From c3ac87ae9b21c77b3ecd7e0f253499ce94762cd5 Mon Sep 17 00:00:00 2001
From: Bruno Carlin <bruno.carlin@waarp.org>
Date: Fri, 19 Nov 2021 13:21:46 +0100
Subject: [PATCH] initial commit

---
 .golangci.yml | 805 ++++++++++++++++++++++++++++++++++++++++++++++++++
 cache.go      |  93 ++++++
 cache_test.go | 156 ++++++++++
 go.mod        |   3 +
 4 files changed, 1057 insertions(+)
 create mode 100644 .golangci.yml
 create mode 100644 cache.go
 create mode 100644 cache_test.go
 create mode 100644 go.mod

diff --git a/.golangci.yml b/.golangci.yml
new file mode 100644
index 0000000..04e3e2a
--- /dev/null
+++ b/.golangci.yml
@@ -0,0 +1,805 @@
+# options for analysis running
+run:
+  # default concurrency is a available CPU number
+  concurrency: 4
+
+  # timeout for analysis, e.g. 30s, 5m, default is 1m
+  timeout: 1m
+
+  # exit code when at least one issue was found, default is 1
+  issues-exit-code: 1
+
+  # include test files or not, default is true
+  tests: true
+
+  # list of build tags, all linters use it. Default is empty list.
+  #build-tags:
+  #  - mytag
+
+  # which dirs to skip: issues from them won't be reported;
+  # can use regexp here: generated.*, regexp is applied on full path;
+  # default value is empty list, but default dirs are skipped independently
+  # from this option's value (see skip-dirs-use-default).
+  # "/" will be replaced by current OS file path separator to properly work
+  # on Windows.
+  #skip-dirs:
+  #  - src/external_libs
+  #  - autogenerated_by_my_lib
+
+  # default is true. Enables skipping of directories:
+  #   vendor$, third_party$, testdata$, examples$, Godeps$, builtin$
+  skip-dirs-use-default: true
+
+  # which files to skip: they will be analyzed, but issues from them
+  # won't be reported. Default value is empty list, but there is
+  # no need to include all autogenerated files, we confidently recognize
+  # autogenerated files. If it's not please let us know.
+  # "/" will be replaced by current OS file path separator to properly work
+  # on Windows.
+  #skip-files:
+  #  - ".*\\.my\\.go$"
+  #  - lib/bad.go
+
+  # by default isn't set. If set we pass it to "go list -mod={option}". From "go help modules":
+  # If invoked with -mod=readonly, the go command is disallowed from the implicit
+  # automatic updating of go.mod described above. Instead, it fails when any changes
+  # to go.mod are needed. This setting is most useful to check that go.mod does
+  # not need updates, such as in a continuous integration and testing system.
+  # If invoked with -mod=vendor, the go command assumes that the vendor
+  # directory holds the correct copies of dependencies and ignores
+  # the dependency descriptions in go.mod.
+  #modules-download-mode: readonly|vendor|mod
+
+  # Allow multiple parallel golangci-lint instances running.
+  # If false (default) - golangci-lint acquires file lock on start.
+  allow-parallel-runners: false
+
+
+# output configuration options
+output:
+  # colored-line-number|line-number|json|tab|checkstyle|code-climate|junit-xml|github-actions
+  # default is "colored-line-number"
+  #format: colored-line-number
+
+  # print lines of code with issue, default is true
+  print-issued-lines: true
+
+  # print linter name in the end of issue text, default is true
+  print-linter-name: true
+
+  # make issues output unique by line, default is true
+  #uniq-by-line: true
+
+  # add a prefix to the output file references; default is no prefix
+  path-prefix: ""
+
+  # sorts results by: filepath, line and column
+  sort-results: true
+
+
+# all available settings of specific linters
+linters-settings:
+
+  cyclop:
+    # the maximal code complexity to report
+    max-complexity: 20
+    # the maximal average package complexity. If it's higher than 0.0 (float) the check is enabled (default 0.0)
+    package-average: 0.0
+    # should ignore tests (default false)
+    skip-tests: true
+
+  dogsled:
+    # checks assignments with too many blank identifiers; default is 2
+    max-blank-identifiers: 2
+
+  dupl:
+    # tokens count to trigger issue, 150 by default
+    threshold: 100
+
+  errcheck:
+    # report about not checking of errors in type assertions: `a := b.(MyStruct)`;
+    # default is false: such cases aren't reported by default.
+    check-type-assertions: true
+
+    # report about assignment of errors to blank identifier: `num, _ := strconv.Atoi(numStr)`;
+    # default is false: such cases aren't reported by default.
+    check-blank: true
+
+    # [deprecated] comma-separated list of pairs of the form pkg:regex
+    # the regex is used to ignore names within pkg. (default "fmt:.*").
