@@ -5,6 +5,9 @@ import (

 	"strings"

 	"github.com/Sirupsen/logrus"

+	"github.com/docker/engine-api/types"

+	"github.com/docker/engine-api/types/versions"

+	"github.com/gorilla/mux"

 )

 // httpStatusError is an interface

@@ -70,13 +73,19 @@ func GetHTTPErrorStatusCode(err error) int {

 	return statusCode

 }

-// WriteError decodes a specific docker error and sends it in the response.

-func WriteError(w http.ResponseWriter, err error) {

-	if err == nil || w == nil {

-		logrus.WithFields(logrus.Fields{"error": err, "writer": w}).Error("unexpected HTTP error handling")

-		return

+// MakeErrorHandler makes an HTTP handler that decodes a Docker error and

+// returns it in the response.

+func MakeErrorHandler(err error) http.HandlerFunc {

+	return func(w http.ResponseWriter, r *http.Request) {

+		statusCode := GetHTTPErrorStatusCode(err)

+		vars := mux.Vars(r)

+		if vars["version"] == "" || versions.GreaterThan(vars["version"], "1.23") {

+			response := &types.ErrorResponse{

+				Message: err.Error(),

+			}

+			WriteJSON(w, statusCode, response)

+		} else {

+			http.Error(w, err.Error(), statusCode)

+		}

 	}

-

-	statusCode := GetHTTPErrorStatusCode(err)

-	http.Error(w, err.Error(), statusCode)

 }

@@ -2,6 +2,7 @@ package server

 import (

 	"crypto/tls"

+	"fmt"

 	"net"

 	"net/http"

 	"strings"

@@ -10,6 +11,7 @@ import (

 	"github.com/docker/docker/api/server/httputils"

 	"github.com/docker/docker/api/server/middleware"

 	"github.com/docker/docker/api/server/router"

+	"github.com/docker/docker/errors"

 	"github.com/gorilla/mux"

 	"golang.org/x/net/context"

 )

@@ -136,7 +138,7 @@ func (s *Server) makeHTTPHandler(handler httputils.APIFunc) http.HandlerFunc {

 		if err := handlerFunc(ctx, w, r, vars); err != nil {

 			logrus.Errorf("Handler for %s %s returned error: %v", r.Method, r.URL.Path, err)

-			httputils.WriteError(w, err)

+			httputils.MakeErrorHandler(err)(w, r)

 		}

 	}

 }

@@ -172,6 +174,11 @@ func (s *Server) createMux() *mux.Router {

 		}

 	}

+	err := errors.NewRequestNotFoundError(fmt.Errorf("page not found"))

+	notFoundHandler := httputils.MakeErrorHandler(err)

+	m.HandleFunc(versionMatcher+"/{path:.*}", notFoundHandler)

+	m.NotFoundHandler = notFoundHandler

+

 	return m

 }

@@ -131,6 +131,7 @@ This section lists each version from latest to oldest.  Each listing includes a

 * `POST /images/(name)/tag` no longer has a `force` query parameter.

 * `GET /images/search` now supports maximum returned search results `limit`.

 * `POST /containers/{name:.*}/copy` is now removed and errors out starting from this API version.

+* API errors are now returned as JSON instead of plain text.

 ### v1.23 API changes

@@ -262,4 +263,3 @@ end point now returns the new boolean fields `CpuCfsPeriod`, `CpuCfsQuota`, and

 * `CgroupParent` can be passed in the host config to setup container cgroups under a specific cgroup.

 * `POST /build` closing the HTTP request cancels the build

 * `POST /containers/(id)/exec` includes `Warnings` field to response.

-

@@ -22,9 +22,19 @@ weight=-5

  - When the client API version is newer than the daemon's, these calls return an HTTP

    `400 Bad Request` error message.

