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MEL.Flex

What is this?

MEL.Flex (FSharp Logging EXtensions for Microsoft.Extensions.Logging) adds the ability to use string interpolation for strongly typed strings while getting the benefits of structured logging by converting the interpolated string into a message template transparently.

Why does this exist?

Structured logging with message templates are great, except they do one a few problems.

  1. They are (usually) positional. If I have the following code:

    let userName = "KirkJ1701"
logger.LogWarning("Some user: {UserName} has logged in", userName)

    if I wanted to add an IpAddress

    let userName = "KirkJ1701"
let ipAddress = "KirkJ1701"
logger.LogWarning("Some user: {UserName} has logged in from {IpAddress}", ipAddress, userName)

    I can easily mess up the arguments. This of course looks easy but gets more difficult as you add more logs to structure or rearrange your logs.

  2. Normalizing your keys with semantic convetions makes it easier for you to search across your logs.

    let userName = "SpockV"
logger.LogWarning("Some user: {user_name} has logged in", userName)

    Adding this log to our application logs the user_name but earlier we were logging a UserName. If I needed to search across these logs, I would need to know each potential variation of that key name. (Yes some tools allow you to do that mapping on their side but not all).

How do I use it?

Tupled Arguments

One of the currently supported ways is to use tuples. Taking an example above:

// Some file that containts your normalized names
module LoggerKeyConsts =
    let [<Literal>] UserName = "UserName"

// .. Some function

let userName = "SpockV"
logger.LogFWarning($"Some user: {(LoggerKeyConsts.UserName, userName)} has logged in")

The important changes are:

  1. LogWarning -> LogFWarning
  2. $ in front of the string
  3. {Username} became {(LoggerKeyConsts.UserName, userName)}
    • The latter part of this syntax is a tuple with two values.

Slightly better would be to create helper functions that generate the tuples:

module LogConsts =
    let [<Literal>] ``user.name`` = "user.name"
    let inline userName (s : string) = struct (``user.name``, s)

// .. Some function
let userName = "SpockV"
logger.LogFWarning($"Some user: {LogConsts.userName userName} has logged in")

This way, you could apply any type safety or normalization to your log data.

Caveats

  • Unfortunately F# does not yet support DefaultInterpolatedStringHandler which means you will still take the interpolated creation hit. However, this library does implement it's own log formatter which allows for lazy construction of the interpolated string -> message template until it is required or possibly not at all if the LogLevel configuration is set to a higher threadshold than the log statement.

Builds

GitHub Actions
GitHub Actions
Build History

NuGet

Package Stable Prerelease
MEL.Flex NuGet Badge NuGet Badge

Developing

Make sure the following requirements are installed on your system:

or

Environment Variables

  • CONFIGURATION will set the configuration of the dotnet commands. If not set, it will default to Release.
    • CONFIGURATION=Debug ./build.sh will result in -c additions to commands such as in dotnet build -c Debug
  • GITHUB_TOKEN will be used to upload release notes and Nuget packages to GitHub.
    • Be sure to set this before releasing
  • DISABLE_COVERAGE Will disable running code coverage metrics. AltCover can have severe performance degradation so it's worth disabling when looking to do a quicker feedback loop.
    • DISABLE_COVERAGE=1 ./build.sh

Building

> build.cmd <optional buildtarget> // on windows
$ ./build.sh  <optional buildtarget>// on unix

The bin of your library should look similar to:

$ tree src/MEL.Flex/bin/
src/MEL.Flex/bin/
└── Debug
    └── net50
        ├── MEL.Flex.deps.json
        ├── MEL.Flex.dll
        ├── MEL.Flex.pdb
        └── MEL.Flex.xml

Build Targets

  • Clean - Cleans artifact and temp directories.
  • DotnetRestore - Runs dotnet restore on the solution file.
  • DotnetBuild - Runs dotnet build on the solution file.
  • DotnetTest - Runs dotnet test on the solution file.
  • GenerateCoverageReport - Code coverage is run during DotnetTest and this generates a report via ReportGenerator.
  • WatchTests - Runs dotnet watch with the test projects. Useful for rapid feedback loops.
  • GenerateAssemblyInfo - Generates AssemblyInfo for libraries.
  • DotnetPack - Runs dotnet pack. This includes running Source Link.
  • SourceLinkTest - Runs a Source Link test tool to verify Source Links were properly generated.
  • PublishToNuGet - Publishes the NuGet packages generated in DotnetPack to NuGet via paket push.
  • GitRelease - Creates a commit message with the Release Notes and a git tag via the version in the Release Notes.
  • GitHubRelease - Publishes a GitHub Release with the Release Notes and any NuGet packages.
  • FormatCode - Runs Fantomas on the solution file.
  • BuildDocs - Generates Documentation from docsSrc and the XML Documentation Comments from your libraries in src.
  • WatchDocs - Generates documentation and starts a webserver locally. It will rebuild and hot reload if it detects any changes made to docsSrc files, libraries in src, or the docsTool itself.
  • ReleaseDocs - Will stage, commit, and push docs generated in the BuildDocs target.
  • Release - Task that runs all release type tasks such as PublishToNuGet, GitRelease, ReleaseDocs, and GitHubRelease. Make sure to read Releasing to setup your environment correctly for releases.

Releasing

git add .
git commit -m "Scaffold"
git remote add origin https://github.com/user/MEL.Flex.git
git push -u origin master

  • Create your NuGeT API key

    paket config add-token "https://www.nuget.org" 4003d786-cc37-4004-bfdf-c4f3e8ef9b3a
    • or set the environment variable NUGET_TOKEN to your key

  • Create a GitHub OAuth Token

    • You can then set the environment variable GITHUB_TOKEN to upload release notes and artifacts to github
    • Otherwise it will fallback to username/password

  • Then update the CHANGELOG.md with an "Unreleased" section containing release notes for this version, in KeepAChangelog format.

NOTE: Its highly recommend to add a link to the Pull Request next to the release note that it affects. The reason for this is when the RELEASE target is run, it will add these new notes into the body of git commit. GitHub will notice the links and will update the Pull Request with what commit referenced it saying "added a commit that referenced this pull request". Since the build script automates the commit message, it will say "Bump Version to x.y.z". The benefit of this is when users goto a Pull Request, it will be clear when and which version those code changes released. Also when reading the CHANGELOG, if someone is curious about how or why those changes were made, they can easily discover the work and discussions.

Here's an example of adding an "Unreleased" section to a CHANGELOG.md with a 0.1.0 section already released.

## [Unreleased]

### Added
- Does cool stuff!

### Fixed
- Fixes that silly oversight

## [0.1.0] - 2017-03-17
First release

### Added
- This release already has lots of features

[Unreleased]: https://github.com/user/MEL.Flex.git/compare/v0.1.0...HEAD
[0.1.0]: https://github.com/user/MEL.Flex.git/releases/tag/v0.1.0
  • You can then use the Release target, specifying the version number either in the RELEASE_VERSION environment variable, or else as a parameter after the target name. This will:
    • update CHANGELOG.md, moving changes from the Unreleased section into a new 0.2.0 section
      • if there were any prerelease versions of 0.2.0 in the changelog, it will also collect their changes into the final 0.2.0 entry
    • make a commit bumping the version: Bump version to 0.2.0 and adds the new changelog section to the commit's body
    • publish the package to NuGet
    • push a git tag
    • create a GitHub release for that git tag

macOS/Linux Parameter:

./build.sh Release 0.2.0

macOS/Linux Environment Variable:

RELEASE_VERSION=0.2.0 ./build.sh Release