[PATCH v2] doc: cmd: wget: document lwIP syntax

[Jerome Forissier]

The lwIP version of wget supports a different syntax with a URL,
in addition to the legacy syntax. Document that.

While we're at it, fix a couple of minor issues in the legacy
syntax:
- hostIPaddr can be a DNS name if CONFIG_CMD_DNS is enabled
- path is mandatory

Signed-off-by: Jerome Forissier <jerome.forissier at linaro.org>
Reviewed-by: Simon Glass <sjg at chromium.org>
---
 doc/usage/cmd/wget.rst | 71 +++++++++++++++++++++++++++++++++++-------
 1 file changed, 60 insertions(+), 11 deletions(-)

Changes in v2:
- Using a host name is possible only when CONFIG_CMD_DNS is enabled

diff --git a/doc/usage/cmd/wget.rst b/doc/usage/cmd/wget.rst
index b8ca35bb140..f9522ce58c6 100644
--- a/doc/usage/cmd/wget.rst
+++ b/doc/usage/cmd/wget.rst
@@ -11,29 +11,51 @@ Synopsis
 
 ::
 
-    wget address [[hostIPaddr:]path]
+    wget [address] [host:]path
+    wget [address] url          # lwIP only
+
 
 Description
 -----------
 
-The wget command is used to download a file from an HTTP server.
+The wget command is used to download a file from an HTTP(S) server.
+In order to use HTTPS you will need to compile wget with lwIP support.
+
+Legacy syntax
+~~~~~~~~~~~~~
+
+The legacy syntax is supported with the legacy network stack as well as
+lwIP. It allows only HTTP.
 
-wget command will use HTTP over TCP to download files from an HTTP server.
 By default the destination port is 80 and the source port is pseudo-random.
-The environment variable *httpdstp* can be used to set the destination port.
+The environment variable *httpdstp* can be used to set the destination port
+(legacy nework stack only).
 
 address
     memory address for the data downloaded
 
-hostIPaddr
-    IP address of the HTTP server, defaults to the value of environment
-    variable *serverip*
+host
+    IP address (or host name if `CONFIG_CMD_DNS` is enabled) of the HTTP
+    server, defaults to the value of environment variable *serverip*.
 
 path
     path of the file to be downloaded.
 
-Example
--------
+
+New syntax (lwIP only)
+~~~~~~~~~~~~~~~~~~~~~~
+
+In addition to the syntax described above, wget accepts URLs if the network
+stack is lwIP.
+
+address
+    memory address for the data downloaded
+
+url
+    HTTP or HTTPS URL, that is: http[s]://<host>[:<port>]/<path>.
+
+Example with the legacy network stack
+-------------------------------------
 
 In the example the following steps are executed:
 
@@ -52,13 +74,40 @@ In the example the following steps are executed:
     HTTP/1.0 302 Found
     Packets received 4, Transfer Successful
 
+Example with lwIP
+-----------------
+
+In the example the following steps are executed:
+
+* setup client network address
+* download a file from the HTTPS server
+
+::
+
+   => dhcp
+   DHCP client bound to address 10.0.2.15 (3 ms)
+   => wget https://download.rockylinux.org/pub/rocky/9/isos/aarch64/Rocky-9.4-aarch64-minimal.iso
+   ##########################################################################
+   ##########################################################################
+   ##########################################################################
+   [...]
+   1694892032 bytes transferred in 492181 ms (3.3 MiB/s)
+   Bytes transferred = 1694892032 (65060000 hex)
+
 Configuration
 -------------
 
 The command is only available if CONFIG_CMD_WGET=y.
+To enable lwIP support set CONFIG_NET_LWIP=y.
 
-TCP Selective Acknowledgments can be enabled via CONFIG_PROT_TCP_SACK=y.
-This will improve the download speed.
+TCP Selective Acknowledgments in the legacy network stack can be enabled via
+CONFIG_PROT_TCP_SACK=y. This will improve the download speed. Selective
+Acknowledgments are enabled by default with lwIP.
+
+**Note**: U-Boot currently has no way to verify certificates for HTTPS.
+A place to store the root CA certificates is needed, and then MBed TLS would
+need to walk the entire chain. Therefore, man-in-the middle attacks are
+possible and HTTPS should not be relied upon for payload authentication.
 
 Return value
 ------------
-- 
2.40.1