Add a HTTP cache for remote resources.

Fixes #12502
Closes #11891

cache/httpcache/httpcache.go

@@ -0,0 +1,208 @@
+// Copyright 2024 The Hugo Authors. All rights reserved.
+//
+// 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.
+
+package httpcache
+
+import (
+	"encoding/json"
+	"time"
+
+	"github.com/gobwas/glob"
+	"github.com/gohugoio/hugo/common/predicate"
+	"github.com/gohugoio/hugo/config"
+	"github.com/mitchellh/mapstructure"
+)
+
+// DefaultConfig holds the default configuration for the HTTP cache.
+var DefaultConfig = Config{
+	Cache: Cache{
+		For: GlobMatcher{
+			Excludes: []string{"**"},
+		},
+	},
+	Polls: []PollConfig{
+		{
+			For: GlobMatcher{
+				Includes: []string{"**"},
+			},
+			Disable: true,
+		},
+	},
+}
+
+// Config holds the configuration for the HTTP cache.
+type Config struct {
+	// Configures the HTTP cache behaviour (RFC 9111).
+	// When this is not enabled for a resource, Hugo will go straight to the file cache.
+	Cache Cache
+
+	// Polls holds a list of configurations for polling remote resources to detect changes in watch mode.
+	// This can be disabled for some resources, typically if they are known to not change.
+	Polls []PollConfig
+}
+
+type Cache struct {
+	// Enable HTTP cache behaviour (RFC 9111) for these rsources.
+	For GlobMatcher
+}
+
+func (c *Config) Compile() (ConfigCompiled, error) {
+	var cc ConfigCompiled
+
+	p, err := c.Cache.For.CompilePredicate()
+	if err != nil {
+		return cc, err
+	}
+
+	cc.For = p
+
+	for _, pc := range c.Polls {
+
+		p, err := pc.For.CompilePredicate()
+		if err != nil {
+			return cc, err
+		}
+
+		cc.PollConfigs = append(cc.PollConfigs, PollConfigCompiled{
+			For:    p,
+			Config: pc,
+		})
+	}
+
+	return cc, nil
+}
+
+// PollConfig holds the configuration for polling remote resources to detect changes in watch mode.
+// TODO1 make sure this enabled only in watch mode.
+type PollConfig struct {
+	// What remote resources to apply this configuration to.
+	For GlobMatcher
+
+	// Disable polling for this configuration.
+	Disable bool
+
+	// Low is the lower bound for the polling interval.
+	// This is the starting point when the resource has recently changed,
+	// if that resource stops changing, the polling interval will gradually increase towards High.
+	Low time.Duration
+
+	// High is the upper bound for the polling interval.
+	// This is the interval used when the resource is stable.
+	High time.Duration
+}
+
+func (c PollConfig) MarshalJSON() (b []byte, err error) {
+	// Marshal the durations as strings.
+	type Alias PollConfig
+	return json.Marshal(&struct {
+		Low  string
+		High string
+		Alias
+	}{
+		Low:   c.Low.String(),
+		High:  c.High.String(),
+		Alias: (Alias)(c),
+	})
+}
+
+type GlobMatcher struct {
+	// Excludes holds a list of glob patterns that will be excluded.
+	Excludes []string
+
+	// Includes holds a list of glob patterns that will be included.
+	Includes []string
+}
+
+type ConfigCompiled struct {
+	For         predicate.P[string]
+	PollConfigs []PollConfigCompiled
+}
+
+func (c *ConfigCompiled) PollConfigFor(s string) PollConfigCompiled {
+	for _, pc := range c.PollConfigs {
+		if pc.For(s) {
+			return pc
+		}
+	}
+	return PollConfigCompiled{}
+}
+
+func (c *ConfigCompiled) IsPollingDisabled() bool {
+	for _, pc := range c.PollConfigs {
+		if !pc.Config.Disable {
+			return false
+		}
+	}
+	return true
+}
+
+type PollConfigCompiled struct {
+	For    predicate.P[string]
+	Config PollConfig
+}
+
+func (p PollConfigCompiled) IsZero() bool {
+	return p.For == nil
+}
+
+func (gm *GlobMatcher) CompilePredicate() (func(string) bool, error) {
+	var p predicate.P[string]
+	for _, include := range gm.Includes {
+		g, err := glob.Compile(include, '/')
+		if err != nil {
+			return nil, err
+		}
+		fn := func(s string) bool {
+			return g.Match(s)
+		}
+		p = p.Or(fn)
+	}
+
+	for _, exclude := range gm.Excludes {
+		g, err := glob.Compile(exclude, '/')
+		if err != nil {
+			return nil, err
+		}
+		fn := func(s string) bool {
+			return !g.Match(s)
+		}
+		p = p.And(fn)
+	}
+
+	return p, nil
+}
+
+func DecodeConfig(bcfg config.BaseConfig, m map[string]any) (Config, error) {
+	if len(m) == 0 {
+		return DefaultConfig, nil
+	}
+
+	var c Config
+
+	dc := &mapstructure.DecoderConfig{
+		Result:           &c,
+		DecodeHook:       mapstructure.StringToTimeDurationHookFunc(),
+		WeaklyTypedInput: true,
+	}
+
+	decoder, err := mapstructure.NewDecoder(dc)
+	if err != nil {
+		return c, err
+	}
+
+	if err := decoder.Decode(m); err != nil {
+		return c, err
+	}
+
+	return c, nil
+}