+    # see https://github.com/kisielk/errcheck#the-deprecated-method for details
+    ignore: fmt:.*,io/ioutil:^Read.*
+
+    # [deprecated] use exclude-functions instead.
+    # path to a file containing a list of functions to exclude from checking
+    # see https://github.com/kisielk/errcheck#excluding-functions for details
+    #exclude: /path/to/file.txt
+
+    # list of functions to exclude from checking, where each entry is a single function to exclude.
+    # see https://github.com/kisielk/errcheck#excluding-functions for details
+    exclude-functions:
+      - io/ioutil.ReadFile
+      - io.Copy(*bytes.Buffer)
+      - io.Copy(os.Stdout)
+
+  errorlint:
+    # Check whether fmt.Errorf uses the %w verb for formatting errors. See the readme for caveats
+    errorf: true
+    # Check for plain type assertions and type switches
+    asserts: true
+    # Check for plain error comparisons
+    comparison: true
+
+  exhaustive:
+    # check switch statements in generated files also
+    check-generated: false
+    # indicates that switch statements are to be considered exhaustive if a
+    # 'default' case is present, even if all enum members aren't listed in the
+    # switch
+    default-signifies-exhaustive: true
+
+  #exhaustivestruct:
+  #  # Struct Patterns is list of expressions to match struct packages and names
+  #  # The struct packages have the form example.com/package.ExampleStruct
+  #  # The matching patterns can use matching syntax from https://pkg.go.dev/path#Match
+  #  # If this list is empty, all structs are tested.
+  #  struct-patterns:
+  #    - '*.Test'
+  #    - 'example.com/package.ExampleStruct'
+
+  forbidigo:
+    # Forbid the following identifiers (identifiers are written using regexp):
+    forbid:
+      - ^print.*$
+      - 'fmt\.Print.*'
+    # Exclude godoc examples from forbidigo checks.  Default is true.
+    exclude_godoc_examples: true
+
+  funlen:
+    lines: 60
+    statements: 40
+
+  gci:
+    # put imports beginning with prefix after 3rd-party packages;
+    # only support one prefix
+    # if not set, use goimports.local-prefixes
+    #local-prefixes: github.com/org/project
+
+  gocognit:
+    # minimal code complexity to report, 30 by default (but we recommend 10-20)
+    min-complexity: 30
+
+  nestif:
+    # minimal complexity of if statements to report, 5 by default
+    min-complexity: 8
+
+  goconst:
+    # minimal length of string constant, 3 by default
+    min-len: 3
+    # minimum occurrences of constant string count to trigger issue, 3 by default
+    min-occurrences: 3
+    # ignore test files, false by default
+    ignore-tests: false
+    # look for existing constants matching the values, true by default
+    match-constant: true
+    # search also for duplicated numbers, false by default
+    numbers: false
+    # minimum value, only works with goconst.numbers, 3 by default
+    min: 3
+    # maximum value, only works with goconst.numbers, 3 by default
+    max: 3
+    # ignore when constant is not used as function argument, true by default
+    ignore-calls: true
+
+  gocritic:
+    # Which checks should be enabled; can't be combined with 'disabled-checks';
+    # See https://go-critic.github.io/overview#checks-overview
+    # To check which checks are enabled run `GL_DEBUG=gocritic golangci-lint run`
+    # By default list of stable checks is used.
+    #enabled-checks:
+    #  - rangeValCopy
+
+    # Which checks should be disabled; can't be combined with 'enabled-checks'; default is empty
+    #disabled-checks:
+    #  - regexpMust
+
+    # Enable multiple checks by tags, run `GL_DEBUG=gocritic golangci-lint run` to see all tags and checks.
+    # Empty list by default. See https://github.com/go-critic/go-critic#usage -> section "Tags".
+    enabled-tags:
+      - diagnostic
+      - opinionated
+      - performance
+      - style
+    disabled-tags:
+      - experimental
+
+    # Settings passed to gocritic.
+    # The settings key is the name of a supported gocritic checker.
+    # The list of supported checkers can be find in https://go-critic.github.io/overview.
