2 files changed, 153 insertions, 0 deletions
diff --git a/srv/src/post/asset.go b/srv/src/post/asset.go
new file mode 100644
index 0000000..3e6ae28
--- /dev/null
+++ b/srv/src/post/asset.go
@@ -0,0 +1,86 @@
+package post
+
+import (
+	"bytes"
+	"database/sql"
+	"errors"
+	"fmt"
+	"io"
+)
+
+var (
+	// ErrAssetNotFound is used to indicate an Asset could not be found in the
+	// AssetStore.
+	ErrAssetNotFound = errors.New("asset not found")
+)
+
+// AssetStore implements the storage and retrieval of binary assets, which are
+// intended to be used by posts (e.g. images).
+type AssetStore 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.
+	Get(id string, into io.Writer) error
+
+	// Delete's the body stored for the id, if any.
+	Delete(id string) error
+}
+
+type assetStore struct {
+	db *sql.DB
+}
+
+// NewAssetStore initializes a new AssetStore using an existing SQLDB.
+func NewAssetStore(db *SQLDB) AssetStore {
+	return &assetStore{
+		db: db.db,
+	}
+}
+
+func (s *assetStore) Set(id string, from io.Reader) error {
+
+	body, err := io.ReadAll(from)
+	if err != nil {
+		return fmt.Errorf("reading body fully into memory: %w", err)
+	}
+
+	_, err = s.db.Exec(
+		`INSERT INTO assets (id, body)
+		VALUES (?, ?)
+		ON CONFLICT (id) DO UPDATE SET body=excluded.body`,
+		id, body,
+	)
+
+	if err != nil {
+		return fmt.Errorf("inserting into assets: %w", err)
+	}
+
+	return nil
+}
+
+func (s *assetStore) 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
+	} else if err != nil {
+		return fmt.Errorf("selecting from assets: %w", err)
+	}
+
+	if _, err := io.Copy(into, bytes.NewReader(body)); err != nil {
+		return fmt.Errorf("writing body to io.Writer: %w", err)
+	}
+
+	return nil
+}
+
+func (s *assetStore) Delete(id string) error {
+	_, err := s.db.Exec(`DELETE FROM assets WHERE id = ?`, id)
+	return err
+}
diff --git a/srv/src/post/asset_test.go b/srv/src/post/asset_test.go
new file mode 100644
index 0000000..4b88000
--- /dev/null
+++ b/srv/src/post/asset_test.go
@@ -0,0 +1,67 @@
+package post
+
+import (
+	"bytes"
+	"io"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+type assetTestHarness struct {
+	store AssetStore
+}
+
+func newAssetTestHarness(t *testing.T) assetTestHarness {
+
+	db := NewInMemSQLDB()
+	t.Cleanup(func() { db.Close() })
+
+	store := NewAssetStore(db)
+
+	return assetTestHarness{
+		store: store,
+	}
+}
+
+func (h *assetTestHarness) assertGet(t *testing.T, exp, id string) {
+	t.Helper()
+	buf := new(bytes.Buffer)
+	err := h.store.Get(id, buf)
+	assert.NoError(t, err)
+	assert.Equal(t, exp, buf.String())
+}
+
+func (h *assetTestHarness) assertNotFound(t *testing.T, id string) {
+	t.Helper()
+	err := h.store.Get(id, io.Discard)
+	assert.ErrorIs(t, ErrAssetNotFound, err)
+}
+
+func TestAssetStore(t *testing.T) {
+
+	h := newAssetTestHarness(t)
+
+	h.assertNotFound(t, "foo")
+	h.assertNotFound(t, "bar")
+
+	err := h.store.Set("foo", bytes.NewBufferString("FOO"))
+	assert.NoError(t, err)
+
+	h.assertGet(t, "FOO", "foo")
+	h.assertNotFound(t, "bar")
+
+	err = h.store.Set("foo", bytes.NewBufferString("FOOFOO"))
+	assert.NoError(t, err)
+
+	h.assertGet(t, "FOOFOO", "foo")
+	h.assertNotFound(t, "bar")
+
+	assert.NoError(t, h.store.Delete("foo"))
+	h.assertNotFound(t, "foo")
+	h.assertNotFound(t, "bar")
+
+	assert.NoError(t, h.store.Delete("bar"))
+	h.assertNotFound(t, "foo")
+	h.assertNotFound(t, "bar")
+}