1# OpenBMC Webserver Development 2 31. ### Performance targets 4 As OpenBMC is intended to be deployed on an embedded system, care should be 5 taken to avoid expensive constructs, and memory usage. In general, our 6 performance and metric targets are: 7 8 - Binaries and static files should take up < 1MB of filesystem size 9 - Memory usage should remain below 10MB at all times 10 - Application startup time should be less than 1 second on target hardware 11 (AST2500) 12 132. ### Asynchronous programming 14 Care should be taken to ensure that all code is written to be asynchronous in 15 nature, to avoid blocking methods from stopping the processing of other 16 tasks. At this time the webserver uses boost::asio for it async framework. 17 Threads should be avoided if possible, and instead use async tasks within 18 boost::asio. 19 203. ### Secure coding guidelines 21 Secure coding practices should be followed in all places in the webserver 22 23 In general, this means: 24 - All buffer boundaries must be checked before indexing or using values 25 - All pointers and iterators must be checked for null before dereferencing 26 - All input from outside the application is considered untrusted, and should 27 be escaped, authorized and filtered accordingly. This includes files in 28 the filesystem. 29 - All error statuses are checked and accounted for in control flow. 30 - Where applicable, noexcept methods should be preferred to methods that use 31 exceptions 32 - Explicitly bounded types should be preferred over implicitly bounded types 33 (like std::array<int, size> as opposed to int[size]) 34 - no use of [Banned 35 functions](https://github.com/intel/safestringlib/wiki/SDL-List-of-Banned-Functions 36 "Banned function list") 37 384. ### Error handling 39 Error handling should be constructed in such a way that all possible errors 40 return valid HTTP responses. The following HTTP codes will be used commonly 41 - 200 OK - Request was properly handled 42 - 201 Created - Resource was created 43 - 401 Unauthorized - Request didn't posses the necessary authentication 44 - 403 Forbidden - Request was authenticated, but did not have the necessary 45 permissions to accomplish the requested task 46 - 404 Not found - The url was not found 47 - 500 Internal error - Something has broken within the OpenBMC web server, 48 and should be filed as a bug 49 50 Where possible, 307 and 308 redirects should be avoided, as they introduce 51 the possibility for subtle security bugs. 52 535. ### Startup times 54 Given that the most common target of OpenBMC is an ARM11 processor, care 55 needs to be taken to ensure startup times are low. In general this means: 56 57 - Minimizing the number of files read from disk at startup. Unless a 58 feature is explicitly intended to be runtime configurable, its logic 59 should be "baked in" to the application at compile time. For cases where 60 the implementation is configurable at runtime, the default values should 61 be included in application code to minimize the use of nonvolatile 62 storage. 63 - Avoid excessive memory usage and mallocs at startup. 64 656. ### Compiler features 66 - At this point in time, the webserver sets a number of security flags in 67 compile time options to prevent misuse. The specific flags and what 68 optimization levels they are enabled at are documented in the 69 CMakeLists.txt file. 70 - Exceptions are currently enabled for webserver builds, but their use is 71 discouraged. Long term, the intent is to disable exceptions, so any use 72 of them for explicit control flow will likely be rejected in code review. 73 Any use of exceptions should be cases where the program can be reasonably 74 expected to crash if the exception occurs, as this will be the future 75 behavior once exceptions are disabled. 76 - Run time type information is disabled 77 - Link time optimization is enabled 78 797. ### Authentication 80 The webserver shall provide the following authentication mechanisms. 81 - Basic authentication 82 - Cookie authentication 83 - Token authentication 84 85 There shall be connection between the authentication mechanism used and 86 resources that are available over it. The webserver shall employ an 87 authentication scheme that is in line with the rest of OpenBMC, and allows 88 users and privileges to be provisioned from other interfaces. 