+    settings:
+      captLocal: # must be valid enabled check name
+        # whether to restrict checker to params only (default true)
+        paramsOnly: true
+      elseif:
+        # whether to skip balanced if-else pairs (default true)
+        skipBalanced: true
+      hugeParam:
+        # size in bytes that makes the warning trigger (default 80)
+        sizeThreshold: 80
+      #nestingReduce:
+      #  # min number of statements inside a branch to trigger a warning (default 5)
+      #  bodyWidth: 5
+      rangeExprCopy:
+        # size in bytes that makes the warning trigger (default 512)
+        sizeThreshold: 512
+        # whether to check test functions (default true)
+        skipTestFuncs: true
+      rangeValCopy:
+        # size in bytes that makes the warning trigger (default 128)
+        sizeThreshold: 128
+        # whether to check test functions (default true)
+        skipTestFuncs: true
+      # ruleguard:
+      #   # path to a gorules file for the ruleguard checker
+      #   rules: ''
+      # truncateCmp:
+      #   # whether to skip int/uint/uintptr types (default true)
+      #   skipArchDependent: true
+      underef:
+        # whether to skip (*x).method() calls where x is a pointer receiver (default true)
+        skipRecvDeref: true
+      #unnamedResult:
+      #  # whether to check exported functions
+      #  checkExported: true
+
+  gocyclo:
+    # minimal code complexity to report, 30 by default (but we recommend 10-20)
+    min-complexity: 20
+
+  godot:
+    # comments to be checked: `declarations`, `toplevel`, or `all`
+    scope: all
+    # list of regexps for excluding particular comment lines from check
+    exclude:
+      # example: exclude comments which contain numbers
+      # - '[0-9]+'
+    # check that each sentence starts with a capital letter
+    capital: true
+
+  godox:
+    # report any comments starting with keywords, this is useful for TODO or FIXME comments that
+    # might be left in the code accidentally and should be resolved before merging
+    keywords: # default keywords are TODO, BUG, and FIXME, these can be overwritten by this setting
+      - NOTE
+      - OPTIMIZE # marks code that should be optimized before merging
+      - HACK # marks hack-arounds that should be removed before merging
+
+  gofmt:
+    # simplify code: gofmt with `-s` option, true by default
+    simplify: true
+
+  gofumpt:
+    # Select the Go version to target. The default is `1.15`.
+    #lang-version: "1.15"
+
+    # Choose whether or not to use the extra rules that are disabled
+    # by default
+    extra-rules: false
+
+  goheader:
+    values:
+      const:
+        # define here const type values in format k:v, for example:
+        # COMPANY: MY COMPANY
+      regexp:
+        # define here regexp type values, for example
+        # AUTHOR: .*@mycompany\.com
+    template: # |-
+      # put here copyright header template for source code files, for example:
+      # Note: {{ YEAR }} is a builtin value that returns the year relative to the current machine time.
+      #
+      # {{ AUTHOR }} {{ COMPANY }} {{ YEAR }}
+      # SPDX-License-Identifier: Apache-2.0
+
+      # Licensed under the Apache License, Version 2.0 (the "License");
+      # you may not use this file except in compliance with the License.
+      # You may obtain a copy of the License at:
+
+      #   http://www.apache.org/licenses/LICENSE-2.0
+
+      # Unless required by applicable law or agreed to in writing, software
+      # distributed under the License is distributed on an "AS IS" BASIS,
+      # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+      # See the License for the specific language governing permissions and
+      # limitations under the License.
+    template-path:
+      # also as alternative of directive 'template' you may put the path to file with the template source
+
+  goimports:
+    # put imports beginning with prefix after 3rd-party packages;
+    # it's a comma-separated list of prefixes
+    local-prefixes: code.waarp.fr/apps/gateway/gateway
+
+  golint:
+    # minimal confidence for issues, default is 0.8
+    min-confidence: 0.8
+
+  gomnd:
+    settings:
+      mnd:
+        # the list of enabled checks, see https://github.com/tommy-muehle/go-mnd/#checks for description.
+        checks: argument,case,condition,operation,return,assign
+        # for files perm: 384=0o600
+        ignored-numbers: 0o600,384,0o700,0o744
+        # test files are ignored by default
+        # ignored-files: 
+        # ignored-functions: math.*
+
+  gomoddirectives:
+    # Allow local `replace` directives. Default is false.
+    replace-local: false
+    # List of allowed `replace` directives. Default is empty.
+    replace-allow-list:
+      - launchpad.net/gocheck
+    # Allow to not explain why the version has been retracted in the `retract` directives. Default is false.
+    retract-allow-no-explanation: false
+    # Forbid the use of the `exclude` directives. Default is false.
+    exclude-forbidden: false
+
+  gomodguard:
+    allowed:
+      modules:                                                        # List of allowed modules
+        # - gopkg.in/yaml.v2
+      domains:                                                        # List of allowed module domains
+        # - golang.org
+    blocked:
+      modules:                                                        # List of blocked modules
+        # - github.com/uudashr/go-module:                             # Blocked module
+        #     recommendations:                                        # Recommended modules that should be used instead (Optional)
+        #       - golang.org/x/mod
+        #     reason: "`mod` is the official go.mod parser library."  # Reason why the recommended module should be used (Optional)
+      versions:                                                       # List of blocked module version constraints
+        # - github.com/mitchellh/go-homedir:                          # Blocked module with version constraint
+        #     version: "< 1.1.0"                                      # Version constraint, see https://github.com/Masterminds/semver#basic-comparisons
+        #     reason: "testing if blocked version constraint works."  # Reason why the version constraint exists. (Optional)
+      local_replace_directives: false                                 # Set to true to raise lint issues for packages that are loaded from a local path via replace directive
+
+  gosec:
+    # To select a subset of rules to run.
