Implement asset.Loader

This moved a bunch of logic out of http and into the asset package,
making it available for gmit too.

src/cmd/load-test-data/main.go

@@ -9,6 +9,7 @@ import (
 
 	cfgpkg "github.com/mediocregopher/blog.mediocregopher.com/srv/cfg"
 	"github.com/mediocregopher/blog.mediocregopher.com/srv/post"
+	"github.com/mediocregopher/blog.mediocregopher.com/srv/post/asset"
 	"github.com/mediocregopher/mediocre-go-lib/v2/mctx"
 	"github.com/mediocregopher/mediocre-go-lib/v2/mlog"
 	"gopkg.in/yaml.v3"
@@ -99,7 +100,7 @@ func main() {
 	}
 
 	{
-		assetStore := post.NewAssetStore(postDB)
+		assetStore := asset.NewStore(postDB)
 
 		setAsset := func(assetID, assetPath string) error {
 			assetFullPath := filepath.Join(testDataDir, assetPath)

src/cmd/mediocre-blog/main.go

@@ -13,6 +13,7 @@ import (
 	"github.com/mediocregopher/blog.mediocregopher.com/srv/http"
 	"github.com/mediocregopher/blog.mediocregopher.com/srv/mailinglist"
 	"github.com/mediocregopher/blog.mediocregopher.com/srv/post"
+	"github.com/mediocregopher/blog.mediocregopher.com/srv/post/asset"
 	"github.com/mediocregopher/blog.mediocregopher.com/srv/pow"
 	"github.com/mediocregopher/mediocre-go-lib/v2/mctx"
 	"github.com/mediocregopher/mediocre-go-lib/v2/mlog"
@@ -100,7 +101,13 @@ func main() {
 	defer postSQLDB.Close()
 
 	postStore := post.NewStore(postSQLDB)
-	postAssetStore := post.NewAssetStore(postSQLDB)
+
+	postAssetStore := asset.NewStore(postSQLDB)
+
+	postAssetLoader := asset.NewStoreLoader(postAssetStore)
+	postAssetLoader = asset.NewArchiveLoader(postAssetLoader)
+	postAssetLoader = asset.NewImageLoader(postAssetLoader)
+
 	postDraftStore := post.NewDraftStore(postSQLDB)
 
 	cache := cache.New(5000)
@@ -110,6 +117,7 @@ func main() {
 	httpParams.PowManager = powMgr
 	httpParams.PostStore = postStore
 	httpParams.PostAssetStore = postAssetStore
+	httpParams.PostAssetLoader = postAssetLoader
 	httpParams.PostDraftStore = postDraftStore
 	httpParams.MailingList = ml
 	httpParams.GeminiPublicURL = gmiParams.PublicURL
@@ -131,7 +139,7 @@ func main() {
 	gmiParams.Logger = logger.WithNamespace("gmi")
 	gmiParams.Cache = cache
 	gmiParams.PostStore = postStore
-	gmiParams.PostAssetStore = postAssetStore
+	gmiParams.PostAssetLoader = postAssetLoader
 	gmiParams.HTTPPublicURL = httpParams.PublicURL
 
 	logger.Info(ctx, "starting gmi api")

src/gmi/gmi.go

@@ -2,13 +2,16 @@
 package gmi
 
 import (
+	"bytes"
 	"context"
 	"errors"
 	"fmt"
+	"io"
 	"mime"
 	"net/url"
 	"os"
 	"path"
+	"path/filepath"
 	"strings"
 
 	"git.sr.ht/~adnano/go-gemini"
@@ -16,6 +19,7 @@ import (
 	"github.com/mediocregopher/blog.mediocregopher.com/srv/cache"
 	"github.com/mediocregopher/blog.mediocregopher.com/srv/cfg"
 	"github.com/mediocregopher/blog.mediocregopher.com/srv/post"
+	"github.com/mediocregopher/blog.mediocregopher.com/srv/post/asset"
 	"github.com/mediocregopher/mediocre-go-lib/v2/mctx"
 	"github.com/mediocregopher/mediocre-go-lib/v2/mlog"
 )
@@ -26,8 +30,8 @@ type Params struct {
 	Logger *mlog.Logger
 	Cache  cache.Cache
 
