563 lines
22 KiB
Markdown
563 lines
22 KiB
Markdown
---
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stage: none
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group: unassigned
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info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#assignments
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---
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# Go standards and style guidelines
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This document describes various guidelines and best practices for GitLab
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projects using the [Go language](https://go.dev/).
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## Overview
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GitLab is built on top of [Ruby on Rails](https://rubyonrails.org/), but we're
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also using Go for projects where it makes sense. Go is a very powerful
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language, with many advantages, and is best suited for projects with a lot of
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IO (disk/network access), HTTP requests, parallel processing, and so on. Since we
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have both Ruby on Rails and Go at GitLab, we should evaluate carefully which of
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the two is best for the job.
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This page aims to define and organize our Go guidelines, based on our various
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experiences. Several projects were started with different standards and they
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can still have specifics. They are described in their respective
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`README.md` or `PROCESS.md` files.
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## Go language versions
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The Go upgrade documentation [provides an overview](go_upgrade.md#overview)
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of how GitLab manages and ships Go binary support.
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If a GitLab component requires a newer version of Go, please
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follow the [upgrade process](go_upgrade.md#updating-go-version) to ensure no customer, team, or component is adversely impacted.
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Sometimes, individual projects must also [manage builds with multiple versions of Go](go_upgrade.md#supporting-multiple-go-versions).
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## Dependency Management
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Go uses a source-based strategy for dependency management. Dependencies are
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downloaded as source from their source repository. This differs from the more
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common artifact-based strategy where dependencies are downloaded as artifacts
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from a package repository that is separate from the dependency's source
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repository.
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Go did not have first-class support for version management prior to 1.11. That
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version introduced Go modules and the use of semantic versioning. Go 1.12
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introduced module proxies, which can serve as an intermediate between clients
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and source version control systems, and checksum databases, which can be used to
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verify the integrity of dependency downloads.
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See [Dependency Management in Go](dependencies.md) for more details.
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## Code Review
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We follow the common principles of
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[Go Code Review Comments](https://github.com/golang/go/wiki/CodeReviewComments).
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Reviewers and maintainers should pay attention to:
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- `defer` functions: ensure the presence when needed, and after `err` check.
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- Inject dependencies as parameters.
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- Void structs when marshaling to JSON (generates `null` instead of `[]`).
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### Security
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Security is our top priority at GitLab. During code reviews, we must take care
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of possible security breaches in our code:
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- XSS when using text/template
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- CSRF Protection using Gorilla
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- Use a Go version without known vulnerabilities
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- Don't leak secret tokens
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- SQL injections
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Remember to run
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[SAST](../../user/application_security/sast/index.md) and [Dependency Scanning](../../user/application_security/dependency_scanning/index.md)
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**(ULTIMATE)** on your project (or at least the
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[`gosec` analyzer](https://gitlab.com/gitlab-org/security-products/analyzers/gosec)),
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and to follow our [Security requirements](../code_review.md#security).
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Web servers can take advantages of middlewares like [Secure](https://github.com/unrolled/secure).
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### Finding a reviewer
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Many of our projects are too small to have full-time maintainers. That's why we
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have a shared pool of Go reviewers at GitLab. To find a reviewer, use the
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["Go" section](https://about.gitlab.com/handbook/engineering/projects/#gitlab_reviewers_go)
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of the "GitLab" project on the Engineering Projects
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page in the handbook.
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To add yourself to this list, add the following to your profile in the
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[`team.yml`](https://gitlab.com/gitlab-com/www-gitlab-com/blob/master/data/team.yml)
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file and ask your manager to review and merge.
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```yaml
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projects:
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gitlab: reviewer go
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```
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## Code style and format
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- Avoid global variables, even in packages. By doing so you introduce side
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effects if the package is included multiple times.
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- Use `goimports` before committing.
