diff --git a/fbchat/_client.py b/fbchat/_client.py
index 838e004..c0550cd 100644
--- a/fbchat/_client.py
+++ b/fbchat/_client.py
@@ -418,10 +418,11 @@ class Client:
         Warning:
             This is not finished, and the API may change at any point!
         """
+        at = datetime.datetime.utcnow()
         form = {
             "folders[0]": "inbox",
             "client": "mercury",
-            "last_action_timestamp": _util.now() - 60 * 1000
+            "last_action_timestamp": _util.datetime_to_millis(at),
             # 'last_action_timestamp': 0
         }
         j = self.session._payload_post("/ajax/mercury/unread_threads.php", form)
@@ -547,11 +548,10 @@ class Client:
         """
         return self._read_status(False, threads, at)
 
-    def mark_as_seen(self):
+    def mark_as_seen(self, at: datetime.datetime):
         # TODO: Documenting this
-        j = self.session._payload_post(
-            "/ajax/mercury/mark_seen.php", {"seen_timestamp": _util.now()}
-        )
+        data = {"seen_timestamp": _util.datetime_to_millis(at)}
+        j = self.session._payload_post("/ajax/mercury/mark_seen.php", data)
 
     def move_threads(
         self, location: _models.ThreadLocation, threads: Iterable[_threads.ThreadABC]
diff --git a/fbchat/_graphql.py b/fbchat/_graphql.py
index b2d9b78..bb8a990 100644
--- a/fbchat/_graphql.py
+++ b/fbchat/_graphql.py
@@ -34,12 +34,12 @@ def queries_to_json(*queries):
     return _util.json_minimal(rtn)
 
 
-def response_to_json(content):
-    content = _util.strip_json_cruft(content)  # Usually only needed in some error cases
+def response_to_json(text):
+    text = _util.strip_json_cruft(text)  # Usually only needed in some error cases
     try:
-        j = json.loads(content, cls=ConcatJSONDecoder)
+        j = json.loads(text, cls=ConcatJSONDecoder)
     except Exception as e:
-        raise _exception.ParseError("Error while parsing JSON", data=content) from e
+        raise _exception.ParseError("Error while parsing JSON", data=text) from e
 
     rtn = [None] * (len(j))
     for x in j:
diff --git a/fbchat/_models/_location.py b/fbchat/_models/_location.py
index a4d46b2..07ee607 100644
--- a/fbchat/_models/_location.py
+++ b/fbchat/_models/_location.py
@@ -1,7 +1,7 @@
 import attr
 from . import Image, Attachment
 from .._common import attrs_default
-from .. import _util
+from .. import _util, _exception
 
 
 @attrs_default
@@ -26,6 +26,8 @@ class LocationAttachment(Attachment):
     def _from_graphql(cls, data):
         url = data.get("url")
         address = _util.get_url_parameter(_util.get_url_parameter(url, "u"), "where1")
+        if not address:
+            raise _exception.ParseError("Could not find location address", data=data)
         try:
             latitude, longitude = [float(x) for x in address.split(", ")]
             address = None
diff --git a/fbchat/_session.py b/fbchat/_session.py
index cbf95ca..5e42522 100644
--- a/fbchat/_session.py
+++ b/fbchat/_session.py
@@ -1,5 +1,6 @@
 import attr
 import bs4
+import datetime
 import re
 import requests
 import random
@@ -13,6 +14,32 @@ from typing import Optional, Tuple, Mapping, BinaryIO, Sequence, Iterable, Calla
 FB_DTSG_REGEX = re.compile(r'name="fb_dtsg" value="(.*?)"')
 
 
+def base36encode(number: int) -> str:
+    """Convert from Base10 to Base36."""
+    # Taken from https://en.wikipedia.org/wiki/Base36#Python_implementation
+    chars = "0123456789abcdefghijklmnopqrstuvwxyz"
+
+    sign = "-" if number < 0 else ""
+    number = abs(number)
+    result = ""
+
+    while number > 0:
+        number, remainder = divmod(number, 36)
+        result = chars[remainder] + result
+
+    return sign + result
+
+
+def prefix_url(url: str) -> str:
+    return "https://www.facebook.com" + url
+
+
+def generate_message_id(now: datetime.datetime, client_id: str) -> str:
+    k = _util.datetime_to_millis(now)
+    l = int(random.random() * 4294967295)
+    return "<{}:{}-{}@mail.projektitan.com>".format(k, l, client_id)
+
+
 def get_user_id(session: requests.Session) -> str:
     # TODO: Optimize this `.get_dict()` call!
     cookies = session.cookies.get_dict()
@@ -106,7 +133,7 @@ def get_error_data(html: str, url: str) -> Tuple[Optional[int], Optional[str]]:
     code = None
     try:
         code = int(_util.get_url_parameter(url, "e"))
-    except (IndexError, ValueError):
+    except (TypeError, ValueError):
         pass
 
