Parsing of range header

src/calibre/srv/respond.py

@@ -12,6 +12,49 @@ from io import DEFAULT_BUFFER_SIZE, BytesIO
 from calibre import force_unicode
 from calibre.srv.errors import IfNoneMatch
 
+def get_ranges(headervalue, content_length):
+    """Return a list of (start, num_of_bytes) indices from a Range header, or None.
+    If this function returns an empty list, it indicates no valid range was found.
+    """
+    if not headervalue:
+        return None
+
+    result = []
+    try:
+        bytesunit, byteranges = headervalue.split("=", 1)
+    except Exception:
+        return None
+    if bytesunit.strip() != 'bytes':
+        return None
+
+    for brange in byteranges.split(","):
+        start, stop = [x.strip() for x in brange.split("-", 1)]
+        if start:
+            if not stop:
+                stop = content_length - 1
+            try:
+                start, stop = int(start), int(stop)
+            except Exception:
+                continue
+            if start >= content_length:
+                continue
+            if stop < start:
+                continue
+            result.append((start, stop - start + 1))
+        elif stop:
+            # Negative subscript (last N bytes)
+            try:
+                stop = int(stop)
+            except Exception:
+                continue
+            if stop > content_length:
+                result.append((0, content_length))
+            else:
+                result.append((content_length - stop, stop))
+
+    return result
+
+
 def acceptable_encoding(val, allowed=frozenset({'gzip'})):
     def enc(x):
         e, r = x.partition(';')[::2]

src/calibre/srv/tests/http.py

@@ -63,7 +63,28 @@ class TestHTTP(BaseTest):
         test('Case insensitive', 'GZIp', 'gzip')
         test('Multiple', 'gzip, identity', 'gzip')
         test('Priority', '1;q=0.5, 2;q=0.75, 3;q=1.0', '3', {'1', '2', '3'})
-        # }}}
+    # }}}
+
+    def test_range_parsing(self):  # {{{
+        'Test parsing of Range header'
+        from calibre.srv.respond import get_ranges
+        def test(val, *args):
+            pval = get_ranges(val, 100)
+            if len(args) == 1 and args[0] is None:
+                self.assertIsNone(pval, val)
+            else:
+                self.assertListEqual(pval, list(args), val)
+        test('crap', None)
+        test('crap=', None)
+        test('crap=1', None)
+        test('crap=1-2', None)
+        test('bytes=a-2')
+        test('bytes=0-99', (0, 100))
+        test('bytes=0-0,-1', (0, 1), (99, 1))
+        test('bytes=-5', (95, 5))
+        test('bytes=95-', (95, 5))
+        test('bytes=-200', (0, 100))
+    # }}}
 
     def test_http_basic(self):  # {{{
         'Test basic HTTP protocol conformance'
@@ -194,4 +215,3 @@ class TestHTTP(BaseTest):
             self.ae(r.status, httplib.OK), self.ae(zlib.decompress(r.read(), 16+zlib.MAX_WBITS), b'an_etagged_path')
 
     # }}}
-