all: support %{ENV_VAR} placeholders in yaml configs in all the vm* components

Such placeholders are substituted by the corresponding environment variable values.

Updates https://github.com/VictoriaMetrics/VictoriaMetrics/issues/583

README.md

@@ -288,6 +288,8 @@ Currently the following [scrape_config](https://prometheus.io/docs/prometheus/la
 
 In the future other `*_sd_config` types will be supported.
 
+The file pointed by `-promscrape.config` may contain `%{ENV_VAR}` placeholders, which are substituted by the corresponding `ENV_VAR` environment variable values.
+
 VictoriaMetrics also supports [importing data in Prometheus exposition format](#how-to-import-data-in-prometheus-exposition-format).
 
 See also [vmagent](https://github.com/VictoriaMetrics/VictoriaMetrics/blob/master/app/vmagent/README.md), which can be used as drop-in replacement for Prometheus.
@@ -768,7 +770,7 @@ and importing them concurrently. Note that the original file must be split on ne
 VictoriaMetrics supports Prometheus-compatible relabeling for all the ingested metrics if `-relabelConfig` command-line flag points
 to a file containing a list of [relabel_config](https://prometheus.io/docs/prometheus/latest/configuration/configuration/#relabel_config) entries.
 
-Additionally VictoriaMetrics provides the following extra actions for relabeling rules:
+VictoriaMetrics provides the following extra actions for relabeling rules:
 
 * `replace_all`: replaces all the occurences of `regex` in the values of `source_labels` with the `replacement` and stores the result in the `target_label`.
 * `labelmap_all`: replaces all the occurences of `regex` in all the label names with the `replacement`.

app/vmagent/README.md

@@ -161,6 +161,8 @@ Note that `vmagent` doesn't support `refresh_interval` option these scrape confi
 command-line flag instead. For example, `-promscrape.consulSDCheckInterval=60s` sets `refresh_interval` for all the `consul_sd_configs`
 entries to 60s. Run `vmagent -help` in order to see default values for `-promscrape.*CheckInterval` flags.
 
+The file pointed by `-promscrape.config` may contain `%{ENV_VAR}` placeholders, which are substituted by the corresponding `ENV_VAR` environment variable values.
+
 
 ### Adding labels to metrics
 

app/vmalert/config/config.go

@@ -10,6 +10,7 @@ import (
 	"time"
 
 	"github.com/VictoriaMetrics/VictoriaMetrics/app/vmalert/notifier"
+	"github.com/VictoriaMetrics/VictoriaMetrics/lib/envtemplate"
 	"github.com/VictoriaMetrics/metricsql"
 	"gopkg.in/yaml.v2"
 )
@@ -179,6 +180,7 @@ func parseFile(path string) ([]Group, error) {
 	if err != nil {
 		return nil, fmt.Errorf("error reading alert rule file: %w", err)
 	}
+	data = envtemplate.Replace(data)
 	g := struct {
 		Groups []Group `yaml:"groups"`
 		// Catches all undefined fields and must be empty after parsing.

app/vmalert/main.go

@@ -31,7 +31,8 @@ Supports patterns. Flag can be specified multiple times.
 Examples:
  -rule /path/to/file. Path to a single file with alerting rules
  -rule dir/*.yaml -rule /*.yaml. Relative path to all .yaml files in "dir" folder, 
-absolute path to all .yaml files in root.`)
+absolute path to all .yaml files in root.
+Rule files may contain %{ENV_VAR} placeholders, which are substituted by the corresponding env vars.`)
 
 	httpListenAddr     = flag.String("httpListenAddr", ":8880", "Address to listen for http connections")
 	evaluationInterval = flag.Duration("evaluationInterval", time.Minute, "How often to evaluate the rules")