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[`goimports`](https://pkg.go.dev/golang.org/x/tools/cmd/goimports)
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is a tool that automatically formats Go source code using
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[`Gofmt`](https://pkg.go.dev/cmd/gofmt), in addition to formatting import lines,
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adding missing ones and removing unreferenced ones.
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Most editors/IDEs allow you to run commands before/after saving a file, you can set it
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up to run `goimports` so that it's applied to every file when saving.
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- Place private methods below the first caller method in the source file.
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### Automatic linting
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All Go projects should include these GitLab CI/CD jobs:
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```yaml
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lint:
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image: registry.gitlab.com/gitlab-org/gitlab-build-images:golangci-lint-alpine
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stage: test
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script:
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# Use default .golangci.yml file from the image if one is not present in the project root.
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- '[ -e .golangci.yml ] || cp /golangci/.golangci.yml .'
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# Write the code coverage report to gl-code-quality-report.json
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# and print linting issues to stdout in the format: path/to/file:line description
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# remove `--issues-exit-code 0` or set to non-zero to fail the job if linting issues are detected
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- golangci-lint run --issues-exit-code 0 --out-format code-climate | tee gl-code-quality-report.json | jq -r '.[] | "\(.location.path):\(.location.lines.begin) \(.description)"'
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artifacts:
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reports:
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codequality: gl-code-quality-report.json
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paths:
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- gl-code-quality-report.json
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```
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Including a `.golangci.yml` in the root directory of the project allows for
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configuration of `golangci-lint`. All options for `golangci-lint` are listed in
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this [example](https://github.com/golangci/golangci-lint/blob/master/.golangci.example.yml).
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Once [recursive includes](https://gitlab.com/gitlab-org/gitlab-foss/-/issues/56836)
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become available, you can share job templates like this
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[analyzer](https://gitlab.com/gitlab-org/security-products/ci-templates/raw/master/includes-dev/analyzer.yml).
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Go GitLab linter plugins are maintained in the [`gitlab-org/language-tools/go/linters`](https://gitlab.com/gitlab-org/language-tools/go/linters/) namespace.
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## Dependencies
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Dependencies should be kept to the minimum. The introduction of a new
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dependency should be argued in the merge request, as per our [Approval
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Guidelines](../code_review.md#approval-guidelines). Both [License
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Scanning](../../user/compliance/license_compliance/index.md)
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**(ULTIMATE)** and [Dependency
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Scanning](../../user/application_security/dependency_scanning/index.md)
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**(ULTIMATE)** should be activated on all projects to ensure new dependencies
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security status and license compatibility.
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### Modules
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In Go 1.11 and later, a standard dependency system is available behind the name [Go
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Modules](https://github.com/golang/go/wiki/Modules). It provides a way to
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define and lock dependencies for reproducible builds. It should be used
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whenever possible.
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When Go Modules are in use, there should not be a `vendor/` directory. Instead,
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Go automatically downloads dependencies when they are needed to build the
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project. This is in line with how dependencies are handled with Bundler in Ruby
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projects, and makes merge requests easier to review.
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In some cases, such as building a Go project for it to act as a dependency of a
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CI run for another project, removing the `vendor/` directory means the code must
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be downloaded repeatedly, which can lead to intermittent problems due to rate
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limiting or network failures. In these circumstances, you should [cache the
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downloaded code between](../../ci/caching/index.md#cache-go-dependencies).
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There was a
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[bug on modules checksums](https://github.com/golang/go/issues/29278) in Go versions earlier than v1.11.4, so make
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sure to use at least this version to avoid `checksum mismatch` errors.
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### ORM
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We don't use object-relational mapping libraries (ORMs) at GitLab (except
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[ActiveRecord](https://guides.rubyonrails.org/active_record_basics.html) in
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Ruby on Rails). Projects can be structured with services to avoid them.
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[`pgx`](https://github.com/jackc/pgx) should be enough to interact with PostgreSQL
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databases.
