Merge pull request #2332 from dalf/metrology-errors

[enh] record exception details per engine

24 files changed, 597 insertions, 169 deletions

diff --git a/docs/dev/engine_overview.rst b/docs/dev/engine_overview.rst
index 5e3483fd7..0f58af765 100644
--- a/docs/dev/engine_overview.rst
+++ b/docs/dev/engine_overview.rst
@@ -134,16 +134,18 @@ The function ``def request(query, params):`` always returns the ``params``
 variable.  Inside searx, the following paramters can be used to specify a search
 request:
 
-============ =========== =========================================================
-argument     type        information
-============ =========== =========================================================
-url          string      requested url
-method       string      HTTP request method
-headers      set         HTTP header information
-data         set         HTTP data information (parsed if ``method != 'GET'``)
-cookies      set         HTTP cookies
-verify       boolean     Performing SSL-Validity check
-============ =========== =========================================================
+================== =========== ========================================================================
+argument           type        information
+================== =========== ========================================================================
+url                string      requested url
+method             string      HTTP request method
+headers            set         HTTP header information
+data               set         HTTP data information (parsed if ``method != 'GET'``)
+cookies            set         HTTP cookies
+verify             boolean     Performing SSL-Validity check
+max_redirects      int         maximum redirects, hard limit
+soft_max_redirects int         maximum redirects, soft limit. Record an error but don't stop the engine
+================== =========== ========================================================================
 
 
 example code
diff --git a/searx/engines/1337x.py b/searx/engines/1337x.py
index 9e045bc51..18478876a 100644
--- a/searx/engines/1337x.py
+++ b/searx/engines/1337x.py
@@ -1,6 +1,6 @@
 from urllib.parse import quote, urljoin
 from lxml import html
-from searx.utils import extract_text, get_torrent_size
+from searx.utils import extract_text, get_torrent_size, eval_xpath, eval_xpath_list, eval_xpath_getindex
 
 
 url = 'https://1337x.to/'
@@ -20,12 +20,12 @@ def response(resp):
 
     dom = html.fromstring(resp.text)
 
-    for result in dom.xpath('//table[contains(@class, "table-list")]/tbody//tr'):
-        href = urljoin(url, result.xpath('./td[contains(@class, "name")]/a[2]/@href')[0])
-        title = extract_text(result.xpath('./td[contains(@class, "name")]/a[2]'))
-        seed = extract_text(result.xpath('.//td[contains(@class, "seeds")]'))
-        leech = extract_text(result.xpath('.//td[contains(@class, "leeches")]'))
-        filesize_info = extract_text(result.xpath('.//td[contains(@class, "size")]/text()'))
+    for result in eval_xpath_list(dom, '//table[contains(@class, "table-list")]/tbody//tr'):
+        href = urljoin(url, eval_xpath_getindex(result, './td[contains(@class, "name")]/a[2]/@href', 0))
+        title = extract_text(eval_xpath(result, './td[contains(@class, "name")]/a[2]'))
+        seed = extract_text(eval_xpath(result, './/td[contains(@class, "seeds")]'))
+        leech = extract_text(eval_xpath(result, './/td[contains(@class, "leeches")]'))
+        filesize_info = extract_text(eval_xpath(result, './/td[contains(@class, "size")]/text()'))
         filesize, filesize_multiplier = filesize_info.split()
         filesize = get_torrent_size(filesize, filesize_multiplier)
 
diff --git a/searx/engines/__init__.py b/searx/engines/__init__.py
index a78c4a8c3..ddd6a7feb 100644
--- a/searx/engines/__init__.py
+++ b/searx/engines/__init__.py
@@ -132,8 +132,9 @@ def load_engine(engine_data):
                 lambda: engine._fetch_supported_languages(get(engine.supported_languages_url)))
 
     engine.stats = {
+        'sent_search_count': 0,  # sent search
+        'search_count': 0,  # succesful search
         'result_count': 0,
-        'search_count': 0,
         'engine_time': 0,
         'engine_time_count': 0,
         'score_count': 0,
diff --git a/searx/engines/acgsou.py b/searx/engines/acgsou.py
index a436df283..b8b367c24 100644
--- a/searx/engines/acgsou.py
+++ b/searx/engines/acgsou.py
@@ -11,7 +11,7 @@
 
 from urllib.parse import urlencode
 from lxml import html
-from searx.utils import extract_text, get_torrent_size
+from searx.utils import extract_text, get_torrent_size, eval_xpath_list, eval_xpath_getindex
 
 # engine dependent config
 categories = ['files', 'images', 'videos', 'music']
@@ -37,29 +37,26 @@ def request(query, params):
 def response(resp):
     results = []
     dom = html.fromstring(resp.text)
-    for result in dom.xpath(xpath_results):
+    for result in eval_xpath_list(dom, xpath_results):
         # defaults
         filesize = 0
         magnet_link = "magnet:?xt=urn:btih:{}&tr=http://tracker.acgsou.com:2710/announce"
 
-        try:
-            category = extract_text(result.xpath(xpath_category)[0])
-        except:
-            pass
-
-        page_a = result.xpath(xpath_title)[0]
+        category = extract_text(eval_xpath_getindex(result, xpath_category, 0, default=[]))
+        page_a = eval_xpath_getindex(result, xpath_title, 0)
         title = extract_text(page_a)
         href = base_url + page_a.attrib.get('href')
 
         magnet_link = magnet_link.format(page_a.attrib.get('href')[5:-5])
 
-        try:
-            filesize_info = result.xpath(xpath_filesize)[0]
-            filesize = filesize_info[:-2]
-            filesize_multiplier = filesize_info[-2:]
-            filesize = get_torrent_size(filesize, filesize_multiplier)
-        except:
-            pass
+        filesize_info = eval_xpath_getindex(result, xpath_filesize, 0, default=None)
+        if filesize_info:
+            try:
+                filesize = filesize_info[:-2]
+                filesize_multiplier = filesize_info[-2:]
+                filesize = get_torrent_size(filesize, filesize_multiplier)
+            except:
+                pass
         # I didn't add download/seed/leech count since as I figured out they are generated randomly everytime
         content = 'Category: "{category}".'
         content = content.format(category=category)
diff --git a/searx/engines/ahmia.py b/searx/engines/ahmia.py
index d9fcc6ca7..7a2ae0075 100644
--- a/searx/engines/ahmia.py
+++ b/searx/engines/ahmia.py
@@ -12,7 +12,7 @@
 
 from urllib.parse import urlencode, urlparse, parse_qs
 from lxml.html import fromstring
-from searx.engines.xpath import extract_url, extract_text
+from searx.engines.xpath import extract_url, extract_text, eval_xpath_list, eval_xpath
 
 # engine config
 categories = ['onions']
@@ -50,17 +50,17 @@ def response(resp):
 
     # trim results so there's not way too many at once
     first_result_index = page_size * (resp.search_params.get('pageno', 1) - 1)
-    all_results = dom.xpath(results_xpath)
+    all_results = eval_xpath_list(dom, results_xpath)
     trimmed_results = all_results[first_result_index:first_result_index + page_size]
 
     # get results
     for result in trimmed_results:
         # remove ahmia url and extract the actual url for the result
-        raw_url = extract_url(result.xpath(url_xpath), search_url)
+        raw_url = extract_url(eval_xpath_list(result, url_xpath, min_len=1), search_url)
         cleaned_url = parse_qs(urlparse(raw_url).query).get('redirect_url', [''])[0]
 
