Add file attachment context handling (#141)

- Support text file attachments alongside images
- Persist, validate, and forward file context through server and UI
- Relax attachment lookup to handle non-image files

Author: BunsDev

apps/server/src/attachmentStore.ts

@@ -1,15 +1,13 @@
 import { randomUUID } from "node:crypto";
-import { existsSync } from "node:fs";
+import { existsSync, readdirSync } from "node:fs";
 
 import type { ChatAttachment } from "@okcode/contracts";
 
 import {
   normalizeAttachmentRelativePath,
   resolveAttachmentRelativePath,
 } from "./attachmentPaths.ts";
-import { inferImageExtension, SAFE_IMAGE_FILE_EXTENSIONS } from "./imageMime.ts";
-
-const ATTACHMENT_FILENAME_EXTENSIONS = [...SAFE_IMAGE_FILE_EXTENSIONS, ".bin"];
+import { inferAttachmentExtension } from "./imageMime.ts";
 const ATTACHMENT_ID_THREAD_SEGMENT_MAX_CHARS = 80;
 const ATTACHMENT_ID_THREAD_SEGMENT_PATTERN = "[a-z0-9_]+(?:-[a-z0-9_]+)*";
 const ATTACHMENT_ID_UUID_PATTERN = "[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}";
@@ -55,8 +53,9 @@ export function parseThreadSegmentFromAttachmentId(attachmentId: string): string
 
 export function attachmentRelativePath(attachment: ChatAttachment): string {
   switch (attachment.type) {
-    case "image": {
-      const extension = inferImageExtension({
+    case "image":
+    case "file": {
+      const extension = inferAttachmentExtension({
         mimeType: attachment.mimeType,
         fileName: attachment.name,
       });
@@ -83,10 +82,20 @@ export function resolveAttachmentPathById(input: {
   if (!normalizedId || normalizedId.includes("/") || normalizedId.includes(".")) {
     return null;
   }
-  for (const extension of ATTACHMENT_FILENAME_EXTENSIONS) {
+  let entries: string[];
+  try {
+    entries = readdirSync(input.attachmentsDir);
+  } catch {
+    return null;
+  }
+  for (const entry of entries) {
+    const entryId = parseAttachmentIdFromRelativePath(entry);
+    if (entryId !== normalizedId) {
+      continue;
+    }
     const maybePath = resolveAttachmentRelativePath({
       attachmentsDir: input.attachmentsDir,
-      relativePath: `${normalizedId}${extension}`,
+      relativePath: entry,
     });
     if (maybePath && existsSync(maybePath)) {
       return maybePath;

