From 5fd397563e6ccf1d2cd237f4338c2f006922822e Mon Sep 17 00:00:00 2001
From: Zack Buhman <zack@buhman.org>
Date: Mon, 20 Jan 2025 01:30:12 -0600
Subject: [PATCH] libcinputstream: implement available

---
 c/native.c                                |  6 ++++++
 c/native/libcinputstream.c                | 19 +++++++++++++++++++
 c/native/libcinputstream.h                |  1 +
 classes/jvm/internal/LibcInputStream.java | 11 +++++++++--
 classes/test/TestInputStream.java         | 12 ++++++++++--
 5 files changed, 45 insertions(+), 4 deletions(-)

diff --git a/c/native.c b/c/native.c
index b62ef24..ca3a784 100644
--- a/c/native.c
+++ b/c/native.c
@@ -168,6 +168,12 @@ const static struct native_method native_method[] = {
     .method_descriptor = "([B)I",
     .func = native_jvm_internal_libcinputstream_open_1,
   },
+  {
+    .class_name = "jvm/internal/LibcInputStream",
+    .method_name = "_available",
+    .method_descriptor = "(I)I",
+    .func = native_jvm_internal_libcinputstream_available_1,
+  },
   {
     .class_name = "jvm/internal/LibcInputStream",
     .method_name = "_close",
diff --git a/c/native/libcinputstream.c b/c/native/libcinputstream.c
index 002e62e..ca221df 100644
--- a/c/native/libcinputstream.c
+++ b/c/native/libcinputstream.c
@@ -16,6 +16,25 @@ void native_jvm_internal_libcinputstream_open_1(struct vm * vm, uint32_t * args)
   operand_stack_push_u32(vm->current_frame, (uint32_t)file);
 }
 
+void native_jvm_internal_libcinputstream_available_1(struct vm * vm, uint32_t * args)
+{
+  FILE * file = (FILE *)args[0];
+  assert(file != nullptr);
+
+  int current = fseek(file, 0L, SEEK_CUR);
+  int ret_end = fseek(file, 0L, SEEK_END);
+  assert(ret_end != -1);
+  int ftell_end = ftell(file);
+  assert(ftell_end != -1);
+  int ret_set = fseek(file, current, SEEK_SET);
+  assert(ret_set != -1);
+
+  assert(ftell_end >= current);
+  int available = ftell_end - current;
+
+  operand_stack_push_u32(vm->current_frame, available);
+}
+
 void native_jvm_internal_libcinputstream_close_1(struct vm * vm, uint32_t * args)
 {
   FILE * file = (FILE *)args[0];
diff --git a/c/native/libcinputstream.h b/c/native/libcinputstream.h
index 070327a..8b06ad3 100644
--- a/c/native/libcinputstream.h
+++ b/c/native/libcinputstream.h
@@ -5,5 +5,6 @@
 #include "vm.h"
 
 void native_jvm_internal_libcinputstream_open_1(struct vm * vm, uint32_t * args);
+void native_jvm_internal_libcinputstream_available_1(struct vm * vm, uint32_t * args);
 void native_jvm_internal_libcinputstream_close_1(struct vm * vm, uint32_t * args);
 void native_jvm_internal_libcinputstream_read_1(struct vm * vm, uint32_t * args);
diff --git a/classes/jvm/internal/LibcInputStream.java b/classes/jvm/internal/LibcInputStream.java
index ffd026b..f64d601 100644
--- a/classes/jvm/internal/LibcInputStream.java
+++ b/classes/jvm/internal/LibcInputStream.java
@@ -1,6 +1,7 @@
 package jvm.internal;
 
 import java.io.InputStream;
+import java.io.IOException;
 
 public class LibcInputStream extends InputStream {
     private int file; // is actually FILE *
@@ -11,15 +12,21 @@ public class LibcInputStream extends InputStream {
         file = _open(path.path);
     }
 
+    private static native int _available(int file);
+
+    public int available() throws IOException {
+        return _available(file);
+    }
+
     private static native void _close(int file);
 
-    public void close() {
+    public void close() throws IOException {
         _close(file);
     }
 
     private static native int _read(int file);
 
-    public int read() {
+    public int read() throws IOException {
         return _read(file);
     }
 }
diff --git a/classes/test/TestInputStream.java b/classes/test/TestInputStream.java
index 188e5ae..d5040cf 100644
--- a/classes/test/TestInputStream.java
+++ b/classes/test/TestInputStream.java
@@ -10,7 +10,15 @@ class TestInputStream {
     public static void main() throws IOException {
         Path path = FileSystems.getDefault().getPath("/home/bilbo/source.txt");
         InputStream is = Files.newInputStream(path);
-        char c = (char)is.read();
-        System.out.println(c);
+        int available = is.available();
+        System.out.print("available: ");
+        System.out.println(available);
+
+        byte[] buf = new byte[available];
+        int read = is.read(buf, 0, available);
+        System.out.print("read: ");
+        System.out.println(read);
+
+        System.out.println(buf);
     }
 }