fix: various PR feedback

context.go

@@ -85,7 +85,7 @@ func (c *hcontext) WriteHeader(status int) {
 			}
 
 			if !found {
-				panic(fmt.Errorf("Header %s is not declared for %s %s (allowed: %s)", name, c.r.Method, c.r.URL.Path, allowed))
+				panic(fmt.Errorf("Response header %s is not declared for %s %s with status code %d (allowed: %s)", name, c.r.Method, c.r.URL.Path, status, allowed))
 			}
 		}
 	}
@@ -102,6 +102,10 @@ func (c *hcontext) Write(data []byte) (int, error) {
 }
 
 func (c *hcontext) WriteError(status int, message string, errors ...error) {
+	if c.closed {
+		panic(fmt.Errorf("Trying to write to response after WriteModel or WriteError for %s %s", c.r.Method, c.r.URL.Path))
+	}
+
 	details := []*ErrorDetail{}
 
 	c.errors = append(c.errors, errors...)
@@ -135,6 +139,10 @@ func (c *hcontext) WriteError(status int, message string, errors ...error) {
 }
 
 func (c *hcontext) WriteModel(status int, model interface{}) {
+	if c.closed {
+		panic(fmt.Errorf("Trying to write to response after WriteModel or WriteError for %s %s", c.r.Method, c.r.URL.Path))
+	}
+
 	// Get the negotiated content type the client wants and we are willing to
 	// provide.
 	ct := selectContentType(c.r)

error.go

@@ -9,9 +9,9 @@ type ErrorDetailer interface {
 
 // ErrorDetail provides details about a specific error.
 type ErrorDetail struct {
-	Message  string      `json:"message,omitempty"`
-	Location string      `json:"location,omitempty"`
-	Value    interface{} `json:"value,omitempty"`
+	Message  string      `json:"message,omitempty" doc:"Error message text"`
+	Location string      `json:"location,omitempty" doc:"Where the error occured, e.g. 'body.items[3].tags' or 'path.thing-id'"`
+	Value    interface{} `json:"value,omitempty" doc:"The value at the given location"`
 }
 
 // Error returns the error message / satisfies the `error` interface.

middleware/logger.go

@@ -8,6 +8,7 @@ import (
 
 	"github.com/go-chi/chi"
 	"github.com/mattn/go-isatty"
+	"github.com/opentracing/opentracing-go"
 	"github.com/spf13/viper"
 	"go.uber.org/zap"
 	"go.uber.org/zap/zapcore"
@@ -22,6 +23,11 @@ var logConfig zap.Config
 // middleware. This can be changed dynamically at runtime.
 var LogLevel *zap.AtomicLevel
 
+// LogTracePrefix is used to prefix OpenTracing trace and span ID key names in
+// emitted log message tag names. Use this to integrate with DataDog and other
+// tracing service providers.
+var LogTracePrefix = "dd."
+
 // NewDefaultLogger returns a new low-level `*zap.Logger` instance. If the
 // current terminal is a TTY, it will try ot use colored output automatically.
 func NewDefaultLogger() (*zap.Logger, error) {
@@ -86,6 +92,17 @@ func Logger(next http.Handler) http.Handler {
 			zap.String("http.url", r.URL.String()),
 			zap.String("network.client.ip", r.RemoteAddr),
 		)
+
+		if span := opentracing.SpanFromContext(r.Context()); span != nil {
+			// We have a span context, so log its info to help with correlation.
+			if sc, ok := span.Context().(spanContext); ok {
+				contextLog = contextLog.With(
+					zap.Uint64(LogTracePrefix+"trace_id", sc.TraceID()),
+					zap.Uint64(LogTracePrefix+"span_id", sc.SpanID()),
+				)
+			}
+		}
+
 		r = r.WithContext(context.WithValue(r.Context(), logContextKey, contextLog.Sugar()))
 		nw := &statusRecorder{ResponseWriter: w}
 

middleware/minimal.go

@@ -22,7 +22,7 @@ func (w *minimalWriter) Write(data []byte) (int, error) {
 }
 
 func (w *minimalWriter) WriteHeader(statusCode int) {
-	if statusCode >= 200 && statusCode < 300 {
+	if statusCode >= 200 && statusCode < 300 && statusCode != 201 {
 		statusCode = http.StatusNoContent
 	}
 

middleware/opentracing.go

@@ -8,6 +8,14 @@ import (
 	"github.com/opentracing/opentracing-go/ext"
 )
 
+type spanContext interface {
+	// SpanID returns the span ID that this context is carrying.
+	SpanID() uint64
+
+	// TraceID returns the trace ID that this context is carrying.
+	TraceID() uint64
+}
+
 // OpenTracing provides a middleware for cross-service tracing support.
 func OpenTracing(next http.Handler) http.Handler {
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {