[k2] fix fgets (#1522)

Author: denisichh

runtime-light/k2-platform/k2-api.h

@@ -216,8 +216,8 @@ inline size_t pread(k2::descriptor descriptor, std::span<std::byte> buffer, uint
   return k2_pread(descriptor, buffer.size(), static_cast<void*>(buffer.data()), offset);
 }
 
-inline size_t fgets(k2::descriptor descriptor, std::span<std::byte> buffer) noexcept {
-  return k2_fgets(descriptor, buffer.size(), static_cast<void*>(buffer.data()));
+inline size_t readline(k2::descriptor descriptor, std::span<std::byte> buffer) noexcept {
+  return k2_readline(descriptor, buffer.size(), static_cast<void*>(buffer.data()));
 }
 
 inline void* mmap(k2::descriptor* md, void* addr, size_t length, int32_t prot, int32_t flags, k2::descriptor fd, uint64_t offset) noexcept {

runtime-light/k2-platform/k2-header.h

@@ -357,11 +357,11 @@ size_t k2_read(uint64_t stream_d, size_t buf_len, void* buf);
 size_t k2_pread(uint64_t stream_d, size_t buf_len, void* buf, uint64_t offset);
 
 /**
- * equivalent to libc's `fgets` function
+ * behavior is similar to libc's `fgets` function, except that EOF and empty string return the same result.
  *
  * @return `0` if EOF is reached or an error occurs. total number of bytes read otherwise
  */
-size_t k2_fgets(uint64_t stream_d, size_t buf_len, void* buf);
+size_t k2_readline(uint64_t stream_d, size_t buf_len, void* buf);
 
 /**
  * Semantically equivalent to libc's `mmap` function.

runtime-light/stdlib/file/file-system-functions.cpp

@@ -396,6 +396,10 @@ Optional<string> f$fgets(const resource& stream, int64_t length) noexcept {
     return false;
   }
 
+  if (length == 1) {
+    return string{};
+  }
+
   auto file_resource{from_mixed<class_instance<kphp::fs::file>>(stream, {})};
   if (file_resource.is_null()) {
     return false;
@@ -418,7 +422,7 @@ Optional<string> f$fgets(const resource& stream, int64_t length) noexcept {
     return false;
   }
   string res{static_cast<string::size_type>(length), false};
-  auto read_res{k2::fgets(file.descriptor(), std::as_writable_bytes(std::span<char>{res.buffer(), res.size()}))};
+  auto read_res{k2::readline(file.descriptor(), std::as_writable_bytes(std::span<char>{res.buffer(), res.size()}))};
 
   if (read_res == 0) {
     return false;

tests/phpt/dl/473_fgets.php

@@ -1,5 +1,6 @@
 @ok
 <?php
+
 function init() {
     $stream = fopen(__DIR__.'/fgets.txt', 'w');
     fwrite ($stream, "123\n");
@@ -20,7 +21,7 @@ function test_fgets() {
     var_dump (fgets ($stream)); // line = "\n"
 
     var_dump (fgets ($stream, 4)); // `length` less than length of the line. line = "php < kphp\n"
-    var_dump (fgets ($stream, 1)); // always false
+//     var_dump (fgets ($stream, 1));   kphp expects "", php expects false
     var_dump (fgets ($stream)); // rest of the line
 
     var_dump (fgets ($stream)); // last line. line = "bang"