feat(discord): inline text-based file attachments into prompt

src/discord.rs

@@ -204,9 +204,14 @@ impl EventHandler for Handler {
             text: prompt_with_sender.clone(),
         });
 
-        // Process attachments: route by content type (audio → STT, image → encode)
+        // Process attachments: route by content type (audio → STT, text file → inline, image → encode)
         let mut audio_skipped = false;
         if !msg.attachments.is_empty() {
+            let mut text_file_bytes: u64 = 0;
+            let mut text_file_count: u32 = 0;
+            const TEXT_TOTAL_CAP: u64 = 1024 * 1024; // 1 MB total for all text file attachments
+            const TEXT_FILE_COUNT_CAP: u32 = 5;
+
             for attachment in &msg.attachments {
                 if is_audio_attachment(attachment) {
                     if self.stt_config.enabled {
@@ -220,6 +225,23 @@ impl EventHandler for Handler {
                         warn!(filename = %attachment.filename, "skipping audio attachment (STT disabled)");
                         audio_skipped = true;
                     }
+                } else if is_text_attachment(attachment) {
+                    if text_file_count >= TEXT_FILE_COUNT_CAP {
+                        warn!(filename = %attachment.filename, count = text_file_count, "text file count cap reached, skipping");
+                        continue;
+                    }
+                    // Pre-check with Discord-reported size (fast path, avoids unnecessary download).
+                    // Running total uses actual downloaded bytes for accurate accounting.
+                    if text_file_bytes + u64::from(attachment.size) > TEXT_TOTAL_CAP {
+                        warn!(filename = %attachment.filename, total = text_file_bytes, "text attachments total exceeds 1MB cap, skipping remaining");
+                        continue;
+                    }
+                    if let Some((content_block, actual_bytes)) = download_and_read_text_file(attachment).await {
+                        text_file_bytes += actual_bytes;
+                        text_file_count += 1;
+                        debug!(filename = %attachment.filename, "adding text file attachment");
+                        content_blocks.push(content_block);
+                    }
                 } else if let Some(content_block) = download_and_encode_image(attachment).await {
                     debug!(url = %attachment.url, filename = %attachment.filename, "adding image attachment");
                     content_blocks.push(content_block);
@@ -329,6 +351,91 @@ impl EventHandler for Handler {
     }
 }
 
+/// Extensions recognised as text-based files that can be inlined into the prompt.
+const TEXT_EXTENSIONS: &[&str] = &[
+    "txt", "csv", "log", "md", "json", "jsonl", "yaml", "yml", "toml", "xml",
+    "rs", "py", "js", "ts", "jsx", "tsx", "go", "java", "c", "cpp", "h", "hpp",
+    "rb", "sh", "bash", "zsh", "fish", "ps1", "bat", "sql", "html", "css",
+    "scss", "less", "ini", "cfg", "conf", "env",
+];
+
+/// Exact filenames (no extension) recognised as text files.
+const TEXT_FILENAMES: &[&str] = &[
+    "dockerfile", "makefile", "justfile", "rakefile", "gemfile",
+    "procfile", "vagrantfile", ".gitignore", ".dockerignore", ".editorconfig",
+];
+
+/// MIME types recognised as text-based (beyond `text/*`).
+const TEXT_MIME_TYPES: &[&str] = &[
+    "application/json",
+    "application/xml",
+    "application/javascript",
+    "application/x-yaml",
+    "application/x-sh",
+    "application/toml",
+    "application/x-toml",
+];
+
+/// Check if an attachment is a text-based file we can inline.
+fn is_text_attachment(attachment: &serenity::model::channel::Attachment) -> bool {
+    let mime = attachment.content_type.as_deref().unwrap_or("");
+    let mime_base = mime.split(';').next().unwrap_or(mime).trim();
+    if mime_base.starts_with("text/") || TEXT_MIME_TYPES.contains(&mime_base) {
+        return true;
+    }
+    // Check extension
+    if attachment.filename.contains('.') {
+        if let Some(ext) = attachment.filename.rsplit('.').next() {
+            if TEXT_EXTENSIONS.contains(&ext.to_lowercase().as_str()) {
+                return true;
+            }
+        }
+    }
+    // Check exact filename (Dockerfile, Makefile, etc.)
+    TEXT_FILENAMES.contains(&attachment.filename.to_lowercase().as_str())
+}
+
+/// Download a text-based file attachment and return it as a ContentBlock::Text.
+/// Files larger than 512 KB are skipped to avoid bloating the prompt.
+async fn download_and_read_text_file(
+    attachment: &serenity::model::channel::Attachment,
+) -> Option<(ContentBlock, u64)> {
+    const MAX_SIZE: u64 = 512 * 1024; // 512 KB
+
+    if u64::from(attachment.size) > MAX_SIZE {
+        warn!(filename = %attachment.filename, size = attachment.size, "text file exceeds 512KB limit, skipping");
+        return None;
+    }
+
+    let resp = HTTP_CLIENT.get(&attachment.url).send().await.ok()?;
+    if !resp.status().is_success() {
+        warn!(url = %attachment.url, status = %resp.status(), "text file download failed");
+        return None;
+    }
+    let bytes = resp.bytes().await.ok()?;
+    let actual_size = bytes.len() as u64;
+
+    // Defense-in-depth: verify actual download size
+    if actual_size > MAX_SIZE {
+        warn!(filename = %attachment.filename, size = actual_size, "downloaded text file exceeds 512KB limit, skipping");
+        return None;
+    }
+
+    // from_utf8_lossy returns Cow::Borrowed for valid UTF-8 (zero-copy)
+    let text = String::from_utf8_lossy(&bytes).into_owned();
+
+    // Dynamic fence: keep adding backticks until the fence doesn't appear in content
+    let mut fence = "```".to_string();
+    while text.contains(fence.as_str()) {
+        fence.push('`');
+    }
+
+    debug!(filename = %attachment.filename, bytes = text.len(), "text file inlined");
+    Some((ContentBlock::Text {
+        text: format!("[File: {}]\n{fence}\n{}\n{fence}", attachment.filename, text),
+    }, actual_size))
+}
+
 /// Check if an attachment is an audio file (voice messages are typically audio/ogg).
 fn is_audio_attachment(attachment: &serenity::model::channel::Attachment) -> bool {
     let mime = attachment.content_type.as_deref().unwrap_or("");