+    # Available rules: https://github.com/securego/gosec#available-rules
+    #includes:
+    #  - G401
+    #  - G306
+    #  - G101
+    # To specify a set of rules to explicitly exclude.
+    # Available rules: https://github.com/securego/gosec#available-rules
+    #excludes:
+    #  - G204
+    # To specify the configuration of rules.
+    # The configuration of rules is not fully documented by gosec:
+    # https://github.com/securego/gosec#configuration
+    # https://github.com/securego/gosec/blob/569328eade2ccbad4ce2d0f21ee158ab5356a5cf/rules/rulelist.go#L60-L102
+    #config:
+    #  G306: "0600"
+    #  G101:
+    #    pattern: "(?i)example"
+    #    ignore_entropy: false
+    #    entropy_threshold: "80.0"
+    #    per_char_threshold: "3.0"
+    #    truncate: "32"
+
+  gosimple:
+    # Select the Go version to target. The default is '1.13'.
+    #go: "1.15"
+    # https://staticcheck.io/docs/options#checks
+    checks: [ "all" ]
+
+  govet:
+    # report about shadowed variables
+    check-shadowing: true
+
+    # settings per analyzer
+    #settings:
+    #  printf: # analyzer name, run `go tool vet help` to see all analyzers
+    #    funcs: # run `go tool vet help printf` to see available settings for `printf` analyzer
+    #      - (github.com/golangci/golangci-lint/pkg/logutils.Log).Infof
+    #      - (github.com/golangci/golangci-lint/pkg/logutils.Log).Warnf
+    #      - (github.com/golangci/golangci-lint/pkg/logutils.Log).Errorf
+    #      - (github.com/golangci/golangci-lint/pkg/logutils.Log).Fatalf
+
+    # enable or disable analyzers by name
+    # run `go tool vet help` to see all analyzers
+    #enable:
+    #  - atomicalign
+    #enable-all: false
+    #disable:
+    #  - shadow
+    #disable-all: false
+
+  depguard:
+    list-type: blacklist
+    include-go-root: false
+    packages:
+      - github.com/sirupsen/logrus
+    packages-with-error-message:
+      # specify an error message to output when a blacklisted package is used
+      - github.com/sirupsen/logrus: "logging is allowed only by logutils.Log"
+
+  ifshort:
+    # Maximum length of variable declaration measured in number of lines, after which linter won't suggest using short syntax.
+    # Has higher priority than max-decl-chars.
+    #max-decl-lines: 1
+    # Maximum length of variable declaration measured in number of characters, after which linter won't suggest using short syntax.
+    #max-decl-chars: 30
+
+  importas:
+    # if set to `true`, force to use alias.
+    no-unaliased: false
+    # List of aliases
+    alias:
+      # using `servingv1` alias for `knative.dev/serving/pkg/apis/serving/v1` package
+      #- pkg: knative.dev/serving/pkg/apis/serving/v1
+      #  alias: servingv1
+      # using `autoscalingv1alpha1` alias for `knative.dev/serving/pkg/apis/autoscaling/v1alpha1` package
+      #- pkg: knative.dev/serving/pkg/apis/autoscaling/v1alpha1
+      #  alias: autoscalingv1alpha1
+      # You can specify the package path by regular expression,
+      # and alias by regular expression expansion syntax like below.
+      # see https://github.com/julz/importas#use-regular-expression for details
+      #- pkg: knative.dev/serving/pkg/apis/(\w+)/(v[\w\d]+)
+      #  alias: $1$2
+      #
+
+    # By default, it allows using errors, empty interfaces, anonymous interfaces,
+    # and interfaces provided by the standard library.
+    allow:
+      - error
+      - empty
+      - stdlib
+    # Reject patterns
+    reject:
+
+  lll:
+    # max line length, lines longer will be reported. Default is 120.
+    # '\t' is counted as 1 character by default, and can be changed with the tab-width option
+    line-length: 120
+    # tab width in spaces. Default to 1.
+    tab-width: 1
+
+  makezero:
+    # Allow only slices initialized with a length of zero. Default is false.
+    always: false
+
+  maligned:
+    # print struct with more effective memory layout or not, false by default
+    suggest-new: true
+
+  misspell:
+    # Correct spellings using locale preferences for US or UK.