-	PostStore      post.Store
-	PostAssetStore post.AssetStore
+	PostStore       post.Store
+	PostAssetLoader asset.Loader
 
 	PublicURL        *url.URL
 	ListenAddr       string
@@ -207,18 +211,20 @@ func (a *api) assetsMiddleware() gemini.Handler {
 		r *gemini.Request,
 	) {
 
-		id := path.Base(r.URL.Path)
-		mimeType := mime.TypeByExtension(path.Ext(id))
+		path := strings.TrimPrefix(r.URL.Path, "/assets/")
+		mimeType := mime.TypeByExtension(filepath.Ext(path))
 
-		ctx = mctx.Annotate(ctx, "assetID", id, "mimeType", mimeType)
+		ctx = mctx.Annotate(ctx, "assetPath", path, "mimeType", mimeType)
 
 		if mimeType != "" {
 			rw.SetMediaType(mimeType)
 		}
 
-		err := a.params.PostAssetStore.Get(id, rw)
+		buf := new(bytes.Buffer)
 
-		if errors.Is(err, post.ErrAssetNotFound) {
+		err := a.params.PostAssetLoader.Load(path, buf, asset.LoadOpts{})
+
+		if errors.Is(err, asset.ErrNotFound) {
 			rw.WriteHeader(gemini.StatusNotFound, "Asset not found, sorry!")
 			return
 
@@ -227,6 +233,12 @@ func (a *api) assetsMiddleware() gemini.Handler {
 			rw.WriteHeader(gemini.StatusTemporaryFailure, err.Error())
 			return
 		}
+
+		if _, err := io.Copy(rw, buf); err != nil {
+			a.params.Logger.Error(ctx, "error copying asset", err)
+			rw.WriteHeader(gemini.StatusTemporaryFailure, err.Error())
+			return
+		}
 	})
 }
 

src/http/assets.go

@@ -2,67 +2,17 @@ package http
 
 import (
 	"bytes"
-	"compress/gzip"
 	"errors"
 	"fmt"
-	"image"
-	"image/jpeg"
-	"image/png"
-	"io"
-	"io/fs"
 	"net/http"
 	"path/filepath"
 	"strings"
 	"time"
 
 	"github.com/mediocregopher/blog.mediocregopher.com/srv/http/apiutil"
-	"github.com/mediocregopher/blog.mediocregopher.com/srv/post"
-	"github.com/omeid/go-tarfs"
-	"golang.org/x/image/draw"
+	"github.com/mediocregopher/blog.mediocregopher.com/srv/post/asset"
 )
 
-func isImgResizable(path string) bool {
-	switch strings.ToLower(filepath.Ext(path)) {
-	case ".jpg", ".jpeg", ".png":
-		return true
-	default:
-		return false
-	}
-}
-
-func resizeImage(out io.Writer, in io.Reader, maxWidth float64) error {
-
-	img, format, err := image.Decode(in)
-	if err != nil {
-		return fmt.Errorf("decoding image: %w", err)
-	}
-
-	imgRect := img.Bounds()
-	imgW, imgH := float64(imgRect.Dx()), float64(imgRect.Dy())
-
-	if imgW > maxWidth {
-
-		newH := imgH * maxWidth / imgW
-		newImg := image.NewRGBA(image.Rect(0, 0, int(maxWidth), int(newH)))
-
-		// Resize
-		draw.BiLinear.Scale(
-			newImg, newImg.Bounds(), img, img.Bounds(), draw.Over, nil,
-		)
-
-		img = newImg
-	}
-
-	switch format {
-	case "jpeg":
-		return jpeg.Encode(out, img, nil)
-	case "png":
-		return png.Encode(out, img)
-	default:
-		return fmt.Errorf("unknown image format %q", format)
-	}
-}
-
 func (a *api) managePostAssetsHandler() http.Handler {
 
 	tpl := a.mustParseBasedTpl("post-assets-manage.html")
@@ -88,173 +38,47 @@ func (a *api) managePostAssetsHandler() http.Handler {
 	})
 }
 