-        title = extract_text(result.xpath(title_xpath))
-        content = extract_text(result.xpath(content_xpath))
+        title = extract_text(eval_xpath(result, title_xpath))
+        content = extract_text(eval_xpath(result, content_xpath))
 
         results.append({'url': cleaned_url,
                         'title': title,
@@ -68,11 +68,11 @@ def response(resp):
                         'is_onion': True})
 
     # get spelling corrections
-    for correction in dom.xpath(correction_xpath):
+    for correction in eval_xpath_list(dom, correction_xpath):
         results.append({'correction': extract_text(correction)})
 
     # get number of results
-    number_of_results = dom.xpath(number_of_results_xpath)
+    number_of_results = eval_xpath(dom, number_of_results_xpath)
     if number_of_results:
         try:
             results.append({'number_of_results': int(extract_text(number_of_results))})
diff --git a/searx/engines/apkmirror.py b/searx/engines/apkmirror.py
index a8ff499af..3a948dcb4 100644
--- a/searx/engines/apkmirror.py
+++ b/searx/engines/apkmirror.py
@@ -11,7 +11,7 @@
 
 from urllib.parse import urlencode
 from lxml import html
-from searx.utils import extract_text
+from searx.utils import extract_text, eval_xpath_list, eval_xpath_getindex
 
 
 # engine dependent config
@@ -42,12 +42,13 @@ def response(resp):
     dom = html.fromstring(resp.text)
 
     # parse results
-    for result in dom.xpath('.//div[@id="content"]/div[@class="listWidget"]/div[@class="appRow"]'):
+    for result in eval_xpath_list(dom, './/div[@id="content"]/div[@class="listWidget"]/div[@class="appRow"]'):
 
-        link = result.xpath('.//h5/a')[0]
+        link = eval_xpath_getindex(result, './/h5/a', 0)
         url = base_url + link.attrib.get('href') + '#downloads'
         title = extract_text(link)
-        thumbnail_src = base_url + result.xpath('.//img')[0].attrib.get('src').replace('&w=32&h=32', '&w=64&h=64')
+        thumbnail_src = base_url\
+            + eval_xpath_getindex(result, './/img', 0).attrib.get('src').replace('&w=32&h=32', '&w=64&h=64')
 
         res = {
             'url': url,
diff --git a/searx/engines/archlinux.py b/searx/engines/archlinux.py
index 8f93f4f38..04117c07d 100644
--- a/searx/engines/archlinux.py
+++ b/searx/engines/archlinux.py
@@ -13,7 +13,7 @@
 
 from urllib.parse import urlencode, urljoin
 from lxml import html
-from searx.utils import extract_text
+from searx.utils import extract_text, eval_xpath_list, eval_xpath_getindex
 
 # engine dependent config
 categories = ['it']
@@ -131,8 +131,8 @@ def response(resp):
     dom = html.fromstring(resp.text)
 
     # parse results
-    for result in dom.xpath(xpath_results):
-        link = result.xpath(xpath_link)[0]
+    for result in eval_xpath_list(dom, xpath_results):
+        link = eval_xpath_getindex(result, xpath_link, 0)
         href = urljoin(base_url, link.attrib.get('href'))
         title = extract_text(link)
 
diff --git a/searx/engines/arxiv.py b/searx/engines/arxiv.py
index 6e231c382..c702c5987 100644
--- a/searx/engines/arxiv.py
+++ b/searx/engines/arxiv.py
@@ -13,6 +13,7 @@
 
 from lxml import html
 from datetime import datetime
+from searx.utils import eval_xpath_list, eval_xpath_getindex
 
 
 categories = ['science']
@@ -42,29 +43,26 @@ def response(resp):
     results = []
 
     dom = html.fromstring(resp.content)
-    search_results = dom.xpath('//entry')
 
-    for entry in search_results:
-        title = entry.xpath('.//title')[0].text
+    for entry in eval_xpath_list(dom, '//entry'):
+        title = eval_xpath_getindex(entry, './/title', 0).text
 
-        url = entry.xpath('.//id')[0].text
+        url = eval_xpath_getindex(entry, './/id', 0).text
 
         content_string = '{doi_content}{abstract_content}'
 
-        abstract = entry.xpath('.//summary')[0].text
+        abstract = eval_xpath_getindex(entry, './/summary', 0).text
 
         #  If a doi is available, add it to the snipppet
-        try:
-            doi_content = entry.xpath('.//link[@title="doi"]')[0].text
-            content = content_string.format(doi_content=doi_content, abstract_content=abstract)
-        except:
-            content = content_string.format(doi_content="", abstract_content=abstract)
+        doi_element = eval_xpath_getindex(entry, './/link[@title="doi"]', 0, default=None)
+        doi_content = doi_element.text if doi_element is not None else ''
+        content = content_string.format(doi_content=doi_content, abstract_content=abstract)
 
         if len(content) > 300:
             content = content[0:300] + "..."
         # TODO: center snippet on query term
 
-        publishedDate = datetime.strptime(entry.xpath('.//published')[0].text, '%Y-%m-%dT%H:%M:%SZ')
+        publishedDate = datetime.strptime(eval_xpath_getindex(entry, './/published', 0).text, '%Y-%m-%dT%H:%M:%SZ')
 
         res_dict = {'url': url,
                     'title': title,
diff --git a/searx/engines/bing_news.py b/searx/engines/bing_news.py
index 5489c7549..b95def48b 100644
--- a/searx/engines/bing_news.py
+++ b/searx/engines/bing_news.py
@@ -15,7 +15,8 @@ from datetime import datetime
 from dateutil import parser
 from urllib.parse import urlencode, urlparse, parse_qsl
 from lxml import etree
-from searx.utils import list_get, match_language
+from lxml.etree import XPath
+from searx.utils import match_language, eval_xpath_getindex
 from searx.engines.bing import language_aliases
 from searx.engines.bing import _fetch_supported_languages, supported_languages_url  # NOQA # pylint: disable=unused-import
 
@@ -94,12 +95,12 @@ def response(resp):
     # parse results
     for item in rss.xpath('./channel/item'):
         # url / title / content
-        url = url_cleanup(item.xpath('./link/text()')[0])
-        title = list_get(item.xpath('./title/text()'), 0, url)
-        content = list_get(item.xpath('./description/text()'), 0, '')
+        url = url_cleanup(eval_xpath_getindex(item, './link/text()', 0, default=None))
+        title = eval_xpath_getindex(item, './title/text()', 0, default=url)
+        content = eval_xpath_getindex(item, './description/text()', 0, default='')
 
         # publishedDate
-        publishedDate = list_get(item.xpath('./pubDate/text()'), 0)
+        publishedDate = eval_xpath_getindex(item, './pubDate/text()', 0, default=None)
         try:
             publishedDate = parser.parse(publishedDate, dayfirst=False)
         except TypeError:
@@ -108,7 +109,7 @@ def response(resp):
             publishedDate = datetime.now()
 