+    # Default is to use a neutral variety of English.
+    # Setting locale to US will correct the British spelling of 'colour' to 'color'.
+    locale: US
+    ignore-words:
+      - someword
+
+  nakedret:
+    # make an issue if func has more lines of code than this setting and it has naked returns; default is 30
+    max-func-lines: 30
+
+  prealloc:
+    # XXX: we don't recommend using this linter before doing performance profiling.
+    # For most programs usage of prealloc will be a premature optimization.
+
+    # Report preallocation suggestions only on simple loops that have no returns/breaks/continues/gotos in them.
+    # True by default.
+    simple: true
+    range-loops: true # Report preallocation suggestions on range loops, true by default
+    for-loops: false # Report preallocation suggestions on for loops, false by default
+
+  promlinter:
+    # Promlinter cannot infer all metrics name in static analysis.
+    # Enable strict mode will also include the errors caused by failing to parse the args.
+    strict: false
+    # Please refer to https://github.com/yeya24/promlinter#usage for detailed usage.
+    disabled-linters:
+    #  - "Help"
+    #  - "MetricUnits"
+    #  - "Counter"
+    #  - "HistogramSummaryReserved"
+    #  - "MetricTypeInName"
+    #  - "ReservedChars"
+    #  - "CamelCase"
+    #  - "lintUnitAbbreviations"
+
+  predeclared:
+    # comma-separated list of predeclared identifiers to not report on
+    ignore: ""
+    # include method names and field names (i.e., qualified names) in checks
+    q: false
+
+  nolintlint:
+    # Enable to ensure that nolint directives are all used. Default is true.
+    allow-unused: true
+    # Disable to ensure that nolint directives don't have a leading space. Default is true.
+    allow-leading-space: no
+    # Exclude following linters from requiring an explanation.  Default is [].
+    allow-no-explanation: []
+    # Enable to require an explanation of nonzero length after each nolint directive. Default is false.
+    require-explanation: true
+    # Enable to require nolint directives to mention the specific linter being suppressed. Default is false.
+    require-specific: true
+
+  rowserrcheck:
+    #packages:
+    #  - github.com/jmoiron/sqlx
+
+  revive:
+    # see https://github.com/mgechev/revive#available-rules for details.
+    ignore-generated-header: true
+    severity: warning
+    #rules:
+    #  - name: indent-error-flow
+    #    severity: warning
+    #  - name: add-constant
+    #    severity: warning
+    #    arguments:
+    #      - maxLitCount: "3"
+    #        allowStrs: '""'
+    #        allowInts: "0,1,2"
+    #        allowFloats: "0.0,0.,1.0,1.,2.0,2."
+
+  staticcheck:
+    # Select the Go version to target. The default is '1.13'.
+    #go: "1.15"
+    # https://staticcheck.io/docs/options#checks
+    checks: [ "all" ]
+
+  stylecheck:
+    # Select the Go version to target. The default is '1.13'.
+    #go: "1.15"
+    # https://staticcheck.io/docs/options#checks
+    #checks: [ "all", "-ST1000", "-ST1003", "-ST1016", "-ST1020", "-ST1021", "-ST1022" ]
+    checks: [ "all" ]
+    # https://staticcheck.io/docs/options#dot_import_whitelist
+    dot-import-whitelist:
+      - fmt
+    # https://staticcheck.io/docs/options#initialisms
+    initialisms: [ "ACL", "API", "ASCII", "CPU", "CSS", "DNS", "EOF", "GUID", "HTML", "HTTP", "HTTPS", "ID", "IP", "JSON", "PEM", "QPS", "RAM", "RPC", "SLA", "SMTP", "SQL", "SSH", "TCP", "TLS", "TTL", "UDP", "UI", "GID", "UID", "UUID", "URI", "URL", "UTF8", "VM", "XML", "XMPP", "XSRF", "XSS" ]
+    # https://staticcheck.io/docs/options#http_status_code_whitelist
+    http-status-code-whitelist: [ "200", "400", "404", "500" ]
+
+  tagliatelle:
+    # check the struck tag name case
+    case:
+      # use the struct field name to check the name of the struct tag
+      use-field-name: true
+      rules:
+        # any struct tag type can be used.
+        # support string case: `camel`, `pascal`, `kebab`, `snake`, `goCamel`, `goPascal`, `goKebab`, `goSnake`, `upper`, `lower`
+        json: camel
+        yaml: camel
+        xml: camel
+        bson: camel
+        avro: snake
+        mapstructure: kebab
+
+  testpackage:
+    # regexp pattern to skip files
+    skip-regexp: (export|internal)_test\.go
+
+  thelper:
+    # The following configurations enable all checks. It can be omitted because all checks are enabled by default.