-type postAssetArchiveInfo struct {
-	path      string
-	id        string
-	subPath   string
-	isGzipped bool
-}
-
-func extractPostAssetArchiveInfo(path string) (postAssetArchiveInfo, bool) {
-
-	var info postAssetArchiveInfo
-
-	info.path = strings.TrimPrefix(path, "/")
-
-	info.id, info.subPath, _ = strings.Cut(info.path, "/")
-
-	switch {
-
-	case strings.HasSuffix(info.id, ".tar.gz"),
-		strings.HasSuffix(info.id, ".tgz"):
-		info.isGzipped = true
-
-	case strings.HasSuffix(info.id, ".tar"):
-		// ok
-
-	default:
-		// unsupported
-		return postAssetArchiveInfo{}, false
-	}
-
-	return info, true
-}
-
-func (a *api) writePostAsset(
-	rw http.ResponseWriter,
-	r *http.Request,
-	path string,
-	from io.ReadSeeker,
-) {
-
-	maxWidth, err := apiutil.StrToInt(r.FormValue("w"), 0)
-	if err != nil {
-		apiutil.BadRequest(rw, r, fmt.Errorf("invalid w parameter: %w", err))
-		return
-	}
-
-	if maxWidth == 0 {
-		http.ServeContent(rw, r, path, time.Time{}, from)
-		return
-	}
-
-	if !isImgResizable(path) {
-		apiutil.BadRequest(rw, r, fmt.Errorf("cannot resize asset %q", path))
-		return
-	}
-
-	resizedBuf := new(bytes.Buffer)
-
-	if err := resizeImage(resizedBuf, from, float64(maxWidth)); err != nil {
-		apiutil.InternalServerError(
-			rw, r,
-			fmt.Errorf(
-				"resizing image %q to size %d: %w",
-				path, maxWidth, err,
-			),
-		)
-	}
-
-	http.ServeContent(
-		rw, r, path, time.Time{}, bytes.NewReader(resizedBuf.Bytes()),
-	)
-}
-
-func (a *api) handleGetPostAssetArchive(
-	rw http.ResponseWriter,
-	r *http.Request,
-	info postAssetArchiveInfo,
-) {
-
-	buf := new(bytes.Buffer)
-
-	err := a.params.PostAssetStore.Get(info.id, buf)
-
-	if errors.Is(err, post.ErrAssetNotFound) {
-		http.Error(rw, "asset not found", 404)
-		return
-	} else if err != nil {
-		apiutil.InternalServerError(
-			rw, r,
-			fmt.Errorf("fetching archive asset with id %q: %w", info.id, err),
-		)
-		return
-	}
-
-	var from io.Reader = buf
-
-	if info.isGzipped {
-
-		if from, err = gzip.NewReader(from); err != nil {
-			apiutil.InternalServerError(
-				rw, r,
-				fmt.Errorf("decompressing archive asset with id %q: %w", info.id, err),
-			)
-			return
-		}
-	}
-
-	tarFS, err := tarfs.New(from)
-
-	if err != nil {
-		apiutil.InternalServerError(
-			rw, r,
-			fmt.Errorf("reading archive asset with id %q as fs: %w", info.id, err),
-		)
-		return
-	}
-
-	f, err := tarFS.Open(info.subPath)
-
-	if errors.Is(err, fs.ErrExist) {
-		http.Error(rw, "Asset not found", 404)
-		return
-
-	} else if err != nil {
-
-		apiutil.InternalServerError(
-			rw, r,
-			fmt.Errorf(
-				"opening path %q from archive asset with id %q as fs: %w",
-				info.subPath, info.id, err,
-			),
-		)
-		return
-	}
-
-	defer f.Close()
-
-	a.writePostAsset(rw, r, info.path, f)
-}
-
 func (a *api) getPostAssetHandler() http.Handler {
 
 	return http.HandlerFunc(func(rw http.ResponseWriter, r *http.Request) {
 
-		archiveInfo, ok := extractPostAssetArchiveInfo(r.URL.Path)
-
-		if ok {
-			a.handleGetPostAssetArchive(rw, r, archiveInfo)
+		maxWidth, err := apiutil.StrToInt(r.FormValue("w"), 0)
+		if err != nil {
+			apiutil.BadRequest(rw, r, fmt.Errorf("invalid w parameter: %w", err))
 			return
 		}
 