app/vmauth/README.md

@@ -64,6 +64,9 @@ users:
   url_prefix: "http://vminsert:8480/insert/42/prometheus"
 ```
 
+The config may contain `%{ENV_VAR}` placeholders, which are substituted by the corresponding `ENV_VAR` environment variable values.
+This may be useful for passing secrets to the config.
+
 
 ### Security
 

app/vmauth/auth_config.go

@@ -9,6 +9,7 @@ import (
 	"sync"
 	"sync/atomic"
 
+	"github.com/VictoriaMetrics/VictoriaMetrics/lib/envtemplate"
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/logger"
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/procutil"
 	"github.com/VictoriaMetrics/metrics"
@@ -93,6 +94,7 @@ func readAuthConfig(path string) (map[string]*UserInfo, error) {
 }
 
 func parseAuthConfig(data []byte) (map[string]*UserInfo, error) {
+	data = envtemplate.Replace(data)
 	var ac AuthConfig
 	if err := yaml.UnmarshalStrict(data, &ac); err != nil {
 		return nil, fmt.Errorf("cannot unmarshal AuthConfig data: %w", err)

docs/Single-server-VictoriaMetrics.md

@@ -288,6 +288,8 @@ Currently the following [scrape_config](https://prometheus.io/docs/prometheus/la
 
 In the future other `*_sd_config` types will be supported.
 
+The file pointed by `-promscrape.config` may contain `%{ENV_VAR}` placeholders, which are substituted by the corresponding `ENV_VAR` environment variable values.
+
 VictoriaMetrics also supports [importing data in Prometheus exposition format](#how-to-import-data-in-prometheus-exposition-format).
 
 See also [vmagent](https://github.com/VictoriaMetrics/VictoriaMetrics/blob/master/app/vmagent/README.md), which can be used as drop-in replacement for Prometheus.
@@ -768,7 +770,7 @@ and importing them concurrently. Note that the original file must be split on ne
 VictoriaMetrics supports Prometheus-compatible relabeling for all the ingested metrics if `-relabelConfig` command-line flag points
 to a file containing a list of [relabel_config](https://prometheus.io/docs/prometheus/latest/configuration/configuration/#relabel_config) entries.
 
-Additionally VictoriaMetrics provides the following extra actions for relabeling rules:
+VictoriaMetrics provides the following extra actions for relabeling rules:
 
 * `replace_all`: replaces all the occurences of `regex` in the values of `source_labels` with the `replacement` and stores the result in the `target_label`.
 * `labelmap_all`: replaces all the occurences of `regex` in all the label names with the `replacement`.

docs/vmagent.md

@@ -161,6 +161,8 @@ Note that `vmagent` doesn't support `refresh_interval` option these scrape confi
 command-line flag instead. For example, `-promscrape.consulSDCheckInterval=60s` sets `refresh_interval` for all the `consul_sd_configs`
 entries to 60s. Run `vmagent -help` in order to see default values for `-promscrape.*CheckInterval` flags.
 
+The file pointed by `-promscrape.config` may contain `%{ENV_VAR}` placeholders, which are substituted by the corresponding `ENV_VAR` environment variable values.
+
 
 ### Adding labels to metrics
 

docs/vmauth.md

@@ -64,6 +64,9 @@ users:
   url_prefix: "http://vminsert:8480/insert/42/prometheus"
 ```
 
+The config may contain `%{ENV_VAR}` placeholders, which are substituted by the corresponding `ENV_VAR` environment variable values.
+This may be useful for passing secrets to the config.
+
 
 ### Security
 

go.mod

@@ -16,6 +16,7 @@ require (
 	github.com/klauspost/compress v1.10.10
 	github.com/valyala/fastjson v1.5.4
 	github.com/valyala/fastrand v1.0.0
+	github.com/valyala/fasttemplate v1.2.1
 	github.com/valyala/gozstd v1.7.0
 	github.com/valyala/histogram v1.1.2
 	github.com/valyala/quicktemplate v1.6.2

go.sum

@@ -168,6 +168,8 @@ github.com/valyala/fastjson v1.5.4 h1:r8gpiVwdzDU09NrlN38OyL5dUFpdwGQR5RQEBqY+hL
 github.com/valyala/fastjson v1.5.4/go.mod h1:CLCAqky6SMuOcxStkYQvblddUtoRxhYMGLrsQns1aXY=
 github.com/valyala/fastrand v1.0.0 h1:LUKT9aKer2dVQNUi3waewTbKV+7H17kvWFNKs2ObdkI=
 github.com/valyala/fastrand v1.0.0/go.mod h1:HWqCzkrkg6QXT8V2EXWvXCoow7vLwOFN002oeRzjapQ=
+github.com/valyala/fasttemplate v1.2.1 h1:TVEnxayobAdVkhQfrfes2IzOB6o+z4roRkPF52WA1u4=
+github.com/valyala/fasttemplate v1.2.1/go.mod h1:KHLXt3tVN2HBp8eijSv/kGJopbvo7S+qRAEEKiv+SiQ=
 github.com/valyala/gozstd v1.7.0 h1:Ljh5c9zboqLhwTI33al32R72iCZfn0mCbVGcFWbGwRQ=
 github.com/valyala/gozstd v1.7.0/go.mod h1:y5Ew47GLlP37EkTB+B4s7r6A5rdaeB7ftbl9zoYiIPQ=
 github.com/valyala/histogram v1.1.2 h1:vOk5VrGjMBIoPR5k6wA8vBaC8toeJ8XO0yfRjFEc1h8=