         # thumbnail
-        thumbnail = list_get(item.xpath('./News:Image/text()', namespaces=ns), 0)
+        thumbnail = eval_xpath_getindex(item, XPath('./News:Image/text()', namespaces=ns), 0, default=None)
         if thumbnail is not None:
             thumbnail = image_url_cleanup(thumbnail)
 
diff --git a/searx/engines/duckduckgo_images.py b/searx/engines/duckduckgo_images.py
index 438a8d54c..009f81cca 100644
--- a/searx/engines/duckduckgo_images.py
+++ b/searx/engines/duckduckgo_images.py
@@ -15,6 +15,7 @@
 
 from json import loads
 from urllib.parse import urlencode
+from searx.exceptions import SearxEngineAPIException
 from searx.engines.duckduckgo import get_region_code
 from searx.engines.duckduckgo import _fetch_supported_languages, supported_languages_url  # NOQA # pylint: disable=unused-import
 from searx.poolrequests import get
@@ -37,7 +38,7 @@ def get_vqd(query, headers):
     res = get(query_url, headers=headers)
     content = res.text
     if content.find('vqd=\'') == -1:
-        raise Exception('Request failed')
+        raise SearxEngineAPIException('Request failed')
     vqd = content[content.find('vqd=\'') + 5:]
     vqd = vqd[:vqd.find('\'')]
     return vqd
@@ -71,10 +72,7 @@ def response(resp):
     results = []
 
     content = resp.text
-    try:
-        res_json = loads(content)
-    except:
-        raise Exception('Cannot parse results')
+    res_json = loads(content)
 
     # parse results
     for result in res_json['results']:
diff --git a/searx/engines/elasticsearch.py b/searx/engines/elasticsearch.py
index 99e93d876..081736c1c 100644
--- a/searx/engines/elasticsearch.py
+++ b/searx/engines/elasticsearch.py
@@ -1,5 +1,6 @@
 from json import loads, dumps
 from requests.auth import HTTPBasicAuth
+from searx.exceptions import SearxEngineAPIException
 
 
 base_url = 'http://localhost:9200'
@@ -107,7 +108,7 @@ def response(resp):
 
     resp_json = loads(resp.text)
     if 'error' in resp_json:
-        raise Exception(resp_json['error'])
+        raise SearxEngineAPIException(resp_json['error'])
 
     for result in resp_json['hits']['hits']:
         r = {key: str(value) if not key.startswith('_') else value for key, value in result['_source'].items()}
diff --git a/searx/engines/google.py b/searx/engines/google.py
index 83b18a9a0..17ab21f6a 100644
--- a/searx/engines/google.py
+++ b/searx/engines/google.py
@@ -20,9 +20,10 @@ Definitions`_.
 
 from urllib.parse import urlencode, urlparse
 from lxml import html
-from flask_babel import gettext
 from searx import logger
-from searx.utils import match_language, extract_text, eval_xpath
+from searx.utils import match_language, extract_text, eval_xpath, eval_xpath_list, eval_xpath_getindex
+from searx.exceptions import SearxEngineCaptchaException
+
 
 logger = logger.getChild('google engine')
 
@@ -131,14 +132,6 @@ suggestion_xpath = '//div[contains(@class, "card-section")]//a'
 spelling_suggestion_xpath = '//div[@class="med"]/p/a'
 
 
-def extract_text_from_dom(result, xpath):
-    """returns extract_text on the first result selected by the xpath or None"""
-    r = eval_xpath(result, xpath)
-    if len(r) > 0:
-        return extract_text(r[0])
-    return None
-
-
 def get_lang_country(params, lang_list, custom_aliases):
     """Returns a tuple with *langauage* on its first and *country* on its second
     position."""
@@ -210,10 +203,10 @@ def response(resp):
     # detect google sorry
     resp_url = urlparse(resp.url)
     if resp_url.netloc == 'sorry.google.com' or resp_url.path == '/sorry/IndexRedirect':
-        raise RuntimeWarning('sorry.google.com')
+        raise SearxEngineCaptchaException()
 
     if resp_url.path.startswith('/sorry'):
-        raise RuntimeWarning(gettext('CAPTCHA required'))
+        raise SearxEngineCaptchaException()
 
     # which subdomain ?
     # subdomain = resp.search_params.get('google_subdomain')
@@ -229,18 +222,17 @@ def response(resp):
         logger.debug("did not found 'answer'")
 
     # results --> number_of_results
-    try:
-        _txt = eval_xpath(dom, '//div[@id="result-stats"]//text()')[0]
-        _digit = ''.join([n for n in _txt if n.isdigit()])
-        number_of_results = int(_digit)
-        results.append({'number_of_results': number_of_results})
-
-    except Exception as e:  # pylint: disable=broad-except
-        logger.debug("did not 'number_of_results'")
-        logger.error(e, exc_info=True)
+        try:
+            _txt = eval_xpath_getindex(dom, '//div[@id="result-stats"]//text()', 0)
+            _digit = ''.join([n for n in _txt if n.isdigit()])
+            number_of_results = int(_digit)
+            results.append({'number_of_results': number_of_results})
+        except Exception as e:  # pylint: disable=broad-except
+            logger.debug("did not 'number_of_results'")
+            logger.error(e, exc_info=True)
 
     # parse results
-    for result in eval_xpath(dom, results_xpath):
+    for result in eval_xpath_list(dom, results_xpath):
 
         # google *sections*
         if extract_text(eval_xpath(result, g_section_with_header)):
@@ -248,14 +240,14 @@ def response(resp):
             continue
 
         try:
-            title_tag = eval_xpath(result, title_xpath)
-            if not title_tag:
+            title_tag = eval_xpath_getindex(result, title_xpath, 0, default=None)
+            if title_tag is None:
                 # this not one of the common google results *section*
                 logger.debug('ingoring <div class="g" ../> section: missing title')
                 continue
-            title = extract_text(title_tag[0])
-            url = eval_xpath(result, href_xpath)[0]
-            content = extract_text_from_dom(result, content_xpath)
+            title = extract_text(title_tag)
+            url = eval_xpath_getindex(result, href_xpath, 0)
+            content = extract_text(eval_xpath_getindex(result, content_xpath, 0, default=None), allow_none=True)
             results.append({
                 'url': url,
                 'title': title,
@@ -270,11 +262,11 @@ def response(resp):
             continue
 
     # parse suggestion
-    for suggestion in eval_xpath(dom, suggestion_xpath):
+    for suggestion in eval_xpath_list(dom, suggestion_xpath):
         # append suggestion
         results.append({'suggestion': extract_text(suggestion)})
 
-    for correction in eval_xpath(dom, spelling_suggestion_xpath):
+    for correction in eval_xpath_list(dom, spelling_suggestion_xpath):
         results.append({'correction': extract_text(correction)})
 
     # return results
@@ -286,7 +278,7 @@ def _fetch_supported_languages(resp):
     ret_val = {}
     dom = html.fromstring(resp.text)
 
-    radio_buttons = eval_xpath(dom, '//*[@id="langSec"]//input[@name="lr"]')
+    radio_buttons = eval_xpath_list(dom, '//*[@id="langSec"]//input[@name="lr"]')
 
     for x in radio_buttons:
         name = x.get("data-name")
diff --git a/searx/engines/google_images.py b/searx/engines/google_images.py
index a3daf6070..9ef1be753 100644
--- a/searx/engines/google_images.py
+++ b/searx/engines/google_images.py
@@ -26,8 +26,8 @@ Definitions`_.
 
 from urllib.parse import urlencode, urlparse, unquote
 from lxml import html
-from flask_babel import gettext
 from searx import logger
+from searx.exceptions import SearxEngineCaptchaException
 from searx.utils import extract_text, eval_xpath
 from searx.engines.google import _fetch_supported_languages, supported_languages_url  # NOQA # pylint: disable=unused-import
 
@@ -128,10 +128,10 @@ def response(resp):
     # detect google sorry
     resp_url = urlparse(resp.url)
     if resp_url.netloc == 'sorry.google.com' or resp_url.path == '/sorry/IndexRedirect':
-        raise RuntimeWarning('sorry.google.com')
+        raise SearxEngineCaptchaException()
 
     if resp_url.path.startswith('/sorry'):
-        raise RuntimeWarning(gettext('CAPTCHA required'))
+        raise SearxEngineCaptchaException()
 