+    # You can enable only required checks deleting unnecessary checks.
+    test:
+      first: true
+      name: true
+      begin: true
+    benchmark:
+      first: true
+      name: true
+      begin: true
+    tb:
+      first: true
+      name: true
+      begin: true
+
+  unparam:
+    # Inspect exported functions, default is false. Set to true if no external program/library imports your code.
+    # XXX: if you enable this setting, unparam will report a lot of false-positives in text editors:
+    # if it's called for subdir of a project it can't find external interfaces. All text editor integrations
+    # with golangci-lint call it on a directory with the changed file.
+    check-exported: false
+
+  unused:
+    # Select the Go version to target. The default is '1.13'.
+    #go: "1.15"
+
+  varnamelen:
+    # The longest distance, in source lines, that is being considered a "small scope." (defaults to 5)
+    # Variables used in at most this many lines will be ignored.
+    max-distance: 15
+    # The minimum length of a variable's name that is considered "long." (defaults to 3)
+    # Variable names that are at least this long will be ignored.
+    min-name-length: 3
+    # Check method receiver names. (defaults to false)
+    check-receiver: false
+    # Check named return values. (defaults to false)
+    check-return: false
+    # Optional list of variable names that should be ignored completely. (defaults to empty list)
+    ignore-names:
+      - err
+      - db
+      - tx
+      - c
+      - wg
+      - r
+      - w
+
+  whitespace:
+    multi-if: false   # Enforces newlines (or comments) after every multi-line if statement
+    multi-func: false # Enforces newlines (or comments) after every multi-line function signature
+
+  wrapcheck:
+    # An array of strings that specify substrings of signatures to ignore.
+    # If this set, it will override the default set of ignored signatures.
+    # See https://github.com/tomarrell/wrapcheck#configuration for more information.
+    ignoreSigs:
+      - .Errorf(
+      - errors.New(
+      - errors.Unwrap(
+      - .Wrap(
+      - .Wrapf(
+      - .WithMessage(
+
+  wsl:
+    # See https://github.com/bombsimon/wsl/blob/master/doc/configuration.md for
+    # documentation of available settings. These are the defaults for
+    # `golangci-lint`.
+    allow-assign-and-anything: false
+    allow-assign-and-call: true
+    allow-cuddle-declarations: false
+    allow-multiline-assign: true
+    allow-separated-leading-comment: false
+    allow-trailing-comment: false
+    force-case-trailing-whitespace: 0
+    force-err-cuddling: false
+    force-short-decl-cuddling: false
+    strict-append: true
+
+linters:
+  disable-all: false
+    #enable:
+    #  - megacheck
+    #  - govet
+  enable-all: true
+  disable:
+    - depguard
+    - dogsled
+    - exhaustivestruct
+    - godox
+    - goheader
+    - golint
+    - interfacer
+    - ireturn
+    - maligned
+    - nilerr
+    - paralleltest
+    - prealloc
+    - scopelint
+    - testpackage
+  #presets:
+  #  - bugs
+  #  - unused
+  #fast: false
+
+
+issues:
+  # List of regexps of issue texts to exclude, empty list by default.
+  # But independently from this option we use default exclude patterns,
+  # it can be disabled by `exclude-use-default: false`. To list all
+  # excluded by default patterns execute `golangci-lint run --help`
+  exclude:
+    - abcdef
+
+  # Excluding configuration per-path, per-linter, per-text and per-source
+  exclude-rules:
+    # Exclude some linters from running on tests files.
+    - path: _test\.go
+      linters:
+        - dupl
+        - errcheck
+        - funlen
+        - goconst
+        - gocognit
+        - gocyclo
+        - gosec
+        - varnamelen
+
+    # Exclude known linters from partially hard-vendored code,
+    # which is impossible to exclude via "nolint" comments.
+    - path: internal/hmac/
+      text: "weak cryptographic primitive"
+      linters:
+        - gosec
+
+    # Exclude some staticcheck messages
+    - linters:
+        - staticcheck
+      text: "SA9003:"
+
+    # Exclude lll issues for long lines with go:generate
+    - linters:
+        - lll
+      source: "^//go:generate "
+
+    # dupl can mark code as duplicated when it finds matches in test files.
+    - linters:
+      - dupl
+      text: "_test.go"
+
+    # tagliatelle does not consider mac as a word
+    - linters:
+      - tagliatelle
+      text: "got 'macs' want 'maCs'"
+
+  # Independently from option `exclude` we use default exclude patterns,
+  # it can be disabled by this option. To list all
+  # excluded by default patterns execute `golangci-lint run --help`.
+  # Default value for this option is true.
