add uc_read_fd function

include/ucore/read_file.h

@@ -21,6 +21,14 @@ extern "C" {
 char *
 uc_read_file(const char *file_name, size_t *length, size_t max);
 
+/** Read the content of a file descriptor as a stream.
+ * @see uc_read_file
+ * This is similar but reads from a file descriptor,
+ * of any type as long as it supports the read() call.
+ */
+char *
+uc_read_fd(int fd, size_t *length, size_t max);
+
 #ifdef __cplusplus
 }
 #endif

src/read_file.c

@@ -10,9 +10,8 @@
 #define CHUNK_SZ 1024
 
 char *
-uc_read_file(const char *f, size_t *length, size_t max)
+uc_read_fd(int fd, size_t *length, size_t max)
 {
-    int fd;
     char *s = NULL;
     char *p;
     struct stat statb;
@@ -20,9 +19,6 @@ uc_read_file(const char *f, size_t *length, size_t max)
 
     *length = 0;
 
-    if ((fd = open(f, O_RDONLY)) == -1)
-        return NULL;
-
     if (fstat(fd, &statb) == -1) {
         goto out_close;
     }
@@ -85,3 +81,15 @@ out_close:
     return s;
 }
 
+char *
+uc_read_file(const char *f, size_t *length, size_t max)
+{
+    int fd;
+
+    if ((fd = open(f, O_RDONLY)) == -1) {
+        *length = 0;
+        return NULL;
+    }
+
+    return uc_read_fd(fd, length, max);
+}