From 8e14b27749e425f8f4496bdeec767070ec7ed2b0 Mon Sep 17 00:00:00 2001
From: Justine Tunney <jtunney@gmail.com>
Date: Sat, 17 Aug 2024 02:57:22 -0700
Subject: [PATCH] Make fread() more consistent with glibc

---
 libc/stdio/fread_unlocked.c  | 46 ++++++++++++++++++------------------
 test/libc/stdio/fputc_test.c |  4 ++++
 test/libc/stdio/fread_test.c | 31 +++++++++++++++++++++++-
 3 files changed, 57 insertions(+), 24 deletions(-)

diff --git a/libc/stdio/fread_unlocked.c b/libc/stdio/fread_unlocked.c
index 2ebc08713..ef341d8ec 100644
--- a/libc/stdio/fread_unlocked.c
+++ b/libc/stdio/fread_unlocked.c
@@ -28,21 +28,27 @@
 #include "libc/sysv/consts/o.h"
 #include "libc/sysv/errfuns.h"
 
-static ssize_t readvall(int fd, struct iovec *iov, int iovlen) {
+static ssize_t readvall(FILE *f, struct iovec *iov, int iovlen, size_t need) {
   ssize_t rc;
   size_t got, toto;
-  toto = 0;
-  do {
-    if ((rc = readv(fd, iov, iovlen)) == -1) {
-      if (toto) {
-        if (errno == EINTR)
-          continue;
+  for (toto = 0;;) {
+
+    // perform i/o
+    if ((rc = readv(f->fd, iov, iovlen)) == -1) {
+      f->state = errno;
+      if (toto)
         return toto;
-      }
       return -1;
     }
     got = rc;
     toto += got;
+    if (!got) {
+      f->state = EOF;
+      return toto;
+    }
+
+    // roll forward iov
+    // skip over empty elements
     for (;;) {
       if (!iov->iov_len) {
         --iovlen;
@@ -56,9 +62,14 @@ static ssize_t readvall(int fd, struct iovec *iov, int iovlen) {
         iov->iov_len -= got;
         break;
       }
+      if (!iovlen)
+        return toto;
     }
-  } while (got && iovlen);
-  return toto;
+
+    // don't trigger eof condition if we're rolling greed to fill buffer
+    if (toto >= need)
+      return toto;
+  }
 }
 
 /**
@@ -134,27 +145,16 @@ size_t fread_unlocked(void *buf, size_t stride, size_t count, FILE *f) {
     iov[1].iov_base = NULL;
     iov[1].iov_len = 0;
   }
-  if (f->bufmode == _IONBF) {
-    rc = readv(f->fd, iov, 2);
-  } else {
-    rc = readvall(f->fd, iov, 2);
-  }
-  if (rc == -1) {
-    f->state = errno;
+  rc = readvall(f, iov, 2, need);
+  if (rc == -1)
     return 0;
-  }
   got = rc;
 
   // handle partial fulfillment
   if (got < need) {
     got += m;
-    if (got % stride) {
-      f->state = eio();
-      return 0;
-    }
     f->beg = 0;
     f->end = 0;
-    f->state = EOF;
     return got / stride;
   }
 
diff --git a/test/libc/stdio/fputc_test.c b/test/libc/stdio/fputc_test.c
index 6520e77bb..b63ecc1c3 100644
--- a/test/libc/stdio/fputc_test.c
+++ b/test/libc/stdio/fputc_test.c
@@ -33,9 +33,13 @@ void SetUpOnce(void) {
 TEST(fputc, test) {
   ASSERT_NE(NULL, (f = fopen("hog", "w+")));
   EXPECT_EQ('h', fputc('h', f));
+  EXPECT_FALSE(feof(f));
   EXPECT_EQ(0xFF, fputc(-1, f));
+  EXPECT_FALSE(feof(f));
   EXPECT_NE(-1, fseek(f, 0, SEEK_SET));
+  EXPECT_FALSE(feof(f));
   EXPECT_EQ('h', fgetc(f));
+  EXPECT_FALSE(feof(f));
   EXPECT_EQ(0, fread(NULL, 0, 0, f));
   EXPECT_FALSE(feof(f));
   EXPECT_EQ(0xFF, fgetc(f));
diff --git a/test/libc/stdio/fread_test.c b/test/libc/stdio/fread_test.c
index 8e5e690e5..2fc4f00a5 100644
--- a/test/libc/stdio/fread_test.c
+++ b/test/libc/stdio/fread_test.c
@@ -17,6 +17,7 @@
 │ PERFORMANCE OF THIS SOFTWARE.                                                │
 ╚─────────────────────────────────────────────────────────────────────────────*/
 #include "libc/calls/calls.h"
+#include "libc/errno.h"
 #include "libc/stdio/stdio.h"
 #include "libc/testlib/testlib.h"
 
@@ -45,7 +46,7 @@ TEST(fread, eofIsSticky) {
 }
 
 TEST(fread, seekWithBuffer) {
-  FILE *f;
+  FILE* f;
   char b[8] = "hellosup";
   char c[8] = {0};
   char d[8] = {0};
@@ -60,3 +61,31 @@ TEST(fread, seekWithBuffer) {
   ASSERT_STREQ("ellos", d);
   ASSERT_EQ(0, fclose(f));
 }
+
+TEST(fread, zero) {
+  FILE* f;
+  char buf[8] = {0};
+  ASSERT_NE(NULL, (f = fopen("foo", "w")));
+  ASSERT_EQ(2, fwrite("hi", 1, 2, f));
+  ASSERT_EQ(0, fclose(f));
+  ASSERT_NE(NULL, (f = fopen("foo", "r")));
+  ASSERT_EQ(0, fread(buf, 0, 0, f));
+  ASSERT_EQ(0, ferror(stdin));
+  ASSERT_EQ(0, feof(stdin));
+  ASSERT_STREQ("", buf);
+  ASSERT_EQ(0, fclose(f));
+}
+
+TEST(fread, partial) {
+  FILE* f;
+  char buf[8] = {0};
+  ASSERT_NE(NULL, (f = fopen("foo", "w")));
+  ASSERT_EQ(2, fwrite("hi", 1, 2, f));
+  ASSERT_EQ(0, fclose(f));
+  ASSERT_NE(NULL, (f = fopen("foo", "r")));
+  ASSERT_EQ(0, fread(buf, 8, 1, f));
+  ASSERT_EQ(0, ferror(stdin));
+  ASSERT_EQ(0, feof(stdin));
+  ASSERT_EQ(0, fclose(f));
+  ASSERT_STREQ("hi", buf);
+}