     soup = bs4.BeautifulSoup(
@@ -143,7 +170,7 @@ class Session:
         self._counter += 1  # TODO: Make this operation atomic / thread-safe
         return {
             "__a": 1,
-            "__req": _util.str_base(self._counter, 36),
+            "__req": base36encode(self._counter),
             "__rev": self._revision,
             "fb_dtsg": self._fb_dtsg,
         }
@@ -244,14 +271,14 @@ class Session:
         """
         logout_h = self._logout_h
         if not logout_h:
-            url = _util.prefix_url("/bluebar/modern_settings_menu/")
+            url = prefix_url("/bluebar/modern_settings_menu/")
             try:
                 h_r = self._session.post(url, data={"pmid": "4"})
             except requests.RequestException as e:
                 _exception.handle_requests_error(e)
             logout_h = re.search(r'name=\\"h\\" value=\\"(.*?)\\"', h_r.text).group(1)
 
-        url = _util.prefix_url("/logout.php")
+        url = prefix_url("/logout.php")
         try:
             r = self._session.get(url, params={"ref": "mb", "h": logout_h})
         except requests.RequestException as e:
@@ -264,7 +291,7 @@ class Session:
         user_id = get_user_id(session)
 
         try:
-            r = session.get(_util.prefix_url("/"))
+            r = session.get(prefix_url("/"))
         except requests.RequestException as e:
             _exception.handle_requests_error(e)
 
@@ -320,26 +347,24 @@ class Session:
         session.cookies = requests.cookies.merge_cookies(session.cookies, cookies)
         return cls._from_session(session=session)
 
-    def _get(self, url, params, error_retries=3):
-        params.update(self._get_params())
-        try:
-            r = self._session.get(_util.prefix_url(url), params=params)
-        except requests.RequestException as e:
-            _exception.handle_requests_error(e)
-        content = _util.check_request(r)
-        return _util.to_json(content)
-
     def _post(self, url, data, files=None, as_graphql=False):
         data.update(self._get_params())
         try:
-            r = self._session.post(_util.prefix_url(url), data=data, files=files)
+            r = self._session.post(prefix_url(url), data=data, files=files)
         except requests.RequestException as e:
             _exception.handle_requests_error(e)
-        content = _util.check_request(r)
+        # Facebook's encoding is always UTF-8
+        r.encoding = "utf-8"
+        _exception.handle_http_error(r.status_code)
+        if r.text is None or len(r.text) == 0:
+            raise _exception.HTTPError("Error when sending request: Got empty response")
         if as_graphql:
-            return _graphql.response_to_json(content)
+            return _graphql.response_to_json(r.text)
         else:
-            return _util.to_json(content)
+            text = _util.strip_json_cruft(r.text)
+            j = parse_json(text)
+            log.debug(j)
+            return j
 
     def _payload_post(self, url, data, files=None):
         j = self._post(url, data, files=files)
@@ -393,14 +418,15 @@ class Session:
         ]
 
     def _do_send_request(self, data):
+        now = datetime.datetime.utcnow()
         offline_threading_id = _util.generate_offline_threading_id()
         data["client"] = "mercury"
         data["author"] = "fbid:{}".format(self._user_id)
-        data["timestamp"] = _util.now()
+        data["timestamp"] = _util.datetime_to_millis(now)
         data["source"] = "source:chat:web"
         data["offline_threading_id"] = offline_threading_id
         data["message_id"] = offline_threading_id
-        data["threading_id"] = _util.generate_message_id(self._client_id)
+        data["threading_id"] = generate_message_id(now, self._client_id)
         data["ephemeral_ttl_mode:"] = "0"
         j = self._post("/messaging/send/", data)
 
diff --git a/fbchat/_util.py b/fbchat/_util.py
index 9083966..ad411f2 100644
--- a/fbchat/_util.py
+++ b/fbchat/_util.py
@@ -38,10 +38,6 @@ def get_limits(limit: Optional[int], max_limit: int) -> Iterable[int]:
         yield remainder
 
 
-def now():
-    return int(time.time() * 1000)
-
-
 def json_minimal(data: Any) -> str:
     """Get JSON data in minimal form."""
     return json.dumps(data, separators=(",", ":"))
@@ -55,73 +51,21 @@ def strip_json_cruft(text: str) -> str:
         raise _exception.ParseError("No JSON object found", data=text) from e
 