lib/envtemplate/envtemplate.go

@@ -0,0 +1,25 @@
+package envtemplate
+
+import (
+	"bytes"
+	"io"
+	"os"
+
+	"github.com/valyala/fasttemplate"
+)
+
+// Replace replaces `%{ENV_VAR}` placeholders in b with the corresponding ENV_VAR values.
+func Replace(b []byte) []byte {
+	if !bytes.Contains(b, []byte("%{")) {
+		// Fast path - nothing to replace.
+		return b
+	}
+	s := fasttemplate.ExecuteFuncString(string(b), "%{", "}", func(w io.Writer, tag string) (int, error) {
+		v := os.Getenv(tag)
+		if v == "" {
+			v = "%{" + tag + "}"
+		}
+		return w.Write([]byte(v))
+	})
+	return []byte(s)
+}

lib/envtemplate/envtemplate_test.go

@@ -0,0 +1,19 @@
+package envtemplate
+
+import (
+	"testing"
+)
+
+func TestReplace(t *testing.T) {
+	f := func(s, resultExpected string) {
+		t.Helper()
+		result := Replace([]byte(s))
+		if string(result) != resultExpected {
+			t.Fatalf("unexpected result;\ngot\n%q\nwant\n%q", result, resultExpected)
+		}
+	}
+	f("", "")
+	f("foo", "foo")
+	f("%{foo}", "%{foo}")
+	f("foo %{bar} %{baz}", "foo %{bar} %{baz}")
+}

lib/promrelabel/config.go

@@ -6,6 +6,7 @@ import (
 	"regexp"
 	"strings"
 
+	"github.com/VictoriaMetrics/VictoriaMetrics/lib/envtemplate"
 	"gopkg.in/yaml.v2"
 )
 
@@ -28,6 +29,7 @@ func LoadRelabelConfigs(path string) ([]ParsedRelabelConfig, error) {
 	if err != nil {
 		return nil, fmt.Errorf("cannot read `relabel_configs` from %q: %w", path, err)
 	}
+	data = envtemplate.Replace(data)
 	var rcs []RelabelConfig
 	if err := yaml.UnmarshalStrict(data, &rcs); err != nil {
 		return nil, fmt.Errorf("cannot unmarshal `relabel_configs` from %q: %w", path, err)

lib/promscrape/config.go

@@ -11,6 +11,7 @@ import (
 	"sync/atomic"
 	"time"
 
+	"github.com/VictoriaMetrics/VictoriaMetrics/lib/envtemplate"
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/logger"
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/promauth"
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/prompbmarshal"
@@ -105,6 +106,7 @@ func loadStaticConfigs(path string) ([]StaticConfig, error) {
 	if err != nil {
 		return nil, fmt.Errorf("cannot read `static_configs` from %q: %w", path, err)
 	}
+	data = envtemplate.Replace(data)
 	var stcs []StaticConfig
 	if err := yaml.UnmarshalStrict(data, &stcs); err != nil {
 		return nil, fmt.Errorf("cannot unmarshal `static_configs` from %q: %w", path, err)
@@ -153,6 +155,7 @@ func (cfg *Config) parse(data []byte, path string) error {
 }
 
 func unmarshalMaybeStrict(data []byte, dst interface{}) error {
+	data = envtemplate.Replace(data)
 	var err error
 	if *strictParse || *dryRun {
 		err = yaml.UnmarshalStrict(data, dst)

lib/promscrape/scraper.go

@@ -34,7 +34,7 @@ var (
 		"This works only if `gce_sd_configs` is configured in '-promscrape.config' file. "+
 		"See https://prometheus.io/docs/prometheus/latest/configuration/configuration/#gce_sd_config for details")
 	promscrapeConfigFile = flag.String("promscrape.config", "", "Optional path to Prometheus config file with 'scrape_configs' section containing targets to scrape. "+
-		"See https://prometheus.io/docs/prometheus/latest/configuration/configuration/#scrape_config for details")
+		"See https://victoriametrics.github.io/#how-to-scrape-prometheus-exporters-such-as-node-exporter for details")
 )
 