+  exclude-use-default: false
+
+  # The default value is false. If set to true exclude and exclude-rules
+  # regular expressions become case sensitive.
+  exclude-case-sensitive: false
+
+  # The list of ids of default excludes to include or disable. By default it's empty.
+  #include:
+  #  - EXC0002 # disable excluding of issues about comments from golint
+
+  # Maximum issues count per one linter. Set to 0 to disable. Default is 50.
+  max-issues-per-linter: 0
+
+  # Maximum count of issues with the same text. Set to 0 to disable. Default is 3.
+  max-same-issues: 0
+
+  # Show only new issues: if there are unstaged changes or untracked files,
+  # only those changes are analyzed, else only changes in HEAD~ are analyzed.
+  # It's a super-useful option for integration of golangci-lint into existing
+  # large codebase. It's not practical to fix all existing issues at the moment
+  # of integration: much better don't allow issues in new code.
+  # Default is false.
+  new: false
+
+  # Show only new issues created after git revision `REV`
+  #new-from-rev: REV
+
+  # Show only new issues created in git patch with set file path.
+  #new-from-patch: path/to/patch/file
+
+  # Fix found issues (if it's supported by the linter)
+  fix: false
+
+severity:
+  # Default value is empty string.
+  # Set the default severity for issues. If severity rules are defined and the issues
+  # do not match or no severity is provided to the rule this will be the default
+  # severity applied. Severities should match the supported severity names of the
+  # selected out format.
+  # - Code climate: https://docs.codeclimate.com/docs/issues#issue-severity
+  # -   Checkstyle: https://checkstyle.sourceforge.io/property_types.html#severity
+  # -       Github: https://help.github.com/en/actions/reference/workflow-commands-for-github-actions#setting-an-error-message
+  default-severity: error
+
+  # The default value is false.
+  # If set to true severity-rules regular expressions become case sensitive.
+  case-sensitive: false
+
+  # Default value is empty list.
+  # When a list of severity rules are provided, severity information will be added to lint
+  # issues. Severity rules have the same filtering capability as exclude rules except you
+  # are allowed to specify one matcher per severity rule.
+  # Only affects out formats that support setting severity information.
+  rules:
+    - linters:
+      - dupl
+      severity: info
diff --git a/cache.go b/cache.go
new file mode 100644
index 0000000..ccb6a9a
--- /dev/null
+++ b/cache.go
@@ -0,0 +1,93 @@
+// Package cache defines an in-memory key-value store.
+//
+// It supports exîration dates andcan store arbitrary values of any type.
+// Keys must be strings.
+package cache
+
+import (
+	"sync"
+	"time"
+)
+
+type entry struct {
+	expirationDate time.Time
+	value          interface{}
+}
+
+// Cache is an in-memory key-value store.
+type Cache struct {
+	data map[string]entry
+	mu   *sync.RWMutex
+}
+
+// New instantiate a new cache.
+func New() *Cache {
+	return &Cache{
+		data: make(map[string]entry),
+		mu:   &sync.RWMutex{},
+	}
+}
+
+// Put stores a value in the cache under the given key.
+func (c *Cache) Put(key string, val interface{}) {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+
+	c.data[key] = entry{time.Time{}, val}
+}
+
+// PutTTL stores a value in the cache under the given key. The value will
+// be expired after the given ttl.
+//
+// A 0 ttl value disables the expiration of the value.
+func (c *Cache) PutTTL(key string, val interface{}, ttl time.Duration) {
+	var exp time.Time
+
+	if ttl == 0 {
+		exp = time.Time{}
+	} else {
+		exp = time.Now().Add(ttl)
+	}
+
+	c.mu.Lock()
+	defer c.mu.Unlock()
+
+	c.data[key] = entry{exp, val}
+}
+
+// Get returns the value asspciated with the given key.
+// The second return values indicates if the cache hs been hit or not.
+func (c Cache) Get(key string) (interface{}, bool) {
+	c.mu.RLock()
+	v, ok := c.data[key]
+	c.mu.RUnlock()
+
+	if !ok {
+		return nil, false
+	}
+
+	if !v.expirationDate.IsZero() && v.expirationDate.Before(time.Now()) {
+		c.Del(key)
+
+		return nil, false
+	}
+
+	return v.value, ok
+}
+
+// Del deletes the entry for the givzn key.
+// It does not fail if the key does not exist.
+func (c *Cache) Del(key string) {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+
+	delete(c.data, key)
+}
+
+// Count returns the total number of entries in the cache (vamid and expired).
