# IPFS Retry Implementation & Error Handling

## Overview
This document outlines the comprehensive retry mechanism and error handling improvements implemented for IPFS metadata fetching to resolve `AbortError: signal is aborted without reason` issues and CORS-related problems.

## Key Features Implemented

### 1. Enhanced IPFS Utility (`app/utils/ipfs.ts`)

#### Retry Configuration
- **Max Retries**: 5 attempts per gateway (automatic fallback)
- **Timeout**: 8 seconds per individual request
- **Gateway Rotation**: Automatic fallback to next gateway on failure

#### CORS-Friendly Gateway Strategy
```typescript
const IPFS_GATEWAYS = [
  'https://dweb.link/ipfs/',
  'https://nftstorage.link/ipfs/',
  'https://cloudflare-ipfs.com/ipfs/',
  'https://gateway.pinata.cloud/ipfs/',
  'https://ipfs.io/ipfs/'
];
```

**Gateway Selection Strategy:**
- Prioritizes CORS-friendly gateways (`dweb.link`, `nftstorage.link`)
- Falls back to other reliable gateways
- Automatic rotation on failure

#### Smart Error Handling
- **Content-Type Validation**: Ensures response is JSON before parsing
- **Network Error Detection**: Distinguishes between network and parsing errors
- **Graceful Degradation**: Returns `null` on failure instead of throwing errors
- **Gateway Isolation**: Individual gateway failures don't affect others

#### Caching Mechanism
- **Simple Map-based Cache**: Prevents duplicate requests for same URIs
- **Memory Management**: Configurable cache with statistics
- **Cache Utilities**: `clearMetadataCache()` and `getCacheStats()` functions

### 2. Enhanced TokenCard Component (`app/components/TokenCard.vue`)

#### Direct Metadata Integration
- **Non-blocking Loading**: Metadata loads after component mounts
- **Individual Error Handling**: Card failures don't affect others
- **Visual Feedback**: Loading spinners and error indicators

#### Social Media Integration
```typescript
// Automatic detection of social links
const socialLinks = extractSocialLinks(metadata);
// Returns: { type: 'twitter', url: string, icon: string }[]
```

**Supported Platforms:**
- Twitter/X (twitter.com, x.com)
- Telegram (t.me, telegram.org)
- Discord (discord.gg, discord.com)
- Generic Website (fallback)

#### Image Handling
- **IPFS Image Support**: Automatic IPFS hash extraction and gateway routing
- **Fallback Avatars**: Gradient avatars with token symbol when images fail
- **Error Recovery**: Graceful handling of image load failures

## Core Functions

### Primary Functions

#### `fetchTokenMetadata(uri: string): Promise<TokenMetadata | null>`
- Fetches metadata from IPFS URI
- Handles multiple URI formats (ipfs://, https://ipfs.io/ipfs/, direct hash)
- Returns `null` on failure (no exceptions thrown)
- Automatic caching to prevent duplicate requests

#### `getTokenImage(metadata: TokenMetadata): string | null`
- Extracts and formats token image URL
- Handles IPFS URIs and direct URLs
- Uses reliable gateways for IPFS images

#### `extractSocialLinks(metadata: TokenMetadata)`
- Extracts social media links from metadata
- Returns array of social link objects with icons
- Validates and cleans URLs

### Utility Functions

#### `extractIpfsHash(uri: string): string | null`
- Extracts IPFS hash from various URI formats
- Supports ipfs://, gateway URLs, and direct hashes

#### `getSocialIcon(url: string): string | null`
- Determines appropriate icon for social media URL
- Returns icon identifier for UI rendering

#### `cleanSocialUrl(url: string): string | null`
- Validates and normalizes social media URLs
- Adds https:// prefix when missing

## CORS Resolution

### Problem Identified
Initial implementation encountered CORS errors:
```
Access to fetch at 'https://ipfs.io/ipfs/...' from origin 'http://localhost:3000' 
has been blocked by CORS policy: Request header field cache-control is not 
allowed by Access-Control-Allow-Headers in preflight response.
```

### Solutions Attempted

#### 1. Server API Route Approach (Abandoned)
- Created Nuxt server API route to proxy IPFS requests
- Issues: Returned HTML instead of JSON in Electron environment
- Not compatible with Electron + Nuxt setup

#### 2. CORS-Friendly Gateway Strategy (Final Solution)
- Prioritized gateways with proper CORS headers
- `dweb.link` and `nftstorage.link` as primary gateways
- Removed problematic headers from requests
- Simplified request configuration

