Improve sprintf number handling

Previously, all numbers were converted to strings before invoking
fmt.Sprintf. As a result, policies could not use fmt verbs for integer
and floating point values.

With these changes, OPA will try to convert numbers to int or float64
before falling back to string for values greater than max/min
int64/float64.

Fixes open-policy-agent#748

Signed-off-by: Torin Sandall <torinsandall@gmail.com>

topdown/strings.go

@@ -245,17 +245,26 @@ func builtinSprintf(a, b ast.Value) (ast.Value, error) {
 		return nil, builtins.NewOperandTypeErr(2, b, "array")
 	}
 
-	strArr := []interface{}{}
+	args := make([]interface{}, len(astArr))
+
 	for i := range astArr {
-		if str, ok := astArr[i].Value.(ast.String); ok {
-			strArr = append(strArr, string(str))
-		} else {
-			strArr = append(strArr, astArr[i].Value.String())
+		switch v := astArr[i].Value.(type) {
+		case ast.Number:
+			if n, ok := v.Int(); ok {
+				args[i] = n
+			} else if f, ok := v.Float64(); ok {
+				args[i] = f
+			} else {
+				args[i] = v.String()
+			}
+		case ast.String:
+			args[i] = string(v)
+		default:
+			args[i] = astArr[i].String()
 		}
 	}
 
-	fmtStr := fmt.Sprintf(string(s), strArr...)
-	return ast.String(fmtStr), nil
+	return ast.String(fmt.Sprintf(string(s), args...)), nil
 }
 
 func init() {

topdown/topdown_test.go

@@ -1306,10 +1306,12 @@ func TestTopDownStrings(t *testing.T) {
 		{"trim: multi-cutset-none", []string{`p = x { trim("...foo.bar...", ".o", x) }`}, `"foo.bar"`},
 		{"sprintf: none", []string{`p = x { sprintf("hi", [], x) }`}, `"hi"`},
 		{"sprintf: string", []string{`p = x { sprintf("hi %s", ["there"], x) }`}, `"hi there"`},
-		{"sprintf: int", []string{`p = x { sprintf("hi %s", [5], x) }`}, `"hi 5"`},
-		{"sprintf: float", []string{`p = x { sprintf("hi %s", [3.14], x) }`}, `"hi 3.14"`},
+		{"sprintf: int", []string{`p = x { sprintf("hi %02d", [5], x) }`}, `"hi 05"`},
+		{"sprintf: hex", []string{`p = x { sprintf("hi %02X.%02X", [127, 1], x) }`}, `"hi 7F.01"`},
+		{"sprintf: float", []string{`p = x { sprintf("hi %.2f", [3.1415], x) }`}, `"hi 3.14"`},
+		{"sprintf: float too big", []string{`p = x { sprintf("hi %v", [2e308], x) }`}, `"hi 2e+308"`},
 		{"sprintf: bool", []string{`p = x { sprintf("hi %s", [true], x) }`}, `"hi true"`},
-		{"sprintf: composite", []string{`p = x { sprintf("hi %s", [["there", 5, 3.14]], x) }`}, `"hi [\"there\", 5, 3.14]"`},
+		{"sprintf: composite", []string{`p = x { sprintf("hi %v", [["there", 5, 3.14]], x) }`}, `"hi [\"there\", 5, 3.14]"`},
 	}
 
 	data := loadSmallTestData()