+func (c Cache) Count() int {
+	c.mu.RLock()
+	defer c.mu.RUnlock()
+
+	return len(c.data)
+}
diff --git a/cache_test.go b/cache_test.go
new file mode 100644
index 0000000..135c693
--- /dev/null
+++ b/cache_test.go
@@ -0,0 +1,156 @@
+package cache
+
+import (
+	"testing"
+	"time"
+)
+
+func TestCache(t *testing.T) {
+	key := "test"
+
+	c := New()
+
+	t.Log("simple put and get")
+
+	value := "foo"
+
+	c.Put(key, value)
+
+	if n := c.Count(); n != 1 {
+		t.Fatalf("Expected %d entries in the cache, got %d", 1, n)
+	}
+
+	val, ok := c.Get(key)
+	if !ok {
+		t.Fatalf("Expected cache to have an entry for key %q, but it did not", key)
+	}
+
+	val2, ok := val.(string)
+	if !ok {
+		t.Fatalf("Expected '%v' to have type string, but it has type %T", val, val)
+	}
+
+	if val2 != value {
+		t.Fatalf("Expected '%v' to equal 'foo', but it does not", val2)
+	}
+
+	t.Log("Using the same key overwrites the value")
+
+	value = "bar"
+
+	c.Put(key, value)
+
+	if n := c.Count(); n != 1 {
+		t.Fatalf("Expected %d entries in the cache, got %d", 1, n)
+	}
+
+	val, ok = c.Get(key)
+	if !ok {
+		t.Fatalf("Expected cache to have an entry for key %q, but it did not", key)
+	}
+
+	val2, ok = val.(string)
+	if !ok {
+		t.Fatalf("Expected '%v' to have type string, but it has type %T", val, val)
+	}
+
+	if val2 != value {
+		t.Fatalf("Expected '%v' to equal 'foo', but it does not", val2)
+	}
+
+	t.Log("It should tell if the cache is missed")
+
+	val, ok = c.Get("does-not-exist")
+	if ok {
+		t.Fatalf("Expected cache to not have an entry for key %q, but it did", key)
+	}
+
+	if val != nil {
+		t.Fatalf("Expected '%v' to be nil, but it was not", val2)
+	}
+}
+
+func TestCacheTTL(t *testing.T) {
+	key := "test"
+	value := "foo"
+
+	c := New()
+
+	t.Log("Simple put and get a non-expired entry")
+
+	c.PutTTL(key, value, 1*time.Hour)
+
+	if n := c.Count(); n != 1 {
+		t.Fatalf("Expected %d entries in the cache, got %d", 1, n)
+	}
+
+	_, ok := c.Get(key)
+	if !ok {
+		t.Fatalf("Expected cache to have an entry for key %q, but it did not", key)
+	}
+
+	t.Log("Simple put and get a 0 TTL")
+
+	c.PutTTL(key, value, 0)
+
+	if n := c.Count(); n != 1 {
+		t.Fatalf("Expected %d entries in the cache, got %d", 1, n)
+	}
+
+	_, ok = c.Get(key)
+	if !ok {
+		t.Fatalf("Expected cache to have an entry for key %q, but it did not", key)
+	}
+
+	t.Log("Simple put and get an expired entry")
+
+	c.PutTTL(key, value, -1*time.Hour)
+
+	if n := c.Count(); n != 1 {
+		t.Fatalf("Expected %d entries in the cache, got %d", 1, n)
+	}
+
+	_, ok = c.Get(key)
+	if ok {
+		t.Fatalf("Expected cache to not have an entry for key %q, but it did", key)
+	}
+
+	if n := c.Count(); n != 0 {
+		t.Fatalf("Expected %d entries in the cache, got %d", 0, n)
+	}
+}
+
+func TestCacheDel(t *testing.T) {
+	key := "test"
+	value := "foo"
+
+	c := New()
+
+	c.Put(key, value)
+
+	if n := c.Count(); n != 1 {
+		t.Fatalf("Expected %d entries in the cache, got %d", 1, n)
+	}
+
+	t.Log("Delete an existing key from the cache")
+
+	c.Del(key)
+
+	if n := c.Count(); n != 0 {
+		t.Fatalf("Expected %d entries in the cache, got %d", 0, n)
+	}
+
+	c.Put(key, value)
+
+	if n := c.Count(); n != 1 {
+		t.Fatalf("Expected %d entries in the cache, got %d", 1, n)
+	}
+
+	t.Log("Delete an existing key from the cache")
+
+	c.Del("does-not-exist")
+
+	if n := c.Count(); n != 1 {
+		t.Fatalf("Expected %d entries in the cache, got %d", 1, n)
+	}
+}
diff --git a/go.mod b/go.mod
new file mode 100644
index 0000000..87ed6c9
--- /dev/null
+++ b/go.mod
@@ -0,0 +1,3 @@
+module code.bcarlin.xyz/go/cache
+
+go 1.17