Allow to request log instead of PDF on error

Signed-off-by: Knut Ahlers <knut@ahlers.me>

README.md

@@ -48,7 +48,7 @@ main.log
 main.pdf
 
 # Using the default-env and exchanging a TeX file for a PDF
-# curl -sSL -H 'Accept: application/pdf' --data-binary @main.tex -o main.pdf localhost:3000/job
+# curl -L -H 'Accept: application/pdf' --data-binary @main.tex -OJ localhost:3000/job
 ```
 
 What happened here is we packed all assets required for generating the letter into the ZIP archive, pushed it to the API, waited for it to build a TAR and extracted the resulting files from it.
@@ -69,3 +69,5 @@ GET   /job/{uuid}/download  Download the resulting archive (You may specify an
                             Accept header to select whether to receive a ZIP, a
                             TAR archive or just the raw PDF.)
 ```
+
+All routes accept the `log-on-error` parameter: If set a PDF download (`Accept` header set to `application/pdf`) will return the log instead of the PDF if no PDF is found.

assets.go

@@ -5,6 +5,7 @@ import (
 	"archive/zip"
 	"bytes"
 	"io"
+	"io/fs"
 	"os"
 	"path"
 	"path/filepath"
@@ -109,7 +110,7 @@ func buildAssetsZIP(uid uuid.UUID) (io.Reader, error) {
 	return buf, errors.Wrap(w.Close(), "closing zip file")
 }
 
-func getAssetsPDF(uid uuid.UUID) (io.Reader, error) {
+func getAssetsFile(uid uuid.UUID, ext string) (io.Reader, error) {
 	var (
 		buf   = new(bytes.Buffer)
 		found bool
@@ -121,7 +122,7 @@ func getAssetsPDF(uid uuid.UUID) (io.Reader, error) {
 			return err
 		}
 
-		if path.Ext(info.Name()) != ".pdf" {
+		if path.Ext(info.Name()) != ext {
 			return nil
 		}
 
@@ -131,7 +132,7 @@ func getAssetsPDF(uid uuid.UUID) (io.Reader, error) {
 		}
 		defer func() {
 			if err := osFile.Close(); err != nil {
-				logrus.WithError(err).Error("closing output pdf file (leaked fd)")
+				logrus.WithError(err).Error("closing output file (leaked fd)")
 			}
 		}()
 
@@ -145,7 +146,7 @@ func getAssetsPDF(uid uuid.UUID) (io.Reader, error) {
 
 	if !found {
 		// We found no file
-		return nil, errors.New("no pdf found")
+		return nil, fs.ErrNotExist
 	}
 
 	return buf, errors.Wrap(err, "walking source dir")

main.go

@@ -3,6 +3,7 @@ package main
 import (
 	"fmt"
 	"io"
+	"io/fs"
 	"net/http"
 	"os"
 	"time"
@@ -109,8 +110,14 @@ func downloadAssets(res http.ResponseWriter, r *http.Request) {
 
 	case "application/pdf":
 		contentType = "application/pdf"
-		content, err = getAssetsPDF(uid)
 		filename = uid.String() + ".pdf"
+		content, err = getAssetsFile(uid, ".pdf")
+
+		if errors.Is(err, fs.ErrNotExist) && r.URL.Query().Has("log-on-error") {
+			contentType = "application/octet-stream"
+			filename = uid.String() + ".log"
+			content, err = getAssetsFile(uid, ".log")
+		}
 
 	default:
 		content, err = buildAssetsZIP(uid)

processing.go

@@ -6,7 +6,6 @@ import (
 	"io"
 	"math"
 	"net/http"
-	"net/url"
 	"os"
 	"os/exec"
 	"path"
@@ -133,6 +132,7 @@ func startNewJob(res http.ResponseWriter, r *http.Request) {
 	go jobProcessor(jobUUID)
 
 	u := urlMust(router.Get("waitForJob").URL("uid", jobUUID.String()))
+	u.RawQuery = r.URL.Query().Encode()
 	http.Redirect(res, r, u.String(), http.StatusFound)
 }
 
@@ -163,19 +163,30 @@ func waitForJob(res http.ResponseWriter, r *http.Request) {
 		fallthrough
 
 	case statusStarted:
-		u := urlMust(router.Get("waitForJob").URL("uid", uid.String()))
-		u.RawQuery = url.Values{"loop": []string{strconv.Itoa(loop)}}.Encode()
-
 		<-time.After(time.Duration(math.Pow(sleepBase, float64(loop))) * time.Second)
 
+		params := r.URL.Query()
+		params.Set("loop", strconv.Itoa(loop))
+
+		u := urlMust(router.Get("waitForJob").URL("uid", uid.String()))
+		u.RawQuery = params.Encode()
+
 		http.Redirect(res, r, u.String(), http.StatusFound)
 		return
 
 	case statusError:
+		if r.URL.Query().Has("log-on-error") {
+			u := urlMust(router.Get("downloadAssets").URL("uid", uid.String()))
+			u.RawQuery = r.URL.Query().Encode()
+			http.Redirect(res, r, u.String(), http.StatusFound)
+			return
+		}
+
 		http.Error(res, "Processing ran into an error.", http.StatusInternalServerError)
 
 	case statusFinished:
 		u := urlMust(router.Get("downloadAssets").URL("uid", uid.String()))
+		u.RawQuery = r.URL.Query().Encode()
 		http.Redirect(res, r, u.String(), http.StatusFound)
 	}
 }