141 lines
3.5 KiB
Go
141 lines
3.5 KiB
Go
// Package mcfg provides a simple foundation for complex service/binary
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// configuration, initialization, and destruction
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package mcfg
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import (
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"context"
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"crypto/md5"
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"encoding/hex"
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"encoding/json"
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"fmt"
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"sort"
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"github.com/mediocregopher/mediocre-go-lib/mctx"
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"github.com/mediocregopher/mediocre-go-lib/merr"
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)
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// TODO Sources:
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// - JSON file
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// - YAML file
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func sortParams(params []Param) {
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sort.Slice(params, func(i, j int) bool {
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a, b := params[i], params[j]
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aPath, bPath := mctx.Path(a.Context), mctx.Path(b.Context)
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for {
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switch {
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case len(aPath) == 0 && len(bPath) == 0:
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return a.Name < b.Name
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case len(aPath) == 0 && len(bPath) > 0:
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return false
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case len(aPath) > 0 && len(bPath) == 0:
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return true
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case aPath[0] != bPath[0]:
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return aPath[0] < bPath[0]
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default:
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aPath, bPath = aPath[1:], bPath[1:]
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}
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}
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})
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}
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// returns all Params gathered by recursively retrieving them from this Context
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// and its children. Returned Params are sorted according to their Path and
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// Name.
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func collectParams(ctx context.Context) []Param {
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var params []Param
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var visit func(context.Context)
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visit = func(ctx context.Context) {
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for _, param := range getLocalParams(ctx) {
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params = append(params, param)
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}
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for _, childCtx := range mctx.Children(ctx) {
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visit(childCtx)
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}
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}
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visit(ctx)
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sortParams(params)
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return params
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}
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func paramHash(path []string, name string) string {
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h := md5.New()
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for _, pathEl := range path {
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fmt.Fprintf(h, "pathEl:%q\n", pathEl)
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}
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fmt.Fprintf(h, "name:%q\n", name)
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hStr := hex.EncodeToString(h.Sum(nil))
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// we add the displayName to it to make debugging easier
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return paramFullName(path, name) + "/" + hStr
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}
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func populate(params []Param, src Source) error {
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if src == nil {
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src = ParamValues(nil)
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}
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// map Params to their hash, so we can match them to their ParamValues
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// later. There should not be any duplicates here.
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pM := map[string]Param{}
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for _, p := range params {
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path := mctx.Path(p.Context)
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hash := paramHash(path, p.Name)
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if _, ok := pM[hash]; ok {
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panic("duplicate Param: " + paramFullName(path, p.Name))
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}
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pM[hash] = p
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}
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pvs, err := src.Parse(params)
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if err != nil {
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return err
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}
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// dedupe the ParamValues based on their hashes, with the last ParamValue
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// taking precedence. Also filter out those with no corresponding Param.
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pvM := map[string]ParamValue{}
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for _, pv := range pvs {
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hash := paramHash(pv.Path, pv.Name)
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if _, ok := pM[hash]; !ok {
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continue
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}
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pvM[hash] = pv
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}
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// check for required params
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for hash, p := range pM {
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if !p.Required {
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continue
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} else if _, ok := pvM[hash]; !ok {
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ctx := mctx.Annotate(p.Context,
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"param", paramFullName(mctx.Path(p.Context), p.Name))
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return merr.New("required parameter is not set", ctx)
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}
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}
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// do the actual populating
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for hash, pv := range pvM {
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// at this point, all ParamValues in pvM have a corresponding pM Param
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p := pM[hash]
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if err := json.Unmarshal(pv.Value, p.Into); err != nil {
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return err
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}
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}
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return nil
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}
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// Populate uses the Source to populate the values of all Params which were
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// added to the given Context, and all of its children. Populate may be called
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// multiple times with the same Context, each time will only affect the values
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// of the Params which were provided by the respective Source.
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//
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// Source may be nil to indicate that no configuration is provided. Only default
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// values will be used, and if any parameters are required this will error.
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func Populate(ctx context.Context, src Source) error {
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return populate(collectParams(ctx), src)
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}
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