syscall: refactor environment handling

* Move environment functions to their own files.
  * Rewrite the WASIp2 version of environment variables to be much
    simpler (don't go through C functions).

src/syscall/env_wasip2.go

@@ -2,6 +2,19 @@
 
 package syscall
 
+import (
+	"internal/wasi/cli/v0.2.0/environment"
+)
+
+var libc_envs map[string]string
+
+func populateEnvironment() {
+	libc_envs = make(map[string]string)
+	for _, kv := range environment.GetEnvironment().Slice() {
+		libc_envs[kv[0]] = kv[1]
+	}
+}
+
 func Environ() []string {
 	var env []string
 	for k, v := range libc_envs {
@@ -9,3 +22,35 @@ func Environ() []string {
 	}
 	return env
 }
+
+func Getenv(key string) (value string, found bool) {
+	value, found = libc_envs[key]
+	return
+}
+
+func Setenv(key, val string) (err error) {
+	if len(key) == 0 {
+		return EINVAL
+	}
+	for i := 0; i < len(key); i++ {
+		if key[i] == '=' || key[i] == 0 {
+			return EINVAL
+		}
+	}
+	for i := 0; i < len(val); i++ {
+		if val[i] == 0 {
+			return EINVAL
+		}
+	}
+	libc_envs[key] = val
+	return nil
+}
+
+func Unsetenv(key string) (err error) {
+	delete(libc_envs, key)
+	return nil
+}
+
+func Clearenv() {
+	clear(libc_envs)
+}