 // CheckConfig checks -promscrape.config for errors and unsupported options.

vendor/github.com/valyala/fasttemplate/LICENSE

@@ -0,0 +1,22 @@
+The MIT License (MIT)
+
+Copyright (c) 2015 Aliaksandr Valialkin
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
+

vendor/github.com/valyala/fasttemplate/README.md

@@ -0,0 +1,85 @@
+fasttemplate
+============
+
+Simple and fast template engine for Go.
+
+Fasttemplate performs only a single task - it substitutes template placeholders
+with user-defined values. At high speed :)
+
+Take a look at [quicktemplate](https://github.com/valyala/quicktemplate) if you  need fast yet powerful html template engine.
+
+*Please note that fasttemplate doesn't do any escaping on template values
+unlike [html/template](http://golang.org/pkg/html/template/) do. So values
+must be properly escaped before passing them to fasttemplate.*
+
+Fasttemplate is faster than [text/template](http://golang.org/pkg/text/template/),
+[strings.Replace](http://golang.org/pkg/strings/#Replace),
+[strings.Replacer](http://golang.org/pkg/strings/#Replacer)
+and [fmt.Fprintf](https://golang.org/pkg/fmt/#Fprintf) on placeholders' substitution.
+
+Below are benchmark results comparing fasttemplate performance to text/template,
+strings.Replace, strings.Replacer and fmt.Fprintf:
+
+```
+$ go test -bench=. -benchmem
+PASS
+BenchmarkFmtFprintf-4                   	 2000000	       790 ns/op	       0 B/op	       0 allocs/op
+BenchmarkStringsReplace-4               	  500000	      3474 ns/op	    2112 B/op	      14 allocs/op
+BenchmarkStringsReplacer-4              	  500000	      2657 ns/op	    2256 B/op	      23 allocs/op
+BenchmarkTextTemplate-4                 	  500000	      3333 ns/op	     336 B/op	      19 allocs/op
+BenchmarkFastTemplateExecuteFunc-4      	 5000000	       349 ns/op	       0 B/op	       0 allocs/op
+BenchmarkFastTemplateExecute-4          	 3000000	       383 ns/op	       0 B/op	       0 allocs/op
+BenchmarkFastTemplateExecuteFuncString-4	 3000000	       549 ns/op	     144 B/op	       1 allocs/op
+BenchmarkFastTemplateExecuteString-4    	 3000000	       572 ns/op	     144 B/op	       1 allocs/op
+BenchmarkFastTemplateExecuteTagFunc-4   	 2000000	       743 ns/op	     144 B/op	       3 allocs/op
+```
+
+
+Docs
+====
+
+See http://godoc.org/github.com/valyala/fasttemplate .
+
+
+Usage
+=====
+
+```go
+	template := "http://{{host}}/?q={{query}}&foo={{bar}}{{bar}}"
+	t := fasttemplate.New(template, "{{", "}}")
+	s := t.ExecuteString(map[string]interface{}{
+		"host":  "google.com",
+		"query": url.QueryEscape("hello=world"),
+		"bar":   "foobar",
+	})
+	fmt.Printf("%s", s)
+
+	// Output:
+	// http://google.com/?q=hello%3Dworld&foo=foobarfoobar
+```
+
+
+Advanced usage
+==============
+
+```go
+	template := "Hello, [user]! You won [prize]!!! [foobar]"
+	t, err := fasttemplate.NewTemplate(template, "[", "]")
+	if err != nil {
+		log.Fatalf("unexpected error when parsing template: %s", err)
+	}
+	s := t.ExecuteFuncString(func(w io.Writer, tag string) (int, error) {
+		switch tag {
+		case "user":
+			return w.Write([]byte("John"))
+		case "prize":
+			return w.Write([]byte("$100500"))
+		default:
+			return w.Write([]byte(fmt.Sprintf("[unknown tag %q]", tag)))
+		}
+	})
+	fmt.Printf("%s", s)
+
+	// Output:
+	// Hello, John! You won $100500!!! [unknown tag "foobar"]
+```

vendor/github.com/valyala/fasttemplate/go.mod

@@ -0,0 +1,5 @@
+module github.com/valyala/fasttemplate
+
+go 1.12
+
+require github.com/valyala/bytebufferpool v1.0.0