-# 2. Endpoints

+# 2. Errors

-## 2.1 Containers

+The Remote API uses standard HTTP status codes to indicate the success or failure of the API call. The body of the response will be JSON in the following format:

+

+    {

+        "message": "page not found"

+    }

+

+The status codes that are returned for each endpoint are specified in the endpoint documentation below.

+

+# 3. Endpoints

+

+## 3.1 Containers

 ### List containers

@@ -1504,7 +1514,7 @@ Status Codes:

     - no such file or directory (**path** resource does not exist)

 - **500** – server error

-## 2.2 Images

+## 3.2 Images

 ### List Images

@@ -2112,7 +2122,7 @@ Status Codes:

 -   **200** – no error

 -   **500** – server error

-## 2.3 Misc

+## 3.3 Misc

 ### Check auth configuration

@@ -2834,7 +2844,7 @@ Status Codes:

 -   **404** – no such exec instance

 -   **500** - server error

-## 2.4 Volumes

+## 3.4 Volumes

 ### List volumes

@@ -2972,7 +2982,7 @@ Status Codes

 -   **409** - volume is in use and cannot be removed

 -   **500** - server error

-## 2.5 Networks

+## 3.5 Networks

 ### List networks

@@ -3296,9 +3306,9 @@ Status Codes

 -   **404** - no such network

 -   **500** - server error

-# 3. Going further

+# 4. Going further

-## 3.1 Inside `docker run`

+## 4.1 Inside `docker run`

 As an example, the `docker run` command line makes the following API calls:

@@ -3316,7 +3326,7 @@ As an example, the `docker run` command line makes the following API calls:

 - If in detached mode or only `stdin` is attached, display the container's id.

-## 3.2 Hijacking

+## 4.2 Hijacking

 In this version of the API, `/attach`, uses hijacking to transport `stdin`,

 `stdout`, and `stderr` on the same socket.

@@ -3331,7 +3341,7 @@ When Docker daemon detects the `Upgrade` header, it switches its status code

 from **200 OK** to **101 UPGRADED** and resends the same headers.

-## 3.3 CORS Requests

+## 4.3 CORS Requests

 To set cross origin requests to the remote api please give values to

 `--api-cors-header` when running Docker in daemon mode. Set * (asterisk) allows all,

@@ -85,8 +85,8 @@ func (s *DockerSuite) TestGetContainersWsAttachContainerNotFound(c *check.C) {

 	status, body, err := sockRequest("GET", "/containers/doesnotexist/attach/ws", nil)

 	c.Assert(status, checker.Equals, http.StatusNotFound)

 	c.Assert(err, checker.IsNil)

-	expected := "No such container: doesnotexist\n"

-	c.Assert(string(body), checker.Contains, expected)

+	expected := "No such container: doesnotexist"

+	c.Assert(getErrorMessage(c, body), checker.Contains, expected)

 }

 func (s *DockerSuite) TestPostContainersAttach(c *check.C) {

@@ -16,9 +16,10 @@ func (s *DockerSuite) TestAuthApi(c *check.C) {

 		Password: "no-password",

 	}

-	expected := "Get https://registry-1.docker.io/v2/: unauthorized: incorrect username or password\n"

+	expected := "Get https://registry-1.docker.io/v2/: unauthorized: incorrect username or password"

 	status, body, err := sockRequest("POST", "/auth", config)

 	c.Assert(err, check.IsNil)

 	c.Assert(status, check.Equals, http.StatusUnauthorized)

-	c.Assert(string(body), checker.Contains, expected, check.Commentf("Expected: %v, got: %v", expected, string(body)))

+	msg := getErrorMessage(c, body)

+	c.Assert(msg, checker.Contains, expected, check.Commentf("Expected: %v, got: %v", expected, msg))

 }

@@ -480,10 +480,10 @@ func (s *DockerSuite) TestContainerApiBadPort(c *check.C) {

 	jsonData := bytes.NewBuffer(nil)

 	json.NewEncoder(jsonData).Encode(config)

-	status, b, err := sockRequest("POST", "/containers/create", config)

