refactor: better error handling

lambda/go.mod

@@ -4,7 +4,7 @@ go 1.22.5
 
 require (
 	github.com/aws/aws-lambda-go v1.47.0
-	github.com/chialab/print2pdf-go/print2pdf v0.0.0-20240801003124-bff0528902dd
+	github.com/chialab/print2pdf-go/print2pdf v0.1.6
 )
 
 require (
@@ -21,13 +21,13 @@ require (
 	github.com/aws/aws-sdk-go-v2/service/internal/checksum v1.3.17 // indirect
 	github.com/aws/aws-sdk-go-v2/service/internal/presigned-url v1.11.17 // indirect
 	github.com/aws/aws-sdk-go-v2/service/internal/s3shared v1.17.15 // indirect
-	github.com/aws/aws-sdk-go-v2/service/s3 v1.58.2 // indirect
+	github.com/aws/aws-sdk-go-v2/service/s3 v1.58.3 // indirect
 	github.com/aws/aws-sdk-go-v2/service/sso v1.22.4 // indirect
 	github.com/aws/aws-sdk-go-v2/service/ssooidc v1.26.4 // indirect
 	github.com/aws/aws-sdk-go-v2/service/sts v1.30.3 // indirect
 	github.com/aws/smithy-go v1.20.3 // indirect
-	github.com/chromedp/cdproto v0.0.0-20240721024200-dac8efcb39ce // indirect
-	github.com/chromedp/chromedp v0.9.5 // indirect
+	github.com/chromedp/cdproto v0.0.0-20240801214329-3f85d328b335 // indirect
+	github.com/chromedp/chromedp v0.10.0 // indirect
 	github.com/chromedp/sysutil v1.0.0 // indirect
 	github.com/gobwas/httphead v0.1.0 // indirect
 	github.com/gobwas/pool v0.2.1 // indirect