vendor/github.com/valyala/fasttemplate/go.sum

@@ -0,0 +1,2 @@
+github.com/valyala/bytebufferpool v1.0.0 h1:GqA5TC/0021Y/b9FG4Oi9Mr3q7XYx6KllzawFIhcdPw=
+github.com/valyala/bytebufferpool v1.0.0/go.mod h1:6bBcMArwyJ5K/AmCkWv1jt77kVWyCJ6HpOuEn7z0Csc=

vendor/github.com/valyala/fasttemplate/template.go

@@ -0,0 +1,437 @@
+// Package fasttemplate implements simple and fast template library.
+//
+// Fasttemplate is faster than text/template, strings.Replace
+// and strings.Replacer.
+//
+// Fasttemplate ideally fits for fast and simple placeholders' substitutions.
+package fasttemplate
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+
+	"github.com/valyala/bytebufferpool"
+)
+
+// ExecuteFunc calls f on each template tag (placeholder) occurrence.
+//
+// Returns the number of bytes written to w.
+//
+// This function is optimized for constantly changing templates.
+// Use Template.ExecuteFunc for frozen templates.
+func ExecuteFunc(template, startTag, endTag string, w io.Writer, f TagFunc) (int64, error) {
+	s := unsafeString2Bytes(template)
+	a := unsafeString2Bytes(startTag)
+	b := unsafeString2Bytes(endTag)
+
+	var nn int64
+	var ni int
+	var err error
+	for {
+		n := bytes.Index(s, a)
+		if n < 0 {
+			break
+		}
+		ni, err = w.Write(s[:n])
+		nn += int64(ni)
+		if err != nil {
+			return nn, err
+		}
+
+		s = s[n+len(a):]
+		n = bytes.Index(s, b)
+		if n < 0 {
+			// cannot find end tag - just write it to the output.
+			ni, _ = w.Write(a)
+			nn += int64(ni)
+			break
+		}
+
+		ni, err = f(w, unsafeBytes2String(s[:n]))
+		nn += int64(ni)
+		if err != nil {
+			return nn, err
+		}
+		s = s[n+len(b):]
+	}
+	ni, err = w.Write(s)
+	nn += int64(ni)
+
+	return nn, err
+}
+
+// Execute substitutes template tags (placeholders) with the corresponding
+// values from the map m and writes the result to the given writer w.
+//
+// Substitution map m may contain values with the following types:
+//   * []byte - the fastest value type
+//   * string - convenient value type
+//   * TagFunc - flexible value type
+//
+// Returns the number of bytes written to w.
+//
+// This function is optimized for constantly changing templates.
+// Use Template.Execute for frozen templates.
+func Execute(template, startTag, endTag string, w io.Writer, m map[string]interface{}) (int64, error) {
+	return ExecuteFunc(template, startTag, endTag, w, func(w io.Writer, tag string) (int, error) { return stdTagFunc(w, tag, m) })
+}
+
+// ExecuteStd works the same way as Execute, but keeps the unknown placeholders.
+// This can be used as a drop-in replacement for strings.Replacer
+//
+// Substitution map m may contain values with the following types:
+//   * []byte - the fastest value type
+//   * string - convenient value type
+//   * TagFunc - flexible value type
+//
+// Returns the number of bytes written to w.
+//
+// This function is optimized for constantly changing templates.
+// Use Template.ExecuteStd for frozen templates.
+func ExecuteStd(template, startTag, endTag string, w io.Writer, m map[string]interface{}) (int64, error) {
+	return ExecuteFunc(template, startTag, endTag, w, func(w io.Writer, tag string) (int, error) { return keepUnknownTagFunc(w, startTag, endTag, tag, m) })
+}
+
+// ExecuteFuncString calls f on each template tag (placeholder) occurrence
+// and substitutes it with the data written to TagFunc's w.
+//
+// Returns the resulting string.
+//
+// This function is optimized for constantly changing templates.
+// Use Template.ExecuteFuncString for frozen templates.
+func ExecuteFuncString(template, startTag, endTag string, f TagFunc) string {
+	s, err := ExecuteFuncStringWithErr(template, startTag, endTag, f)
+	if err != nil {
+		panic(fmt.Sprintf("unexpected error: %s", err))
+	}
+	return s
+}
+
+// ExecuteFuncStringWithErr is nearly the same as ExecuteFuncString
+// but when f returns an error, ExecuteFuncStringWithErr won't panic like ExecuteFuncString
+// it just returns an empty string and the error f returned
+func ExecuteFuncStringWithErr(template, startTag, endTag string, f TagFunc) (string, error) {
+	tagsCount := bytes.Count(unsafeString2Bytes(template), unsafeString2Bytes(startTag))
+	if tagsCount == 0 {
+		return template, nil
+	}
+
+	bb := byteBufferPool.Get()
+	if _, err := ExecuteFunc(template, startTag, endTag, bb, f); err != nil {
+		bb.Reset()
+		byteBufferPool.Put(bb)
+		return "", err
+	}
+	s := string(bb.B)
+	bb.Reset()
+	byteBufferPool.Put(bb)
+	return s, nil
+}
+
+var byteBufferPool bytebufferpool.Pool
+
+// ExecuteString substitutes template tags (placeholders) with the corresponding
+// values from the map m and returns the result.
+//
+// Substitution map m may contain values with the following types:
+//   * []byte - the fastest value type
+//   * string - convenient value type