+	status, body, err := sockRequest("POST", "/containers/create", config)

 	c.Assert(err, checker.IsNil)

 	c.Assert(status, checker.Equals, http.StatusInternalServerError)

-	c.Assert(strings.TrimSpace(string(b)), checker.Equals, `Invalid port specification: "aa80"`, check.Commentf("Incorrect error msg: %s", string(b)))

+	c.Assert(getErrorMessage(c, body), checker.Equals, `Invalid port specification: "aa80"`, check.Commentf("Incorrect error msg: %s", body))

 }

 func (s *DockerSuite) TestContainerApiCreate(c *check.C) {

@@ -509,12 +509,12 @@ func (s *DockerSuite) TestContainerApiCreate(c *check.C) {

 func (s *DockerSuite) TestContainerApiCreateEmptyConfig(c *check.C) {

 	config := map[string]interface{}{}

-	status, b, err := sockRequest("POST", "/containers/create", config)

+	status, body, err := sockRequest("POST", "/containers/create", config)

 	c.Assert(err, checker.IsNil)

 	c.Assert(status, checker.Equals, http.StatusInternalServerError)

-	expected := "Config cannot be empty in order to create a container\n"

-	c.Assert(string(b), checker.Equals, expected)

+	expected := "Config cannot be empty in order to create a container"

+	c.Assert(getErrorMessage(c, body), checker.Equals, expected)

 }

 func (s *DockerSuite) TestContainerApiCreateMultipleNetworksConfig(c *check.C) {

@@ -530,14 +530,15 @@ func (s *DockerSuite) TestContainerApiCreateMultipleNetworksConfig(c *check.C) {

 		},

 	}

-	status, b, err := sockRequest("POST", "/containers/create", config)

+	status, body, err := sockRequest("POST", "/containers/create", config)

 	c.Assert(err, checker.IsNil)

 	c.Assert(status, checker.Equals, http.StatusBadRequest)

+	msg := getErrorMessage(c, body)

 	// network name order in error message is not deterministic

-	c.Assert(string(b), checker.Contains, "Container cannot be connected to network endpoints")

-	c.Assert(string(b), checker.Contains, "net1")

-	c.Assert(string(b), checker.Contains, "net2")

-	c.Assert(string(b), checker.Contains, "net3")

+	c.Assert(msg, checker.Contains, "Container cannot be connected to network endpoints")

+	c.Assert(msg, checker.Contains, "net1")

+	c.Assert(msg, checker.Contains, "net2")

+	c.Assert(msg, checker.Contains, "net3")

 }

 func (s *DockerSuite) TestContainerApiCreateWithHostName(c *check.C) {

@@ -997,7 +998,7 @@ func (s *DockerSuite) TestContainerApiDeleteNotExist(c *check.C) {

 	status, body, err := sockRequest("DELETE", "/containers/doesnotexist", nil)

 	c.Assert(err, checker.IsNil)

 	c.Assert(status, checker.Equals, http.StatusNotFound)

-	c.Assert(string(body), checker.Matches, "No such container: doesnotexist\n")

+	c.Assert(getErrorMessage(c, body), checker.Matches, "No such container: doesnotexist")

 }

 func (s *DockerSuite) TestContainerApiDeleteForce(c *check.C) {

@@ -1247,8 +1248,8 @@ func (s *DockerSuite) TestPostContainersCreateWithWrongCpusetValues(c *check.C)

 	status, body, err := sockRequest("POST", "/containers/create?name="+name, c1)

 	c.Assert(err, checker.IsNil)

 	c.Assert(status, checker.Equals, http.StatusInternalServerError)

-	expected := "Invalid value 1-42,, for cpuset cpus\n"

-	c.Assert(string(body), checker.Equals, expected)

+	expected := "Invalid value 1-42,, for cpuset cpus"