     # which subdomain ?
     # subdomain = resp.search_params.get('google_subdomain')
diff --git a/searx/engines/google_videos.py b/searx/engines/google_videos.py
index 1e6c8b3ee..eedefbf45 100644
--- a/searx/engines/google_videos.py
+++ b/searx/engines/google_videos.py
@@ -13,7 +13,7 @@
 from datetime import date, timedelta
 from urllib.parse import urlencode
 from lxml import html
-from searx.utils import extract_text
+from searx.utils import extract_text, eval_xpath, eval_xpath_list, eval_xpath_getindex
 import re
 
 # engine dependent config
@@ -66,11 +66,11 @@ def response(resp):
     dom = html.fromstring(resp.text)
 
     # parse results
-    for result in dom.xpath('//div[@class="g"]'):
+    for result in eval_xpath_list(dom, '//div[@class="g"]'):
 
-        title = extract_text(result.xpath('.//h3'))
-        url = result.xpath('.//div[@class="r"]/a/@href')[0]
-        content = extract_text(result.xpath('.//span[@class="st"]'))
+        title = extract_text(eval_xpath(result, './/h3'))
+        url = eval_xpath_getindex(result, './/div[@class="r"]/a/@href', 0)
+        content = extract_text(eval_xpath(result, './/span[@class="st"]'))
 
         # get thumbnails
         script = str(dom.xpath('//script[contains(., "_setImagesSrc")]')[0].text)
diff --git a/searx/engines/xpath.py b/searx/engines/xpath.py
index a569d9160..d420e250a 100644
--- a/searx/engines/xpath.py
+++ b/searx/engines/xpath.py
@@ -1,6 +1,6 @@
 from lxml import html
 from urllib.parse import urlencode
-from searx.utils import extract_text, extract_url, eval_xpath
+from searx.utils import extract_text, extract_url, eval_xpath, eval_xpath_list
 
 search_url = None
 url_xpath = None
@@ -42,21 +42,22 @@ def response(resp):
     is_onion = True if 'onions' in categories else False
 
     if results_xpath:
-        for result in eval_xpath(dom, results_xpath):
-            url = extract_url(eval_xpath(result, url_xpath), search_url)
-            title = extract_text(eval_xpath(result, title_xpath))
-            content = extract_text(eval_xpath(result, content_xpath))
+        for result in eval_xpath_list(dom, results_xpath):
+            url = extract_url(eval_xpath_list(result, url_xpath, min_len=1), search_url)
+            title = extract_text(eval_xpath_list(result, title_xpath, min_len=1))
+            content = extract_text(eval_xpath_list(result, content_xpath, min_len=1))
             tmp_result = {'url': url, 'title': title, 'content': content}
 
             # add thumbnail if available
             if thumbnail_xpath:
-                thumbnail_xpath_result = eval_xpath(result, thumbnail_xpath)
+                thumbnail_xpath_result = eval_xpath_list(result, thumbnail_xpath)
                 if len(thumbnail_xpath_result) > 0:
                     tmp_result['img_src'] = extract_url(thumbnail_xpath_result, search_url)
 
             # add alternative cached url if available
             if cached_xpath:
-                tmp_result['cached_url'] = cached_url + extract_text(result.xpath(cached_xpath))
+                tmp_result['cached_url'] = cached_url\
+                    + extract_text(eval_xpath_list(result, cached_xpath, min_len=1))
 
             if is_onion:
                 tmp_result['is_onion'] = True
@@ -66,19 +67,19 @@ def response(resp):
         if cached_xpath:
             for url, title, content, cached in zip(
                 (extract_url(x, search_url) for
-                 x in dom.xpath(url_xpath)),
-                map(extract_text, dom.xpath(title_xpath)),
-                map(extract_text, dom.xpath(content_xpath)),
-                map(extract_text, dom.xpath(cached_xpath))
+                 x in eval_xpath_list(dom, url_xpath)),
+                map(extract_text, eval_xpath_list(dom, title_xpath)),
+                map(extract_text, eval_xpath_list(dom, content_xpath)),
+                map(extract_text, eval_xpath_list(dom, cached_xpath))
             ):
                 results.append({'url': url, 'title': title, 'content': content,
                                 'cached_url': cached_url + cached, 'is_onion': is_onion})
         else:
             for url, title, content in zip(
                 (extract_url(x, search_url) for
-                 x in dom.xpath(url_xpath)),
-                map(extract_text, dom.xpath(title_xpath)),
-                map(extract_text, dom.xpath(content_xpath))
+                 x in eval_xpath_list(dom, url_xpath)),
+                map(extract_text, eval_xpath_list(dom, title_xpath)),
+                map(extract_text, eval_xpath_list(dom, content_xpath))
             ):
                 results.append({'url': url, 'title': title, 'content': content, 'is_onion': is_onion})
 
diff --git a/searx/engines/youtube_api.py b/searx/engines/youtube_api.py
index 4a205ed6c..8c12ac4d2 100644
--- a/searx/engines/youtube_api.py
+++ b/searx/engines/youtube_api.py
@@ -11,6 +11,7 @@
 from json import loads
 from dateutil import parser
 from urllib.parse import urlencode
+from searx.exceptions import SearxEngineAPIException
 
 # engine dependent config
 categories = ['videos', 'music']
@@ -48,7 +49,7 @@ def response(resp):
     search_results = loads(resp.text)
 
     if 'error' in search_results and 'message' in search_results['error']:
-        raise Exception(search_results['error']['message'])
+        raise SearxEngineAPIException(search_results['error']['message'])
 
     # return empty array if there are no results
     if 'items' not in search_results:
diff --git a/searx/exceptions.py b/searx/exceptions.py
index 2d1b1167e..82c1d76dc 100644
--- a/searx/exceptions.py
+++ b/searx/exceptions.py
@@ -34,8 +34,45 @@ class SearxParameterException(SearxException):
 
 
 class SearxSettingsException(SearxException):
+    """Error while loading the settings"""
 