lambda/go.sum

@@ -28,6 +28,8 @@ github.com/aws/aws-sdk-go-v2/service/internal/s3shared v1.17.15 h1:246A4lSTXWJw/
 github.com/aws/aws-sdk-go-v2/service/internal/s3shared v1.17.15/go.mod h1:haVfg3761/WF7YPuJOER2MP0k4UAXyHaLclKXB6usDg=
 github.com/aws/aws-sdk-go-v2/service/s3 v1.58.2 h1:sZXIzO38GZOU+O0C+INqbH7C2yALwfMWpd64tONS/NE=
 github.com/aws/aws-sdk-go-v2/service/s3 v1.58.2/go.mod h1:Lcxzg5rojyVPU/0eFwLtcyTaek/6Mtic5B1gJo7e/zE=
+github.com/aws/aws-sdk-go-v2/service/s3 v1.58.3 h1:hT8ZAZRIfqBqHbzKTII+CIiY8G2oC9OpLedkZ51DWl8=
+github.com/aws/aws-sdk-go-v2/service/s3 v1.58.3/go.mod h1:Lcxzg5rojyVPU/0eFwLtcyTaek/6Mtic5B1gJo7e/zE=
 github.com/aws/aws-sdk-go-v2/service/sso v1.22.4 h1:BXx0ZIxvrJdSgSvKTZ+yRBeSqqgPM89VPlulEcl37tM=
 github.com/aws/aws-sdk-go-v2/service/sso v1.22.4/go.mod h1:ooyCOXjvJEsUw7x+ZDHeISPMhtwI3ZCB7ggFMcFfWLU=
 github.com/aws/aws-sdk-go-v2/service/ssooidc v1.26.4 h1:yiwVzJW2ZxZTurVbYWA7QOrAaCYQR72t0wrSBfoesUE=
@@ -38,11 +40,21 @@ github.com/aws/smithy-go v1.20.3 h1:ryHwveWzPV5BIof6fyDvor6V3iUL7nTfiTKXHiW05nE=
 github.com/aws/smithy-go v1.20.3/go.mod h1:krry+ya/rV9RDcV/Q16kpu6ypI4K2czasz0NC3qS14E=
 github.com/chialab/print2pdf-go/print2pdf v0.0.0-20240801003124-bff0528902dd h1:86yHQJAgswmXKf/ejWdYPy0h5WG4w0KheDEKW15i1WA=
 github.com/chialab/print2pdf-go/print2pdf v0.0.0-20240801003124-bff0528902dd/go.mod h1:r70w2eB4GpO/Zn3Sw+pzWSo7kJn206wNHA35hcx6V0I=
+github.com/chialab/print2pdf-go/print2pdf v0.1.4 h1:SMsbEABbTCDZo2v3VidbVok1tfbOyLewkE12eepxT8c=
+github.com/chialab/print2pdf-go/print2pdf v0.1.4/go.mod h1:zBUOgJd/WGICjtzth3XGkkpBm2wV2VezmJtw72Hmnv8=
+github.com/chialab/print2pdf-go/print2pdf v0.1.5 h1:p+NdE4z7jBKXvzpwyS0Le5ipDRYX9X9QpLUtK9zEzmc=
+github.com/chialab/print2pdf-go/print2pdf v0.1.5/go.mod h1:zBUOgJd/WGICjtzth3XGkkpBm2wV2VezmJtw72Hmnv8=
+github.com/chialab/print2pdf-go/print2pdf v0.1.6 h1:9VPqq1iLSdYi1w56q6R//r6GMdoGTdRmCbZP2TTr+Tg=
+github.com/chialab/print2pdf-go/print2pdf v0.1.6/go.mod h1:zBUOgJd/WGICjtzth3XGkkpBm2wV2VezmJtw72Hmnv8=
 github.com/chromedp/cdproto v0.0.0-20240202021202-6d0b6a386732/go.mod h1:GKljq0VrfU4D5yc+2qA6OVr8pmO/MBbPEWqWQ/oqGEs=
 github.com/chromedp/cdproto v0.0.0-20240721024200-dac8efcb39ce h1:pvzUsAunw3R7swXkLT6vqv81Awhnds43mbZHAzhn2pQ=
 github.com/chromedp/cdproto v0.0.0-20240721024200-dac8efcb39ce/go.mod h1:GKljq0VrfU4D5yc+2qA6OVr8pmO/MBbPEWqWQ/oqGEs=
+github.com/chromedp/cdproto v0.0.0-20240801214329-3f85d328b335 h1:bATMoZLH2QGct1kzDxfmeBUQI/QhQvB0mBrOTct+YlQ=
+github.com/chromedp/cdproto v0.0.0-20240801214329-3f85d328b335/go.mod h1:GKljq0VrfU4D5yc+2qA6OVr8pmO/MBbPEWqWQ/oqGEs=
 github.com/chromedp/chromedp v0.9.5 h1:viASzruPJOiThk7c5bueOUY91jGLJVximoEMGoH93rg=
 github.com/chromedp/chromedp v0.9.5/go.mod h1:D4I2qONslauw/C7INoCir1BJkSwBYMyZgx8X276z3+Y=
+github.com/chromedp/chromedp v0.10.0 h1:bRclRYVpMm/UVD76+1HcRW9eV3l58rFfy7AdBvKab1E=
+github.com/chromedp/chromedp v0.10.0/go.mod h1:ei/1ncZIqXX1YnAYDkxhD4gzBgavMEUu7JCKvztdomE=
 github.com/chromedp/sysutil v1.0.0 h1:+ZxhTpfpZlmchB58ih/LBHX52ky7w2VhQVKQMucy3Ic=
 github.com/chromedp/sysutil v1.0.0/go.mod h1:kgWmDdq8fTzXYcKIBqIYvRRTnYb9aNS9moAV0xufSww=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=

lambda/main.go

@@ -3,6 +3,7 @@ package main
 import (
 	"context"
 	"encoding/json"
+	"fmt"
 	"os"
 	"slices"
 	"strings"
@@ -12,57 +13,92 @@ import (
 	"github.com/chialab/print2pdf-go/print2pdf"
 )
 
-var BucketName = os.Getenv("BUCKET")
+type ErrorResponse struct {
+	Message string `json:"message"`
+}
+
 var CorsAllowedHosts = os.Getenv("CORS_ALLOWED_HOSTS")
 
+func main() {
+	lambda.Start(handler)
+}
+
 // Handle a request.
 func handler(ctx context.Context, event events.APIGatewayProxyRequest) (events.APIGatewayProxyResponse, error) {
-	responseHeaders := map[string]string{"Content-Type": "application/json"}
+	headers := map[string]string{"Content-Type": "application/json"}
 	origin, ok := event.Headers["Origin"]
 	if !ok {
 		origin = event.Headers["origin"]
 	}
 	if CorsAllowedHosts != "" && origin != "" {
 		if CorsAllowedHosts == "*" {
-			responseHeaders["Access-Control-Allow-Origin"] = "*"
+			headers["Access-Control-Allow-Origin"] = "*"
 		} else {
-			allowedHosts := strings.Split(CorsAllowedHosts, ",")
-			if slices.Contains(allowedHosts, origin) {
-				responseHeaders["Access-Control-Allow-Origin"] = origin
+			hosts := strings.Split(CorsAllowedHosts, ",")
+			if slices.Contains(hosts, origin) {
+				headers["Access-Control-Allow-Origin"] = origin
 			}
 		}
 	}
 
-	var requestData print2pdf.RequestData
-	err := json.Unmarshal([]byte(event.Body), &requestData)
+	var data print2pdf.RequestData
+	err := json.Unmarshal([]byte(event.Body), &data)
 	if err != nil {
-		return events.APIGatewayProxyResponse{}, err
+		fmt.Fprintf(os.Stderr, "error decoding JSON: %s\noriginal request body: %s\n", err, event.Body)
+
+		return JsonError("internal server error", 500), nil
 	}
 
 	var buf []byte
-	err = print2pdf.GetPDFBuffer(ctx, requestData, &buf)
-	if err != nil {
-		return events.APIGatewayProxyResponse{}, err
+	err = print2pdf.GetPDFBuffer(ctx, data, &buf)
+	if ve, ok := err.(print2pdf.ValidationError); ok {
+		fmt.Fprintf(os.Stderr, "request validation error: %s\n", ve)
+
+		return JsonError(ve.Error(), 400), nil
+	} else if err != nil {
+		fmt.Fprintf(os.Stderr, "error getting PDF buffer: %s\n", err)
+
+		return JsonError("internal server error", 500), nil
 	}
 
-	url, err := print2pdf.UploadFile(ctx, BucketName, requestData.FileName, &buf)
+	url, err := print2pdf.UploadFile(ctx, data.FileName, &buf)
 	if err != nil {
-		return events.APIGatewayProxyResponse{}, err
+		fmt.Fprintf(os.Stderr, "error uploading file: %s\n", err)
+
+		return JsonError("internal server error", 500), nil
 	}
 
-	responseData := print2pdf.ResponseData{Url: url}
-	responseJson, err := json.Marshal(responseData)
+	body, err := json.Marshal(print2pdf.ResponseData{Url: url})
 	if err != nil {
-		return events.APIGatewayProxyResponse{}, err
+		fmt.Fprintf(os.Stderr, "error encoding response to JSON: %s\n", err)
+
+		return JsonError("internal server error", 500), nil
 	}
 
 	return events.APIGatewayProxyResponse{
 		StatusCode: 200,
-		Body:       string(responseJson),
-		Headers:    responseHeaders,
+		Body:       string(body),
+		Headers:    headers,
 	}, nil
 }
 
-func main() {
-	lambda.Start(handler)
+// Prepare an HTTP error response.
+func JsonError(message string, code int) events.APIGatewayProxyResponse {
+	ct := "application/json"
+	body, err := json.Marshal(ErrorResponse{message})
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "error encoding error message to JSON: %s\noriginal error: %s\n", err, message)
+		body = []byte("internal server error")
+		code = 500
+		ct = "text/plain"
+	}
+
+	return events.APIGatewayProxyResponse{
+		StatusCode: code,
+		Body:       string(body),
+		Headers: map[string]string{
+			"Content-Type":           ct,
+			"X-Content-Type-Options": "nosniff",
+		},
+	}
 }

plain/go.mod

@@ -2,7 +2,7 @@ module github.com/chialab/print2pdf-go/plain
 
 go 1.22.5
 
-require github.com/chialab/print2pdf-go/print2pdf v0.0.0-20240801004620-b2cc33f39506
+require github.com/chialab/print2pdf-go/print2pdf v0.1.6
 
