Add WithEnv and WithMount oci options

Signed-off-by: Paul Knopf <pauldotknopf@gmail.com>

oci/spec_opts.go

@@ -2,6 +2,7 @@ package oci
 
 import (
 	"context"
+	"strings"
 
 	"github.com/containerd/containerd/containers"
 	specs "github.com/opencontainers/runtime-spec/specs-go"
@@ -33,3 +34,59 @@ func WithHostname(name string) SpecOpts {
 		return nil
 	}
 }
+
+// WithEnv appends environment variables
+func WithEnv(environmnetVariables []string) SpecOpts {
+	return func(_ context.Context, _ Client, _ *containers.Container, s *specs.Spec) error {
+		if len(environmnetVariables) > 0 {
+			s.Process.Env = replaceOrAppendEnvValues(s.Process.Env, environmnetVariables)
+		}
+		return nil
+	}
+}
+
+// WithMounts appends mounts
+func WithMounts(mounts []specs.Mount) SpecOpts {
+	return func(_ context.Context, _ Client, _ *containers.Container, s *specs.Spec) error {
+		s.Mounts = append(s.Mounts, mounts...)
+		return nil
+	}
+}
+
+// replaceOrAppendEnvValues returns the defaults with the overrides either
+// replaced by env key or appended to the list
+func replaceOrAppendEnvValues(defaults, overrides []string) []string {
+	cache := make(map[string]int, len(defaults))
+	for i, e := range defaults {
+		parts := strings.SplitN(e, "=", 2)
+		cache[parts[0]] = i
+	}
+
+	for _, value := range overrides {
+		// Values w/o = means they want this env to be removed/unset.
+		if !strings.Contains(value, "=") {
+			if i, exists := cache[value]; exists {
+				defaults[i] = "" // Used to indicate it should be removed
+			}
+			continue
+		}
+
+		// Just do a normal set/update
+		parts := strings.SplitN(value, "=", 2)
+		if i, exists := cache[parts[0]]; exists {
+			defaults[i] = value
+		} else {
+			defaults = append(defaults, value)
+		}
+	}
+
+	// Now remove all entries that we want to "unset"
+	for i := 0; i < len(defaults); i++ {
+		if defaults[i] == "" {
+			defaults = append(defaults[:i], defaults[i+1:]...)
+			i--
+		}
+	}
+
+	return defaults
+}