Add fetchPage() with axios, timeout, and retry logic

Implement fetchPage() function for HTTP scraping:
- Uses axios for HTTP GET requests
- Configurable timeout (default 30s) and User-Agent header
- Retry with exponential backoff (1s, 2s, 4s) on 5xx and network errors
- Does not retry on 4xx client errors
- Logs each attempt with attempt number and error details
- Returns HTML string on success, throws after retries exhausted

services/scraperService.js

@@ -0,0 +1,114 @@
+/**
+ * Scraper Service
+ *
+ * Core scraper logic including HTTP fetching, HTML parsing,
+ * data transformation, and database operations.
+ */
+
+const axios = require('axios');
+const config = require('../config/scraper');
+
+/**
+ * Sleep utility for retry delays
+ * @param {number} ms - Milliseconds to sleep
+ * @returns {Promise<void>}
+ */
+function sleep(ms) {
+  return new Promise(resolve => setTimeout(resolve, ms));
+}
+
+/**
+ * Determine if an error is retryable
+ * @param {Error} error - Axios error
+ * @returns {boolean} True if should retry
+ */
+function isRetryableError(error) {
+  // Network errors (timeout, DNS, connection) don't have a response property
+  if (!error.response) {
+    return true;
+  }
+
+  const status = error.response.status;
+
+  // 5xx server errors are retryable
+  if (status >= 500) {
+    return true;
+  }
+
+  // 429 Too Many Requests - do not retry immediately
+  if (status === 429) {
+    return false;
+  }
+
+  // 4xx client errors - do not retry
+  return false;
+}
+
+/**
+ * Fetch page HTML with retry logic
+ * @param {string} url - Target URL
+ * @param {Object} logger - Logger instance
+ * @returns {Promise<string>} HTML content
+ * @throws {Error} After all retries exhausted
+ */
+async function fetchPage(url, logger) {
+  const { maxRetries, baseDelay, timeout } = config.RETRY_CONFIG;
+  let lastError;
+
+  for (let attempt = 1; attempt <= maxRetries + 1; attempt++) {
+    try {
+      logger.info('Fetching page', { url, attempt });
+
+      const response = await axios.get(url, {
+        timeout,
+        headers: {
+          'User-Agent': config.USER_AGENT
+        },
+        maxRedirects: 5,
+        validateStatus: (status) => status < 400 // Accept 2xx and 3xx
+      });
+
+      logger.info('Page fetched successfully', {
+        status: response.status,
+        contentLength: response.data.length
+      });
+
+      return response.data;
+
+    } catch (error) {
+      lastError = error;
+
+      // Determine if error is retryable
+      const isRetryable = isRetryableError(error);
+
+      logger.warn('Fetch attempt failed', {
+        attempt,
+        errorType: error.name,
+        errorMessage: error.message,
+        statusCode: error.response?.status,
+        isRetryable
+      });
+
+      // Don't retry non-retryable errors (4xx)
+      if (!isRetryable) {
+        throw error;
+      }
+
+      // Don't wait after last attempt
+      if (attempt <= maxRetries) {
+        const delay = baseDelay * Math.pow(2, attempt - 1); // Exponential backoff
+        logger.info('Waiting before retry', { delay });
+        await sleep(delay);
+      }
+    }
+  }
+
+  throw lastError;
+}
+
+module.exports = {
+  fetchPage,
+  // Export for testing
+  isRetryableError,
+  sleep
+};