feat: add ChatGPTError with more info on HTTP errors

src/chatgpt-api.test.ts

 import test from 'ava'
 import dotenv from 'dotenv-safe'
 
+import * as types from './types'
 import { ChatGPTAPI } from './chatgpt-api'
 
 dotenv.config()
@@ -20,6 +21,7 @@ test('ChatGPTAPI invalid session token', async (t) => {
       await chatgpt.ensureAuth()
     },
     {
+      instanceOf: types.ChatGPTError,
       message: 'ChatGPT failed to refresh auth token. Error: Unauthorized'
     }
   )
@@ -64,6 +66,7 @@ if (!isCI) {
         await chatgpt.ensureAuth()
       },
       {
+        instanceOf: types.ChatGPTError,
         message:
           'ChatGPT failed to refresh auth token. Error: session token may have expired'
       }

src/chatgpt-api.ts

 import ExpiryMap from 'expiry-map'
-import pTimeout, { TimeoutError } from 'p-timeout'
+import pTimeout from 'p-timeout'
 import { v4 as uuidv4 } from 'uuid'
 
 import * as types from './types'
@@ -68,7 +68,7 @@ export class ChatGPTAPI {
     this._accessTokenCache = new ExpiryMap<string, string>(accessTokenTTL)
 
     if (!this._sessionToken) {
-      throw new Error('ChatGPT invalid session token')
+      throw new types.ChatGPTError('ChatGPT invalid session token')
     }
   }
 
@@ -238,6 +238,7 @@ export class ChatGPTAPI {
       return cachedAccessToken
     }
 
+    let response: Response
     try {
       const res = await fetch('https://chat.openai.com/api/auth/session', {
         headers: {
@@ -245,8 +246,14 @@ export class ChatGPTAPI {
           'user-agent': this._userAgent
         }
       }).then((r) => {
+        response = r
+
         if (!r.ok) {
-          throw new Error(`${r.status} ${r.statusText}`)
+          const error = new types.ChatGPTError(`${r.status} ${r.statusText}`)
+          error.response = r
+          error.statusCode = r.status
+          error.statusText = r.statusText
+          throw error
         }
 
         return r.json() as any as types.SessionResult
@@ -255,22 +262,41 @@ export class ChatGPTAPI {
       const accessToken = res?.accessToken
 
       if (!accessToken) {
-        throw new Error('Unauthorized')
+        const error = new types.ChatGPTError('Unauthorized')
+        error.response = response
+        error.statusCode = response?.status
+        error.statusText = response?.statusText
+        throw error
       }
 
-      const error = res?.error
-      if (error) {
-        if (error === 'RefreshAccessTokenError') {
-          throw new Error('session token may have expired')
+      const appError = res?.error
+      if (appError) {
+        if (appError === 'RefreshAccessTokenError') {
+          const error = new types.ChatGPTError('session token may have expired')
+          error.response = response
+          error.statusCode = response?.status
+          error.statusText = response?.statusText
+          throw error
         } else {
-          throw new Error(error)
+          const error = new types.ChatGPTError(appError)
+          error.response = response
+          error.statusCode = response?.status
+          error.statusText = response?.statusText
+          throw error
         }
       }
 
       this._accessTokenCache.set(KEY_ACCESS_TOKEN, accessToken)
       return accessToken
     } catch (err: any) {
-      throw new Error(`ChatGPT failed to refresh auth token. ${err.toString()}`)
+      const error = new types.ChatGPTError(
+        `ChatGPT failed to refresh auth token. ${err.toString()}`
+      )
+      error.response = response
+      error.statusCode = response?.status
+      error.statusText = response?.statusText
+      error.originalError = err
+      throw error
     }
   }
 

src/fetch-sse.ts

 import { createParser } from 'eventsource-parser'
 
+import * as types from './types'
 import { fetch } from './fetch'
 import { streamAsyncIterable } from './stream-async-iterable'
 
@@ -10,7 +11,12 @@ export async function fetchSSE(
   const { onMessage, ...fetchOptions } = options
   const res = await fetch(url, fetchOptions)
   if (!res.ok) {
-    throw new Error(`ChatGPTAPI error ${res.status || res.statusText}`)
+    const msg = `ChatGPTAPI error ${res.status || res.statusText}`
+    const error = new types.ChatGPTError(msg)
+    error.statusCode = res.status
+    error.statusText = res.statusText
+    error.response = res
+    throw error
   }
 
   const parser = createParser((event) => {
@@ -25,7 +31,7 @@ export async function fetchSSE(
     const body: NodeJS.ReadableStream = res.body as any
 
     if (!body.on || !body.read) {
-      throw new Error('unsupported "fetch" implementation')
+      throw new types.ChatGPTError('unsupported "fetch" implementation')
     }
 
     body.on('readable', () => {

src/types.ts

@@ -287,3 +287,10 @@ export type SendConversationMessageOptions = Omit<
   SendMessageOptions,
   'conversationId' | 'parentMessageId'
 >
+
+export class ChatGPTError extends Error {
+  statusCode?: number
+  statusText?: string
+  response?: Response
+  originalError?: Error
+}