implement conditional requests

- currently only applies to single thread get
- still exploring internal API design for this
- will maybe look at proper caching layer too

Author: Southclaws

api/openapi.yaml

@@ -1150,11 +1150,14 @@ paths:
       parameters:
         - $ref: "#/components/parameters/ThreadMarkParam"
         - $ref: "#/components/parameters/PaginationQuery"
+        - $ref: "#/components/parameters/If-None-Match"
+        - $ref: "#/components/parameters/If-Modified-Since"
       responses:
         default: { $ref: "#/components/responses/InternalServerError" }
         "404": { $ref: "#/components/responses/NotFound" }
         "401": { $ref: "#/components/responses/Unauthorised" }
         "200": { $ref: "#/components/responses/ThreadGet" }
+        "304": { description: cached }
     patch:
       operationId: ThreadUpdate
       description: Publish changes to a thread.
@@ -1910,6 +1913,21 @@ components:
   #
 
   parameters:
+    "If-None-Match":
+      description: If-None-Match cache control header.
+      name: If-None-Match
+      in: header
+      required: false
+      schema:
+        type: string
+    "If-Modified-Since":
+      description: If-Modified-Since cache control header.
+      name: If-Modified-Since
+      in: header
+      required: false
+      schema:
+        type: string
+
     IconSize:
       description: Icon sizes.
       example: "512x512"
@@ -2789,6 +2807,10 @@ components:
 
     ThreadGet:
       description: The information about a thread and its posts.
+      headers:
+        Cache-Control: { $ref: "#/components/headers/Cache-Control" }
+        Last-Modified: { $ref: "#/components/headers/Last-Modified" }
+        ETag: { $ref: "#/components/headers/ETag" }
       content:
         application/json:
           schema: { $ref: "#/components/schemas/Thread" }
@@ -3024,6 +3046,18 @@ components:
   #  "Y8888P"   "Y8888P"  888    888 8888888888 888       888 d88P     888  "Y8888P"
   #
 
+  headers:
+    Cache-Control:
+      schema:
+        type: string
+    Last-Modified:
+      schema:
+        type: string
+        format: RFC1123
+    ETag:
+      schema:
+        type: string
+
   schemas:
     #
     #  .d8888b.

app/resources/cachecontrol/query.go

@@ -0,0 +1,61 @@
+package cachecontrol
+
+import (
+	"time"
+
+	"github.com/Southclaws/opt"
+
+	"github.com/Southclaws/storyden/app/transports/http/openapi"
+)
+
+// Query represents a HTTP conditional request query.
+type Query struct {
+	ETag          opt.Optional[string]
+	ModifiedSince opt.Optional[time.Time]
+}
+
+// NewQuery must be constructed from a HTTP request's conditional headers.
+func NewQuery(
+	IfNoneMatch *string,
+	IfModifiedSince *string,
+) opt.Optional[Query] {
+	if IfNoneMatch == nil && IfModifiedSince == nil {
+		return opt.NewEmpty[Query]()
+	}
+
+	modifiedSince, err := opt.MapErr(opt.NewPtr(IfModifiedSince), parseConditionalRequestTime)
+	if err != nil {
+		return opt.NewEmpty[Query]()
+	}
+
+	return opt.New(Query{
+		ETag:          opt.NewPtr((*string)(IfNoneMatch)),
+		ModifiedSince: modifiedSince,
+	})
+}
+
+// NotModified takes the current updated date of a resource and returns true if
+// the cache control query includes a Is-Modified-Since header and the resource
+// updated date is not after the header value. True means a 304 response header.
+func (q Query) NotModified(resourceUpdated time.Time) bool {
+	// truncate the resourceUpdated to the nearest second because the actual
+	// HTTP header is already truncated but the database time is in nanoseconds.
+	// If we didn't do this, the resource updated will always be slightly ahead.
+	truncated := resourceUpdated.Truncate(time.Second)
+
+	if ms, ok := q.ModifiedSince.Get(); ok {
+
+		// If the resource update time is ahead of the HTTP Last-Modified check,
+		// modified = 1, meaning the resource has been modified since the last
+		// request and should be returned from the DB, instead of a 304 status.
+		modified := truncated.Compare(ms)
+
+		return modified <= 0
+	}
+
+	return false
+}
+
+func parseConditionalRequestTime(in openapi.IfModifiedSince) (time.Time, error) {
+	return time.Parse(time.RFC1123, in)
+}

