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# OpenBMC Webserver Development
1. ### Performance targets
As OpenBMC is intended to be deployed on an embedded system, care should be
taken to avoid expensive constructs, and memory usage. In general, our
performance and metric targets are:
- Binaries and static files should take up < 1MB of filesystem size
- Memory usage should remain below 10MB at all times
- Application startup time should be less than 1 second on target hardware
(AST2500)
2. ### Asynchronous programming
Care should be taken to ensure that all code is written to be asynchronous in
nature, to avoid blocking methods from stopping the processing of other
tasks. At this time the webserver uses boost::asio for it async framework.
Threads should be avoided if possible, and instead use async tasks within
boost::asio.
3. ### Secure coding guidelines
Secure coding practices should be followed in all places in the webserver
In general, this means:
- All buffer boundaries must be checked before indexing or using values
- All pointers and iterators must be checked for null before dereferencing
- All input from outside the application is considered untrusted, and should
be escaped, authorized and filtered accordingly. This includes files in
the filesystem.
- All error statuses are checked and accounted for in control flow.
- Where applicable, noexcept methods should be preferred to methods that use
exceptions
- Explicitly bounded types should be preferred over implicitly bounded types
(like std::array<int, size> as opposed to int[size])
- no use of [Banned
functions](https://github.com/intel/safestringlib/wiki/SDL-List-of-Banned-Functions
"Banned function list")
4. ### Error handling
Error handling should be constructed in such a way that all possible errors
return valid HTTP responses. The following HTTP codes will be used commonly
- 200 OK - Request was properly handled
- 201 Created - Resource was created
- 401 Unauthorized - Request didn't posses the necessary authentication
- 403 Forbidden - Request was authenticated, but did not have the necessary
permissions to accomplish the requested task
- 404 Not found - The url was not found
- 500 Internal error - Something has broken within the OpenBMC web server,
and should be filed as a bug
Where possible, 307 and 308 redirects should be avoided, as they introduce
the possibility for subtle security bugs.
5. ### Startup times
Given that the most common target of OpenBMC is an ARM11 processor, care
needs to be taken to ensure startup times are low. In general this means:
- Minimizing the number of files read from disk at startup. Unless a
feature is explicitly intended to be runtime configurable, its logic
should be "baked in" to the application at compile time. For cases where
the implementation is configurable at runtime, the default values should
be included in application code to minimize the use of nonvolatile
storage.
- Avoid excessive memory usage and mallocs at startup.
6. ### Compiler features
- At this point in time, the webserver sets a number of security flags in
compile time options to prevent misuse. The specific flags and what
optimization levels they are enabled at are documented in the
CMakeLists.txt file.
- Exceptions are currently enabled for webserver builds, but their use is
discouraged. Long term, the intent is to disable exceptions, so any use
of them for explicit control flow will likely be rejected in code review.
Any use of exceptions should be cases where the program can be reasonably
expected to crash if the exception occurs, as this will be the future
behavior once exceptions are disabled.
- Run time type information is disabled
- Link time optimization is enabled
7. ### Authentication
The webserver shall provide the following authentication mechanisms.
- Basic authentication
- Cookie authentication
- Token authentication
There shall be connection between the authentication mechanism used and
resources that are available over it. The webserver shall employ an
authentication scheme that is in line with the rest of OpenBMC, and allows
users and privileges to be provisioned from other interfaces.
8. ### Web security
The OpenBMC webserver shall follow the latest OWASP recommendations for
authentication, session management, and security.
9. ### Performance
The performance priorities for the OpenBMC webserver are (in order):
1. Code is readable and clear
2. Code follows secure guidelines
3. Code is performant, and does not unnecessarily abstract concepts at the
expense of performance
4. Code does not employ constructs which require continuous system
resources, unless required to meet performance targets. (example:
caching sensor values which are expected to change regularly)
10. ### Abstraction/interfacing
In general, the OpenBMC webserver is built using the data driven design.
Abstraction and Interface guarantees should be used when multiple
implementations exist, but for implementations where only a single
implementation exists, prefer to make the code correct and clean rather than
implement a concrete interface.
11. ### phosphor webui
The webserver should be capable of hosting phosphor-webui, and impelmenting
the required flows to host the application. In general, all access methods
should be available to the webui.
12. ### Developing and Testing
There are a variety of ways to develop and test bmcweb software changes.
Here are the steps for using the SDK and QEMU.
- Follow all [development environment setup](https://github.com/openbmc/docs/blob/master/development/dev-environment.md)
directions in the development environment setup document. This will get
QEMU started up and you in the SDK environment.
- Follow all of the [gerrit setup](https://github.com/openbmc/docs/blob/master/development/gerrit-setup.md)
directions in the gerrit setup document.
- Clone bmcweb from gerrit
```
git clone ssh://openbmc.gerrit/bmcweb/
```
- Ensure it compiles
```
cmake ./ && make
```
**Note:** If you'd like to enable debug traces in bmcweb, use the
following command for cmake
```
cmake ./ -DCMAKE_BUILD_TYPE:type=Debug
```
- Make your changes as needed, rebuild with `make`
- Reduce binary size by stripping it when ready for testing
```
arm-openbmc-linux-gnueabi-strip bmcweb
```
**Note:** Stripping is not required and having the debug symbols could be
useful depending on your testing. Leaving them will drastically increase
your transfer time to the BMC.
- Copy your bmcweb you want to test to /tmp/ in QEMU
```
scp -P 2222 bmcweb root@127.0.0.1:/tmp/
```
**Special Notes:**
The address and port shown here (127.0.0.1 and 2222) reaches the QEMU session
you set up in your development environment as described above.
- Stop bmcweb service within your QEMU session
```
systemctl stop bmcweb
```
**Note:** bmcweb supports being started directly in parallel with the bmcweb
running as a service. The standalone bmcweb will be available on port 18080.
An advantage of this is you can compare between the two easily for testing.
In QEMU you would need to open up port 18080 when starting QEMU. Your curl
commands would need to use 18080 to communicate.
- If running within a system that has read-only /usr/ filesystem, issue
the following commands one time per QEMU boot to make the filesystem
writeable
```
mkdir -p /var/persist/usr
mkdir -p /var/persist/work/usr
mount -t overlay -o lowerdir=/usr,upperdir=/var/persist/usr,workdir=/var/persist/work/usr overlay /usr
```
- Remove the existing bmcweb from the filesystem in QEMU
```
rm /usr/bin/bmcweb
```
- Link to your new bmcweb in /tmp/
```
ln -sf /tmp/bmcweb /usr/bin/bmcweb
```
- Test your changes. bmcweb will be started automatically upon your
first REST or Redfish command
```
curl -c cjar -b cjar -k -X POST https://127.0.0.1:2443/login -d "{\"data\": [ \"root\", \"0penBmc\" ] }"
curl -c cjar -b cjar -k -X GET https://127.0.0.1:2443/xyz/openbmc_project/state/bmc0
```
- Stop the bmcweb service and scp new file over to /tmp/ each time you
want to retest a change.
See the [REST](https://github.com/openbmc/docs/blob/master/REST-cheatsheet.md)
and [Redfish](https://github.com/openbmc/docs/blob/master/REDFISH-cheatsheet.md) cheatsheets for valid commands.
|