apps/server/src/attachmentText.ts

@@ -0,0 +1,213 @@
+import {
+  PROVIDER_SEND_TURN_MAX_INPUT_CHARS,
+  type ChatFileAttachment,
+} from "@okcode/contracts";
+
+const MAX_FILE_CONTEXT_TOTAL_CHARS = 80_000;
+const MAX_FILE_CONTEXT_CHARS_PER_FILE = 24_000;
+const TEXT_DECODER = new TextDecoder("utf-8", { fatal: false });
+const TEXTUAL_MIME_SUBSTRINGS = [
+  "json",
+  "xml",
+  "yaml",
+  "toml",
+  "javascript",
+  "typescript",
+  "markdown",
+  "csv",
+  "graphql",
+  "sql",
+  "x-sh",
+  "x-shellscript",
+];
+const TEXTUAL_FILE_EXTENSIONS = new Set([
+  "c",
+  "cc",
+  "cfg",
+  "conf",
+  "cpp",
+  "cs",
+  "css",
+  "csv",
+  "env",
+  "go",
+  "graphql",
+  "h",
+  "hpp",
+  "html",
+  "ini",
+  "java",
+  "js",
+  "json",
+  "jsx",
+  "kt",
+  "log",
+  "lua",
+  "md",
+  "mjs",
+  "php",
+  "pl",
+  "py",
+  "rb",
+  "rs",
+  "scss",
+  "sh",
+  "sql",
+  "svg",
+  "swift",
+  "toml",
+  "ts",
+  "tsx",
+  "txt",
+  "vue",
+  "xml",
+  "yaml",
+  "yml",
+  "zsh",
+]);
+
+function attachmentExtension(fileName: string): string {
+  const match = /\.([a-z0-9]{1,12})$/i.exec(fileName.trim());
+  return match?.[1]?.toLowerCase() ?? "";
+}
+
+function looksTextLikeMimeType(mimeType: string): boolean {
+  const normalized = mimeType.trim().toLowerCase();
+  if (normalized.startsWith("text/")) {
+    return true;
+  }
+  return TEXTUAL_MIME_SUBSTRINGS.some((part) => normalized.includes(part));
+}
+
+function looksTextLikeFileName(fileName: string): boolean {
+  return TEXTUAL_FILE_EXTENSIONS.has(attachmentExtension(fileName));
+}
+
+function hasSuspiciousControlBytes(text: string): boolean {
+  let suspiciousCount = 0;
+  let visibleCount = 0;
+  for (let index = 0; index < text.length; index += 1) {
+    const codePoint = text.charCodeAt(index);
+    if (codePoint === 0) {
+      return true;
+    }
+    if (codePoint < 32 && codePoint !== 9 && codePoint !== 10 && codePoint !== 13) {
+      suspiciousCount += 1;
+      continue;
+    }
+    visibleCount += 1;
+  }
+  if (visibleCount === 0) {
+    return suspiciousCount > 0;
+  }
+  return suspiciousCount / Math.max(visibleCount, 1) > 0.02;
+}
+
+export function extractTextAttachmentContents(input: {
+  readonly mimeType: string;
+  readonly fileName: string;
+  readonly bytes: Uint8Array;
+}): string | null {
+  if (input.bytes.byteLength === 0) {
+    return "";
+  }
+  const decoded = TEXT_DECODER.decode(input.bytes);
+  if (hasSuspiciousControlBytes(decoded)) {
+    return null;
+  }
+  const replacementCount = decoded.split("\uFFFD").length - 1;
+  const replacementRatio = replacementCount / Math.max(decoded.length, 1);
+  const expectedText =
+    looksTextLikeMimeType(input.mimeType) || looksTextLikeFileName(input.fileName);
+  if (replacementRatio > (expectedText ? 0.02 : 0.005)) {
+    return null;
+  }
+  if (!expectedText && decoded.trim().length === 0) {
+    return null;
+  }
+  return decoded.replace(/\r\n?/g, "\n");
+}
+
+export function buildFileAttachmentContextText(input: {
+  readonly baseText: string;
+  readonly attachments: ReadonlyArray<{
+    readonly attachment: ChatFileAttachment;
+    readonly text: string;
+  }>;
+  readonly maxChars?: number;
+}): string {
+  if (input.attachments.length === 0) {
+    return input.baseText;
+  }
+
+  const maxChars = Math.max(
+    1,
+    Math.floor(input.maxChars ?? PROVIDER_SEND_TURN_MAX_INPUT_CHARS),
+  );
+  let result = input.baseText;
+  let usedFileContextChars = 0;
+  let omittedCount = 0;
+
+  const append = (chunk: string): boolean => {
+    if (chunk.length === 0) {
+      return true;
+    }
+    if (result.length + chunk.length > maxChars) {
+      return false;
+    }
+    result += chunk;
+    return true;
+  };
+
+  const header = `${result.length > 0 ? "\n\n" : ""}Attached file context:`;
+  if (!append(header)) {
+    return result;
+  }
+
+  for (const [index, entry] of input.attachments.entries()) {
+    const openBlock =
+      "\n\n<attached_file>\n" +
+      `name: ${entry.attachment.name}\n` +
+      `mime_type: ${entry.attachment.mimeType}\n` +
+      `size_bytes: ${entry.attachment.sizeBytes}\n` +
+      "content:\n";
+    const closeBlock = "\n</attached_file>";
+    const remainingContextBudget =
+      MAX_FILE_CONTEXT_TOTAL_CHARS - usedFileContextChars - openBlock.length - closeBlock.length;
+    const remainingTotalBudget = maxChars - result.length - openBlock.length - closeBlock.length;
+    const maxContentChars = Math.min(
+      MAX_FILE_CONTEXT_CHARS_PER_FILE,
+      remainingContextBudget,
+      remainingTotalBudget,
+    );
+
+    if (maxContentChars <= 0) {
+      omittedCount = input.attachments.length - index;
+      break;
+    }
+
+    const truncationNote = "\n[content truncated to fit input limits]";
+    const needsTruncation = entry.text.length > maxContentChars;
+    const availableContentChars = needsTruncation
+      ? Math.max(0, maxContentChars - truncationNote.length)
+      : maxContentChars;
+    if (availableContentChars <= 0) {
+      omittedCount = input.attachments.length - index;
+      break;
+    }
+
+    const blockBody = entry.text.slice(0, availableContentChars);
+    const block = `${openBlock}${blockBody}${needsTruncation ? truncationNote : ""}${closeBlock}`;
+    if (!append(block)) {
+      omittedCount = input.attachments.length - index;
+      break;
+    }
+    usedFileContextChars += block.length;
+  }
+
+  if (omittedCount > 0) {
+    append(`\n\n[${omittedCount} attached file(s) omitted due to input size limits.]`);
+  }
+
+  return result;
+}

