From 93670aa129bcb76b7f859f5a23509e3e921d4391 Mon Sep 17 00:00:00 2001
From: Julius Volz <julius.volz@gmail.com>
Date: Fri, 18 Jan 2013 01:54:26 +0100
Subject: [PATCH] Return API errors in JSON format.

---
 api/query.go         | 7 ++++---
 rules/ast/printer.go | 4 ++--
 2 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/api/query.go b/api/query.go
index 77ceec65e2..b041232474 100644
--- a/api/query.go
+++ b/api/query.go
@@ -2,6 +2,7 @@ package api
 
 import (
 	"code.google.com/p/gorest"
+	"errors"
 	"github.com/matttproud/prometheus/rules"
 	"github.com/matttproud/prometheus/rules/ast"
 	"sort"
@@ -11,7 +12,7 @@ import (
 func (serv MetricsService) Query(Expr string, Json string) (result string) {
 	exprNode, err := rules.LoadExprFromString(Expr)
 	if err != nil {
-		return err.Error()
+		return ast.ErrorToJSON(err)
 	}
 
 	timestamp := time.Now()
@@ -32,10 +33,10 @@ func (serv MetricsService) Query(Expr string, Json string) (result string) {
 func (serv MetricsService) QueryRange(Expr string, End int64, Range int64, Step int64) string {
 	exprNode, err := rules.LoadExprFromString(Expr)
 	if err != nil {
-		return err.Error()
+		return ast.ErrorToJSON(err)
 	}
 	if exprNode.Type() != ast.VECTOR {
-		return "Expression does not evaluate to vector type" // TODO return errors correctly everywhere
+		return ast.ErrorToJSON(errors.New("Expression does not evaluate to vector type"))
 	}
 	rb := serv.ResponseBuilder()
 	rb.SetContentType(gorest.Application_Json)
diff --git a/rules/ast/printer.go b/rules/ast/printer.go
index ce070f4c41..17c17fcec9 100644
--- a/rules/ast/printer.go
+++ b/rules/ast/printer.go
@@ -129,7 +129,7 @@ func (matrix Matrix) ToString() string {
 	return strings.Join(metricStrings, "\n")
 }
 
-func errorToJSON(err error) string {
+func ErrorToJSON(err error) string {
 	errorStruct := struct {
 		Type  string
 		Error string
@@ -155,7 +155,7 @@ func TypedValueToJSON(data interface{}, typeStr string) string {
 	}
 	dataJSON, err := json.MarshalIndent(dataStruct, "", "\t")
 	if err != nil {
-		return errorToJSON(err)
+		return ErrorToJSON(err)
 	}
 	return string(dataJSON)
 }