 require (
 	github.com/aws/aws-sdk-go-v2 v1.30.3 // indirect
@@ -18,13 +18,13 @@ require (
 	github.com/aws/aws-sdk-go-v2/service/internal/checksum v1.3.17 // indirect
 	github.com/aws/aws-sdk-go-v2/service/internal/presigned-url v1.11.17 // indirect
 	github.com/aws/aws-sdk-go-v2/service/internal/s3shared v1.17.15 // indirect
-	github.com/aws/aws-sdk-go-v2/service/s3 v1.58.2 // indirect
+	github.com/aws/aws-sdk-go-v2/service/s3 v1.58.3 // indirect
 	github.com/aws/aws-sdk-go-v2/service/sso v1.22.4 // indirect
 	github.com/aws/aws-sdk-go-v2/service/ssooidc v1.26.4 // indirect
 	github.com/aws/aws-sdk-go-v2/service/sts v1.30.3 // indirect
 	github.com/aws/smithy-go v1.20.3 // indirect
-	github.com/chromedp/cdproto v0.0.0-20240721024200-dac8efcb39ce // indirect
-	github.com/chromedp/chromedp v0.9.5 // indirect
+	github.com/chromedp/cdproto v0.0.0-20240801214329-3f85d328b335 // indirect
+	github.com/chromedp/chromedp v0.10.0 // indirect
 	github.com/chromedp/sysutil v1.0.0 // indirect
 	github.com/gobwas/httphead v0.1.0 // indirect
 	github.com/gobwas/pool v0.2.1 // indirect

plain/go.sum

@@ -26,6 +26,8 @@ github.com/aws/aws-sdk-go-v2/service/internal/s3shared v1.17.15 h1:246A4lSTXWJw/
 github.com/aws/aws-sdk-go-v2/service/internal/s3shared v1.17.15/go.mod h1:haVfg3761/WF7YPuJOER2MP0k4UAXyHaLclKXB6usDg=
 github.com/aws/aws-sdk-go-v2/service/s3 v1.58.2 h1:sZXIzO38GZOU+O0C+INqbH7C2yALwfMWpd64tONS/NE=
 github.com/aws/aws-sdk-go-v2/service/s3 v1.58.2/go.mod h1:Lcxzg5rojyVPU/0eFwLtcyTaek/6Mtic5B1gJo7e/zE=
+github.com/aws/aws-sdk-go-v2/service/s3 v1.58.3 h1:hT8ZAZRIfqBqHbzKTII+CIiY8G2oC9OpLedkZ51DWl8=
+github.com/aws/aws-sdk-go-v2/service/s3 v1.58.3/go.mod h1:Lcxzg5rojyVPU/0eFwLtcyTaek/6Mtic5B1gJo7e/zE=
 github.com/aws/aws-sdk-go-v2/service/sso v1.22.4 h1:BXx0ZIxvrJdSgSvKTZ+yRBeSqqgPM89VPlulEcl37tM=
 github.com/aws/aws-sdk-go-v2/service/sso v1.22.4/go.mod h1:ooyCOXjvJEsUw7x+ZDHeISPMhtwI3ZCB7ggFMcFfWLU=
 github.com/aws/aws-sdk-go-v2/service/ssooidc v1.26.4 h1:yiwVzJW2ZxZTurVbYWA7QOrAaCYQR72t0wrSBfoesUE=
@@ -36,11 +38,21 @@ github.com/aws/smithy-go v1.20.3 h1:ryHwveWzPV5BIof6fyDvor6V3iUL7nTfiTKXHiW05nE=
 github.com/aws/smithy-go v1.20.3/go.mod h1:krry+ya/rV9RDcV/Q16kpu6ypI4K2czasz0NC3qS14E=
 github.com/chialab/print2pdf-go/print2pdf v0.0.0-20240801004620-b2cc33f39506 h1:HPYUc6DVZX7Ja736075Fqs4LZU/EdcRCAu7hevsFPF0=
 github.com/chialab/print2pdf-go/print2pdf v0.0.0-20240801004620-b2cc33f39506/go.mod h1:r70w2eB4GpO/Zn3Sw+pzWSo7kJn206wNHA35hcx6V0I=
+github.com/chialab/print2pdf-go/print2pdf v0.1.4 h1:SMsbEABbTCDZo2v3VidbVok1tfbOyLewkE12eepxT8c=
+github.com/chialab/print2pdf-go/print2pdf v0.1.4/go.mod h1:zBUOgJd/WGICjtzth3XGkkpBm2wV2VezmJtw72Hmnv8=
+github.com/chialab/print2pdf-go/print2pdf v0.1.5 h1:p+NdE4z7jBKXvzpwyS0Le5ipDRYX9X9QpLUtK9zEzmc=
+github.com/chialab/print2pdf-go/print2pdf v0.1.5/go.mod h1:zBUOgJd/WGICjtzth3XGkkpBm2wV2VezmJtw72Hmnv8=
+github.com/chialab/print2pdf-go/print2pdf v0.1.6 h1:9VPqq1iLSdYi1w56q6R//r6GMdoGTdRmCbZP2TTr+Tg=
+github.com/chialab/print2pdf-go/print2pdf v0.1.6/go.mod h1:zBUOgJd/WGICjtzth3XGkkpBm2wV2VezmJtw72Hmnv8=
 github.com/chromedp/cdproto v0.0.0-20240202021202-6d0b6a386732/go.mod h1:GKljq0VrfU4D5yc+2qA6OVr8pmO/MBbPEWqWQ/oqGEs=
 github.com/chromedp/cdproto v0.0.0-20240721024200-dac8efcb39ce h1:pvzUsAunw3R7swXkLT6vqv81Awhnds43mbZHAzhn2pQ=
 github.com/chromedp/cdproto v0.0.0-20240721024200-dac8efcb39ce/go.mod h1:GKljq0VrfU4D5yc+2qA6OVr8pmO/MBbPEWqWQ/oqGEs=
+github.com/chromedp/cdproto v0.0.0-20240801214329-3f85d328b335 h1:bATMoZLH2QGct1kzDxfmeBUQI/QhQvB0mBrOTct+YlQ=
+github.com/chromedp/cdproto v0.0.0-20240801214329-3f85d328b335/go.mod h1:GKljq0VrfU4D5yc+2qA6OVr8pmO/MBbPEWqWQ/oqGEs=
 github.com/chromedp/chromedp v0.9.5 h1:viASzruPJOiThk7c5bueOUY91jGLJVximoEMGoH93rg=
 github.com/chromedp/chromedp v0.9.5/go.mod h1:D4I2qONslauw/C7INoCir1BJkSwBYMyZgx8X276z3+Y=
+github.com/chromedp/chromedp v0.10.0 h1:bRclRYVpMm/UVD76+1HcRW9eV3l58rFfy7AdBvKab1E=
+github.com/chromedp/chromedp v0.10.0/go.mod h1:ei/1ncZIqXX1YnAYDkxhD4gzBgavMEUu7JCKvztdomE=
 github.com/chromedp/sysutil v1.0.0 h1:+ZxhTpfpZlmchB58ih/LBHX52ky7w2VhQVKQMucy3Ic=
 github.com/chromedp/sysutil v1.0.0/go.mod h1:kgWmDdq8fTzXYcKIBqIYvRRTnYb9aNS9moAV0xufSww=
 github.com/gobwas/httphead v0.1.0 h1:exrUm0f4YX0L7EBwZHuCF4GDp8aJfVeBrlLQrs6NqWU=

