[chore] The Big Middleware and API Refactor (tm) (#1250)

* interim commit: start refactoring middlewares into package under router

* another interim commit, this is becoming a big job

* another fucking massive interim commit

* refactor bookmarks to new style

* ambassador, wiz zeze commits you are spoiling uz

* she compiles, we're getting there

* we're just normal men; we're just innocent men

* apiutil

* whoopsie

* i'm glad noone reads commit msgs haha :blob_sweat:

* use that weirdo go-bytesize library for maxMultipartMemory

* fix media module paths

internal/api/fileserver/servefile.go

@@ -0,0 +1,130 @@
+/*
+   GoToSocial
+   Copyright (C) 2021-2022 GoToSocial Authors admin@gotosocial.org
+
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU Affero General Public License as published by
+   the Free Software Foundation, either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU Affero General Public License for more details.
+
+   You should have received a copy of the GNU Affero General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+package fileserver
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"net/http"
+	"strconv"
+
+	"github.com/gin-gonic/gin"
+	apimodel "github.com/superseriousbusiness/gotosocial/internal/api/model"
+	apiutil "github.com/superseriousbusiness/gotosocial/internal/api/util"
+	"github.com/superseriousbusiness/gotosocial/internal/gtserror"
+	"github.com/superseriousbusiness/gotosocial/internal/log"
+	"github.com/superseriousbusiness/gotosocial/internal/oauth"
+)
+
+// ServeFile is for serving attachments, headers, and avatars to the requester from instance storage.
+//
+// Note: to mitigate scraping attempts, no information should be given out on a bad request except "404 page not found".
+// Don't give away account ids or media ids or anything like that; callers shouldn't be able to infer anything.
+func (m *Module) ServeFile(c *gin.Context) {
+	authed, err := oauth.Authed(c, false, false, false, false)
+	if err != nil {
+		apiutil.ErrorHandler(c, gtserror.NewErrorNotFound(err), m.processor.InstanceGet)
+		return
+	}
+
+	// We use request params to check what to pull out of the database/storage so check everything. A request URL should be formatted as follows:
+	// "https://example.org/fileserver/[ACCOUNT_ID]/[MEDIA_TYPE]/[MEDIA_SIZE]/[FILE_NAME]"
+	// "FILE_NAME" consists of two parts, the attachment's database id, a period, and the file extension.
+	accountID := c.Param(AccountIDKey)
+	if accountID == "" {
+		err := fmt.Errorf("missing %s from request", AccountIDKey)
+		apiutil.ErrorHandler(c, gtserror.NewErrorNotFound(err), m.processor.InstanceGet)
+		return
+	}
+
+	mediaType := c.Param(MediaTypeKey)
+	if mediaType == "" {
+		err := fmt.Errorf("missing %s from request", MediaTypeKey)
+		apiutil.ErrorHandler(c, gtserror.NewErrorNotFound(err), m.processor.InstanceGet)
+		return
+	}
+
+	mediaSize := c.Param(MediaSizeKey)
+	if mediaSize == "" {
+		err := fmt.Errorf("missing %s from request", MediaSizeKey)
+		apiutil.ErrorHandler(c, gtserror.NewErrorNotFound(err), m.processor.InstanceGet)
+		return
+	}
+
+	fileName := c.Param(FileNameKey)
+	if fileName == "" {
+		err := fmt.Errorf("missing %s from request", FileNameKey)
+		apiutil.ErrorHandler(c, gtserror.NewErrorNotFound(err), m.processor.InstanceGet)
+		return
+	}
+
+	content, errWithCode := m.processor.FileGet(c.Request.Context(), authed, &apimodel.GetContentRequestForm{
+		AccountID: accountID,
+		MediaType: mediaType,
+		MediaSize: mediaSize,
+		FileName:  fileName,
+	})
+	if errWithCode != nil {
+		apiutil.ErrorHandler(c, errWithCode, m.processor.InstanceGet)
+		return
+	}
+
+	defer func() {
+		// close content when we're done
+		if content.Content != nil {
+			if err := content.Content.Close(); err != nil {
+				log.Errorf("ServeFile: error closing readcloser: %s", err)
+			}
+		}
+	}()
+
+	if content.URL != nil {
+		c.Redirect(http.StatusFound, content.URL.String())
+		return
+	}
+
+	// TODO: if the requester only accepts text/html we should try to serve them *something*.
+	// This is mostly needed because when sharing a link to a gts-hosted file on something like mastodon, the masto servers will
+	// attempt to look up the content to provide a preview of the link, and they ask for text/html.
+	format, err := apiutil.NegotiateAccept(c, apiutil.MIME(content.ContentType))
+	if err != nil {
+		apiutil.ErrorHandler(c, gtserror.NewErrorNotAcceptable(err, err.Error()), m.processor.InstanceGet)
+		return
+	}
+
+	// if this is a head request, just return info + throw the reader away
+	if c.Request.Method == http.MethodHead {
+		c.Header("Content-Type", format)
+		c.Header("Content-Length", strconv.FormatInt(content.ContentLength, 10))
+		c.Status(http.StatusOK)
+		return
+	}
+
+	// try to slurp the first few bytes to make sure we have something
+	b := bytes.NewBuffer(make([]byte, 0, 64))
+	if _, err := io.CopyN(b, content.Content, 64); err != nil {
+		err = fmt.Errorf("ServeFile: error reading from content: %w", err)
+		apiutil.ErrorHandler(c, gtserror.NewErrorNotFound(err, err.Error()), m.processor.InstanceGet)
+		return
+	}
+
+	// we're good, return the slurped bytes + the rest of the content
+	c.DataFromReader(http.StatusOK, content.ContentLength, format, io.MultiReader(b, content.Content), nil)
+}