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### Migrations
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In the rare event of managing a hosted database, it's necessary to use a
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migration system like ActiveRecord is providing. A simple library like
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[Journey](https://github.com/db-journey/journey), designed to be used in
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`postgres` containers, can be deployed as long-running pods. New versions
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deploy a new pod, migrating the data automatically.
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## Testing
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### Testing frameworks
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We should not use any specific library or framework for testing, as the
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[standard library](https://pkg.go.dev/std) provides already everything to get
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started. If there is a need for more sophisticated testing tools, the following
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external dependencies might be worth considering in case we decide to use a specific
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library or framework:
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- [Testify](https://github.com/stretchr/testify)
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- [`httpexpect`](https://github.com/gavv/httpexpect)
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### Subtests
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Use [subtests](https://go.dev/blog/subtests) whenever possible to improve
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code readability and test output.
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### Better output in tests
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When comparing expected and actual values in tests, use
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[`testify/require.Equal`](https://pkg.go.dev/github.com/stretchr/testify/require#Equal),
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[`testify/require.EqualError`](https://pkg.go.dev/github.com/stretchr/testify/require#EqualError),
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[`testify/require.EqualValues`](https://pkg.go.dev/github.com/stretchr/testify/require#EqualValues),
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and others to improve readability when comparing structs, errors,
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large portions of text, or JSON documents:
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```golang
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type TestData struct {
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// ...
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}
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func FuncUnderTest() TestData {
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// ...
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}
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func Test(t *testing.T) {
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t.Run("FuncUnderTest", func(t *testing.T) {
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want := TestData{}
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got := FuncUnderTest()
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require.Equal(t, want, got) // note that expected value comes first, then comes the actual one ("diff" semantics)
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})
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}
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```
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### Table-Driven Tests
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Using [Table-Driven Tests](https://github.com/golang/go/wiki/TableDrivenTests)
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is generally good practice when you have multiple entries of
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inputs/outputs for the same function. Below are some guidelines one can
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follow when writing table-driven test. These guidelines are mostly
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extracted from Go standard library source code. Keep in mind it's OK not
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to follow these guidelines when it makes sense.
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#### Defining test cases
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Each table entry is a complete test case with inputs and expected
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results, and sometimes with additional information such as a test name
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to make the test output easily readable.
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- [Define a slice of anonymous struct](https://github.com/golang/go/blob/50bd1c4d4eb4fac8ddeb5f063c099daccfb71b26/src/encoding/csv/reader_test.go#L16)
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inside of the test.
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- [Define a slice of anonymous struct](https://github.com/golang/go/blob/55d31e16c12c38d36811bdee65ac1f7772148250/src/cmd/go/internal/module/module_test.go#L9-L66)
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outside of the test.
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- [Named structs](https://github.com/golang/go/blob/2e0cd2aef5924e48e1ceb74e3d52e76c56dd34cc/src/cmd/go/internal/modfetch/coderepo_test.go#L54-L69)
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for code reuse.
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- [Using `map[string]struct{}`](https://github.com/golang/go/blob/6d5caf38e37bf9aeba3291f1f0b0081f934b1187/src/cmd/trace/annotations_test.go#L180-L235).
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#### Contents of the test case
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- Ideally, each test case should have a field with a unique identifier
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to use for naming subtests. In the Go standard library, this is commonly the
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`name string` field.
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- Use `want`/`expect`/`actual` when you are specifying something in the
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test case that is used for assertion.
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#### Variable names
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- Each table-driven test map/slice of struct can be named `tests`.
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- When looping through `tests` the anonymous struct can be referred
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to as `tt` or `tc`.
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- The description of the test can be referred to as
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`name`/`testName`/`tn`.
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### Benchmarks
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Programs handling a lot of IO or complex operations should always include
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[benchmarks](https://pkg.go.dev/testing#hdr-Benchmarks), to ensure
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performance consistency over time.
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## Error handling
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### Adding context
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Adding context before you return the error can be helpful, instead of
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just returning the error. This allows developers to understand what the
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program was trying to do when it entered the error state making it much
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easier to debug.
