Implement skipstone_message_unpack()

include/skipstone/message.h

@@ -14,4 +14,8 @@ ssize_t skipstone_message_pack(void *message,
                                size_t len,
                                const char *template, ...);
 
+ssize_t skipstone_message_unpack(void *message,
+                                 size_t len,
+                                 const char *template, ...);
+
 #endif /* _SKIPSTONE_MESSAGE_H */

src/message.c

@@ -95,3 +95,77 @@ error_invalid_template:
 
     return -1;
 }
+
+#define case_unpack(t, bytes) \
+    case t: \
+        if (len < offset + bytes) { \
+            goto done; \
+        } \
+        memcpy(va_arg(args, void *), (uint8_t *)message + offset, bytes); \
+        offset += bytes; \
+        break;
+
+ssize_t skipstone_message_unpack(void *message,
+                                 size_t len,
+                                 const char *template, ...) {
+    va_list args;
+    size_t offset = 0,
+           i;
+
+    va_start(args, template);
+
+    for (i=0; template[i]; i++) {
+        char c = template[i];
+
+        switch (c) {
+            case_unpack('c', sizeof(int8_t));
+            case_unpack('C', sizeof(uint8_t));
+            case_unpack('s', sizeof(int16_t));
+            case_unpack('S', sizeof(uint16_t));
+            case_unpack('l', sizeof(int32_t));
+            case_unpack('L', sizeof(uint32_t));
+            case_unpack('q', sizeof(int64_t));
+            case_unpack('Q', sizeof(uint64_t));
+
+            case 'z': {
+                uint8_t sz;
+                void *dest;
+
+                if (len < offset + 1) {
+                    goto done;
+                }
+
+                sz = ((uint8_t *)message)[offset++];
+
+                if (len < offset + sz + 1) {
+                    goto done;
+                }
+
+                dest = va_arg(args, void *);
+
+                memcpy(dest, (uint8_t *)message + offset, sz);
+
+                offset += sz;
+
+                ((uint8_t *)message)[offset++] = '\0';
+
+                break;
+            }
+
+            default:
+                errno = EINVAL;
+
+                goto error_invalid;
+        }
+    }
+
+    va_end(args);
+
+done:
+    return offset;
+
+error_invalid:
+    va_end(args);
+
+    return -1;
+}