+//   * TagFunc - flexible value type
+//
+// This function is optimized for constantly changing templates.
+// Use Template.ExecuteString for frozen templates.
+func ExecuteString(template, startTag, endTag string, m map[string]interface{}) string {
+	return ExecuteFuncString(template, startTag, endTag, func(w io.Writer, tag string) (int, error) { return stdTagFunc(w, tag, m) })
+}
+
+// ExecuteStringStd works the same way as ExecuteString, but keeps the unknown placeholders.
+// This can be used as a drop-in replacement for strings.Replacer
+//
+// Substitution map m may contain values with the following types:
+//   * []byte - the fastest value type
+//   * string - convenient value type
+//   * TagFunc - flexible value type
+//
+// This function is optimized for constantly changing templates.
+// Use Template.ExecuteStringStd for frozen templates.
+func ExecuteStringStd(template, startTag, endTag string, m map[string]interface{}) string {
+	return ExecuteFuncString(template, startTag, endTag, func(w io.Writer, tag string) (int, error) { return keepUnknownTagFunc(w, startTag, endTag, tag, m) })
+}
+
+// Template implements simple template engine, which can be used for fast
+// tags' (aka placeholders) substitution.
+type Template struct {
+	template string
+	startTag string
+	endTag   string
+
+	texts          [][]byte
+	tags           []string
+	byteBufferPool bytebufferpool.Pool
+}
+
+// New parses the given template using the given startTag and endTag
+// as tag start and tag end.
+//
+// The returned template can be executed by concurrently running goroutines
+// using Execute* methods.
+//
+// New panics if the given template cannot be parsed. Use NewTemplate instead
+// if template may contain errors.
+func New(template, startTag, endTag string) *Template {
+	t, err := NewTemplate(template, startTag, endTag)
+	if err != nil {
+		panic(err)
+	}
+	return t
+}
+
+// NewTemplate parses the given template using the given startTag and endTag
+// as tag start and tag end.
+//
+// The returned template can be executed by concurrently running goroutines
+// using Execute* methods.
+func NewTemplate(template, startTag, endTag string) (*Template, error) {
+	var t Template
+	err := t.Reset(template, startTag, endTag)
+	if err != nil {
+		return nil, err
+	}
+	return &t, nil
+}
+
+// TagFunc can be used as a substitution value in the map passed to Execute*.
+// Execute* functions pass tag (placeholder) name in 'tag' argument.
+//
+// TagFunc must be safe to call from concurrently running goroutines.
+//
+// TagFunc must write contents to w and return the number of bytes written.
+type TagFunc func(w io.Writer, tag string) (int, error)
+
+// Reset resets the template t to new one defined by
+// template, startTag and endTag.
+//
+// Reset allows Template object re-use.
+//
+// Reset may be called only if no other goroutines call t methods at the moment.
+func (t *Template) Reset(template, startTag, endTag string) error {
+	// Keep these vars in t, so GC won't collect them and won't break
+	// vars derived via unsafe*
+	t.template = template
+	t.startTag = startTag
+	t.endTag = endTag
+	t.texts = t.texts[:0]
+	t.tags = t.tags[:0]
+
+	if len(startTag) == 0 {
+		panic("startTag cannot be empty")
+	}
+	if len(endTag) == 0 {
+		panic("endTag cannot be empty")
+	}
+
+	s := unsafeString2Bytes(template)
+	a := unsafeString2Bytes(startTag)
+	b := unsafeString2Bytes(endTag)
+
+	tagsCount := bytes.Count(s, a)
+	if tagsCount == 0 {
+		return nil
+	}
+
+	if tagsCount+1 > cap(t.texts) {
+		t.texts = make([][]byte, 0, tagsCount+1)
+	}
+	if tagsCount > cap(t.tags) {
+		t.tags = make([]string, 0, tagsCount)
+	}
+
+	for {
+		n := bytes.Index(s, a)
+		if n < 0 {
+			t.texts = append(t.texts, s)
+			break
+		}
+		t.texts = append(t.texts, s[:n])
+
+		s = s[n+len(a):]
+		n = bytes.Index(s, b)
+		if n < 0 {
+			return fmt.Errorf("Cannot find end tag=%q in the template=%q starting from %q", endTag, template, s)
+		}
+
+		t.tags = append(t.tags, unsafeBytes2String(s[:n]))
+		s = s[n+len(b):]
+	}
+
+	return nil
+}
+
+// ExecuteFunc calls f on each template tag (placeholder) occurrence.
+//
+// Returns the number of bytes written to w.
+//
+// This function is optimized for frozen templates.
+// Use ExecuteFunc for constantly changing templates.
+func (t *Template) ExecuteFunc(w io.Writer, f TagFunc) (int64, error) {
+	var nn int64
+
+	n := len(t.texts) - 1
+	if n == -1 {
+		ni, err := w.Write(unsafeString2Bytes(t.template))
+		return int64(ni), err
+	}
+
+	for i := 0; i < n; i++ {
+		ni, err := w.Write(t.texts[i])
+		nn += int64(ni)
+		if err != nil {
+			return nn, err
+		}
+
+		ni, err = f(w, t.tags[i])
+		nn += int64(ni)
+		if err != nil {
+			return nn, err
+		}
+	}
+	ni, err := w.Write(t.texts[n])
+	nn += int64(ni)
+	return nn, err
