Add a bash-based implementation of replace_bash_vars().

You can choose at configure time if you want the old
c++ variable string replacement implementation or the
new one that execs bash -c 'echo blah blah'. It supports
using both EnvReal and EnvFake.

meson.build

@@ -12,5 +12,14 @@ conf.set('PROJECT_NAME', meson.project_name())
 conf.set('PROJECT_VERSION', meson.project_version())
 conf.set('COPYRIGHT_YEAR', '2020')
 conf.set('PROJECT_REPO_URL', 'https://alarmpi.no-ip.org/gitan/King_DuckZ/user-gcc')
+if get_option('bash_method') == 'naive'
+	conf.set('USE_NAIVE_BASH_METHOD', true)
+else
+	conf.set('USE_NATIVE_BASH_METHOD', true)
+	bash_found = find_program('bash', required: false)
+	if not bash_found.found()
+		warning('bash was not found on your system, you will still be able to build ' + meson.project_name() + ' but you won\'t be able to run it correctly')
+	endif
+endif
 
 subdir('src')

meson_options.txt

@@ -0,0 +1 @@
+option('bash_method', type: 'combo', description: 'Select the implementation of the Bash script parsing method', choices: ['naive', 'native'], value: 'native')

src/config.h.in

@@ -21,3 +21,5 @@
 #define PROJECT_VERSION "@PROJECT_VERSION@"
 #define COPYRIGHT_YEAR "@COPYRIGHT_YEAR@"
 #define PROJECT_REPO_URL "@PROJECT_REPO_URL@"
+#mesondefine USE_NATIVE_BASH_METHOD
+#mesondefine USE_NAIVE_BASH_METHOD

src/main.cpp

@@ -59,6 +59,7 @@ int main(int argc, char* argv[]) {
 
 	duck::RunContext syspaths;
 	syspaths.add_to_env(g_simple_colours);
+	syspaths.env().set("argv0", PROJECT_NAME);
 #if !defined(NDEBUG)
 	std::cout << syspaths << '\n';
 #endif

src/replace_bash_vars.cpp

@@ -19,25 +19,30 @@
 #include "config.h"
 #include "run_context.hpp"
 #include <cassert>
-#include <cctype>
+#if defined(USE_NAIVE_BASH_METHOD)
+#	include <cctype>
+#else
+#	include "run_cmd.hpp"
+#	include "env_real.hpp"
+#	include "env_fake.hpp"
+#	include <spawn.h>
+#	include <unistd.h>
+#	include <sys/wait.h>
+#	include <stdexcept>
+#	include <cstdlib>
+#	include <poll.h>
+#endif
 
 namespace duck {
+#if defined(USE_NAIVE_BASH_METHOD)
+
 	namespace {
 		struct VarInfo {
 			std::string_view name;
 			std::size_t orig_len{};
 		};
 
-		//std::string replaced_all (std::string text, std::string_view search, std::string_view repl) {
-		//	std::size_t pos = 0;
-		//	while ((pos = text.find(search, pos)) != std::string::npos) {
-		//		text.replace(pos, search.size(), repl);
-		//		pos += repl.size();
-		//	}
-		//	return text;
-		//}
-
-		VarInfo extract_var_name (const RunContext& sp, std::string_view text) {
+		VarInfo extract_var_name (const RunContext& rc, std::string_view text) {
 			assert(not text.empty());
 			assert(text.front() == '$');
 			if (text.size() == 1) {
@@ -59,7 +64,7 @@ namespace duck {
 						std::string_view token(text.substr(2, end - 2));
 						std::string_view retval(token.empty() || token.front() != '!' ? token : token.substr(1));
 						if (not token.empty() and token.front() == '!') {
-							return {sp.env()[retval], end + 1};
+							return {rc.env()[retval], end + 1};
 						}
 						else {
 							return {retval, end + 1};
@@ -76,7 +81,7 @@ namespace duck {
 		}
 	} //unnamed namespace
 
-	std::string replace_bash_vars (const RunContext& sp, std::string_view text) {
+	std::string replace_bash_vars (const RunContext& rc, std::string_view text) {
 		std::size_t pos = 0;
 		std::size_t prev_start = 0;
 		std::string rtext;
@@ -84,7 +89,7 @@ namespace duck {
 
