Shell: Allow redirections and pipes on builtins

Fixes #3072.

Shell/Builtin.cpp

@@ -757,23 +757,41 @@ int Shell::builtin_unset(int argc, const char** argv)
     return 0;
 }
 
-bool Shell::run_builtin(int argc, const char** argv, int& retval)
+bool Shell::run_builtin(const AST::Command& command, const NonnullRefPtrVector<AST::Rewiring>& rewirings, int& retval)
 {
-    if (argc == 0)
+    if (command.argv.is_empty())
         return false;
 
-    StringView name { argv[0] };
+    if (!has_builtin(command.argv.first()))
+        return false;
 
-#define __ENUMERATE_SHELL_BUILTIN(builtin)      \
+    Vector<const char*> argv;
-    if (name == #builtin) {                     \
+    for (auto& arg : command.argv)
-        retval = builtin_##builtin(argc, argv); \
+        argv.append(arg.characters());
-        return true;                            \
+
+    argv.append(nullptr);
+
+    StringView name = command.argv.first();
+
+    SavedFileDescriptors fds { rewirings };
+
+    for (auto& rewiring : rewirings) {
+        int rc = dup2(rewiring.dest_fd, rewiring.source_fd);
+        if (rc < 0) {
+            perror("dup2(run)");
+            return false;
+        }
+    }
+
+#define __ENUMERATE_SHELL_BUILTIN(builtin)                        \
+    if (name == #builtin) {                                       \
+        retval = builtin_##builtin(argv.size() - 1, argv.data()); \
+        return true;                                              \
     }
 
     ENUMERATE_SHELL_BUILTINS();
 
 #undef __ENUMERATE_SHELL_BUILTIN
-
     return false;
 }
 

Shell/Execution.h

@@ -26,7 +26,9 @@
 
 #pragma once
 
+#include "Forward.h"
 #include <AK/Forward.h>
+#include <AK/NonnullRefPtrVector.h>
 #include <AK/String.h>
 #include <AK/Vector.h>
 #include <LibCore/ElapsedTimer.h>
@@ -42,3 +44,18 @@ public:
 private:
     Vector<int, 32> m_fds;
 };
+
+class SavedFileDescriptors {
+public:
+    SavedFileDescriptors(const NonnullRefPtrVector<AST::Rewiring>&);
+    ~SavedFileDescriptors();
+
+private:
+    struct SavedFileDescriptor {
+        int original { -1 };
+        int saved { -1 };
+    };
+
+    Vector<SavedFileDescriptor> m_saves;
+    FileDescriptionCollector m_collector;
+};

Shell/Forward.h

@@ -33,5 +33,6 @@ class Node;
 class Value;
 class SyntaxError;
 class Pipeline;
+class Rewiring;
 
 }

Shell/Shell.cpp

@@ -500,6 +500,10 @@ RefPtr<Job> Shell::run_command(const AST::Command& command)
             return nullptr;
     }
 
+    int retval = 0;
+    if (run_builtin(command, rewirings, retval))
+        return nullptr;
+
     Vector<const char*> argv;
     Vector<String> copy_argv = command.argv;
     argv.ensure_capacity(command.argv.size() + 1);
@@ -509,10 +513,6 @@ RefPtr<Job> Shell::run_command(const AST::Command& command)
 
     argv.append(nullptr);
 
-    int retval = 0;
-    if (run_builtin(argv.size() - 1, argv.data(), retval))
-        return nullptr;
-
     int sync_pipe[2];
     if (pipe(sync_pipe) < 0) {
         perror("pipe");

Shell/Shell.h

@@ -78,7 +78,7 @@ public:
     RefPtr<Job> run_command(const AST::Command&);
     NonnullRefPtrVector<Job> run_commands(Vector<AST::Command>&);
     bool run_file(const String&, bool explicitly_invoked = true);
-    bool run_builtin(int argc, const char** argv, int& retval);
+    bool run_builtin(const AST::Command&, const NonnullRefPtrVector<AST::Rewiring>&, int& retval);
     bool has_builtin(const StringView&) const;
     void block_on_job(RefPtr<Job>);
     String prompt() const;

Shell/main.cpp

@@ -56,6 +56,38 @@ void FileDescriptionCollector::add(int fd)
     m_fds.append(fd);
 }
 
+SavedFileDescriptors::SavedFileDescriptors(const NonnullRefPtrVector<AST::Rewiring>& intended_rewirings)
+{
+    for (auto& rewiring : intended_rewirings) {
+        int new_fd = dup(rewiring.source_fd);
+        if (new_fd < 0) {
+            if (errno != EBADF)
+                perror("dup");
+            // The fd that will be overwritten isn't open right now,
+            // it will be cleaned up by the exec()-side collector
+            // and we have nothing to do here, so just ignore this error.
+            continue;
+        }
+
+        auto flags = fcntl(new_fd, F_GETFL);
+        auto rc = fcntl(new_fd, F_SETFL, flags | FD_CLOEXEC);
+        ASSERT(rc == 0);
+
+        m_saves.append({ rewiring.source_fd, new_fd });
+        m_collector.add(new_fd);
+    }
+}
+
+SavedFileDescriptors::~SavedFileDescriptors()
+{
+    for (auto& save : m_saves) {
+        if (dup2(save.saved, save.original) < 0) {
+            perror("dup2(~SavedFileDescriptors)");
+            continue;
+        }
+    }
+}
+
 int main(int argc, char** argv)
 {
     Core::EventLoop loop;