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For example:
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```golang
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// Wrap the error
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return nil, fmt.Errorf("get cache %s: %w", f.Name, err)
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// Just add context
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return nil, fmt.Errorf("saving cache %s: %v", f.Name, err)
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```
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A few things to keep in mind when adding context:
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- Decide if you want to expose the underlying error
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to the caller. If so, use `%w`, if not, you can use `%v`.
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- Don't use words like `failed`, `error`, `didn't`. As it's an error,
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the user already knows that something failed and this might lead to
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having strings like `failed xx failed xx failed xx`. Explain _what_
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failed instead.
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- Error strings should not be capitalized or end with punctuation or a
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newline. You can use `golint` to check for this.
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### Naming
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- When using sentinel errors they should always be named like `ErrXxx`.
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- When creating a new error type they should always be named like
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`XxxError`.
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### Checking Error types
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- To check error equality don't use `==`. Use
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[`errors.Is`](https://pkg.go.dev/errors?tab=doc#Is) instead (for Go
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versions >= 1.13).
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- To check if the error is of a certain type don't use type assertion,
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use [`errors.As`](https://pkg.go.dev/errors?tab=doc#As) instead (for
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Go versions >= 1.13).
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### References for working with errors
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- [Go 1.13 errors](https://go.dev/blog/go1.13-errors).
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- [Programing with
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errors](https://peter.bourgon.org/blog/2019/09/11/programming-with-errors.html).
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- [Don't just check errors, handle them
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gracefully](https://dave.cheney.net/2016/04/27/dont-just-check-errors-handle-them-gracefully).
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## CLIs
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Every Go program is launched from the command line.
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[`cli`](https://github.com/urfave/cli) is a convenient package to create command
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line apps. It should be used whether the project is a daemon or a simple CLI
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tool. Flags can be mapped to [environment
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variables](https://github.com/urfave/cli#values-from-the-environment) directly,
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which documents and centralizes at the same time all the possible command line
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interactions with the program. Don't use `os.GetEnv`, it hides variables deep
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in the code.
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## Daemons
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### Logging
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The usage of a logging library is strongly recommended for daemons. Even
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though there is a `log` package in the standard library, we generally use
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[Logrus](https://github.com/sirupsen/logrus). Its plugin ("hooks") system
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makes it a powerful logging library, with the ability to add notifiers and
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formatters at the logger level directly.
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#### Structured (JSON) logging
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Every binary ideally must have structured (JSON) logging in place as it helps
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with searching and filtering the logs. At GitLab we use structured logging in
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JSON format, as all our infrastructure assumes that. When using
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[Logrus](https://github.com/sirupsen/logrus) you can turn on structured
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logging simply by using the build in [JSON
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formatter](https://github.com/sirupsen/logrus#formatters). This follows the
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same logging type we use in our [Ruby applications](../logging.md#use-structured-json-logging).
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#### How to use Logrus
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There are a few guidelines one should follow when using the
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[Logrus](https://github.com/sirupsen/logrus) package:
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- When printing an error use
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[WithError](https://pkg.go.dev/github.com/sirupsen/logrus#WithError). For
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example, `logrus.WithError(err).Error("Failed to do something")`.
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- Since we use [structured logging](#structured-json-logging) we can log
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fields in the context of that code path, such as the URI of the request using
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[`WithField`](https://pkg.go.dev/github.com/sirupsen/logrus#WithField) or
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[`WithFields`](https://pkg.go.dev/github.com/sirupsen/logrus#WithFields). For
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example, `logrus.WithField("file", "/app/go").Info("Opening dir")`. If you
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have to log multiple keys, always use `WithFields` instead of calling
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`WithField` more than once.
