|
| 1 | +/** |
| 2 | + * Context Overflow Handler |
| 3 | + * |
| 4 | + * Handles "Prompt too long" / context length exceeded errors by returning |
| 5 | + * a synthetic SSE response that advises the user to use /compact or /clear. |
| 6 | + * This prevents the OpenCode session from getting locked on 400 errors. |
| 7 | + */ |
| 8 | + |
| 9 | +import { PLUGIN_NAME } from "./constants.js"; |
| 10 | + |
| 11 | +/** |
| 12 | + * Error patterns that indicate context overflow |
| 13 | + */ |
| 14 | +const CONTEXT_OVERFLOW_PATTERNS = [ |
| 15 | + "prompt is too long", |
| 16 | + "prompt_too_long", |
| 17 | + "context length exceeded", |
| 18 | + "context_length_exceeded", |
| 19 | + "maximum context length", |
| 20 | + "token limit exceeded", |
| 21 | + "too many tokens", |
| 22 | +]; |
| 23 | + |
| 24 | +/** |
| 25 | + * Check if an error body indicates context overflow |
| 26 | + */ |
| 27 | +export function isContextOverflowError(status: number, bodyText: string): boolean { |
| 28 | + if (status !== 400) return false; |
| 29 | + if (!bodyText) return false; |
| 30 | + |
| 31 | + const lowerBody = bodyText.toLowerCase(); |
| 32 | + return CONTEXT_OVERFLOW_PATTERNS.some(pattern => lowerBody.includes(pattern)); |
| 33 | +} |
| 34 | + |
| 35 | +/** |
| 36 | + * The message shown to users when context overflow occurs |
| 37 | + */ |
| 38 | +const CONTEXT_OVERFLOW_MESSAGE = `[Plugin Notice] Context is too long for this model. |
| 39 | +
|
| 40 | +Please use one of these commands to reduce context size: |
| 41 | +
|
| 42 | +• **/compact** - Compress conversation history (recommended) |
| 43 | +• **/clear** - Start fresh with empty context |
| 44 | +• **/undo** - Remove recent messages |
| 45 | +
|
| 46 | +Then retry your request. |
| 47 | +
|
| 48 | +Alternatively, you can switch to a model with a larger context window.`; |
| 49 | + |
| 50 | +/** |
| 51 | + * Creates a synthetic SSE response for context overflow errors. |
| 52 | + * This returns a 200 OK with the error message as assistant text, |
| 53 | + * preventing the session from getting locked. |
| 54 | + */ |
| 55 | +export function createContextOverflowResponse(model: string = "unknown"): Response { |
| 56 | + const messageId = `msg_synthetic_overflow_${Date.now()}`; |
| 57 | + const events: string[] = []; |
| 58 | + |
| 59 | + // message_start |
| 60 | + events.push(`event: message_start\ndata: ${JSON.stringify({ |
| 61 | + type: "message_start", |
| 62 | + message: { |
| 63 | + id: messageId, |
| 64 | + type: "message", |
| 65 | + role: "assistant", |
| 66 | + content: [], |
| 67 | + model, |
| 68 | + usage: { input_tokens: 0, output_tokens: 0 }, |
| 69 | + }, |
| 70 | + })}\n\n`); |
| 71 | + |
| 72 | + // content_block_start |
| 73 | + events.push(`event: content_block_start\ndata: ${JSON.stringify({ |
| 74 | + type: "content_block_start", |
| 75 | + index: 0, |
| 76 | + content_block: { type: "text", text: "" }, |
| 77 | + })}\n\n`); |
| 78 | + |
| 79 | + // content_block_delta (the actual message) |
| 80 | + events.push(`event: content_block_delta\ndata: ${JSON.stringify({ |
| 81 | + type: "content_block_delta", |
| 82 | + index: 0, |
| 83 | + delta: { type: "text_delta", text: CONTEXT_OVERFLOW_MESSAGE }, |
| 84 | + })}\n\n`); |
| 85 | + |
| 86 | + // content_block_stop |
| 87 | + events.push(`event: content_block_stop\ndata: ${JSON.stringify({ |
| 88 | + type: "content_block_stop", |
| 89 | + index: 0, |
| 90 | + })}\n\n`); |
| 91 | + |
| 92 | + // message_delta (end_turn) |
| 93 | + events.push(`event: message_delta\ndata: ${JSON.stringify({ |
| 94 | + type: "message_delta", |
| 95 | + delta: { stop_reason: "end_turn" }, |
| 96 | + usage: { output_tokens: 0 }, |
| 97 | + })}\n\n`); |
| 98 | + |
| 99 | + // message_stop |
| 100 | + events.push(`event: message_stop\ndata: ${JSON.stringify({ |
| 101 | + type: "message_stop", |
| 102 | + })}\n\n`); |
| 103 | + |
| 104 | + return new Response(events.join(""), { |
| 105 | + status: 200, |
| 106 | + headers: { |
| 107 | + "Content-Type": "text/event-stream", |
| 108 | + "X-Codex-Plugin-Synthetic": "true", |
| 109 | + "X-Codex-Plugin-Error-Type": "context_overflow", |
| 110 | + }, |
| 111 | + }); |
| 112 | +} |
| 113 | + |
| 114 | +/** |
| 115 | + * Check response for context overflow and return synthetic response if needed |
| 116 | + */ |
| 117 | +export async function handleContextOverflow( |
| 118 | + response: Response, |
| 119 | + model?: string, |
| 120 | +): Promise<{ handled: true; response: Response } | { handled: false }> { |
| 121 | + if (response.status !== 400) { |
| 122 | + return { handled: false }; |
| 123 | + } |
| 124 | + |
| 125 | + try { |
| 126 | + const bodyText = await response.clone().text(); |
| 127 | + if (isContextOverflowError(response.status, bodyText)) { |
| 128 | + console.log(`[${PLUGIN_NAME}] Context overflow detected, returning synthetic response`); |
| 129 | + return { |
| 130 | + handled: true, |
| 131 | + response: createContextOverflowResponse(model), |
| 132 | + }; |
| 133 | + } |
| 134 | + } catch { |
| 135 | + // Ignore read errors |
| 136 | + } |
| 137 | + |
| 138 | + return { handled: false }; |
| 139 | +} |
0 commit comments