+}
+
+// Execute substitutes template tags (placeholders) with the corresponding
+// values from the map m and writes the result to the given writer w.
+//
+// Substitution map m may contain values with the following types:
+//   * []byte - the fastest value type
+//   * string - convenient value type
+//   * TagFunc - flexible value type
+//
+// Returns the number of bytes written to w.
+func (t *Template) Execute(w io.Writer, m map[string]interface{}) (int64, error) {
+	return t.ExecuteFunc(w, func(w io.Writer, tag string) (int, error) { return stdTagFunc(w, tag, m) })
+}
+
+// ExecuteStd works the same way as Execute, but keeps the unknown placeholders.
+// This can be used as a drop-in replacement for strings.Replacer
+//
+// Substitution map m may contain values with the following types:
+//   * []byte - the fastest value type
+//   * string - convenient value type
+//   * TagFunc - flexible value type
+//
+// Returns the number of bytes written to w.
+func (t *Template) ExecuteStd(w io.Writer, m map[string]interface{}) (int64, error) {
+	return t.ExecuteFunc(w, func(w io.Writer, tag string) (int, error) { return keepUnknownTagFunc(w, t.startTag, t.endTag, tag, m) })
+}
+
+// ExecuteFuncString calls f on each template tag (placeholder) occurrence
+// and substitutes it with the data written to TagFunc's w.
+//
+// Returns the resulting string.
+//
+// This function is optimized for frozen templates.
+// Use ExecuteFuncString for constantly changing templates.
+func (t *Template) ExecuteFuncString(f TagFunc) string {
+	s, err := t.ExecuteFuncStringWithErr(f)
+	if err != nil {
+		panic(fmt.Sprintf("unexpected error: %s", err))
+	}
+	return s
+}
+
+// ExecuteFuncStringWithErr calls f on each template tag (placeholder) occurrence
+// and substitutes it with the data written to TagFunc's w.
+//
+// Returns the resulting string.
+//
+// This function is optimized for frozen templates.
+// Use ExecuteFuncString for constantly changing templates.
+func (t *Template) ExecuteFuncStringWithErr(f TagFunc) (string, error) {
+	bb := t.byteBufferPool.Get()
+	if _, err := t.ExecuteFunc(bb, f); err != nil {
+		bb.Reset()
+		t.byteBufferPool.Put(bb)
+		return "", err
+	}
+	s := string(bb.Bytes())
+	bb.Reset()
+	t.byteBufferPool.Put(bb)
+	return s, nil
+}
+
+// ExecuteString substitutes template tags (placeholders) with the corresponding
+// values from the map m and returns the result.
+//
+// Substitution map m may contain values with the following types:
+//   * []byte - the fastest value type
+//   * string - convenient value type
+//   * TagFunc - flexible value type
+//
+// This function is optimized for frozen templates.
+// Use ExecuteString for constantly changing templates.
+func (t *Template) ExecuteString(m map[string]interface{}) string {
+	return t.ExecuteFuncString(func(w io.Writer, tag string) (int, error) { return stdTagFunc(w, tag, m) })
+}
+
+// ExecuteStringStd works the same way as ExecuteString, but keeps the unknown placeholders.
+// This can be used as a drop-in replacement for strings.Replacer
+//
+// Substitution map m may contain values with the following types:
+//   * []byte - the fastest value type
+//   * string - convenient value type
+//   * TagFunc - flexible value type
+//
+// This function is optimized for frozen templates.
+// Use ExecuteStringStd for constantly changing templates.
+func (t *Template) ExecuteStringStd(m map[string]interface{}) string {
+	return t.ExecuteFuncString(func(w io.Writer, tag string) (int, error) { return keepUnknownTagFunc(w, t.startTag, t.endTag, tag, m) })
+}
+
+func stdTagFunc(w io.Writer, tag string, m map[string]interface{}) (int, error) {
+	v := m[tag]
+	if v == nil {
+		return 0, nil
+	}
+	switch value := v.(type) {
+	case []byte:
+		return w.Write(value)
+	case string:
+		return w.Write([]byte(value))
+	case TagFunc:
+		return value(w, tag)
+	default:
+		panic(fmt.Sprintf("tag=%q contains unexpected value type=%#v. Expected []byte, string or TagFunc", tag, v))
+	}
+}
+
+func keepUnknownTagFunc(w io.Writer, startTag, endTag, tag string, m map[string]interface{}) (int, error) {
+	v, ok := m[tag]
+	if !ok {
+		if _, err := w.Write(unsafeString2Bytes(startTag)); err != nil {
+			return 0, err
+		}
+		if _, err := w.Write(unsafeString2Bytes(tag)); err != nil {
+			return 0, err
+		}
+		if _, err := w.Write(unsafeString2Bytes(endTag)); err != nil {
+			return 0, err
+		}
+		return len(startTag) + len(tag) + len(endTag), nil
+	}
+	if v == nil {
+		return 0, nil
+	}
+	switch value := v.(type) {
+	case []byte:
+		return w.Write(value)
+	case string:
+		return w.Write([]byte(value))
+	case TagFunc:
+		return value(w, tag)
+	default:
+		panic(fmt.Sprintf("tag=%q contains unexpected value type=%#v. Expected []byte, string or TagFunc", tag, v))
+	}
+}