89 908. ### Web security 91 The OpenBMC webserver shall follow the latest OWASP recommendations for 92 authentication, session management, and security. 93 949. ### Performance 95 The performance priorities for the OpenBMC webserver are (in order): 96 1. Code is readable and clear 97 2. Code follows secure guidelines 98 3. Code is performant, and does not unnecessarily abstract concepts at the 99 expense of performance 100 4. Code does not employ constructs which require continuous system 101 resources, unless required to meet performance targets. (example: 102 caching sensor values which are expected to change regularly) 103 10410. ### Abstraction/interfacing 105 In general, the OpenBMC webserver is built using the data driven design. 106 Abstraction and Interface guarantees should be used when multiple 107 implementations exist, but for implementations where only a single 108 implementation exists, prefer to make the code correct and clean rather than 109 implement a concrete interface. 110 11111. ### phosphor webui 112 The webserver should be capable of hosting phosphor-webui, and impelmenting 113 the required flows to host the application. In general, all access methods 114 should be available to the webui. 115 11612. ### Developing and Testing 117 There are a variety of ways to develop and test bmcweb software changes. 118 Here are the steps for using the SDK and QEMU. 119 120 - Follow all [development environment setup](https://github.com/openbmc/docs/blob/master/development/dev-environment.md) 121 directions in the development environment setup document. This will get 122 QEMU started up and you in the SDK environment. 123 - Follow all of the [gerrit setup](https://github.com/openbmc/docs/blob/master/development/gerrit-setup.md) 124 directions in the gerrit setup document. 125 - Clone bmcweb from gerrit 126 ``` 127 git clone ssh://openbmc.gerrit/bmcweb/ 128 ``` 129 130 - Ensure it compiles 131 ``` 132 cmake ./ && make 133 ``` 134 **Note:** If you'd like to enable debug traces in bmcweb, use the 135 following command for cmake 136 ``` 137 cmake ./ -DCMAKE_BUILD_TYPE:type=Debug 138 ``` 139 140 - Make your changes as needed, rebuild with `make` 141 142 - Reduce binary size by stripping it when ready for testing 143 ``` 144 arm-openbmc-linux-gnueabi-strip bmcweb 145 ``` 146 **Note:** Stripping is not required and having the debug symbols could be 147 useful depending on your testing. Leaving them will drastically increase 148 your transfer time to the BMC. 149 150 - Copy your bmcweb you want to test to /tmp/ in QEMU 151 ``` 152 scp -P 2222 bmcweb root@127.0.0.1:/tmp/ 153 ``` 154 **Special Notes:** 155 The address and port shown here (127.0.0.1 and 2222) reaches the QEMU session 156 you set up in your development environment as described above. 157 158 - Stop bmcweb service within your QEMU session 159 ``` 160 systemctl stop bmcweb 161 ``` 162 **Note:** bmcweb supports being started directly in parallel with the bmcweb 163 running as a service. The standalone bmcweb will be available on port 18080. 164 An advantage of this is you can compare between the two easily for testing. 165 In QEMU you would need to open up port 18080 when starting QEMU. Your curl 166 commands would need to use 18080 to communicate. 167 168 - If running within a system that has read-only /usr/ filesystem, issue 169 the following commands one time per QEMU boot to make the filesystem 170 writeable 171 ``` 172 mkdir -p /var/persist/usr 173 mkdir -p /var/persist/work/usr 174 mount -t overlay -o lowerdir=/usr,upperdir=/var/persist/usr,workdir=/var/persist/work/usr overlay /usr 175 ``` 176 177 - Remove the existing bmcweb from the filesystem in QEMU 178 ``` 179 rm /usr/bin/bmcweb 180 ``` 181 182 - Link to your new bmcweb in /tmp/ 183 ``` 184 ln -sf /tmp/bmcweb /usr/bin/bmcweb 185 ``` 186 187 - Test your changes. bmcweb will be started automatically upon your 188 first REST or Redfish command 189 ``` 190 curl -c cjar -b cjar -k -X POST https://127.0.0.1:2443/login -d "{\"data\": [ \"root\", \"0penBmc\" ] }" 191 curl -c cjar -b cjar -k -X GET https://127.0.0.1:2443/xyz/openbmc_project/state/bmc0 192 ``` 193 194 - Stop the bmcweb service and scp new file over to /tmp/ each time you 195 want to retest a change. 196 197 See the [REST](https://github.com/openbmc/docs/blob/master/REST-cheatsheet.md) 198 and [Redfish](https://github.com/openbmc/docs/blob/master/REDFISH-cheatsheet.md) cheatsheets for valid commands. 199