-		id := filepath.Base(r.URL.Path)
+		var (
+			path = strings.TrimPrefix(r.URL.Path, "/")
+			buf  = new(bytes.Buffer)
+		)
 
-		buf := new(bytes.Buffer)
+		err = a.params.PostAssetLoader.Load(
+			path,
+			buf,
+			asset.LoadOpts{
+				ImageWidth: maxWidth,
+			},
+		)
 
-		err := a.params.PostAssetStore.Get(id, buf)
-
-		if errors.Is(err, post.ErrAssetNotFound) {
+		if errors.Is(err, asset.ErrNotFound) {
 			http.Error(rw, "Asset not found", 404)
 			return
+
+		} else if errors.Is(err, asset.ErrCannotResize) {
+			http.Error(rw, "Image resizing not supported", 400)
+			return
+
 		} else if err != nil {
 			apiutil.InternalServerError(
-				rw, r, fmt.Errorf("fetching asset with id %q: %w", id, err),
+				rw, r, fmt.Errorf("fetching asset at path %q: %w", path, err),
 			)
 			return
 		}
 
-		a.writePostAsset(rw, r, id, bytes.NewReader(buf.Bytes()))
+		http.ServeContent(
+			rw, r, path, time.Time{}, bytes.NewReader(buf.Bytes()),
+		)
 	})
 }
 
@@ -297,7 +121,7 @@ func (a *api) deletePostAssetHandler() http.Handler {
 
 		err := a.params.PostAssetStore.Delete(id)
 
-		if errors.Is(err, post.ErrAssetNotFound) {
+		if errors.Is(err, asset.ErrNotFound) {
 			http.Error(rw, "Asset not found", 404)
 			return
 		} else if err != nil {

src/http/http.go

@@ -20,6 +20,7 @@ import (
 	"github.com/mediocregopher/blog.mediocregopher.com/srv/http/apiutil"
 	"github.com/mediocregopher/blog.mediocregopher.com/srv/mailinglist"
 	"github.com/mediocregopher/blog.mediocregopher.com/srv/post"
+	"github.com/mediocregopher/blog.mediocregopher.com/srv/post/asset"
 	"github.com/mediocregopher/blog.mediocregopher.com/srv/pow"
 	"github.com/mediocregopher/mediocre-go-lib/v2/mctx"
 	"github.com/mediocregopher/mediocre-go-lib/v2/mlog"
@@ -35,9 +36,10 @@ type Params struct {
 	PowManager pow.Manager
 	Cache      cache.Cache
 
-	PostStore      post.Store
-	PostAssetStore post.AssetStore
-	PostDraftStore post.DraftStore
+	PostStore       post.Store
+	PostAssetStore  asset.Store
+	PostAssetLoader asset.Loader
+	PostDraftStore  post.DraftStore
 
 	MailingList mailinglist.MailingList
 

src/http/posts.go

@@ -18,6 +18,7 @@ import (
 	"github.com/mediocregopher/blog.mediocregopher.com/srv/gmi"
 	"github.com/mediocregopher/blog.mediocregopher.com/srv/http/apiutil"
 	"github.com/mediocregopher/blog.mediocregopher.com/srv/post"
+	"github.com/mediocregopher/blog.mediocregopher.com/srv/post/asset"
 	"github.com/mediocregopher/mediocre-go-lib/v2/mctx"
 )
 
@@ -49,7 +50,7 @@ func (a *api) postPreprocessFuncImage(args ...string) (string, error) {
 	}{
 		ID:        id,
 		Descr:     descr,
-		Resizable: isImgResizable(id),
+		Resizable: asset.IsImageResizable(id),
 	}
 
 	buf := new(bytes.Buffer)

src/post/asset/asset.go

@@ -1,4 +1,4 @@
-package post
+package asset
 
 import (
 	"bytes"
@@ -6,23 +6,25 @@ import (
 	"errors"
 	"fmt"
 	"io"
+
+	"github.com/mediocregopher/blog.mediocregopher.com/srv/post"
 )
 
 var (
-	// ErrAssetNotFound is used to indicate an Asset could not be found in the
-	// AssetStore.
-	ErrAssetNotFound = errors.New("asset not found")
+	// ErrNotFound is used to indicate an Asset could not be found in the
+	// Store.
+	ErrNotFound = errors.New("asset not found")
 )
 
