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Kyle Carberry
b65c0766d2
## Summary Adds a new line-based file reading endpoint to the workspace agent, replacing the unbounded byte-based approach for the `read_file` chat tool and `coder_workspace_read_file` MCP tool. **Problem**: The current `read_file` tool returns the entire file contents with no limits, which can blow up LLM context windows and cause OOM issues with large files. **Solution**: Inspired by [`coder/mux`](https://github.com/coder/mux) and [`openai/codex`](https://github.com/openai/codex), implement a line-based reader with safety limits. ## Changes ### Agent (`agent/agentfiles/`) - New `/read-file-lines` endpoint with `HandleReadFileLines` handler - Line-based `offset` (1-based line number, default: 1) and `limit` (line count, default: 2000) - Safety constants: | Constant | Value | Purpose | |---|---|---| | `MaxFileSize` | 1 MB | Reject files larger than this at stat | | `MaxLineBytes` | 1,024 | Per-line truncation with `... [truncated]` marker | | `MaxResponseLines` | 2,000 | Max lines per response | | `MaxResponseBytes` | 32 KB | Max total response size | | `DefaultLineLimit` | 2,000 | Default when no limit specified | - Line numbering format: `1\tcontent` (tab-separated) - Structured JSON response: `{ success, file_size, total_lines, lines_read, content, error }` - Hard errors when limits exceeded — tells the LLM to use `offset`/`limit` - Existing byte-based `/read-file` endpoint preserved (used by `instruction.go`) ### SDK (`codersdk/workspacesdk/`) - `ReadFileLinesResponse` type added - `ReadFileLines` method added to `AgentConn` interface - Mock regenerated ### Chat tool (`coderd/chatd/chattool/`) - `read_file` tool now uses `conn.ReadFileLines()` instead of `conn.ReadFile()` - Updated tool description to document line-based parameters - Response includes `file_size`, `total_lines`, `lines_read` metadata ### MCP tool (`codersdk/toolsdk/`) - `coder_workspace_read_file` updated to use line-based reading - Schema descriptions updated for line-based offset/limit - Removed `maxFileLimit` constant (agent handles limits now) ### Tests - 13 new test cases for `TestReadFileLines`: - Path validation (empty, relative, non-existent, directory, no permissions) - Empty file handling - Basic read, offset, limit, offset+limit combinations - Offset beyond file length - Long line truncation (>1024 bytes) - Large file rejection (>1MB) - All existing tests pass unchanged ## Design decisions | Decision | Rationale | |---|---| | Line-based, not byte-based | Both coder/mux and openai/codex use line-based — matches how LLMs reason about code | | Default limit of 2000 | Matches codex; prevents accidental full-file dumps while being generous | | 32 KB response cap | Compromise between mux (16 KB) and codex (no cap) | | 1024 byte/line truncation with marker | More generous than codex (500), marker helps LLM know data is missing | | Hard errors on overflow | Matches mux; forces LLM to paginate rather than getting partial data | | Preserve byte-based endpoint | `instruction.go` needs raw byte access for AGENTS.md |