fix(read): prevent unsupported image formats from being sending to provider (#21114)

Co-authored-by: Aiden Cline <[email protected]>

2 files changed, 23 insertions, 2 deletions

diff --git a/packages/opencode/src/tool/read.ts b/packages/opencode/src/tool/read.ts
index ef33a48de..78436489f 100644
--- a/packages/opencode/src/tool/read.ts
+++ b/packages/opencode/src/tool/read.ts
@@ -10,7 +10,7 @@ import DESCRIPTION from "./read.txt"
 import { InstanceState } from "@/effect/instance-state"
 import { assertExternalDirectoryEffect } from "./external-directory"
 import { Instruction } from "../session/instruction"
-import { isImageAttachment, isPdfAttachment, sniffAttachmentMime } from "@/util/media"
+import { isPdfAttachment, sniffAttachmentMime } from "@/util/media"
 
 const DEFAULT_READ_LIMIT = 2000
 const MAX_LINE_LENGTH = 2000
@@ -18,6 +18,7 @@ const MAX_LINE_SUFFIX = `... (line truncated to ${MAX_LINE_LENGTH} chars)`
 const MAX_BYTES = 50 * 1024
 const MAX_BYTES_LABEL = `${MAX_BYTES / 1024} KB`
 const SAMPLE_BYTES = 4096
+const SUPPORTED_IMAGE_MIMES = new Set(["image/jpeg", "image/png", "image/gif", "image/webp"])
 
 // `offset` and `limit` were originally `z.coerce.number()` — the runtime
 // coercion was useful when the tool was called from a shell but serves no
@@ -220,7 +221,9 @@ export const ReadTool = Tool.define(
       const sample = yield* readSample(filepath, Number(stat.size), SAMPLE_BYTES)
 
       const mime = sniffAttachmentMime(sample, AppFileSystem.mimeType(filepath))
-      if (isImageAttachment(mime) || isPdfAttachment(mime)) {
+      const isImage = SUPPORTED_IMAGE_MIMES.has(mime)
+
+      if (isImage || isPdfAttachment(mime)) {
         const bytes = yield* fs.readFile(filepath)
         const msg = isPdfAttachment(mime) ? "PDF read successfully" : "Image read successfully"
         return {
diff --git a/packages/opencode/test/tool/read.test.ts b/packages/opencode/test/tool/read.test.ts
index db6678754..c20b08437 100644
--- a/packages/opencode/test/tool/read.test.ts
+++ b/packages/opencode/test/tool/read.test.ts
@@ -440,6 +440,24 @@ root_type Monster;`
       expect(result.output).toContain("table Monster")
     }),
   )
+
+  it.live("falls through unsupported image mime types to text", () =>
+    Effect.gen(function* () {
+      const dir = yield* tmpdirScoped()
+      const cases = [
+        ["image.bmp", "BM text content"],
+        ["photo.tiff", "II text content"],
+        ["photo.avif", "avif text content"],
+      ] as const
+
+      for (const item of cases) {
+        yield* put(path.join(dir, item[0]), item[1])
+        const result = yield* exec(dir, { filePath: path.join(dir, item[0]) })
+        expect(result.attachments).toBeUndefined()
+        expect(result.output).toContain(item[1])
+      }
+    }),
+  )
 })
 
 describe("tool.read loaded instructions", () => {