write "format" section

README.md

@@ -4,7 +4,7 @@ Mitm-Archive consists of two parts:
 - [Addon for mitmproxy](https://git.dc09.ru/mitm-archive/addon) intercepting and saving (archiving) all HTTP responses, written in Python
 - [Server](https://git.dc09.ru/mitm-archive/server) giving exactly the same responses as in an archive for corresponding method+domain+port+path+query, written in Go
 
-"Archive" is an SQLite3 database and a directory storing headers and body for each archived response. See Format section for details.
+"Archive" is an SQLite3 database and a directory storing headers and body for each archived response. See [Format](#format) section for details.
 
 # User guide: addon
 
@@ -69,6 +69,9 @@ $ export STORAGE=storage
 $ mitmproxy -s addon.py
 ```
 
+# User guide: server
+// TODO
+
 # What's not implemented
 - Filter host instead of archiving everything (literally 2 lines of code, could be added soon after I figure out the best way to configure this)
 - Addon is configured with env vars, Server uses command-line options; should be unified?
@@ -89,3 +92,31 @@ Harder to implement and definitely will overcomplicate the project while neither
 For these usage screnarios, especially with cookies, it's simplier and overall better
 to self-host the web site server you are trying to archive
 or re-implement it in your favourite programming language and self-host.
+
+# Format
+SQLite3 database contains `data` table with the following columns:
+- `id` - integer primary key for each archived response
+- `method` - string, specifies the request method, default `"GET"`
+- `url` - string, URL formatted as `$scheme://$host:$port$path$query` (e.g. `https://dc09.ru:443/path?key=val`), required
+- `code` - integer, HTTP response status code, default `200`
+
+INSERT query is executed with `RETURNING id` clause.
+
+In file system storage, the addon creates a directory (if not exists) with the numeric ID returned by SQLite as its name,
+writes raw binary body data without any modifications to `{id}/body` file,
+writes headers in HTTP/1 format (`name: value\r\n`) to `{id}/headers` file.
+
+The FS storage structure can be represented graphically this way:
+```
+storage/
+|- 1/
+|  |- headers
+|  |- body
+|
+|- 2/
+|  |- headers
+|  |- body
+|
+|- {id}/
+...
+```