+	c.Assert(getErrorMessage(c, body), checker.Equals, expected)

 	c2 := struct {

 		Image      string

@@ -1258,8 +1259,8 @@ func (s *DockerSuite) TestPostContainersCreateWithWrongCpusetValues(c *check.C)

 	status, body, err = sockRequest("POST", "/containers/create?name="+name, c2)

 	c.Assert(err, checker.IsNil)

 	c.Assert(status, checker.Equals, http.StatusInternalServerError)

-	expected = "Invalid value 42-3,1-- for cpuset mems\n"

-	c.Assert(string(body), checker.Equals, expected)

+	expected = "Invalid value 42-3,1-- for cpuset mems"

+	c.Assert(getErrorMessage(c, body), checker.Equals, expected)

 }

 func (s *DockerSuite) TestPostContainersCreateShmSizeNegative(c *check.C) {

@@ -1273,7 +1274,7 @@ func (s *DockerSuite) TestPostContainersCreateShmSizeNegative(c *check.C) {

 	status, body, err := sockRequest("POST", "/containers/create", config)

 	c.Assert(err, check.IsNil)

 	c.Assert(status, check.Equals, http.StatusInternalServerError)

-	c.Assert(string(body), checker.Contains, "SHM size must be greater than 0")

+	c.Assert(getErrorMessage(c, body), checker.Contains, "SHM size must be greater than 0")

 }

 func (s *DockerSuite) TestPostContainersCreateShmSizeHostConfigOmitted(c *check.C) {

@@ -1409,9 +1410,11 @@ func (s *DockerSuite) TestPostContainersCreateWithOomScoreAdjInvalidRange(c *che

 	status, b, err := sockRequest("POST", "/containers/create?name="+name, config)

 	c.Assert(err, check.IsNil)

 	c.Assert(status, check.Equals, http.StatusInternalServerError)

+

 	expected := "Invalid value 1001, range for oom score adj is [-1000, 1000]"

-	if !strings.Contains(string(b), expected) {

-		c.Fatalf("Expected output to contain %q, got %q", expected, string(b))

+	msg := getErrorMessage(c, b)

+	if !strings.Contains(msg, expected) {

+		c.Fatalf("Expected output to contain %q, got %q", expected, msg)

 	}

 	config = struct {

@@ -1423,8 +1426,9 @@ func (s *DockerSuite) TestPostContainersCreateWithOomScoreAdjInvalidRange(c *che

 	c.Assert(err, check.IsNil)

 	c.Assert(status, check.Equals, http.StatusInternalServerError)

 	expected = "Invalid value -1001, range for oom score adj is [-1000, 1000]"

-	if !strings.Contains(string(b), expected) {

-		c.Fatalf("Expected output to contain %q, got %q", expected, string(b))

+	msg = getErrorMessage(c, b)

+	if !strings.Contains(msg, expected) {

+		c.Fatalf("Expected output to contain %q, got %q", expected, msg)

 	}

 }

@@ -2,7 +2,6 @@ package main

 import (

 	"net/http"

-	"strings"

 	"github.com/docker/docker/pkg/integration/checker"

 	"github.com/go-check/check"

@@ -15,31 +14,31 @@ func (s *DockerSuite) TestApiCreateWithNotExistImage(c *check.C) {

 		"Volumes": map[string]struct{}{"/tmp": {}},

 	}

-	status, resp, err := sockRequest("POST", "/containers/create?name="+name, config)

+	status, body, err := sockRequest("POST", "/containers/create?name="+name, config)

 	c.Assert(err, check.IsNil)

 	c.Assert(status, check.Equals, http.StatusNotFound)

 	expected := "No such image: test456:v1"

-	c.Assert(strings.TrimSpace(string(resp)), checker.Contains, expected)

+	c.Assert(getErrorMessage(c, body), checker.Contains, expected)

 	config2 := map[string]interface{}{

 		"Image":   "test456",

 		"Volumes": map[string]struct{}{"/tmp": {}},

 	}

-	status, resp, err = sockRequest("POST", "/containers/create?name="+name, config2)

