feat: add --from flag, refactor source providers (#2610)

Signed-off-by: Keith Zantow <kzantow@gmail.com>

syft/get_source.go

@@ -0,0 +1,101 @@
+package syft
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"os"
+
+	"github.com/anchore/syft/syft/source"
+)
+
+// GetSource uses all of Syft's known source providers to attempt to resolve the user input to a usable source.Source
+func GetSource(ctx context.Context, userInput string, cfg *GetSourceConfig) (source.Source, error) {
+	if cfg == nil {
+		cfg = DefaultGetSourceConfig()
+	}
+
+	providers, err := cfg.getProviders(userInput)
+	if err != nil {
+		return nil, err
+	}
+
+	var errs []error
+	var fileNotfound error
+
+	// call each source provider until we find a valid source
+	for _, p := range providers {
+		src, err := p.Provide(ctx)
+		if err != nil {
+			err = eachError(err, func(err error) error {
+				if errors.Is(err, os.ErrNotExist) {
+					fileNotfound = err
+					return nil
+				}
+				return err
+			})
+			if err != nil {
+				errs = append(errs, err)
+			}
+		}
+		if src != nil {
+			// if we have a non-image type and platform is specified, it's an error
+			if cfg.SourceProviderConfig.Platform != nil {
+				meta := src.Describe().Metadata
+				switch meta.(type) {
+				case *source.ImageMetadata, source.ImageMetadata:
+				default:
+					return src, fmt.Errorf("platform specified with non-image source")
+				}
+			}
+			return src, nil
+		}
+	}
+
+	if fileNotfound != nil {
+		errs = append([]error{fileNotfound}, errs...)
+	}
+	return nil, sourceError(userInput, errs...)
+}
+
+func sourceError(userInput string, errs ...error) error {
+	switch len(errs) {
+	case 0:
+		return nil
+	case 1:
+		return fmt.Errorf("an error occurred attempting to resolve '%s': %w", userInput, errs[0])
+	}
+	errorTexts := ""
+	for _, e := range errs {
+		errorTexts += fmt.Sprintf("\n  - %s", e)
+	}
+	return fmt.Errorf("errors occurred attempting to resolve '%s':%s", userInput, errorTexts)
+}
+
+func eachError(err error, fn func(error) error) error {
+	out := fn(err)
+	// unwrap singly wrapped errors
+	if e, ok := err.(interface {
+		Unwrap() error
+	}); ok {
+		wrapped := e.Unwrap()
+		got := eachError(wrapped, fn)
+		// return the outer error if received the same wrapped error
+		if errors.Is(got, wrapped) {
+			return err
+		}
+		return got
+	}
+	// unwrap errors from errors.Join
+	if errs, ok := err.(interface {
+		Unwrap() []error
+	}); ok {
+		for _, e := range errs.Unwrap() {
+			e = eachError(e, fn)
+			if e != nil {
+				out = errors.Join(out, e)
+			}
+		}
+	}
+	return out
+}