plain/main.go

@@ -4,6 +4,7 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
+	"io"
 	"net/http"
 	"os"
 	"slices"
@@ -12,13 +13,20 @@ import (
 	"github.com/chialab/print2pdf-go/print2pdf"
 )
 
+type ErrorResponse struct {
+	Message string `json:"message"`
+}
+
 var Port = os.Getenv("PORT")
-var BucketName = os.Getenv("BUCKET")
 var CorsAllowedHosts = os.Getenv("CORS_ALLOWED_HOSTS")
 
 func main() {
+	if Port == "" {
+		Port = "3000"
+	}
+
 	http.HandleFunc("/print", printHandler)
-	fmt.Printf("server listening on port %s", Port)
+	fmt.Printf("server listening on port %s\n", Port)
 	err := http.ListenAndServe(":"+Port, nil)
 	if errors.Is(err, http.ErrServerClosed) {
 		fmt.Println("server closed")
@@ -30,16 +38,14 @@ func main() {
 
 // Handle requests to "/print" endpoint.
 func printHandler(w http.ResponseWriter, r *http.Request) {
-	go func() {
-		switch r.Method {
-		case "OPTIONS":
-			handlePrintOptions(w, r)
-		case "POST":
-			handlePrintPost(w, r)
-		default:
-			http.Error(w, "Method not allowed", http.StatusMethodNotAllowed)
-		}
-	}()
+	switch r.Method {
+	case "OPTIONS":
+		handlePrintOptions(w, r)
+	case "POST":
+		handlePrintPost(w, r)
+	default:
+		http.Error(w, "Method not allowed", http.StatusMethodNotAllowed)
+	}
 }
 
