From 65243164fc1e6836aa6bed4a49b894d4228f1ef6 Mon Sep 17 00:00:00 2001
From: Fedor Indutny <fedor@indutny.com>
Date: Sat, 4 Jun 2016 11:05:05 -0400
Subject: docs: implementation guide

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 docs/implementation-guide.md | 57 ++++++++++++++++++++++++++++++++++++++++++++
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+# Implementation Guide
+
+`uv_link_t` behaves very similar to [`uv_stream_t`][0]. All `uv_link_methods_t`
+MUST conform to this semantics.
+
+## uv_link_init()
+
+Links start in non-reading mode, `alloc_cb`/`read_cb` MUST NOT be called until
+`uv_link_read_start(link)` will be invoked with zero return code.
+
+## uv_link_read_start()/uv_link_read_stop()
+
+This switch link to and from the reading mode. After the switch to the reading
+mode either:
+
+* `alloc_cb` + `read_cb` will be invoked for a particular link (NOTE: `read_cb`
+  MUST follow every `alloc_cb`)
+* `read_cb(..., err, ...)` will be called to indicate a error. In this case user
+  MUST call `uv_read_stop()` on the error'ed link.
+
+NOTE: `buf` argument of `read_cb` may be `NULL` in case of error.
+
+NOTE: If `alloc_cb` sets `buf->len = 0;` - `read_cb(..., UV_ENOBUFS, ...)` MUST
+be called by a link implementation.
+
+## uv_link_close()
+
+Links MAY be closed at any time, unless they are already closed or weren't
+initialized with `uv_link_init()`. However, the `methods->close()` may not be
+called immediately on `uv_link_close()` if close attempt is happening on the
+link's call stack:
+
+```c
+static void read_cb(uv_link_t* link, ssize_t nread, uv_buf_t* buf) {
+  uv_link_close(link, ...);
+}
+
+link->read_cb = read_cb;
+
+uv_link_propagate_read_cb(link, UV_EOF, NULL);
+/* link->methods->close() call will happen upon returning from
+   `uv_link_propagate_read_cb` */
+```
+
+uv_link_t public APIs MUST NOT be used on a link after `uv_link_close(link)`.
+
+When several links are chained together, `uv_link_close()` SHOULD be called only
+on a last (leaf) link in a chain. Otherwise `uv_link_t` API is allowed to crash.
+
+When closing leaf link in a chain:
+
+1. All links will be unchained
+2. Each link starting from the deepest link (from the leaf) will be closed one
+   by one
+3. `close_cb` will be invoked upon close of all links in a chain
+
+[0]: http://docs.libuv.org/en/v1.x/stream.html
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