app/resources/post/thread_cache/cache.go

@@ -0,0 +1,40 @@
+package thread_cache
+
+import (
+	"context"
+
+	"github.com/Southclaws/fault"
+	"github.com/Southclaws/fault/fctx"
+	"github.com/Southclaws/opt"
+	"github.com/rs/xid"
+
+	"github.com/Southclaws/storyden/app/resources/cachecontrol"
+	"github.com/Southclaws/storyden/internal/ent"
+	"github.com/Southclaws/storyden/internal/ent/post"
+)
+
+type Cache struct {
+	db *ent.Client
+}
+
+func New(db *ent.Client) *Cache {
+	return &Cache{
+		db: db,
+	}
+}
+
+func (c *Cache) IsNotModified(ctx context.Context, cq opt.Optional[cachecontrol.Query], id xid.ID) (bool, error) {
+	query, ok := cq.Get()
+	if !ok {
+		return false, nil
+	}
+
+	r, err := c.db.Post.Query().Select(post.FieldUpdatedAt).Where(post.ID(id)).Only(ctx)
+	if err != nil {
+		return false, fault.Wrap(err, fctx.With(ctx))
+	}
+
+	notModified := query.NotModified(r.UpdatedAt)
+
+	return notModified, nil
+}

app/resources/resources.go

@@ -40,6 +40,7 @@ import (
 	"github.com/Southclaws/storyden/app/resources/post/reaction"
 	"github.com/Southclaws/storyden/app/resources/post/reply"
 	"github.com/Southclaws/storyden/app/resources/post/thread"
+	"github.com/Southclaws/storyden/app/resources/post/thread_cache"
 	"github.com/Southclaws/storyden/app/resources/profile/follow_querier"
 	"github.com/Southclaws/storyden/app/resources/profile/follow_writer"
 	"github.com/Southclaws/storyden/app/resources/profile/profile_search"
@@ -72,6 +73,7 @@ func Build() fx.Option {
 			tag_querier.New,
 			tag_writer.New,
 			thread.New,
+			thread_cache.New,
 			reaction.New,
 			like_querier.New,
 			like_writer.New,

app/transports/http/bindings/threads.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"net/url"
 	"strconv"
+	"time"
 
 	"github.com/Southclaws/dt"
 	"github.com/Southclaws/fault"
@@ -13,10 +14,12 @@ import (
 	"github.com/rs/xid"
 
 	"github.com/Southclaws/storyden/app/resources/account/account_querier"
+	"github.com/Southclaws/storyden/app/resources/cachecontrol"
 	"github.com/Southclaws/storyden/app/resources/datagraph"
 	"github.com/Southclaws/storyden/app/resources/tag/tag_ref"
 
 	"github.com/Southclaws/storyden/app/resources/post/category"
+	"github.com/Southclaws/storyden/app/resources/post/thread_cache"
 	"github.com/Southclaws/storyden/app/resources/visibility"
 	"github.com/Southclaws/storyden/app/services/authentication/session"
 	thread_service "github.com/Southclaws/storyden/app/services/thread"
@@ -25,17 +28,19 @@ import (
 )
 
 type Threads struct {
+	thread_cache    *thread_cache.Cache
 	thread_svc      thread_service.Service
 	thread_mark_svc thread_mark.Service
 	accountQuery    *account_querier.Querier
 }
 
 func NewThreads(
+	thread_cache *thread_cache.Cache,
 	thread_svc thread_service.Service,
 	thread_mark_svc thread_mark.Service,
 	accountQuery *account_querier.Querier,
 ) Threads {
-	return Threads{thread_svc, thread_mark_svc, accountQuery}
+	return Threads{thread_cache, thread_svc, thread_mark_svc, accountQuery}
 }
 
 func (i *Threads) ThreadCreate(ctx context.Context, request openapi.ThreadCreateRequestObject) (openapi.ThreadCreateResponseObject, error) {
@@ -211,6 +216,15 @@ func (i *Threads) ThreadGet(ctx context.Context, request openapi.ThreadGetReques
 		return nil, fault.Wrap(err, fctx.With(ctx))
 	}
 
+	notModified, err := i.thread_cache.IsNotModified(ctx, cachecontrol.NewQuery(request.Params.IfNoneMatch, request.Params.IfModifiedSince), xid.ID(postID))
+	if err != nil {
+		return nil, fault.Wrap(err, fctx.With(ctx))
+	}
+
+	if notModified {
+		return openapi.ThreadGet304Response{}, nil
+	}
+
 	pp := deserialisePageParams(request.Params.Page, 50)
 
 	thread, err := i.thread_svc.Get(ctx, postID, pp)
@@ -219,7 +233,13 @@ func (i *Threads) ThreadGet(ctx context.Context, request openapi.ThreadGetReques
 	}
 
 	return openapi.ThreadGet200JSONResponse{
-		ThreadGetJSONResponse: openapi.ThreadGetJSONResponse(serialiseThread(thread)),
+		ThreadGetJSONResponse: openapi.ThreadGetJSONResponse{
+			Body: serialiseThread(thread),
+			Headers: openapi.ThreadGetResponseHeaders{
+				CacheControl: "max-age=1",
+				LastModified: thread.UpdatedAt.Format(time.RFC1123),
+			},
+		},
 	}, nil
 }