+	status, body, err = sockRequest("POST", "/containers/create?name="+name, config2)

 	c.Assert(err, check.IsNil)

 	c.Assert(status, check.Equals, http.StatusNotFound)

 	expected = "No such image: test456:latest"

-	c.Assert(strings.TrimSpace(string(resp)), checker.Equals, expected)

+	c.Assert(getErrorMessage(c, body), checker.Equals, expected)

 	config3 := map[string]interface{}{

 		"Image": "sha256:0cb40641836c461bc97c793971d84d758371ed682042457523e4ae701efeaaaa",

 	}

-	status, resp, err = sockRequest("POST", "/containers/create?name="+name, config3)

+	status, body, err = sockRequest("POST", "/containers/create?name="+name, config3)

 	c.Assert(err, check.IsNil)

 	c.Assert(status, check.Equals, http.StatusNotFound)

 	expected = "No such image: sha256:0cb40641836c461bc97c793971d84d758371ed682042457523e4ae701efeaaaa"

-	c.Assert(strings.TrimSpace(string(resp)), checker.Equals, expected)

+	c.Assert(getErrorMessage(c, body), checker.Equals, expected)

 }

@@ -24,7 +24,7 @@ func (s *DockerSuite) TestExecApiCreateNoCmd(c *check.C) {

 	c.Assert(status, checker.Equals, http.StatusInternalServerError)

 	comment := check.Commentf("Expected message when creating exec command with no Cmd specified")

-	c.Assert(string(body), checker.Contains, "No exec command specified", comment)

+	c.Assert(getErrorMessage(c, body), checker.Contains, "No exec command specified", comment)

 }

 func (s *DockerSuite) TestExecApiCreateNoValidContentType(c *check.C) {

@@ -44,7 +44,7 @@ func (s *DockerSuite) TestExecApiCreateNoValidContentType(c *check.C) {

 	c.Assert(err, checker.IsNil)

 	comment := check.Commentf("Expected message when creating exec command with invalid Content-Type specified")

-	c.Assert(string(b), checker.Contains, "Content-Type specified", comment)

+	c.Assert(getErrorMessage(c, b), checker.Contains, "Content-Type specified", comment)

 }

 func (s *DockerSuite) TestExecApiCreateContainerPaused(c *check.C) {

@@ -59,7 +59,7 @@ func (s *DockerSuite) TestExecApiCreateContainerPaused(c *check.C) {

 	c.Assert(status, checker.Equals, http.StatusConflict)

 	comment := check.Commentf("Expected message when creating exec command with Container %s is paused", name)

-	c.Assert(string(body), checker.Contains, "Container "+name+" is paused, unpause the container before exec", comment)

+	c.Assert(getErrorMessage(c, body), checker.Contains, "Container "+name+" is paused, unpause the container before exec", comment)

 }

 func (s *DockerSuite) TestExecApiStart(c *check.C) {

@@ -60,9 +60,7 @@ func (s *DockerSuite) TestLogsApiNoStdoutNorStderr(c *check.C) {

 	c.Assert(err, checker.IsNil)

 	expected := "Bad parameters: you must choose at least one stream"

-	if !bytes.Contains(body, []byte(expected)) {

-		c.Fatalf("Expected %s, got %s", expected, string(body[:]))

-	}

+	c.Assert(getErrorMessage(c, body), checker.Contains, expected)

 }

 // Regression test for #12704

@@ -40,5 +40,5 @@ func (s *DockerSuite) TestResizeApiResponseWhenContainerNotStarted(c *check.C) {

 	c.Assert(status, check.Equals, http.StatusInternalServerError)

 	c.Assert(err, check.IsNil)

-	c.Assert(string(body), checker.Contains, "is not running", check.Commentf("resize should fail with message 'Container is not running'"))

+	c.Assert(getErrorMessage(c, body), checker.Contains, "is not running", check.Commentf("resize should fail with message 'Container is not running'"))

