cleanup(userspace/libscap): avoid the usage of non-portable (glibc specific) __gnu_cxx::stdio_filebuf

userspace/libscap/engine/gvisor/runsc.cpp

@@ -16,10 +16,6 @@ limitations under the License.
 */
 
 #include <unistd.h>
-#include <sys/wait.h>
-#include <ext/stdio_filebuf.h>
-#include <iostream>
-#include <fstream>
 #include <string>
 
 #include <libscap/engine/gvisor/gvisor.h>
@@ -30,36 +26,37 @@ namespace runsc {
 
 result runsc(char *argv[]) {
 	result res;
-	int pipefds[2];
 
-	int ret = pipe(pipefds);
-	if(ret) {
-		return res;
+	std::string full_command;
+	int i = 0;
+	while(true) {
+		if(argv[i] == nullptr) {
+			break;
+		}
+		full_command.append(argv[i]);
+		full_command.append(" ");
+		i++;
 	}
-
-	pid_t pid = vfork();
-	if(pid > 0) {
-		int status;
-
-		close(pipefds[1]);
-		wait(&status);
+	FILE *cmd_out = popen(full_command.c_str(), "r");
+	if(cmd_out == nullptr) {
+		res.error = -errno;
+	} else {
+		char *out = nullptr;
+		size_t len = 0;
+		ssize_t readbytes;
+		while((readbytes = getline(&out, &len, cmd_out)) >= 0) {
+			// getline() returns string comprehensive of newline char;
+			// drop it if found.
+			if(out[readbytes - 1] == '\n') {
+				out[readbytes - 1] = '\0';
+			}
+			res.output.emplace_back(out);
+		}
+		free(out);
+		int status = pclose(cmd_out);
 		if(!WIFEXITED(status) || WEXITSTATUS(status) != 0) {
 			res.error = status;
-			return res;
 		}
-
-		__gnu_cxx::stdio_filebuf<char> filebuf(pipefds[0], std::ios::in);
-		std::string line;
-		std::istream is(&filebuf);
-
-		while(std::getline(is, line)) {
-			res.output.emplace_back(std::string(line));
-		}
-	} else {
-		close(pipefds[0]);
-		dup2(pipefds[1], STDOUT_FILENO);
-		execvp("runsc", argv);
-		exit(1);
 	}
 
 	return res;