-// AssetStore implements the storage and retrieval of binary assets, which are
+// Store implements the storage and retrieval of binary assets, which are
 // intended to be used by posts (e.g. images).
-type AssetStore interface {
+type Store interface {
 
 	// Set sets the id to the contents of the given io.Reader.
 	Set(id string, from io.Reader) error
 
 	// Get writes the id's body to the given io.Writer, or returns
-	// ErrAssetNotFound.
+	// ErrNotFound.
 	Get(id string, into io.Writer) error
 
 	// Delete's the body stored for the id, if any.
@@ -32,18 +34,18 @@ type AssetStore interface {
 	List() ([]string, error)
 }
 
-type assetStore struct {
-	db *sql.DB
+type store struct {
+	db *post.SQLDB
 }
 
-// NewAssetStore initializes a new AssetStore using an existing SQLDB.
-func NewAssetStore(db *SQLDB) AssetStore {
-	return &assetStore{
-		db: db.db,
+// NewStore initializes a new Store using an existing SQLDB.
+func NewStore(db *post.SQLDB) Store {
+	return &store{
+		db: db,
 	}
 }
 
-func (s *assetStore) Set(id string, from io.Reader) error {
+func (s *store) Set(id string, from io.Reader) error {
 
 	body, err := io.ReadAll(from)
 	if err != nil {
@@ -64,14 +66,14 @@ func (s *assetStore) Set(id string, from io.Reader) error {
 	return nil
 }
 
-func (s *assetStore) Get(id string, into io.Writer) error {
+func (s *store) Get(id string, into io.Writer) error {
 
 	var body []byte
 
 	err := s.db.QueryRow(`SELECT body FROM assets WHERE id = ?`, id).Scan(&body)
 
 	if errors.Is(err, sql.ErrNoRows) {
-		return ErrAssetNotFound
+		return ErrNotFound
 	} else if err != nil {
 		return fmt.Errorf("selecting from assets: %w", err)
 	}
@@ -83,12 +85,12 @@ func (s *assetStore) Get(id string, into io.Writer) error {
 	return nil
 }
 
-func (s *assetStore) Delete(id string) error {
+func (s *store) Delete(id string) error {
 	_, err := s.db.Exec(`DELETE FROM assets WHERE id = ?`, id)
 	return err
 }
 
-func (s *assetStore) List() ([]string, error) {
+func (s *store) List() ([]string, error) {
 
 	rows, err := s.db.Query(`SELECT id FROM assets ORDER BY id ASC`)
 

src/post/asset/asset_test.go

@@ -1,30 +1,31 @@
-package post
+package asset
 
 import (
 	"bytes"
 	"io"
 	"testing"
 
+	"github.com/mediocregopher/blog.mediocregopher.com/srv/post"
 	"github.com/stretchr/testify/assert"
 )
 
-type assetTestHarness struct {
-	store AssetStore
+type testHarness struct {
+	store Store
 }
 
-func newAssetTestHarness(t *testing.T) *assetTestHarness {
+func newTestHarness(t *testing.T) *testHarness {
 
-	db := NewInMemSQLDB()
+	db := post.NewInMemSQLDB()
 	t.Cleanup(func() { db.Close() })
 
-	store := NewAssetStore(db)
+	store := NewStore(db)
 
-	return &assetTestHarness{
+	return &testHarness{
 		store: store,
 	}
 }
 
-func (h *assetTestHarness) assertGet(t *testing.T, exp, id string) {
+func (h *testHarness) assertGet(t *testing.T, exp, id string) {
 	t.Helper()
 	buf := new(bytes.Buffer)
 	err := h.store.Get(id, buf)
@@ -32,15 +33,15 @@ func (h *assetTestHarness) assertGet(t *testing.T, exp, id string) {
 	assert.Equal(t, exp, buf.String())
 }
 
-func (h *assetTestHarness) assertNotFound(t *testing.T, id string) {
+func (h *testHarness) assertNotFound(t *testing.T, id string) {
 	t.Helper()
 	err := h.store.Get(id, io.Discard)
-	assert.ErrorIs(t, ErrAssetNotFound, err)
+	assert.ErrorIs(t, ErrNotFound, err)
 }
 