 }

@@ -60,7 +60,7 @@ func (s *DockerSuite) TestApiClientVersionNewerThanServer(c *check.C) {

 	c.Assert(err, checker.IsNil)

 	c.Assert(status, checker.Equals, http.StatusBadRequest)

 	expected := fmt.Sprintf("client is newer than server (client API version: %s, server API version: %s)", version, api.DefaultVersion)

-	c.Assert(strings.TrimSpace(string(body)), checker.Equals, expected)

+	c.Assert(getErrorMessage(c, body), checker.Equals, expected)

 }

 func (s *DockerSuite) TestApiClientVersionOldNotSupported(c *check.C) {

@@ -99,3 +99,44 @@ func (s *DockerSuite) TestApiDockerApiVersion(c *check.C) {

 		c.Fatalf("Out didn't have 'xxx' for the API version, had:\n%s", out)

 	}

 }

+

+func (s *DockerSuite) TestApiErrorJSON(c *check.C) {

+	httpResp, body, err := sockRequestRaw("POST", "/containers/create", strings.NewReader(`{}`), "application/json")

+	c.Assert(err, checker.IsNil)

+	c.Assert(httpResp.StatusCode, checker.Equals, http.StatusInternalServerError)

+	c.Assert(httpResp.Header.Get("Content-Type"), checker.Equals, "application/json")

+	b, err := readBody(body)

+	c.Assert(err, checker.IsNil)

+	c.Assert(getErrorMessage(c, b), checker.Equals, "Config cannot be empty in order to create a container")

+}

+

+func (s *DockerSuite) TestApiErrorPlainText(c *check.C) {

+	httpResp, body, err := sockRequestRaw("POST", "/v1.23/containers/create", strings.NewReader(`{}`), "application/json")

+	c.Assert(err, checker.IsNil)

+	c.Assert(httpResp.StatusCode, checker.Equals, http.StatusInternalServerError)

+	c.Assert(httpResp.Header.Get("Content-Type"), checker.Contains, "text/plain")

+	b, err := readBody(body)

+	c.Assert(err, checker.IsNil)

+	c.Assert(strings.TrimSpace(string(b)), checker.Equals, "Config cannot be empty in order to create a container")

+}

+

+func (s *DockerSuite) TestApiErrorNotFoundJSON(c *check.C) {

+	// 404 is a different code path to normal errors, so test separately

+	httpResp, body, err := sockRequestRaw("GET", "/notfound", nil, "application/json")

+	c.Assert(err, checker.IsNil)

+	c.Assert(httpResp.StatusCode, checker.Equals, http.StatusNotFound)

+	c.Assert(httpResp.Header.Get("Content-Type"), checker.Equals, "application/json")

+	b, err := readBody(body)

+	c.Assert(err, checker.IsNil)

+	c.Assert(getErrorMessage(c, b), checker.Equals, "page not found")

+}

+

+func (s *DockerSuite) TestApiErrorNotFoundPlainText(c *check.C) {

+	httpResp, body, err := sockRequestRaw("GET", "/v1.23/notfound", nil, "application/json")

+	c.Assert(err, checker.IsNil)

+	c.Assert(httpResp.StatusCode, checker.Equals, http.StatusNotFound)

+	c.Assert(httpResp.Header.Get("Content-Type"), checker.Contains, "text/plain")

+	b, err := readBody(body)

+	c.Assert(err, checker.IsNil)

+	c.Assert(strings.TrimSpace(string(b)), checker.Equals, "page not found")

+}

@@ -1507,3 +1507,10 @@ func waitForGoroutines(expected int) error {

 		}

 	}

 }

+

+// getErrorMessage returns the error message from an error API response

+func getErrorMessage(c *check.C, body []byte) string {

+	var resp types.ErrorResponse

+	c.Assert(json.Unmarshal(body, &resp), check.IsNil)

+	return strings.TrimSpace(resp.Message)

+}