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### Tracing and Correlation
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[LabKit](https://gitlab.com/gitlab-org/labkit) is a place to keep common
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libraries for Go services. Currently it's vendored into two projects:
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Workhorse and Gitaly, and it exports two main (but related) pieces of
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functionality:
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- [`gitlab.com/gitlab-org/labkit/correlation`](https://gitlab.com/gitlab-org/labkit/tree/master/correlation):
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for propagating and extracting correlation ids between services.
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- [`gitlab.com/gitlab-org/labkit/tracing`](https://gitlab.com/gitlab-org/labkit/tree/master/tracing):
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for instrumenting Go libraries for distributed tracing.
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This gives us a thin abstraction over underlying implementations that is
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consistent across Workhorse, Gitaly, and, in future, other Go servers. For
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example, in the case of `gitlab.com/gitlab-org/labkit/tracing` we can switch
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from using `Opentracing` directly to using `Zipkin` or Gokit's own tracing wrapper
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without changes to the application code, while still keeping the same
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consistent configuration mechanism (that is, the `GITLAB_TRACING` environment
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variable).
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### Context
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Since daemons are long-running applications, they should have mechanisms to
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manage cancellations, and avoid unnecessary resources consumption (which could
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lead to DDoS vulnerabilities). [Go Context](https://github.com/golang/go/wiki/CodeReviewComments#contexts)
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should be used in functions that can block and passed as the first parameter.
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## Dockerfiles
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Every project should have a `Dockerfile` at the root of their repository, to
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build and run the project. Since Go program are static binaries, they should
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not require any external dependency, and shells in the final image are useless.
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We encourage [Multistage
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builds](https://docs.docker.com/develop/develop-images/multistage-build/):
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- They let the user build the project with the right Go version and
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dependencies.
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- They generate a small, self-contained image, derived from `Scratch`.
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Generated Docker images should have the program at their `Entrypoint` to create
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portable commands. That way, anyone can run the image, and without parameters
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it displays its help message (if `cli` has been used).
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## Secure Team standards and style guidelines
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The following are some style guidelines that are specific to the Secure Team.
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### Code style and format
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Use `goimports -local gitlab.com/gitlab-org` before committing.
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[`goimports`](https://pkg.go.dev/golang.org/x/tools/cmd/goimports)
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is a tool that automatically formats Go source code using
|
|
[`Gofmt`](https://pkg.go.dev/cmd/gofmt), in addition to formatting import lines,
|
|
adding missing ones and removing unreferenced ones.
|
|
By using the `-local gitlab.com/gitlab-org` option, `goimports` groups locally referenced
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packages separately from external ones. See
|
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[the imports section](https://github.com/golang/go/wiki/CodeReviewComments#imports)
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|
of the Code Review Comments page on the Go wiki for more details.
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Most editors/IDEs allow you to run commands before/after saving a file, you can set it
|
|
up to run `goimports -local gitlab.com/gitlab-org` so that it's applied to every file when saving.
|
|
|
|
### Initializing slices
|
|
|
|
If initializing a slice, provide a capacity where possible to avoid extra
|
|
allocations.
|
|
|
|
<table>
|
|
<tr><th>:white_check_mark: Do</th><th>:x: Don't</th></tr>
|
|
<tr>
|
|
<td>
|
|
|
|
```golang
|
|
s2 := make([]string, 0, size)
|
|
for _, val := range s1 {
|
|
s2 = append(s2, val)
|
|
}
|
|
```
|
|
|
|
</td>
|
|
<td>
|
|
|
|
```golang
|
|
var s2 []string
|
|
for _, val := range s1 {
|
|
s2 = append(s2, val)
|
|
}
|
|
```
|
|
|
|
</td>
|
|
</tr>
|
|
</table>
|
|
|
|
If no capacity is passed to `make` when creating a new slice, `append`
|
|
will continuously resize the slice's backing array if it cannot hold
|
|
the values. Providing the capacity ensures that allocations are kept
|
|
to a minimum. It is recommended that the [`prealloc`](https://github.com/alexkohler/prealloc)
|
|
golanci-lint rule automatically check for this.
