Allows users to set a dependency mirror

postal/fakes/mirror_resolver.go

@@ -0,0 +1,31 @@
+package fakes
+
+import "sync"
+
+type MirrorResolver struct {
+	FindDependencyMirrorCall struct {
+		mutex     sync.Mutex
+		CallCount int
+		Receives  struct {
+			Uri         string
+			PlatformDir string
+		}
+		Returns struct {
+			String string
+			Error  error
+		}
+		Stub func(string, string) (string, error)
+	}
+}
+
+func (f *MirrorResolver) FindDependencyMirror(param1 string, param2 string) (string, error) {
+	f.FindDependencyMirrorCall.mutex.Lock()
+	defer f.FindDependencyMirrorCall.mutex.Unlock()
+	f.FindDependencyMirrorCall.CallCount++
+	f.FindDependencyMirrorCall.Receives.Uri = param1
+	f.FindDependencyMirrorCall.Receives.PlatformDir = param2
+	if f.FindDependencyMirrorCall.Stub != nil {
+		return f.FindDependencyMirrorCall.Stub(param1, param2)
+	}
+	return f.FindDependencyMirrorCall.Returns.String, f.FindDependencyMirrorCall.Returns.Error
+}

postal/internal/dependency_mirror.go

@@ -0,0 +1,138 @@
+package internal
+
+import (
+	"fmt"
+	"net/url"
+	"os"
+	"strings"
+)
+
+type DependencyMirrorResolver struct {
+	bindingResolver BindingResolver
+}
+
+func NewDependencyMirrorResolver(bindingResolver BindingResolver) DependencyMirrorResolver {
+	return DependencyMirrorResolver{
+		bindingResolver: bindingResolver,
+	}
+}
+
+func formatAndVerifyMirror(mirror, uri string) (string, error) {
+	mirrorURL, err := url.Parse(mirror)
+	if err != nil {
+		return "", err
+	}
+
+	uriURL, err := url.Parse(uri)
+	if err != nil {
+		return "", err
+	}
+
+	if mirrorURL.Scheme != "https" && mirrorURL.Scheme != "file" {
+		return "", fmt.Errorf("invalid mirror scheme")
+	}
+
+	mirrorURL.Path = strings.Replace(mirrorURL.Path, "{originalHost}", uriURL.Host+uriURL.Path, 1)
+	return mirrorURL.String(), nil
+}
+
+func (d DependencyMirrorResolver) FindDependencyMirror(uri, platformDir string) (string, error) {
+	mirror, err := d.findMirrorFromEnv(uri)
+	if err != nil {
+		return "", err
+	}
+
+	if mirror != "" {
+		return formatAndVerifyMirror(mirror, uri)
+	}
+
+	mirror, err = d.findMirrorFromBinding(uri, platformDir)
+	if err != nil {
+		return "", err
+	}
+
+	if mirror != "" {
+		return formatAndVerifyMirror(mirror, uri)
+	}
+
+	return "", nil
+}
+
+func (d DependencyMirrorResolver) findMirrorFromEnv(uri string) (string, error) {
+	const DefaultMirror = "BP_DEPENDENCY_MIRROR"
+	const NonDefaultMirrorPrefix = "BP_DEPENDENCY_MIRROR_"
+	mirrors := make(map[string]string)
+	environmentVariables := os.Environ()
+	for _, ev := range environmentVariables {
+		pair := strings.SplitN(ev, "=", 2)
+		key := pair[0]
+		value := pair[1]
+
+		if !strings.Contains(key, DefaultMirror) {
+			continue
+		}
+
+		if key == DefaultMirror {
+			mirrors["default"] = value
+			continue
+		}
+
+		// convert key
+		hostname := strings.SplitN(key, NonDefaultMirrorPrefix, 2)[1]
+		hostname = strings.ReplaceAll(strings.ReplaceAll(hostname, "__", "-"), "_", ".")
+		hostname = strings.ToLower(hostname)
+		mirrors[hostname] = value
+
+		if !strings.Contains(uri, hostname) {
+			continue
+		}
+
+		return value, nil
+	}
+
+	if mirrorUri, ok := mirrors["default"]; ok {
+		return mirrorUri, nil
+	}
+
+	return "", nil
+}
+
+func (d DependencyMirrorResolver) findMirrorFromBinding(uri, platformDir string) (string, error) {
+	bindings, err := d.bindingResolver.Resolve("dependency-mirror", "", platformDir)
+	if err != nil {
+		return "", fmt.Errorf("failed to resolve 'dependency-mirror' binding: %w", err)
+	}
+
+	if len(bindings) > 1 {
+		return "", fmt.Errorf("cannot have multiple bindings of type 'dependency-mirror'")
+	}
+
+	if len(bindings) == 0 {
+		return "", nil
+	}
+
+	mirror := ""
+	entries := bindings[0].Entries
+	for hostname, entry := range entries {
+		if hostname == "default" {
+			mirror, err = entry.ReadString()
+			if err != nil {
+				return "", err
+			}
+			continue
+		}
+
+		if !strings.Contains(uri, hostname) {
+			continue
+		}
+
+		mirror, err = entry.ReadString()
+		if err != nil {
+			return "", err
+		}
+
+		return mirror, nil
+	}
+
+	return mirror, nil
+}