mediocre-go-lib/mcfg/mcfg.go
2019-04-04 16:25:02 -04:00

149 lines
4.1 KiB
Go

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