     def __init__(self, message, filename):
         super().__init__(message)
         self.message = message
         self.filename = filename
+
+
+class SearxEngineException(SearxException):
+    """Error inside an engine"""
+
+
+class SearxXPathSyntaxException(SearxEngineException):
+    """Syntax error in a XPATH"""
+
+    def __init__(self, xpath_spec, message):
+        super().__init__(str(xpath_spec) + " " + message)
+        self.message = message
+        # str(xpath_spec) to deal with str and XPath instance
+        self.xpath_str = str(xpath_spec)
+
+
+class SearxEngineResponseException(SearxEngineException):
+    """Impossible to parse the result of an engine"""
+
+
+class SearxEngineAPIException(SearxEngineResponseException):
+    """The website has returned an application error"""
+
+
+class SearxEngineCaptchaException(SearxEngineResponseException):
+    """The website has returned a CAPTCHA"""
+
+
+class SearxEngineXPathException(SearxEngineResponseException):
+    """Error while getting the result of an XPath expression"""
+
+    def __init__(self, xpath_spec, message):
+        super().__init__(str(xpath_spec) + " " + message)
+        self.message = message
+        # str(xpath_spec) to deal with str and XPath instance
+        self.xpath_str = str(xpath_spec)
diff --git a/searx/metrology/__init__.py b/searx/metrology/__init__.py
new file mode 100644
index 000000000..e69de29bb
--- /dev/null
+++ b/searx/metrology/__init__.py
diff --git a/searx/metrology/error_recorder.py b/searx/metrology/error_recorder.py
new file mode 100644
index 000000000..4b67235e1
--- /dev/null
+++ b/searx/metrology/error_recorder.py
@@ -0,0 +1,142 @@
+import typing
+import inspect
+import logging
+from json import JSONDecodeError
+from urllib.parse import urlparse
+from requests.exceptions import RequestException
+from searx.exceptions import SearxXPathSyntaxException, SearxEngineXPathException
+from searx import logger
+
+
+logging.basicConfig(level=logging.INFO)
+
+errors_per_engines = {}
+
+
+class ErrorContext:
+
+    __slots__ = 'filename', 'function', 'line_no', 'code', 'exception_classname', 'log_message', 'log_parameters'
+
+    def __init__(self, filename, function, line_no, code, exception_classname, log_message, log_parameters):
+        self.filename = filename
+        self.function = function
+        self.line_no = line_no
+        self.code = code
+        self.exception_classname = exception_classname
+        self.log_message = log_message
+        self.log_parameters = log_parameters
+
+    def __eq__(self, o) -> bool:
+        if not isinstance(o, ErrorContext):
+            return False
+        return self.filename == o.filename and self.function == o.function and self.line_no == o.line_no\
+            and self.code == o.code and self.exception_classname == o.exception_classname\
+            and self.log_message == o.log_message and self.log_parameters == o.log_parameters
+
+    def __hash__(self):
+        return hash((self.filename, self.function, self.line_no, self.code, self.exception_classname, self.log_message,
+                     self.log_parameters))
+
+    def __repr__(self):
+        return "ErrorContext({!r}, {!r}, {!r}, {!r}, {!r}, {!r})".\
+            format(self.filename, self.line_no, self.code, self.exception_classname, self.log_message,
+                   self.log_parameters)
+
+
+def add_error_context(engine_name: str, error_context: ErrorContext) -> None:
+    errors_for_engine = errors_per_engines.setdefault(engine_name, {})
+    errors_for_engine[error_context] = errors_for_engine.get(error_context, 0) + 1
+    logger.debug('⚠️ %s: %s', engine_name, str(error_context))
+
+
+def get_trace(traces):
+    previous_trace = traces[-1]
+    for trace in reversed(traces):
+        if trace.filename.endswith('searx/search.py'):
+            if previous_trace.filename.endswith('searx/poolrequests.py'):
+                return trace
+            if previous_trace.filename.endswith('requests/models.py'):
+                return trace
+            return previous_trace
+        previous_trace = trace
+    return traces[-1]
+
+
+def get_hostname(exc: RequestException) -> typing.Optional[None]:
+    url = exc.request.url
+    if url is None and exc.response is not None:
+        url = exc.response.url
+    return urlparse(url).netloc
+
+
+def get_request_exception_messages(exc: RequestException)\
+        -> typing.Tuple[typing.Optional[str], typing.Optional[str], typing.Optional[str]]:
+    url = None
+    status_code = None
+    reason = None
+    hostname = None
+    if exc.request is not None:
+        url = exc.request.url
+    if url is None and exc.response is not None:
+        url = exc.response.url
+    if url is not None:
+        hostname = str(urlparse(url).netloc)
+    if exc.response is not None:
+        status_code = str(exc.response.status_code)
+        reason = exc.response.reason
+    return (status_code, reason, hostname)
+
+
+def get_messages(exc, filename) -> typing.Tuple:
+    if isinstance(exc, JSONDecodeError):
+        return (exc.msg, )
+    if isinstance(exc, TypeError):
+        return (str(exc), )
+    if isinstance(exc, ValueError) and 'lxml' in filename:
+        return (str(exc), )
+    if isinstance(exc, RequestException):
+        return get_request_exception_messages(exc)
+    if isinstance(exc, SearxXPathSyntaxException):
+        return (exc.xpath_str, exc.message)
+    if isinstance(exc, SearxEngineXPathException):
+        return (exc.xpath_str, exc.message)
+    return ()
+
+
+def get_exception_classname(exc: Exception) -> str:
+    exc_class = exc.__class__
+    exc_name = exc_class.__qualname__
+    exc_module = exc_class.__module__
+    if exc_module is None or exc_module == str.__class__.__module__:
+        return exc_name
+    return exc_module + '.' + exc_name
+
+
+def get_error_context(framerecords, exception_classname, log_message, log_parameters) -> ErrorContext:
+    searx_frame = get_trace(framerecords)
+    filename = searx_frame.filename
+    function = searx_frame.function
+    line_no = searx_frame.lineno
+    code = searx_frame.code_context[0].strip()
+    del framerecords
+    return ErrorContext(filename, function, line_no, code, exception_classname, log_message, log_parameters)
+
+
+def record_exception(engine_name: str, exc: Exception) -> None:
+    framerecords = inspect.trace()
+    try:
+        exception_classname = get_exception_classname(exc)
+        log_parameters = get_messages(exc, framerecords[-1][1])
+        error_context = get_error_context(framerecords, exception_classname, None, log_parameters)
+        add_error_context(engine_name, error_context)
+    finally:
+        del framerecords
+
+
+def record_error(engine_name: str, log_message: str, log_parameters: typing.Optional[typing.Tuple] = None) -> None:
+    framerecords = list(reversed(inspect.stack()[1:]))
+    try:
+        error_context = get_error_context(framerecords, None, log_message, log_parameters or ())
+        add_error_context(engine_name, error_context)
+    finally:
+        del framerecords
diff --git a/searx/results.py b/searx/results.py
index 46f44e1ad..5bf4e6b9e 100644
--- a/searx/results.py
+++ b/searx/results.py
@@ -4,6 +4,7 @@ from threading import RLock
 from urllib.parse import urlparse, unquote
 from searx import logger
 from searx.engines import engines
+from searx.metrology.error_recorder import record_error
 
 
 CONTENT_LEN_IGNORED_CHARS_REGEX = re.compile(r'[,;:!?\./\\\\ ()-_]', re.M | re.U)
@@ -161,6 +162,7 @@ class ResultContainer:
 
     def extend(self, engine_name, results):
         standard_result_count = 0
+        error_msgs = set()
         for result in list(results):
             result['engine'] = engine_name
             if 'suggestion' in result:
@@ -177,14 +179,21 @@ class ResultContainer:
                 # standard result (url, title, content)
                 if 'url' in result and not isinstance(result['url'], str):
                     logger.debug('result: invalid URL: %s', str(result))
+                    error_msgs.add('invalid URL')
                 elif 'title' in result and not isinstance(result['title'], str):
                     logger.debug('result: invalid title: %s', str(result))
+                    error_msgs.add('invalid title')
                 elif 'content' in result and not isinstance(result['content'], str):
                     logger.debug('result: invalid content: %s', str(result))
+                    error_msgs.add('invalid content')
                 else:
                     self._merge_result(result, standard_result_count + 1)
                     standard_result_count += 1
 
+        if len(error_msgs) > 0:
+            for msg in error_msgs:
+                record_error(engine_name, 'some results are invalids: ' + msg)
+
         if engine_name in engines:
             with RLock():
                 engines[engine_name].stats['search_count'] += 1
diff --git a/searx/search.py b/searx/search.py
index a3b80249e..8898f1576 100644
--- a/searx/search.py
+++ b/searx/search.py
@@ -20,6 +20,7 @@ import gc
 import threading
 from time import time
 from uuid import uuid4
+from urllib.parse import urlparse
 from _thread import start_new_thread
 
 import requests.exceptions
@@ -31,6 +32,8 @@ from searx.utils import gen_useragent
 from searx.results import ResultContainer
 from searx import logger
 from searx.plugins import plugins
+from searx.exceptions import SearxEngineCaptchaException
+from searx.metrology.error_recorder import record_exception, record_error
 
 
 logger = logger.getChild('search')
@@ -120,6 +123,14 @@ def send_http_request(engine, request_params):
     if hasattr(engine, 'proxies'):
         request_args['proxies'] = requests_lib.get_proxies(engine.proxies)
 
