help with json errors

Signed-off-by: Doug Davis <[email protected]>

registry/utils.go

@@ -369,6 +369,27 @@ func Unmarshal(buf []byte, v any) error {
 	dec := json.NewDecoder(bytes.NewReader(buf))
 	dec.DisallowUnknownFields()
 	if err := dec.Decode(v); err != nil {
+		// Try to grab the json around the error
+		offset := int(dec.InputOffset())
+		nearStart := offset - 200
+		if nearStart < 0 {
+			nearStart = 0
+		}
+		nearEnd := offset + 200
+		if nearEnd >= len(buf) {
+			nearEnd = len(buf)
+		}
+		near := ""
+		if nearStart != offset {
+			if nearStart != 0 {
+				near = ".s."
+			}
+			near = string(buf[nearStart:nearEnd])
+		}
+		if offset > 0 && nearEnd != offset {
+			near += ".e."
+		}
+
 		msg := err.Error()
 
 		if jerr, ok := err.(*json.UnmarshalTypeError); ok {
@@ -384,6 +405,10 @@ func Unmarshal(buf []byte, v any) error {
 			}
 		}
 		msg, _ = strings.CutPrefix(msg, "json: ")
+		if near != "" {
+			msg += " near: " + near
+		}
+
 		return errors.New(msg)
 	}
 	return nil

tests/capabilities_test.go

@@ -229,7 +229,7 @@ func TestCapabilitySimple(t *testing.T) {
 		{
 			Name: "extra key",
 			Cap:  `{"pagination": true, "bad": true}`,
-			Exp:  `Unknown capability: "bad"`,
+			Exp:  `Unknown capability: "bad" near: {"pagination": true, "bad": true}`,
 		},
 	}
 
@@ -557,7 +557,7 @@ func TestCapabilityPath(t *testing.T) {
 
 	// Unknown key
 	xHTTP(t, reg, "PUT", "/capabilities", `{ "foo": [] }`,
-		400, "Unknown capability: \"foo\"\n")
+		400, "Unknown capability: \"foo\" near: { \"foo\": [] }\n")
 }
 
 func TestCapabilityAttr(t *testing.T) {
@@ -765,7 +765,10 @@ func TestCapabilityAttr(t *testing.T) {
 	// Unknown key
 	xHTTP(t, reg, "PUT", "/?inline=capabilities", `{ "capabilities":
 	    {"foo": [] }}`,
-		400, "Unknown capability: \"foo\"\n")
+		400, `Unknown capability: "foo" near: {
+  "foo": []
+}
+`)
 
 }
 

tests/utils_test.go

@@ -261,13 +261,13 @@ func xCheckEqual(t *testing.T, extra string, gotAny any, expAny any) {
 	}
 
 	if pos == len(got) {
-		t.Fatalf("%s"+
+		t.Fatalf("%s\n"+
 			"Expected:\n%s\nGot:\n%s\nGot ended early at(%d)[%02X]:\n%q",
 			extra, exp, got, pos, exp[pos], got[pos:])
 	}
 
 	if pos == len(exp) {
-		t.Fatalf("%s"+
+		t.Fatalf("%s\n"+
 			"Expected:\n%s\nGot:\n%s\nExp ended early at(%d)[%02X]:\n%q",
 			extra, exp, got, pos, got[pos], got[pos:])
 	}