-func TestAssetStore(t *testing.T) {
+func TestStore(t *testing.T) {
 
-	testAssetStore := func(t *testing.T, h *assetTestHarness) {
+	testStore := func(t *testing.T, h *testHarness) {
 		t.Helper()
 
 		h.assertNotFound(t, "foo")
@@ -85,7 +86,7 @@ func TestAssetStore(t *testing.T) {
 	}
 
 	t.Run("sql", func(t *testing.T) {
-		h := newAssetTestHarness(t)
-		testAssetStore(t, h)
+		h := newTestHarness(t)
+		testStore(t, h)
 	})
 }

src/post/asset/loader.go

@@ -0,0 +1,43 @@
+package asset
+
+import (
+	"errors"
+	"io"
+	"path/filepath"
+)
+
+var (
+	ErrCannotResize = errors.New("cannot resize")
+)
+
+// LoadOpts are optional parameters to Loader's Load method. Some may only apply
+// to specific Loader implementations.
+type LoadOpts struct {
+
+	// ImageWidth is used by the ImageLoader to resize images on the fly.
+	ImageWidth int
+}
+
+// Loader is used to load an asset and write its body into the given io.Writer.
+//
+// Errors:
+//	- ErrNotFound
+//	- ErrCannotResize (only if ImageLoader is used)
+type Loader interface {
+	Load(path string, into io.Writer, opts LoadOpts) error
+}
+
+type storeLoader struct {
+	store Store
+}
+
+// NewStoreLoader returns a Loader which loads assets directly from the given
+// Store, with no transformation.
+func NewStoreLoader(store Store) Loader {
+	return &storeLoader{store}
+}
+
+func (l *storeLoader) Load(path string, into io.Writer, opts LoadOpts) error {
+	id := filepath.Base(path)
+	return l.store.Get(id, into)
+}

src/post/asset/loader_archive.go

@@ -0,0 +1,99 @@
+package asset
+
+import (
+	"bytes"
+	"compress/gzip"
+	"errors"
+	"fmt"
+	"io"
+	"io/fs"
+	"strings"
+
+	"github.com/omeid/go-tarfs"
+)
+
+type archiveLoader struct {
+	loader Loader
+}
+
+// NewArchiveLoader wraps an existing Loader in order to support extracting
+// files from within an archive file asset.
+//
+// For example, loading the path `foo.tgz/foo/bar.jpg` will call
+// `Load("foo.tgz")`, load that archive into memory, and serve the file
+// `./foo/bar.jpg` from within the archive.
+func NewArchiveLoader(loader Loader) Loader {
+	return &archiveLoader{loader: loader}
+}
+
+func (l *archiveLoader) Load(path string, into io.Writer, opts LoadOpts) error {
+
+	id, subPath, ok := strings.Cut(strings.TrimPrefix(path, "/"), "/")
+
+	if !ok {
+		return l.loader.Load(path, into, opts)
+	}
+
+	var isGzipped bool
+
+	switch {
+
+	case strings.HasSuffix(id, ".tar.gz"),
+		strings.HasSuffix(id, ".tgz"):
+		isGzipped = true
+
+	case strings.HasSuffix(id, ".tar"):
+		// ok
+
+	default:
+		// unsupported
+		return l.loader.Load(path, into, opts)
+	}
+
+	buf := new(bytes.Buffer)
+
+	if err := l.loader.Load(id, buf, opts); err != nil {
+		return fmt.Errorf("loading archive into buffer: %w", err)
+	}
+
+	var (
+		from io.Reader = buf
+		err  error
+	)
+
+	if isGzipped {
+
+		if from, err = gzip.NewReader(from); err != nil {
+			return fmt.Errorf("decompressing archive asset with id %q: %w", id, err)
+		}
+	}
+
+	tarFS, err := tarfs.New(from)
+
+	if err != nil {
+		return fmt.Errorf("reading archive asset with id %q as fs: %w", id, err)
+	}
+
+	f, err := tarFS.Open(subPath)
+
+	if errors.Is(err, fs.ErrExist) {
+		return ErrNotFound
+
+	} else if err != nil {
+		return fmt.Errorf(
+			"opening path %q from archive asset with id %q as fs: %w",
+			subPath, id, err,
+		)
+	}
+
+	defer f.Close()
+
+	if _, err = io.Copy(into, f); err != nil {
+		return fmt.Errorf(
+			"reading %q from archive asset with id %q as fs: %w",
+			subPath, id, err,
+		)
+	}
+
+	return nil
+}

src/post/asset/loader_image.go

@@ -0,0 +1,85 @@
+package asset
+
+import (
+	"bytes"
+	"fmt"
+	"image"
+	"image/jpeg"
+	"image/png"
+	"io"
+	"path/filepath"
+	"strings"
+
+	"golang.org/x/image/draw"
+)
+
+// IsImageResizable returns whether or not an image can be resized, based on its
+// extension.
+func IsImageResizable(path string) bool {
+	switch strings.ToLower(filepath.Ext(path)) {
+	case ".jpg", ".jpeg", ".png":
+		return true
+	default:
+		return false
+	}
+}
+
+type imageLoader struct {
+	loader Loader
+}
+
+// NewImageLoader wraps an existing Loader in order to perform various
+// image-related transformations on any image assets being loaded. Non-image
+// assets are loaded as-is.
+func NewImageLoader(loader Loader) Loader {
+	return &imageLoader{loader}
+}
+
+func (l *imageLoader) Load(path string, into io.Writer, opts LoadOpts) error {
+
+	if opts.ImageWidth == 0 {
+		return l.loader.Load(path, into, opts)
+	}
+
+	if !IsImageResizable(path) {
+		return ErrCannotResize
+	}
+
+	buf := new(bytes.Buffer)
+
+	if err := l.loader.Load(path, buf, opts); err != nil {
+		return fmt.Errorf("loading image into buffer: %w", err)
+	}
+
+	img, format, err := image.Decode(buf)
+	if err != nil {
+		return fmt.Errorf("decoding image: %w", err)
+	}
+
+	maxWidth := float64(opts.ImageWidth)
+	imgRect := img.Bounds()
+	imgW, imgH := float64(imgRect.Dx()), float64(imgRect.Dy())
+
+	if imgW > maxWidth {
+
+		newH := imgH * maxWidth / imgW
+		newImg := image.NewRGBA(image.Rect(0, 0, int(maxWidth), int(newH)))
+
+		// Resize
+		draw.BiLinear.Scale(
+			newImg, newImg.Bounds(), img, img.Bounds(), draw.Over, nil,
+		)
+
+		img = newImg
+	}
+
+	switch format {
+	case "jpeg":
+		return jpeg.Encode(into, img, nil)
+	case "png":
+		return png.Encode(into, img)
+	default:
+		return fmt.Errorf("unknown image format %q", format)
+	}
+
+}

src/post/draft_post.go

@@ -47,7 +47,7 @@ func (s *draftStore) Set(post Post) error {
 		return fmt.Errorf("json marshaling tags %#v: %w", post.Tags, err)
 	}
 
-	_, err = s.db.db.Exec(
+	_, err = s.db.Exec(
 		`INSERT INTO post_drafts (
 				id, title, description, tags, series, body, format
 			)
@@ -145,7 +145,7 @@ func (s *draftStore) get(
 
 func (s *draftStore) Get(page, count int) ([]Post, bool, error) {
 
-	posts, err := s.get(s.db.db, count+1, page*count, ``)
+	posts, err := s.get(s.db, count+1, page*count, ``)
 
 	if err != nil {
 		return nil, false, fmt.Errorf("querying post_drafts: %w", err)
@@ -163,7 +163,7 @@ func (s *draftStore) Get(page, count int) ([]Post, bool, error) {
 
 func (s *draftStore) GetByID(id string) (Post, error) {
 
-	posts, err := s.get(s.db.db, 0, 0, `WHERE p.id=?`, id)
+	posts, err := s.get(s.db, 0, 0, `WHERE p.id=?`, id)
 
 	if err != nil {
 		return Post{}, fmt.Errorf("querying post_drafts: %w", err)
@@ -182,7 +182,7 @@ func (s *draftStore) GetByID(id string) (Post, error) {
 
 func (s *draftStore) Delete(id string) error {
 
-	if _, err := s.db.db.Exec(`DELETE FROM post_drafts WHERE id = ?`, id); err != nil {
+	if _, err := s.db.Exec(`DELETE FROM post_drafts WHERE id = ?`, id); err != nil {
 		return fmt.Errorf("deleting from post_drafts: %w", err)
 	}
 

src/post/post.go

@@ -96,7 +96,7 @@ func (s *store) Set(post Post, now time.Time) (bool, error) {
 
 	var first bool
 
-	err := s.db.withTx(func(tx *sql.Tx) error {
+	err := s.db.WithTx(func(tx *sql.Tx) error {
 
 		nowTS := now.Unix()
 
@@ -244,7 +244,7 @@ func (s *store) get(
 
 func (s *store) Get(page, count int) ([]StoredPost, bool, error) {
 
-	posts, err := s.get(s.db.db, count+1, page*count, ``)
+	posts, err := s.get(s.db, count+1, page*count, ``)
 
 	if err != nil {
 		return nil, false, fmt.Errorf("querying posts: %w", err)
@@ -262,7 +262,7 @@ func (s *store) Get(page, count int) ([]StoredPost, bool, error) {
 
 func (s *store) GetByID(id string) (StoredPost, error) {
 
-	posts, err := s.get(s.db.db, 0, 0, `WHERE p.id=?`, id)
+	posts, err := s.get(s.db, 0, 0, `WHERE p.id=?`, id)
 
 	if err != nil {
 		return StoredPost{}, fmt.Errorf("querying posts: %w", err)
@@ -280,14 +280,14 @@ func (s *store) GetByID(id string) (StoredPost, error) {
 }
 
 func (s *store) GetBySeries(series string) ([]StoredPost, error) {
-	return s.get(s.db.db, 0, 0, `WHERE p.series=?`, series)
+	return s.get(s.db, 0, 0, `WHERE p.series=?`, series)
 }
 
 func (s *store) GetByTag(tag string) ([]StoredPost, error) {
 
 	var posts []StoredPost
 
-	err := s.db.withTx(func(tx *sql.Tx) error {
+	err := s.db.WithTx(func(tx *sql.Tx) error {
 
 		rows, err := tx.Query(`SELECT post_id FROM post_tags WHERE tag = ?`, tag)
 
@@ -331,7 +331,7 @@ func (s *store) GetByTag(tag string) ([]StoredPost, error) {
 
 func (s *store) GetTags() ([]string, error) {
 
-	rows, err := s.db.db.Query(`SELECT tag FROM post_tags GROUP BY tag`)
+	rows, err := s.db.Query(`SELECT tag FROM post_tags GROUP BY tag`)
 	if err != nil {
 		return nil, fmt.Errorf("querying all tags: %w", err)
 	}
@@ -355,7 +355,7 @@ func (s *store) GetTags() ([]string, error) {
 
 func (s *store) Delete(id string) error {
 
-	return s.db.withTx(func(tx *sql.Tx) error {
+	return s.db.WithTx(func(tx *sql.Tx) error {
 
 		if _, err := tx.Exec(`DELETE FROM post_tags WHERE post_id = ?`, id); err != nil {
 			return fmt.Errorf("deleting from post_tags: %w", err)

src/post/sql.go

@@ -78,7 +78,7 @@ var migrations = &migrate.MemoryMigrationSource{Migrations: []*migrate.Migration
 // SQLDB is a sqlite3 database which can be used by storage interfaces within
 // this package.
 type SQLDB struct {
-	db *sql.DB
+	*sql.DB
 }
 
 // NewSQLDB initializes and returns a new sqlite3 database for storage
@@ -116,12 +116,14 @@ func NewInMemSQLDB() *SQLDB {
 
 // Close cleans up loose resources being held by the db.
 func (db *SQLDB) Close() error {
-	return db.db.Close()
+	return db.DB.Close()
 }
 
-func (db *SQLDB) withTx(cb func(*sql.Tx) error) error {
+// WithTx initializes a transaction, runs the callback using it, and either
+// commits or rolls it back depending on if the callback returns an error.
+func (db *SQLDB) WithTx(cb func(*sql.Tx) error) error {
 
-	tx, err := db.db.Begin()
+	tx, err := db.DB.Begin()
 
 	if err != nil {
 		return fmt.Errorf("starting transaction: %w", err)