|
|
|
|
### Analyzer Tests
|
|
|
|
The conventional Secure [analyzer](https://gitlab.com/gitlab-org/security-products/analyzers/) has a [`convert` function](https://gitlab.com/gitlab-org/security-products/analyzers/command/-/blob/main/convert.go#L15-17) that converts SAST/DAST scanner reports into [GitLab Security Reports](https://gitlab.com/gitlab-org/security-products/security-report-schemas). When writing tests for the `convert` function, we should make use of [test fixtures](https://dave.cheney.net/2016/05/10/test-fixtures-in-go) using a `testdata` directory at the root of the analyzer's repository. The `testdata` directory should contain two subdirectories: `expect` and `reports`. The `reports` directory should contain sample SAST/DAST scanner reports which are passed into the `convert` function during the test setup. The `expect` directory should contain the expected GitLab Security Report that the `convert` returns. See Secret Detection for an [example](https://gitlab.com/gitlab-org/security-products/analyzers/secrets/-/blob/160424589ef1eed7b91b59484e019095bc7233bd/convert_test.go#L13-66).
|
|
|
|
If the scanner report is small, less than 35 lines, then feel free to [inline the report](https://gitlab.com/gitlab-org/security-products/analyzers/sobelow/-/blob/8bd2428a/convert/convert_test.go#L13-77) rather than use a `testdata` directory.
|
|
|
|
#### Test Diffs
|
|
|
|
The [go-cmp](https://github.com/google/go-cmp) package should be used when comparing large structs in tests. It makes it possible to output a specific diff where the two structs differ, rather than seeing the whole of both structs printed out in the test logs. Here is a small example:
|
|
|
|
```golang
|
|
package main
|
|
|
|
import (
|
|
"reflect"
|
|
"testing"
|
|
|
|
"github.com/google/go-cmp/cmp"
|
|
)
|
|
|
|
type Foo struct {
|
|
Desc Bar
|
|
Point Baz
|
|
}
|
|
|
|
type Bar struct {
|
|
A string
|
|
B string
|
|
}
|
|
|
|
type Baz struct {
|
|
X int
|
|
Y int
|
|
}
|
|
|
|
func TestHelloWorld(t *testing.T) {
|
|
want := Foo{
|
|
Desc: Bar{A: "a", B: "b"},
|
|
Point: Baz{X: 1, Y: 2},
|
|
}
|
|
|
|
got := Foo{
|
|
Desc: Bar{A: "a", B: "b"},
|
|
Point: Baz{X: 2, Y: 2},
|
|
}
|
|
|
|
t.Log("reflect comparison:")
|
|
if !reflect.DeepEqual(got, want) {
|
|
t.Errorf("Wrong result. want:\n%v\nGot:\n%v", want, got)
|
|
}
|
|
|
|
t.Log("cmp comparison:")
|
|
if diff := cmp.Diff(want, got); diff != "" {
|
|
t.Errorf("Wrong result. (-want +got):\n%s", diff)
|
|
}
|
|
}
|
|
```
|
|
|
|
The output demonstrates why `go-cmp` is far superior when comparing large structs. Even though you could spot the difference with this small difference, it quickly gets unwieldy as the data grows.
|
|
|
|
```plaintext
|
|
main_test.go:36: reflect comparison:
|
|
main_test.go:38: Wrong result. want:
|
|
{{a b} {1 2}}
|
|
Got:
|
|
{{a b} {2 2}}
|
|
main_test.go:41: cmp comparison:
|
|
main_test.go:43: Wrong result. (-want +got):
|
|
main.Foo{
|
|
Desc: {A: "a", B: "b"},
|
|
Point: main.Baz{
|
|
- X: 1,
|
|
+ X: 2,
|
|
Y: 2,
|
|
},
|
|
}
|
|
```
|
|
|
|
---
|
|
|
|
[Return to Development documentation](../index.md).
|