vendor/github.com/valyala/fasttemplate/unsafe.go

@@ -0,0 +1,21 @@
+// +build !appengine
+
+package fasttemplate
+
+import (
+	"reflect"
+	"unsafe"
+)
+
+func unsafeBytes2String(b []byte) string {
+	return *(*string)(unsafe.Pointer(&b))
+}
+
+func unsafeString2Bytes(s string) (b []byte) {
+	sh := (*reflect.StringHeader)(unsafe.Pointer(&s))
+	bh := (*reflect.SliceHeader)(unsafe.Pointer(&b))
+	bh.Data = sh.Data
+	bh.Cap = sh.Len
+	bh.Len = sh.Len
+	return b
+}

vendor/github.com/valyala/fasttemplate/unsafe_gae.go

@@ -0,0 +1,11 @@
+// +build appengine
+
+package fasttemplate
+
+func unsafeBytes2String(b []byte) string {
+	return string(b)
+}
+
+func unsafeString2Bytes(s string) []byte {
+	return []byte(s)
+}

vendor/modules.txt

@@ -104,6 +104,8 @@ github.com/valyala/fastjson
 github.com/valyala/fastjson/fastfloat
 # github.com/valyala/fastrand v1.0.0
 github.com/valyala/fastrand
+# github.com/valyala/fasttemplate v1.2.1
+github.com/valyala/fasttemplate
 # github.com/valyala/gozstd v1.7.0
 github.com/valyala/gozstd
 # github.com/valyala/histogram v1.1.2