fix(random): review comments

spec/02-random_spec.lua

@@ -5,32 +5,32 @@ describe("Random:", function()
   describe("random()", function()
 
     it("should return random bytes for a valid number of bytes", function()
-        local num_bytes = system.MAX_RANDOM_BUFFER_SIZE
+        local num_bytes = 1
         local result, err_msg = system.random(num_bytes)
         assert.is_nil(err_msg)
         assert.is.string(result)
         assert.is_equal(num_bytes, #result)
     end)
 
 
-    it("should return an error message for an invalid number of bytes", function()
+    it("should return an empty string for 0 bytes", function()
         local num_bytes = 0
         local result, err_msg = system.random(num_bytes)
-        assert.is.falsy(result)
-        assert.are.equal("invalid number of bytes, must be between 1 and 1024", err_msg)
+        assert.is_nil(err_msg)
+        assert.are.equal("", result)
     end)
 
 
-    it("should return an error message for exceeding the maximum buffer size", function()
-        local num_bytes = system.MAX_RANDOM_BUFFER_SIZE + 1
+    it("should return an error message for an invalid number of bytes", function()
+        local num_bytes = -1
         local result, err_msg = system.random(num_bytes)
         assert.is.falsy(result)
-        assert.are.equal("invalid number of bytes, must be between 1 and 1024", err_msg)
+        assert.are.equal("invalid number of bytes, must not be less than 0", err_msg)
     end)
 
 
     it("should not return duplicate results", function()
-      local num_bytes = 10
+      local num_bytes = 1025
       local result1, err_msg = system.random(num_bytes)
       assert.is_nil(err_msg)
       assert.is.string(result1)

src/compat.h

@@ -8,4 +8,31 @@
 void luaL_setfuncs(lua_State *L, const luaL_Reg *l, int nup);
 #endif
 
+// Windows doesn't have ssize_t, so we define it here
+#ifdef _WIN32
+#if SIZE_MAX == UINT_MAX
+typedef int ssize_t;        /* common 32 bit case */
+#define SSIZE_MIN  INT_MIN
+#define SSIZE_MAX  INT_MAX
+#elif SIZE_MAX == ULONG_MAX
+typedef long ssize_t;       /* linux 64 bits */
+#define SSIZE_MIN  LONG_MIN
+#define SSIZE_MAX  LONG_MAX
+#elif SIZE_MAX == ULLONG_MAX
+typedef long long ssize_t;  /* windows 64 bits */
+#define SSIZE_MIN  LLONG_MIN
+#define SSIZE_MAX  LLONG_MAX
+#elif SIZE_MAX == USHRT_MAX
+typedef short ssize_t;      /* is this even possible? */
+#define SSIZE_MIN  SHRT_MIN
+#define SSIZE_MAX  SHRT_MAX
+#elif SIZE_MAX == UINTMAX_MAX
+typedef uintmax_t ssize_t;  /* last resort, chux suggestion */
+#define SSIZE_MIN  INTMAX_MIN
+#define SSIZE_MAX  INTMAX_MAX
+#else
+#error platform has exotic SIZE_MAX
+#endif
+#endif
+
 #endif

src/random.c

@@ -8,34 +8,44 @@
 #include "windows.h"
 #include "wincrypt.h"
 #else
+#include <errno.h>
 #include <unistd.h>
+#include <string.h>
 #endif
 
 
-// Maximum buffer size for random bytes
-#define MAX_RANDOM_BUFFER_SIZE 1024
-
-
 /***
 Generate random bytes.
-This uses `getrandom()` on Linux, `CryptGenRandom()` on Windows, and `/dev/urandom` on macOS.
+This uses `CryptGenRandom()` on Windows, and `/dev/urandom` on other platforms. It will return the
+requested number of bytes, or an error, never a partial result.
 @function random
-@tparam[opt=1] int length number of bytes to get, must be less than or equal to `MAX_RANDOM_BUFFER_SIZE` (1024)
+@tparam[opt=1] int length number of bytes to get
 @treturn[1] string string of random bytes
 @treturn[2] nil
 @treturn[2] string error message
 */
 static int lua_get_random_bytes(lua_State* L) {
     int num_bytes = luaL_optinteger(L, 1, 1); // Number of bytes, default to 1 if not provided
 
-    if (num_bytes <= 0 || num_bytes > MAX_RANDOM_BUFFER_SIZE) {
+    if (num_bytes <= 0) {
+        if (num_bytes == 0) {
+            lua_pushliteral(L, "");
+            return 1;
+        }
         lua_pushnil(L);
-        lua_pushfstring(L, "invalid number of bytes, must be between 1 and %d", MAX_RANDOM_BUFFER_SIZE);
+        lua_pushstring(L, "invalid number of bytes, must not be less than 0");
         return 2;
     }
 
-    unsigned char buffer[MAX_RANDOM_BUFFER_SIZE];
-    size_t n;
+    unsigned char* buffer = (unsigned char*)lua_newuserdata(L, num_bytes);
+    if (buffer == NULL) {
+        lua_pushnil(L);
+        lua_pushstring(L, "failed to allocate memory for random buffer");
+        return 2;
+    }
+
+    ssize_t n;
+    ssize_t total_read = 0;
 
 #ifdef _WIN32
     HCRYPTPROV hCryptProv;
@@ -56,33 +66,34 @@ static int lua_get_random_bytes(lua_State* L) {
 
     CryptReleaseContext(hCryptProv, 0);
 #else
-#ifndef __APPLE__
-    // Neither Apple nor Windows
-    n = getrandom(buffer, num_bytes, 0);
 
-    if (n < 0) {
-        lua_pushnil(L);
-        lua_pushstring(L, "failed to get random data");
-        return 2;
-    }
-#else
-    // macOS uses /dev/urandom for non-blocking
-    int fd = open("/dev/urandom", O_RDONLY);
+    // for macOS/unixes use /dev/urandom for non-blocking
+    int fd = open("/dev/urandom", O_RDONLY | O_CLOEXEC);
     if (fd < 0) {
         lua_pushnil(L);
         lua_pushstring(L, "failed opening /dev/urandom");
         return 2;
     }
-    n = read(fd, buffer, num_bytes);
-    close(fd);
-    if (n < 0) {
-      lua_pushnil(L);
-      lua_pushstring(L, "failed reading /dev/urandom");
-    return 2;
-}
 
-#endif
+    while (total_read < num_bytes) {
+        n = read(fd, buffer + total_read, num_bytes - total_read);
+
+        if (n < 0) {
+            if (errno == EINTR) {
+                continue;  // Interrupted, retry
 
+            } else {
+                lua_pushnil(L);
+                lua_pushfstring(L, "failed reading /dev/urandom: %s", strerror(errno));
+                close(fd);
+                return 2;
+            }
+        }
+
+        total_read += n;
+    }
+
+    close(fd);
 #endif
 
     lua_pushlstring(L, (const char*)buffer, num_bytes);
@@ -103,6 +114,4 @@ static luaL_Reg func[] = {
  *-------------------------------------------------------------------------*/
 void random_open(lua_State *L) {
     luaL_setfuncs(L, func, 0);
-    lua_pushinteger(L, MAX_RANDOM_BUFFER_SIZE);
-    lua_setfield(L, -2, "MAX_RANDOM_BUFFER_SIZE");
 }