 		while ((pos = text.find('$', pos)) != std::string::npos) {
 			if (0 == pos or rtext[pos-1] != '\\') {
-				auto var = extract_var_name(sp, text.substr(pos));
+				auto var = extract_var_name(rc, text.substr(pos));
 				if (not var.orig_len) {
 					++pos;
 					continue;
@@ -95,7 +100,7 @@ namespace duck {
 				if (var.name == "argv0")
 					rtext += PROJECT_NAME;
 				else
-					rtext += sp.env()[var.name];
+					rtext += rc.env()[var.name];
 				pos += var.orig_len;
 				prev_start = pos;
 			}
@@ -107,4 +112,103 @@ namespace duck {
 		rtext.append(text.begin() + prev_start, text.end());
 		return rtext;
 	}
+
+#elif defined(USE_NATIVE_BASH_METHOD)
+
+	namespace {
+		std::string replaced_all (std::string text, std::string_view search, std::string_view repl) {
+			std::size_t pos = 0;
+			while ((pos = text.find(search, pos)) != std::string::npos) {
+				text.replace(pos, search.size(), repl);
+				pos += repl.size();
+			}
+			return text;
+		}
+
+		struct Pipes {
+			Pipes() {
+				if(pipe(cout_pipe) or pipe(cerr_pipe))
+					throw std::runtime_error("Error in pipe() in replace_bash_vars()");
+			}
+
+			~Pipes() noexcept {
+				close(cout_pipe[0]), close(cerr_pipe[0]);
+				close(cout_pipe[1]), close(cerr_pipe[1]);
+			}
+
+			void close_child_side() noexcept {
+				close(cout_pipe[1]), close(cerr_pipe[1]);
+				cout_pipe[1] = cerr_pipe[1] = 0;
+			}
+
+			int cout_pipe[2];
+			int cerr_pipe[2];
+		};
+
+		struct FileAction {
+			FileAction() { posix_spawn_file_actions_init(&action); }
+			~FileAction() noexcept { posix_spawn_file_actions_destroy(&action); }
+
+			posix_spawn_file_actions_t action;
+		};
+	} //unnamed namespace
+
+	std::string replace_bash_vars (const RunContext& rc, std::string_view text) {
+		Pipes p;
+		FileAction fa;
+
+		//see: https://stackoverflow.com/questions/13893085/posix-spawnp-and-piping-child-output-to-a-string
+		posix_spawn_file_actions_addclose(&fa.action, p.cout_pipe[0]);
+		posix_spawn_file_actions_addclose(&fa.action, p.cerr_pipe[0]);
+		posix_spawn_file_actions_adddup2(&fa.action, p.cout_pipe[1], 1);
+		posix_spawn_file_actions_adddup2(&fa.action, p.cerr_pipe[1], 2);
+		posix_spawn_file_actions_addclose(&fa.action, p.cout_pipe[1]);
+		posix_spawn_file_actions_addclose(&fa.action, p.cerr_pipe[1]);
+
+		char shell_cpy[] = {'b', 'a', 's', 'h', '\0'};
+		char c_arg_cpy[] = {'-', 'c', '\0'};
+		std::vector<char> command;
+		{
+			std::string san_text = "\"" + replaced_all(to_string(text), "\"", "\\\"") + "\"";
+			command.reserve(5 + san_text.size() + 1);
+			command.insert(command.begin(), "echo ", "echo " + 5);
+			std::copy(san_text.begin(), san_text.end(), std::back_inserter(command));
+			command.push_back('\0');
+		}
+		char* const argv[] = {shell_cpy, c_arg_cpy, command.data(), nullptr};
+
+		const auto new_env = rc.env().to_c_array();
+		pid_t pid;
+		const int spawn_ret = posix_spawnp(&pid, argv[0], &fa.action, nullptr, argv, new_env.get());
+		p.close_child_side();
+
+		if (spawn_ret)
+			throw std::runtime_error("posix_spawnp() failed with code " + std::to_string(spawn_ret));
+
+		// Read from pipes
+		std::string retval;
+		std::string buffer(1024,' ');
+		std::vector<pollfd> plist = { {p.cout_pipe[0], POLLIN}, {p.cerr_pipe[0], POLLIN} };
+		constexpr const int timeout = -1;
+		for (int rval; (rval = poll(&plist[0], plist.size(), timeout)) > 0;) {
+			if (plist[0].revents & POLLIN) {
+				const int bytes_read = read(p.cout_pipe[0], &buffer[0], buffer.length());
+				retval.append(buffer.begin(), buffer.begin() + bytes_read);
+			}
+			else if (plist[1].revents & POLLIN) {
+				/*const int bytes_read =*/ read(p.cerr_pipe[0], &buffer[0], buffer.length());
+				//cout << buffer.substr(0, static_cast<size_t>(bytes_read)) << "\n";
+			}
+			else break; // nothing left to read
+		}
+
+		int exit_code;
+		waitpid(pid, &exit_code, 0);
+
+		return retval;
+	}
+
+#else
+#	error "None of the known bash parsing method has been selected by the user"
+#endif
 } //namespace duck