+          )
+          buffer = buffer.slice(boundary.index + boundary.delimiterLength)
           controller.enqueue(encoder.encode(stripToolPrefix(completeEvent)))
           return
         }

Since rebuilding and using it as a local plugin, I had no more issues. 🤷