docs: Updated for docker cp and its API changes

Documented changes to API to enable new `docker cp` behavior.

Added documentation on `docker cp` usage and behavior.

Docker-DCO-1.1-Signed-off-by: Josh Hawn <josh.hawn@docker.com> (github: jlhawn)

docs/reference/api/docker_remote_api.md

@@ -68,6 +68,23 @@ Running `docker rmi` emits an **untag** event when removing an image name.  The
 
 ### What's new
 
+`GET /containers/(id)/archive`
+
+**New!**
+Get an archive of filesystem content from a container.
+
+`PUT /containers/(id)/archive`
+
+**New!**
+Upload an archive of content to be extracted to an
+existing directory inside a container's filesystem.
+
+`POST /containers/(id)/copy`
+
+**Deprecated!**
+This copy endpoint has been deprecated in favor of the above `archive` endpoint
+which can be used to download files and directories from a container.
+
 **New!**
 The `hostConfig` option now accepts the field `GroupAdd`, which specifies a list of additional
 groups that the container process will run as.

docs/reference/api/docker_remote_api_v1.20.md

@@ -1039,6 +1039,8 @@ Status Codes:
 
 Copy files or folders of container `id`
 
+**Deprecated** in favor of the `archive` endpoint below.
+
 **Example request**:
 
     POST /containers/4fa6e0f0c678/copy HTTP/1.1
@@ -1061,6 +1063,120 @@ Status Codes:
 -   **404** – no such container
 -   **500** – server error
 
+### Retrieving information about files and folders in a container
+
+`HEAD /containers/(id)/archive`
+
+See the description of the `X-Docker-Container-Path-Stat` header in the
+folowing section.
+
+### Get an archive of a filesystem resource in a container
+
+`GET /containers/(id)/archive`
+
+Get an tar archive of a resource in the filesystem of container `id`.
+
+Query Parameters:
+
+- **path** - resource in the container's filesystem to archive. Required.
+
+    If not an absolute path, it is relative to the container's root directory.
+    The resource specified by **path** must exist. To assert that the resource
+    is expected to be a directory, **path** should end in `/` or  `/.`
+    (assuming a path separator of `/`). If **path** ends in `/.` then this
+    indicates that only the contents of the **path** directory should be
+    copied. A symlink is always resolved to its target.
+
+    **Note**: It is not possible to copy certain system files such as resources
+    under `/proc`, `/sys`, `/dev`, and mounts created by the user in the
+    container.
+
+**Example request**:
+
+        GET /containers/8cce319429b2/archive?path=/root HTTP/1.1
+
+**Example response**:
+
+        HTTP/1.1 200 OK
+        Content-Type: application/x-tar
+        X-Docker-Container-Path-Stat: eyJuYW1lIjoicm9vdCIsInBhdGgiOiIvcm9vdCIsInNpemUiOjQwOTYsIm1vZGUiOjIxNDc0ODQwOTYsIm10aW1lIjoiMjAxNC0wMi0yN1QyMDo1MToyM1oifQ==
+
+        {{ TAR STREAM }}
+
+On success, a response header `X-Docker-Container-Path-Stat` will be set to a
+base64-encoded JSON object containing some filesystem header information about
+the archived resource. The above example value would decode to the following
+JSON object (whitespace added for readability):
+
+        {
+            "name": "root",
+            "path": "/root",
+            "size": 4096,
+            "mode": 2147484096,
+            "mtime": "2014-02-27T20:51:23Z"
+        }
+
+A `HEAD` request can also be made to this endpoint if only this information is
+desired.
+
+Status Codes:
+
+- **200** - success, returns archive of copied resource
+- **400** - client error, bad parameter, details in JSON response body, one of:
+    - must specify path parameter (**path** cannot be empty)
+    - not a directory (**path** was asserted to be a directory but exists as a
+      file)
+- **404** - client error, resource not found, one of:
+    – no such container (container `id` does not exist)
+    - no such file or directory (**path** does not exist)
+- **500** - server error
+
+### Extract an archive of files or folders to a directory in a container
+
+`PUT /containers/(id)/archive`
+
+Upload a tar archive to be extracted to a path in the filesystem of container
+`id`.
+
+Query Parameters:
+
+- **path** - path to a directory in the container
+    to extract the archive's contents into. Required.
+
+    If not an absolute path, it is relative to the container's root directory.
+    The **path** resource must exist.
+- **noOverwriteDirNonDir** - If "1", "true", or "True" then it will be an error
+    if unpacking the given content would cause an existing directory to be
+    replaced with a non-directory and vice versa.
+
+**Example request**:
+
+        PUT /containers/8cce319429b2/archive?path=/vol1 HTTP/1.1
+        Content-Type: application/x-tar
+
+        {{ TAR STREAM }}
+
+**Example response**:
+
+        HTTP/1.1 200 OK
+
+Status Codes:
+
+- **200** – the content was extracted successfully
+- **400** - client error, bad parameter, details in JSON response body, one of:
+    - must specify path parameter (**path** cannot be empty)
+    - not a directory (**path** should be a directory but exists as a file)
+    - unable to overwrite existing directory with non-directory
+      (if **noOverwriteDirNonDir**)
+    - unable to overwrite existing non-directory with directory
+      (if **noOverwriteDirNonDir**)
+- **403** - client error, permission denied, the volume
+    or container rootfs is marked as read-only.
+- **404** - client error, resource not found, one of:
+    – no such container (container `id` does not exist)
+    - no such file or directory (**path** resource does not exist)
+- **500** – server error
+
 ## 2.2 Images
 
 ### List Images