config: treat BufferWindowDays as int and validate range

cmd/main.go

@@ -59,8 +59,9 @@ func main() {
 			log.Printf("current: %v requested: %v", currentTime, requestedTime)
 			log.Printf("difference: %v configured: %v", numberOfDays, config.BufferWindowDays)
 
-			// found a case where action is needed
-			if uint8(numberOfDays) == config.BufferWindowDays {
+			// found a case where action is needed; both sides are ints now so
+			// the comparison is straightforward and cannot wrap around.
+			if numberOfDays == config.BufferWindowDays {
 				// do as scheduled on this date
 				projectInstance := client.GetProject(project)
 				errInfo := projectInstance.CreateIssue(schedule)

internal/pkg/configs/configuration.go

@@ -1,6 +1,7 @@
 package configs
 
 import (
+	"fmt"
 	"github-issue-schedule/internal/pkg/utils"
 	"io/ioutil"
 	"log"
@@ -10,7 +11,12 @@ import (
 
 // Configuration to run the program
 type Configuration struct {
-	BufferWindowDays uint8     `yaml:"buffer_window_days"`
+	// BufferWindowDays indicates how many days in advance a reminder
+	// issue should be created.  Use a signed integer so configs can
+	// express reasonable values without worrying about overflow when
+	// comparing against days-calculated-from-the-clock. Negative values
+	// are invalid and the reader enforces this.
+	BufferWindowDays int       `yaml:"buffer_window_days"`
 	Projects         []Project `yaml:"projects"`
 }
 
@@ -44,5 +50,23 @@ func ReadConfiguration() Configuration {
 	if err != nil {
 		log.Fatalf("Error while parsing the config file %v, Err: %v", configFile, err)
 	}
+
+	if err := config.validate(); err != nil {
+		log.Fatalf("invalid configuration: %v", err)
+	}
+
 	return config
 }
+
+// validate checks that fields in Configuration contain reasonable
+// values.  callers may use this directly in tests; ReadConfiguration
+// itself fatals on any error.
+func (c *Configuration) validate() error {
+	if c.BufferWindowDays < 0 {
+		return fmt.Errorf("buffer_window_days must be non-negative")
+	}
+	if c.BufferWindowDays > 100000 {
+		return fmt.Errorf("buffer_window_days is unreasonably large (%d)", c.BufferWindowDays)
+	}
+	return nil
+}

internal/pkg/configs/configuration_test.go

@@ -0,0 +1,30 @@
+package configs
+
+import (
+	"testing"
+)
+
+func TestConfigurationValidate(t *testing.T) {
+	cases := []struct {
+		desc   string
+		conf   Configuration
+		broken bool
+	}{
+		{"negative", Configuration{BufferWindowDays: -1}, true},
+		{"too large", Configuration{BufferWindowDays: 100001}, true},
+		{"zero", Configuration{BufferWindowDays: 0}, false},
+		{"normal", Configuration{BufferWindowDays: 7}, false},
+	}
+
+	for _, c := range cases {
+		t.Run(c.desc, func(t *testing.T) {
+			err := c.conf.validate()
+			if c.broken && err == nil {
+				t.Fatalf("expected error for config %+v", c.conf)
+			}
+			if !c.broken && err != nil {
+				t.Fatalf("did not expect error: %v", err)
+			}
+		})
+	}
+}