+    # max_redirects
+    max_redirects = request_params.get('max_redirects')
+    if max_redirects:
+        request_args['max_redirects'] = max_redirects
+
+    # soft_max_redirects
+    soft_max_redirects = request_params.get('soft_max_redirects', max_redirects or 0)
+
     # specific type of request (GET or POST)
     if request_params['method'] == 'GET':
         req = requests_lib.get
@@ -129,7 +140,23 @@ def send_http_request(engine, request_params):
     request_args['data'] = request_params['data']
 
     # send the request
-    return req(request_params['url'], **request_args)
+    response = req(request_params['url'], **request_args)
+
+    # check HTTP status
+    response.raise_for_status()
+
+    # check soft limit of the redirect count
+    if len(response.history) > soft_max_redirects:
+        # unexpected redirect : record an error
+        # but the engine might still return valid results.
+        status_code = str(response.status_code or '')
+        reason = response.reason or ''
+        hostname = str(urlparse(response.url or '').netloc)
+        record_error(engine.name,
+                     '{} redirects, maximum: {}'.format(len(response.history), soft_max_redirects),
+                     (status_code, reason, hostname))
+
+    return response
 
 
 def search_one_http_request(engine, query, request_params):
@@ -183,8 +210,9 @@ def search_one_http_request_safe(engine_name, query, request_params, result_cont
                 # update stats with the total HTTP time
                 engine.stats['page_load_time'] += page_load_time
                 engine.stats['page_load_count'] += 1
-
     except Exception as e:
+        record_exception(engine_name, e)
+
         # Timing
         engine_time = time() - start_time
         page_load_time = requests_lib.get_time_for_thread()
@@ -195,23 +223,29 @@ def search_one_http_request_safe(engine_name, query, request_params, result_cont
             engine.stats['errors'] += 1
 
         if (issubclass(e.__class__, requests.exceptions.Timeout)):
-            result_container.add_unresponsive_engine(engine_name, 'timeout')
+            result_container.add_unresponsive_engine(engine_name, 'HTTP timeout')
             # requests timeout (connect or read)
             logger.error("engine {0} : HTTP requests timeout"
                          "(search duration : {1} s, timeout: {2} s) : {3}"
                          .format(engine_name, engine_time, timeout_limit, e.__class__.__name__))
             requests_exception = True
         elif (issubclass(e.__class__, requests.exceptions.RequestException)):
-            result_container.add_unresponsive_engine(engine_name, 'request exception')
+            result_container.add_unresponsive_engine(engine_name, 'HTTP error')
             # other requests exception
             logger.exception("engine {0} : requests exception"
                              "(search duration : {1} s, timeout: {2} s) : {3}"
                              .format(engine_name, engine_time, timeout_limit, e))
             requests_exception = True
+        elif (issubclass(e.__class__, SearxEngineCaptchaException)):
+            result_container.add_unresponsive_engine(engine_name, 'CAPTCHA required')
+            logger.exception('engine {0} : CAPTCHA')
         else:
-            result_container.add_unresponsive_engine(engine_name, 'unexpected crash', str(e))
+            result_container.add_unresponsive_engine(engine_name, 'unexpected crash')
             # others errors
             logger.exception('engine {0} : exception : {1}'.format(engine_name, e))
+    else:
+        if getattr(threading.current_thread(), '_timeout', False):
+            record_error(engine_name, 'Timeout')
 
     # suspend or not the engine if there are HTTP errors
     with threading.RLock():
@@ -255,12 +289,17 @@ def search_one_offline_request_safe(engine_name, query, request_params, result_c
                 engine.stats['engine_time_count'] += 1
 
     except ValueError as e:
+        record_exception(engine_name, e)
         record_offline_engine_stats_on_error(engine, result_container, start_time)
         logger.exception('engine {0} : invalid input : {1}'.format(engine_name, e))
     except Exception as e:
+        record_exception(engine_name, e)
         record_offline_engine_stats_on_error(engine, result_container, start_time)
         result_container.add_unresponsive_engine(engine_name, 'unexpected crash', str(e))
         logger.exception('engine {0} : exception : {1}'.format(engine_name, e))
+    else:
+        if getattr(threading.current_thread(), '_timeout', False):
+            record_error(engine_name, 'Timeout')
 
 
 def search_one_request_safe(engine_name, query, request_params, result_container, start_time, timeout_limit):
@@ -278,6 +317,7 @@ def search_multiple_requests(requests, result_container, start_time, timeout_lim
             args=(engine_name, query, request_params, result_container, start_time, timeout_limit),
             name=search_id,
         )
+        th._timeout = False
         th._engine_name = engine_name
         th.start()
 
@@ -286,6 +326,7 @@ def search_multiple_requests(requests, result_container, start_time, timeout_lim
             remaining_time = max(0.0, timeout_limit - (time() - start_time))
             th.join(remaining_time)
             if th.is_alive():
+                th._timeout = True
                 result_container.add_unresponsive_engine(th._engine_name, 'timeout')
                 logger.warning('engine timeout: {0}'.format(th._engine_name))
 
@@ -385,6 +426,9 @@ class Search:
         request_params['category'] = engineref.category
         request_params['pageno'] = self.search_query.pageno
 
+        with threading.RLock():
+            engine.stats['sent_search_count'] += 1
+
         return request_params, engine.timeout
 
     # do search-request
diff --git a/searx/utils.py b/searx/utils.py
index 738f2c4d5..057e9d004 100644
--- a/searx/utils.py
+++ b/searx/utils.py
@@ -10,7 +10,7 @@ from html.parser import HTMLParser
 from urllib.parse import urljoin, urlparse
 
 from lxml import html
-from lxml.etree import XPath, _ElementStringResult, _ElementUnicodeResult
+from lxml.etree import ElementBase, XPath, XPathError, XPathSyntaxError, _ElementStringResult, _ElementUnicodeResult
 from babel.core import get_global
 
 
@@ -18,6 +18,7 @@ from searx import settings
 from searx.data import USER_AGENTS
 from searx.version import VERSION_STRING
 from searx.languages import language_codes
+from searx.exceptions import SearxXPathSyntaxException, SearxEngineXPathException
 from searx import logger
 
 
@@ -33,6 +34,13 @@ xpath_cache = dict()
 lang_to_lc_cache = dict()
 
 
+class NotSetClass:
+    pass
+
+
+NOTSET = NotSetClass()
+
+
 def searx_useragent():
     """Return the searx User Agent"""
     return 'searx/{searx_version} {suffix}'.format(
@@ -125,7 +133,7 @@ def html_to_text(html_str):
     return s.get_text()
 
 
-def extract_text(xpath_results):
+def extract_text(xpath_results, allow_none=False):
     """Extract text from a lxml result
 
       * if xpath_results is list, extract the text from each result and concat the list
@@ -133,22 +141,27 @@ def extract_text(xpath_results):
         ( text_content() method from lxml )
       * if xpath_results is a string element, then it's already done
     """
-    if type(xpath_results) == list:
+    if isinstance(xpath_results, list):
         # it's list of result : concat everything using recursive call
         result = ''
         for e in xpath_results:
             result = result + extract_text(e)
         return result.strip()
-    elif type(xpath_results) in [_ElementStringResult, _ElementUnicodeResult]:
-        # it's a string
-        return ''.join(xpath_results)
-    else:
+    elif isinstance(xpath_results, ElementBase):
         # it's a element
         text = html.tostring(
             xpath_results, encoding='unicode', method='text', with_tail=False
         )
         text = text.strip().replace('\n', ' ')
         return ' '.join(text.split())
+    elif isinstance(xpath_results, (_ElementStringResult, _ElementUnicodeResult, str, Number, bool)):
+        return str(xpath_results)
+    elif xpath_results is None and allow_none:
+        return None
+    elif xpath_results is None and not allow_none:
+        raise ValueError('extract_text(None, allow_none=False)')
+    else:
+        raise ValueError('unsupported type')
 
 
 def normalize_url(url, base_url):
@@ -170,7 +183,7 @@ def normalize_url(url, base_url):
         >>> normalize_url('', 'https://example.com')
         'https://example.com/'
         >>> normalize_url('/test', '/path')
-        raise Exception
+        raise ValueError
 
     Raises:
         * lxml.etree.ParserError
@@ -194,7 +207,7 @@ def normalize_url(url, base_url):
 
     # add a / at this end of the url if there is no path
     if not parsed_url.netloc:
-        raise Exception('Cannot parse url')
+        raise ValueError('Cannot parse url')
     if not parsed_url.path:
         url += '/'
 
@@ -224,17 +237,17 @@ def extract_url(xpath_results, base_url):
         >>> f('', 'https://example.com')
         raise lxml.etree.ParserError
         >>> searx.utils.extract_url([], 'https://example.com')
-        raise Exception
+        raise ValueError
 
     Raises:
-        * Exception
+        * ValueError
         * lxml.etree.ParserError
 
     Returns:
         * str: normalized URL
     """
     if xpath_results == []:
-        raise Exception('Empty url resultset')
+        raise ValueError('Empty url resultset')
 
     url = extract_text(xpath_results)
     return normalize_url(url, base_url)
@@ -256,25 +269,6 @@ def dict_subset(d, properties):
     return result
 
 
-def list_get(a_list, index, default=None):
-    """Get element in list or default value
-
-    Examples:
-        >>> list_get(['A', 'B', 'C'], 0)
-        'A'
-        >>> list_get(['A', 'B', 'C'], 3)
-        None
-        >>> list_get(['A', 'B', 'C'], 3, 'default')
-        'default'
-        >>> list_get(['A', 'B', 'C'], -1)
-        'C'
-    """
-    if len(a_list) > index:
-        return a_list[index]
-    else:
-        return default
-
-
 def get_torrent_size(filesize, filesize_multiplier):
     """
 
@@ -310,7 +304,7 @@ def get_torrent_size(filesize, filesize_multiplier):
             filesize = int(filesize * 1000 * 1000)
         elif filesize_multiplier == 'KiB':
             filesize = int(filesize * 1000)
-    except:
+    except ValueError:
         filesize = None
 
     return filesize
@@ -506,20 +500,110 @@ def get_engine_from_settings(name):
     return {}
 
 
-def get_xpath(xpath_str):
+def get_xpath(xpath_spec):
     """Return cached compiled XPath
 
     There is no thread lock.
     Worst case scenario, xpath_str is compiled more than one time.
+
+    Args:
+        * xpath_spec (str|lxml.etree.XPath): XPath as a str or lxml.etree.XPath
+
+    Returns:
+        * result (bool, float, list, str): Results.
+
+    Raises:
+        * TypeError: Raise when xpath_spec is neither a str nor a lxml.etree.XPath
+        * SearxXPathSyntaxException: Raise when there is a syntax error in the XPath
     """
-    result = xpath_cache.get(xpath_str, None)
-    if result is None:
-        result = XPath(xpath_str)
-        xpath_cache[xpath_str] = result
+    if isinstance(xpath_spec, str):
+        result = xpath_cache.get(xpath_spec, None)
+        if result is None:
+            try:
+                result = XPath(xpath_spec)
+            except XPathSyntaxError as e:
+                raise SearxXPathSyntaxException(xpath_spec, str(e.msg))
+            xpath_cache[xpath_spec] = result
+        return result
+
+    if isinstance(xpath_spec, XPath):
+        return xpath_spec
+
+    raise TypeError('xpath_spec must be either a str or a lxml.etree.XPath')
+
+
+def eval_xpath(element, xpath_spec):
+    """Equivalent of element.xpath(xpath_str) but compile xpath_str once for all.
+    See https://lxml.de/xpathxslt.html#xpath-return-values
+
+    Args:
+        * element (ElementBase): [description]
+        * xpath_spec (str|lxml.etree.XPath): XPath as a str or lxml.etree.XPath
+
+    Returns:
+        * result (bool, float, list, str): Results.
+
+    Raises:
+        * TypeError: Raise when xpath_spec is neither a str nor a lxml.etree.XPath
+        * SearxXPathSyntaxException: Raise when there is a syntax error in the XPath
+        * SearxEngineXPathException: Raise when the XPath can't be evaluated.
+    """
+    xpath = get_xpath(xpath_spec)
+    try:
+        return xpath(element)
+    except XPathError as e:
+        arg = ' '.join([str(i) for i in e.args])
+        raise SearxEngineXPathException(xpath_spec, arg)
+
+
+def eval_xpath_list(element, xpath_spec, min_len=None):
+    """Same as eval_xpath, check if the result is a list
+
+    Args:
+        * element (ElementBase): [description]
+        * xpath_spec (str|lxml.etree.XPath): XPath as a str or lxml.etree.XPath
+        * min_len (int, optional): [description]. Defaults to None.
+
+    Raises:
+        * TypeError: Raise when xpath_spec is neither a str nor a lxml.etree.XPath
+        * SearxXPathSyntaxException: Raise when there is a syntax error in the XPath
+        * SearxEngineXPathException: raise if the result is not a list
+
+    Returns:
+        * result (bool, float, list, str): Results.
+    """
+    result = eval_xpath(element, xpath_spec)
+    if not isinstance(result, list):
+        raise SearxEngineXPathException(xpath_spec, 'the result is not a list')
+    if min_len is not None and min_len > len(result):
+        raise SearxEngineXPathException(xpath_spec, 'len(xpath_str) < ' + str(min_len))
     return result
 
 
-def eval_xpath(element, xpath_str):
-    """Equivalent of element.xpath(xpath_str) but compile xpath_str once for all."""
-    xpath = get_xpath(xpath_str)
-    return xpath(element)
+def eval_xpath_getindex(elements, xpath_spec, index, default=NOTSET):
+    """Call eval_xpath_list then get one element using the index parameter.
+    If the index does not exist, either aise an exception is default is not set,
+    other return the default value (can be None).
+
+    Args:
+        * elements (ElementBase): lxml element to apply the xpath.
+        * xpath_spec (str|lxml.etree.XPath): XPath as a str or lxml.etree.XPath.
+        * index (int): index to get
+        * default (Object, optional): Defaults if index doesn't exist.
+
+    Raises:
+        * TypeError: Raise when xpath_spec is neither a str nor a lxml.etree.XPath
+        * SearxXPathSyntaxException: Raise when there is a syntax error in the XPath
+        * SearxEngineXPathException: if the index is not found. Also see eval_xpath.
+
+    Returns:
+        * result (bool, float, list, str): Results.
+    """
+    result = eval_xpath_list(elements, xpath_spec)
+    if index >= -len(result) and index < len(result):
+        return result[index]
+    if default == NOTSET:
+        # raise an SearxEngineXPathException instead of IndexError
+        # to record xpath_spec
+        raise SearxEngineXPathException(xpath_spec, 'index ' + str(index) + ' not found')
+    return default
diff --git a/searx/webapp.py b/searx/webapp.py
index e73322a77..ace5a12dc 100755
--- a/searx/webapp.py
+++ b/searx/webapp.py
@@ -79,6 +79,7 @@ from searx.plugins.oa_doi_rewrite import get_doi_resolver
 from searx.preferences import Preferences, ValidationException, LANGUAGE_CODES
 from searx.answerers import answerers
 from searx.poolrequests import get_global_proxies
+from searx.metrology.error_recorder import errors_per_engines
 