 // Handle OPTIONS requests to "/print" endpoint.
@@ -61,6 +67,7 @@ func handlePrintOptions(w http.ResponseWriter, r *http.Request) {
 
 // Handle POST requests to "/print" endpoint.
 func handlePrintPost(w http.ResponseWriter, r *http.Request) {
+	r.Context()
 	w.Header().Set("Content-Type", "application/json")
 
 	if CorsAllowedHosts == "" || CorsAllowedHosts == "*" {
@@ -73,49 +80,77 @@ func handlePrintPost(w http.ResponseWriter, r *http.Request) {
 		}
 	}
 
-	var requestData print2pdf.RequestData
-	err := json.NewDecoder(r.Body).Decode(&requestData)
+	body, err := io.ReadAll(r.Body)
 	if err != nil {
-		JsonError(w, "Error reading request data", http.StatusInternalServerError)
+		fmt.Fprintf(os.Stderr, "error reading request data: %s\n", err)
+		JsonError(w, "internal server error", http.StatusInternalServerError)
+
+		return
+	}
+
+	var data print2pdf.RequestData
+	err = json.Unmarshal(body, &data)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "error decoding JSON: %s\noriginal request body: %s\n", err, string(body))
+		JsonError(w, "internal server error", http.StatusInternalServerError)
 
 		return
 	}
 
 	var buf []byte
-	err = print2pdf.GetPDFBuffer(r.Context(), requestData, &buf)
-	if e, ok := err.(print2pdf.ValidationError); ok {
-		JsonError(w, e.Error(), http.StatusBadRequest)
+	err = print2pdf.GetPDFBuffer(r.Context(), data, &buf)
+	if ve, ok := err.(print2pdf.ValidationError); ok {
+		fmt.Fprintf(os.Stderr, "request validation error: %s\n", ve)
+		JsonError(w, ve.Error(), http.StatusBadRequest)
 
 		return
 	} else if err != nil {
-		fmt.Fprintf(os.Stderr, "error getting PDF buffer: %s", err)
-		JsonError(w, "Internal server error", http.StatusInternalServerError)
+		fmt.Fprintf(os.Stderr, "error getting PDF buffer: %s\n", err)
+		JsonError(w, "internal server error", http.StatusInternalServerError)
 
 		return
 	}
 
-	url, err := print2pdf.UploadFile(r.Context(), BucketName, requestData.FileName, &buf)
+	url, err := print2pdf.UploadFile(r.Context(), data.FileName, &buf)
 	if err != nil {
-		fmt.Fprintf(os.Stderr, "error uploading file: %s", err)
-		JsonError(w, "Internal server error", http.StatusInternalServerError)
+		fmt.Fprintf(os.Stderr, "error uploading file: %s\n", err)
+		JsonError(w, "internal server error", http.StatusInternalServerError)
 
 		return
 	}
 
-	w.WriteHeader(http.StatusOK)
-	json.NewEncoder(w).Encode(print2pdf.ResponseData{Url: url})
-}
+	body, err = json.Marshal(print2pdf.ResponseData{Url: url})
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "error encoding response to JSON: %s\n", err)
+		JsonError(w, "internal server error", http.StatusInternalServerError)
 
-type ErrorResponse struct {
-	Message string `json:"message"`
+		return
+	}
+
+	w.WriteHeader(http.StatusOK)
+	_, err = w.Write(body)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "error writing response: %s\n", err)
+	}
 }
 
 // JsonError replies to the request with the specified error message and HTTP code.
 // It does not otherwise end the request; the caller should ensure no further
 // writes are done to w.
 func JsonError(w http.ResponseWriter, message string, code int) {
 	w.Header().Set("Content-Type", "application/json")
+	body, err := json.Marshal(ErrorResponse{message})
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "error encoding error message to JSON: %s\noriginal error: %s\n", err, message)
+		body = []byte("internal server error")
+		code = http.StatusInternalServerError
+		w.Header().Set("Content-Type", "text/plain")
+	}
+
 	w.Header().Set("X-Content-Type-Options", "nosniff")
 	w.WriteHeader(code)
-	json.NewEncoder(w).Encode(ErrorResponse{message})
+	_, err = w.Write(body)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "error writing error response: %s\noriginal response: %s\n", err, string(body))
+	}
 }