feat(ltm): initial write function

ltm/include/ltm/common.h

@@ -17,12 +17,16 @@
     }                                                                          \
   }
 
+#define LTM_MIN(x, y) ((x) < (y) ? (x) : (y))
+#define LTM_MAX(x, y) ((x) > (y) ? (x) : (y))
+
 typedef enum ltm_err {
   ltm_err_ok = 0,
   ltm_err_invalid_template,
   ltm_err_failed_alloc,
   ltm_err_not_found,
   ltm_err_wrong_block_type,
+  ltm_err_done,
 } ltm_err;
 
 #endif

ltm/include/ltm/template.h

@@ -70,4 +70,23 @@ ltm_err ltm_instance_block_add_var(ltm_instance *instance, const char *name,
 ltm_err ltm_instance_block_add_nested(ltm_instance **out,
                                       ltm_instance *instance, const char *name);
 
+/**
+ * Calculate the size of the resulting output of this instance.
+ */
+size_t ltm_instance_size(const ltm_instance *instance);
+
+/**
+ * Write at most `len` bytes to the given buffer.
+ *
+ * @param written outputs how many bytes were written to `buf`
+ * @param buf buffer to write to
+ * @param len length of the buffer
+ * @param instance instance to write
+ * @return `ltm_err_ok` if write was successful but there's more to be written,
+ * `ltm_err_done` if everything has been written successfully, or some other
+ * error code
+ */
+ltm_err ltm_instance_write(size_t *written, char *buf, size_t len,
+                           ltm_instance *instance);
+
 #endif