 
-def get_decoded_r(r):
-    return get_decoded(r._content)
-
-
-def get_decoded(content):
-    return content.decode("utf-8")
-
-
-def parse_json(content: str) -> Any:
+def parse_json(text: str) -> Any:
     try:
-        return json.loads(content)
+        return json.loads(text)
     except ValueError as e:
-        raise _exception.ParseError("Error while parsing JSON", data=content) from e
-
-
-def digit_to_char(digit):
-    if digit < 10:
-        return str(digit)
-    return chr(ord("a") + digit - 10)
-
-
-def str_base(number, base):
-    if number < 0:
-        return "-" + str_base(-number, base)
-    (d, m) = divmod(number, base)
-    if d > 0:
-        return str_base(d, base) + digit_to_char(m)
-    return digit_to_char(m)
-
-
-def generate_message_id(client_id=None):
-    k = now()
-    l = int(random.random() * 4294967295)
-    return "<{}:{}-{}@mail.projektitan.com>".format(k, l, client_id)
-
-
-def get_signature_id():
-    return hex(int(random.random() * 2147483648))
+        raise _exception.ParseError("Error while parsing JSON", data=text) from e
 
 
 def generate_offline_threading_id():
-    ret = now()
+    ret = _util.datetime_to_millis(datetime.datetime.utcnow())
     value = int(random.random() * 4294967295)
     string = ("0000000000000000000000" + format(value, "b"))[-22:]
     msgs = format(ret, "b") + string
     return str(int(msgs, 2))
 
 
-def check_request(r):
-    _exception.handle_http_error(r.status_code)
-    content = get_decoded_r(r)
-    check_content(content)
-    return content
-
-
-def check_content(content, as_json=True):
-    if content is None or len(content) == 0:
-        raise _exception.HTTPError("Error when sending request: Got empty response")
-
-
-def to_json(content):
-    content = strip_json_cruft(content)
-    j = parse_json(content)
-    log.debug(j)
-    return j
-
-
 def get_jsmods_require(j, index):
     if j.get("jsmods") and j["jsmods"].get("require"):
         try:
@@ -145,19 +89,11 @@ def mimetype_to_key(mimetype: str) -> str:
     return "file_id"
 
 
-def get_url_parameters(url: str, *args):
+def get_url_parameter(url: str, param: str) -> Optional[str]:
     params = urllib.parse.parse_qs(urllib.parse.urlparse(url).query)
-    return [params[arg][0] for arg in args if params.get(arg)]
-
-
-def get_url_parameter(url: str, param: str) -> str:
-    return get_url_parameters(url, param)[0]
-
-
-def prefix_url(url: str) -> str:
-    if url.startswith("/"):
-        return "https://www.facebook.com" + url
-    return url
+    if not params.get(param):
+        return None
+    return params[param][0]
 
 
 def seconds_to_datetime(timestamp_in_seconds: float) -> datetime.datetime:
diff --git a/tests/test_graphql.py b/tests/test_graphql.py
index 7f48101..2392da2 100644
--- a/tests/test_graphql.py
+++ b/tests/test_graphql.py
@@ -4,7 +4,7 @@ from fbchat._graphql import ConcatJSONDecoder, queries_to_json, response_to_json
 
 
 @pytest.mark.parametrize(
-    "content,result",
+    "text,result",
     [
         ("", []),
         ('{"a":"b"}', [{"a": "b"}]),
@@ -12,8 +12,8 @@ from fbchat._graphql import ConcatJSONDecoder, queries_to_json, response_to_json
         (' \n{"a":  "b"  }     \n {  "b" \n\n : "c" }', [{"a": "b"}, {"b": "c"}]),
     ],
 )
-def test_concat_json_decoder(content, result):
-    assert result == json.loads(content, cls=ConcatJSONDecoder)
+def test_concat_json_decoder(text, result):
+    assert result == json.loads(text, cls=ConcatJSONDecoder)
 
