initial pass

include/aws/common/file.h

@@ -47,6 +47,8 @@ struct aws_directory_entry {
     int64_t file_size;
 };
 
+struct aws_file_handle;
+
 /**
  * Invoked during calls to aws_directory_traverse() as an entry is encountered. entry will contain
  * the parsed directory entry info.
@@ -207,6 +209,18 @@ int aws_fseek(FILE *file, int64_t offset, int whence);
 AWS_COMMON_API
 int aws_file_get_length(FILE *file, int64_t *length);
 
+/**
+ * @brief Wrapper for os-specific pwrite implementation.
+ *
+ * @param fd
+ * @param buf
+ * @param count
+ * @param offset
+ * @return AWS_COMMON_API
+ */
+AWS_COMMON_API
+int aws_pwrite(int fd, const void *buf, size_t count, uint64_t offset, size_t *bytes_written);
+
 AWS_EXTERN_C_END
 AWS_POP_SANE_WARNING_LEVEL
 

source/posix/file.c

@@ -309,3 +309,21 @@ int aws_file_get_length(FILE *file, int64_t *length) {
 
     return AWS_OP_SUCCESS;
 }
+
+int aws_pwrite(int fd, const void *buf, size_t count, uint64_t offset, size_t *bytes_written) {
+    if (fd == -1) {
+        return aws_raise_error(AWS_ERROR_INVALID_FILE_HANDLE);
+    }
+#ifdef AWS_OS_MACOS
+    /* MacOS doesn't have pwrite64. */
+    *bytes_written = pwrite(fd, buf, count, offset);
+#else
+    *bytes_written = pwrite64(fd, buf, count, offset);
+#endif
+    int errno_value = errno; /* Always cache errno before potential side-effect */
+    if (*bytes_written == -1) {
+        /* TODO: maybe some other default error? */
+        return aws_translate_and_raise_io_error_or(errno_value, AWS_ERROR_UNKNOWN);
+    }
+    return AWS_OP_SUCCESS;
+}

source/windows/file.c

@@ -544,3 +544,37 @@ int aws_file_get_length(FILE *file, int64_t *length) {
 
     return AWS_OP_SUCCESS;
 }
+
+int aws_pwrite(int fd, const void *buf, size_t count, uint64_t offset, size_t *bytes_written) {
+    if (fd == -1) {
+        return aws_raise_error(AWS_ERROR_INVALID_FILE_HANDLE);
+    }
+
+    HANDLE os_file = (HANDLE)_get_osfhandle(fd);
+    if (os_file == INVALID_HANDLE_VALUE) {
+        int errno_value = errno; /* Always cache errno before potential side-effect */
+        return aws_translate_and_raise_io_error(errno_value);
+    }
+    DWORD bytesWritten;
+    OVERLAPPED ol = {0};
+    LARGE_INTEGER li;
+
+    /* Convert uint64_t offset to OVERLAPPED */
+    li.QuadPart = offset;
+    ol.Offset = li.LowPart;
+    ol.OffsetHigh = li.HighPart;
+
+    if (!WriteFile(os_file, buf, (DWORD)count, &bytesWritten, &ol)) {
+        int error = GetLastError();
+
+        if (error == ERROR_IO_PENDING) {
+            /* TODO: check for different errors. */
+            return aws_raise_error(AWS_ERROR_INVALID_FILE_HANDLE);
+        }
+        return aws_raise_error(AWS_ERROR_UNKNOWN);
+    }
+    *bytes_written = (size_t)bytesWritten;
+    /* TODO: verify the fd offset is not affected. */
+    /* Never call CloseHandle on the return value of _get_osfhandle */
+    return AWS_OP_SUCCESS;
+}

tests/CMakeLists.txt

@@ -490,6 +490,7 @@ add_test_case(test_home_directory_not_null)
 add_test_case(test_normalize_posix_directory_separator)
 add_test_case(test_normalize_windows_directory_separator)
 add_test_case(test_byte_buf_init_from_file)
+add_test_case(test_aws_pwrite)
 
 add_test_case(test_json_parse_from_string)
 add_test_case(test_json_parse_to_string)

tests/file_test.c

@@ -9,14 +9,11 @@
 #include <aws/testing/aws_test_harness.h>
 
 #include <fcntl.h>
+#include <unistd.h>
 
-static int s_aws_fopen_test_helper(char *file_path, char *content) {
+static int s_read_and_verify_helper(char *file_path, char *content) {
     char read_result[100];
     AWS_ZERO_ARRAY(read_result);
-    FILE *file = aws_fopen(file_path, "w+");
-    ASSERT_NOT_NULL(file);
-    fprintf(file, "%s", content);
-    fclose(file);
     FILE *readfile = aws_fopen(file_path, "r");
     ASSERT_NOT_NULL(readfile);
     size_t read_len = fread(read_result, sizeof(char), strlen(content), readfile);
@@ -36,6 +33,14 @@ static int s_aws_fopen_test_helper(char *file_path, char *content) {
     return AWS_OP_SUCCESS;
 }
 
+static int s_aws_fopen_test_helper(char *file_path, char *content) {
+    FILE *file = aws_fopen(file_path, "w+");
+    ASSERT_NOT_NULL(file);
+    fprintf(file, "%s", content);
+    fclose(file);
+    return s_read_and_verify_helper(file_path, content);
+}
+
 static int s_aws_fopen_content_matches(char *file_path, char *content) {
     char read_result[100];
     AWS_ZERO_ARRAY(read_result);
@@ -542,3 +547,23 @@ static int s_test_byte_buf_init_from_file(struct aws_allocator *allocator, void
 }
 
 AWS_TEST_CASE(test_byte_buf_init_from_file, s_test_byte_buf_init_from_file)
+
+static int s_test_aws_pwrite(struct aws_allocator *allocator, void *ctx) {
+    (void)ctx;
+    char file_path[] = "sample.txt";
+    int fd = open(file_path, O_RDWR | O_NONBLOCK | O_CREAT, 0666);
+    struct aws_byte_cursor contents = aws_byte_cursor_from_c_str("hello world");
+
+    size_t byte_written = 0;
+    aws_pwrite(fd, contents.ptr, contents.len, 0, &byte_written);
+    aws_pwrite(fd, contents.ptr, contents.len, contents.len, &byte_written);
+    close(fd);
+
+    /* Verify the written content match expected */
+    ASSERT_SUCCESS(s_read_and_verify_helper(file_path, "hello worldhello world"));
+
+    /* TODO: test error handling. */
+    return AWS_OP_SUCCESS;
+}
+
+AWS_TEST_CASE(test_aws_pwrite, s_test_aws_pwrite)