### Final Working Configuration
```typescript
const response = await fetch(url, {
  method: 'GET',
  mode: 'cors',
  headers: {
    'Accept': 'application/json',
  },
  signal: AbortSignal.timeout(8000)
});
```

## Architecture Decisions

### Why Direct Implementation Over Composables
1. **Simplicity**: Direct metadata fetching in components is easier to debug
2. **Performance**: Eliminates unnecessary abstraction layers
3. **Maintenance**: Fewer files to maintain and update
4. **Debugging**: Clearer error tracking and logging

### Why Multiple Gateways
1. **Reliability**: Fallback ensures higher success rate
2. **Performance**: Different gateways have varying response times
3. **CORS Compatibility**: Not all gateways support CORS properly
4. **Geographic Distribution**: Better global accessibility

### Why Simple Caching
1. **Memory Efficiency**: Map-based cache with minimal overhead
2. **Request Deduplication**: Prevents multiple requests for same URI
3. **No Persistence**: Cache clears on app restart (prevents stale data)
4. **Statistics**: Built-in cache monitoring

## Error Handling Strategy

### Non-Blocking Operations
- Individual token failures don't affect others
- UI remains responsive during metadata fetching
- Graceful degradation with fallback content

### User Experience
- **Loading States**: Clear visual feedback during fetching
- **Error Indicators**: Subtle error icons with tooltips
- **Fallback Content**: Token symbol avatars when images fail
- **Retry Capability**: Users can refresh individual tokens

### Developer Experience
- **No Console Spam**: Removed all debugging output
- **Clear Error Types**: Distinguishable error conditions
- **Cache Management**: Tools for cache inspection and clearing

## Performance Optimizations

### Request Optimization
- 8-second timeout prevents hanging requests
- Automatic gateway rotation minimizes wait time
- Content-type validation prevents unnecessary parsing
- Simple caching reduces duplicate requests

### UI Optimization
- Non-blocking metadata loading
- Individual component error isolation
- Efficient social link extraction
- Optimized image loading with fallbacks

## Implementation Status

### ✅ Completed Features
- [x] Multiple CORS-friendly IPFS gateways
- [x] Automatic retry with gateway fallback
- [x] Simple metadata caching
- [x] Social media link extraction and icons
- [x] Image handling with IPFS support
- [x] Error handling without console spam
- [x] Non-blocking UI operations
- [x] Clean TypeScript implementation

### 🚫 Removed Features
- [x] Complex composable abstractions
- [x] Batch processing utilities
- [x] Server API proxy routes
- [x] Debugging console output
- [x] Exponential backoff (replaced with gateway rotation)

## Usage Examples

### Basic Metadata Fetching
```typescript
import { fetchTokenMetadata } from '../utils/ipfs';

const metadata = await fetchTokenMetadata('https://ipfs.io/ipfs/bafkreixxx');
if (metadata) {
  console.log(metadata.name, metadata.symbol);
}
```

### Image Handling
```typescript
import { getTokenImage } from '../utils/ipfs';

const imageUrl = getTokenImage(metadata);
if (imageUrl) {
  // Use imageUrl for img src
}
```

### Social Links
```typescript
import { extractSocialLinks } from '../utils/ipfs';

const socialLinks = extractSocialLinks(metadata);
socialLinks.forEach(link => {
  console.log(link.type, link.url, link.icon);
});
```

## Testing and Validation

### Manual Testing Performed
- [x] IPFS metadata fetching from various URIs
- [x] Gateway fallback functionality
- [x] CORS compatibility across gateways
- [x] Image loading and fallback behavior
- [x] Social media link detection
- [x] Error handling and recovery
- [x] Cache functionality and statistics

### Known Working URIs
```
https://ipfs.io/ipfs/bafkreigr67ogup7ijve5mq7vh22nyydsvksfqtctxu3bdtsgs47uihlaka
https://ipfs.io/ipfs/bafkreido7xq6dx2m7nxlnoeoz562uapvpfs4yup2eyckerzvggylgttcoa
```

## Maintenance Notes

### Cache Management
```typescript
import { clearMetadataCache, getCacheStats } from '../utils/ipfs';

// Clear cache when needed
clearMetadataCache();

// Monitor cache usage
const stats = getCacheStats();
console.log(`Cache size: ${stats.size}, hits: ${stats.hits}`);
```

### Gateway Management
- Monitor gateway performance and update priority as needed
- Add new CORS-friendly gateways when available
- Remove unreliable gateways from the list

### Error Monitoring
- Monitor for new types of IPFS errors
- Update error handling as needed
- Track gateway success rates for optimization

---

**Last Updated**: December 22, 2024  
**Status**: Production Ready ✅