[ruby/prism] Parse files from Ruby API using fread, not mmap

https://github.com/ruby/prism/commit/62d4376a53

prism/extension.c

@@ -254,7 +254,7 @@ file_options(int argc, VALUE *argv, pm_string_t *input, pm_options_t *options) {
 
     const char * string_source = (const char *) pm_string_source(&options->filepath);
 
-    if (!pm_string_mapped_init(input, string_source)) {
+    if (!pm_string_file_init(input, string_source)) {
         pm_options_free(options);
 
 #ifdef _WIN32

prism/util/pm_string.c

@@ -58,7 +58,7 @@ pm_string_constant_init(pm_string_t *string, const char *source, size_t length)
  * `MapViewOfFile`, on POSIX systems that have access to `mmap` we'll use
  * `mmap`, and on other POSIX systems we'll use `read`.
  */
-bool
+PRISM_EXPORTED_FUNCTION bool
 pm_string_mapped_init(pm_string_t *string, const char *filepath) {
 #ifdef _WIN32
     // Open the file for reading.
@@ -143,6 +143,108 @@ pm_string_mapped_init(pm_string_t *string, const char *filepath) {
 #endif
 }
 
+/**
+ * Read the file indicated by the filepath parameter into source and load its
+ * contents and size into the given `pm_string_t`. The given `pm_string_t`
+ * should be freed using `pm_string_free` when it is no longer used.
+ */
+PRISM_EXPORTED_FUNCTION bool
+pm_string_file_init(pm_string_t *string, const char *filepath) {
+#ifdef _WIN32
+    // Open the file for reading.
+    HANDLE file = CreateFile(filepath, GENERIC_READ, FILE_SHARE_READ, NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);
+
+    if (file == INVALID_HANDLE_VALUE) {
+        return false;
+    }
+
+    // Get the file size.
+    DWORD file_size = GetFileSize(file, NULL);
+    if (file_size == INVALID_FILE_SIZE) {
+        CloseHandle(file);
+        return false;
+    }
+
+    // If the file is empty, then we don't need to do anything else, we'll set
+    // the source to a constant empty string and return.
+    if (file_size == 0) {
+        CloseHandle(file);
+        const uint8_t source[] = "";
+        *string = (pm_string_t) { .type = PM_STRING_CONSTANT, .source = source, .length = 0 };
+        return true;
+    }
+
+    // Create a buffer to read the file into.
+    uint8_t *source = malloc(file_size);
+    if (source == NULL) {
+        CloseHandle(file);
+        return false;
+    }
+
+    // Read the contents of the file
+    DWORD bytes_read;
+    if (!ReadFile(file, source, file_size, &bytes_read, NULL)) {
+        CloseHandle(file);
+        return false;
+    }
+
+    // Check the number of bytes read
+    if (bytes_read != file_size) {
+        free(source);
+        CloseHandle(file);
+        return false;
+    }
+
+    CloseHandle(file);
+    *string = (pm_string_t) { .type = PM_STRING_OWNED, .source = source, .length = (size_t) file_size };
+    return true;
+#elif defined(_POSIX_MAPPED_FILES)
+    FILE *file = fopen(filepath, "rb");
+    if (file == NULL) {
+        return false;
+    }
+
+    fseek(file, 0, SEEK_END);
+    long file_size = ftell(file);
+
+    if (file_size == -1) {
+        fclose(file);
+        return false;
+    }
+
+    if (file_size == 0) {
+        fclose(file);
+        const uint8_t source[] = "";
+        *string = (pm_string_t) { .type = PM_STRING_CONSTANT, .source = source, .length = 0 };
+        return true;
+    }
+
+    size_t length = (size_t) file_size;
+    uint8_t *source = malloc(length);
+    if (source == NULL) {
+        fclose(file);
+        return false;
+    }
+
+    fseek(file, 0, SEEK_SET);
+    size_t bytes_read = fread(source, length, 1, file);
+    fclose(file);
+
+    if (bytes_read != 1) {
+        free(source);
+        return false;
+    }
+
+    *string = (pm_string_t) { .type = PM_STRING_OWNED, .source = source, .length = length };
+    return true;
+#else
+    (void) string;
+    (void) filepath;
+    perror("pm_string_file_init is not implemented for this platform");
+    return false;
+#endif
+}
+
 /**
  * Returns the memory size associated with the string.
  */

prism/util/pm_string.h

@@ -109,6 +109,17 @@ void pm_string_constant_init(pm_string_t *string, const char *source, size_t len
  */
 PRISM_EXPORTED_FUNCTION bool pm_string_mapped_init(pm_string_t *string, const char *filepath);
 
+/**
+ * Read the file indicated by the filepath parameter into source and load its
+ * contents and size into the given `pm_string_t`. The given `pm_string_t`
+ * should be freed using `pm_string_free` when it is no longer used.
+ *
+ * @param string The string to initialize.
+ * @param filepath The filepath to read.
+ * @return Whether or not the file was successfully read.
+ */
+PRISM_EXPORTED_FUNCTION bool pm_string_file_init(pm_string_t *string, const char *filepath);
+
 /**
  * Returns the memory size associated with the string.
  *