 
 # serve pages with HTTP/1.1
@@ -943,6 +944,34 @@ def stats():
     )
 
 
+@app.route('/stats/errors', methods=['GET'])
+def stats_errors():
+    result = {}
+    engine_names = list(errors_per_engines.keys())
+    engine_names.sort()
+    for engine_name in engine_names:
+        error_stats = errors_per_engines[engine_name]
+        sent_search_count = max(engines[engine_name].stats['sent_search_count'], 1)
+        sorted_context_count_list = sorted(error_stats.items(), key=lambda context_count: context_count[1])
+        r = []
+        percentage_sum = 0
+        for context, count in sorted_context_count_list:
+            percentage = round(20 * count / sent_search_count) * 5
+            percentage_sum += percentage
+            r.append({
+                'filename': context.filename,
+                'function': context.function,
+                'line_no': context.line_no,
+                'code': context.code,
+                'exception_classname': context.exception_classname,
+                'log_message': context.log_message,
+                'log_parameters': context.log_parameters,
+                'percentage': percentage,
+            })
+        result[engine_name] = sorted(r, reverse=True, key=lambda d: d['percentage'])
+    return jsonify(result)
+
+
 @app.route('/robots.txt', methods=['GET'])
 def robots():
     return Response("""User-agent: *
diff --git a/tests/unit/test_utils.py b/tests/unit/test_utils.py
index f3a98ad71..2c244966b 100644
--- a/tests/unit/test_utils.py
+++ b/tests/unit/test_utils.py
@@ -3,6 +3,7 @@ import lxml.etree
 from lxml import html
 
 from searx.testing import SearxTestCase
+from searx.exceptions import SearxXPathSyntaxException, SearxEngineXPathException
 from searx import utils
 
 
@@ -57,8 +58,16 @@ class TestUtils(SearxTestCase):
         dom = html.fromstring(html_str)
         self.assertEqual(utils.extract_text(dom), 'Test text')
         self.assertEqual(utils.extract_text(dom.xpath('//span')), 'Test text')
+        self.assertEqual(utils.extract_text(dom.xpath('//span/text()')), 'Test text')
+        self.assertEqual(utils.extract_text(dom.xpath('count(//span)')), '3.0')
+        self.assertEqual(utils.extract_text(dom.xpath('boolean(//span)')), 'True')
         self.assertEqual(utils.extract_text(dom.xpath('//img/@src')), 'test.jpg')
         self.assertEqual(utils.extract_text(dom.xpath('//unexistingtag')), '')
+        self.assertEqual(utils.extract_text(None, allow_none=True), None)
+        with self.assertRaises(ValueError):
+            utils.extract_text(None)
+        with self.assertRaises(ValueError):
+            utils.extract_text({})
 
     def test_extract_url(self):
         def f(html_str, search_url):
@@ -136,3 +145,84 @@ class TestHTMLTextExtractor(SearxTestCase):
         text = '<p><b>Lorem ipsum</i>dolor sit amet</p>'
         with self.assertRaises(utils.HTMLTextExtractorException):
             self.html_text_extractor.feed(text)
+
+
+class TestXPathUtils(SearxTestCase):
+
+    TEST_DOC = """<ul>
+        <li>Text in <b>bold</b> and <i>italic</i> </li>
+        <li>Another <b>text</b> <img src="data:image/gif;base64,R0lGODlhAQABAIAAAAUEBAAAACwAAAAAAQABAAACAkQBADs="></li>
+        </ul>"""
+
+    def test_get_xpath_cache(self):
+        xp1 = utils.get_xpath('//a')
+        xp2 = utils.get_xpath('//div')
+        xp3 = utils.get_xpath('//a')
+
+        self.assertEqual(id(xp1), id(xp3))
+        self.assertNotEqual(id(xp1), id(xp2))
+
+    def test_get_xpath_type(self):
+        utils.get_xpath(lxml.etree.XPath('//a'))
+
+        with self.assertRaises(TypeError):
+            utils.get_xpath([])
+
+    def test_get_xpath_invalid(self):
+        invalid_xpath = '//a[0].text'
+        with self.assertRaises(SearxXPathSyntaxException) as context:
+            utils.get_xpath(invalid_xpath)
+
+        self.assertEqual(context.exception.message, 'Invalid expression')
+        self.assertEqual(context.exception.xpath_str, invalid_xpath)
+
+    def test_eval_xpath_unregistered_function(self):
+        doc = html.fromstring(TestXPathUtils.TEST_DOC)
+
+        invalid_function_xpath = 'int(//a)'
+        with self.assertRaises(SearxEngineXPathException) as context:
+            utils.eval_xpath(doc, invalid_function_xpath)
+
+        self.assertEqual(context.exception.message, 'Unregistered function')
+        self.assertEqual(context.exception.xpath_str, invalid_function_xpath)
+
+    def test_eval_xpath(self):
+        doc = html.fromstring(TestXPathUtils.TEST_DOC)
+
+        self.assertEqual(utils.eval_xpath(doc, '//p'), [])
+        self.assertEqual(utils.eval_xpath(doc, '//i/text()'), ['italic'])
+        self.assertEqual(utils.eval_xpath(doc, 'count(//i)'), 1.0)
+
+    def test_eval_xpath_list(self):
+        doc = html.fromstring(TestXPathUtils.TEST_DOC)
+
+        # check a not empty list
+        self.assertEqual(utils.eval_xpath_list(doc, '//i/text()'), ['italic'])
+
+        # check min_len parameter
+        with self.assertRaises(SearxEngineXPathException) as context:
+            utils.eval_xpath_list(doc, '//p', min_len=1)
+        self.assertEqual(context.exception.message, 'len(xpath_str) < 1')
+        self.assertEqual(context.exception.xpath_str, '//p')
+
+    def test_eval_xpath_getindex(self):
+        doc = html.fromstring(TestXPathUtils.TEST_DOC)
+
+        # check index 0
+        self.assertEqual(utils.eval_xpath_getindex(doc, '//i/text()', 0), 'italic')
+
+        # default is 'something'
+        self.assertEqual(utils.eval_xpath_getindex(doc, '//i/text()', 1, default='something'), 'something')
+
+        # default is None
+        self.assertEqual(utils.eval_xpath_getindex(doc, '//i/text()', 1, default=None), None)
+
+        # index not found
+        with self.assertRaises(SearxEngineXPathException) as context:
+            utils.eval_xpath_getindex(doc, '//i/text()', 1)
+        self.assertEqual(context.exception.message, 'index 1 not found')
+
+        # not a list
+        with self.assertRaises(SearxEngineXPathException) as context:
+            utils.eval_xpath_getindex(doc, 'count(//i)', 1)
+        self.assertEqual(context.exception.message, 'the result is not a list')