apps/server/src/imageMime.ts

@@ -1,5 +1,7 @@
 import Mime from "@effect/platform-node/Mime";
 
+const SAFE_ATTACHMENT_FILE_EXTENSION_PATTERN = /^[a-z0-9]{1,12}$/i;
+
 export const IMAGE_EXTENSION_BY_MIME_TYPE: Record<string, string> = {
   "image/avif": ".avif",
   "image/bmp": ".bmp",
@@ -29,6 +31,10 @@ export const SAFE_IMAGE_FILE_EXTENSIONS = new Set([
   ".webp",
 ]);
 
+export function isImageMimeType(mimeType: string): boolean {
+  return mimeType.trim().toLowerCase().startsWith("image/");
+}
+
 export function parseBase64DataUrl(
   dataUrl: string,
 ): { readonly mimeType: string; readonly base64: string } | null {
@@ -77,3 +83,25 @@ export function inferImageExtension(input: { mimeType: string; fileName?: string
 
   return ".bin";
 }
+
+export function inferAttachmentExtension(input: { mimeType: string; fileName?: string }): string {
+  if (isImageMimeType(input.mimeType)) {
+    return inferImageExtension(input);
+  }
+
+  const mimeExtension = Mime.getExtension(input.mimeType);
+  if (
+    typeof mimeExtension === "string" &&
+    SAFE_ATTACHMENT_FILE_EXTENSION_PATTERN.test(mimeExtension.replace(/^\./, ""))
+  ) {
+    return mimeExtension.startsWith(".") ? mimeExtension : `.${mimeExtension}`;
+  }
+
+  const fileName = input.fileName?.trim() ?? "";
+  const extensionMatch = /\.([a-z0-9]{1,12})$/i.exec(fileName);
+  if (extensionMatch?.[1]) {
+    return `.${extensionMatch[1].toLowerCase()}`;
+  }
+
+  return ".bin";
+}

apps/server/src/orchestration/Layers/ProjectionPipeline.ts

@@ -221,9 +221,6 @@ function collectThreadAttachmentRelativePaths(
   const relativePaths = new Set<string>();
   for (const message of messages) {
     for (const attachment of message.attachments ?? []) {
-      if (attachment.type !== "image") {
-        continue;
-      }
       const attachmentThreadSegment = parseThreadSegmentFromAttachmentId(attachment.id);
       if (!attachmentThreadSegment || attachmentThreadSegment !== threadSegment) {
         continue;