feat: libc - add SYS_GETCHAR_NB and a non-blocking stdin readiness probe

Co-Authored-By: Claude Opus 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01NQRTGoYgnZQsh7uCh6Jsxm

kernel/src/Api/BuildNo.hpp

@@ -12,4 +12,4 @@
 
 #pragma once
 
-#define MONTAUK_BUILD_NUMBER 91
+#define MONTAUK_BUILD_NUMBER 92

kernel/src/Api/Keyboard.hpp

@@ -15,9 +15,14 @@ namespace montauk::abi {
     static bool Sys_IsKeyAvailable() {
         auto* proc = Sched::GetCurrentProcessPtr();
         if (proc && proc->redirected) {
-            Ipc::HandleSnapshot snapshot;
-            Ipc::Mailbox* mailbox = GetRedirKeyMailbox(proc, snapshot);
-            if (mailbox != nullptr) return Ipc::MailboxHasMessage(mailbox);
+            Ipc::HandleSnapshot inputSnapshot;
+            Ipc::HandleSnapshot mailboxSnapshot;
+            Ipc::Stream* input = GetRedirInStream(proc, inputSnapshot);
+            Ipc::Mailbox* mailbox = GetRedirKeyMailbox(proc, mailboxSnapshot);
+            if (input != nullptr || mailbox != nullptr) {
+                if (input != nullptr && Ipc::StreamHasData(input)) return true;
+                return mailbox != nullptr && Ipc::MailboxHasMessage(mailbox);
+            }
         }
         return Drivers::PS2::Keyboard::IsKeyAvailable();
     }
@@ -97,4 +102,41 @@ namespace montauk::abi {
         }
         return Drivers::PS2::Keyboard::GetChar();
     }
+
+    /*
+     * Non-blocking counterpart of Sys_GetChar: returns the next character, or
+     * 0 when none is pending. IsKeyAvailable is not enough to make GetChar
+     * safe to call -- a queued key-release or modifier event reports as
+     * "available" but carries no ascii, and GetChar would go on to block. So
+     * the drain has to happen on this side of the syscall boundary.
+     */
+    static char Sys_GetCharNb() {
+        auto* proc = Sched::GetCurrentProcessPtr();
+        if (proc && proc->redirected) {
+            Ipc::HandleSnapshot inputSnapshot;
+            Ipc::HandleSnapshot mailboxSnapshot;
+            Ipc::Stream* input = GetRedirInStream(proc, inputSnapshot);
+            Ipc::Mailbox* mailbox = GetRedirKeyMailbox(proc, mailboxSnapshot);
+            if (input != nullptr || mailbox != nullptr) {
+                if (input != nullptr) {
+                    uint8_t c = 0;
+                    if (Ipc::StreamRead(input, &c, 1, true) > 0) return (char)c;
+                }
+
+                while (mailbox != nullptr) {
+                    KeyEvent ev{};
+                    uint16_t len = sizeof(ev);
+                    if (Ipc::MailboxRecv(mailbox, nullptr, &ev, &len, true) <= 0) break;
+                    if (ev.pressed && ev.ascii != 0) return ev.ascii;
+                }
+                return 0;
+            }
+        }
+
+        while (Drivers::PS2::Keyboard::IsKeyAvailable()) {
+            auto k = Drivers::PS2::Keyboard::GetKey();
+            if (k.Pressed && k.Ascii != 0) return k.Ascii;
+        }
+        return 0;
+    }
 };

kernel/src/Api/Syscall.cpp

@@ -134,6 +134,8 @@ namespace montauk::abi {
                 return 0;
             case SYS_GETCHAR:
                 return (int64_t)Sys_GetChar();
+            case SYS_GETCHAR_NB:
+                return (int64_t)Sys_GetCharNb();
             case SYS_PING:
                 return (int64_t)Sys_Ping((uint32_t)frame->arg1, (uint32_t)frame->arg2);
             case SYS_SPAWN:

kernel/src/Api/Syscall.hpp

@@ -307,6 +307,9 @@ namespace montauk::abi {
     static constexpr uint64_t SYS_WIFI_CONNECT_ASYNC  = 164;  // (ssid, password) -> 0 accepted, <0 on error
     static constexpr uint64_t SYS_NETIFS              = 165;  // (NetIfInfo*, maxCount) -> count
 
+    /* Keyboard.hpp */
+    static constexpr uint64_t SYS_GETCHAR_NB          = 166;  // () -> ascii, 0 if nothing pending; never blocks
+
     // Tunable parameters (for SYS_SDR_SETPARAM / SYS_SDR_GETPARAM).
     static constexpr int SDR_PARAM_FREQ        = 0;  // center frequency, Hz
     static constexpr int SDR_PARAM_SAMPLE_RATE = 1;  // sample rate, Hz