fix: replace error messages with more user friendly versions (#446)

Closes #422
Closes #439

cmd/duffle/install.go

@@ -159,7 +159,7 @@ Verifying and --insecure:
 func bundleFileOrArg2(args []string, bun string, w io.Writer, insecure bool) (string, error) {
 	switch {
 	case len(args) < 1:
-		return "", errors.New("This command requires at least one argument: NAME (name for the installation). It also requires a BUNDLE (CNAB bundle name) or file (using -f)\nValid inputs:\n\t$ duffle install NAME BUNDLE\n\t$ duffle install NAME -f path-to-bundle.json")
+		return "", errors.New("this command requires at least one argument: NAME (name for the installation). It also requires a BUNDLE (CNAB bundle name) or file (using -f)\nValid inputs:\n\t$ duffle install NAME BUNDLE\n\t$ duffle install NAME -f path-to-bundle.json")
 	case len(args) == 2 && bun != "":
 		return "", errors.New("please use either -f or specify a BUNDLE, but not both")
 	case len(args) < 2 && bun == "":
@@ -183,11 +183,7 @@ func optBundleFileOrArg2(args []string, bun string, w io.Writer, insecure bool)
 		// No bundle provided
 		return "", nil
 	case len(args) == 2:
-		var err error
-		bun, err = pullBundle(args[1], insecure)
-		if err != nil {
-			return "", err
-		}
+		return pullBundle(args[1], insecure)
 	}
 	return bun, nil
 }
@@ -202,7 +198,7 @@ func loadOrPullBundle(bun string, insecure bool) (string, error) {
 	// read the bundle reference from repositories.json
 	index, err := repo.LoadIndex(home.Repositories())
 	if err != nil {
-		return "", fmt.Errorf("cannot open %s: %v\n try running duffle init first", home.Repositories(), err)
+		return "", fmt.Errorf("cannot open %s: %v", home.Repositories(), err)
 	}
 
 	digest, err := index.Get(ref.Name(), ref.Tag())
@@ -237,7 +233,7 @@ func overrides(overrides []string, paramDefs map[string]bundle.ParameterDefiniti
 		var err error
 		res[pair[0]], err = def.ConvertValue(pair[1])
 		if err != nil {
-			return res, fmt.Errorf("can't use %s as value of %s: %s", pair[1], pair[0], err)
+			return res, fmt.Errorf("cannot use %s as value of %s: %s", pair[1], pair[0], err)
 		}
 	}
 	return res, nil
@@ -288,7 +284,7 @@ func calculateParamValues(bun *bundle.Bundle, valuesFile string, setParams, setF
 		}
 		content, err := ioutil.ReadFile(parts[1])
 		if err != nil {
-			return vals, fmt.Errorf("error while reading file %q: %s", parts[1], err)
+			return vals, fmt.Errorf("could not read file %q: %s", parts[1], err)
 		}
 		vals[parts[0]] = string(content)
 	}

cmd/duffle/pull.go

@@ -1,6 +1,7 @@
 package main
 
 import (
+	"errors"
 	"fmt"
 	"io"
 	"io/ioutil"
@@ -102,7 +103,7 @@ func getLoader(insecure bool) (loader.Loader, error) {
 	} else {
 		kr, err := loadVerifyingKeyRings(homePath())
 		if err != nil {
-			return nil, err
+			return nil, fmt.Errorf("cannot securely load bundle: %s", err)
 		}
 		load = loader.NewSecureLoader(kr)
 	}
@@ -123,7 +124,7 @@ func getReference(bundleName string) (reference.NamedTagged, error) {
 	}
 	normalizedRef, err := reference.ParseNormalizedNamed(name)
 	if err != nil {
-		return nil, fmt.Errorf("failed to parse image name: %s: %v", name, err)
+		return nil, fmt.Errorf("%q is not a valid bundle name: %v", name, err)
 	}
 	if reference.IsNameOnly(normalizedRef) {
 		ref, err = reference.WithTag(normalizedRef, "latest")
@@ -167,5 +168,19 @@ func loadBundle(bundleFile string, insecure bool) (*bundle.Bundle, error) {
 	if err != nil {
 		return nil, err
 	}
-	return l.Load(bundleFile)
+	// Issue #439: Errors that come back from the loader can be
+	// pretty opaque.
+	var bun *bundle.Bundle
+	if bun, err := l.Load(bundleFile); err != nil {
+		if err.Error() == "no signature block in data" {
+			return bun, errors.New("bundle is not signed")
+		}
+		// Dear Go, Y U NO TERNARY, kthxbye
+		secflag := "secure"
+		if insecure {
+			secflag = "insecure"
+		}
+		return bun, fmt.Errorf("cannot load %s bundle: %s", secflag, err)
+	}
+	return bun, nil
 }

pkg/reference/normalize.go

@@ -30,7 +30,7 @@ type normalizedNamed interface {
 // use ParseAnyReference.
 func ParseNormalizedNamed(s string) (Named, error) {
 	if ok := anchoredIdentifierRegexp.MatchString(s); ok {
-		return nil, fmt.Errorf("invalid repository name (%s), cannot specify 64-byte hexadecimal strings", s)
+		return nil, fmt.Errorf("repository name (%s) cannot be a 64-byte hexadecimal strings", s)
 	}
 	domain, remainder := splitDockerDomain(s)
 	var remoteName string
@@ -40,7 +40,7 @@ func ParseNormalizedNamed(s string) (Named, error) {
 		remoteName = remainder
 	}
 	if strings.ToLower(remoteName) != remoteName {
-		return nil, errors.New("invalid reference format: repository name must be lowercase")
+		return nil, errors.New("in a reference name, the repository part must be lowercase")
 	}
 
 	ref, err := Parse(domain + "/" + remainder)