 
 def test_queries_to_json():
diff --git a/tests/test_session.py b/tests/test_session.py
new file mode 100644
index 0000000..7bf56f3
--- /dev/null
+++ b/tests/test_session.py
@@ -0,0 +1,73 @@
+import datetime
+import pytest
+from fbchat._session import (
+    base36encode,
+    prefix_url,
+    generate_message_id,
+    client_id_factory,
+    is_home,
+    get_error_data,
+)
+
+
+@pytest.mark.parametrize(
+    "number,expected",
+    [(1, "1"), (10, "a"), (123, "3f"), (1000, "rs"), (123456789, "21i3v9")],
+)
+def test_base36encode(number, expected):
+    assert base36encode(number) == expected
+
+
+def test_prefix_url():
+    assert prefix_url("/") == "https://www.facebook.com/"
+    assert prefix_url("/abc") == "https://www.facebook.com/abc"
+
+
+def test_generate_message_id():
+    # Returns random output, so hard to test more thoroughly
+    assert generate_message_id(datetime.datetime.utcnow(), "def")
+
+
+def test_client_id_factory():
+    # Returns random output, so hard to test more thoroughly
+    assert client_id_factory()
+
+
+def test_is_home():
+    assert not is_home("https://m.facebook.com/login/?...")
+    assert is_home("https://m.facebook.com/home.php?refsrc=...")
+
+
+@pytest.mark.skip
+def test_get_error_data():
+    html = """<?xml version="1.0" encoding="utf-8"?>
+    <!DOCTYPE html PUBLIC "-//WAPFORUM//DTD XHTML Mobile 1.0//EN" "http://www.wapforum.org/DTD/xhtml-mobile10.dtd">
+    <html xmlns="http://www.w3.org/1999/xhtml">
+
+    <head>
+        <title>Log in to Facebook | Facebook</title>
+        <meta name="referrer" content="origin-when-crossorigin" id="meta_referrer" />
+        <style type="text/css">...</style>
+        <meta name="description" content="..." />
+        <link rel="canonical" href="https://www.facebook.com/login/" />
+    </head>
+
+    <body tabindex="0" class="b c d e f g">
+    <div class="h"><div id="viewport">...<div id="objects_container"><div class="g" id="root" role="main">
+    <table class="x" role="presentation"><tbody><tr><td class="y">
+    <div class="z ba bb" style="" id="login_error">
+        <div class="bc">
+            <span>The password you entered is incorrect. <a href="/recover/initiate/?ars=facebook_login_pw_error&amp;email=abc@mail.com&amp;__ccr=XXX" class="bd" aria-label="Have you forgotten your password?">Did you forget your password?</a></span>
+        </div>
+    </div>
+    ...
+    </td></tr></tbody></table>
+    <div style="display:none"></div><span><img src="https://facebook.com/security/hsts-pixel.gif" width="0" height="0" style="display:none" /></span>
+    </div></div><div></div></div></div>
+    </body>
+
+    </html>
+    """
+    url = "https://m.facebook.com/login/?email=abc@mail.com&li=XXX&e=1348092"
+    msg = "The password you entered is incorrect. Did you forget your password?"
+    assert (1348092, msg) == get_error_data(html)
diff --git a/tests/test_util.py b/tests/test_util.py
index b2dc131..aae1343 100644
--- a/tests/test_util.py
+++ b/tests/test_util.py
@@ -4,13 +4,9 @@ import datetime
 from fbchat._util import (
     strip_json_cruft,
     parse_json,
-    str_base,
-    generate_message_id,
-    get_signature_id,
     get_jsmods_require,
     mimetype_to_key,
     get_url_parameter,
-    prefix_url,
     seconds_to_datetime,
     millis_to_datetime,
     datetime_to_seconds,
@@ -42,31 +38,6 @@ def test_parse_json_invalid():
         parse_json("No JSON object here!")
 
 
-@pytest.mark.parametrize(
-    "number,base,expected",
-    [
-        (123, 10, "123"),
-        (1, 36, "1"),
-        (10, 36, "a"),
-        (123, 36, "3f"),
-        (1000, 36, "rs"),
-        (123456789, 36, "21i3v9"),
-    ],
-)
-def test_str_base(number, base, expected):
-    assert str_base(number, base) == expected
-
-
-def test_generate_message_id():
-    # Returns random output, so hard to test more thoroughly
-    generate_message_id("abc")
-
-
-def test_get_signature_id():
-    # Returns random output, so hard to test more thoroughly
-    get_signature_id()
-
-
 def test_get_jsmods_require_get_image_url():
     data = {
         "__ar": 1,
@@ -118,15 +89,7 @@ def test_mimetype_to_key():
 def test_get_url_parameter():
     assert get_url_parameter("http://example.com?a=b&c=d", "c") == "d"
     assert get_url_parameter("http://example.com?a=b&a=c", "a") == "b"
-    with pytest.raises(IndexError):
-        get_url_parameter("http://example.com", "a")
-
-
-def test_prefix_url():
-    assert prefix_url("/") == "https://www.facebook.com/"
-    assert prefix_url("/abc") == "https://www.facebook.com/abc"
-    assert prefix_url("abc") == "abc"
-    assert prefix_url("https://m.facebook.com/abc") == "https://m.facebook.com/abc"
+    assert get_url_parameter("http://example.com", "a") is None
 
 
 DT_0 = datetime.datetime(1970, 1, 1, 0, 0, tzinfo=datetime.timezone.utc)