Added the ability to unset headers

Closes #476

CHANGELOG.rst

@@ -12,6 +12,8 @@ This project adheres to `Semantic Versioning <http://semver.org/>`_.
 * Added Python 3 as a dependency for Homebrew installations
   to ensure some of the newer HTTP features work out of the box
   for macOS users (starting with HTTPie 0.9.4.).
+* Added the ability to unset a request header with ``Header:``, and send an
+  empty value with ``Header;``.
 
 
 `0.9.4`_ (2016-07-01)

README.rst

@@ -560,7 +560,23 @@ There are a couple of default headers that HTTPie sets:
     Host: <taken-from-URL>
 
 
-Any of the default headers can be overwritten.
+Any of the default headers can be overwritten and some of them unset.
+
+To unset a header that has already been specified (such a one of the default
+headers), use ``Header:``:
+
+
+.. code-block:: bash
+
+    $ http httpbin.org/headers Accept: User-Agent:
+
+
+To send a header with an empty value, use ``Header;``:
+
+
+.. code-block:: bash
+
+    $ http httpbin.org/headers 'Header;'
 
 
 ==============

httpie/input.py

@@ -34,6 +34,7 @@ HTTPS = 'https://'
 
 # Various separators used in args
 SEP_HEADERS = ':'
+SEP_HEADERS_EMPTY = ';'
 SEP_CREDENTIALS = ':'
 SEP_PROXY = ':'
 SEP_DATA = '='
@@ -67,6 +68,7 @@ SEP_GROUP_RAW_JSON_ITEMS = frozenset([
 # Separators allowed in ITEM arguments
 SEP_GROUP_ALL_ITEMS = frozenset([
     SEP_HEADERS,
+    SEP_HEADERS_EMPTY,
     SEP_QUERY,
     SEP_DATA,
     SEP_DATA_RAW_JSON,
@@ -655,11 +657,20 @@ def parse_items(items,
     data = []
     files = []
     params = []
-
     for item in items:
         value = item.value
-
         if item.sep == SEP_HEADERS:
+            if value == '':
+                # No value => unset the header
+                value = None
+            target = headers
+        elif item.sep == SEP_HEADERS_EMPTY:
+            if item.value:
+                raise ParseError(
+                    'Invalid item "%s" '
+                    '(to specify an empty header use `Header;`)'
+                    % item.orig
+                )
             target = headers
         elif item.sep == SEP_QUERY:
             target = params

tests/test_httpie.py

@@ -1,5 +1,7 @@
 """High-level tests."""
 import pytest
+
+from httpie.input import ParseError
 from utils import TestEnvironment, http, HTTP_OK
 from fixtures import FILE_PATH, FILE_CONTENT
 
@@ -75,6 +77,27 @@ def test_headers(httpbin_both):
     assert '"Foo": "bar"' in r
 
 
+def test_headers_unset(httpbin_both):
+    r = http('GET', httpbin_both + '/headers')
+    assert 'Accept' in r.json['headers']  # default Accept present
+
+    r = http('GET', httpbin_both + '/headers', 'Accept:')
+    assert 'Accept' not in r.json['headers']   # default Accept unset
+
+
+def test_headers_empty_value(httpbin_both):
+    r = http('GET', httpbin_both + '/headers')
+    assert r.json['headers']['Accept']  # default Accept has value
+
+    r = http('GET', httpbin_both + '/headers', 'Accept;')
+    assert r.json['headers']['Accept'] == ''   # Accept has no value
+
+
+def test_headers_empty_value_with_value_gives_error(httpbin):
+    with pytest.raises(ParseError):
+        http('GET', httpbin + '/headers', 'Accept;SYNTAX_ERROR')
+
+
 @pytest.mark.skipif(
     is_py26,
     reason='the `object_pairs_hook` arg for `json.loads()` is Py>2.6 only'