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+<a id="dir-spec.txt-6"></a>
+
+# Standards compliance
+
+All clients and servers MUST support HTTP 1.0.  Clients and servers MAY
+support later versions of HTTP as well.
+
+<a id="dir-spec.txt-6.1"></a>
+
+## HTTP headers
+
+Servers SHOULD set Content-Encoding to the algorithm used to compress the
+document(s) being served.  Recognized algorithms are:
+
+```text
+     - "identity"     -- RFC2616 section 3.5
+     - "deflate"      -- RFC2616 section 3.5
+     - "gzip"         -- RFC2616 section 3.5
+     - "x-zstd"       -- The zstandard compression algorithm (www.zstd.net)
+     - "x-tor-lzma"   -- The lzma compression algorithm, with a "preset"
+                         value no higher than 6.
+```
+
+Clients SHOULD use Accept-Encoding on most directory requests to indicate
+which of the above compression algorithms they support.  If they omit it
+(as Tor clients did before 0.3.1.1-alpha), then the server should serve
+only "deflate" or "identity" encoded documents, based on the presence or
+absence of the ".z" suffix on the requested URL.
+
+Note that for anonymous directory requests (that is, requests made over
+multi-hop circuits, like those for onion service lookups) implementations
+SHOULD NOT advertise any Accept-Encoding values other than deflate.  To do
+so would be to create a fingerprinting opportunity.
+
+When receiving multiple documents, clients MUST accept compressed
+concatenated documents and concatenated compressed documents as
+equivalent.
+
+Servers MAY set the Content-Length: header.  When they do, it should
+match the number of compressed bytes that they are sending.
+
+Servers MAY include an X-Your-Address-Is: header, whose value is the
+apparent IP address of the client connecting to them (as a dotted quad).
+For directory connections tunneled over a BEGIN_DIR stream, servers SHOULD
+report the IP from which the circuit carrying the BEGIN_DIR stream reached
+them.
+
+Servers SHOULD disable caching of multiple network statuses or multiple
+server descriptors.  Servers MAY enable caching of single descriptors,
+single network statuses, the list of all server descriptors, a v1
+directory, or a v1 running routers document.  XXX mention times.
+
+<a id="dir-spec.txt-6.2"></a>
+
+## HTTP status codes
+
+Tor delivers the following status codes.  Some were chosen without much
+thought; other code SHOULD NOT rely on specific status codes yet.
+
+```text
+  200 -- the operation completed successfully
+      -- the user requested statuses or serverdescs, and none of the ones we
+         requested were found (0.2.0.4-alpha and earlier).
+
+  304 -- the client specified an if-modified-since time, and none of the
+         requested resources have changed since that time.
+
+  400 -- the request is malformed, or
+      -- the URL is for a malformed variation of one of the URLs we support,
+          or
+      -- the client tried to post to a non-authority, or
+      -- the authority rejected a malformed posted document, or
+
+  404 -- the requested document was not found.
+      -- the user requested statuses or serverdescs, and none of the ones
+         requested were found (0.2.0.5-alpha and later).
+
+  503 -- we are declining the request in order to save bandwidth
+      -- user requested some items that we ordinarily generate or store,
+         but we do not have any available.
+```